BioEn Part1 Answers

MBpS and MBq

2014-2015

Bioenergetics - Application problems – solutions Part I 1. a) [ribulose-5P]= 0.01 M ; [Pi]= 0.01 M ; [ribulose-1,5-bisP]= 4.5x10-7 M

The reaction does not proceed to products. b) The reaction is coupled to ATP hydrolysis:

o

ΔG

’= +13.4 –30.5 = -17.1 kJmol -1

= - 44.39 + 49.4 = + 5.01 kJmol-1 In standard conditions the reaction is not favourable. Keq<1 There will be more reagents than products at equilibrium.

2. a)

o’ 

ΔG

[GAP]/[1,3BPG] > 7554

b) c) •

In aerobic eukaryotic cells NADH is reoxidised in the respiratory chain, where O 2  is used as terminal electron acceptor. acceptor. Global reaction: NADH + H+ + ½ O2 → NAD+ + H2O

•

In anaerobic yeast cells NADH is reoxidised by alcoholic fermentation. The global reaction is: piruvato + NADH + H + → etanol + CO2 + NAD+ In active muscle cells NADH is reoxidised by lactic fermentation. The global reaction is: piruvato + NADH + H+ → lactato + NAD+

d) 2 ATP would be lost in the glycolytic pathway. Under anaerobiose the net production of ATO

would be zero. Under aerobic conditions 30 instead of 32 ATP would be produced, because oxidative phosphorylation would not be affected. 3.

a) i) Lactic acid fermentation;

C6H12O6 → 2 C3H5O3- + 2H+ ii) Aerobic respiration using O2 as terminal electron acceptor;

C6H12O6 + 6 O2

→

6 CO2 + 6 H2O

iii) Anaerobic respiration using NO3– as terminal electron acceptor.

C6H12O6 + 12 NO3b)

→

6 CO2 + 12 NO2- + 6 H2O

Total energy associated with 10 NADH reoxidation 1430 kJ. Total energy associated with 2 FADH 2 reoxidation 139 kJ. Total energy available 1569 kJ. 43% (674.6 kJ) are used in ATP synthesis. 17.7 moles of ATP would be formed by oxidative phosphorylation 4 ATP would be formed by substrate level phosphorylation. Total 21.7 moles of ATP per mole of glucose.

c)  Very fast with oxygen, fast with nitrate and very slow doing fermentati fermentation. on. The rate of growth

should be proportional to the number of ATP/glucose. 4. ΔG= -18 kJmol-1. The transport is thermodynamically thermodynamically favourable as expected expected.. 1

Teresa Catarino and Ricardo Louro

MBpS and MBq 5.

2014-2015

The citric acid cycle is directly connected to the respiratory chain: if the redox cofactors are not reoxidised there will be no NAD + to continue the reactions of the cycle. Glycolysis is not necessarily linked to respiration because the NADH can be reoxidised by fermentation. It makes sense that it is controlled by the energetic charge since energy production is one of the main objectives of this pathway.

6.

In gluconeogenesis pyruvate is converted into oxaloacetate, which in turn is converted to malate by the enzyme present in the mitochondrial matrix. Malate is transported to the cytosol. In the cytosol malate is converted back into oxaloacetate, by the cytosolic enzyme, that continues the pathway. The advantage of this strategy is the “transport” of NADH to the cytosol, where it will be necessary for one of the gluconeogenesis steps: 1,3-bisfosfoglicerato

→

gliceraldeído 3-fosfato).

7. a) In the presence of oxygen the lactic acid fermentation stops because i tis more advantageous b) c)

8.

to respire O 2. What is maintained is the energetic charge. The rate of glucose consumption decreases because much more ATP is produced per glucose molecule Increase in energetic charge → electron transport in the respiratory chain slows down → the [NADH]/[NAD+] ratio increases →  Krebs cycle slows down →  citrate accumulates and inhibits PFK (the main regulator of gycolysis) → glycolysis slows down.  ATP is both substrate and a negatived effector of PFK.

9. a) In liver, gluconeogenesis goes faster than glycolysis. In muscle, it is the other way around.

Remember that the muscle needs ATP for muscle contraction and the liver is responsible for keeping the blood glucose levels. b)

It can be explained by a difference in the concentration of the enzymes in the two tissues.  Vmax=k cat ET

10. The entry of these compounds in the glycolytic pathway involves the foloowing reactions:

glycerol + ATP → glycerol 3-P + ADP glycerol 3-P + NAD + → DHAP + NADH glyceraldehyde + ATP glycerate + ATP

→ glyceraldehyde

→ 3-phosphoglycerate

3-P + ADP

+ ADP

The complete route to lactate: substrate

ATP balance

NADH balance

glycerol → lactate

-1 + 2 = +1

+2 – 1 = +1

glyceraldehyde → lactate

-1 + 2 = +1

+1 – 1 = 0

glycerate → lactate

-1 + 1 = 0

0 – 1 = -1

Only glyceraldehyde can be used: it has a positive ATP balance and the redox balance is fulfilled.

2

Teresa Catarino and Ricardo Louro