Exam 2: Mitochondria Genetics

Question 1

t/f: mitochondria and chloroplasts contian DNA

Answer 1

true

Question 2

what does mito DNA encode?

Answer 2

encodes some polypeptides used by the organelle, rRNA, and some tRNAs

Question 3

what is the endosymbiotic theory?

Answer 3

proposes an aerobic eubacterial cell were once free-living bacteria that were engulfed by anaerobic euk cell through endocytosis. The aerobic endosymbiont evolved into mitochondria and led to the evolution of modern euk cells with mitochondria and chloroplasts

Question 4

what is the evidence for the endosymbiotic theory?

Answer 4

mitochondria and chloroplasts were once free-living bacteria and both organelles are similar to eubacteria and dna sequences found within them are also similar to eubacteria

• circular dna
• no histones
• 70S ribosome

Question 5

animal mtDNA inherited most exclusively from

Answer 5

female parent; ovum contains most cytoplasm

Question 6

heteroplasmic cells

Answer 6

replicative segregation = each cell has hundreds to thousands of organelles; heteroplasmic cells = organelles segregate randomly and there is variation in the mtDNA

Question 7

why are mitochondrial dna prone to mutations

Answer 7

they don’t have efficient repair mechanisms

Question 8

DNA sequence variation in mtDNA occurs by

Answer 8

mutation; results in heteroplasmy (the presence of more than one type of organellar genome DNA)

Question 9

mutations in mtDNA results in

Answer 9

heteroplasmy (presence of more than one type of organellar genome DNA)

Question 10

traits encoded by mtDNA:

Answer 10

petite mutations in yeast (unable to grow w/ nonfermentable carbon sources like glycerol) and human diseases (MERRF, LHON, NARP, KSS, CEOP, Leigh syndrome)

Question 11

the petite phenotype results from

Answer 11

large deletion in mtDNA preventing cells from carrying out OxPhos

Question 12

compared to yeast mtDNA, human mtDNA is

Answer 12

small encodes 13 functional proteins; has no noncoding dna all functional whereas yeast have much noncoding dna

Question 13

explain this: human mtDNA, most mito genes have moved to the nucleus

Answer 13

this is a protective role but left behind is a small number of genes susceptible to defects/mutations

Question 14

t/f: most copies of mtDNA are identical

Answer 14

true; genome is pretty stable

Question 15

concept of senescence and mtDNA

Answer 15

mito is necessary for the pro-oxidant and pro-inflamm phenotype during senescence and senescence can be induced by mito biogenesis (mito biogenesis stabilizes senescence via a positive feedback loop involving ROS and the DDR (DNA damage response). thus, targeting mito reduces deleterious impact of senescence in ageing tissues

Question 16

many human genetic diseases associated with damaged mtDNA appear in middle age or later. what could be a possible reason?

Answer 16

mito is prone to accumulate mutations over TIME. the longer you live, the longer that mito has time to accumulate mutations that make them less optimal and when the level of damage reach a certain point, phenotype is presented

Question 17

pronuclear transfer in human embryos and why is it advantageous to select for a boy baby?

Answer 17

3 genomes; ovum from female w/ no mtDNA defects nucleus is taken out and nucleus added from the female with damaged mtDNA. fertilized in vitro from dad. advantageous to have a boy baby because if mutations do arise in this child, when he has babies, he will not pass on much (if at all) mtDNA

Question 18

Oxphos and mtDNA

Answer 18

Oxidative phosphorylation 
capacity declines with age; 
those with mutations in 
mtDNA start life with 
decreased oxidative 
phosphorylation capacity