Lecture 11: Intro to Prokaryotic Gene Structure
The evolutionary process of endosymbiosis created organisms
with typically "prokaryotic" genes in organelles and typically
"eukaryotic" genes in the nucleus. Wow.
relative sizes of typical mitochondrial, chloroplast and nuclear genomes
- Mitochondrion – small genome (16kb)
- Chloroplast – pretty small genome (200kb)
o Circular chromosomes present in many copies of chromosomes in each organelle
- Nucleus – very large genome (120 000kb)
- If genes don’t code for proteins (mRNA) they are coding for tRNA and rRNA.
rubisco structure and assembly from components coded by different genomes
possible reasons why modern organelle genomes have become dramatically smaller over evolutionary time
- Evolved to be very specific – only carry out certain processes – don’t need anymore genes.
- Genes have moved to nucleus – so there is no need for it to be in organelles anymore – no redundancy.
- Genes have been deleted - organelles can afford to lose genes.
o Genes that are useful for free-living bacteria but not for mito (e.g. flagella coding genes)
o Hexokynase, glycolysis genes not needed in mito anymore
- Hosts that have suffered a mutation/deletion of genes – are at a favorable advantage – delete genes in organelles that are
not needed there anymore - reduces energy use
- Selection favoring organelles getting rid of all genes they can.
o Lateral gene transfer
possible reasons why genes have moved to the nucleus from organelles over evolutionary time
- Nucleus can have more control.
- Part of subverted cellular rejection system.
- Organelles involved in electron transport and ox metabolism that generates ROS (oxygen + electron) – ROS very reactive
o Get DNA out of organelles to get away from mutation
- What can nuclear DNA do that organelle DNA can’t? Sexual recombination
o Generates diversity
possible reasons why certain genes have not moved to the nucleus from organelles