Chapter 3: Movement of Substances Across The Plasma Membrane
WATER
Hydrophilic head Hydrophobic tail WATER
3.1
The Movements Movements of Substances Across The Plasma Membrane
1. The movem movement ent of of substa substances nces in and out of of cells cells occur occurss across plasma membrane. 2. The The Pla Plasm sma a Mem Membr bran ane: e: is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell. 3. Functi Function on of the Plasm Plasma a Mem Membr brane ane:: -Protects the cell. -Separates the intracellular components from the extracellular environment. -Controls what enters and exits the cell 4. Necessities for the Movement of Substances across the Plasma Membrane: -To transport nutrients into the cell. -For gases exchange. -To -To excrete metabolic metaboli c waste. -To maintain the pH value and ionic concentration of the cell.
The Structure of Plasma Membrane and Its Components
Glycoprotein
Carbohydrate
Glycolipid EXTRACELLULAR SIDE OF MEMBRANE
Microfilaments of cytoskeleton
Cholesterol
Peripheral Protein (hanya sebahagian drpd. badan protein yg terbenam dlm. Phospholipid bilayer)
Glycoprotein = Carbohydrate+Protein Carbohydrate+Protein Glycolipid = Carbohydrate+Lipid Carbohydrate+Lipid
Integral Protein (seluruh badan protein terbenam dlm. Phospholipid bilayer)
CYTOPLASMIC SIDE OF MEMBRANE
Hydrophilic head
Hydrophobic tail
Phospholipid bilayer
Lateral movement (~107 times per second)
(a) Movement of phospholipids
Flip-flop (~ once per month)
The Structure of Plasma Membrane 5. The plasma membrane membrane consists mainly of phospholipids of phospholipids and proteins. 6. Each Each phosph phospholip olipid id molec molecules ules consist consist of 2 parts: parts: -a polar hydrophilic head (hydro=water, (hydro=water, philic=love) -a non-polar hyrophobic tail (hydro=water, (hydro=water, phobic=hate) 7. In plasma membrane, phospholipids are arranged in 2 layers called phospholipid bilayer. bilayer. 8. The plasma membrane membrane display the fluid mosaic model (FMM). FMM: 9. FMM: - phospholipids, proteins and other components of membrane are not rigid or static. b ilayerr. - the protein molecules float freely in phospholipid bilaye membrane . It -the proteins and phospholipids can move side-by-side within membrane. ch aracteristic. tic. shows fluid characteris 10. Contains cholesterol stabilize and strengthen plasma membrane 11. Pore/channel protein forms channel/pore 12. Carrier protein acts as carrier 13. Glycoprotein protein with carbohydrate attached 14. Glycolipid
lipid with carbohydrate attached
Act as cell-cell recognition
14. The plasma membrane = semi-permeable/partially permeable = certain substances can move in/out of the cell. 15. Membranes that envelope nucleus, mitochondria and chloroplast are semi-permeable. 16. Other example of semi-permeable membrane: Visking tube, cellophane tape, egg membranes. 15. The permeability of the phospholipids bilayer is determined determined by: - the size - the charge and - the polarity of the substances pass through it.
Two ways of the Movement of Substances Across The Plasma Membrane Movement of Substances Across The Plasma Membrane
Passive Transport Transport
ActiveTransport ActiveTransport
Molecules transported down the concentration gradient
Molecules transported against (berlawanan) (berlawanan) the concentration gradient
Simple Diffusion
Osmosis
Facilitated Diffusion
16. What is passive transport? - Passive transport is the movement of substances across the cell membrane without the use of energy by the cell. - During passive transport, substances move down their concentration gradient , hence no energy is required. - Passive transports can happen through three different channels, namely a) lipid bilayer b) pore/channel protein c) carrier protein
17. What is diffusion? movement of molecules/ions from a high concentration region to a low - Diffusion is the movement concentration region . - No energy is needed and no membrane involves in diffusion.
18. What is “down the concentration gradient”? - is the difference in the concentration of a substances between 2 regions.
19. Particles that Move Through the Plasma Membrane Through Diffusion (A ,D,E,K) - Substances soluble in fat : fatty acid, glycerol, some vitamins (A,D,E,K)
- Neutral particles : water, oxygen, carbon dioxide, 20. Examples of Simple Diffusion: - gaseous exchange in alveolus and blood capillary - gaseous exchange through stomata of leaves during photosynthesis - gaseous exchange exchange in unicellular organism organism such as Amoeba sp.
21. The Dynamic Equilibrium - Diffusion will continue until the concentration in all region is the same. - When this happen, we say it has reached the dynamic equilibrium. 22. Factors Affecting the Rate of Diffusion (How fast diffusion happens)
Water Molecules=Solvent (Pelarut)
=Solutes (Benda yg dilarutkan)
(a) (b) (c) (d) (a) 1st, the sugar is concentrated in 1 area. (b) The sugar sugar and water water molecules molecules move randomly in all direction. (c) The rando random m movements movements result results s in net movements of both molecules; from region of high concentration to region of low concentration, down the concentration gradient. (d) The sugar molecule finally evenly dispersed (tersebar rata). This stage is called a dynamic equilibrium.
23. What is Osmosis? -
Osmosis sis is is th the di diffusio sion of a water through a semi-permeable membrane , from a region of low solute concentration to a region with high solute concentration
( or high [water] to low [water] ) Important Points: •
It is the diffusion of water (normally) through a semi-permeable membrane.
•
It is from a dilute solution to a more concentrated solution.
•
NO ENERGY REQUIRED (TAK PERLU TENAGA).
•
Water molecules move through phospholipid bilayer and pore protein.
DILUTE SOLUTION = HIGH CONCENTRATION OF WATER = LOW CONCENTRATION OF SOLUTES (bhn. yg. dilarutkan)
CONCENTRATED SOLUTION = LOW CONCENTRATION OF WATER = HIGH CONCENTRATION OF SOLUTES (bhn. yg. dilarutkan) 24. Examples of Osmosis: - Absorption of water from soil solution by plant root hairs. - Reabsorption of water by kidney tubules. - Osmoregulation in aquatic organisms.
Lower concentration of solute
Higher concentration of solute
Equal concentration of solute
H2O Solute molecule Selectively permeable membrane Water molecule
Solute molecule with cluster of water molecules Net flow of water
The Mechanism of Osmosis: (a) - the left side of u-tube contains high [water], low [solutes]. - the right side of u-tube contains low [water], high [solutes]. - between left and right side of u-tube is semi permeable membrane. - water molecules move in both directions. Water molecules move from a region of high [water] at the left side to a region of low [water] at the right side . - as water flows from left to right, the osmotic pressure is created within right side of u-tube . - since water molecules can pass through semi permeable membrane but not sugar molecules , the level of the solution at the right side of u-tube rises .
(b) A dynamic equilibrium is reached
Facilitated Diffusion? 25. What is Facilitated -
Facil acilit itat ated ed diff diffus usio ion n is is the the move moveme ment nt of hydrophilic molecules or ions across the plasma membrane with the help of transport proteins.
-
It moves down the concentration gradient.
26. What Substances Can Pass through the Plasma Membrane through Facilitated Diffusion? Particles undergo facilitated diffusion are the particles that cannot diffuse through the phospholipid bilayer such as: •
Large particles such as glucose, amino acids, proteins and nucleic acids
•
Some ions such as the sodium ions and chloride ions
27. Facilitated diffusion occurs through 2 types of transport protein , namely: •
Channel/Pore Protein
•
Carrier Protein
28. Examples of Facilitated Diffusion: - Movement of small molecules such as glucose and amino acids into the blood capillaries of the villi.
Channel/Pore Proteins: -Provide corridors corridors (lorong/laluan) that allow a specific molecule or ion to cross the membrane.
EXTRACELLULAR FLUID
(Outside the cell)
Channel protein Solute
(Inside the cell) CYTOPLASM
(a)
A channel protein (purple) has a channel through which water molecules or a specific solute can pass.
Carrier Proteins: - Undergo a subtle change in shape that translocates the solute-binding site across the membrane.
Carrier protein
(b)
A carrier protein alternates alternates between two conformations, moving a solute across the membrane as the shape of the protein protein changes. The protein can transport the solute in either direction, with the net movement being down the concentration gradient of the solute.
Solute
THE MECHANISM of CARIER PROTEINS IN FACILITATED DIFFUSION
1. The The sol solut ute e mov moves es to the the bind bindin ing g sit site of of the the specific carrier prot p rotein. ein. 2. Th The e solu solutte bin binds ds to to the the car carri rier er pr prot otei ein n at at the the binding site & triggers (mendorong) the carrier protein protein to change its shape. 3. The The car carri rier er prot protei ein n cha chang nges es its its sha shape pe & moves the solute across the membrane. mem brane. 4. Th The e car carri rier er pr prot otei ein n ret retur urns ns ba back ck to its its original shape.
29. What is Active Transport? -
Active tr transport is is th the movement movement of molecules/ions across the plasma membrane of cells against (berlawanan) the concentration gradient (From lower concentration to higher concentration).
-
Sinc Since e it it is is aga again inst st the the con conce cent ntrratio ation n grad gradie ient nt,, energy is needed in the process.
30. Basic Requirements (keperluan) in Active Transport: •
Presence of the carrier protein (carrier proteins in active transport often called as PUMPS)
•
Presence of ATP (Adenosine Triphosphate)
31. Function of the ATP: -
ATP is the source of energy in active transport. It supplies energy to the carrier protein to carry out the process. It is converted into ADP (Adenosine Diphosphate) after the reaction .
32. Active transport results in the accumulation and elimination of molecules/ions from the cell. 33. Examples of Active Transport -
Intake of mineral salts and ions by the root hairs of a plant.
-
The movement of sodium ions into the cells lining the kidney tubules.
-
The accumulation (pengumpulan) of iodine in the cells of the thyroid gland.
Mechanism of Active Transport The diagram below is one type of active transport system which shows how sodium ions and potassium ions are transported through the plasma membrane by a carrier protein. [Na+] high [K+] low
1. Cytoplasmic Na+ ions binds to the sodium-potassium pump.
Na+
Na+
The shape of sodium-potassium pump allows it to take up 3 sodium ions at a time.
•
2
Na+
Na+
Na+
+
[Na ] low [K+] high
Na+
CYTOPLASM
ATP
P
2. Na+ ions binding stimulates (mendorong) Splitting (memisah) ATP ATP to ADP + P to RELEASE ENERGY.
ADP
Na+ Na+
6. K+ ions is released and Na+ sites are receptive again; the cycle repeats.
3. The one phosphate group attach to the carrier protein. Energy from the ATP, TP, changes the shape of carrier protein, and expelling (mengeluarkan) Na+ ions to the outside.
Na+
K+
P
K+
K+
5. Loss of the phosphate restores (mengembalikan) the protein’s original shape.
4. Extracellular K+ ions binds to the Carrier protein and stimulates the release of the Phosphate group.
K+ K+
K+
P
P
Review: Passive and active transport compared Passive transport. Substances diffuse spontaneously down their concentration gradients, crossing a membrane with no expenditure of energy by the cell. The rate of diffusion can be greatly increased by transport proteins in the membrane.
Active transport. Some transport proteins act as pumps, moving substances across a membrane against their concentration gradients. Energy for this work is usually supplied by ATP. ATP.
ATP
Diffusion. Hydrophobic Facilitated diffusion. Many hydrophilic molecules and (at a slow substances diffuse through membranes with rate) very small uncharged the assistance of transport proteins, polar molecules can diffuse through the either channel or carrier proteins. lipid bilayer.
Characteristics Characterist ics
Types of transport
Passive Transport
Simple Diffusion
Active Transport
Facilitated Diffusion
Osmosis
Active Transport Transport
Transport Transport of substances across the plasma membrane.
Ways of transport
Need concentration concentration gradient (or difference in the concentration of substances) between extracellular extracellular cell and intracellular cell. Concentration gradient
Follow concentration gradient
Against concentration gradient
Cellular energy; ATP
Cellular energy; ATP IS NOT REQUIRED
Cellular energy; ATP IS REQUIRED
Outcome of the process
Until an equilibrium is reached
Depends on the cells requirement (no need to reach an equilibrium)
Occurs in
Non-living & living organisms
Living organisms only
Molecules which can pass through
Lipid- soluble molecules (vitamins A,D,E,K, fatty acids, glycerols), small molecules (H2O), dissolved gases (O2,
Large molecules (glucose, amino acids), specific ions.
Water only
Specific ions usually sodium ions (Na+) and potassium ions (K+)
3.2
The Movements of Substances Across The Plasma Membrane in Everyday Life
1. What What is Hypo Hypoto toni nicc Sol Solut utio ion? n? Hypotonic solution is the solution with a lower solute concentration . (Hypo=less). 2. Water Water Conce Concentr ntratio ation n and Solute Solute Concent Concentra ration tion of a Cell Cell in a Hypoton Hypotonic ic Solution: Solution: Water concentration: Water concentration Water concentration inside the cell is lower than outside the cell. Solute Concentration: Concentration: Solute concentration inside the cell is higher than outside the cell.
3. What What is Isot Isoton onic ic Solu Soluti tion on? ? In isotonic solutions, both solutions have equal concentration of solutes. (iso=same). 4. Water Water Conce Concentr ntratio ation n and Solute Solute Concent Concentra ration tion of a Cell Cell in a Isotoni Isotonicc Solution Solution Water Wat er concentration and solute concentration are equal in both solutions. 5. What What is Hype Hypert rton onic ic Solu Soluti tion on? ? Hypotonic solution is the solution with a higher solute concentration . (Hyper=more). 6. Water Water Conce Concentr ntratio ation n and Solute Solute Concent Concentra ration tion of a Cell Cell in a Hypert Hypertonic onic Solution Solution Water Wat er concentration: Water concentration concentration inside the cell is higher than outside the cell. Solute Concentration: Concentration: Solute concentration inside the cell is lower than outside the cell. c ell.
7. The movement of water across plasma membrane is determine by the concentration of the
substances in the interstitial fluid which bathes (membasahi) cells. 8. Since living cells need to be in the stable internal environment , the interstitial fluid of animal cells is usually isotonic to the cytoplasmic fluid within the cells.
WHY MUST BE ISOTONIC? To ensure the shape of the cell remains same and prevent the cells from shrinking (mengecut) or swelling (mengembung).
Cytoplasmic fluid A portion of internal environment
Cells Interstitial fluid
Animal & plant cells in Isotonic solutions 9.
If an animal cell such as red blood cell (RBC) is placed into an isotonic solution , amount of water molecules is transported into the red blood cells by osmosis is equal to the amount of water molecules transported out from the cell (as shown in the diagram beside).
10. Therefore the amount of water in the cell remain unchanged (no net movement of water across plasma membrane). 11. 11. The red red blood blood cell cellss maintain their shape . 12. When a plant cell is placed in an isotonic solution, solute concentration in the external solution is equal to the solute concentration concentration in the cell sap. 13. Therefore the rate of diffusion of water into the cell is equal to the rate of diffusion of water out from the cell . 14. As a result, the shape of the cell remain unchanged.
Animal & plant cells in Hypotonic solutions 15. If an animal cell such as red blood cell is placed into a hypotonic solution , water molecules is transported into the red blood cells by osmosis(as shown in the diagram beside). 16. 16. The The red red blood blood cell cellss will will inflate (mengembung) and finally burst (pecah) because the thin membrane cannot withstand withstand the high pressure inside the cell (tidak mampu menahan tekanan yg. tinggi di dalam sel). 17. 17. The red red blood blood cells cells are are said to to underg undergo o haemolysis.
18. When a plant cell is placed in a hypotonic solution, water molecules is transported into the cell by osmosis . 19. The water water is then then stored stored in vacuole vacuole causing causing it to expand (mengembang) and exerts exerts (mengenakan) (mengenakan) pressure on the cell wall . This pressure is called turgor pressure. 20. The turgor pressure caused the plant cell to become firm or turgid. 21. The rig rigiid cell wall prevents cell from bursting .
22. 22. Turgidi urgidity ty of of a plant plant cell cellss is also responsible for causing the GUARD CELLS in leaves to swell so that stomata can remain open for
Animal & plant cells in Hypertonic solutions
23. If an animal cell such as red blood cell is solution, water placed into a hypertonic solution,
molecules is transported out from the red blood cells by osmosis (as shown in the diagram beside).
24. 24. The red red blood blood cell cellss will will shrink or crenate (mengecut) because of the lost of water from the cell and probably die. 25. The red red blood blood cells are are said to underg undergo o crenation. 26. When a plant cell is placed in a hypertonic solution, solution, water molecules is transported
out from the cell by osmosis . 27. The vacuole and cytoplasm are then shrink due to lost of water . 28. The plasma membrane is pulled away from the cell wall. 29. The cell wall maintain its shape. 30. 30. The proce process ss is call called ed plasmolysed.
31. If a plasmolys plasmolysed ed plant plant cell is immer immersed sed back (direndam semula) in a hypotonic solution, the cell become turgid again.
The Effects Effects and Applications of Osmosis O smosis in Daily Life 32. Wilting Wilting (Layu) (Layu) in plants: plants: -
Wilting occurs in plants when too much fertilizers like potassium nitrate is given.
-
The fertilisers + Soil = dissolves in the soil water.
-
Then turn soil water into hypertonic to the cell sap of the plant root.
-
As a result, water diffuses from the cell sap into the soil by osmosis and the cell is plasmolysed.
-
Water shortage (kekurangan) (kekurangan) in soil also causes the plant to wilt.
-
When soil dries out = the soil become more concentrated or hypertonic.
-
Makes the water diffuse out from plant cell into the soil = the plant cell loss water to soil.
33. Food Preservation (Pengawet): -
Foods such as mushrooms, fruits and fish can be preserved using natural preservatives (salt and sugar).
-
The preservatives makes the surroundings more hypertonic to the food and causes water to leave through osmosis.
-
The food becomes dehydrated (the food become very-very dry).
-
Microbes lose water to the surrounding. Without water, bacteria and fungus cannot survive and dies.
3.3
Appreciating The Movements Movements of Substances Across The Plasma Membrane
34. The proper functioning of plasma membrane is important to: -
Controls/regulates Controls/regulates what goes in and out of the cell as the plasma membrane membrane acts as selective permeable or ‘gatekeeper’ ‘gatekeeper’ (pengawal pintu). Maintain a suitable pH and ionic concentration inside the cell for enzymatic activities. Obtain certain food supplies for energy and raw materials. Remove waste products and toxic substances out of the cell.
35. To maintain proper functioning of a plasma membrane and the whole cells , it is important to: -
Apply balanced diet (makan pelbagai jenis kelas makanan macam karbohydrat, proteins, lipids, serat, vitamins) Drink sufficient water (minum air secukupnya) everyday to prevent our body cells from dehydrated.
