Mitochondria + Peroxisomes

Question 1

Describe the structure of mitochondria?

Answer 1

2 membranes=> inner + outer membrane
Between the 2 membranes are called the intermembrane space
Inner membrane form Cristae
Matrix- inner most space

Question 2

Mitochondrial morphology changes during:

Answer 2

Apoptosis= cell death
Ca2+ transfer
Cell cycle
Nutrient starvation- mitochondria elongates

Question 3

Mitochondria contain their own DNA

Answer 3

Mitochondria chromosome are circular in bacteria
Mitochondrial genes are inherited cytoplasmically from mother
Mitochondrial DNA (mtDNA) is located matrix
Mitochondria contain their own ribosomes
Other mitochondrial proteins are encoded in nucleus, translated in cytoplasm + imported into mitochondria
Mitochondrial genetic code differed from standard nuclear code

Question 4

Describe the endosymbiosis theory for origin of mitochondria?

Answer 4

Mitochondria evolved from ancient bacteria
Got incorporated into cells when eukaryotic cells evolved
Aerobic bacteria is taken by ancestral anaerobic eukaryote + then it multiples
Aerobic metabolism uses O2 that can break down nutrient molecules much more efficiently thereby generates vastly more ATP than anaerobic bacterium would have been able to produce

Question 5

What are functions of mitochondria?

Answer 5

Breakdown of fatty acids into acetyl coA which takes place in matrix
Decarboxylation of pyruvate into acetyl coA which is important in metabolism
Citric acid cycle
Oxidative phosphorylation
Thermogenesis=> generation of heat. Important in hibernating animals
Play a role during apoptosis

Question 6

Localisation of mitochondria near sites of high ATP utilisation

Answer 6

Cardiac muscle=> within muscle fibres are mitochondria. Muscle contraction requires ATP
Sperm cell=> ATP is required for sperm cell to rotate, to have motility so they can move. Mitochondria is wrapped around flagellar axoneme

Question 7

What is the disease Beriberi?

Answer 7

Caused by dietary deficiency thiamine (vitamin B1)
Is neurologic + cardiovascular disorder
Thiamine pyrophosphate => prosthetic group for 2 mitochondrial enzymes
Substrates of enzyme accumulate in patients suffering from disease

Question 8

What are effect of Beriberi on patients?

Answer 8

Damage to peripheral nervous system 
Pain in limbs 
Weakness of musculature 
Distorted skin sensation 
Heart may be enlarged + cardiac output inadequate

Question 9

What are peroxisomes?

Answer 9

Extremely rich, highly concentrated enzymes that carry specific aspects of oxidative reactions, metabolism. Concentration may be so high that proteins form crystals

Question 10

Describe the structure of peroxisomes?

Answer 10

Approximately 0.2-1 um in diameter
Are surrounded by single membrane
Contain no DNA or ribosomes
Most peroxisomal proteins encoded in nucleus, translated in cytoplasm + then imported
At least some peroxisomal membrane proteins originate in ER
All peroxisomes contain enzymes that use molecular oxygen to oxidise various substrates
Reactions produce hydrogen peroxide which is broken to water by enzyme catalase

Question 11

What is function of peroxisomes?

Answer 11

Important for metabolism of long-chain fatty acids
Perform critical steps in synthesis of certain lipids e.g. cholesterol
Breakdown of excess purines (AMP, GMP) to Uric acid