Lecture 27 - Introduction, a handy reminder

Question 1

Take our fuel molecules from digestion and ….

Answer 1

Break them down in this metabolic pathway to make ATP which goes off to do cellular work

Question 2

First Law of thermodynamics reminder

Answer 2

Energy cannot be created or destroyed, energy can be converted

Question 3

ATP

Answer 3

Adenosine triphosphate is the major energy intermediate (currency) of the cell

Question 4

Gibbs free energy

Answer 4

The delta G of a reaction tells us about…
The relative abundance of the substrates and products
The energy stored in the chemical bonds of the products and substrates

Question 5

Delta G < 0 for A to B

Answer 5

Then the reaction is spontaneous/energy released/energetically favourable

Means that we have more energy stored in the bond of A than we do in the bonds of B and this means that the reaction is going to be spontaneous i.e. this reaction will happen

Question 6

Delta G = 0 for A to B

Answer 6

Then the reaction is at equilibrium/no change in energy

Question 7

Delta G > 0 for A to B

Answer 7

Then the reaction is not spontaneous/energy required/energetically unfavourable

This time we have more energy stored in the bonds of B than stored in the chemical bonds of A so this reaction is non spontaneous and won’t happen as B requires more energy than A so it is energetically unfavourable

Question 8

ATP hydrolysis and synthesis in terms of Gibbs energy

Answer 8

ATP hydrolysis is energetically favourable with a delta G of -30

ATP synthesis is energetically unfavourable with a delta G of +30

Measured in delta G under standard conditions

Question 9

Delta G under standard conditions

Answer 9

All at 1 molL-1
Specific temperature

Everything is at 1molL-1 except H+ (protons) - if it was at 1 then it would give a pH that is close to zero which is not actually very reflective of what happens in a cell, it is distant from physiological pH and the enzyme might not work, adapt conditions and make a pH of 7

Question 10

Reaction/energy coupling

Answer 10

If you have one reaction that has delta G of greater than zero and then another reaction that has a delta G of less than zero - you can couple these reactions

If adding these reactions together means that the collective delta G is still negative then the coupled reaction is still energetically favourable

Enzymes often couple reactions to drive necessary unfavourable reactions

Question 11

Unfavourable reactions can be coupled with…

Answer 11

ATP hydrolysis
For example the hexokinase reaction in glycolysis (same reaction is catalysed by glucokinase (glucose sensor))
In this example, converting glucose + phosphate to glucose-6-phosphate + water is positive delta G and then ATP hydrolysis is negative delta G

Coupled reaction is energetically favourable so now both of the reactions can occur

Question 12

Pathways for processing food molecules for ATP synthesis

Answer 12

Two key types of reactions:
1- Phosphorylation of ADP to ATP
2- Redox reactions (fuel molecule gets oxidised, so there needs to be something that provides the oxidising power/gets reduced)

Question 13

Redox reactions

Answer 13

Involves the transfer of electrons

Question 14

Oxidation

Answer 14

Loss of electrons = oxidised
OIL = Oxidation is loss
The thing that is oxidised is the reducing agent/provides reducing power

Question 15

Reduction

Answer 15

Gains electrons = reduced
RIG = Reduction is gain
The thing that is reduced is an oxidising agent/provides oxidising power

Question 16

Energy is released from fuel molecules by…

Answer 16

Oxidation reactions

Fuel molecules such as carbohydrates (glucose) and lipids (palmitate) are being oxidised
Energetically favourable and therefore release energy

Question 17

Stepwise oxidation

Answer 17

Of fuel molecules occurs in the pathways

Direct burning of sugar = all of the energy is released as heat
Stepwise oxidation of sugar = energy captured for ATP production

Question 18

Coenzymes NAD and FAD

Answer 18

These are the things that are reduced when the fuel molecules are oxidised

They interact with various enzymes to accept and donate reducing equivalents

Question 19

Reducing equivalents

Answer 19

Biological redox reactions often involve the transfer of hydrogen atoms (includes an electron)
H=H+ + e- (proton + electron)
Hydrogen is referred to as a reducing equivalent
The enzymes that catalyse these reactions are called dehydrogenase, you know that when you see one of these enzymes there is going to be a redox reaction and you are using one of the reducing equivalents when moving hydrogen

Question 20

Coenzymes reminder

Answer 20

Subclass of cofactors 
Small organic molecules 
Often derived from vitamins 
Low concentration in cell 
Act as carriers 
Exist in 2 forms

Question 21

NAD

Answer 21

Nicotinamide adenine dinucleotide

Dervied from niacin (vitamin B3)
Accepts hydrogens and electrons in metabolic pathways (glycolysis, fatty acid oxidation, citric acid cycle)

Question 22

NAD undergoes …

Answer 22

NAD undergoes a two electron reduction (accepts two reducing equivalents)

NAD+ is the oxidised form
NADH + H+ is the reduced form

Question 23

FAD

Answer 23

Flavin adenine dinucleotide

Dervived from riboflavin (vitamin B2)
Accepts hydrogens in pathways (fatty acid oxidation, citric acid cycle)
Flavin coenzymes are tightly bound to the proteins with which they interact (flavoproteins)

Question 24

FAD undergoes …

Answer 24

FAD undergoes a two electron reduction (access two reducing equivalents)

FAD is the oxidised form
FADH2 is the reduced form

Question 25

Coenzyme A (CoA) is another important…

Answer 25

Coenzyme in the pathways

Derived from pantothenic acid (vitamin B5)
Not a carrier of electrons (it is not reduced/oxidised)

Carries acyl groups

Two forms - free coenzyme A = CoASH or acyl group attached = Acyl-CoA (AcCoA)

Reactive sit is the SH

Question 26

Two forms of CoA

Answer 26

Two forms - free coenzyme A = CoASH or acyl group attached = Acyl-CoA (AcCoA)