Kreb's Cycle

Question 1

Key CENTRAL metabolic pathway that connects carbohydrate, fat and protein metabolism

Answer 1

TCA cycle

Question 2

Kreb’s cycle is used to generate

Answer 2

NADH
FADH

Molecules that can go in ETC and generate energy

Question 3

Krebs cycle release stored energy or fats, carbs and proteins through

Answer 3

Oxidation

Question 4

Originates even before life started

Origin of life from nonliving things

Answer 4

Abiogenesis

Question 5

2 C acetate that enters the Krebs release these 2 molecules through

Answer 5

CO2

oxidation

Question 6

In eukaryotic cells, citric acid cycle occurs in the

Answer 6

matrix of mitochondria

Question 7

In prokaryotic cells, the citric acid is performed in the

Answer 7

Cytosol

Question 8

Acetyl CoA comes from

Answer 8

Breakdown of 6C glucose to 3C compound pyruvate with transfer of 2 C from pyruvate to acetyl coA

additional carbon lost and 1 molecule of NADH produced

Question 9

Converts pyruvate dehydrogenase to acetyl coA

Answer 9

Pyruvate dehydrogenase

Question 10

Pyruvate dehydrogenase that converts pyruvate to acetyl coa needs the coenzyme to function effectively

Answer 10

Vitamin B5 Pantothenic Acid

Coenzyme A

Question 11

Deficiency of pyruvate dehydrogenase
Decreased levels of Cytochromes a and aa3

Spasticity
Myoclonia
Demenita with hepatic cirrhosis

Answer 11

Alpers disease

Progressive Sclerosing Poliodystrophy

Question 12

First step in TCA

by the enzyme

Answer 12

2 C acetyl CoA + 4 C oxaloacetate -> 6 C citrate

citrate synthase

Question 13

Second step:

Citrate is converted into

by the enzyme

Answer 13

Isocitrate

Aconitase

Question 14

Inhibitor of aconitase

Causes citrate accumulation -> block citric acid cycle

Answer 14

Fluorocitrate

Question 15

Contained in rat poisons, flouroacetate is converted to this chemical by citrate synthase

Answer 15

Fluorocitrate

Question 16

Step 3: Isocitrate is converted into

by the enzyme

with production of

Answer 16

Alpha ketoglutarate

Isocitrate dehydrogenase

NADH
*removes hydrogen aka oxidation
NAD -> NADH

H must be passed on to another molecule hence reduced

Question 17

First oxidation reduction reaction of Krebs

Answer 17

6C Iso-citrate -> 5C Alpha ketoglutarate by isocitrate dehydrogenase

NAD -> NADH

Carbon atom removed from isocitrate in the form of CO2

“oxidative decarboxylation”

Question 18

Step4: Alpha ketoglutarate becomes

by the enzyme

and yields

Answer 18

3 C Succinyl CoA

Alpha ketoglutarate dehydrogenase

NADH

Again, “oxidative decarboxylation”

Uses coenzyme A

NAD - NADH + CO2

Question 19

Step 5: Succinyl CoA becomes

by the enzyme

Answer 19

4 C Succinate

Succinyl CoA SYNTHETASE

GDP -> GTP

Coenzyme A gets released, succinyl CoA loses its high free energy

Question 20

The substrate level phosphorylation reaction in TCA

Answer 20

Succinyl CoA -> Succinate by Succinyl Coa synthetase

GDP -> GTP

Question 21

Step 6: Succinate becomes

by the enzyme

produces

Answer 21

Fumarate

Removes H from succinate and accepted by FAD becoming FADH

FAD used because it requires lesser energy since 4C compound na lang sila

Question 22

This enzyme uses Fe-S complex as in ETC

Answer 22

Succinate dehydrogenase

Complex II

Question 23

Step 7: Fumarate becomes

by the enzyme

Answer 23

Malate

Fumarase
Water is added to fumarate

Question 24

Step 8: Malate becomes

by the enzyme

Answer 24

Oxaloacetate

Malate dehydrogenase

“Oxidation”

NAD -> NADH for ETC
Because oxaloacetate is rapidly utilized for ETC and to generate citrate

Standard free energy for this cycle is significantly POSITIVE

Question 25

+G of the TCA

Answer 25

Malate -> Oxaloacetate by malate dehydrogenase

NAD -> NADH

Question 26

3 molecules of NADH generated from the TCA come from these enzymes

Answer 26

Isocitrate dehydrogenase
Alpha ketoglutarate dehydrogenase
Malate dehydrogenase

Question 27

1 molecule of FADH is generated from this enzyme

Answer 27

Succinate dehydrogenase

Question 28

Acetyl CoA + 3 NAD + FAD + GDP + P04 + 2H20 ->

Answer 28

2 CO2 + 3 NADH + FADH2 + GTP + CoA

Question 29

1 molecule of GTP is formed by the enzyme

Answer 29

Succinyl CoA synthase

Also releases CoA

Succinyl CoA -> Succinate

Question 30

2 molecules of water is formed by the enzyme

Answer 30

Citrate synthase (oxaloacetate + acetyl coa)
Fumarase (fumarate -> malate)

Question 31

How many ATPs in TCA

Answer 31

3 NADH (2.5 x 3)
1 FADH  (1.5 x 1)
1 GTP 
————————
10 ATPs = 1 acetyl CoA in one turn 

10 x 2 acetyl CoAs entered = 20 ATPs

Question 32

High energy compound regenerated in TCA

Answer 32

Oxaloacetate

Question 33

Synthesis and degradation

Pathway for oxidation of 2-C units
Provides substrates for AA synthesis by transamination
Provides substrates for gluconeogenesis and FA synthesis

Answer 33

Amphibolic pathway

TCA

Question 34

Citrate synthase is inhibited by

Answer 34

ATP

Question 35

Key cytoplasmic enzyme that facilitates the net transfer out of the Kreb’s cycle into the main pathway or GLUCONEOGENESIS

Answer 35

Phosphoenolpyruvate carboxykinase

PEPCK

Question 36

Catalyzes the decarboxylation of oxaloacetate to phosphoenolpyruvate

Answer 36

Phosphoenolpyruvate carboxykinase

PEPCK

Question 37

Phosphoenolpyruvate carboxykinase is induced by

Answer 37

Glucagon

Cortisol

Question 38

End product (with energy) of TCA

Answer 38

3 NADH

1 FADH2

Question 39

Rate limiting step of Krebs

Answer 39

Isocitrate -> alpha ketoglutarate by enzyme isocitrate dehydrogenase

Question 40

TCA is stimulated by inc

Answer 40

ADP

Question 41

TCA is inhibited by inc

Answer 41

ATP
NADH
FADH2

Question 42

Amino acids that can enter TCA

Answer 42

Alanine (Pyruvate, Acetyl Coa)
Aspartate (Oxaloacetate)
Glutamate (a-ketoglutarate)

Question 43

Discovered by Hans Krebs
Central pathway for recovering energy
Final common pathway for metabolism of CHO, lipids, proteins

1 cycle: 2 molecules CO2, 3 NADH, 1 FAD and 1 high energy compound (oxaloacetate)

Answer 43

Kreb’s cycle