Lecture 33

Question 1

Oocyte vs sperm cytoplasmic factor

Answer 1

The oocyte is much much bigger than the sperm, carries the same amount of DNA but cytoplasmically theres much more in the oocyte, meaning that most cytoplasmic factors are provided by the mother, oocyte, at least until the zygote is more established
Cytoplasm includes things like mRNA, organelles like mitochondria, etc

Question 2

Organelle vs cellular replication

Answer 2

These processes are not synced, organelle is mitochondria or chloroplast, in either case they do not divide and replicate at the same time as the cellular DNA does, happens randomly

Question 3

How many mitochondria per cell

Answer 3

Dozens to hundreds, depending on cell type and energy demands, and they each contain multiple copies of the mitochondrial DNA
About 37 genes encoded, 13 polypeptides, 13 involved in electron transport chain and the others are exported out

Question 4

Mitochondrial proteins

Answer 4

Only about 37 genes in mitochondrial genome, 13 polypeptides, 13 proteins end up in electron transport chain
Majority these proteins in mitochondria are translated in cytoplasm and then imported back in

Question 5

Cytoplasmic inheritance of mitochondria

Answer 5

Mitochondria are inherited by the maternal cell, even though the sperm does contribute some
A little bit after fusion, the zygote undergoes a process that destroys the paternal mitochondria, there are only a few and they are actively eliminated
Evolutionary reason unclear
Note that the cytoplasmic inheritance implies random segregation to daughter cells, distribution being more or less even

Question 6

What is heteroplasmy

Answer 6

Idea that there can be 2 or more unique populations of mitochondria within a single cell, even if they all came from mom, due to mutations
Mitochondrial DNA is much more prone to mutation and does not have DNA repair mechanisms, also more frequently replicated so that doesnt help
Can lead to different phenotypes

Question 7

Homoplasmic cells

Answer 7

Cells that have all the same kind of mitochondrial DNA, no diversity, normal, all the same phenotype

Question 8

What causes variegation in plants

Answer 8

Light and normal green patches on stems and leaves, phenotypes from having different chloroplasts (equivalent to mitochondria) so some chloroplasts are homoplasmic dark, homoplasmic light, others heteroplasmic aka variegated and are spotted

Question 9

What are the key landmarks of human pedigrees for mitochondrial diseases

Answer 9

Any mother with the disease is affected, all of her children will be affected, and the children of any of her daughters will be affected
Note: children of affected men will not be affected, their mitochondria arent kept in future offspring
Note: if a mother is heteroplasmic and has enough unaffected mitochondria, it is possible for her to have an unaffected child, but that would be the exception

Question 10

Pronuclear transfers

Answer 10

A way to prevent mitochondrial diseases by using a donor egg, but not in the normal way
The egg is fertilized, we get a zygote with the pronucleus, but that maternal mitochondria are no good, so we get a donor egg, remove its genetic info, replace it with the zygotes genetic info, and implant it
So technically theres 3 parents, donor mitochondria will stay, mother and father DNA