5 - Mitochondria

Question 1

Mitochondria

Answer 1

site of cellular respiration
Mitochondria change their position inside the cells and are moved by the microtubules of the cytoskeleton.
Often found in regions of high ATP consumption, e.g in the myofibrils of muscle cells

Question 2

Mitochondria structure

Answer 2

All mitochondria have an inner and an outer membrane, the inner
membrane is formed into cristae.
There are two compartments in the mitochondria, the matrix inside the inner membrane and the intermembrane space between the inner and outer membranes.

Question 3

The outer membrane

Answer 3

This is very similar to most other eukaryotic membranes.

Its major protein component is porin which forms large aqueous channels through the outer membrane

Question 4

The inner membrane

Answer 4

This is formed into cristae which increase its surface area.
It is the energy transducing membrane and is impermeable to most small ions (due to cardiolipin)
The number of metabolite transporters varies according to tissue and cell
type.
Liver mitochondria have the greatest variety of transporters since they are involved in the initial reactions of several anabolic pathways.

Question 5

3 major types of membrane complexes found in the inner membrane

Answer 5

1. The components of the electron transport chain
   2 ATP synthase
2. Specific transporters which move metabolites into and out of the
   mitochondria matrix.

Question 6

The matrix

Answer 6

Contains the enzymes which catalyse Krebs cycle and fatty acid oxidation.
The matrix also contains ribosomes and the mitochondrial DNA

Question 7

where does glycolyisis take place

Answer 7

within the cell cytosol and only releases a small amount of the energy stored in glucose (through substrate level phosphorylation)
most of the energy remains in the two molecules of pyruvate

Question 8

Where does the Krebs cycle take place?

Answer 8

in the matrix of the mitochondria

Question 9

where is the ETC located

Answer 9

on the inner membrane of the mitochondria

Question 10

what do NAD and FAD do?

Answer 10

collect electrons from Krebs cycle and transfer them to the ETC

Question 11

Krebs cycle

Answer 11

Before the cycle begins pyruvate is converted to Acetyl CoA with the loss
of CO2
2C enters the cycle as the acetyl fragments of acetyl CoA and 2C exits as CO2.
Most of the energy that was present in the acetate group transferred via the transfer of electrons to NAD and FAD only a small amount of ATP is produced through substrate level phosphorylation
The electron carriers relay their electrons to the ETC

Question 12

Electron Transport Chain function

Answer 12

It generates energy via redox reactions
The electron transport chain consists of a collection of molecules embedded in the inner membrane of the mitochondria
The electron transport chain pumps hydrogen ions across the inner
membrane to generate an ion gradient.
This ion gradient is used by another molecule in the inner membrane ATP synthase to generate ATP

Question 13

Electron Transport Chain function

Answer 13

It generates energy via redox reactions

The electron transport chain consists of a collection of molecules embedded in the inner membrane of the mitochondria

Question 14

What is a redox reaction?

Answer 14

A reaction that releases energy when electrons are transferred from one reactant to another

Question 15

Why do proteins in the electron transport chain have prosthetic groups attached to them?

Answer 15

Prosthetic groups are non protein components that are essential to catalytic functions

Question 16

What happens to each member of the ETC when it accepts an eletcron?

Answer 16

It becomes reduced

Question 17

What are cytochromes?

Answer 17

Electrons carriers that are found in the electron transport chain
The prosthetic groups of cytochromes have four organic rings surrounding an iron atom

Question 18

FADH2

Answer 18

transfers electrons into the electron transport chain but adds its electrons at a lower energy than that of NADH.
FADH2 adds its electrons direct to ubiquinone.

Question 19

The electron transport chain produces ATP directly. True or false?

Answer 19

False - ATP is generated indirectly by chemiosmosis, which occurs due to the ion gradient set up by the electron transport chain.

Question 20

What is the ion gradient involved in the electron transport chain which allows chemiosmosis and therefore ATP synthesis to occur?

Answer 20

Hydrogen ion gradient

Question 21

What is the role of ATP synthase in the electron transport chain?

Answer 21

ATP synthase makes ATP by adding a inorganic phosphate group to ADP

Question 22

ATP synthase

Answer 22

large molecule which can be seen under the electron microscope in the inner membrane of the mitochondria and has a mushroom-like appearance

Question 23

how does the ETC maintain the ion gradient?

Answer 23

The electron transport chain uses the energy from the exergenic flow of
electrons to pump hydrogen ions from the matrix of the mitochondria into the intermembrane space

Question 24

Mitochondrial

Answer 24

Cyanide and DNP

Question 25

Cyanide

Answer 25

prevents the passage of electrons from one of the cytochromes thereby blocking the electron transport chains. It is probably the fastest poison known to man.

Question 26

2,4-Dinitrophenol (DNP)

Answer 26

make the inner membrane leaky to hydrogen ions so that a gradient cannot be generated
The electron transport chain still works but instead of producing ATP all the energy is released as heat.
DNP has been investigated as a diet drug in the past, it is extremely
dangerous and has caused numerous deaths, sadly several in the last few
years.

Question 27

Mitochondrial in brown fat

Answer 27

Brown fat is a specialized type of adipose tissue present in many mammals
including humans.
The function of the mitochondria in brown fat is to produce heat

Question 28

function of mitochondria in brown fat

Answer 28

Cells in brown fat have mitochondria which have a special protein on their inner membrane that functions as a H+ ion channel through the
membrane (thermogenin).
H+ ions pumped across the membrane by the ETC leak back immediately without passing through the ATP synthase molecule.
Thus the energy produced by the ETC is released as heat and does not generate any ATP.

Question 29

MERRF

Answer 29

• Myoclonic epilepsy and ragged-red fiber disease (MERRF), which is caused by a mutation in the mitochondrially encoded tRNA Lys gene
• It is a multisystem disease primarily affecting muscles but also causing epilepsy and general weakness.

Question 30

Mitochondrial diseases

Answer 30

• Mitochondrial defects have been implicated in a wide variety of degenerative diseases, eg MERRF.
• Mitochondrial disease is an new and emerging area of medicine.
• An new IVF technique has been developed which avoids passing on defective mitochondria, the embryo has 3 genetic parents. 1. Egg nucleus 2. Sperm 3. Egg Mitochondria.
• 1, 2 and 3 are different individuals, so 3 “parents”