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METABOLISME KARBOHIDRAT 21 NOVEMBER 2011

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Page 1: Kuliah 21 Nov

METABOLISME KARBOHIDRAT

21 NOVEMBER 2011

Page 2: Kuliah 21 Nov

TUGAS

1. TULISKAN JUMLAH TOTAL ATP YANG DIHASILKAN PADA PROSES GLIKOLISIS DAN PERSAMAAN TOTAL REAKSI GLIKOLISIS

(DG MENGABAIKAN ION H+)

Page 3: Kuliah 21 Nov

Glycolysis - total pathway, omitting H+: glucose + 2 NAD+ + 2 ADP + 2 Pi 2 pyruvate + 2 NADH + 2 ATP

Jumlah total ATP yang dihasilkan : 2

Kalau ATP dari NADH dihitung

(2x3) + 2 = 8 ATP

Page 4: Kuliah 21 Nov
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2. Jalur glikolisis diregulasi oleh 3 enzim yang mengkatalisis reaksi-reaksi yang yg berjalan spontan, yaitu :

heksokinase, fosfofruktokinase, dan piruvat kinase.

Jelaskan masing-masing regulasinya !

Page 7: Kuliah 21 Nov

Hexokinase is inhibited by product glucose-6-phosphate: by competition at the active site by allosteric interaction at a separate enzyme site.

Cells trap glucose by phosphorylating it, preventing exit on glucose carriers.

Product inhibition of Hexokinase ensures that cells will not continue to accumulate glucose from the blood, if [glucose-6-phosphate] within the cell is sufficient

H O

O H

H

O HH

O H

CH 2O H

H

O H

H H O

O H

H

O HH

O H

CH 2O PO 32

H

O H

H

23

4

5

6

1 1

6

5

4

3 2

A T P A D P

M g 2+

glu co se g lu co se -6 -p h o sp h ate

H ex o k in ase

Page 8: Kuliah 21 Nov

Glucokinase has a high KM for glucose. It is active only at high [glucose].

Glucokinase is not subject to product inhibition by glucose-6-phosphate. Liver will take up & phosphorylate glucose even when liver [glucose-6-phosphate] is high.

H O

O H

H

O HH

O H

CH 2O H

H

O H

H H O

O H

H

O HH

O H

CH 2O PO 32

H

O H

H

23

4

5

6

1 1

6

5

4

3 2

A T P A D P

M g 2+

glu co se g lu co se -6 -p h osp h ate

H ex ok in ase

Glucokinase is a variant of Hexokinase found in liver.

Page 9: Kuliah 21 Nov

Phosphofructokinase is usually the rate-limiting step of the Glycolysis pathway.

Phosphofructokinase is allosterically inhibited by ATP. At low concentration, the substrate ATP binds only at the

active site.

At high concentration, ATP binds also at a low-affinity regulatory site, promoting the tense conformation.

CH 2 O PO 32

O H

CH 2 O H

H

O H H

H HO

O6

5

4 3

2

1 CH 2 O PO 32

O H

CH 2 O PO 32

H

O H H

H HO

O6

5

4 3

2

1

A T P A D P

M g 2 +

f r u c t o s e - 6 - p h o s p h a t e f r u c t o s e - 1 , 6 - b i s p h o s p h a t e

P h o s p h o f r u c t o k i n a s e

Page 10: Kuliah 21 Nov

Inhibition of Phosphofructokinase when [ATP] is high prevents breakdown of glucose in a pathway whose main role is to make ATP.

It is more useful to the cell to store glucose as glycogen when ATP is plentiful.

Page 11: Kuliah 21 Nov

C

C

CH 3

O O

O2

3

1A D P A T PC

C

CH 2

O O

O PO 32

2

3

1

p h o s p h o e n o l p y r u v a t e p y r u v a t e

P y r u v a t e K i n a s e

Pyruvate Kinase, the last step Glycolysis, is controlled in liver partly by modulation of the amount of enzyme.

Page 12: Kuliah 21 Nov

High [glucose] within liver cells causes a transcription factor carbohydrate responsive element binding protein (ChREBP) to be transferred into the nucleus, where it activates transcription of the gene for Pyruvate Kinase.

This facilitates converting excess glucose to pyruvate, which is metabolized to acetyl-CoA, the main precursor for synthesis of fatty acids, for long term energy storage.

Page 13: Kuliah 21 Nov

13

Complete the following statements:A. When 1 acetyl CoA enters the

citric acid cycle, the C atoms produce ____CO2.

B. In 1 cycle, a total of ____NADH are produced.

C. In 1 cycle, a total of ____FADH2 are produced.

KREBS CYCLE TRIVIA QUIZ

Page 14: Kuliah 21 Nov

14

Complete the following statements:A. When 1 acetyl CoA enters the

citric acid cycle, the C atoms produce 2 CO2.

B. In 1 cycle, a total of 3 NADH are produced.

C. In 1 cycle, a total of 1 FADH2 are produced.

KREBS CYCLE TRIVIA QUIZ

Page 15: Kuliah 21 Nov

• 3. Jelaskan fungsi-fungsi utama (peranan) dari siklus krebs!

• (minimal 2)

Page 16: Kuliah 21 Nov

The function of TCA cycle :

• 1. Oxidized of Acetyl CoA ATP ( 1 mol Acetyl CoA 12 mol

ATP )• 2. The citric acid cycle is AMPHIBOLIC : - it can oxidized to yield ATP 3. It also has a central role in

gluconeogenesis, lipogenesis, and interconversion of amino acids.

Page 17: Kuliah 21 Nov

4. The final common pathway for the aerobic oxidation of carbohydrate, lipid and protein

Page 18: Kuliah 21 Nov

• The citric acid cycle is the final common pathway for the oxidation of carbohydrate, lipid, and protein because glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA

Page 19: Kuliah 21 Nov

• ANGGOTA TCA CYCLE BERSIFAT AMFIBOLIK• Dapat dioksidasi lebih lanjut menjadi energi * katabolisme asam amino anggota tca cycle energi * oksidasi beta asam lemak asetil KoA anggota siklus krebs energi * oksidasi glukosa piruvat asetil KoA anggota siklus krebs energi• Dapat disintesis menjadi senyawa lain, misalnya men- jadi : * glukosa (melalui glukoneogenesis) * asam amino tertentu * asam lemak (lipogenesis)

Page 20: Kuliah 21 Nov

• Tugas no 4Jelaskan inhibitor-inhibitor pada siklus krebs ? (minimal 2)

Page 21: Kuliah 21 Nov

INHIBITOR SIKLUS ASAM SITRAT• Fluoroasetat : * Dgn KoA-SH membentuk fluoroasetil-KoA * Fluoroasetil-KoA berkondensasi dgn

oksaloasetat membentuk fluorositrat ( dikatalisis oleh sitrat sintase)

* Fluorositrat menghambat enzim akonitase terjadi akumulasi sitrat

* Fluoroasetat didapatkan misalnya dari pestisida

• Malonat : menghambat enzim suksinat dehidrogenase

• Arsenit : menghambat enzim α-ketoglutarat dehidrogenase kompleks

Page 22: Kuliah 21 Nov

VITAMINS PLAY KEY ROLES IN KREBS CYCLE

• Four of the B vitamins are essential in the citric acid cycle

(1) riboflavin, (VIT B2) in the form of flavin adenine dinucleotide (FAD), a cofactor for succinate dehydrogenase

(2)niacin, in the form of nicotinamide adenine dinucleotide (NAD), the electron acceptor for isocitrate dehydrogenase,-ketoglutarate dehydrogenase, and malate dehydrogenase

Page 23: Kuliah 21 Nov

3. thiamin (vitamin B1), as thiamin diphosphate, the coenzyme for decarboxylation in the -ketoglutarate dehydrogenase reaction

4 pantothenic acid, as part of coenzyme A, the cofactor attached to "active" carboxylic acid residues such as acetyl-CoA and succinyl-CoA.

Page 24: Kuliah 21 Nov

VITAMIN KOENSIM

B1 (Thiamine) TPP = Thiamine Pyrophosphate

B2 (Riboflavin) FAD = Flavin Adenine Dinucleotide

B3(Pantothenate) CoA = Coenzyme-A

B6(Pyridoxine) PLP = Pyridoxal Phosphate

B12 (Cobalamine) 5- deoxy adenocyl cobalamine

Niacin=Nicotinat NAD⁺ = Niacin Adenine Dinucleotide

Folic Acid Tetrahydrofolate

Biotin Biotin

Page 25: Kuliah 21 Nov

Citric Acid Cycle

Page 26: Kuliah 21 Nov

26

Regulation of Citric Acid Cycle

• Operates when ATP is needed• High levels of ATP and/or NADH inhibit citrate synthetase (first step in cycle)

• High levels of ADP and NAD+ activate isocitrate dehydrogenase

• Low levels of ATP or high levels of acetyl CoA speed up the cycle to give energy

Page 27: Kuliah 21 Nov

Summary Krebs cycle reactions

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FAD FADH2

Page 31: Kuliah 21 Nov

Cellular respiration

Page 32: Kuliah 21 Nov

32

• The final stage of aerobic respiration occurs in the electron systems embedded in the inner membrane of the mitochondrion.

• Oxidation phosphorylation (which takes place on the cristae of the mitochondria) processes the H+ ions and electrons to generate high yields of ATP.

• NADH and FADH2 give up their electrons to transport (enzyme) systems embedded in the mitochondrial inner membrane.

Page 33: Kuliah 21 Nov

Diagram of the Process

Occurs in

Cytoplasm Occurs

in Matrix

Occurs across Cristae

Page 34: Kuliah 21 Nov

Review of Mitochondria Structure

• SmoothSmooth outer outer MembraneMembrane

• FoldedFolded inner inner membrane called membrane called CristaeCristae

• Space inside Space inside cristae called the cristae called the MatrixMatrix

Page 35: Kuliah 21 Nov

definitions

• Electron Transport: Electrons carried by reduced coenzymes (NADH or FADH2) are passed sequentially through a chain of proteins and coenzymes (so called electron transport chain) to O2 .

• Oxidative Phosphorylation: Coupling e- Transport (Oxidation) and ATP synthesis (Phosphorylation) .

Page 36: Kuliah 21 Nov

Organization of Chain NADH dehydrogenase or NADH-Q

oxidoreductase (complex I) Succinate-Q reductase (complex II) Coenzyme Q (CoQ) (also called ubiquinone) Cytochrome c oxidase (complex III) Cytochrome c (Cyt c) Cytochrome c oxidase (complex IV)

Succinate-Q reductase (Complex II), incontrast with the other complexes, does not pump protons.

Page 37: Kuliah 21 Nov

• Each complex accepts and donates electrons to a relatively mobile electron carriers.

• The electrons ultimately combine with oxygen and protons to form water.

• It requires oxygen that is why it is also called respiratory chain.

• It accounts for the greatest portion of the body's use of oxygen.

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Electron Transport Chain

Page 40: Kuliah 21 Nov

Coenzymes which take part are:1. NAD2. NADP3. FAD4. FMN5. Coenzyme Q (CoQ)6. Fe-S proteins

Page 41: Kuliah 21 Nov

Coenzyme Q• It is also called ubiquinone. • They contain isoprene units in their side

chains.

• Can accept H atoms from both FMNH2

and FADH2.

• the only electron carrier not bound to a protein.

• it can accept/donate 1 or 2 e-. • Q can mediate e- transfer between 2 e- that

transfer and 1 e- carriers

Page 42: Kuliah 21 Nov

O

O

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3

O H

O H

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3

e + 2 H +

c o e n zy m e Q

c o e n zy m e Q H 2

O

O

C H 3 O

CH 3C H 3 O

(CH 2 CH C CH 2 )n H

CH 3e

c o e n zy m e Q •

When bound to special sites in respiratory complexes, CoQ can accept 1 e- to form a semiquinone radical (Q•-).

Page 43: Kuliah 21 Nov

Iron-sulfur centers (Fe-S) are prosthetic groups containing 1-4 iron atoms

Iron-sulfur centers transfer only one electron, even if they contain two or more iron atoms.

E.g., a 4-Fe center might cycle between redox states:

Fe+++3, Fe++

1 (oxidized) + 1 e Fe+++2, Fe++

2

(reduced)

Iron-sulfur Centers (clusters)

Page 44: Kuliah 21 Nov

FeFe

S

S

S

Fe

Fe

S

S

S

SS

Cys

Cys

Cys

Cys

S

Fe

S

Fe

S

S

S

S

Cys

CysCys

Cys

Iron-Sulfur Centers

Page 45: Kuliah 21 Nov

Complex I. Steps

1. The initial step is the binding of the NADH and transfer of 2 electrons to the FMN (Flavin mononucleotide) to give the reduced form of FMNH2

2. Electrons are then transferred from FMNH2 to a series of iron-sulfur clusters (Fe-S cluster), the second type of prosthetic group in complex I.3. Electrons in the iron-sulfur clusters of NADH-Q oxidoreductase are shuttled to coenzyme Q.

Page 46: Kuliah 21 Nov

The initial electron transfers are: NADH + H+ + FMN NAD+ + FMNH2

FMNH2 + (Fe-S)ox FMNH· + (Fe-S)red + H+

After Fe-S is reoxidized by transfer of the electron to the next iron-sulfur center in the pathway: FMNH· + (Fe-S)ox FMN + (Fe-S)red + H+

Electrons pass through a series of iron-sulfur centers, and are eventually transferred to coenzyme Q.

Coenzyme Q accepts 2 e and picks up 2 H+ to yield the fully reduced QH2.

Page 47: Kuliah 21 Nov

• The flow of two electrons from NADH to coenzyme Q through NADH-Q oxidoreductase leads to the pumping of four hydrogen ions out of the matrix of the mitochondrion.

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Complex II

1. Complex II accepts electrons from succinate formed during the TCA cycle.

2. Electrons flow from succinate to FAD (flavin-adenine dinucleotide) coenzyme, through an iron-sulfur protein and a cytochrome b550 protein (the number refers to the wavelength where the protein absorbs), and to coenzyme Q.

Page 51: Kuliah 21 Nov

• No protons are translocated by Complex II. • Coenzyme Q is not bound to a protein; instead it

is a mobile electron carrier and can float within the inner membrane, where it can transfer electrons from Complex I and Complex II to Complex III.

• Coenzyme Q can accept electrons from both FMNH₂ (produced by complex I), and from FADH₂ (complex II) which is produced by succinate dehydrogenase and acyl CoA dehydrogenase.

Page 52: Kuliah 21 Nov

Complex III

•Complex III accepts electrons from reduced coenzyme Q, moves them within the complex through two cytochromes b, an iron-sulfur protein, and cytochrome c1.

•Electron flow through Complex II transfers proton(s) through the membrane into the intermembrane space.

Page 53: Kuliah 21 Nov

• Cytochrome c transfers its electrons to the final electron transport component, Complex IV, or cytochrome oxidase.

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Cytochromes are electron carriers containing hemes .

Hemes in the 3 classes of cytochrome (a, b, c) differ in substituents on the porphyrin ring.

Some cytochromes(b,c1,a,a3) are part of large integral membrane protein complexes.

Cytochrome c is a small, water-soluble protein.

Cytochromes

Page 56: Kuliah 21 Nov
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The heme iron can undergo 1 e- transition between ferric and ferrous states: Fe3+ + e- Fe2+

Copper ions besides two heme A groups (a and a3) act as electron carriers in Cyta,a3 Cu2++e- Cu+

Heme is a prosthetic group of cytochromes. Heme contains an iron atom in a porphyrin ring system.

Page 58: Kuliah 21 Nov

Complex IV(cytochrome c oxidase)

• Complex IV transfers electrons through a copper-containing protein, cytochrome a, and cytochrome a3, and finally to molecular oxygen.

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•Cytochrome a+a₃ also called Cytochrome oxidase is the only electron carrier that has got a free ligand i.e. bound copper that can react directly with molecular oxygen and produce water.

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Composition of Respiratory Chain Complexes

Complex NameNo. of Proteins

Prosthetic Groups

Complex I NADH Dehydrogenase

46 FMN, 9 Fe-S cntrs.

Complex II Succinate-CoQ Reductase

5 FAD, cyt b560, 3 Fe-S cntrs.

Complex III CoQ-cyt c Reductase

11 cyt bH, cyt bL, cyt c1, Fe-SRieske

Complex IV Cytochrome Oxidase

13 cyt a, cyt a3, CuA, CuB

Page 63: Kuliah 21 Nov

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

NAD+ or FAD

There are 2 sites of entry for electrons into the electron transport chain:

Both are coenzymes for dehydrogenase enzymes

The transfer of electrons is not directly to oxygen but through coenzymes

Page 64: Kuliah 21 Nov

NAD+

FMN

FeS

ubiquinoneFAD FeS

Cyt b

FeS Cyt c1 Cyt c Cyt a Cyt a3

1/2 O2

ubiquinone

I

II

III IV

Mitochondrial Complexes

NADH Dehydrogenase

Succinate dehydrogenase

CoQ-cyt c Reductase

Cytochrome Oxidase

Page 65: Kuliah 21 Nov

H+ Transport Complex I, III, IV drive H+ transport from

matrix to the cytosol When e- flow through, which creates proton gradient(electrochemical potential) across the inner membrane

Complex I and Complex IV : The mechanism of H+ transport is still not known.

The mechanism of H+ transport in Complex III is Q cycle.

Page 66: Kuliah 21 Nov

4H+ are pumped per 2e passing through complex III.

The H+/eratio is less certain for the other complexes: probably 4H+/2e for complex I; 2H+/2e for complex IV.

Matrix

H+ + NADH NAD+

+ 2H+ 2H+ + ½ O2 H2O

2 e – –

I Q III IV

+ +

4H+ 4H+ 2H+ Intermembrane Space

cyt c

Page 67: Kuliah 21 Nov

2 H+

Q Q QH2 QH2

cyt bH cyt bL QH2

Q Q Fe-S cyt c1

2 H+ cyt c

matrix

Complex III

e

intermembrane space

.

. e

• Q Cycle :The mechanism of H+ transport in Complex III

Page 68: Kuliah 21 Nov

1.Electrons are transported along the inner mitochondrial membrane, through a series of electron carriers 2.Protons (indicated by + charge) are translocated across the membrane, from the matrix to the intermembrane space 3.Oxygen is the terminal electron acceptor, combining with electrons and H+ ions to produce water 4. As NADH delivers more H+ and electrons into the ETS, the proton gradient increases, with H+ building up outside the inner mitochondrial membrane, and OH- inside the membrane.

Page 69: Kuliah 21 Nov

The overall pathway for electron transport is therefore:

Page 70: Kuliah 21 Nov

•How is the oxidation of NADH coupled to the phosphorylation of ADP?