Mitochondria and Oxidative Phosphorylation

prokaryote grows plasma membrane forms infoldings and pinches off in places forming membrane around organelles/ endomembrane system engulfs aerobic bacterium have their own genome, own machinery for making RNA and proteins

single circular chromosome in mitochondrial matrix 37 genes in total

number of mtDNA copies increases or decreases through fusion and fission mtDNA replicates like nuclear dna before mitosis before fission, mtDNA localise mitochondrial to ensure they are incorporated into new mitochondria can’t make mitochondria from nothing/ from new

increase in abundance of mitochondrial proteins, mtDNA and mitochondrial number eg response to training

2 rRNA genes in mitochondrial genome rRNA form the subunits of ribosomes large subunit- 39S (16S rRNA + 50 proteins) small subunit- 28S (12 rRNA +30 proteins) mitochondria have their own ribosomes

mitochondrial ribosomes can be used to synthesise proteins encoded by mtDNA over 1000 proteins are required to make and maintain mitochondria- encoded by nuclear DNA and synthesised on cystolic ribosomes

cell recognises proteins signal sequence on protein binds to import receptor on large complex (TOM) of outer membrane of mitochondria once bound, complex will grab and pull the protein enters the intermembrane space by ratchet motion if protein is entering matrix it will go through TIM complex protein binds to TIM and by ratchet motion brings it in to matrix protein will be folded and protease will remove (cleave off) signal sequence

outer mitochondria membrane contain small channel proteins called porins alllow small molecules into intermembrane space pyruvate transported through porins pyruvate passes into matrix via mitchondrial pyruvate carriers (inner mitochondrial membrane) in matrix pyruvate is decarboxylated to form acetyl coA

fatty acyl coA combines with carnitine by CPT1 (enzyme) on outer mitochondrial membrane acyl carnitine can move through pores of OMM IMM harder to get through (less permeable) translocase protein- acyl carnitine translocase acyl carnitite moves from intermembrane space to matrix, in return carnitine moves from matrix to IMS (type of active transport- antiport) in matrix- CPT2 does reverse reaction - acyl carnitine broken up and forms acyl coA and carnitine

in cytosol malate aspartate shuttle nadh from glycolysis oxidised to form nad (IMS) same time oxaloacetate reduced to malate by malate dehydrogenase malate holds electrons from nadh malate enters matrix through transporter in return for alpha ketoglutarate malate can be oxidised to form oxaloacetate again nad can be reduced to nadh using electrons from malate (originally from nadh from glycolysis)

high energy electrons carried by NADH and FADH2 are passed into the ETC + accepted by electron carriers high energy electrons lose energy as they are passed along the chain this energy is used to pump protons across the IMM electrons are passed to oxygen (final electron acceptor) and h2o is formed

nadh- coq reductase largest complex in respiratory chain nadh transfers its electrons into complex 1 (oxidised to form NAD) electrons accepted by iron sulfur clusters- redox reactions occur complex 1 passes electrons + 2H+ to CoQ (reduced) to form CoQH2 energy released used to pump 4H+ across membrane into IMS

oxidation of succinate to fumarate (step 6 of TCA cycle)- generation of fadh2 fadh2 remains coupled to succinate dehydrogenase + electrons are passed into complex 2 to Fe S clusters electrons and 2H+ are passed to CoQ to form CoQH2 fad is recycled not enough energy released to pump H+ across membrane

CoQH2 from 1 or 2 donates electrons to complex 3 via Fe-S clusters and passed to cytochrome C each cytochrome C can accept 1 electron so 2 cyt C molecules are reduced 2H+ from CoQ are released into IMS energy released pumps 2 more H+ across membrane

cytochrome C carries 2 electrons per NADH electrons bind with protons and oxygen to form water complex 4 holds onto electrons until there is 4- enter, combine with 4H+ and O2 to form 2H2O per nadh- 2h+ pumped across membrane into IMS

H+ enter atp subunit through F0 alpha subunit H+ move into c subunit of F0 causing it to rotate (H+ exit into matrix) gamma subunit (shaft) rotates F1 alpha and beta subunits have ADP and Pi bound to specific sites when y subunit rotates, causes conformational change to F1 region catalysing the formation of ATP from adp and pi