Mitochondria and Peroxisomes

Question 1

Describe the structure of a mitochondrion.

Answer 1

It has 2 membranes and is usually rod-shaped.
The INNER MEMBRANE is folded into cristae, which project inwards, increasing the surface area of the inner membrane and the ATP Synthase (where ATP is generated).
The space inside the inner membrane is called the matrix, and the space between the membranes is called the intermembrane space.

Question 2

Describe mitochondrial DNA (mtDNA).

Answer 2

Mitochondrial chromosomes are circular, as they are in bacteria. Mitochondrial genes are inherited cytoplasmically. MtDNA is located in the matrix. The mitochondrial genetic code differs from the standard nuclear code.
The mitochondria also contain their own ribosomes and make some of their own proteins. Other mitochondrial proteins are encoded in the nucleus, translated in the cytoplasm and imported into the mitochondria.

Question 3

List some functions of the mitochondria.

Answer 3

• breakdown of fatty acids to Acetyl CoA
• decarboxylation of pyruvate to Acetyl CoA
• citric acid cycle (pivotal metabolic pathway generating reducing equivalents for ATP generation and metabolic intermediates for anabolic pathways)
• oxidative phosphorylation (formation of ATP and water from ADP, Pi, reducing equivalents and O2)
• thermogenesis (generation of heat)
• mitochondria play an important signaling role in cell apoptosis (programmed cell death)

Question 4

What causes Beriberi?

Answer 4

Beriberi is a Vit B1 deficiency, also known as thiamine deficiency.
Thiamine pyrophosphate is a prosthetic group for two mitochondrial enzymes: pyruvate dehydrogenase and α-ketoglutarate dehydrogenase.
Patients suffering from Beriberi have a higher than normal serum levels of pyruvate and α-ketoglutarate.

Question 5

What are some symptoms of Beriberi?

Answer 5

• damage to the peripheral nervous system
• pain in the limbs
• weakness of the musculature
• distorted skin sensation
• the heart may be enlarged and cardiac output inadequate

Question 6

Describe the structure of peroxisomes.

Answer 6

They are approximately 0.1-1 μm in diameter. They’re surrounded by a single lipid bilayer membrane. They contain no DNA or ribosomes (meaning they do not make the proteins that they contain, they instead acquire them).

Question 7

Where do we get peroxisomal proteins from?

Answer 7

The peroxisomal proteins are encoded in the nucleus, synthesised in the cytoplasm and imported (some peroxisomal membrane proteins originate in the ER). They contain a Peroxisomal Targeting Signal (PTS) which binds to a receptor molecule that takes the protein into the peroxisome.

Question 8

List some functions of peroxisomes.

Answer 8

• contain enzymes that use molecular oxygen to oxidise various substances
• produce hydrogen peroxide (H2O2), which is broken down to water by catalase
• important in the breakdown (by oxidation) of excess long-chain fatty acids
• play a role in the production of cholesterol and phospholipids