Mitochondria and Peroxisomes

Question 1

Describe the structure of mitochondria

Answer 1

· Between the inner and outer is the inter-membrane space. Located in the inner membrane is the matrix where metabolic process occurs
· Small circular genome, double membrane
· The outer membrane contains many channels formed by the protein porin and acts like a sieve and filters out molecules that are too big.

The inner membrane is highly folded so structures called cristae form which increase the surface area for respiratory enzymes to work on.

They range between 1-10um in length, mitochondria change shape rapidly and appear to be moving around the cell
Present in all eukaryotic organism.

Question 2

What happens to cells that dont have mitochondria?

Answer 2

Retain a similar organelle

Question 3

Why do mature RBCs not have mitochondria?

Answer 3

They are destroyed during maturation

Question 4

What is organisation of mitochondria dependent on?

Answer 4

Type of cell

Question 5

Describe the difference between mitochondria in fibroblast cell and cardiac cells

Answer 5

· In fibroblast mitochondria they are interconnected forming networks which is hardly dynamic.

· In cardiac cells they are highly abundant and found in distinct zones- mitochondria may perform zonal functions

Question 6

Explain the endosymbiotic theory

Answer 6

· All of mitochondria ever existed can be trace back to one mitochondrion.

· Primitive form of eukaryotic cell forms a symbiotic relationship with a prokaryote.

The larger organism providing the smaller one with nutrients and the mitochondria providing ATP.

Prokaryote divided inside the host and producing daughter cells so when host divided, it would contain the mitochondria”

Question 7

What evidence is there for mitochondria being a prehistoric mitochondria?

Answer 7

·Evidence comes from phylogenetics
· If the mitochondrial genome is sequenced they all share similarity to the typhus bacteria, which exist today and these bacteria are symbionts of eukaryotes.

· The proteins made in the mitochondria are made by its own ribosomes, some proteins are encoded for in the nucleus and are imported into the mitochondria.

Question 8

Describe mitochondria transportation

Answer 8

· Facilitated by microtubules- requiring moto proteins eg Dynein and Kinesin to which mitochondria binds by the adaptor proteins (Milton and miro) located on surface of mitochondria
Milton and miro bind to Kinesin

· Important in cells such as neurons- delivered to synapses where they are required for neural signalling

Question 9

Describe the cycle life of mitochondria(4)

Answer 9

· Like bacterial mitochondria can divide and fuse together.

· New mitochondrion is not made from scratch- making new ones involve growing the mass of existing ones which undergo fission.

· Macromolecules inside the mitochondria become damaged because of oxidative insult.

· Damaged mitochondria are destroyed via mitophagy, a form of autophagy.

Question 10

What are the functions of mitochondria? (9)

Answer 10

· Produce ATP in process of oxidative phosphorylation

· Central hubs of metabolism

· Anabolic synthesis of nucleotide required for DNA replication

· Calcium homeostasis- critical for muscle contraction

· Production of amino acids such as glutamates- function as neurotransmitters.

· Important in apoptosis- cell death-release of proteins from the space between themitochondrialinner and outer membrane that, once in the cytosol, activate caspase proteases that dismantle cells

· Immune response- protein receptors that detect invading viral RNA molecules. Protein receptors are located on the outer membrane- activate innate immune response

· Energy conversion: generation of ATP by phosphorylation (OXPHOS)

· Nutrients in food are oxidized to produce acetyl co enzyme A- processed in the Kreb’s cycle

Question 11

Describe the oxidation of NADH and FADH

Answer 11

NADH and FADH serve as electron donors in the electron transport chain. They are oxidized and leads to production of ATP

Question 12

Where is Acetyl-CoA derived from?

Answer 12

Acetyl-CoA is derived from carbohydrates in the cytoplasm and fatty acids metabolized by beta oxidation inside the mitochondria

Question 13

Explain the importance of citric acid

Answer 13

Produce reduced electron donors used for production of ATP in oxidative phosphorylation

Provide biosynthetic precursors for the synthesis of fatty acids and amino acids.

Question 14

Where does citric acid take place?

Answer 14

In the matrix

Question 15

where is succinate dehydrogenase found?

Answer 15

It is found in the inner membrane unlike other citric acid cycle enzymes which are soluble inside the membrane
It is involved in oxidative phosphorylation

Question 16

What process are NADH and FADH2 involved in?

Answer 16

ETC to produce ATP

Question 17

Describe the oxidative phosphorylation process(5)

Answer 17

Electrons derived from NADH and FADH 2 generated in the citric acid cycle flow through respiratory chain complexes.

2, Flow of electrons leads to protons being pumped out of the matrix into inter membrane space.

3. Build-up of protons generate a proton motive force consisting of a transmembrane potential and a pH gradient
4. Protons are transported back into the matrix by protein complex called ATP synthase in a process known as chemiosmosis.
5. Flow of protons through ATPase drive the process of ATP Involve 5 protein complexes embedded in the inner mitochondrial membrane

Question 18

Describe each of the five complexes involved in oxidative phosphorylation

Answer 18

Complexes 1-4 are involved in transfer of electrons and generation of proton motive force.

Part of electron transport chain- respiratory chain complexes. There are two electron carries- ubiquinone and cytochrome C

Complex 2 does not pump proton so does not contribute to proton motive force.

The 5th complex is not respiratory chain complex.

High membrane potential Protons flow back into the membrane through complex 5 which harness energy to generate ATP

Question 19

Describe the structure of peroxisomes

Answer 19

· Single bilayer
Two main functions
· Approximately 0.1-1 μm in diameter
· Contains no DNA or ribosomes

Question 20

What are the functions of peroxisomes?

Answer 20

· Metabolic roles: Some fatty acids are broken down inside peroxisomes in beta oxidation.

· Beta oxidation takes place in mitochondria, but mitochondria is unable to break down long chain fatty acids by peroxisome can

· Detoxification of hydrogen peroxide by enzyme catalase - highly reactive that can react and damage- contribute to aging process.

· Catalase is abundant in peroxisome but not elsewhere

· Metabolism of bile acids- important for synthesis of cholesterol
Peroxisome proteins contain a Peroxisomal targeting signal (PTS), which binds to a receptor molecule that take the protein into the Peroxisome

Question 21

How do mitochondria replicate?

Answer 21

Replicate by fission
Requires a set of proteins- some of these proteins are involve in fission of both mitochondria and peroxisome eg. DNM1L, and FIS1

Question 22

What are some shared features between mitochondria and peroxisomes?

Answer 22

Important in cell metabolism eg fatty acids Able to divide and the protein machinery are locate don the outside of these organelles

Antiviral signaling- mitochondrial antiviral signalling complex is found don the mitochondria and peroxisomes”

Question 23

What is peroxisomes biogenesis?

Answer 23

Peroxisome biogenesis disorders in the Zellweger spectrum (PBD-ZSD) is anautosomal recessive disordercaused by mutations in genes that encode peroxins, proteins required for the normal assembly of peroxisomes.

Question 24

Recall in order the intermediates in the TCA cycle

Answer 24

1. Citrate
2. cis- aconitase
   isocitrate
3. alpha-ketoglutarate(5C)
4. succinyl- CoA(4C)
5. succinate
6. fumerate
7. malate
8. oxaloacetate(4C)

Question 25

Recall the products of the the TCA cycle

Answer 25

3x NADH
2x CO2
1x FADH2
1xGTP