etc and the kreb cycle 2

8/3/2019 Etc and the Kreb Cycle 2

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The Electron Transport Chain



NAD FMN

FAD

H + H+ H2

H2

CoQFe

+2FeFe

+2 +2

H2

Cyto b Cyto c

COMPLEX I

COMPLEX II

COMPLEX

III

COMPLEX

IVCOMPLEX

V

Cyto a + a3

+3 +3+3 +3 +3

2H+ + 2e -O + H2O

O

ETC ends here, whenhydrogen finally combines

with oxygen to form water

F r e e

E n e r g y

When free energy drops, it means the rxn

provides adequate energy for work: in this

case, pumping of H+

from the matrix to theintermembrane space



Chemiosmotic Theory



INTERMEMBRANE SPACEINTERMEMBRANE SPACE

M A T R I XM A T R I X

H+

H+ H+ H+

H+

H+

H+H+

H+

H+

H+

H+H+H+

H+

ADP Pi+ ATP

LESS ACIDIC

MORE ACIDIC

LOWER

POTENTIAL

ENERGY

HIGHER

POTENTIALENERGY

MORE

POSITIVE

LESS

POSITIVE

H+

POTENTIAL

DIFFERENCE

(VOLTAGE)

Releases

energy

I III IV



Oxidative Phosphorylation



The Kreb Cycle



General Info

Also called Citric Acid Cycle or Tricarboxylic acid(TCA) cycle

Occurs inside the matrix of mitochondria

Uses Acetyl CoA as its raw material 1 Acetyl CoA is used up per cycle.

Provides 4 pairs of hydrogens, 3 of which arepicked up by the NAD and 1 by the F AD

Gives off 2 molecules of CO2 per molecule of Acetyl CoA (or per cycle)

Produces 1 GTP per cycle, which is convertibleto ATP



FUNCTIONSFUNCTIONS

Produces most of theCO2

Source of pairs of Hwhich drive the ETC

Means by w/c excessenergy is available for fatty acid biosynthesis

Provides importantprecursors needed for biosynthesis of essentialbiomolecules

Some of its componentsprovide direct or indirectcontrol of other enzymes.



SUMMARYSUMMARY

2-carbon molecule (acetyl CoA) attaches to apreexisting 4-carbon molecule (Oxaloacetate) toform a 6-carbon compound (citrate)

Then, one by one, 2 carbons will leave thestructure consecutively as CO2

From 6 to 5 to 4-carbon remnant molecule.

The 4-carbon remnant molecule will be

converted back to oxaloacetate The oxaloacetate is again ready to accept a new

acetyl CoA for another cycle.



Carbohydrates

Glucose

pyruvate

Lipids

Fatty acid

Protein

Amino acid

glycolysis Beta-

oxidation

Catabolism of

amino acid

digestion digestion digestion

1

3

2

4

5

6

7

8

9This is a

³bridge¶

reaction

between

glycolysisand the Kreb

cycle



OX ALO ACETATE

C

COO -

O

C

- OOC

H

H

Acetyl CoA attaches here. The reaction involved

is the typical nucleophilic addition reaction of

carbonyl group

- Preexisting inside the matrix



The Individual Reaction of the

Kreb Cycle



Oxidative decarboxylation of Pyruvate

Occurs inside the matrix

Bridge between glycolysis and the Kreb cycle

Provides 1 pair of H to the ETC via the NAD

C

C

C

H

H H

O

O- O

C

C

H

H H

OCoAS

CoASH NADNADH CO2

++ +

+

O f ETC

Undergoes

decarboxylation

Undergoes

oxidation

HO

pyruvate

Acetyl CoA

This product, w/c is now

in the matrix, needs a

preexisting oxaloacetateto entre the kreb cycle



C

C

C

CO

O

O- O

HH

-

CC

O

H

H

CC

O

H

H

H

CoAS

O

CoAS-O

citrate

Synthesis of Citrate R egulates the Kreb cycle

Citrate inhibits phosphofructokinase, the ratesetting enzyme for glycolysis

Citrate activates acetyl CoA carboxylase, therate-limiting step for fatty acid synthesis

Acetyl CoA

Oxaloacetate

H



Isomerization of

CitrateC

C

CC

O

O- O

HH

- O

C

C

O -

O

H

OH

H

CitrateIsocitrate

OH

H

Acetyl CoA

component

Oxaloacetate

component



C

C

C

O- O

HH

C

C

O -

O

H

O

C

O

- OHH isocitrate

A-ketoglutarate

H

Oxidation and decarboxylation of isocitrate

Another rate-limiting

step

1st

decarboxylation

One pair of H

w/c is swiftlyhanded to the

NAD of the

ETC



H

C

C

C

O- O

HH

C

H

O

C

O O -

A- ketoglutarateSuccinyl-CoA

Oxidative decarboxylation of a-

Ketoglutarate

CoAS H

CoAS

2nd

decarboxylation

Another pair of

H given to theNAD of ETC

Succinyl CoA is also

formed from fatty

acids with odd # of

carbons



H

C

C

C

O- O

HH

C

H

OCoAS- O

Succinyl CoASuccinate

Cleavage of

Succinyl CoA

Succinyl CoA is

used in

biosynthesis of

Heme

This r xn producesGTP which is

convertible to ATP

This type of ATP production

w/out using the ETC is called

substrate level phosphorylation



Oxidation of Succinate

- O

C

C

C

O- O

H

C

H

O

H

HSuccinateFumarate

Another pair of H is

produced here, but

this time it is theF ADin the ETC accepts

the pair



- O

C

C

C

O- O

H

C

H

O

Hydration of Fumarate

HOH

FumarateL-Malate

OH

H



Oxidation of L-Malate

O

H

- O

C

C

C

O- O

H

CO

HH

L-Malate

Oxaloacetate

The last pair of H

produced by the

cycle

The pair of H is

accepted by the

NAD of ETC

The cycle returns to

oxaloacetate



ATP produced Per Cycle Note that each cycle uses one Acetyl CoA

Total # of Pairs of

Hydrogen produced= 4 pairs

# of pairs of H received

by the NAD

3 pairs

# of pairs of H received

by the F AD

1 pair

X

Each pair

can produce

3 ATP¶s =

2

ATP¶s

Each pair can

produce 2

ATP¶s

9

ATP¶s

X

=

= =

= = # of GTP produced 1 GTPEach GTP Can

be converted to

1 ATP

1 ATP

X

Oxidative

phosphorylation

Substrate levelphosphorylation

Total 12 ATP¶s per cycle

etc and the kreb cycle 2

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