Biochemical reactions

Question 1

What is bioenergetics?

Answer 1

The quantitative study of energy transductions - changes of one form of energy into another, that occurs in living cells

Question 2

What is the first law of thermodynamics?

Answer 2

For any chemical or physical change, the total amount of energy in the universe remains constant, it cannot be created or destroyed

Question 3

What is the second law of thermodynamics?

Answer 3

In all natural processes the entropy of the universe increases

Question 4

What type of system are biological organisms? can these systems be at equilibrium with their surroundings?

Answer 4

• open systems

- No, they cannot be at an equilibrium with their surroundings

Question 5

Define gibbs free energy and enthalpy?

Answer 5

GFE= the amount of energy capable of completing work whilst a reaction is occurring at a constant temperature and pressure

Enthalpy= the heat content of the reacting system, it can be used to determine whether the reaction is endergonic (+H) or exergonic (-H)

Question 6

What is exothermic VS endothermic?

Answer 6

exo = when a chemical reaction releases heat
endo= when a chemical reaction takes up heat from its surroundings

Question 7

Is heat flow a source of energy for cells?

Answer 7

No. As heat can do work only as it passes to a zone or object at a lower temperature

Question 8

What happens to the free energy in two sequential reactions?

Answer 8

Each reaction has it’s own equilibrium constant and a characteristic standard free energy change, however the change in gibbs energy values in the two reactions are additive

Question 9

How can covalent bonds be broken?

Answer 9

1) Homolytic cleavage = each atom leaves the bond as a radical, carrying one unpaired electron
2) Heterolytic cleavage = one atom retains both bonding electrons

Question 10

What bond is cleaved through hydrolytic cleavage in ATP? + the effect

Answer 10

• the terminal phosphoric acid anhydride bond
• this separates one of the 3 negatively charged phosphates and relieves some electrostatic repulsion in ATP, the pi released is stabilised by the formation of several resonance forms

Question 11

What happens when ATP levels drop?

Answer 11

the fuel decreases and loses it’s potency, the phosphorylation potential for its hydrolysis is diminished

Question 12

What are the four complexes involved in the electron transport chain?

Answer 12

1. NADH dehydrogenase
2. Succinate deyhdrogenase
3. Cytochrome c oxidoreductase
4. Cytochrome oxidase

Question 13

How many protons are released through 1 molecule of NADH and 1 molecule of FADH2?

Answer 13

1 molecule of NADH gives 10 H+

1 molecule of FADH2 gives 6H+

Question 14

What occurs at complex 1 (ETC)

Answer 14

NADH arrives in reduced form and is oxidised into NAD+

• The electrons are transferred to Q to reduce this molecule to QH2
• This process in exergonic and is utilised to actively pump 4 H+ out of the membrane into the inter-membrane space
• The QH2 produced diffuses into the complex 3 through the inter- membrane space

Question 15

What occurs at complex 2 (ETC)

Answer 15

• reduced FADH2 is created from FAD accepting electrons, however is eventually oxidised in order to reduce Q to QH2
• no proton pumping occurs

Question 16

What occurs at complex 3 (ETC)

Answer 16

• there are multiple cytochromes present within this complex
• QH2 is oxidised and donates it’s electrons to cytochrome c, it then returns to complex 1 to re - begin the process
• 4 protons are released

Question 17

What occurs at complex 4 (ETC)

Answer 17

Cytochrome c is oxidised and donates its electrons to oxygen which is reduced into H2O
- oxygen requires 4 electrons to be reduced to water
Two protons are actively pumped out