Mitochondrial synthesis of ATP

Question 1

How many weeks’ worth of stored energy do we have on average?

Answer 1

4-6 weeks

Question 2

How much ATP do you use every day?

Answer 2

Your body weight’s worth

Question 3

How much of the energy in food is converted to ATP?

Answer 3

50%

Question 4

What is the size limit for passage of molecules across OUTER mitochondiral membrane?

Answer 4

5000 da (Daltons)

Question 5

What are the folds in the inner membrane of mitochondria called?

Answer 5

christae

Question 6

Why is the inner membrane of mitochondria such a good electrical insulator?

Answer 6

capable of maintaining large ionic and electrical gradients

Question 7

What are the two spaces in mitochondria called?

Answer 7

Matrix and intermembrane space

Question 8

What is contained in the Matrix space?

Answer 8

contains wide range of enzymes – Krebs cycle, fatty acid oxidation, urea cycle (in liver)
high concentrations of substrates, cofactors & ions
contains mitochondrial DNA, RNA & ribosomes (these resemble bacterial components) though few mitochondrial proteins are coded on mitochondrial DNA

Question 9

What is in the intermembrane space?

Answer 9

has metabolite & ion concentrations similar to cytosol

contains cytochrome c (electron carrier)

Question 10

Where are mitochondrial proteins coded for?

Answer 10

In the nucleus of the cell

Question 11

What is the link reaction?

Answer 11

Pyruvate dehydrogenase catalyses conversion to acetyl CoA

Question 12

What is vitamin B1?

Answer 12

Thiamine

Question 13

What is Wernicke-Korsakoff syndrome?

Answer 13

Lack of thiamine seen in alcoholics

neuro/cardio symptoms

Question 14

Why is pyruvate dehydrogenase a key ‘decision point’ in metabolism?

Answer 14

Acetyl CoA cannot be converted back to glucose in humans

Conversion of pyruvate to acetyl CoA commits the C atoms of glucose to energy production or lipid synthesis

Question 15

What are the main 2 stages of the Krebs cycle?

Answer 15

Synthesis of 6-C compound (citrate) which then loses 2 C as CO2 to become 4-C compound (succinyl CoA)

Oxidation of 4-C compound to regenerate oxaloacetate and initiate another round of the cycle

Question 16

What are the main outputs of the Krebs cycle?

Answer 16

Reduced coenzymes NADH & FADH2 – electron carriers

CO2 – waste product

1 GTP = 1 ATP

Question 17

What are the 3 key enzymes in the Krebs cycle?

Answer 17

citrate synthase
isocitrate dehydrogenase
α-ketoglutarate dehydrogenase

Question 18

Why do patients with type 1 diabetes synthesise ketones?

Answer 18

In the absence of insulin, fatty acids are mobilised from adipose tissue and oxidised to acetyl CoA – acetyl CoA levels HIGH

But lack of oxaloacetate prevents acetyl CoA from entering the Krebs cycle

So ketones are synthesised instead

Question 19

What two processes is oxidative phosphorylation made up of?

Answer 19

Electron Transport (oxidation)

ATP synthesis (phosphorylation)

Question 20

What membrane proteins make up the electron transport chain?

Answer 20

Complexes I to IV
ubiquinone
cytochrome c

Question 21

How does cyanide work?

Answer 21

Cyanide inhibits transfer of electrons from complex IV to oxygen

Question 22

What happens to the energy released by electron transfer across complexes?

Answer 22

used to pump H+ ions into intermembrane space

Question 23

For each pair of electrons from NADH, how many electrons are translocated?

Answer 23

10

This creates a large proton gradient across the well insulated inner membrane

Question 24

What happens when the H+ ions move back down the concentration gradient into the mitochondrial matrix?

Answer 24

H+ ions flow through ATPase enzyme and help create ATP from ADP and Pi.

Question 25

How many ATPs synthesised for pair of electrons from NADH?

Answer 25

2.5 ATPs

Question 26

How many protons are required to synthesise 1 molecule of ATP?

Answer 26

4

Question 27

Why won’t ATP synthesis work if electron transport isn’t working?

Answer 27

lack of reduced substrates or more commonly lack of oxygen - there is no proton gradient to drive ATPase enzyme

Question 28

Why does electron transport stop if ATP synthesis is blocked?

Answer 28

Proton gradient builds up to the level where the complexes have insufficient energy to pump more protons across the membrane

(gradient too large)

Energy cannot be released from the electron carriers, so they can’t accept any more electrons

Question 29

How do uncouplers work?

Answer 29

Weak acids, associarte with protons in intermembrane space and help prevent gradient from reaching stage where carriers can’t accept more electrons

Question 30

What is the function of uncoupling in humans?

Answer 30

generate heat in newborns - non-shivering thermogenesis