Lecture 11: Intro to Prokaryotic Gene Structure
Devolution of eukaryotes: endomembrane and endosymbiosis
Modern Chlamydomonas cell have three different genomes…
o Nuclear, mitochondrial and chloroplast genomes
Modern endoymbiont genomes are greatly diminished…
o Nucleus: 120 000 kb, biggest
o Mitochondrion: 16 kb, smallest
o Chloroplast: 200 kb, second biggest
Mitochondrial and chloroplast are circular genomes, lots of copies of each
E. coli has about 5000 genes in about 5000 kb of circular DNA
o On average 1 gene is about 333 amino acids
Vaucheria (algae) has only 169 genes in only 115 kb of circular cpDNA (chloroplast)
Humans have only 37 genes in only 16kb of circular mtDNA (mitochondria)
o Only about a dozen proteins
o Why the genome have 37 genes only a dozen proteins
Why are there disconnect from number of genes to number of proteins?
o Maybe they’re not protein coding genes
Dead gene, not expressed
What do they code for?
tRNA, rRNA, RNA
All RNA are made by transcription of genes
Modern endosymbiont genomes are greatly diminished…
o Why? From 5000 to 37 genes, why would cell want it’s mtDNA to nucleus
What kind of genes that can be lost
Genes that the organism that they do not need anymore
o Exokinase, glycolysis genes, flagellum, don’t need get rid
o Organelles that have less genes are easier to be replicated, so that less genes it has the
it is better for them to have.
o Transfer genes to the nucleus
Why to the nucleus?
Nucleus have more control, coordinated control
They have reactive oxygen species during ETC, in the organelles, ROS is
very mutagenic, so that it makes sense to get rid of the genes to put it in
a safe place
What can DNA in nucleus that organelles can’t do?
o It can be transcribed
o Organelles have their own transcription and translation systems,
ribosomes in mitochondria and chloroplast