Mitochondria

Question 1

Explain the Outer Membrane of the mitochondria ?

Answer 1

• Outer membrane contains porins, which act as a pore allowing some specific molecules to diffuse through, like channel proteins.
• Permeable to proteins 5kDa or less

Question 2

Explain the Inner Membrane of the mitochondria ?

Answer 2

• The composition of this region is similar to the cytoplasm since the porins in the outer membrane are believed to be conduits for regulated water transport.
• This region has a higher protein composition than the matrix.
• The pH is lower than the matrix since protons are pumped across the inner membrane into this space.

Question 3

Explain the Matrix of the mitochondria ?

Answer 3

• The matrix is viscous, containing less water than the cytoplasm.
• The matrix contains the DNA, ribosomes, enzymes, organic molecules, and inorganic ions.
• The enzymes in the matrix enable the reactions of the TCA cycle, beta oxidation of fatty acids and oxidative phosphorylation.
• The pH is more alkaline than the intermembrane space.

Question 4

Explain the Cristae of the mitochondria ?

Answer 4

• The inner mitochondrial membrane is extensively folded into cristae.
• Cristae increase total membrane surface area, allowing more oxidative phosphorylation to occur (than if it were smooth).
• The inner membrane is freely permeable only to O2, CO2 and H2O, but less permeable to ions and small molecules than the outer membrane.

Question 5

Explain the Cristae arrangements in different cell types ?

Answer 5

Liver - arranged like a series of shelves
Kidney - tightly packed like a stack of coins
Nerve - form network of tubes

Question 6

Where did Mitochondrion originate from ?

Answer 6

Bacteria that were engulfed by an ancestral pre-eukaryotic cell and survived inside, living in symbiosis with their host.
1.5 billion years ago!

Question 7

Evidence for Endosymbiotic theory ?

Answer 7

• The mitochondrion and chloroplast have many similarities

- A mitochondrion can divide like a bacterium (binary fission)

Question 8

Explain Mitochondrial DNA?

Answer 8

• Mitochondria have their own circular DNA, which is extragenomic to the cells they are found in.
• Over time some of the mt genes have been moved to the host genome, but some have remained within the organelle.
• The mtDNA-encoded polypeptides are all subunits of enzyme complexes of the oxidative phosphorylation system.
• Mitochondria are not self-supporting; instead they require imported proteins from the cell.

Question 9

Nuclear DNA vs Mitochondrial DNA (mtDNA)

Answer 9

Nuclear DNA - inherited from all ancestors

Mitochondrial DNA - Inherited from a maternal lineage

Question 10

What are some functions of the Mitochondrion ?

Answer 10

• Aerobic carbohydrate metabolism via TCA cycle in matrix
• Fatty acid metabolism via TCA cycle in matrix
• ATP production via oxidative phosphorylation in inner mitochondrial membrane

Question 11

What products do you get when at the end of one cycle of the TCA cycle ?

Answer 11

• 3 NADH
• 1 FADH2
• 1 ATP
• 2 CO2

Question 12

Explain what β Oxidation does ?

Answer 12

• The triglycerides are broken into fatty acids and glycerol and can all be converted into Acetyl CoA
• One Actyl CoA is made per cycle, and this then enters the TCA cycle

Question 13

What are the products of β Oxidation ?

Answer 13

• Acetyl CoA

- FADH2, NADH, H+

Question 14

What do the reactions of the TCA cycle & oxidation of fatty acids produce ?

Answer 14

Activated electron carriers (reduced coenzymes) that are used in oxidative phosphorylation

Question 15

What is Proton-motive force ?

Answer 15

Proton pumping creates an imbalance of protons (& a charge difference) between the matrix & intermembrane space

Question 16

What is NADH reductase and what does it do (inner mitochondrial membrane)?

Answer 16

NADH reductase is an electron carrier (complex I) in the membrane & oxidises NADH to NAD+ + H+ + e. It simultaneously pumps protons to the intermembrane space & carries electrons to ubiquinone

Question 17

What happens to FADH2 and what does it do (inner mitochondrial membrane)?

Answer 17

FADH2 is oxidised by complex II (succinate dehydrogenase) into FAD + 2H+ + 2e. It transfers the electrons to ubiquinone, but NOT THE H+

Question 18

What do Complex III & IV pump ?

Answer 18

Complex III & IV pumps H+ ions con-currently with electrons. III receives electrons from ubiquinone, so the H+ ions will be displaced to the intermembrane space

Question 19

Complex IV is the last electron carrier. What is the final electron acceptor ?

Answer 19

Oxygen

Question 20

When protons have accumulated the proton motive force drives ?

Answer 20

Protons back to the matrix via the ATP synthase. This is coupled to ATP synthesis.

Question 21

Explain Chemiosmosis ?

Answer 21

The pH gradient set up by pumping protons into the inner mitochondrial space is harnessed and used by ATP synthase in the inner mitochondrial membrane (IMM) to add phosphate onto ADP (ie make ATP)

Question 22

What is the term given for disrupting oxidative phosphorylation ?

Answer 22

Uncoupling

Question 23

What are some examples of Uncouplers ?

Answer 23

Aspirin and DNP (2,4-Dinitrophenol)

Question 24

What do Uncouplers do ?

Answer 24

They act by binding to protons and effectively uncouples pH gradient from ATP synthesis, causing ATP depletion and for the energy generated by electron transfer to be lost as heat

Question 25

What relies on this process ?

Answer 25

There are a number of so called ‘diet pills’ that rely on this process containing 2,4 DNP which has been fatal in a number of incidences, since it leads to organ failure and is untreatable.

Question 26

What is Thermogenin ?

Answer 26

Thermogenin is an uncoupling protein found in brown adipose tissue of newborn mammals

Question 27

What does Thermogenin act as ?

Answer 27

• It acts as a proton channel increasing permeability for protons, allowing them back into the mitochondrial matrix without passing through ATP synthase.
• This means energy is not conserved into ATP but is used to generate heat instead

Question 28

What is Apoptosis ?

Answer 28

It is a way to get rid of potentially dangerous cells & those not needed by organism

Question 29

Explain the process of an Apoptotic cell ?

Answer 29

• A normal cell
• The cell shrinks & Chromatin condenses
• Membrane starts blebbing & Organelles disintegrate
• Nucleus and organelles collapse & Membrane continues to bleb
• Apoptotic bodies form
• Macrophages phagocytose apoptotic bodies

Question 30

Explain the Mitochondrial Involvement in Apoptosis ?

Answer 30

1. Bcl2 family of proteins regulate apoptosis. When members Bak or Bax are activated by an apoptotic stimulus, they aggregate in the outer mitochondrial membrane, leading to the release of cytochrome c.
2. The cytochrome c is
   released into the cytosol
   from the mitochondrial
   intermembrane space.
3. Cytochrome c then binds to an adaptor protein, causing it to assemble into a seven-armed complex.
4. The procaspase-9 proteins become activated within the apoptosome and then go on to activate executioner procaspases in the cytosol, leading to a caspase cascade and apoptosis.
5. This complex then recruits seven molecules of initiator procaspase-9 to form a structure called an apoptosome.

Question 31

Where are Calcium ions stored ?

Answer 31

In the ER (& sarcolasmic reticulum) but the mitochondrion also

Question 32

Explain Calcium Ion Regulation ?

Answer 32

It can regulate cytosolic Calcium rises and after Ca2+ has been released from the ER it determines whether the cell survives or continues to apoptosis.