Mitochondria and Oxidative Phosphorylation

Question 1

mitochondrial endosymbiosis

Answer 1

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

Question 2

mitochondrial genome

Answer 2

single circular chromosome in mitochondrial matrix
37 genes in total

Question 3

mitochondrial dna

Answer 3

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

Question 4

mitochondrial biogenesis

Answer 4

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

Question 5

mitochondrial ribosomes (55S)

Answer 5

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

Question 6

mitochondrial proteins

Answer 6

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

Question 7

protein transport into the mitochondria

Answer 7

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

Question 8

pyruvate transport into mitochondria

Answer 8

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

Question 9

fatty acid transport into mitochondria

Answer 9

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

Question 10

NADH transport into mitochondria

Answer 10

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)

Question 11

ETC

Answer 11

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

Question 12

complex 1

Answer 12

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

Question 13

complex 2

Answer 13

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

Question 14

complex 3

Answer 14

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

Question 15

complex 4

Answer 15

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

Question 16

oxidative phopshorylation

Answer 16

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