Biochem 10

UNIVERSITY Of JORDAN

Faculty OF Medicine

LECfURE NO:

11

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DONE BY: Nrld Haddad

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• In this lecture we ullk about certain inhibilO~t disorders and how metabolites enter the inner mitochondrial membrane. • Energy utilization: As we ean see from lIle figure in the slides that 90-95% of the inhaled oltygen is consumed by the mitochondria. The remaining 0lCYgen (5­ 10%) is used by a group of enzymes called Oxidases including Mono Oxygenases,Di Oxygenases which we will sLUdy later during the course. A large portion of the energy produced is coupled to A TP synthesis.

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Some of the energy dissipates without A1P synthesis. This encrgy is produced in thc form of heat ATP produced can be used for a variety of cellular activities such as: prolein synthesis. sodiumlpotassiwn ATPase and muscle contraction. More cltamplcs are found in the slide. •

Respiratory chain inhibitors: These substances block the electron transport chain. All components of the electron Inll1SJXlrt chain before the block are reduced while components after lIle block are oxidized. -EJWmples on these inhibitors: I) lnhibilors of electron flow:

a) Amytal & Rotenone: They aet on complex I b) Antimycin A: Acts on complex III c) Cyanide. carbon monox..ide and sodiwn azide: They aet on complex IV - Cyanide is a very powerful inhibitor. This makes i! cxtremely da.ngerous and lethal. CylUlide can also bind to haemoglobin. 2) Oligomycin: Binds tu the Fo ponion. It causes the blockage of protons. Phosphorylation slopS and prolOrts will be kept in the intennembrane space.

3) Uncoupl~rs: Chemical uncouplers

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a) 2.4-DNP (Oi Nitro Phenol): it allows proton5 to re enter the inncr mitochondrial membrane. so energy is released in the form of heat and nol being captured as ATP. b) Arsenale: It acts as a substitute for phosphate during ATP synthesis. So instead of binding of phosphate group to ATP, arsenate binds to il. !­

- Arsenate: HAs04

,­ -Arsenite (trivalent) As02: binds IxIth ofthe -SH groups of the co factor lipoic acid. It is considered more toxic. 4) Atraetyloside: It causes the blockage of the ATP/ADP antiponer (il is one type oflranspon proleins found in the inner mitochondrial membrane. it transpons ATP outside the membrane and ADP inside).

• Natural Uncoupling Proteins (UCP): - Uncoupling proteins create a proton leak allowing protons to re enler the mitochondrial matrix which result in the production ofenergy in the form of heat. - These proteins are foWld in the inner membmne of the mitoChondria. • Types or Uncoupling Proteins:

a) UCPI (Thennogenin): Found in brown fat. Brown fat is found in

newly born babies. and animals espedtdly the hibemating..animals. "Production of heat in response to cold". b) UCP2: Found in most cells. c) UCP3: Found in skeletal muscles. d) UCP 4 & UCP5: Found in the brain.

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• Uncoupling proteins nre

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in small amounts in the human adults.

• Aspirin. which is used tor relieving pain and reduction of fever, Clln act as uncoupling proteins under high doses. This explains the high fever whieh accompanies the overdose of aspirin. •

Inherited defects in oxidative phosphorylation: - 13 of the approximately 100 polypeptides required for oxidative

phosphorylation are coded for by milochondrial DNA.

- Defects in oxidative phOSphorylation an: more likely to be as a result of alterations in mitochondrial DNA, since it has a mutation rate 10 times greater than that of nuclear DNA.

• We said above that 13 afme polypeptides are coded by mitochondrial

DNA. They are distributed as the following:

A) One in complex nI.

B) Three in complex IV.

C) Seven in complex L

D) Two in Fo.

• Mitochondrial DNA is maternally inheriled because mitochondrion

from the sperm does not enter the fertilized egg.

- These disorders indude:

1) Mitochondrial myopathies.

2) Leber's heredilary tlptic neuropathy: defect in the NADH

Dehydrogenase polypeptide.

• Transpon systems afthe inner mitochondrial membnmo:: • The outer membrane of lhe mitochondria is highly ptnno:able to many substances.

1) Antipon (most common): 1bey are transpon proteins which exchange 2 molC(u!es of similar charges. Example: ATP/ADP antiport... ATP out· ADP in. 2) Sympon: Co transporting of2 molecules of opposite charges. Example: proton co transponing phosphale & proton co transponing pyruvate. 3) Calcium ion unipon protein: No other ions are involved. calcium ions (positive) move from a positive region to a negative region. (See figure in the slides). • NAD+ mulecules are reduced either in "milOChondrial matrix" or ~cytosol"

Those of which reduced in the cytosol require a special shuttle to get a way inside the mitochondria, because the inner mitochondrial membrnne is irnpenneable to NADH. and no transport protein exists that can direi::tly trunslocate NADH across this membrane.

• There are two alternate shuttles for NADH translocation: A) The Malate.Aspartate Shuttle:

• Mechanism: I) NADR(cytosol) mluees Oxaloacetate (OM) 10 malate.

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2) Malate crosses the inner mitothondrial membrane. and then reoxidized to (OAA). • This step regenerates NADH, and reserves energy. - (OAA) can't cross the mcmbrnne, so it's converted to aspartate. J) Aspartate crosses the inner m~mbrane back to the cytosol.

4) To complete the cycle. aspartate is converted back to (OAA).

B) The Glyceropbosphau: Shuttle:

1) Dihydroxyace1one-p (DHAP) is reduced to glycerol-J-p, using

eytosolic glycerol.3.p dehydrogenase. 2) Glycerol-3-p reaches the inner membrane, then become oxidized

reducing FAD to FADII.

3) (DHAP) goes back to cytosol.

NOTES;

1. In mlllillte--aspartate sbuttle, reserving energy in the form ofNADH.

resuhs in J ATP molecules:

NADH (cystol) + NAD+ ( mll1 riw) ~ NADt (crystal)+­ NADH(matrix)

2. In Gly«rol ]- phosphite ,fl.ttle, FADH2 results in 2 ATP molecules, that's why oxidative phosphorylation generales (36-38) ATP molecules.

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3. When

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remove an amino group from aspartate we get o,>taloacetatc.

4. When we remove an amino group from glutamate we get alpha-keto gluterate. <;<;<;<;<;«««««-:CllECK 1HE DOCTOR"S SlIDt:S»»»»»»»»»>

THE END

Done by Nael baddad

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