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MCAT BIochem > Kreb's Cycle and Oxidative Phosphorylation > Flashcards

Kreb's Cycle and Oxidative Phosphorylation Flashcards

1
Q

Where does the citric acid cycle take place?

A

Mitochondria matrix

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2
Q

What is the main function of the citric acid cycle?

A

Oxidize Acetyl-CoA to CO2 and H20 and produce NADH and FADH2 energy molecules

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3
Q

What product of glycolysis enters the mitochondria?

A

Pyruvate via active transport

Oxidized and decarboxylated

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4
Q

Where is pyruvate dehydrogenase complex?

A

In the mitochondrial matrix

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5
Q

How many carbons are in pyruvate?

A

3

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6
Q

How many carbons are in acetyl-CoA

A

2

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7
Q

Is conversion from pyruvate to acetyl-CoA reversible?

A

No

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8
Q

Is pyruvate dehydrogenase reaction spontanteous?

A

Yes Delta G=-33.4 kJ/mol

Exergonic

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9
Q

What inhibits pyruvate dehydrogenase?

A

Acetyl-CoA accumulation and NADH

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10
Q

What are the enzymes of pyruvate dehydrogenase complex?

A 
Pyruvate dehydrogenase (PDH)
DIhydrolipoyl transacetylase
Dihydrolipoyl dehydrogenase 
^Conversion
Pyruvate dehydrogenase kinase
Pyruvate dehydrogenase phosphatase
^Regulate PDH
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11
Q

What kind of group is CoA

A

Thiol

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12
Q

What kind of bond does pyruvate dehydrogenase create?

A

Thioester

High energy properties

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13
Q

Pyruvate dehydrogenase (PDH)

A

Pyruvate is oxidized to yield CO2

Two carbon remaining binds to Thiamine pyrophosphate (Vitamin B1) Mg2+ is required

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14
Q

Dihydrolipoyl transacetylase

A

Two carbon molecule transferred to lipoic acid from TPP
Lipoic acid has a disulfide group acts as an oxidizing agent and forms the acetyl group
Transfers acetyl group to new thiolester link

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15
Q

Dihydorlipoyl dehydrogenase

A

FAD reoxidizes lipoic acid and is oxidized to FADH2

NAD+ used to reoxidize FAD+

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16
Q

Fatty acid oxidation (B oxidation) and Acetyl CoA

A

Fatty acyl-CoA is transported to intermembrane space of mitochondria
Fatty acyl is transferred to carnitine via tranesterification (can’t cross inner membrane)
Crosses inner membrane
Converts back to fatty acyl-CoA
B-oxidation removes 2 C from the carboxyl end

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17
Q

Amino acid catabolism and Acetyl CoA

A

Transamination to remove amino group

Form ketone bodies also

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18
Q

Ketones and Acetyl CoA

A

Ketones can be used to make acetyl-CoA

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19
Q

Alcohol and Acetyl CoA

A

Alcohol dehygenase and acetaldehyde dehydrogenase convert alcohol to acetyl-CoA
Although it also causes NADH buildup that inhibits Krebs cycle

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20
Q

Why is the Kreb’s cycle aerobic only?

A

NADH FADH2 will build up if O2 is not available to oxidize it in the ETC

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21
Q

Step 1- Citrate Formation

A

Citrate Synthase

Acetyl-CoA and OAA to Citrate

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22
Q

Step 2- Citrate Isomerized to Isocitrate

A

Aconitase (requires Fe2+) - an Isomerase

Citrate to Isocitrate

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23
Q

Step 3- a-Ketoglutarate and CO2 formation

A

Isocitrate dehydrogenase

Isocitrate to Oxalosuccinate to a-ketoglutarate and CO2

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24
Q

What steps of the citric acid cycle are rate limiting?

A

Isocitrate dehydrogenase

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25
Where is the first NADH produced during the citric acid cycle?
Isocitrate dehydrogenase
26
A dehydrogenase is what type of enzyme?
Oxidoreductase | Oxidation-reduction reactions
27
Step 4- Succinyl-CoA and CO2 formation
a-ketoglutarate dehydrogenase | a-ketoglutarate and CoA to CO2, Succinyl-CoA and NADH
28
Step 5- Succinate Formation
Succinyl-CoA synthetase (creates new bonds with energy input) Succinyl-CoA to Succinate and GTP
29
Where does the energy come from to create GTP?
Thioester hydrolysis of Succinyl-CoA
30
Step 6- Fumarate Formation
Succinate dehyrdrogenase | Succinate to Fumarate and FADH2
31
Where does fumarate formation occur?
In the inner membrane (FADH2 is a integral protein)
32
Step 7- Malate Formation
Fumarase | Fumarate to malate
33
Step 8-Oxaloacetate formation
Malate dehydrogenase | Malate to OAA and NADH
34
Where is NADH made during Citric acid cycle?
Pyruvate dehydrogenase Isocitrate dehydrogenase a-ketoglutarate dehydrogenase Malate dehydrogenase
35
Mnemonic for Citric Acid Cycle Substrates
Please, Can I Keep Selling Seashells for Money, Officer?
36
When in CO2 formed?
isocitrate dehdyrogenase | a-ketoglutarate dehydrogenase
37
How much energy does glycolysis yield?
2 ATP and 2 NADH ( 7 ATP)
38
How much energy does citric acid cycle yield
4 NADH 1 FADH2 1 GTP =12.5 ATP per pyruvate= 25 ATP per glucose
39
What enzymes regulate pyruvate dehydrogenase?
Pyruvate dehydrogenase kinase Pyruvate dehydrogenase phosphatase Phosphorylation inhibits pyruvate dehydrogenase Also Acetyl-CoA negatively feeds back
40
Control of citrate synthase
ATP and NADH allosteric inhibitors Also Citrate and succinyl-CoA Alosterically
41
Control of Isocitrate dehydrogenase
Inhibited by ATP and NADH allosterically
42
Control of a-ketoglutarate dehydrogenase
Inhibited by succinyl-CoA ATP NADH
43
What stimulates a-ketoglutarate dehydrogenase?
ADP | Calcium
44
What drives the production of ATP?
Proton gradient
45
Where is the electron transport chain?
Inner mitochondrial matrix
46
Where are electrons given at the end of the ETC?
Water
47
How are protons moved?
Mitochondrial matrix into intermembrane space | Lower pH in inner membrane space
48
Molecule with higher reduction potential will be?
Reduced, other will oxidized
49
Complex I (NADH- CoQ Oxidoreductase)
Electrons from 2 NADH transferred to Flavin mononucleotide (FMN) Iron-sulfur subunit takes electrons Donates them to Coenzyme Q/ Ubiquinone 4 Hydrogens pumped into inner membrane space
50
Complex II (Succinate-CoQ Oxidoreductase)
Electrons from succinate to FAD FADH2 donates electrons to iron-sulfur protein to Coenzyme Q No hydrogens pass through
51
Complex III (CoQH2 -cytochrome c oxidoreductase)
Electrons from Coenzyme Q to 2 Cytochrome c molecules | Contributes protons via Q cycle
52
Cytochrome
Proteins with heme groups in which iron is reduced to Fe2+ and reoxidized to Fe3+
53
Q cycle
In complex III 2 electrons are shuttled from a molecule of ubiquinol to ubiquinone Displaces 4 H+ into the intermembrane space
54
Complex IV (cytochrome c oxidase)
Transfer of electrons from cytochrome c to oxygen Cytochrome oxidase made of ctochrome a, cytochrome a3 and Cu2+ ions 4 cytochrome c oxidized 2H+ across ETC 2H+ given to water
55
Eletro-chemical gradient
pH decrease in intermembrane space | Voltage difference between intermembrane space and matrix increases
56
Why is ATP produced in a range?
Variable efficiency of NADH from glycolysis cannot directly cross the mitochondrial matrix and must be shuttled in Either shuttle will yield 1.5 or 2.4 ATP
57
Glycerol 3-phosphate shuttle
In cytosol Glycerol 3-phosphate dehydrogenase forms G3P from DHAP Transfers electrons to FAD FADH2 gives electrons to Complex II= 1.5 ATP
58
Malate-aspartate shuttle
Malate dehydrogenase OAA to malate can pass through the mitochondrial membrane Gives electrons from NADH and reconverted back to NADH in cytosol-->give electrons to Complex I Left over OAA converted to aspartate and back into the cytosol
59
Which way does ATP synthase protrude into?
Matrix
60
Fo portion
Spans membrane | An ion channel that protons move through along their gradient into the matrix
61
Chemiosmotic coupling
Allows chemical energy of gradient to be harnessed to phosphorylate ADP
62
F1 portion
Utilizes energy released from this electrochemical gradient to phosphorylate ADP to ATP
63
Conformational coupling
Suggest indirect relationship between ATP and proton gradient
64
Oxidative Phosphorylation is highly?
Exergonic

MCAT BIochem (8 decks)

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