Krebs cycle or Citric acid cycle

 

In this blog we will study about 2nd step of aerobic respiration .In last blog we have studied about the glycolysis in  which glucose or 6 Carbon hexose sugar was converted in to 2 molecules of pyruvate(3 carbon).

Before kreb'cycle we will study about linked reaction in which pyruvate change into product which enter into kreb's cycle and further respiration occurs.

 LINKED REACTION:(CONVERSION OF PYRUVATE INTO ACETYL COENZYME A)

    Pyruvate does not enter kreb's cycle directly before entering kreb's cycle it is first oxidized into a carbon dioxide and 2 carbon molecule Acetyl group.

This acetyl group further attaches to coenzyme A forming acetyl coenzyme A.

Coenzyme A is a nucleotide and a portion of B vitamins.

During linked reaction hydrogen is removed from pyruvate which is taken by NAD and reduced into NADH2 and acetyl co A enter into kreb's cycle for further respiration process.

This reaction is called linked reaction because it links Glycolysis (cytoplasm) with kreb's cycle (inter membrane space of mitochondria).

OVERALL REACTION:

 Pyruvic acid               =   Acetyl group + CO2 + 2H

Acetyl group + Co A = Acetyl Co A

NAD + 2H          =  NADH2

Further oxidation of acetyl Co A occurs in cyclic manner this cyclic manner is called Kreb's cycle.

STEP BY STEP KREB'S CYCLE:

This cycle is also called as citric acid cycle because first product form in it is 6 carbon compound called as citric acid cycle.

This cycle occurs in inter membrane space of mitochondria.

This cycle was discovered by British scientist Sir Hans kreb.

In overall kreb's cycle acetyl group completely oxidized into two molecules of carbon dioxide and hydrogen are removed and NAD and FAD reduced into NADH2 and FADH2.

1-In first step of kreb's cycle Acetyl Co A combines with pre existing oxaloacetate(4 Carbon) in the presence of water molecule to form citric acid (6 carbon) having three carboxylic acid group and CO A is now free and ready to react with 2nd acetyl group.

       Acetyl co A + oxaloacetate = Citrate + Co A 

2-In 2nd step Citrate is isomerize into branch form called as ISOCITRATE.

3-In 3rd step Isocitrate is oxidized to carbon dioxide and hydrogen is removed which added to NAD and reduced into NADH and isocitrate changed into 5 Carbon compound KETOGLUTARATE.

4-In 4th step KETOGLUTARATE (5 carbon) also oxidized into carbon dioxide (2nd CO2 produed ) and hydrogen added to NAD nad reduced into NADH and ketoglutarate and changed into 4 carbon compound SUCCINYL CO A.

5-In fifth step succinyl co A is converted to succinate acid and co A is released.

6- Succinate acid oxidized also but here some energy released during oxidation which used in generation of ATP this is called substrate level phosphorylation.(discussed in detail in previous blog).

Succinate acid oxidized into fumurate(4 Carbon) and coenzyme FAD is reduced into FADH During reaction .

7-Fumurate further converted into MALATE (4 CARBON).

8-In last step  malate oxidized to oxaloacetate and NAD is reduced into NADH .

PRODUCTS OF KREB'S CYCLE:

1 ATP produced through substrate level phosphorylation.

Kreb's cycle occurs two times for one pyruvate molecule.

3 NADH2 AND 1 FADH2 during each kreb's cycle.

6 CO2 are released.

IMPORTANT MCQS IN KREB'S CYCLE:

1-The reaction in which pyruvate oxidized into acetyl group is called as:

Answer: LINKED REACTION

2-Acetyl group is _Carbon molecule:

Answer: 2 CARBON

3-_CO2 produced in kreb's cycle:

Answer: 6

4-1 Pyruvate produce _ATP:

Answer: 15 

5-1 Acetyl group produces _ATP:

Answer: 12 ATP (11 Oxidative level and 1 Substrate level)

6-Pyruvic acid is _in aerobic respiration:

Answer: OXIDIZED

7-Pyruvic acid is _in anaerobic respiration:

Answer: REDUCED

8-When succinate acid oxidized into fumurate which coenzyme reduced:

Answer: FAD (FLAVIN ADENINE DINUCLEOTIDE)

9-Citric acid molecule has _carboxylic acid:

Answer: 3 

10-The enzymes for kreb's cycle present in:

Answer: MITOCHONDRIAL MATRIX EXCEPT SUCCINATE DEHYROGENASE

IF YOU LIKE THIS BLOG FOLLOW ME FOR MORE.........