Lecture 2: Mitochondrial Genomes

Question 1

why mitochondria lost most genes

Answer 1

less selective pressure as not necessary, no longer free living

Question 2

Plant Mitochondrial Genomes

Answer 2

• wide range in size
• circular
• up to 40 protein coding genes (ribosomal and raspatory)
• ribosomal protein content can vary- differential transfer of genes to nucleus
• gene order NOT conserved
• many introns
• large intergenic regions
• C- to U RNA editing through deamination rxn
• low rate of nucleotide substitutions
• very slow evolving
• mutations affect development

Question 3

animal mitochondrial Genomes

Answer 3

• short
• circular
• most have 13 protein genes – all respiratory proteins
• 2 rRNAs and 22 tRNAs
• NO ribosomal proteins
• NO introns and little intergenic space
• gene order conserved
• variation in genetic code
• • stop codons are changed (normal stop is not a stop)-
• high rate of nucleotide substitution

Question 4

Heteroplasmy

Answer 4

some mitochondrial genomes in a cell are normal and some are mutant
- need a threshold to cause disease

Question 5

Cyto-nuclear interactions

Answer 5

cross-talk btw mitochondrial gene expression and nuclear gene expression so complexes can form
mitochondria do not encode Transcription factors
- some TF regulate both mito and nuclear genes
- some TF regulate other TF that regulate mito genes
- also: TFA–> TFB –> Mitochondrial genes
and TFA–> nuclear encoded mitochondrial genes

Question 6

Why is animal mtDNA a desirable molecule for phylogenetic studies

Answer 6

• maternally inheritance
• no recombination
• conserved and less conserved regions
• high mutation rates to compare individuals in a population and within species

Question 7

why do mtDNA being multi-copy per cell facilitate phylogenetic studies

Answer 7

• multiple copies makes amplification easier

- lack of recombination makes tracing lineages easier

Question 8

How is maternal transmission of mtDNA accomplished

Answer 8

male mtDNA in sperm destroyed

- pre and post fertilization

Question 9

why maternal transmission maintained in mtDNA

Answer 9

• prevents spread of selfish mutations

- prevents heteroplasmy which can be linked to some diseases

Question 10

mechanism of egg-sperm mitochondrial recognition that controls uniparental inheritance

Answer 10

factor coded by maternal genome in egg and signal on outer surface of sperm that signals paternal mtDNA destruction