Lecture 14 - Mitochondria

Question 1

List 4 characteristics of mitochondria.

Answer 1

1. Double membrane organelle
2. Semi-autonomous (because it contains mitochondrial DNA)
3. Compartmentalised
4. Actually forms a large network within the cell

Question 2

Can mitochondria move?

Answer 2

Yes, can move to where more energy is required e.g. in the presynaptic junction & then after can go back to the nucleus

Question 3

List 6 functions of mitochondria.

Answer 3

1. Cell growth/cycle
2. Metabolism
3. Cell signalling
4. Thermogenesis
5. Heme, AA & steroid synthesis
6. Energy production!!!!!

Question 4

Define MITOPHAGY & MITOCHONDRIAL BIOGENESIS.

Answer 4

M: removal of damaged or non-useful mitochondria
MB: production of new & healthy mitochondria
*** These processes need to balance with one another.

Question 5

Which part/s of the sperm undergoes oxidative phosphorylation? Which part/s undergo glycolysis?

Answer 5

OP: the midpiece
G: the head and tail (principle piece)

Question 6

What is a Balbani Body?

Answer 6

Yolk nucleus or the dark circular body that appears in the cytoplasm very near the nucleus during the perinuclear stage of oogenesis.
It enriches the best functioning mitochondria in the oocyte & helps in the degradation of poor mitochondria.

Question 7

When does the first mitochondrial bottleneck occur?

Answer 7

During development of the germ cells. With the help of the BB the dysfunctional mitochondria are degraded. Then when it comes time for the oocyte to be fertilised the best functioning mitochondria that are left rapidly divide.

Question 8

What allows the haploid paternal DNA to be integrated into the oocyte?

Answer 8

The acrosome reaction

Question 9

When an egg is fertilised does the fertilised egg get the paternal mitochondrial DNA?

Answer 9

No, it is retained extracellularly

Question 10

When does the second mitochondrial bottleneck occur?

Answer 10

Occurs after fertilisation

Question 11

What is the most common metabolic disease?

Answer 11

Mitochondrial disease

Question 12

What type of person does mitochondrial disease primarily target?

Answer 12

Any age :(

Question 13

Where are first symptoms of mitochondrial disease shown?

Answer 13

The muscles & brain (these require the most energy)

Question 14

Out of the 37 mitDNA seuqences known, how many are associated with mitochondrial disease?

Answer 14

35 of the 37! Therefore very large potential for this disease

Question 15

Can mitochondrial disease be inherited from your mother or father? Or both?

Answer 15

Only mother - at fertilisation the paternal DNA stays outside the cell

Question 16

What are some symptoms of mitochondrial disease seen in children?

Answer 16

Seizures, lactic acidosis, failure to thrive, motor regression, cognitive impairment

Question 17

What are some symptoms of mitochondrial disease seen in adults?

Answer 17

Visual problems, muscle weakness, fatigue, deafness, blindness, diabetes, stroke-like episodes

Question 18

What is zygosity?

Answer 18

Similarity of the alleles. Either homozygous or heterozygous.

Question 19

What is plasmy?

Answer 19

Either heteroplasmy (some mitochondrial DNA that is mutated & some that is not) OR homoplasmy (either all mutated or all normal)

Question 20

What is the “threshold effect”?

Answer 20

You have to meet a certain number of mutated genome for a disease to manifest. This threshold is variable e.g. can have 25% mutation but experience no symptoms because threshold is 50%

Question 21

How does mitochondrial disease affect both males and females in term of fertility?

Answer 21

• Females: primary ovarian failure
• Males: azoospermia
  Why? gametogenesis & fertilisation are very energy dependent processes. Respiratory dysfunction (v common in mit. disease) likely impedes these processes.
  Likely though that the person dies before reaching sexual maturity.

Question 22

What are 2 ways to test/ensure your growing baby doesn’t have mit. disease?

Answer 22

1. Prenatal Genetic Diagnosis - do a test to see if the baby has it before it is born
2. Preimplantation Genetic Diagnosis - only insert the non-mutant fertilised eggs

Question 23

What does mitochondrial replacement therapy involve?

Answer 23

Getting a donor egg (which doesn’t have mutant mitochondria) & taking out the nucleus and replacing it with the oocyte nucleus from the person who does have lots of mutant mitochondria.