Molecular Cell BiologyFifth Edition

Chapter 8:Cellular Energetics

Copyright © 2004 by W. H. Freeman & Company

Harvey Lodish • Arnold Berk • Paul Matsudaira • Chris A. Kaiser • Monty Krieger • Matthew P. Scott •

Lawrence Zipursky • James Darnell

How cell generate ATP?

ATP :

1. synthesis of protein and nucleic acid

2. transport molecules against concentration gradient

3. movement of cilia

Chemiosmosis

ATP generation for bacteria, mitochondria, and

chloroplast

Occur only in sealed membrane

Stepwise movement of electrons for higher energy

state to low energy state through electron carrier

Proton motive force:

Supply energy for transporting small molecule across membrane and against its concentration gradient

ATP synthase

Endocytosis of bacteria by eukaryotic cells forms mitochondria and chloroplast

Bact plasma membrane=

matrix phase of inner

mitochondrial membrane=

stroma face of thylakoid

membrane

Aerobic respiration and photosynthesis both occur in plasma membrane

Eukaryotic cell

Plant

Endocytosis of bacteria by eukaryotic cells

Oxidation of glucose and fatty acid to CO2

ATP formed by substrate level phosphorylation

No-proton motive force involved

Transfer of 4 H+ and 4 e to NAD+

The expanded surface of cristae :

Different in organs

Aerobic oxidation of fatty acid and pyruvate in mitochondria

Oxidation of pyruvate and fatty acid to CO2 and

coupled reduction of NAD+ to NADH and FADH2

Electron transfer from NADH and FADH2 to O2

Harness energy stored in electrochemical gradient

for ATP synthesis by F0F1 complex

TCA cycle

Oxidation of of acetyl coA

No O2 involved in the oxidation

energy stored in the reduced form of NADH and FADH2

Mitochondria membrane is impermeable to NADH

How does NADH enter mitochondria ?

----- malate aspartate shuttle

1. malate/-ketoglutarate antiport

2. glutamate/aspartate antiport

NADH cytosol + NAD+ NAD+ cytosol+ NADHmatrix

2 carbon removed

Peroxisome

single membrane

oxidize long chain fatty acid

generate no ATP

electron from FADH2 produced during

oxidation of FA was transferred O2 and generate H2O2\

NADH is exporeted to cytosol and reoxidize

No citric acid cycle---acetyl coA genetated was send to

cytosol for cholesterol synthesis

Allosteric control of glucose metabolism

1. Hexoinase: inhibited by glucose 6-phosphate

2. Pyruvate kinase: inhibited by ATP

3. Phosphofructokinase :

rate limiting enzyme of glycolic pathway

inhibited by ATP and citrate

stimulated by insulin

activated by fructose 2.6. biphosphate( feed

forward control)

NADH+H++1/2O2 NAD++H2O G=-52.6Kcal/mol

FADH2+H++1/2O2 NAD++H2O G=-43.4Kcal/mol

Total G for 1 glucose molecule CO2 = -613kcal/mol

( 10 NADH +2 FADH2)

Release of respiratory free energy from electron transfer and transfer of energy in proton motive force

Higher redox potential

Different prothetic group

Lower redox potential

Electron flow orders:

b→c1 →c →a →a3

Electron transfer by prothetic protein in electron transport chain

Fe3++e- Fe2+

heme, iron containning prothetic group

Iron sulfur cluster, non-heme , iron containning prothetic group

Electron transfer from NADH or FADH2 to O2 is coupled to pronton transport across the mitochondria membrane

Releasing of protons to the solution

10 protons/pair of electron from NADH to O2

2H+/ e-1H+/ e-2H+/ / e-

CoQ and Three electron transport complex pump protons out of mitochondria matrix

Isolation of individual complex

↓pack by liposome

↓add e- donor and

acceptor

↓ monitoring pH

change

pathway of electron flow

Cytochrome C oxidase: 2 protons/one e- transfer

Q cycle: 2 protons/one e- transfer

Binding of CoQ to Qo site

↓ CoQ H2 bind to Qi

↓ releasing of 2H+ to

intermembrane space

Binding of CoQ to Qo site

↓ CoQ H2 bind to Qi

↓ releasing of 2H+ to intermembrane space

Q cycle: 2 protons/one e- transfer

Synthesis of ATP by FoF1 depends on a pH gradient across membrane

Model of the structure and function of ATP synthase in the FoF1 complex) in the bacterial plasma membrane

hexamer

F0

a1b2c10

Common in bacterial and yeast

12C subunit in donut shape

F1

water soluble

33

Required for ATP synthesis but not for electron transport

The binding change mechanism of ATP synthesis from ADP and Pi by the F0 F1 complex

O: bind ATP poorly, and ADP+Pi weakly

L: bind ADP+Pi more strongly

T: bind ADP+Pi tightly

O: bind ATP poorly, and ADP+Pi weakly

L: bind ADP+Pi more strongly

T: bind ADP+Pi tightly

O: bind ATP poorly, and ADP+Pi weakly

L: bind ADP+Pi more strongly

T: bind ADP+Pi tightly

The phosphate and ATP/ADP transport system in the inner mitochondrial membrane

Powered by pronton motive force for the exchange of ATP formed and ADP+pi

Respiratory control

Rate of Motochondria oxidation normally depends on ATP

level

Oxidation of FADH2 and NADH occur ed only there is a source

of ADP and Pi

Coupling of NADH and FADH2 oxidation and proton transport

across inner mitochondrial membrane and ATP synthesis is

important in maintaining the membrane electro potential

DNP: uncoupler of mitochondria membrane potential

shuttle proton from intermembrane space to matrix and

abolish ATP synthesis

Thermogenin

A natural uncoupler in brown fat mitochondrial membrane

Oxidize NADH and convert the energy to heat

Slow in proton transport

a.a. sequence similar to ATP/ADP anti-port

Photosynthesis

6CO2 + 6H2O → 6O2+ C6H12O6

Cellular structure of leaf and chloroplast

Four stages in photosynthesis

1. Absorption of light

light absorpthin by chlorophyll on thylakoid membrane

2 H2O → O2 + 4H++ 4e- transfer of e- to quinone Q

2. Electron transport and generation of a proton motive force

2 H2O+ 2NADP+ light 2H+ + 2NADPH + O2

3. Synthesis of ATP

4. Carbon fixation

synthesis of polymer of 6-C sugars from CO2 and H2O

Phtosystem

1. Light reaction center

chlorophyll a : function both as light reaction and harvesting

chlorophyll b : seen in vascular plant

carotenoid : seen in plant and bacteria

2. Light harvesting complex( LHCs)

Light harvesting complex( LHCs)

Initiate photoelectric transport

Genomic arrangement for maximun light absorbance

Three dimensional structure of photosynthetic reaction center from purple bacteria

LM

H

Electron acceptor

Reaction center

Cyclic electron flow in the single photosystem of purple bacteria

H+ high

H+ low

Linear electron flow in plants, requires both chliroplast photosystems PSI and PSII

→Combination of different absorbance of light source enhances the rate

of photosynthesis

Splitting of H2O due to lower

reduction energy than p680, replenish

electron in p680

No splitting of H2O

Electron flow and O2 evolution in chloroplast PSIII

Splitting of H2O→O2

A single PSII absorbs a photon and transfers electron four times to one O2

Unbalance excitation of two photosystem

Dissociation of PSII from LHCII

Support cyclic electron flow and ATP synthesis

CO2 fixation in organic compound

Light and Rubisco activase stimulate CO2 fixation

Thioredoxin in Dark Reduced thioredoxin activate calvin cycle enzymes

CO2 fixation and photorespiration

RUBISCO activated in higher CO2 and Mg+2

Leaf anatomy of C4 plant

Assimilate CO2 into 4C molecules at low ambient CO2 and deliver to the interior bundle sheath