Energy II: Acetyl CoA, Mitochondria and Oxygen

Question 1

How is glycolysis related to the tricarboxylic acid cycle?

Answer 1

Glycolysis produces pyruvate, which in the presence of oxygen, will enter into the TCA cycle (krebs cycle)

Question 2

How is glycolysis related to oxidative phosphorylation?

Answer 2

Glycolysis leads to the production of pyruvate in the presence of oxygen, which then will produce products that enter into ATP synthesis (oxidative phosphorylation)

Question 3

Where are enzymes of the TCA?

Answer 3

In the mitochondrial matrix

Question 4

Where does oxidative phosphorylation take place?

Answer 4

Inner mitochondrial membrane

Question 5

Where does the TCA cycle take place?

Answer 5

Mitochondrial matrix

Question 6

What is pyruvate converted into?

Answer 6

2C Acetyl CoA - This is by decarboxylation (removal of CO2)

An NADH molecule is produced in the process

Question 7

What does acetyl CoA react with?

Answer 7

Oxaloacetic acid (4C), forms Citrate (6C)

Question 8

What does citrate undergo?

Answer 8

Citrate undergoes 2 decarboxylations, meaning it loses 2 carbon dioxide molecules, and produces 2 NADH molecules. It forms a 4C compound

The first decarboxylation produce isocitrate

The second decarboxylation produces alpha- ketoglutarate

Question 9

What happens to the 4C compound (alpha-ketoglutarate) produced from citrate?

Answer 9

Produces GTP, FADH2 and NADH to form oxaloacetate (4C).

Question 10

What are the net products of the TCA cycle?

Answer 10

For each glucose:

6 NADH + 2 NADH (from conversion of pyruvate to acetyl CoA)

2 FADH2

2 GTP

4 CO2 + 2 CO2 (from conversion of pyruvate to acetyl CoA)

Question 11

What enzyme regulates entry into the TCA cycle and what is it inhibited by?

Answer 11

Pyruvate dehydrogenase, inhibited by NADH and Acetyl CoA

Regulates conversion of pyruvate into acetyl CoA.

Also regulated through phosphorylation by a kinase and a phosphatase

Question 12

What does Isocitrate dehydrogenase do?

Answer 12

Regulates conversion of 6C isocitrate into alpha-ketoglutarate (5C). Inhibition of this enzyme would lead to a build-up of citrate.

The citrate would act as a source of acetyl CoA for fatty acid synthesis.

Question 13

What does alpha-ketoglutarate dehydrogenase do?

Answer 13

Regulates conversion of alpha-ketoglutarate into Succinyl CoA.

Question 14

What is the electron transport chain?

Answer 14

A series of complexes that transfer electrons from donors to acceptors via redox reactions, and couples this electron transfer with the transfer of protons (H+ ions) across the inner mitochondrial membrane

Question 15

How are NADH and FADH2 involved in the electron transport chain?

Answer 15

Their H atoms can be removed due to these being their reduced states.

NADH donates an electron to complex I, producing NAD+

FADH2 donates electron to complex II (succinate dehydrogenase), produced FAD

Electrons from either complex flow into coenzyme Q (ubiquinone)

Coenzyme Q passes electrons to cytochromes (proteins with heme groups: complex III (cytochromes and c1) → cytochrome c → complex IV (cytochrome oxidase: cytochromes a, a3)→ oxygen (this is when oxygen acts as the terminal electron acceptor)

Question 16

What happens to H atoms in the ETC?

Answer 16

They are split into electrons and protons

Question 17

What happens to the H electron in the ETC?

Answer 17

Passes through a series of enzymes called cytochromes and then reacts with oxygen.

Question 18

What is the role of oxygen in the ETC?

Answer 18

Acts as terminal electron acceptor, reacts with H+ to produce water

Question 19

How much ATP does NADH form?

Answer 19

3 ATP

Question 20

How much ATP does FADH2 form?

Answer 20

2 ATP

Question 21

How does the generation of a proton gradient lead to the formation of ATP?

Answer 21

The energy released from electrons moving throughout the transport chain is what allows protons to cross the inner mitochondrial membrane

This creates an elecrochemical gradient

H + ions flow down gradient back into matrix, passing through enzyme ATP synthases, harness flow of protons to synthesise ATP

Question 22

How is ATP synthesised?

Answer 22

H+ ions pass through Complex V (ATP synthase), where they force the complex to rotate.

As it rotates, ATP synthase binds ADP and a phosphate group together, synthesising ATP

Question 23

How does mitochondria in brown fat differ from mitochondria in other cells?

Answer 23

Brown fat cell mitochondria have higher UCP1 levels and a greater density of cristae, enabling them to generate heat and efficiently produce energy in the form of ATP

UCP1 is mitochondrial uncoupling protein 1.

It generates heat by regulated uncoupling of fatty acid oxidation from the production of ATP. During activation UCP1, energy derived from the oxidation of fat is not available to drive phosphorylation of ATP as it diverts the flow of electrons from making ATP, and is consequently dissipated as heat.

Question 24

Why do newborns have brown fat distribution? Where is it typically located?

Answer 24

Newborns require brown fat to produce heat as they don’t have a shiver reflex

Located around shoulder and neck

Question 25

What is the biological significance of compartmentalisation?

Answer 25

Allows protection of organelle contents e.g DNA protected in nucleus by nuclear membrane

Improves efficiency of cellular functions