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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
What are the 3 benefits of pyruvate dehydrogenase?
The intermediates are passed directly between enzymes No dilution of substrate within the mitochondrial matrix No loss of substrate and no by products
26
What happens to the 2 NADH formed from glycolysis?
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
What is the total amount of ATP derived from total oxidation of glucose?
36 ATP
28
What is yielded from PDH?
1 x acetyl-CoA | 1 x NADH
29
When glucose availability is low, what is used as the energy course?
Fatty acids
30
Where do dietary fatty acids go?
Into the liver
31
Where do dietary triacylglycerols in lipoprotein chylomicra get broken down into fatty acids?
At the cell surface and are then taken up by the cell
32
What is lipolysis?
The breakdown of triacylglycerol into 3 fatty acids and glycerol using lipase
33
Which bonds are broken in lipolysis?
The ester bonds
34
What enzyme esterifies fatty acids to the coenzyme A?
Acyl-CoA synthase
35
Where are fatty acids esterified?
On the outer mitochondrial membrane
36
How many phosphates are removed from ATP in the esterification of fatty acids?
2
37
Why is the esterification of fatty acids irreversible?
The hydrolysis of ATP to AMP + 2P released a lot of energy
38
Where does most of the energy derived from fatty acids come from?
The chains
39
What happens to the coenzyme A fatty acid after it has been synthesised?
The fatty acid part is transported across the mitochondrial matrix by carnitine
40
Describe how the fatty acid region of the CoA derivative is transported across the mitochondrial membrane into the matrix
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
What happens to the fatty acyl-CoA inside the mitochondrial matrix?
It is oxidised to acetyl-CoA where it is used in the Krebs cycle
42
Why is carnitine sometimes advertised as good supplement?
It promotes the oxidation of fatty acids and therefore ATP production
43
How many reactions make up beta oxidation?
4
44
What is the process called where fatty acyl-CoA is degraded into acetyl-CoA
Beta-oxidation
45
How long is the carbon chain in acetyl CoA?
2 carbons
46
What happens to the fatty acyl CoA that is derived after oxidation of the previous fatty acyl CoA?
It repeats the cycle to produce another molecule of acetyl CoA
47
Palmitic acid has 16 carbon chains, how many cycles does it require to become fully oxidised and how many acetyl CoAs are derived?
7 cycles, 8 acetyl CoAs
48
How many acetyl CoAs does the last cycle of oxidation of a fatty acyl-CoA produce?
2
49
How many FADHs and NADHs is derived per cycle of oxidation of a fatty acyl-CoA?
One of each
50
If a fatty acid has 16 carbons, what is the energy yield from complete oxidation to acetyl-CoA?
7 cycles = 7 NADH + 7 FADH + 8 Acetyl-CoA = 14 ATP + 21 ATP + 96 ATP - 2 ATP from esterification before oxidation = 129 ATP
51
What happens if a fatty acid has an odd number of carbons?
The oxidation occurs as normal until 3 carbons are left. This then forms succinyl-CoA which feeds into the Krebs cycle
52
What is the molecule of CoA with 3 carbons called produced from beta-oxidation?
Propionyl-CoA
53
What enzyme converts propionyl-CoA into succinyl-CoA?
Propionyl-CoA carboxylase, it adds CO2 to the molecule
54
What happens to an amino acid in the liver if it is not required for synthesis of proteins?
The alpha amino group is removed (NH4+) and excreted in the urea, the carbon skeleton becomes a major metabolite
55
What is transamination?
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
What happens to glutamate after it has been formed from trasnamination?
Oxidative deamination, it forms ammonia and alpha-ketoglutarate which is catalysed by glutamate dehydrogenase and NAD
57
What happens to the alpha-ketoglutarate produced in oxidative deamination of glutamate?
It can be used for transamination or fed into the Krebs cycle
58
What happens to the ammonia formed from the breakdown of amino acids?
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
Where does transamination, oxidative deamination?
In the liver
60
Why does the lack of any of the urea cycle enzymes result in death?
It is the only way of disposing of ammonia, there are no alternative pathways for urea synthesis
61
What is hyperammonaemia
A condition caused by a partial deficiency of any urea cycle enzyme, symptoms include mental retardation and episodic vomiting
62
Where does the urea cycle occur?
Partly in the mitochondrial matrix and partly in the cytosol
63
What is the molecular composition of urea and where do the components come from?
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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