Lecture 28: Energy and Metabolism (2)

Question 1

Is it true that ΔG tells us whether a reaction will happen or not?

Answer 1

Yes

Question 2

Glucose-6-phosphate Fructose-6-phosphate

Is this the 2nd reaction of glycolysis?

Answer 2

Yes

Question 3

Glucose-6-phosphate Fructose-6-phosphate

Is this reaction close to equlibrium?

Answer 3

Yes

Question 4

Glucose-6-phosphate >< Fructose-6-phosphate

When this reaction is at equilibrium, what will ΔG be?

Answer 4

0. This will only be for a very short period of time and there will be no overall change as G-6-P and F-6-P will be interconverted with equal rate in both directions.

Question 5

Glucose-6-phosphate >< Fructose-6-phosphate

What happens when more [G-6-P ] is added?

Answer 5

• An increase in the formation of F-6-P
• ΔG is negative
• Reaction will occur spontaneously, this is the 2nd reaction of glycolysis

-

Question 6

Glucose-6-phosphate >< Fructose-6-phosphate

What happens when more [F-6-P ] is added?

Answer 6

• An increase in the formation of G-6-P
• ΔG is positive
• This happens during gluconeogenesis (metabolic process that synthesises glucose)

Question 7

Is ΔG dependant on concentration?

Answer 7

Yes

Question 8

Glucose-6-phosphate Fructose-6-phosphate

Does the same enzyme catalyse both the forwards and backwards reaction?

Answer 8

Yes

Question 9

What is the first step of glycolysis?

Answer 9

Glucose + ATP Glucose-6-phosphate + ADP

Question 10

Glucose + ATP Glucose-6-phosphate + ADP

Does this reaction have a large ΔG?

Answer 10

Yes

Question 11

Glucose + ATP Glucose-6-phosphate + ADP

In a living cell, does this reaction happen quite far away from equlibrium?

Answer 11

Yes. So ΔG &laquo_space;0 and under physiological conditions this means irreversible
.

Question 12

Is it true that the further away from equilibrium, the larger the value of ΔG?

Answer 12

Yes

Question 13

What is q?

Answer 13

The mass action ratio

Question 14

What is the equation for the mass action ratio?

Answer 14

A + B C + D

Mass action ratio: q = [C] [D]/
[A] [B]

Question 15

F-1,6-bP G3P + DHP

Put this equation into the mass action ratio

Answer 15

q = [G3P] [DHP] / [F-1,6-bP]

Question 16

If there’s a lot of product in the system, how large will q be?

Answer 16

Very large

Question 17

Effectively, what is the mass action ratio an expression of?

Answer 17

How much product in system vs how much reactant in system

Question 18

If there’s a lot of reactant in the system, how large will q be?

Answer 18

Very small

Question 19

What does the mass action ratio allow us to measure?

Answer 19

how far we are from equilibrium conditions. At equilibrium q = Kp (equilibrium constant)

Question 20

What is the standard free energy equation?

Answer 20

ΔG = ΔG0 +RT lnq

(units J/mol or kcal/mol
R: gas constant
T: absolute temperature
q: mass action ratio
ΔG0: Standard Free Energy )

Question 21

What is ΔG0?

Answer 21

The standard free energy, which is the change in Free Energy when concentration of all reactants and products are 1M at 25oC, 1 atm. (standard conditions)

Tells you if a reaction tends towards the products side or towards the reactants side

Artificial reference point

Question 22

What is our definition of Standard free energy ,ΔG0’?

Answer 22

Standard Free Energy at pH 7 at 25oC and 1 atm

Question 23

What is ΔG dependant on?

Answer 23

The nature of a reaction (whether a reaction tends to the reactant or the product side) AND the concentrations (q from mass action ratio)

Question 24

If ΔG = 0….

Answer 24

… no free energy change takes place and the system is at equilibrium

(rate of degradation = rate of formation)

Question 25

Is the standard free energy just another way of expressing the equilibrium constant?

Answer 25

Yes

Question 26

When ΔG0’ is 0, what is q?

Answer 26

The equilbrium constant

Question 27

q = [C][D] / [A][B] = Keq at equilibrium

Question 28

Does the equilibrium constant tell you whether or not a reaction tends to the reactants or products side?

Answer 28

Yes (standard free energy is another way of expressing this, also dependant on one another)

Question 29

What can the relationship between ΔG0’ and Keq (equilibrium constant) be described as?

Answer 29

Logarithmic

Question 30

Is it true that Relatively small changes in ΔG0’ can lead to big changes in Keq?

Answer 30

Yes

Question 31

How many phosphates does ATP have?

Answer 31

3

Question 32

How many phosphates does ADP have?

Answer 32

2

Question 33

How many phosphates does AMP have?

Answer 33

1

Question 34

Draw out the structure of ATP

Question 35

Draw out the structure of ADP

Question 36

Draw out the structure of AMP

Question 37

ATP + H2O ADP + Pi What is ΔG0’ for this reaction?

Answer 37

– 30.5 kJ/mol

Question 38

ADP + Pi ATP + H2O What is ΔG0’ for this reaction?

Answer 38

ΔG0’ = 30.5 kJ/mol

Question 39

TP + H2O AMP + PPi What is ΔG0’ for this reaction?

Answer 39

ΔG0’ = – 45.6 kJ/mol

Question 40

Why do we usually talk about ATP and ADP, but not AMP?

Answer 40

Because AMP is rapidly converted back to ADP via the adenylate kinase reaction: 2ADP↔ATP+AMP. This ensures AMP does not accumulate significantly in cells, further reducing its direct biochemical relevance.

Question 41

Generally, are most reactions in the body at equilibrium ?

Answer 41

No

Question 42

Does ATP have high energy bond compared to other bonds?

Answer 42

- No, this is a myth - Instead, ΔG0’ is very negative and this favours the product formation - The energy is the potential energy stored in being far from equilibrium i.e. q<

Question 44

What are the roles of ATP?

Answer 44

-

Question 45

Which 2 ways can ATP be made?

Answer 45

From photosynthesis and from respiration

Question 46

Is it true that ATP and ADP are always interconverting between one another?

Answer 46

Yes

Question 47

How much ATP do humans need a day?

Answer 47

About 70kg

Question 48

Can Keq be affected by coupling reactions?

Answer 48

Yes

Question 49

Who got a noble prize in Medicine in 1953 for the discovery of Co-enzyme A, and also for the discovery that ATP is the main energy carrier in the cell?

Answer 49

Friz Lippman

Question 50

Who coined the term ’energy rich phosphate bonds’?

Answer 50

Friz Lippman

Question 51

Glucose + Pi Glucose-6-phosphate + H2O ΔGo’ = + 14.0 kJ/mol; Keq = 3.5 x10-3 ATP + H2O ADP + Pi ΔGo’ = - 30.5 kJ/mol Glucose + ATP Glucose-6-phosphate + ADP ΔGo’ = - 16.5 kJ/mol; Keq = 8.0 x 102

Answer 51

By coupling to ATP the equilibrium has been shifted 5 orders of magnitude (N.B! not this only works because Pi is a shared intermediate ) (created a reaction that will occur under physiological conditions)

Question 52

Are redox reactions used for storing and releasing energy?

Answer 52

Yes

Question 53

What happens to glucose during glycolysis?

Answer 53

It's oxidised

Question 54

Glucose is oxidised during glycolysis. What is the potential energy from this redox reaction used to do?

Answer 54

The potential energy from this redox reaction is used to generate ATP

Question 55

What happens to Acetyl-CoA in the citric acid cycle?

Answer 55

It is oxidised

Question 56

Acetyl-CoA is oxidised in citric acid cycle. What is the potential energy from this redox reaction used to do

Answer 56

Used to generate reduced NADH/ FADH2 i.e., potential energy is stored in redox reaction

Question 57

What happens to NADH/ FADH2 in oxidative phosphorylation?

Answer 57

They're oxidised.

Question 58

NADH/ FADH2 are oxidised in oxidative phosphorylation. What is the potential energy from this redox reaction used to do?

Answer 58

The potential energy from this redox reaction is used to generate ATP.

Question 59

What do redox reactions involve?

Answer 59

The transfer of electrons

Question 60

What happens during oxidation reactions?

Answer 60

A compound donates electrons

Question 61

What happens during reduction reactions?

Answer 61

A compound accepts electrons

Question 62

NADH + ½ O2 H2O + NAD+ Half equations ½ O2+ 2H+ +2e- H2O NADH NAD+ + 2H+ + 2e-

Question 63

What is the redox potential?

Answer 63

How many electrons around before the compound will become reduced (accept electrons)?

Question 64

What is ΔE0’ ?

Answer 64

The standard biochemical redox potential

Question 65

What does a good oxidising agent do?

Answer 65

Takes up electrons, even when there are not many around

Question 66

what does a good reducing agent do ?

Answer 66

Gives off electrons, even when there's many around

Question 67

What equation links free energy to redox potentials?

Answer 67

ΔG0’ = -nFΔE0’, Where n = number of electrons and F = faraday constant 96.48 kJ V-1mol-1 Under standard conditions, A positive ΔE0’ gives a negative ΔG0’

Question 68

Is gibbs free energy available to do work?

Answer 68

Yes

Question 69

Does Gibbs free energy tell us whether a reaction is spontaneous or not?

Answer 69

Yes

Question 70

What is Gibbs free energy dependant on?

Answer 70

on enthalpy (related to total energy) and entropy (disorder)

Question 71

What is free energy dependant on?

Answer 71

the nature of a reaction (standard Gibbs free energy) and the concentrations (mass action ratio)

Question 72

What is the standard free energy defined as?

Answer 72

all concentrations 1 M, 250C and 1 atm or in biology at pH 7

Question 73

IS it true that at equilibrium, the mass action ratio is the equilibrium constant?

Answer 73

Yes

Question 74

'ATP is the main energy carrier and energy ”harvested” as ATP can be used to run endergonic reactions'. Is this statement true?

Answer 74

Yes

Question 75

'The redox potential describes a compounds propensity to accept or donate electrons and is related to the standard free energy'. Is this statement true?

Answer 75

Yes