Bioenergetics

Question 1

What are the two laws of thermodynamics?

Answer 1

1: energy cannot be created nor destroyed

2: entropy of the universe is always increasing and randomness increases are favourable

Question 2

What is the equation for ∆G?

Answer 2

∆G = ∆H - T∆S

∆G’º = -RTlnKeq (use J and K!)

Question 3

What is the difference between an spontaneous and nonspontaneous reaction?

Answer 3

Spontaneous: ∆G is NEGATIVE (exergonic)

Nonspontaneous: ∆G is POSITIVE (endergonic)

Question 4

what is energy coupling?

Answer 4

Energy released from spontaneous exergonic reactions are used to fuel nonspontaneous endergonic reactions.

Question 5

What is the standard state? What about the physiological standard state?

Answer 5

Standard: 1 atm, 25ºC, 1M solute, ph = 0

Standard physio: 1atm, 25C, 1M solute, ph = 7

Question 6

What is the difference between oxidation and reduction?

Answer 6

Oxidation: Loss of electron
Reduction: Gain of electron

Question 7

What is the pathway for a redox couple?

Answer 7

1. donor = e- + acceptor
2. AH2 = A + 2e- + 2H+
3. AH2 + B = A + BH2
4. 2RCH3 + O = 2RCH2OH

Question 8

What is the standard reduction potential?

Answer 8

Voltage needed to pull electrons away from the donor of the redox couple.

Low tendency = high affinity = +ve Eº’

High tendency = low affinity = -ve Eº’

Question 9

How does measuring standard reduction potential work?

Answer 9

1. One cell has H2 = H+ and e-, and the other has a half reaction
2. If the half reaction has a low affinity for its electrons, it will transfer them to the reference cell and give to the proton, voltage will be negative
3. If the half reaction has a high affinity for its electrons, it will cause H2 to give its electrons to its reactants; voltage will be positive

Question 10

How do you find the ∆G of a redox reaction?

Answer 10

∆G = -nF∆Eº

n = # of electrons exchanged per reaction

F = faraday’s constant, 96.1 kJ/Vmol

∆Eº = E(acceptor) - E(donor)

Question 11

How do you find ∆Eº of a spontaneous reaction?

Answer 11

1. Find which half reaction has a higher affinity for the electrons (+ve Eº value), and that will act as the acceptor, while the other will act as the donor.
2. Set up the equation with proper direction and sum them.
3. Calculate ∆Eº = Eº acceptor - Eº donor.

Question 12

How is ATP hydrolysis used to convert Glu + NH3 = Gln?

Answer 12

1. Phosphate from ATP is transferred to an enzyme or substrate which becomes activated
2. Phosphorylation raises free energy of Glu so amidation is a downhill step
3. Reaction is completed by displacement of phosphate (-30.5 + 14.2 = -16.3 kJ/mol)

Question 13

How is glucose phosphorylated?

Answer 13

1. ATP hydrolysis (-30.5 kJ/mol)
2. glucose + Pi formation (+13.8)
3. Net energy release = -16.7

Question 14

Why doesn’t ATP spontaneously decompose?

Answer 14

The reaction is spontaneous (-30.5kJ/mol) but occurs very slowly due to the high activation energy (220kJ/mol) in the absence of enzymes.

Question 15

Why is ATP a good source of energy currency?

Answer 15

1. Hydrolysis of ATP allows relief of charge repulsion in condensed state
2. There is more resonance between ADP + Pi than ATP
3. Post hydrolysis ADP spontaneously releases one more proton which contributes to -ve ∆G’
4. Hydrolysis products are solvated by water molecules which is a favourable interaction that stabilizes the products more than the reactants.

Question 16

What are other compounds have large ∆G of hydrolysis values?

Answer 16

1,3 biphosphoglycerate to 3phosphoglycerate (-49 kJ/mol)

Phosphenolpyruvate to pyruvate (-62 kJ/mol)

Phosphocreatine to creatine (-43 kJ/mol)

Question 17

What is substrate level phosphorylation?

Answer 17

ATP is produced by directly coupling its formation to an energy releasing reaction.

Question 18

What is a high energy phosphate?

Answer 18

Gamma terminal of ATP, releases 30.5 kJ/mol

Question 19

What is the difference between production of AMP from ADP and ATP?

Answer 19

ADP + H2O = AMP + Pi (-33kJ)

ATP + H2O = AMP + PPi (-45kJ + (-20 kJ) from PP)

Question 20

What is a thiolester?

Answer 20

R−CO−S−R groups that are not resonance stabilized and store more G than oxygen esters. (-31.4 kJ/mol)

Question 21

What is glycolysis?

Answer 21

10 enzyme catalyzed steps that transforms glucose into 2 molecules of pyruvate. Includes energy expenditure phase (cost 2 ATP) and energy payoff (production of 2 NADH and 4 ATP)

Question 22

What is lactic acid fermentation?

Answer 22

Pyruvates are converted to lactate by lactate dehydrogenase and NADH

Question 23

What is ethanol fermentation?

Answer 23

Yeast making ethanol from pyruvate and then oxidizes ethanol to acetaldehyde.

Question 24

What is the warburg effect?

Answer 24

Tumour cells dramatically increase glucose uptake and glycolysis by increasing synthesis of hexokinase and glucose transporters.

Question 25

How many products are produced at the end of the citric acid cycle per acetyl-CoA?

Answer 25

2x CO2
3x NADH
1x FADH2
1x GTP/ATP