General Biochemistry 2- Lecture 7 (oxidative phosphorylation, mitochondria)

LECTURE 7: OXIDATIVE PHOSPHORYLATION, MITOCHONDRIA

A. Oxidation of glucose: glucose + 6 oxygen à 6 CO₂ + 6 water; (ΔG=-2823 kJ/mol=-680 kcal/mol)

1.1st half: glucose + 6waterà 6 CO₂ + 24 H⁺ + 24e;

-12 e pairs -from glycolysis and tca cycle transferred to 10 NAD⁺ and 2 FAD

2.2nd half: 24 H⁺ + 24 e + 6 oxygen à 12 water

-oxidative phosphorylation- process of 2^nd half, makes ATP

3. substrate level phosphorylation- unrelated to mitochondrial OP, part of glycolysis makes ATP from ADP; substrate level atp synthases do this.

-(1,3bisPGa)à3Pga+ATPà2PGaàPEP+H₂OàPyruvate+ATP; kinase, mutase, enolase, kinase.

B.Oxidative phosphorylation- atp is made as e- are transferred from NADH/FADH2 to O2 by series of e- carriers (over 10 redox centers in 4 enzyme complexes)

-respiratory assemblies- takes place in inner membrane of mitochondria

-ratio of NADH/FADH₂- oxidation of NADH makes 3 ATP, oxidation of FADH2 makes 2 ATP.

-H⁺ gradient- coupled to pumping H+ out of mito matrix across inner membrane; ATP IS MADE WHEN H⁺ FLOWS BACK IN.

1. Mitochondrion-site of euk oxidative metabolism

-1948: Eugene Kennedy and Albert Lehniger learned that redox proteins in mitochondria (pyruvate dehydrogenase, TCA enzymes, FA oxidation enzymes, and enzymes in redox proteins for ET and OP)

-ellipsoid- (1 um long, .5 um wide), change size/shape; 1 cell=2k mitochondria

-volume- takes up lots of space (liver cells=20% of volume, heart muscle=more than 50%)

2.Outer Membrane- smooth, porous

-porins that allow medium-sized molecules to go through (<10kda p="p">

3.Inner Membrane- cristae(inward folds); contains 75% proteins.;

-freely permeable only to oxygen, CO2, and water. Can create and maintain ionic gradient w inner membrane.

4..Cristae-compartments made by folds in inner membrane. Vary in number/structure

-surface area- increases inner membrane SA in relation to mitochondrial volume

-blowfly flight muscle mito=400m² of inner membrane surface/g of mito protein

5.Matrix-space inside inner membrane; gel like, contains 50% of proteins

-has DNA, RNA, ribosomes

-dramatically changes volume and organization during changes in resp activity.

C. Transporting NADH into mitochondria- NADH molecules made by glycolysis are in cytosol (most NADH made by TCA cycle in mitochondria)

-mito inner membrane permeability- can’t transport NADH

-needs shuttle systems for transporting reducing agents of cystol nadh into mito

1.malate-aspartate shuttle- 1 cystol NADH à 1 mitochondria NADH à 3 ATP.

-in reverse: cystol OAA+NADHàmalate + NAD⁺  à malate into mitoà(mito malate + NAD+àOAA+NADH);

2. glycerophosphate shuttle- 1 cystol NADHà1 mitochondria FADH₂à2 ATP

-flavoprotein dehydrogenase- outer surface of inner membrane; can accept electrons from 3-phospholgycerol and give electrons to ET chain. Similar to succinate dehydrogenase.

-FAD à dihydroxyacetone, NAD à3-phosphoglycerol

D. ATP in cytosol produces ADP and Pi. Making ATP in mitochondria needs them as substrates.

1. ADP-ATP Translocator- transmembrane protein dimer, electrogenic antiport.

-electrogenic antiport- ADP (3-) transported from cytosol to mitochondria in exchange of the transport of ATP (4-) out.

-membrane potential- regulates net transport of ADP in and ATP out (more negative inside mitochondria)

2. Phosphate Transport- Pi in cytosol transported into mitochondria by P carrier

-phosphate carrier- Pi-H⁺ symport, driven by pH gradient (more acidic outside mitochondria)