Lecture 8A Quiz
Question 1
Each of the following is an endoplasmic reticulum function except Answers: a. addition of carbohydrate to proteins to make glycoproteins. b. peptide folding. c. the assembly of multimeric proteins. d. the export of protein that cannot be folded into the cytoplasm for destruction. e. All are endoplasmic reticulum functions.
Question 2
A protein that is normally localized in the cytoplasm has been engineered so that it will be secreted from the cell instead. Which of the following represents the most likely pathway for the protein after it has been completely synthesized? Answers: a. rER → Golgi → secretory vesicle → environment b. rER → Golgi → sER → cytoplasm → environment c. cytoplasm → rER → Golgi → secretory vesicle → environment d. sER → Golgi → secretory vesicle → environment e. rER → secretory vesicle → Golgi → environment
Question 3
The signal-recognition particle (SRP) ... Answers: a. is a heterodimeric protein. b. transiently inhibits translation and polypeptide elongation by binding to and inhibiting the elongation factors c. accompanies the nascent polypeptide all the way into the ER lumen. d. binds GTP. e. is permanently attached to the cytosolic face of the ER membrane, thus bringing the ribosomes into close proximity of the translocon.
Question 4
The following diagram depicts the topology of a multipass transmembrane protein in the endoplasmic reticulum (ER) membrane. Which set of helices act as stop-transfer signals in this protein?
Answers: a. 1, 2, 3 b. 4, 5, 6 c. 1, 3, 5 d. 2, 4, 6 e. 1, 6
Lecture 8B Quiz
Question 1
A protein that is N-glycosylated is expected to be Answers: a.secreted from the cell. b. retained in the endoplasmic reticulum. c. localized in the Golgi body. d. imported into a cell by endocytosis. e. a peroxisome enzyme.
Question 2
What appears to be the purpose of molecular chaperones like BiP?
Answers: a. They recognize and bind to unfolded or misfolded proteins and help them attain their native structure. b. They recognize and bind to unfolded or misfolded DNAs and help them attain their native structure. c. They recognize and bind to unfolded or misfolded RNAs and help them attain their native structure. d. They recognize and bind unfolded or misfolded carbohydrates and help them lose their native shape. e. They transport secretory proteins into secretory vesicles.
Question 3
Misfolded proteins in the ER may actively undergo any of the following EXCEPT ... Answers: a. binding to chaperones such as BiP to allow unfolding and refolding. b. binding to chaperones such as calnexin to prevent aggregation. c. being transported back to the cytosol for degradation. d. being expelled to the Golgi apparatus for disposal. e. being glycosylated and binding to lectins.
Question 4
The oligosaccharide chain that is added to secretory proteins after they enter the ER lumen goes through a number of modifications after its attachment. What is the first modification that occurs? Answers: a. addition of more sugars b. addition of glucose c. trimming of some sugars from the oligosaccharide chain d. chemical modification of the sugars on the oligosaccharide chain e. both addition of more sugars and addition of glucose
Question 5
Which of the following is LEAST likely an ER signal sequence recognized by the signal-recognition particle? All sequences are written with their N-terminus on the left. Answers: a. Met-Lys-Leu-Ser-Leu-Val-Ala-Ala-Met-Leu-Leu-Leu-Leu-Ser-Ala-Ala-Arg-Ala b. Met-Glu-Met-Phe-Gln-Gly-Leu-Leu-Leu-Leu-Leu-Leu-Leu-Leu-Ser-Met-Gly-Gly-Thr-Trp-Ala c. Met-Lys-Ala-Lys-Leu-Leu-Val-Leu-Leu-Tyr-Ala-Phe-Val-Ala-Gly-Asn
d. Met-Met-Ala-Ala-Gly-Pro-Arg-Thr-Ser-Leu-Leu-Leu-Ala-Phe-Ala-Leu-Leu-Cys-Leu-Pro-TrpThr-Gln-Val-Val e. Met-Leu-Ser-Leu-Arg-Gln-Ser-Ile-Arg-Phe-Phe-Lys-Pro-Ala-Thr-Arg-Thr-Leu-Ser-Ser-ArgTyr-Leu
Question 6
Indicate whether the C-terminus (C) or the N-terminus (N) of each of the following proteins is expected to be located in the cytosol upon ER membrane integration of the protein.
• A single-pass transmembrane protein that has one N-terminal signal sequence and one internal stoptransfer signal • A single-pass transmembrane protein that has one internal signal sequence that is preceded by a patch of positively charged residues • An ER tail-anchored protein Answers: a. CNN b. CCN c. NCN d. NNC e. CNC
Lecture 8C Quiz
Question 1
True or False: Synthesis of sphingomyelin occurs on the cytosolic side of the ER membrane: Answers: True False
Question 2
Comparing cells synthesizing secretory proteins and cells secreting steroid hormones, the cells synthesizing the steroid hormones have Answers: a. more rough ER. b. more smooth ER. c. equal amounts of smooth and rough ER. d. equal amounts of smooth and rough ER, but more lysosomes.
e. equal amounts of smooth and rough ER, but fewer lysosomes.
Question 3
How is the orientation of ER membrane proteins in the membrane thought to be accomplished? Answers: a. After synthesis, an enzyme orients the protein properly. b. During synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the cytosol. c. During synthesis, the translocon inner lining orients the nascent polypeptide so the more negative end faces the cytosol. d. During synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the mitochondrial intermembrane space. E .After synthesis, the translocon inner lining orients the nascent polypeptide so the more positive end faces the cytosol.
Question 4
The drugs that lower LDL concentration in the blood function by ________. Answers: a. blocking a key cholesterol-degrading enzyme, HMG CoA reductase b. activating a key cholesterol-degrading enzyme, HMG CoA reductase c. blocking a key cholesterol synthesis enzyme, HMG CoA reductase d. activating a key cholesterol synthesis enzyme, HMG CoA reductase e. blocking a key cholesterol synthesis enzyme, HMG CoA oxidase
Question 5
Phospholipids are made by integral ER membrane enzymes whose active sites face the cytosol and they are inserted into the outer (cytoplasmic. leaflet of the ER membrane). How then do lipids destined for the luminal leaflet of the ER membrane get there? Answers: a. They diffuse freely into the luminal leaflet. b. There are enzymes called flippases that flip these lipids later into the opposite leaflet. c. They are disassembled on the cytoplasmic side and reassembled on the luminal side. d. They move to the cytoplasmic leaflet by osmosis. e. There are enzymes called translocases that flip these lipids later into the opposite leaflet.
Lecture 9A Quiz
Question 1
What enzymes are responsible for determining the sequence of sugars added to growing oligosaccharide chains of membrane proteins or secretory proteins as they travel through the Golgi complex? Answers: a. glycosaminocosidases b. peptidyltransferases c. glycosyltransferase d. amylases e. Rubisco
Question 2
Pancreatic acinar cells produce and store hydrolytic enzymes in zymogen granules until hormones signal the cell to release the enzymes in a process known as Answers: a. transport secretion. b. regulated secretion. c. constitutive secretion. d. intracellular secretion. e. consistent secretion.
Question 3
Indicate whether each of the following descriptions better applies to N-linked (N) or O-linked (O) glycosylation of proteins transported from the ER to the Golgi. • • • •
It is abundant in proteoglycans. It involves the attachment of a preassembled block of oligosaccharide onto a protein. It is attached to a serine or threonine residue in the protein. It involves heavily sulfated sugars. Answers: a. NNON b. ONOO c. OONN d. NONO e. OONO
Question 4
What kind(s) of modifications are made in proteins as they move through the Golgi complex? Answers: a. The protein's carbohydrates are modified by a series of stepwise enzymatic reactions. b. Amino acids can be added to either end of the polypeptide chain. c. Amino acids in the proteins may be chemically altered into nucleic acids. d. Small segments of amino acids can be added into the center of an existing protein. e. All of these are correct.
Question 5
Which of the following carbohydrates is not synthesized in the Golgi complex? Answers: a. glycosaminoglycans in the animal extracellular matrix b. plant cell wall polysaccharides like pectin and hemicellulose c. the carbohydrates of glycolipids d. the carbohydrates of glycoproteins e. glycogen
Lecture 9B Quiz
Question 1
Exocytosis is stimulated by regional increases in cytoplasmic ________ concentration. Answers: a. Sodium b. Potassium c. Protons d. Calcium e. Phosphate
Question 2
What are the recognition signals for lysosomal enzymes that allow them to be localized correctly in lysosomes? Answers: a. Lysosomal enzymes possess sulfated mannose residues on N-l inked carbohydrate chains. b. Lysosomal enzymes possess phosphorylated mannose residues on N-linked carbohydrate chains. c. Lysosomal enzymes possess phosphorylated mannose residues on O-linked carbohydrate chains.
d. Lysosomal enzymes possess sulfated mannose residues on O-linked carbohydrate chains. e. Lysosomal enzymes possess phosphorylated glucose residues on N-li nked carbohydrate chains.
Question 3
During maturation of early endosomes to late endosomes, … Answers: a. the vacuolar domain of the endosome is shed, whereas the tubular domain is retained. b. the endosome migrates along actin filaments away from the cell interior. c. the lumen of the endosome becomes more acidic. d. intralumenal vesicles disappear. e. All of the above.
Question 4
In a lysosomal storage disease, newly synthesized lysosome hydrolases are secreted from the cells rather than being delivered to the lysosomes. What is one possible mechanism for this result? Answers: a. The cis-Golgi cis-Golgi network lacks a proton gradient. b. The ER is unable to produce lysosomal vesicles. c. Lysosomal enzymes are not phosphorylated in the rER. d. Mannose is not phosphorylated in the cis-Golgi network. e. All the hydrolase genes are mutated, resulting in synthesis by ribosomes free in the cytoplasm rather than on the endoplasmic reticulum membrane.
Lecture 9C Quiz
Question 1
Indicate whether each of the following transport processes occurs via the mechanisms described as transmembrane transport (T), or vesicular transport (V).
• • •
Import into mitochondria Return from Golgi to ER Return from ER to cytosol Answers: a. TTV
b. VVT c. VTV d. TTT e. TVT
Question 2
Which of the following is NOT correct regarding M6P receptors and KDEL receptors? Answers: a. They both shuttle back and forth between different membrane-enclosed compartments. b. They are both transmembrane proteins. c. They both release their soluble binding targets at lower pH. d. They both prevent the escape of proteins to the cell exterior by the “default” pathway. “default” pathway.
Question 3
How does the affinity of M6P receptor proteins for the mannose 6-phosphate marker change between the TGN and early endosome? Which coat protein is mainly responsible for their transport from the TGN to the endosome? Answers: a. The affinity is higher in the TGN; clathrin b. The affinity is higher in the TGN; retromer c. The affinity is higher in endosomes; clathrin d. The affinity is higher in endosomes; retromer
Question 4
Consider two N-linked oligosaccharide chains on the same protein. The first chain contains three mannose residues and three negatively charged sialic acid residues, as well as ot her residues. The second chain contains only two N-acetylglucosamine and eight mannose residues. Which chain seems to have been added to the protein such that it is NOT full y accessible to the processing enzymes in the Golgi apparatus? Which chain is Endo H-sensitive? Answers: a. Chain one; chain one b. Chain one; chain two c. Chain two; chain one d. Chain two; chain two
Question 5
When a membrane protein is radioactively labeled during synthesis and followed through the various organelles in the secretory pathway, all the radioactivity is concentrated in the cis-Golgi cis-Golgi apparatus six hours after the protein synthesis. This suggests that the protein Answers: a. was imported directly into the cis-Golgi cis-Golgi post-translationally. b. contains a KDEL sequence near its C-terminus.
cis-Golgi membrane. c. has a membrane-spanning domain length equal to the thickness of the cis-Golgi d. has a mannose-6-phosphate tag. e. is misfolded and being degraded in the cis-Golgi. cis-Golgi.
Lecture 10A Quiz
Question 1 Nuclear lamin proteins Answers: a. make up the nuclear pores. b. are a meshwork of proteins that form distinct compartments in the nucleus. c. make up a meshwork that lie directly beneath and support the inner membrane of the nucleus. d. fold the 30 nm fibers into mitotic chromosomes. e. transport mRNA out of the nucleus.
Question 2
Indicate true (T) and false (F) statements below regarding the nucleus and nuclear protein transport.
• The inner and outer nuclear membranes are continuous with each other, yet maintain distinct protein compositions. • The outer nuclear membrane is studded with ribosomes engaged in protein synthesis. • The endoplasmic reticulum lumen is continuous with the nuclear interior. Answers: a. TTF b. FFT c. TFT d. FTF e. TTT
Question 3
Which of the following statements about nuclear pores is false?
Answers: a. They are comprised of more then 30 different proteins. b. The cytoplasmic and nuclear sides of the pores are distinct. c. All protein trafficking through nuclear pores is receptor mediated. d. All protein trafficking through nuclear pores is unidirectional. e. Transport through the nuclear pores is energy dependent.
Question 4
Which of the following statements statements regarding post-translational protein trafficking of fully synthesized proteins is false? Answers: a. Proteins are translocated from the cytosol to the ER b. Secretory vesicles carry proteins from the Golgi to the plasma membrane c. Proteins are transported from the Golgi to the ER in vesicles d. Secretory vesicles transport proteins between the nucleus and cytosol e. Proteins are translocated from the cytosol to mitochondria
Question 5
Which of the following scenarios does NOT normally occur on a nuclear pore complex? Answers: a.A protein complex is imported into the nucleus, with ONLY one of its subunits containing a nuclear localization signal (NLS). b.In a single pore, an NLS-containing protein is imported, while at the same time a nuclear export signal (NES)-containing protein is exported. c. A nuclear import receptor is exported from the nucleus through the pore. d. A protein is imported on its own through the pore, without the need for a separate import receptor. e. All of the above are possible scenarios and occur naturally.
Lecture 10B Quiz
Question 1
In the Ran/importin pathway ________ provides the energy for transport of proteins into the nucleus.
Answers: a. proton motive force
b. GTP hydrolysis c. GDP phosphorylation d. ATP hydrolysis
Question 2
Another feature of the transport of proteins across the nuclear envelope is that the Answers: a. nuclear pore complex acts as the receptor for the NLS, there is no specific receptor. b. receptors for the NLS are cytoplasmic rather than membrane bound. c. receptors for the NLS are found on both inner and outer nuclear membranes. d. receptors for the NLS also cleave the NLS during translocation of the protein. e. receptors for the NLS unfold the protein to be translocated before it passes through the nuclear pore complex.
Question 3
The formation of a stable ternary complex involving Ran GTPase, a nuclear transport receptor, and a cargo protein occurs in ... Answers: a. both nuclear import and export. b. nuclear import, but not export. c. nuclear export, but not import. d. neither nuclear import nor export.
Question 4
Which of the following statements about mitochondrial protein translocation is false? Answers: a. There is only one type of mitochondrial translocase that transports proteins to different locations in the mitochondrion. b. ATP hydrolysis is required for protein translocation. c. Translocation is receptor mediated. d. Protein translocation is unidirectional. e. The chaperone hsp70 is required both on the cytosolic side of the mitochondrion and the mitochondrial matrix.
Question 5
Transport of a protein (cargo) from the cytoplasm into the nucleus occurs through the translocation of a complex of proteins including the cargo bound to importin proteins (α and β). What mechanism ensures that this complex does not exit the nuclear pore complex (NPC) once it has passed through the nuclear pore and into the nucleus? Answers: a. No specific mechanism is required because transport of proteins is always unidirectional through the NPC. b. The shape of the NPC is such that the basket region on the inner surface of the nuclear membrane allows passage of this protein complex in one direction into the nucleus but not out. c. Export from the nucleus requires distinct NPCs and distinct proteins called exportins. d. Ran-GTP is enriched in the nucleus and binds the complex, causing the disassociation of cargo and importins and trapping the cargo in the nucleus. e. Ran-GTP is enriched in the nucleus and hydrolyzes GTP to GDP to phosphorylate the importins, causing the disassociation of cargo and importins and trapping the cargo in the nucleus.
Lecture 10C Quiz
Question 1
True or False: Mitochondrial proteins are synthesized in the cytosol and then sorted and folded before entering the mitochondria. Answers: True False
Question 2
What kind of molecule has been implicated in preparing polypeptides for mitochondrial uptake, including those that specifically direct mitochondrial proteins to the cytosolic surface of the outer mitochondrial membrane? Answers: a. proteases b. aggregases c. molecular chaperones d. carbohydratase e. pronases
Question 3
The presence of a transit sequence directs a protein from the ________ to the ________. Answers: a. cytosol; mitochondrion or chloroplast b. endoplasmic reticulum; Golgi apparatus
c. cytosol; plasma membrane d. endoplasmic reticulum; nucleus e. signal recognition particle; nucleus
Question 4
Which of the following proteins or protein complexes is directly required for the targeting of mitochondrial inner membrane multipass proteins, such as metabolite transporters, whose signal sequence is normally not cleaved after import? Answers: a. TIM22 b. TIM23 c. OXA d. Mia40 e. SAM
Question 5
Which list below names the compartments into which chloroplast proteins must be imported? Answers: a. inner and outer chloroplast membranes, the intermembrane space, the stroma, thylakoid membranes, thylakoid lumen b. inner and outer chloroplast membranes, the intercristal space, the stroma, thylakoid membranes, thylakoid lumen c. inner and outer chloroplast membranes, the intermembrane space, the cytoplasm, thylakoid membranes, thylakoid lumen d. inner and medial chloroplast membranes, the intermembrane space, the stroma, thylakoid membranes, thylakoid lumen e. inner and outer chloroplast membranes, the intermembrane space, the stroma, cristae membranes, thylakoid lumen
Lecture 10D Quiz
Question 1
Proteins that are destined to be translocated into the stroma must have a transit peptide including _______. Answers: a. a thylakoid transfer domain b. a thylakoid lumen domain c. a transit peptidase
d. a stroma-targeting domain e. a matrix-targeting domain
Question 2
What removes the stroma-targeting domain and where does the removal occur? Answers: a. a processing peptide synthase, stroma b. a processing peptidase, stroma c. a processing peptidase, thylakoid membrane d. a processing peptidase, thylakoid lumen e. a stromal signal peptidase, stroma
Question 3
Which of the following is NOT directly involved in driving protein import into the mitochondrial matrix space? I. ATP hydrolysis inside mitochondria II. ATP hydrolysis outside mitochondria III. Membrane potential across the inner membrane IV. Membrane potential across the outer membrane Answers: a. I b. II c. III d. IV e. II and IV
Question 4
Which one of the following is the most accurate depiction of the mitochondrial protein import mechanism? Answers:
a. Proteins are synthesized in the cytosol, unfolded by hsp70, and carried across by a soluble transport receptor that then recycles to th e cytosol. b. Proteins
are synthesized in the cytosol, captured by hsp70, and are carried across by a translocation channel that spans both membranes; once in the mitochondrial matrix, the signal sequence is cleaved. c. Proteins
are escorted through the mitochondrial membrane by a soluble transport receptor that only recognizes fully functional, properly folded p roteins.
d. Proteins
bind to SRP, and the protein-SRP complex binds to the SRP receptor, which transfers the protein to the translocation channel.
e. Proteins
bind to hsp70 in the cytosol, are carried across in a properly folded shape and the signal sequence is cleaved.
Question 5
Which of the following descriptions (1-5) applies only to protein import into mitochondria? 1. ATP and GTP hydrolysis h ydrolysis drive translocation into the organelle. 2. The organelle has an extra compartment that requires extra signal sequences for p rotein targeting. 3. Transport through the double membrane is driven in part by an H+ gradient across the inner membrane. 4. Imported precursor proteins have amphiphilic N-terminal signal sequences that are usually removed after use. 5. Hsp70 family chaperones inside the organelle assist in protein translocation during import. Answers: a. 1 b. 2 c. 3 d. 4 e. 5
Lecture 11A Quiz
Question 1
True or false? Mitochondria are large enough enou gh to be seen with modern light microscopy, and can occupy as much as 20% of cytoplasmic volume. Answers: a. True b. False
Question 2
What advantage do the cristae confer on the mitochondria? Answers: a. They allow the mitochondria to shrink. b. They greatly increase the surface area for aerobic respiration machinery. c. They confer resiliency on the cells. d. They allow swelling of mitochondria.
e. They activate the matrix.
Question 3
In addition to their respiratory function, mitochondria have other important roles in cellular metabolism. Which of the following processes is NOT carried out mainly by mitochondria? Answers: a. Biosynthesis of cardiolipin b. Biosynthesis of fatty acids c. Catabolism of amino acids d. Biosynthesis of heme
sulfur clusters e. Biosynthesis of iron – sulfur
Question 4
When fission of mitochondria becomes more frequent than fusion, the mitochondria tend to become __________ . Answers: a. more elongated b. more interconnected c. more numerous d. more distinct e. more numerous and more distinct
Question 5
___________ exhibit lower electron affinity. Answers: a. Strong oxidizing agents b. Strong elucidating agents c. Strong reducing agents d. Weak reducing agents e. Weak eliminating agents
Lecture 11B Quiz
Question 1
What is the role of oxygen in the electron transport chain in mitochondria? Answers: a. Oxygen is the final electron acceptor in the respiratory chain and O 2/H2O has the lowest redox potential. b. Oxygen is the final electron acceptor in the respiratory chain and O 2/H2O has the highest redox potential. c. Oxygen accepts electron directly from NADH in the first step of the electron transport chain and O2/H2O has the lowest redox potential. d. Oxygen donates electrons to NAD + and O2/H2O has the lowest redox potential has the lowest redox potential. e. Oxygen is released when electrons are donated to water.
Question 2
Oxidative phosphorylation is the mechanism of electron transport linked to ATP synthesis by coupling electron transport to proton pumping, _____. Answers: a. and using the H + and electrons to react with ADP to make ATP b. which creates a H+ gradient across the inner membrane and when the H + flows back across the membrane it drives the ATP synthase to synthesis ATP from ADP c. which creates a H + gradient across the inner membrane that drives ATP into the mitochondria matrix via active transport d. which creates a H+ gradient across the inner membrane and the low pH causes ADP to react with Pi to make ATP
Question 3
In what ways can pyruvate and NADH be metabolized? Answers: a. fermentation, hydrolysis of Glyceraldehyde 3 Phosphate b. condensation of G3Pand fermentation c. aerobic processes using Krebs cycle, fermentation d. anaerobic processing using Krebs cycle, fermentation
using Krebs cycle, hydrolysis hydrolysis of G3P e. aerobic processing using
Question 4
NADH dehydrogenase and cytochrome oxidase are the first and last protein complexes respectively, in the mitochondrial electron transport chain. What properties do these protein complexes have in common in the ETC?
Answers: a. They are both capable of donating electrons to oxygen. b. They are both capable of both accepting and donating electrons. c. They both undergo conformation changes during electron transfer that moves a proton across the inner membrane of the mitochondria. d. Both B and C are true. e. All of the above are true.
Question 5
The synthetic toxin 2,4-dinitrophenol can uncouple ATP synthesis from mitochondrial respiration by changing the permeability of the inner membrane to protons. What would be the effect of dinitrophenol treatment on the amount of ATP produced by mitochondria, and on the rate of ATP transport across the inner membrane, respectively? Answers: a. Positive; positive b. Positive; negative c. Negative; positive d. Negative; negative
Lecture 11C Quiz
Question 1
The matrix is to the mitochondrion as the ________ is to the chloroplast. Answers: a. thylakoid b. cytoplasm c. cristae d. stroma e. lumen
Question 2
The electrons used in carbon fixation by chloroplasts ultimately come from … Answers: a. Atmospheric oxygen b. Atmospheric carbon dioxide c. Water
d. Glyceraldehyde 3-phosphate
Question 3
The cytochrome b6-f complex that transfers electrons between the two photosystems in photosynthesis is structurally and functionally similar to which of the complexes in the mitochondrial electron-transport chain? Answers: a. NADH dehydrogenase b. Succinate dehydrogenase c. Cytochrome c reductase d. Cytochrome c oxidase e. ATP synthase
Question 4
Why is the conversion of CO 2 to a 6-carbon sugar so energetically expensive? Answers: a. CO2 is the most highly reduced and least energetic form in which carbon can occur. b. CO2 is very unstable. c. CO2 is the most highly oxidized and least energetic form in which carbon can occur. d. CO2 is the most highly oxidized and most energetic form in which carbon can occur. e. CO2 is highly unstable and only moderately energetic which makes the process more expensive energetically.
Question 5
The production of ATP in chloroplasts and mitochondria differs in which of the following ways? Answers: a. The protons move into the stroma in chloroplasts and out of the mitochondria. b. In mitochondria, the force is expressed primarily as an electrochemical potential; in chloroplasts, it is largely, if not exclusively, due to a pH gradient. c. In mitochondria, the force is expressed primarily as a pH gradient; in chloroplasts, it is largely, if not exclusively, due to an electrochemical potential. d. The protons move into the intermembrane space in chloroplasts and into the thylakoid lumen in mitochondria. e. The protons move into the matrix in mitochondria and into the cytoplasm in chloroplasts.
Lecture 11D Quiz
Question 1
Which of the following characteristics do peroxisomes have in common with mitochondria? Answers: a. Contain their own DNA b. Surrounded by two membranes c. Translocate proteins from the cytosol d. Contain their own ribosomes.
Question 2
Which reaction is normally catalyzed by the enzyme catalase in the peroxisome? Answers: a. 2O2 – + + 2H+ → H2O2 + O2 b. FMNH2 + O2 → FMN + H2O2 c. C2H5OH (ethanol) + NAD+ → C2H4O (acetaldehyde) + NADH + H + d. 2H2O2 → 2H2O + O2 e. Both C and D above
Question 3
Sort the following events as they occur during the peroxisomal protein import cycle, starting with the release of cargo from Pex5. Your answer would be a five-letter string composed of numbers (1 – 5) 5) (1) Pex5 deubiquitylation (2) Pex5 ubiquitylation (3) Docking and translocation of the cargo protein along with Pex5 (4) Pex5 export from the peroxisome with the help of ATPases Pex1 and Pex6 (5) Pex5 binding to a cargo protein containing a C-terminal peroxisomal targeting sequence Answers: a. 1,4,2,5,3 b. 2,4,1,5,3 c. 1,5,2,4,3 d. 3,1,2,5,4 e. 2,5,1,4,3
Question 4
Which reason below correctly explains why many peroxisomal disorders result in neurological disease? Answers: a. Catalase and urate oxidase leak out of the peroxisomes and destroy nerve cells.
b. Plasmalogens produced by dysfunctional peroxisomes contain extra ether linkages causing them to myelinate liver cells. c. Cholesterol builds up in nerve cells preventing normal cellular function. d. Toxins build up in nerve cells preventing normal cellular function. e. Very long chain fatty acids build up in the brain and destroy myelin sheaths of nerve cells.
Lecture 12A Quiz
Question 1
Which of the following cytoskeletal filaments are abundant in an animal cell nucleus? Answers: a. Microfilaments b. Microtubules c. Septins d. Intermediate filaments e. Spectrin filaments
Question 2
Under normal physiological conditions during elongation, the barbed end of an actin filament Answers: a. is the so called (+) end. b. is capped by actin-ATP. c. is structurally different than the pointed (-) end. d. only A and B are true. e. A, B and C are true.
Question 3
What is treadmilling of an actin filament? Answers: a. Simultaneous loss of actin monomers from one end and addition of monomers to the other end of an actin filament, without changing the overall length of the filament. b. Simultaneous loss of monomers from both ends of the actin filament. c. Simultaneous growth on one actin filament and shrinkage of another filament in the same cell, so the overall amount of actin filament in the cell does not change. d. Myosin motor proteins moving bidirectionally along the actin filament.
e. Capping of the barbed end of the actin filament to prevent further growth.
Question 4
Match the following actin associated proteins to their correct function.
Answers: a. CEDAB b. BCEDA c. ADBEC d. DAEBC e. ECDAB
Question 5
In vitro and under steady state conditions, the critical concentration (Cc) of the barbed end of a filament is 0.1 um, and the Cc of the pointed end of this filament is 0.6 um. If the concentration of actin-ATP monomers is 0.3 um, what would happen to this actin filament? Answers: a. The barbed end would grow by adding monomers and the pointed end would shrink by losing monomers. b. The barbed end would shrink by losing monomers and the pointed end would grow by adding monomers. c. Both ends would grow by the addition of monomers, but at different rates d. Both ends would shrink by loss of monomers, but at different rates. e. Cannot predict from the information provided.
Lecture 12B Quiz
Question 1
The actin cytoskeleton generates cell movement in the following way:
Answers: a. Directed polymerization of actin filaments against the plasma membrane. b. The interaction of actin filaments and the motor protein myosin. c. Directed polymerization of myosin fibers against the plasma membrane. d. Only A and B are mechanisms of generating cell movement by the actin cytoskeleton. e. A, B and C are mechanisms of generating cell movement by the actin cytoskeleton.
Question 2
Indicate whether each of the following descriptions matches Cdc42 (C), Rac (R), or Rho (H) from the Rho family of monomeric GTPases. Your answer would be a three-letter string composed of letters C, R, and H only, e.g. HRR. - It activates formin. - It inhibits myosin II activity. - When constitutively active, it induces the formation of many prominent stress fibers. Answers: a. CRH b. RCC c. HCH d. HRC e. CCR
Question 3
The actin-nucleating protein formin has flexible “whiskers” containing binding sites that help recruit actin subunits in order to enhance polymerization by this protein. What protein would you expect to bind to these sites? Answers: a. Thymosin b. Profilin c. Cofilin d. Gelsolin e. Tropomodulin
Question 4
Consider an actin subunit that has just been incorporated into an actin filament at the leading edge of a lamellipodium. Before its ATP is hydrolyzed, how does its distance from the leading front edge of the plasma membrane change over time? How does its distance from the F-actin minus end change over time? Answers: a. Decreases; decreases b. Decreases; remains constant
c. Decreases; increases d. Increases; decreases e. Increases; remains constant
Question 5
Actin filaments that are held together by the cross-linking protein fimbrin are not contractile. This is probably because … Answers: a. the very weak cross-linking by this protein cannot convert myosin II activity into a coherent contraction. b. fimbrin arranges the actin filaments in parallel bundles in which all the plus ends point to the same direction. c. the very tight packing of actin filaments by this small protein excludes myosin II filaments and other large proteins. d. fimbrin arranges the actin filaments into gel-like networks in which myosin II activity does not produce contraction. e. fimbrin is a large protein that binds to several actin filaments and resists contraction.
Lecture 12C Quiz
Question 1
What is the major microtubule-organizing center in animal cells? Answers: a. The γ-tubulin ring complex b. The centrosome c. The cell cortex d. The primary cilium e. The spindle pole body
Question 2
In contrast to growing microtubules, shrinking microtubules … Answers: a. have a GTP cap at their plus end. b. have strong lateral interactions at their plus ends. c. have curved protofilaments at their plus ends.
d. cannot be rescued unless microtubule-stabilizing proteins bind and inhibit depolymerization. e. All of the above.
Question 3
Centrosomes Answers: a. nucleate microtubule formation by stabilizing the GTP cap. b. contain γ tubulin rings that act as nucleating sites at the minus end of microtubules. c. attach microtubules to the plasma membrane. d. promote the addition of tubulin to the plus end of microtubules. e. promote microtubule dissociation at the minus end.
Question 4
Which of the following best describes the concept of “dynamic instability” as it applies to the microtubules? Answers: a. Steady growth of a microtubule, which abruptly collapses and shortens b. Substitution of GTP for GDP in the growing end of a microtubule c. Reversible phosphorylation of microtubules by GTP during the cell cycle d. Simultaneous addition of GTP-bound tubulin subunits to the plus end of a microtubule and cleavage of GTP to GDP by tubulin subunits contained within microtubules e. Simultaneous addition and loss of tubulin dimers on the (+) and (-) ends of microtubules, respectively
Question 5
The γγ-tubulin ring complex is to microtubules what … is to actin filaments. Answers: a. the Arp 2/3 complex b. the dynactin complex c. the troponin complex d. formin e. contractile ring
Lecture 12D Quiz
Question 1
True or False: Phosphorylation of stathmin activates tubulin binding to stathmin. Answers: True False
Question 2
Which of the following proteins do you expect to be enriched near the plus end of microtubules? Answers: a. Dynein b. XMAP215 c. γ-Tubulin d. Katanin e. All of the above
Question 3
What are the common features of the motor proteins kinesin and dynein? I. Both types of motor proteins bind microtubules. II. Both types of motor proteins bind and hydrolyze ATP III. Both types of motor proteins undergo conformational changes when the motor travels. IV. Both types of motor proteins “step” from one tubulin to another Answers: a. I. II and III b. I, III and IV c. II, III and IV d. I, II and IV e. I, II, III and IV
Question 4
Which of the following is the best description of the action of the MAP (microtubule associated protein) tau on microtubules in neurons? Answers: a. Tau binds the (+) end of the microtubules and promotes tubulin addition. b. Tau binds the (-) end of the microtubules and inhibits tubulin loss. c. Tau binds alongside the microtubules, binding several tubulin dimers at a time and preventing dynamic instability. d. Tau binds GTP at the (+) end of the microtubule and prevents hydrolysis. e. Tau binds alongside the microtubules and prevents katanin from severing microtubules.
Question 5
In the presence of ATP in a flagellum, an axonemal dynein that is interacting through its tail with the A microtubule of a peripheral doublet can push this doublet toward the ...(1) of the flagellum, but due to the presence of linking proteins such as ...(2), this force is converted i nto a bending motion. Answers: a. (1) tip; (2) nexin b. (1) base; (2) nexin c. (1) tip; (2) nebulin d. (1) base; (2) nebulin e. (1) tip; (2) tau
Lecture 13A Quiz
Question 1
True or False: The number of human cells in our body is greater than the number of bacterial, fungal, and protozoan cells of our normal flora. Answers: True False
Question 2
The differences between gram-positive and gram-negative bacteria include: I. only gram-negative bacteria have an outer membrane. II. only gram-negative produced peptidoglycan in their cell walls. III. only gram-positive bacteria produce teichoic acid in their cell walls. IV. only gram-positive bacteria have crosslinks between peptidoglycan. V. gram-positive bacteria have a thicker cell wall than gram-negative bacteria. Answers: a. I, II, III and V are correct. b. II, III and V are correct. c. I, III and V are correct. d. I, II, III, IV and V are correct. e. None of the above statements are correct.
Question 3
Indicate whether each of the following examples better applies to commensalism (C), mutualism (M), or parasitism (P) in the interaction between a host and a microbe. Your answer would be a four-let ter string composed of letters C, M, and P only, e.g. CCPP.
• • • •
Due to poor public sanitation, a child catches cholera. A mouse is infected with a virus but shows no noticeable health defect whatsoever. Biotin and other vitamins produced by intestinal microbiota are regularly absorbed in the human intestine. Bacteria on the skin of cattle produce antifungal compounds. Answers: a. PCMM b. PMMC c. PCCM d. PP
Question 4
In the following simplified diagram, three mechanisms for the horizontal transfer of virulence genes to an avirulent bacterium are depicted. Indicate which mechanism (A to C) corresponds to conjugation, transduction, and transformation, respectively. Your answer would be a three-letter string composed of letters A to C only, e.g. CAB. .
Answers: a. BCA b. ABC c. CAB d. BAC e. CBA
Question 5
In Gram staining, crystal violet (a violet dye) is used to specifically stain Gram-positive bacteria. After performing Gram staining on a bacterial sample taken from an infected ani mal tissue, you observe the results with a microscope. You find two major types of bacteria in the sample, as shown in the schematic drawing below. According to these results, indicate whether each of the following statements i s correct (C) or incorrect (I). Your answer would be a three-letter string composed of letters C and I only, e.g. CCC.
The Gram-positive bacteria in this sample are bacilli. • • Crystal violet stains lipopolysaccharide (LPS). • The bacteria stained violet in this sample have a thicker layer of peptidoglycan compared to the other bacteria. Answers: a. CCC b. ICI c. CIC d. IIC e. CCI
Lecture 13B Quiz
Question 1
How has pathogenicity in pandemic strains of Vibrio cholerae been cholerae been acquired? Answers: a. By transformation
b. By transduction c. By conjugation d. By vertical gene transfer
Question 2
The type III secretion system of pathogenic bacteria … Answers: a. is a general secretion system found only in Gram-positive bacteria. b. is used to inject effector proteins directly into the cytoplasm of host cells. c. is similar to the eukaryotic secretion system. d. is similar to the bacterial conjugation apparatus. e. All of the above
Question 3
Both Vibrio cholerae and Bacillus anthracis … Answers: a. secrete a lethal factor and an edema factor. b. secrete toxins that enter the cell in endosomes and eventually enter the cytosol after reaching the endoplasmic reticulum. c. raise cyclic AMP levels in the cytosol of their target cells. d. secrete toxins that have enzymatic adenylyl cyclase activity. e. All of the above.
Question 4
A researcher is trying to characterize a novel prokaryotic organism that has been found in the Indian Ocean. When Gram stained, the cells are a light pink color under the microscope. When exposed to antibiotics commonly used in the lab, the bacteria are able to enter the log growth phase in a manner similar to E. coli grown coli grown in media lacking ampicillin. A reasonable explanation is that: Answers: a. this is a Gram-positive bacterium with an additional lipopolysaccharide layer that increases their resistance to antibiotics. b. this is a Gram-positive bacterium with a cell membrane outside its peptidoglycan layer that increases their resistance to antibiotics. c. this is a Gram-negative bacterium with an additional lipopolysaccharide layer that increases their resistance to antibiotics. d. this is a Gram-negative bacterium with a peptidoglycan layer outside the cell membrane that increases their resistance to antibiotics.
Question 5
You infect human epithelial cells in culture with either nonpathogenic bacteria or Vibrio cholerae, cholerae , each without any further treatment, in the presence of MDC (an inhibitor of clathrin-dependent endocytosis) or in the presence of filipin (an inhibitor of a clathrin-independent endocytic pathway). You then measure the intracellular concentration of cyclic AMP (in picomoles per milligram of total cell protein) and summarize the results in the following table. Which row (1 or 2) do you think corresponds to infection with V. cholerae? cholerae? From these results, does cholera toxin enter the cell in clathrin-coated vesicles?
Answers: a. Row 1; yes b. Row 1; no c. Row 2; yes d. Row 2; no
Lecture 13C Quiz
Question 1
True or False: Some intracellular pathogens escape transport to the lysosome by living and replicating in white blood cells. Answers: True False
Question 2
Which of the following is not a characteristic of the intracellular pathogen Listeria monocytogenes? Answers: a. It moves by a “pushing” mechanism “pushing” mechanism (as opposed to a “pulling” mechanism). “pulling” mechanism). b. It can collide with the plasma membrane and create long, thin protrusions from the cell that can then be engulfed by a neighboring cell. c. Its movement is powered by ATP hydrolysis by kinesin and dynein motors. d. Its movement relies on dynamic cytoskeletal filaments.
Question 3
An intracellular pathogen uses one of three major strategies to survive and replicate once inside the host cell, as shown in the schematic drawing below. Indicate which strategy (1, 2, or 3) each of the following pathogens employs for this purpose. Your answer would be a three-digit number composed of digits 1 to 3 only, e.g. 332.
• • •
Listeria monocytogenes Legionella pneumophila Shigella flexneri Answers: a. 112 b. 212 c. 121 d. 221
Question 4
After gaining entry into the host cell by the zipper mechanism, the bacterium Listeria monocytogenes escapes monocytogenes escapes phagosomes by secreting listeriolysin O. This protein … Answers: a. is active at neutral pH and cannot be degraded by the proteasome. b. is active at neutral pH and is rapidly degraded by the proteasome. c. is active at acidic pH and cannot be degraded by the proteasome. d. is active at acidic pH and is rapidly degraded by the proteasome. e. is active at basic pH and cannot be degraded by the proteasome.
Question 5
To enter the host cell, intracellular bacterial pathogens can induce phagocytosis in cells that are normally nonphagocytic. This is done by two major mechanisms depicted in the following schematic diagrams (1 and 2). Indicate whether each of the following descriptions better applies to mechanism 1 or 2. Your answer would be a four-letter string composed of numbers, 1 and 2 only.
It is called the zipper mechanism. It depends on invasin proteins on the surface of the bacterium that bind to their receptors on the surface of the host cell. It depends on the injection of o f effector proteins into the host cell by a bacterial secretion system. It resembles the process of macropinocytosis. Answers: a. 1221 b. 1112 c. 2211 d. 2112 e. 2221
Lecture 13D Quiz
Question 1
Which of the following is the correct sequence of the human-phase of the Plasmodium life Plasmodium life cycle? Answers: a. merozoites, sporozoites, schizont, gametophyte b. gametophyte, merozoite, sporozoite, schizont c. schizont, gametophyte, merozoite, sporozoite d. sporozoite, merozoite, schizont, gametophyte
e. gametophyte, sporozoite, merozoite, schizont
Question 2
Indicate whether each of the following descriptions better applies to enveloped (E) or nonenveloped (N) viruses. Your answer would be a four-letter string composed of letters E and N only, e.g. NNNN. • They include retroviruses. • They include adenoviruses. • To leave the cell, they normally lyse it. • They are more sensitive to treatment with detergents, heat, or drying. Answers: a. ENEN b. NNEE c. ENEE d. EENE e. ENNE
Question 3
HIV belongs to a unique category of viruses termed retroviruses. Which of the following enzymes would be unique to retroviruses? Answers: a. DNA polymerase b. RNA polymerase c. reverse transcriptase d. helicase
Question 4
Indicate true (T) and false (F) statements below regarding viral cell entry. Your answer would be a four-letter string composed of letters T and F only, e.g. FFTF. • Endocytosis inhibitors can block HIV entry but not influenza virus entry. • Adenovirus infection is blocked by membrane-fusion inhibitors. Individuals with a defective CCR5 gene • CCR5 gene are more susceptible to HIV infection. • Most viruses enter the host cell by phagocytosis. Answers: a. TTFT b. FTFF c. TTTT d. FFTF
e. FFFF
Question 5
Cyanide (an inhibitor of the electron transport chain) is added to a culture of virus-infected mammalian cells. The virus has none of the components of electron transport nor any other proteins that are inhibited by cyanide. Which one of the following best describes the effect of cyanide? Answers: a. The mammalian cells will die, and all viruses will be destroyed as well, regardless of their stage of development. b. Mammalian cells are killed, and viral replication halted, but the culture remains infectious. c. Mammalian cells stop growing, and viral replication is unaffected. d. Mammalian cells continue to grow, but viral replication is halted.
Lecture 13E Quiz
Question 1
Do ( – ) strand RNA viruses use host enzymes to catalyze RNA production in transcription or in replication of the genome? Answers: a. Catalyse RNA production in transcription. b. Replication of the genome. c. Both d. Neither
Question 2
Sort the following events to reflect the order in which they typically occur in viral replication after a virus enters a cell. Your answer would be a four-digit string composed of numbers. (1) Replication of the viral genome and transcription transcription of viral genes (2) Virus particle assembly (3) Progeny virion release (4) Virus particle disassembly Answers: a. 2134 b. 4123 c. 1324 d. 3412 e. 3241
Question 3
In which of the following groups of viruses is an RNA-dependent RNA polymerase packaged as a structural protein in each newly made viral particle? Answers: a. DNA viruses b. Viruses with a positive [+] strand RNA genome c. Viruses with a negative [ – ] strand RNA genome d. Retroviruses e. Viruses with a part single- and part double-stranded DNA genome
Question 4
Which of the following conditions is NOT expected to provide protection against HIV-1 infection of helper T cells? Answers: a. A loss-of-function mutation in the CCR5 gene b. Treatment with enfuvirtide, a membrane-fusion inhibitor c. Treatment with concanamycin A, an inhibitor of endosomal proton pumps d. Treatment with AMD-070, a CXCR4 antagonist e. Treatment with PRO-542, a soluble decoy protein containing CD4 sequences
Question 5
Drugs such as AZT and ddI are nucleoside analogs used in HIV-infected patients. Both are chemically modified versions of the nucleotides that make up DNA and RNA. These modified nucleosides interfere with normal replication and transcription. The MOST important goal of these drugs would be: Answers: a. to prevent the replication of host cell DNA so that the host cell cannot function b. to prevent the transcription of host cell RNA so that no proteins can be expressed c. to prevent the viral nucleic acid from entering the host cells d. to prevent replication of the viral genome
Lecture 14A Quiz
Question 1
True or False: The classical pathway of complement activation is triggered by binding of a secreted PRR to mannose-containing glycoproteins or glycolipids on the surface of pathogens. Answers: True
False
Question 2
Which of the following are recognized by pattern recognition receptors as pathogen-associated molecular patterns? Answers: a. Double-stranded viral RNAs b. Formylmethionine-containing proteins c. Unmethylated CpG motifs d. Bacterial flagella components e. All of the above
Question 3
Which of the following cell types is NOT phagocytic? Answers: a. Macrophage b. Monocyte c. Neutrophil d. Lymphocyte e. Dendritic cell
Question 4
Fill in the blank in the following paragraph regarding the innate and adaptive immune systems.
“As key components of the innate immune response, ______ cells provide the link between the innate and adaptive immune responses. Upon exposure to pathogens in tissues, they engulf the microbe, become activated, and travel to nearby lymphoid organs where they present the processed antigens to the lymphocytes of the adaptive immune system.” Answers: a. Blood cells b. Mast cells c. T cells d. Dendritic cells e. Skin cells
Question 5
Indicate whether each of the following descriptions better applies to an Adaptive or Innate immune response.
Question
Correct Match
It is found in invertebrate and vertebrate animals a s well as in plants.
b. Innate Immune Response
It has a long-lasting memory.
a. Adaptive Immune Response
It is highly specific to the particular invading pathogen.
b. Innate Immune Response
It employs natural killer (NK) cells to induce apoptosis in infected host cells.
a. Adaptive Immune Response
Lecture 14B Quiz
Question 1
Which of the following statements about antibodies is true? I. Antibodies are produced by B cells. II. Antibodies only recognize peptide antigens. III. Antibodies can mark an antigen for destruction by killer T cells. Answers: a. I only b. II only c. I and II d. I and III
Question 2
Indicate whether each of the following statements is true or false regarding all the cell-surface immunoglobulin molecules produced by a single, mature, naïve B cell.
Question
Correct Match
They all have the same heavy chain.
b. False
They all have the same light chain.
a. True
They all have the same antigen-binding a ntigen-binding site.
b. False
Question 3
Indicate whether each of the following descriptions better applies to B cells or T cells of the adaptive immune system.
Question
Correct Match
Their effector cells act mainly at short range.
a. T cells
Their receptors recognize protein fragments that have be en processed in antigen presenting cells.
a. T cells
They do NOT normally express CD8 protein on their surface.
b. B cells
They can become “killer” cells. “killer” cells.
a. T cells
Question 4
T-cell antigen receptors are different from antibodies because: Answers: a. T-cell receptors must interact with antigen uniquely presented by other cells but not with free antigen. b. T-cell receptors bind various cytokines. c. T-cell receptors bind complement proteins to lyse cells. d. T-cell receptors are mediators of allergic reactions.
Question 5
Which one of the following best describes the mechanism by which production of specific antibody is achieved in response to antigen exposure? Answers: a. Immature B cell clones expressing several different antibody genes select for one gene and turn off expression of the others. b. Antigen stimulates proliferation of a specific B cell clone expressing a single antibody protein that recognizes that antigen.
c. The variable regions of antibody proteins on an immature B cell clone form a pocket around the antigen, and the antibody genes are recombined to fit the bound antigen.
cell’s surface in different combinations to d. Antibody light and heavy chains are mixed on each B cell’s surface produce different antigen recognition.
Lecture 14C Quiz
Question 1
Normally, naïve cytotoxic and helper T cells interact for t he first time with foreign anti gens presented by dendritic cells in … Answers: a. the thymus. b. the bloodstream. c. peripheral lymphoid organs. d. the bone marrow. e. inflamed tissues.
Question 2
In antigen presentation to helper T cells (TH cells), both the TCR and co- receptor proteins… Answers: a. are expressed on the dendritic cell. b. bind to the class II MHC protein. c. bind to the presented peptide antigen. d. All of the above.
Question 3
Which of the following better describes cross-presentation of protein antigens by professional antigen presenting cells to naïve TC cells? Answers: a. Presentation of intracellular antigens by class I MHC proteins b. Presentation of intracellular antigens by class II MHC proteins c. Presentation of extracellular antigens by class I MHC proteins d. Presentation of extracellular antigens by class II MHC proteins
Question 4
Sort the following events to reflect the order in which they occur in the presentation of viral peptides to cytotoxic T cells by a virus-infected cell. Your answer would be a four-letter string composed of letters A to D only, e.g. BDCA. (A) Peptide transport into the ER lumen (B) Partial proteasomal degradation of the viral protein into peptide fragments (C) Peptide binding to class I MHC protein in the ER lumen (D) The appearance of viral protein in the cytosol Answers: a. BDCA b. CDBA c. ACBD d. DBAC e. DACB
Question 5
How are natural killer (NK) cells different from cytotoxic T (TC) cells? Answers: a. NK cells induce apoptosis in their target cells, whereas T C cells are professional phagocytes. b. NK cells kill virus-infected cells, whereas TC cells kill cancerous cells. c. NK cells kill cells with a hi gh level of class I MHC protein expression, whereas killi ng by TC cells requires low expression levels. d. NK cells respond quickly to a virus infection, whereas the activation of TC cells to become cytotoxic is a slow process. e. NK cells are normally abundant in the tissue even before infection, whereas TC cells are mostly in the bloodstream.
