Carbohydrates Metabolism (Kreb's cycle)

Question 1

Kreb’s cycle other names

Answer 1

Citric acid cycle
Tri carboxylic acid cycle

Question 2

Kreb’s cycle mnemonic

Answer 2

Citrate is krebs starting substance for making Oxaloacetate

Question 3

Kreb’s cycle

Answer 3

• The final common pathway for complete oxidation of carbohydrates, fatty acids and many amino acids
• It is a common pathway for catabolism of acetyl COA, a common intermediate of different catabolic pathways

Question 4

Kreb’s cycle site

Answer 4

Mitochondria matrix

Question 5

One glucose molecule will produce … ATP if oxidized by Kreb’s cycle

Answer 5

24

One round → 12 ATP

But one glucose molecule produce 2 Acetyl CoA

Question 6

One round in Krebs cycle produce … ATP

Answer 6

12

Question 7

Complete the next step in Kreb’s cycle :
Acetyl CoA + Oxaloacetate by …. will produce …

Answer 7

Citrate synthase → Condensation

Citrate

Question 8

Complete the next step in Kreb’s cycle :
Citrate by …. will produce …

Answer 8

Aconitase → Rearrangement

Isocitrate

Question 9

Complete the next step in Kreb’s cycle :
Isocitrate by …. will produce …

Answer 9

Dehydrogenase → Oxidative decarboxylation (Remove 2H2 and CO2)

α-Ketoglutarate

Question 10

Complete the next step in Kreb’s cycle :
α-Ketoglutarate by …. will produce …

Answer 10

Dehydrogenase → Oxidative decarboxylation (Remove 2H2 and CO2)

Succinyl - CoA

• CO2

Question 11

Complete the next step in Kreb’s cycle :
Succinyl - CoA by …. will produce …

Answer 11

Succinyl - CoA synthetase

Succinate “Succinic acid”

Question 12

Complete the next step in Kreb’s cycle :
Succinate by …. will produce …

Answer 12

Dehydrogenase → “Remove H2O”

Fumarate “Fumaric acid”

Question 13

Complete the next step in Kreb’s cycle :
Fumarate by …. will produce …

Answer 13

Fumarase → “Add H2O”

Malate

Question 14

Complete the next step in Kreb’s cycle :
Malate by …. will produce …

Answer 14

Dehydrogenase → Remove 2H2

Oxaloacetate

Question 15

Mention the reactions that produce NADH in Kreb’s cycle

Answer 15

Isocitrate → α-Ketoglutarate
α-Ketoglutarate → Succinyl - CoA
Malate → Oxaloacetate

Question 16

Mention the reaction that produce FADH2 in Kreb’s cycle

Answer 16

Succinate → Fumarate

Question 17

Mention the reaction that produce GTP in Kreb’s cycle

Answer 17

Succinyl - CoA → Succinate

Question 18

…. is responsible for maintain Kreb’s cycle rate

Answer 18

Oxaloacetate

Question 19

Why we called Kreb’s cycle “Tricarboxylic acid cycle” ?

Answer 19

Because , Citrate “Citric acid” have 3 COOH

Question 20

Substrate level phosphoration

Answer 20

Succinyl - CoA → Succinate

Question 21

Intermediate compunds

Answer 21

Citrate → Oxaloacetate

Question 22

Oxidation of isocitrate by isocitrate dehydrogenase gives ..

Answer 22

2 NADH+H that gives 6 ATP

Question 23

Oxidative decarboxylation a-ketoglutarate to succinyl-
CoA gives …

Answer 23

2 NADHH+ that gives 6 ATP

Question 24

Substrate level phosphorylation from succinyl-CoA gives ..

Answer 24

2 ATP

Question 25

Oxidation of succinate to fumarate gives …

Answer 25

2 FADH2 → 4 ATP

Question 26

Oxidation of malate to oxaloacetate gives …

Answer 26

2 NADHH+ → 6 ATP

Question 27

Importance of Kreb’s Cycle

Answer 27

1. Energy production: one molecule of acetyl COA produces 12 ATP
2. It is amphibolic pathway (both catabolic and anabolic functions)

Catabolic function: it is the common pathway for oxidation of carbohydrates, lipids and proteins

Anabolic functions:
1. CO2 used for gluconeogenesis, fatty acid, urea, nucleotide synthesis, and bicarbonate buffer
2. All intermediates are precursors for gluconeogenesis
3. Non-essential a.a synthesis (α-ketoglutarate)
4. Succinyl CoA is used for Hb synthesis, ketolysis, and detoxification
5. Citrate is a precursor of fatty acid synthesis “Steroids”
6. Oxaloacetate → Aspartic acid

Question 28

CO2 that produced by Krebs cycle used for

Answer 28

gluconeogenesis, fatty acid, urea, nucleotide synthesis, and bicarbonate buffer

Question 29

α-ketoglutarate can produce

Answer 29

Non-essential a.a

Question 30

Succinyl CoA that produced by Krebs cycle used for

Answer 30

Hb synthesis, ketolysis, and detoxification

Question 31

Citrate is a precursor of

Answer 31

fatty acid synthesis “Steroids”

Question 32

Oxaloacetate can convert to

Answer 32

Aspartic acid

Question 33

All Krebs cycle reactions are reversible except

Answer 33

1. Citrate synthase
2. Isocitrate dehydrogenase
3. α-Ketoglutarate dehydrogenase complex

Question 34

Citrate synthase enzyme Activators

Answer 34

ADP

Question 35

Isocitrate dehydrogenase enzyme Activators

Answer 35

ADP , Ca “Realsed in muscles during contraction”

Question 36

α-Ketoglutarate dehydrogenase enzyme Activators

Answer 36

ADP

Question 37

Succinate dehydrogenase enzyme Activators

Answer 37

ADP

Question 38

Citrate synthase enzyme Inhibitors

Answer 38

ATP - NADH+H+
Succinyl COA - Acyl COA

Question 39

Key enzyme in krebs cylce

Answer 39

Citrate synthase enzyme

Question 40

Isocitrate dehydrogenase enzyme Inhibitors

Answer 40

ATP
NADH+H+

Question 41

α-Ketoglutarate dehydrogenase enzyme Inhibitors

Answer 41

ATP - GTP
Succinyl COA - Arsenate

Question 42

Succinate dehydrogenase enzyme Inhibitors

Answer 42

Oxaloacetate
Malonate
Mercury

Question 43

Oxaloacetate source

Answer 43

Carboxylation of pyruvate : Through pyruvate carboxylase enzyme

Oxidation of malate : Through malate dehydrogenase enzyme

Cleavage of citrate : Through cytoplasmic citrate lyase enzyme

Transamination of aspartate : Through AST (GOT)

Question 44

Oxaloacetate fate “Not the one in mitochondria”

Answer 44

Reduction into malate
Synthesis of citrate
Transamination into aspartate “Aspartic A.”
Conversion into phosphoenolpyruvate

Question 45

….. Reaction in Kreb’s cycle adds H2O

Answer 45

Fumarate → Malate (by fumarase)

Question 46

….. Reaction in Kreb’s cycle removes H2O

Answer 46

Succinate → Fumarate (by Dehydrogenase )