T2 L2 Roles of ATP in living cells

Question 1

What happens to pyruvate in aerobic conditions?

Answer 1

It undergoes oxidation & complete degradation in the mitochondria

Question 2

Where does glycolysis occur?

Answer 2

In the cytosol

Question 3

What are the roles of pyruvate in metabolism?

Answer 3

Forms lactate using lactate dehydrogenase
Forms oxaloacetate using pyruvate carboxylase
Forms alanine using alanine aminotransferase
Forms acetyl CoA using pyruvate dehydrogenase complex

Question 4

How is pyruvate transported into the mitochondria?

Answer 4

Via a specific carrier protein embedded in the mitochondrial membrane

Question 5

What is the equation for oxidative decarboxylation of pyruvate

Answer 5

Pyruvate + CoA + NAD+ –> acetyl-CoA + CO2 + NADH + H+

The reaction is irreversible & forms the link between glycolysis & the citric acid cycle

Question 6

What makes up the pyruvate dehydrogenase complex?

Answer 6

3 different enzymes
5 different co-enzymes
4 different vitamins

Question 7

What are the 3 enzymes that make up the pyruvate dehydrogenase complex?

Answer 7

Pyruvate dehydrogenase
Dihydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase

Question 8

What are the 5 different co-enzymes that make up the pyruvate dehydrogenase complex?

Answer 8

Thiamine pyrophosphate (TPP)
NAD+
CoA
Flavine adenine dinucleotide (FAD)
Lipoic acid

Question 9

What are the 4 different vitamins in the pyruvate dehydrogenase complex?

Answer 9

Thiamine - in TPP
Riboflavin - in FAD
Niacin - in NAD
Pantothenate - in CoA

Question 10

What is the final pathway for the oxidation of fuel molecules?

Answer 10

Tricarboxylic acid cycle

Question 11

What are the products of the TCA cycle?

Answer 11

3 NADH
1 FADH2
1 GTP (ATP)
2 CO2

Question 12

What are the 4 ways that the TCA cycle is regulated?

Answer 12

1) Conversion of pyruvate to acetyl CoA
2) Entry of acetyl CoA into the TCA cycle
3) Isocitrate dehydrogenase reaction
4) Alpha-ketoglutarate dehydrogenase reaction

All 4 reactions are irreversible & all are activated by calcium. All are inhibited by ATP & NADH

Question 13

What does high levels of ATP & NADH stimulate?

Answer 13

Signals a high energy status of the cell so there is no requirement for increased ATP synthesis

Question 14

What are the products of glycolysis?

Answer 14

Pyruvate

NADH

Question 15

What are NADH & FADH2 oxidised by?

Answer 15

The mitochondrial electron transport chain

Inner mitochondrial membrane is impermeable to NADH & there is no carrier

Question 16

What are the 2 shuttles that transport electrons from NADH?

Answer 16

Glycerol-3-phosphate shuttle
Malate-aspartate shuttle

Both regenerate NAD+

Question 17

Describe the glycerol-3-phosphate shuttle

Answer 17

In the brain & muscle
NADH reduces dihydroxyacetone-P (DHAP) to glycerol-3-phosphate
Catalysed by G-3-P dehydrogenase
G-3-P diffuses into the intramembrane space
Mitochondrial G-3-P dehydrogenase uses FAD to oxidise it to DHAP
FADH2 carries electrons to ubiquinone in the electron transport chain, eventually producing 1.5 ATP

Question 18

Describe the malate-aspartate shuttle

Answer 18

Present in liver & heart
Electrons of cytosolic NADH transfer to cytosolon oxaloacetate, yielding malate
Malate is transported into the matrix via the exchanger protein that transports alpha-KG in the opposite direction
NADH formed transfers its reducing power to the electron transport chain producing 2.5ATP
Oxaloacetate is converted to aspartate
Aspartate is transported to the cytosol via an exchanger protein that transports glutamate into the matrix
Cytosolic aspartate is transaminate to oxaloacetate

Question 19

What are the multi-unit proteins that make up the electron transport chain?

Answer 19

Complex I
Complex II
Complex III
Complex IV
The proteins are intrinsic to the inner mitochondrial membrane complex

Question 20

How is energy released from the electron transport chain?

Answer 20

Tightly coupled to the production of ATP

It is not released as heat

Question 21

What are the complexes in the ETC linked by?

Answer 21

1) Ubiquinone

2) Cytochrome C

Question 22

What is ubiquinone?

Answer 22

Coenzyme Q

Lipid soluble benzoquinone with a long isoprenoid tail

Question 23

What is cytochrome C?

Answer 23

Not part of an enzyme complex

Moves between complex III & complex IV