Lecture 15- The genomes of chloroplasts and mitochondria Flashcards
correns and bauer
documented non-mendelian inheritance in plants- mutation only being present if it is in the female
example of cytoplasmic inheritance
yeast ‘petite’ mutants (less able to grow due to issues with phosphorylation) seemed to have non-mendelian inheritance, due to the trait being related to defective mitochondria
rough percentage of mitochondrial/other cytoplasmic genes encoded in the nucleus
90%
what are these nucleus-encoded mit genes called?
semi-autonomous
example of size variation in mtDNA
16.6kb human vs over 500 in some plants
correlation of mtDNA with nuclear genome size
none
examples of some features of mtDNA
○ Small, gene-dense, circular DNA
○ Lack chromosome features, exist as nucleoids
○ Multiple copies per organelle and often multiple organelles per cell
○ Prokaryotic machinery for transcription/translation
○ Some genes transcribed together from polycistronic RNAs
○ Introns are different- group I or II rather than spliceosomal
○ Genetic code may differ from the standard code
Organelle transcripts csn be subject to RNA editing
proteins involved in the initiation complex for mtDNA
POLRMT, a bacterial type RNAP
TFAM (first) and TF2B (after polymerase) transcription factors
polycistronic RNA
strand which encodes multiple proteins- mitochondrial genomes are heavy with these
mitroribosomes- features
specialised to deal with hydrophobic OxPhos genes, but are otherwise similar to those in bacteria- 55S in mammals but this varies
what are nucleoids/how do they form
DNA packaging using TFAM molecules rather than histones for compaction
features of mitochondrial genomes
AT rich, differences in codon usage, high amounts of editing- especially C to U- which can help create start codons, eliminate premature stop codons etc
mutation rate in plant mtDNA
low- 16x lower than in nuclear genes
mutation rate in animal mtDNA
1-2x higher than nuclear DNA
what is responsible for the low mtDNA mutation rate in plant organelles
MSH1, a MutS homolog which corrects DNA errors very effectively
