015 Formation of ATP

Question 1

How much ATP does the average human produce? How many times is it recycled?

Answer 1

Average human produces 250g of ATP, which is recycled 300 times per day.

Question 2

What is the ATP:ADP ratio in the cell?

Answer 2

5:1, even though it is more energically favorable to be in form of ADP.

Question 3

Describe the structure of the mitochondria

Answer 3

Outer membrane is highly permeable compared to inner membrane. Hence intermembrane space is very similar to cytosol. There is high concentration of H+ in the intermembrane space compared to the matrix.

Question 4

What processes occur in the mitochondrial matrix?

Answer 4

Fatty acid oxidation
Citric acid process
Amino acid oxidation

Question 5

Outline the structure of the electron transport chain (ETC)

Answer 5

Complex I takes the NADH and transfers its electrons to coenzyme Q. This pumps 4H+ out of the matrix and another 2H+ are taken from matrix to reduce coenzyme Q to form QH2.

Complex II (succinate dehydrogenase) gets reduced during the citric acid cycle. It takes FADH2 and transfers electrons to coenzyme Q. This is not exothermic enough to drive any protons out.

Complex III takes reduced QH2 and passes the electrons one at a time to the cytochrome. The 2 protons from QH2 enter the intermembrane space, and also 2 protons are pumped out as well.

Complex IV takes electrons from reduced cytochrome and oxygen is the final electron acceptor – it takes the electrons and protons from the matrix to form water. Four protons are pumped out of the matrix, and 2 are released from the previous complex.

Question 6

What happens at complex I of the ETC? (Include compound names, number of H+)

Answer 6

Catalyzes transfer of electrons from NADH.

Question 7

What happens at complex I of the ETC? (Include compound names, number of H+)

Answer 7

Catalyzes transfer of electrons from NADH. Pumps 4H+ out, and uses 2H+ to reduce coenzyme Q.

Question 8

What happens at complex II of the ETC? (Include compound names, number of H+)

Answer 8

Complex II has an attached FAD. This gets reduced during citric acid cycle to FADH2. It transfers electrons to coenzyme Q. Although it is not exothermic enough to drive any H+ out.

Question 9

What happens at complex III of the ETC? (Include compound names, number of H+)

Answer 9

Complex III takes reduced QH2 and passes the electrons one at a time to the cytochrome C. The 2 protons from QH2 enter the intermembrane space, and also 2 protons are pumped out as well.

Question 10

What happens at complex IV of the ETC? (Include compound names, number of H+)

Answer 10

Complex IV takes electrons from reduced cytochrome and oxygen is the final electron acceptor – it takes the electrons and protons from the matrix to form water. Four protons are pumped out of the matrix, and 2 are released from the previous complex.

Question 11

Outline the structure of ATP synthase

Answer 11

There are two half alpha subunits attached to rotating c subunits. The c subunits are attached to a gamma stalk that correspondingly rotates. The rotation of gamma stalk is able to rotate the 3 Beta subunits resulting in ATP formation.

Question 12

How does H+ cause rotation of ATP synthase?

Answer 12

Due to the concentration gradient, H+ will move into the upper half of the alpha subunit. This H+ binds to the c subunit. There is a -ve unit in each subunit, so when it binds to the first c subunit, the carboxyl group becomes uncharged and the subunit will rotate to turn away from the hydrophilic environment, towards the phospholipids. At the other half of the alpha subunit, H+ is released and enters. As the c subunits rotate, it causes corresponding rotation in the gamma stalk. This causes conformation changes in the B units, which make ATP.

Question 13

What are the 3 compositions of beta subunits? How do these cause ATP synthesis?

Answer 13

There is the open phase, in which beta subunit binds to ADP and Pi.
During the loose stage, the beta subunit holds these in place.
During the tight stage, the beta subunit catalyzes the formation of ATP.
Open phase occurs again in which beta subunit releases the ATP and binds another ADP and Pi.

Question 14

What is a P/O ratio?

Answer 14

The ratio of ADP phosphorylated to the moles of O2- reduced.

Question 15

What is the P/O ratio for malate and succinate and why?

Answer 15

Malate is used to produce NADH with a P/O ratio of 2.5, whilst succinate can produce FADH2 with a P/O ratio of 1.5. NADH has higher energy potential, hence requires less oxygen to form ATP. Succinate needs more electron transport energy to form oxygen in order to produce ATP.

Question 16

What is an uncoupler and how does it work?

Answer 16

It allows the process of electron transport chain and ATP synthase to work independently. There is generation of heat but no ATP production.

Question 17

What is the effect of inhibiting complex III/IV?

Answer 17

It halts the activity of the electron transport chain as no proton gradient is formed. No ATP or O2 is produced.

Question 18

What is the effect of inhibiting complex I or II?

Answer 18

Inhibition of complex I will allow mitochondria to use succinate. Inhibition of complex II will allow mitochondria to use malate.

Question 19

How many ATP molecules are produced per full rotation of beta subunit?

Answer 19

3 ATP molecules

Question 20

How is the P/O ratio determined?

Answer 20

It is determined by the electron transport chain activity that transports h+ ions across the chain.

Question 21

What is thermogenin?

Answer 21

This is found in brown adipose tissues. It is an uncoupler which allows heat production without the formation of ATP.

Question 22

What is dinitrophenol (DNP) and how does it work?

Answer 22

DNP is a weak acid and in its protonated form is lipid soluble. In the intermembrane space, DNP is protonated and dissolves into the cristae membrane down the concentration gradient. Inside the cristae, there is excess OH- ions. DNP gives up the H+ and is trapped inside the cristae as it becomes lipid insoluble again. This allows H+ into the cell, quickening electron transport chain.

Question 23

What are some consequences of using dinitrophenol?

Answer 23

This can cause uncontrolled oxidation of substrates and oxygen regardless of whether ADP phsohphorylation is occuring. Less ATP is formed, reducing P/O ratio.

Question 24

What is oxidative stress?

Answer 24

When the production of reactive oxygen species exceeds removal.

Question 25

What was dinitrophenol used for??

Answer 25

It was originally used to make dynamite during WW1. In the 1930S, doctors used to prescribe this for weight loss but there were huge side effects e.g. death.

Question 26

How does aerobic exercise affect oxidative stress?

Answer 26

Aerobic exercise transiently increases production of ROS, however it leads to increased expression of defense against oxidation stress.

Question 27

What are common symptoms of mitochondrial disease?

Answer 27

Elevated lactic acid or alanine in blood, exercise intolerance, seizures

Question 28

What are common symptoms of mitochondrial disease?

Answer 28

Elevated lactic acid or alanine in blood, exercise intolerance, seizures

Question 29

Why is there variable inheritance?

Answer 29

Mitochondria has its own DNA inherited maternally. Every mitochondria has its own DNA, so some can be faulty, whilst others are not (heteroplasmy).

Question 30

In which kind of mutations causing mitochondrial disease cause all mitochondria to be affected?

Answer 30

Nuclear mutations

Question 31

Is complex II nuclear encoded or mitochondrial encoded?

Answer 31

Nuclear encoded

Question 32

What can potassium cyanide inhibit?

Answer 32

Complex III, IV

Question 33

What does antimycin A inhibit?

Answer 33

Complex III, IV

Question 34

What can amytal or rotenone do?

Answer 34

Amytal and rotenone is able to inhibit complex I, preventing malate as a substrate for ATP production. Succinate will be unaffected.

Question 35

What can amytal or rotenone do?

Answer 35

Amytal and rotenone is able to inhibit complex I, preventing malate as a substrate for ATP production. Succinate will be unaffected.

Question 36

What is a benefit of reactive oxidant species?

Answer 36

Cell signalling. E.g. when immune system deliberately use this to kill bacteria.

Question 37

What is ROS?

Answer 37

When the electron transport chain produces reactive oxidant species e.g. O2-, which can react with, and damage biomolecules.

Question 38

What is superoxide dismutase?

Answer 38

This is used as defence system against reactive oxygen species. This reacts O2- + O2- + 2H+ -> H2O2+o2