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PHAY0003 > Krebs Cycle > Flashcards

Krebs Cycle Flashcards

1
Q

What is the overall outcome of the Krebs/ TCA cycle?

A

Generating NADH and FADH which are then fed into the ETC from acetyl CoA

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2
Q

Where does the Krebs cycle happen?

A

In the mitochondrial matrix

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3
Q

What is the purpose in the Krebs cycle where water is removed from citrate, just to be put back in in the next stage?

A

During this, the OH moves down one carbon

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4
Q

Where does the energy come from in the production of the first NADH in the Krebs cycle?

A

The forming of the C=O bond

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5
Q

What types of catalysers result in the formation of NADH and FADH in the Krebs cycle?

A

Dehydrogenases (removes hydrogen which is used for NADH and FADH synthesis)

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6
Q

In the Krebs cycle, what is lost?

A

2 x CO2

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7
Q

In the Krebs cycle, how much energy is made and in what form?

A

3 x NADH
1 x FADH
1 x GTP (= ATP)

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8
Q

In the Krebs cycle, what is the total yield of ATP generated?

A

12 ATP

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9
Q

How much ATP does FADH and NADH equivalate to?

A 
NADH = 3 x ATP
FADH = 2 x ATP
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10
Q

What is the overall outcome of glycolysis?

A

The conversion of glucose into pyruvate

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11
Q

Under what conditions is glycolysis the major source of ATP?

A

Anaerobic conditions

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12
Q

What happens to pyruvate under anaerobic conditions?

A

It is converted into lactate by lactate dehydrogenase which builds up in muscles and causes muscle cramps

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13
Q

What happens to pyruvate under aerobic conditions?

A

It enters the mitochondria to be converted into acetyl-CoA which is entered into the Krebs cycle

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14
Q

Where does glycolysis occur?

A

In the cytoplasm

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15
Q

How does glucose enter the cell?

A

Using a glucose transporter protein which transports it across the plasma membrane (GLUT1-7), GLUT 1 facilitates glucose diffusion for glycolysis

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16
Q

Describe how GLUT 1 transports glucose

A

Glucose binds to it form outside of the cell, this causes a conformational change resulting in glucose being trapped and then released inside of the cell

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17
Q

What is the role of hexokinase?

A

To phosphorylate glucose so that it is trapped inside the cell using ATP

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18
Q

What is the type of mechanism that the enzyme hexokinase undergoes?

A

Induced fit, glucose binds to it resulting in a conformational change so that the active site closes around it, making a non-polar environment to encourage phosphorylation

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19
Q

Why is it important that hexokinase is able to trap glucose so that a non-polar environment is made?

A

So that the phosphate group is transferred to the glucose and not water

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20
Q

How many ATPs are used in glycolysis?

A

2

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21
Q

What is the net gain of ATP and NADH from glycolysis?

A

2 x NADH

2 x ATP

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22
Q

How many molecules of pyruvate are made in glycolysis from one glucose?

A

2

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23
Q

What converts pyruvate into acetyl-CoA?

A

Pyruvate dehydrogenase

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24
Q

What are the 3 enzymes that make up the pyruvate dehydrogenase complex and their ratios

A

E1 (30), E2 (60), E3 (6)

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25
Q

What are the 3 benefits of pyruvate dehydrogenase?

A

The intermediates are passed directly between enzymes
No dilution of substrate within the mitochondrial matrix
No loss of substrate and no by products

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26
Q

What happens to the 2 NADH formed from glycolysis?

A

It has to be transferred from cytosol to mitochondrion, in the process, it transfers e- to FADH inside the inner mitochondrial membrane and so becomes 2 FADH

27
Q

What is the total amount of ATP derived from total oxidation of glucose?

A

36 ATP

28
Q

What is yielded from PDH?

A

1 x acetyl-CoA

1 x NADH

29
Q

When glucose availability is low, what is used as the energy course?

A

Fatty acids

30
Q

Where do dietary fatty acids go?

A

Into the liver

31
Q

Where do dietary triacylglycerols in lipoprotein chylomicra get broken down into fatty acids?

A

At the cell surface and are then taken up by the cell

32
Q

What is lipolysis?

A

The breakdown of triacylglycerol into 3 fatty acids and glycerol using lipase

33
Q

Which bonds are broken in lipolysis?

A

The ester bonds

34
Q

What enzyme esterifies fatty acids to the coenzyme A?

A

Acyl-CoA synthase

35
Q

Where are fatty acids esterified?

A

On the outer mitochondrial membrane

36
Q

How many phosphates are removed from ATP in the esterification of fatty acids?

A

2

37
Q

Why is the esterification of fatty acids irreversible?

A

The hydrolysis of ATP to AMP + 2P released a lot of energy

38
Q

Where does most of the energy derived from fatty acids come from?

A

The chains

39
Q

What happens to the coenzyme A fatty acid after it has been synthesised?

A

The fatty acid part is transported across the mitochondrial matrix by carnitine

40
Q

Describe how the fatty acid region of the CoA derivative is transported across the mitochondrial membrane into the matrix

A

The enzyme CAT I transfers the fatty acid from the CoA to carnitine on the surface of the outer membrane. A translocase proteins then transfers the fatty acid across the membrane to CAT II on the inner surface where it is then attached to a different CoA

41
Q

What happens to the fatty acyl-CoA inside the mitochondrial matrix?

A

It is oxidised to acetyl-CoA where it is used in the Krebs cycle

42
Q

Why is carnitine sometimes advertised as good supplement?

A

It promotes the oxidation of fatty acids and therefore ATP production

43
Q

How many reactions make up beta oxidation?

A

4

44
Q

What is the process called where fatty acyl-CoA is degraded into acetyl-CoA

A

Beta-oxidation

45
Q

How long is the carbon chain in acetyl CoA?

A

2 carbons

46
Q

What happens to the fatty acyl CoA that is derived after oxidation of the previous fatty acyl CoA?

A

It repeats the cycle to produce another molecule of acetyl CoA

47
Q

Palmitic acid has 16 carbon chains, how many cycles does it require to become fully oxidised and how many acetyl CoAs are derived?

A

7 cycles, 8 acetyl CoAs

48
Q

How many acetyl CoAs does the last cycle of oxidation of a fatty acyl-CoA produce?

A

2

49
Q

How many FADHs and NADHs is derived per cycle of oxidation of a fatty acyl-CoA?

A

One of each

50
Q

If a fatty acid has 16 carbons, what is the energy yield from complete oxidation to acetyl-CoA?

A

7 cycles = 7 NADH + 7 FADH + 8 Acetyl-CoA
= 14 ATP + 21 ATP + 96 ATP
- 2 ATP from esterification before oxidation
= 129 ATP

51
Q

What happens if a fatty acid has an odd number of carbons?

A

The oxidation occurs as normal until 3 carbons are left. This then forms succinyl-CoA which feeds into the Krebs cycle

52
Q

What is the molecule of CoA with 3 carbons called produced from beta-oxidation?

A

Propionyl-CoA

53
Q

What enzyme converts propionyl-CoA into succinyl-CoA?

A

Propionyl-CoA carboxylase, it adds CO2 to the molecule

54
Q

What happens to an amino acid in the liver if it is not required for synthesis of proteins?

A

The alpha amino group is removed (NH4+) and excreted in the urea, the carbon skeleton becomes a major metabolite

55
Q

What is transamination?

A

The transfer of an amino group from an amino acid to alpha-ketoglutarate to form glutamate and a carbon skeleton (e.g pyruvate), this is catalysed by aminotransferase

56
Q

What happens to glutamate after it has been formed from trasnamination?

A

Oxidative deamination, it forms ammonia and alpha-ketoglutarate which is catalysed by glutamate dehydrogenase and NAD

57
Q

What happens to the alpha-ketoglutarate produced in oxidative deamination of glutamate?

A

It can be used for transamination or fed into the Krebs cycle

58
Q

What happens to the ammonia formed from the breakdown of amino acids?

A

It undergoes the urea cycle, it is combined with CO2 to form urea in the liver which is release into the blood for excretion via the kidneys

59
Q

Where does transamination, oxidative deamination?

A

In the liver

60
Q

Why does the lack of any of the urea cycle enzymes result in death?

A

It is the only way of disposing of ammonia, there are no alternative pathways for urea synthesis

61
Q

What is hyperammonaemia

A

A condition caused by a partial deficiency of any urea cycle enzyme, symptoms include mental retardation and episodic vomiting

62
Q

Where does the urea cycle occur?

A

Partly in the mitochondrial matrix and partly in the cytosol

63
Q

What is the molecular composition of urea and where do the components come from?

A

2HNCONH2, CONH2 comes from after the oxidative deamination where ammonia and CO2 combine, the other NH2 comes from aspartate in the cytosol

PHAY0003 (22 decks)

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