Biology 1002B Lecture Notes - Lecture 11: Prokaryote, Transfer Rna, Genetic Drift

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Published on 15 Apr 2013
School
Western University
Department
Biology
Course
Biology 1002B
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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
o Nuclear DNA can do sexual recombination, to generate
diversity
Why haven’t ALL organelle genes moved to the nucleus? Why would they stay?
o Maybe They need local control
o Maybe it takes too much time or too hard to transfer (transport)
o Maybe they’re too big to move
o Maybe the structure might not work in the nucleus
o The general environment in the organelles are prokaryotic environment, the
environment in nucleus is eukaryotic
o Maybe it is just chance, genetic drift
o Maybe there is not enough time yet
“Solar-powered” sea slugs steal chloroplasts from algae
o They eat the algae when they are little, they suck the algae guts
o Elysia takes the chloroplasts from Vaucheria, to in-cooperate them into its body
o It becomes an autotrophic organism, lives of the energy from the sun
o It lives on 10 months, on chloroplast
o Organelle protein complexes are coded from nucleus and some from organelle, coded
by different genomes
o Mystery that it can keep it going, keep the chloroplast
Gene structure/Expression
DNA sequence as music…
o Turn AT, CG into music notes and stuff…, amino acids are base lines
The yellow picture of double helix DNA
mRNA pairs with itself, it complementary base pairs with itself (mRNA and mRNA)
tRNA base pairs with itself
o it pairs with itself complementarily, to get to the functional structure
tRNA pairs with mRNA
ribosomal RNA (orange) base pairs with itself and is catalytic
o rRNA and rRNA pairs with self to form ribozymes to be catalytic
protein: DNA polymerase
o genes for DNA polymerase figured out a way to replicate itself
o gene codes for a protein to make more of the gene
o very important in the evolution in genomes
DNA 3’ -> 5’
o RNA 5’ -> 3’
o Codons 5’ -> 3’
Promoter
o What part of the cell understands promoters?
Prokaryotes RNA polymerase understands promoter
It binds to the promoter and begin replication or transcription
RNA polymerase goes from 3’ -> 5’ so mRNA is made from 5’ -> 3’
Stop codons stop translation, does not stop transcription
o RNA polymerase does not understand genetic code, it just copies it

Document Summary

Modern chlamydomonas cell have three different genomes : nuclear, mitochondrial and chloroplast genomes. Modern endoymbiont genomes are greatly diminished : nucleus: 120 000 kb, biggest, mitochondrion: 16 kb, smallest, 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: 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: only about a dozen proteins, why the genome have 37 genes only a dozen proteins. Why are there disconnect from number of genes to number of proteins: maybe they"re not protein coding genes. What do they code for? trna, rrna, rna. All rna are made by transcription of genes. From 5000 to 37 genes, why would cell want it"s mtdna to nucleus.