Week 6 - Metabolism 3

Question 1

How many genes make up a mitochondrial genome?

Answer 1

37

Question 2

How many of those genes are rRNA?

Answer 2

2

Question 3

How many of those genes are tRNA?

Answer 3

22

Question 4

How many of those genes are protein encoding?

Answer 4

13

Question 5

What do rRNA genes do?

Answer 5

they form the subunits of ribosomes
mitochondria therefore have their own ribosomes

Question 6

What form the small mitochondrial ribosomes?

Answer 6

28S
12S rRNA
30 proteins

Question 7

What form the large mitochondrial ribosomes?

Answer 7

39S
16S rRNA
50 proteins

Question 8

What is endosymbiosis?

Answer 8

a symbiotic relationship where one organism, the endosymbiont, lives inside the cells or body of another organism, called the host. this relationship can be mutually beneficial.

Question 9

What are mitochondrial ribosomes do?

Answer 9

can be used to synthesis proteins encoded by mtDNA

Question 10

Transport into the mitochondria

Answer 10

• signal sequence is recognised by TOM and TIM and pulled through
• needed to pass through both

Question 11

Process of Pyruvate getting into the mitochondria

Answer 11

• the outer mitochondrial membrane contains small channel proteins called porins or voltage dependent anion channels (VDAC)
• VDAC allow small molecules up to 5000DA into the intermembrane space
• pyruvate is transported through porins
• pyruvate is transported into the matrix via recently discovered mitochondrial pyruvate carriers
• in the matrix pyruvate is decarxylated to form acetyl coA

Question 12

What do mitochondrial pyruvate carriers require to function?

Answer 12

a change in pH

Question 13

Process of NADH getting into the mitochondria (malate asparate shuttle)

Answer 13

• NADH from glycolysis is ised to reduce oxaloactate to form malate
• Malate crosses into the matrix
• Malate is oxidised to form oxalacetate and NAD+ is reduced
• malate therefore carries NADHs electrons into the mitochondria
• However this only works if alphaketoglutarate is transported in the opposite direction

Question 14

Process of NADH getting into the mitochondria (glycerol 3 - phosphate shuttle)

Answer 14

• NADH from glycolysis is used to reduce DHAP to glycerol 3 - phosphate in the cytosol
• glycerol 3 - phosphate enters the mitochondria and is oxidised back to DHAP on the inner mitochondrial membrane
• this generates FADH2
• glycerol 3 phosphate therefore carrier NADH electrons and transfers them to FADH2

Question 15

Process of fatty acids getting into the mitochondria

Answer 15

• cartinine transports fatty acyl coA into the matrix
• actyl coA is converted to acetyl carnitine by CPT 1
• acyl carnitine is transported via the acyl carnitine translocase
• acyl carnitine is converted back to acyl CoA by CPT2
• carnitine is regenerated

Question 16

What is the proton gradient behind ATP synthesis?

Answer 16

1 - Electrons are passed from NADH to FADH2 through a chain of large protein complexes to oxygen
2 - The protein complexes use energy from the electrons to pump protons across the inner mitochondrial membrane

Question 17

What is cellular respiration?

Answer 17

The generation of high energy electrons with transfer potential, the flow of these electrons through the respiratory chain (electron transfer chain) and subsequent synthesis of ATP.

Question 18

What is oxidative phosphorylation?

Answer 18

The energy in the electrons carried by NADH and FADH2 is used to form ATP.
Transfer of electrons to oxygen is highly exergonic

Question 19

What is a prosthetic group?

Answer 19

non-protein component of a protein that is permanetly attached

Question 20

What happens at complex 1?

Answer 20

• NADH binds to Flavin Mononucleotide and donates 2x electrons forming FMNH2
• FMN is a prosthetic group for complex 1
• FMN passes electrons to iron sulfur clusters within complex 1
• 2x electrons are passes to coenzyme Q to form QH2
  4 H+ are pumped across the inner membrane and NAD+ is regenerated

Question 21

What are iron sulphur clusters?

Answer 21

prosthetic groups in iron-sulfur proteins
play important role in redox reactions
they accept electrons without accepting or releasing protons

Question 22

What happens at complex 2?

Answer 22

• succinate dehydrogenase catalyses step 6 of TCA cycle
• FADH2 remains coupled to succinate dehydrogenase and transfers electrons to Fe-S clusters
• Electrons are ultimately passed to Q along with 2 H+ to form QH2
  insufficient energy is released to achieve proton pumping across the membrane

Question 23

What are cytochromes?

Answer 23

electron transferring proteins containing heme prosthetic groups

Question 24

What happens at complex 3?

Answer 24

• QH2 passes its 2x electrons into complex 3
• cytochrome C can only carry 1 electron
• The Q cycle enables effective transfer of electrons at complex 3
• When QH2 transfers its electrons, its H+ also gets released into the intermediate space
  per Q cycle 4 H+ are released to the intermembrane space

Question 25

What happens at complex 4?

Answer 25

2 water molecules form 4 H+ are pumped across membrane

Question 26

What is the electrochemical proton gradient?

Answer 26

Termed the proton motive force

Question 27

What is ATP synthase?

Answer 27

- rotation of ATP synthase (F0) does not drive ATP synthesis - Instead it enables ATP release

Question 28

L (loose conformation)

Answer 28

binds ADP + Pi

Question 29

T (tight conformation)

Answer 29

ATP is synthesised here

Question 30

O (open conformation)

Answer 30

will readily release ATP

Question 31

Explain why NADH is well suited to transferring electrons?

Answer 31

NADH has a very low redox potential whereas oxygen has a much higher one making NADH more prone to giving up its electrons and oxygen more prone to accepting them

Question 32

Summarise the function of complexes 1 and 2

Answer 32

to transfer electrons from NADH or FADH2 to coenzyme Q and pumps protons from the matrix to the intermediate space using the nergy released through electron transfer

Question 33

What is the purpose of the Q cycle?

Answer 33

to solve the problem of passing 2 electrons to cytosome C which can only carry 1

Question 34

How many molecules of cytochrome C are required to generate water at complex 4 under physiological conditions? why?

Answer 34

4 molecules of cytochrome C are required. when oxygen accepts the first 2 electrons it forms a free radical. 2 more molecules of cytochrome C (2 electrons) are required along with 4 H+ to from 2H20

Question 35

Describe what is meant by the term proton motive force

Answer 35

the electrochemical gradient that is generated through proton pumping in the respiratory chain, which can then be used to generate ATP

Question 36

What is the interaction between the proton motive force and ATP generstion by ATP synthase?

Answer 36

the protons in the intermediate space which contribute to the proton motive force, return to the matrix along their concentration gradient through ATP synthase. The protons cause the c-subunits in the F0 portion of the enzyme to rotate, which in turn causes the y-unit to rotate. but the alpha and beta subunits of the F1 portion remain fixed and as such their conformation is altered with each rotation. Beta subunits are the ATP synthesis centre of ATP synthase and their altered conformation drives ATP synthesis and release.