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Biochem Exam 2 > Chapter 9 - The Krebs Cycle > Flashcards

Chapter 9 - The Krebs Cycle Flashcards

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1
Q

Which is slower - glycolysis or the krebs cycle?

A

the krebs cycle

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2
Q

Is every oxygen molecule that we breathe utilized in the citric acid cycle?

A

no - but a lot are

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3
Q

What are the 2 electron carriers in the citric acid cycle?

A

NADH and FADH2

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4
Q

What is the NET ATP gain of glycolysis?

A

2 ATP

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5
Q

What is the sole substrate of the krebs cycle?

A

acetyl-coA

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6
Q

What is the pathway product of the krebs cycle?

A

CO2

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7
Q

The overall operation of the krebs cycle _____ the 2 acetyl carbons of acetyl coA completely to _____

A

OXIDIZES to CO2

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8
Q

High energy electrons are captured in which 2 cofactors?

A

NADH and Q (ubiquinone)

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9
Q

Formation of acetylcoA from pyruvate requires an enzyme exclusively found where?

A

in the mitochondria

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10
Q

Where is pyruvate formed? (glycolysis)

A

in the cytosol

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11
Q

Cytosolic pyruvate must….

A

cross the outer mitochondrial membrane and the inner mitochondrial membrane

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12
Q

How does pyruvate cross the outer mitochondrial membrane?

A

through a porin

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13
Q

How does pyruvate cross the inner mitochondrial membrane?

A

inner membrane is impermeable to most molecules so pyruvate entry requires a transport protein - the PYRUVATE TRANSPORTER

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14
Q

Where does the pyruvate transporter transport pyruvate? What other molecule?

A

into the MATRIX along with a HYDROGEN ION

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15
Q

What happens in the matrix space?

A

oxidation takes place

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16
Q

What is the first step of this oxidation?

A

conversion of pyruvate to acetyl-CoA

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17
Q

What enzyme catalyzes the conversion of pyruvate to acetyl-CoA?

A

pyruvate dehydrogenase complex

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18
Q

What is an enzyme complex?

A

a group of enzymes that catalyzes a metabolic sequence WITHOUT RELEASING INTERMEDIATES

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19
Q

Write the overall reaction catalyzed by the pyruvate dehydrogenase complex

A

pyruvate + NAD+ +CoA —> Acetyl-CoA + NADH + CO2

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20
Q

The reaction catalyzed by the pyruvate dehydrogenase complex is ______

A

irreversible

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21
Q

The conversion of pyruvate to acetyl-CoA requires ____ enzymes and ____ cofactors

A

3 enzymes and 6 cofactors

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22
Q

What are the 3 mobile cofactors in the conversion of pyruvate to acetyl-CoA?

A

NAD+, NADH, CoA

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23
Q

What are the 3 bound cofactors in the conversion of pyruvate to acetyl-CoA?

A

thiamine pyrophosphate, lipoic acid, and FAD

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24
Q

Do the bound cofactors appear in the reaction?

A

NO - they act as an extension of the enzyme to which they’re attached

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25
The 3 enzymes catalyzing the conversion of pyruvate to acetyl-CoA are represented as ___,____, and ____
E1, E2, E3
26
What 2 enzymes are involved in the REGULATION of the pyruvate dehydrogenase complex?
PDH kinase PDH phosphatase
27
What molecule represents the "swinging arm" of the pyruvate dehydrogenase complex?
the lipoamide attached to E2
28
What does a kinase enzyme do?
Adds a phosphate to a molecule (usually deactivates it)
29
What is the opposite of a kinase enzyme?
Phosphatase - takes the phosphate off (usually activates molecule)
30
What is the bound cofactor of E1?
TPP -
31
What is the bound cofactor of E2?
Lipoamide
32
What is the bound cofactor of E3?
FAD
33
What mobile cofactor does PDH kinase react with?
ATP
34
Of the 3 - E1, E2, E3 - which reacts with a mobile cofactor?
E3 - reacts with NAD+
35
Which mobile cofactor diffuses away and transports its carried electrons elsewhere?
NADH
36
Describe the cycle that leads to NAD+ gaining 2 electrons and becoming NADH
E3 gives an electron pair to FAD to become FADH2. FADH2 transfers its 2 electrons to NAD+ to become NADH
37
LIPOIC ACID GETS ____ THEN _____
Reduced than oxidized
38
Which enzyme - E1, E2, or E3 - grabs an acetyl group and gives it to CoA to become acetyl CoA?
E2
39
E1 kicks out ____ from TPP
CO2
40
The citric acid cycle consists of ____ reactions
8
41
What does TCA stand for?
Tricarboxylic acid
42
Citric acid can also be called _____ acid. Why?
Tricarboxylic acid because it contains 3 carboxyl groups
43
Many intermediates in the citric acid cycle can be——-
Utilized by other pathways
44
Isocitrate is a ___ of citrate
Isomer
45
Acitonase is _____ an isomerase enzyme
NOT
46
Where is PDH located in the cell?
In the mitochondrial matrix
47
Which bound cofactor can move/swing among E1,E2, and E3?
Lipoamide
48
Enzymes in the krebs cycle generate energy through----
oxidation
49
How many CO2 molecules are releases in the Krebs cycle? They are released as a result of ______
2 CO2 molecules. released as a result of oxidation
50
What enzyme catalyzes the formation of Acetyl-CoA from pyruvate?
the pyruvate dehydrogenase complex
51
How is acetyl-coA formed?
Pyruvate from glycolysis gives up 2 of its carbons and reacts with CoEnzyme A to produce acetyl-CoA
52
What are the byproducts of the formation of Acetyl CoA from pyruvate?
NADH and CO2
53
What class of enzymes is the pyruvate dehydrogenase complex?
oxidoreductase enzyme
54
Acetyl-CoA is a ____ carbon molecule
2
55
What is the first step of the krebs cycle? (include enzyme name, # of carbons, etc)
Acetyl-CoA has TWO CARBONS and reacts with the 4 CARBON MOLECULE OXALOACETATE to form the 6 CARBON MOLECULE - CITRATE catalyzed by citrate synthase
56
What are the byproducts of the reaction catalyzed by citrate synthase?
Coenzyme-A bonded to a sulfhydryl functional group (SH)
57
What is the second reaction of the krebs cycle? (include names, enzyme, etc)
citrate (6 CARBONS) is converted into its isomer - isocitrate (Also 6 CARBONS)
58
What is the 3rd reaction in the krebs cycle? (include names, enzyme, # carbons, etc)
Isocitrate is converted into alpha ketoglutarate. Catalyzed by isocitrate dehydrogenase (5 CARBONS)
59
What are the byproducts of the 3rd reaction in the krebs cycle?
NAD+ IN, NADH + H+ + CO2 OUT
60
What else can you say about the 3rd reaction in the krebs cycle?
1st oxidation reduction reaction (produces energy)
61
What can you say about the 4th reaction of the Krebs Cycle?
VERY SIMILAR to the 3rd
62
State the names, enzymes, byproducts, and # of carbons in the 4th step of the krebs cycle
alpha ketoglutarate (5 CARBONS) is converted into succinyl CoA (4 CARBONS) . Catalyzed by alpha ketoglutarate dehydrogenase. byproducts = NAD+ in, NADH, CO2 and H+ out
63
Succinyl-CoA is a -------- meaning it can do what?
Succinyl-CoA is a HIGH ENERGY MOLECULE, meaning it can partake in substrate level phosphorylation to produce ATP
64
Describe the 5th step of the krebs cycle including names, enzyme, # carbons, BYPRODUCTS, etc
succinyl-CoA is converted into succinate (both have 4 carbons) Succinyl CoA is a high energy molecule and is used for substrate level phosphorylation to produce ATP GDP + Pi in GTP + CoA-SH out Catalyzed by Succinyl CoA SYNTHETASE
65
What is the difference between synthase and synthetase enzymes?
synthetase uses energy such as ATP, GTP, etc
66
Succinate dehydrogenase removes a ___ from ____. The Hydrogen is then accepted by _____
Succinate dehydrogenase removes a HYDROGEN from SUCCINATE. The hydrogen is then accepted by FAD
67
What is the ONLY enzyme of the Krebs Cycle that is membrane bound?
Succinate dehydrogenase
68
Describe the 6th reaction in the Krebs Cycle. Give all details
Succinate is converted to Fumurate by Succinate Dehydrogenase. Both are 4 carbons. Q is reduced to QH2
69
What does Q stand for?
Ubiquinone
70
Describe the 7th reaction in the krebs cycle. give all details
fumurate is converted into malate through a hydration reaction to saturate the double bond (addition of water) catalyzed by fumarase
71
Describe the 8th reaction in the krebs cycle. give all details
malate is oxidized into oxaloacetate (both 4 carbons). catalyzed by malate dehydrogenase. NAD+ Reduced to NADH + H+
72
Throughout the Krebs Cycle when 4 C molecules keep getting converted into other 4C molecules, is energy lost or gained?
lost
73
How many ATP are produced from oxidizing ONE molecule of Acetyl-CoA? Break it down.
12 ATP 3 NADH---->9ATP 1QH2------->2ATP 1GTP-------->1ATP =12ATP
74
The conversion of Glucose to pyruvate produces ____ total ATP when all is said and done. Break it down.
8 ATP 2ATP---> 2ATP 2NADH--> 6ATP =8ATP
75
How many ATP are produced from the conversion of pyruvate to Acetyl-CoA? Break it down
3 ATP 1 NADH---> 3ATP
76
Normally ___(#) pyruvates is converted into ____(#) Acetyl-CoA, meaning that in reality ______ ATP is produced
2 pyruvates are converted into 2 Acetyl-CoA, thus producing 2 NADH molecules and 6 ATP in reality
77
in reality, _____(#) Acetyl-CoA(s) are oxidized into _____(#) molecules of CO2, meaning that _____ATP are produced
2 Acetyl-CoA's are oxidized into 4 molecules of CO2, meaning that 24 ATP are produced for every Krebs cycle
78
Upon COMPLETE OXIDATION, how many ATP are produced? What is the formula to illustrate this reaction?
Glucose ----> 6CO2 38 ATP are produced
79
Which enzyme catalyzes the step where Q is reduced to QH2?
Succinate dehydrogenase
80
Which step in the Krebs Cycle generates GTP?
Succinyl-CoA -----> Succinate catalyzed by succinate synthetase
81
The outer mitochondrial membrane allows the passage of molecules smaller than.....
10kda
82
Pyruvate is ____ to acetyl-CoA
oxidized
83
What are the 2 levels of Krebs Cycle regulation?
-By its supply of substrate (Acetyl-CoA) -By intrinsic activity
84
What are the 3 major nutrients?
fats, carbohydrates, and proteins
85
All major nutrients are converted into _____ for oxidation by the Krebs cycle
acetyl-CoA
86
The Krebs cycle is the final common route for the complete ____ of foods into _____
complete oxidation of foods into CO2
87
How is the oxidation of pyruvate to Acetyl-CoA regulated?
by PDH kinase and PDH phosphatase. -phosphorylation/dephosphorylation of the E1 component of the pyruvate dehydrogenase complex
88
What enzyme puts E1 in its INACTIVE form and how does it accomplish this?
PDH kinase inactivates E1 by placing a phosphate group on it
89
PDH kinase is inhibited by ___ and stimulated by _____
PDH kinase is inhibited by PYRUVATE and stimulated by acetyl-CoA
90
The phosphatase that catalyzes the dephosphorylation of E1-P is stimulated by.....
CALCIUM
91
The citric acid cycle is known as a ________
Metabolic Hub
92
Why is the citric acid cycle known as a metabolic hub?
its enzymes play a role in other metabolic pathways
93
What other metabolic pathways do the enzymes of the krebs cycle play a role in?
Fatty Acid synthesis uses CITRATE Amino acids can be converted into Krebs cycle intermediates (transamination)
94
Glutamate can be converted into what intermediate of the Krebs Cycle?
alpha ketoglutarate
95
Aspartate can be converted into what intermediate of the Krebs cycle?
oxaloacetate

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