20. Mitochondria

Question 1

Describe Mitochondria? (5pts)

Answer 1

1. Vital function in cells
2. Function central in driving evolution of complex eukaryotic organisms.
3. Dysfunction in mitochondria is related to why we age and ageing diseases such as cancer.
4. Inherited mitochondria disorders affect mitochondria function.
5. Mitochondria is important because side effects of antibiotics occur as they inhibit mitochondria function.

Question 2

Describe the endosymbiotic theory of mitochondria? (5pts)

Answer 2

1. 2 billion years ago there was no life on earth
2. Theory proposed that all mitochondria that ever existed can be traced back to one prokaryotic cell.
3. This prokaryotic cell was engulfed by a primitive form of a eukaryotic cell. The two cells therefore formed a symbiotic relationship.
4. The prokaryote divided inside its host thereby producing daughter cells and increasing their number so that when the host cell divided these prokaryotic daughter cells would be passed on.
5. The host gives rise to all known eukaryotic organisms that have ever lived.

• without mitochondria complex life would not have evolved
• evidence comes from phylogenetics

Question 3

Describe the structure of mitochondria? (4pts)

Answer 3

1. The mitochondrial matrix is where advanced number of metabolic reactions take place. Occurs in the inner membrane.
2. The large protein complexes that are responsible for oxidative phosphorylation are embedded in the inner mitochondrial membrane.
3. Mitochondria has a small circular genome with its own DNA,
4. Mitochondria has 2 membranes. This supports the notion that mitochondria originates from a prokaryotic ancestor.

Question 4

Describe mitochondria in skin fibre blast cells? (3pts)

Answer 4

1. Mitochondria are interconnected forming networks off one another.
2. Networks are dynamic whereby the mitochondria are constantly moving inside the cell.
3. Individual mitochondria can separate from the network. They can then divide and fuse with other mitochondria in fission and fusion.

Question 5

Describe mitochondria in cardiac myocytes? (2pts)

Answer 5

1. Mitochondria are highly abundant

2. Mitochondria reside in distinct zones.

Question 6

Describe how mitochondria are transported on cytoskeletal microtubules? (2pts)

Answer 6

1. Mitochondria binds to motor proteins such as dianin and kinsesin via adaptor proteins called Milton and Mira which are located on the surface of the mitochondria.
2. The transport of mitochondria is important in cells such as neurones whereby mitochondria channel across axons and deliver to synapses where they are required for neuronal signalling and function.

Question 7

Describe the mitochondrial life cycle? (4pts)

Answer 7

1. Mitochondria can divide and fuse with one another in fission and fusion
2. When new mitochondria is made the mass of existing mitochondria is grown which are then able to undergo fission.
3. Process of fusion is important for mitochondria.
4. Over time macromolecules inside the mitochondria such as DNA and proteins become damaged. To maintain overall cellular length the damaged mitochondria are removed from the cell in mitophagy which is a form of autophagy.

Question 8

Describe the 7 functions of Mitcohodnria? (7pts)

Answer 8

1. Main function is to produce ATP in oxidative phosphorylation
2. Central hubs of metabolism in the cell
3. Important for anabolic synthesis for nucleotides which are required for DNA replication and growth. This is why mitochondrial function has emerged as an important drug target for cancer therapy.
4. Play a role in calcium homeostasis which is needed for muscle contraction
5. Important for the production of amino acids such as glutamate which function as neurotransmitters.
6. Important in apoptosis which is programmed cell death.
7. Involved in immune response. Protein receptors are located on the outer membrane of mitochondria that detect invading viral RNA molecules which activates an innate immune response.

Question 9

Describe how ATP is produced in the Mitochondria? (3pts)

Answer 9

1. Nutrients from food are oxidised to produce Acetyl-coA which is processed in the Krebs cycle.
2. The molecules NADH and FADH are produced which work as electron donors in the electron transport chain.
3. These electron donors are oxidised in the electron transport chain producing ATP.

Question 10

Describe the Krebbs cycle aka citric acid cycle? (2pts)

Answer 10

1. Fuel molecules enter the kreb cycle as Acetyl co-A which is derived from the metabolism of carbohydrates in the cytoplasm and from fatty acids metabolised by the process of beta oxidation that takes place inside the mitochondria.
2. The Acetyl-CoA is completely oxidised to CO2 in the citric acid cycle.
3. Takes place in the mitochondrial matrix
4. 9 products produced

Question 11

Describe the electron transport chain? (2pts)

Answer 11

1. The build up of protons in the inter membrane space generates a proton motive force consisting of a trans membrane potential and a ph gradient.
2. Chemiosmosis occurs- protons are transported back into the matrix. This flow drives the synthesis of ATP.

• NADH and FADH donate electrons to the electron transport chain.
• ATP synthase is not involved in electron transfer.

Question 12

Describe Peroxisome? (5pts)

Answer 12

1. Simple organelle
2. Single membrane bilayer
3. Do not contain their own DNA
4. Catalase is abundant in peroxisomes. It is the enzyme which detoxifies hydrogen peroxide.
5. Peroxisomes like mitochondria divide in peroxisomal fission using proteins. Some proteins are used in both mitochondrial fission and peroxisomal fission.

Question 13

Describe the function of peroxisomes? (3pts)

Answer 13

1. Peroxisomes are able to break down long chain fatty acids and take them up and metabolise them inside the peroxisomes.
2. Detoxification of hydrogen peroxide- hydrogen peroxide can react with and damage macromolecules such as DNA and proteins. This causes cellular dysfunction and contributes to the ageing process. catalyse used to do this.
3. Metabolism of bile acids- important in digestion and synthesis of cholesterol.

Question 14

What are shared features of mitochondria and peroxisomes? (3pts)

Answer 14

1. Both are important in cellular metabolism especially metabolism off fatty acids.
2. Both divide in fission- proteins required for division are located on the outside of both mitochondria and peroxisomes.
3. Anti-viral signalling- found on the outer membrane of mitochondria and peroxisomes.

Question 15

Why are Mitochondrial disorders more severe?

Answer 15

caused by mutations in DNA