Biochemistry intro 2 - Energy and thermodynamics

Question 1

Name 4 examples of major classes of biomolecules and state their building blocks

Answer 1

1. Peptides and proteins - building blocks are amino acids
2. Lipids - building blocks are triglycerides, phospholipids, steroids
3. Nucleic acids - building blocks are DNA and RNA
4. Carbohydrates - building blocks are mono-, di- and polysaccharides

Question 2

Name 5 functions of biomolecules and give some examples for each

Answer 2

1. Information storage (such as DNA)
2. Structural function (such as teeth, bones, cartilage)
3. Energy generation (such as citric acid cycle, electron transport chain, glycolysis)
4. Energy storage (such as ATP)
5. Recognition/communication/specificity (such as receptors, hormones, enzymes)

Question 3

How are disaccharides formed and why are they important?

Answer 3

Disaccharides are formed by covalent bonds between either carbon 1+4 or carbon 1+2. Disaccharides are important because they provide your body with a rapid source of energy because the oxygen atom linking the two monosaccharides is readily reduced to generate readily metabolised monosaccharides

Question 4

What are polysaccharides?

Answer 4

These are chains of many monosaccharides such as glycogen or cellulose

Question 5

What is meant by thermodynamics?

Answer 5

Thermodynamics is the biophysical discipline which deals with the question of whether a process is energetically favourable

Question 6

Explain the first two laws of thermodynamics

Answer 6

The 1st law of thermodynamics: Energy is neither created nor destroyed - This means that when energy is converted from one form to another, the total energy before and after the conversion remains the same

The 2nd law of thermodynamics: When energy is converted from one form to another, some of that energy becomes unavailable to work - This means that no energy transformation is 100% efficient

Question 7

What is meant by the term enthalpy?

Answer 7

A measure of change in heat content (ΔH)

Question 8

What is meant by the term entropy?

Answer 8

A measure of change in disorder/randomness (ΔS). To impose order on a system, energy is required so unless energy is applied to a system, it will be randomly disordered

Question 9

How do you calculate free energy change for reactions involving changes in thermodynamic quantities?

Answer 9

To calculate free energy change (ΔG) = ΔH - TΔS
So free energy change is ΔG = (energy of products) - (energy of reactants)
Where T is temperature in Kelvin

Question 10

What are exergonic reactions?

Answer 10

Exergonic reactions (think of exothermic) are reactions in which the total free energy of the products is LESS than the total free energy of the reactants. Therefore, this means that ΔG will be NEGATIVE and so such reactions CAN occur spontaneously (doesn’t require energy to happen)

Question 11

What are endergonic reactions?

Answer 11

Endergonic reactions (think of endothermic) are reactions in which the total free energy of the products is MORE than the total free energy of the reactants. Therefore, ΔG is positive and so such reactions CANNOT occur spontaneously (does require energy to happen)

Question 12

What does ΔG°’ mean?

Answer 12

This is the symbol for the change in free energy under STANDARD CONDITIONS (in the body)

Question 13

What is meant by standard conditions in biochemistry?

Answer 13

In biochemistry, standard conditions are:
• T = 298K
• 1 atmosphere of pressure
• 1M concentration of reactants
• pH = 7

Question 14

What formula can be used to calculate ΔG for a given reaction (in equilibrium)?

Answer 14

ΔG = ΔG°’ + RTln([C][D]/[A][B])
Where R is the universal gas constant (8.3 JK-1mol-1)
and T is the absolute temperature (in degrees Kelvin)
The unit for this reaction is kJ/mol

Question 15

True or False: The further towards completion the point of equilibrium is, the more free energy is released

Answer 15

True

Question 16

What does it mean when ΔG values are near zero?

Answer 16

This means that the reaction is readily reversible and nor the products or the reactants are favoured - so the system is at equilibrium (the forward and backwards reactions are balanced)

Question 17

How do you calculate the equilibrium constant?

Answer 17

Equilibrium constant (Keq) = [C][D]/[A][B] which is equal to [Products]/[Reactants]

Question 18

How do many reactions occur within the body?

Answer 18

Many reactions within the body use the coupling process where an unfavourable reaction (one with a positive ΔG) is coupled with a very favourable reaction (one with a negative ΔG)

Question 19

What are anhydride bonds?

Answer 19

These are high energy bonds

Question 20

Explain what is meant by strain in relation to the structure of ATP

Answer 20

The negative charges close together in ATP put a strain on the molecule (known as electrostatic repulsion) which makes it less stable than ADP. Strain can be partially relieved by removing one or more phosphate groups from an ATP molecule

Question 21

Why is ATP constantly regenerated?

Answer 21

This is because cells do not store large amounts of ATP and also some cells, such as active muscle cells, use ATP at a high rate

Question 22

Metabolism is all the reactions taking place in the body. It is divided into two parts called…?

Answer 22

1. Catabolism - The breaking down of complex molecules into smaller ones
2. Anabolism - The synthesis of complex molecules out of smaller ones

Question 23

True or False: Reactions with large negative ΔG values are useful control points in metabolic pathways

Answer 23

True

Question 24

How are carbohydrates composed and how do they provide energy?

Answer 24

Carbohydrates are composed of carbon chains that are primarily linked to hydrogen and oxygen atoms. Their oxidation through metabolic pathways provides an important source of energy release

Question 25

What is the point in coupling processes?

Answer 25

Coupled reactions allow energetically unfavourable reactions to reach completion