6 - Mitochondrial Genetics

Question 1

Mitochondria

Answer 1

• Support most of the activities of our cells
• Have different shapes in diverse cell types and organs
• Number of mitochondria differ between organs and cell types (depending on energy requirements)
• Form reticular networks through which they communicate
• Undergo fusion and fission

Question 2

Mitochondrial genetic material

Answer 2

Called mtDNA and have their own machinery for its expression

Question 3

Four compartments of mitochondria

Answer 3

• Outer membrane
• Inner membrane
• Inner membrane space
• Matrix

Question 4

Mitochondria functions

Answer 4

• Regulate cell death
• Ion homeostasis
• Fat and carb metabolism
• Hormone and steroid production
• ROS defense and production
• Cell signaling
• Redox regulation

Question 5

5 respiratory complexes found in mitochondria

Answer 5

• Complex 1: NADH dehydrogenase
• Complex 2: Succinate dehydrogenase
• Complex 3: Cytochrome bc1 complex
• Complex 4: Cytochrome c oxidase
• Complex 5: ATP Synthase

Question 6

What drives oxidative phosphorylation

Answer 6

Proton motive force (membrane potential x charge difference of pH gradient between inside and outside of matrix)

Question 7

Where does oxidative phosphorylation take place in the mitochondria

Answer 7

inner mitochondrial membrane

Question 8

Mitochondrial DNA

Answer 8

• Circular, dsDNA
• Maternally inherited
• Exclusively encodes membrane proteins
• Compact genome, virtually no non-coding sequences within genes

Question 9

D loop

Answer 9

• Contains regulatory elements for transcription and replication
• Can be used to define phylogenetic relationships between species or define breeding populations

Question 10

Mitochondrial mRNAs

Answer 10

• “naked” start codons (no introns)
• 5’ caps
• Most lack 5’ and 3’ UTRs
• 2 mRNAs are bicistronic
• 10 mRNAs have poly (A) tails
• Translated by mitochondrial ribosomes
• There is variation in the abundance of mt-mRNA levels between different tissues and within individual tissues

Question 11

Non universal genetic code

Answer 11

• AUA is a start (instead of Ile)
• UGA is Trp (not stop)
• AGA and AGG are stop (not Arg)

Question 12

Enzymes that carry out processing of mtDNA

Answer 12

RNase P and RNase Z

Question 13

Mitoribosome

Answer 13

A molecular machine composed of mitochondrial ribosomes and proteins

Question 14

Mt-rRNA

Answer 14

2 rRNAs (12S and 16S that form the small 28S ribosomal subunit and the large 39S ribosomal subunit)

Question 15

Mitochondrial ribosomes

Answer 15

• Reduces rRNA content
• Increased protein content
• Recognize “naked” start codons
• Exclusively translate membrane proteins

Question 16

Mitochondrial tRNAs

Answer 16

• Full complement required for translation of the 13
  polypeptides
• 60 sense codons for 22 tRNAs
• Different classes of tRNAs (type 1-4)
• Modified nucleotides
• Wobble bases
• Mutations in tRNA genes cause defects in protein synthesis and lead to disease

Question 17

Mitochondrial rRNA modifications

Answer 17

• 16 species of modified nucleosides
• 3 mitochondria-specific modifications
• f 5 C is required to recognize the non-universal AUA codon in addition to the AUG codon

Question 18

Mitochrondrial long non coding RNAs

Answer 18

• Prevent translation or pause translation by forming duplexes
• Highly abundant
• Produced by RNase P

Question 19

Regulation of mitochondrial gene expression

Answer 19

• Entire genome transcribed
• Everything encoded on one large polycistronic transcript
• Regulation of RNA stability, translation efficiency, and amount of respiratory proteins produced occurs after has been RNA produced