5.2 - Mitochondrial genes

Question 1

what does mitochondria contain?

Answer 1

several copies of a mini-chromosome that carries 37 genes

Question 2

the inheritance patterns and mutation rates for mtDNA differ from nuclear DNA - true or false?

Answer 2

true

Question 3

why is mitochondrial inheritance maternal?

Answer 3

because the sperm head does not contain mt. the mt are instead found in the sperm midsection

Question 4

in what 6 ways does mtDNA differ from nDNA?

Answer 4

1. mtDNA does not cross over
2. mtDNA mutates faster than nDNA because fewer types of DNA repair are available & DNA-damaging O2 free radicals are produced in energy rxns
3. mt genes are not wrapped in proteins
4. mt genes are not interrupted by DNA sequences that do not encode protein
5. each mitochondrion contains several copies of the mt genome
6. mt w/ diff alleles for the gene can reside in the same cell

Question 5

What do proteins encoded by mt genes participate in?

Answer 5

protein synthesis and energy production

Question 6

what are mt diseases referred to as?

Answer 6

mitochondrial myopathies

Question 7

mt diseases can be the result of what?

Answer 7

-mutations in mt genes or mutations in nuclear genes that encode proteins that are essential for mt function

Question 8

what are common symptoms for mitochondrial diseases?

Answer 8

• fatigue, flaccid muscles, and intolerance to exercise

- muscles appear red and ragged under a light microscope

Question 9

a mutation in a mitochondrial gene that encodes tRNA or rRNA leads to what?

Answer 9

impairment of organelle’s general ability to manufacture proteins

Question 10

How can mt mutations be weeded out during egg formation?

Answer 10

A mitochondria mutation may disrupt energy acquisition so greatly in an oocyte that it cannot survive

Question 11

Can mitochondria donations avoid transmission of the disease to offspring?

Answer 11

Yes; the mom’s mt can be replaced w/ healthy mt from a donor

Question 12

what is heteroplasmy?

Answer 12

when a mutation is present in some mt chromosomes, but not others. Since a cell contains many mt

Question 13

How does heteroplasmy exist?

Answer 13

At each cell division, the mt are distributed at random into daughter cells. Over time, the chromosomes within a mt tend to be all WT or all mutant for a particular gene, but diff mt can have diff alleles pre-dominating

Question 14

What happens to the # of mt in maturing oocyte?

Answer 14

It drops from about 10,000 to 100

Question 15

How can a mother who does not have a mt disease pass the disease to a child?

Answer 15

Since her mt bearing mutations were either rare or not abundant in her affected cell types, she had no symptoms. But by chance, she can produce an oocyte that has mutated mt

Question 16

Severity of mt disease reflects what?

Answer 16

which tissues have cells whose mt bear the mutation

Question 17

give 2 examples of mt disease

Answer 17

Leigh syndrome and MELAS (mitochondiral myopathy encephalopathy lactic acidosis syndrome)

Question 18

What does heteroplasmy cause variance in?

Answer 18

causes variances in expressivity, especially among siblings

Question 19

why is homoplasmy - when all mt bear the mutant allele) rare?

Answer 19

because this too severely impairs protein synthesis or energy production for embryonic development to complete

Question 20

when do severe heteroplasmic diseases produce symptoms?

Answer 20

during adulthood, because it takes many cell divisions & years for a cell to receive enough mt bearing mutant alleles

Question 21

How is mtDNA useful in crime scenes?

Answer 21

it is more likely than nDNA to remain after extensive damage, because cells have many copies of it