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Biology 1002B Lecture Notes - Electron Acceptor, Endomembrane System, Southern Blot

Course Code
BIOL 1002B
Tom Haffie

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Evolution of Eukaryotes
Formation of Endomembrane System
o Ancient prokaryotic cell
o Through gradual in-folding of plasma membrane
o Endomembrane system formed
Golgi apparatus
Nuclear envelope
Energy-Transducing Organelles
o Endosymbiosis
Prokaryotic ancestors of
mitochondria and
chloroplasts were engulfed
by larger prokaryotic cells
Formed mutually
advantageous relationship
Mitochondria came first - capable of using oxygen for aerobic respiration
Chloroplasts developed from ingested cyanobacteria
o Theory Evidence
Form or shape of both organelles is similar to prokaryotic cells
Mitochondria or chloroplasts are derived only from preexisting mitochondria and
chloroplasts divide by binary fission
Genetic Information
Both organelles contain their own DNA codes for the proteins essential for the
organelles function
Transcription & Translation
Contain a complete transcription and translational machinery enzymes and
Similar ribosomes to prokaryotic cells
Electron Transport
Can generate energy in the form of ATP through their own ETC
Driving Evolution of Eukaryotes
Earliest prokaryotes were anaerobic
2.2 bya cyanobacteria evolve
o Oxygenic photosynthesis
o Atmosphere contains oxygen
Oxygen as terminal electron acceptor
o Prokaryotes that undergo aerobic respiration
Oxygenic Phosphorylation
o More ATP
Eukaryotic Cells Are Bigger & More Complex
Endosymbiosis cells overcame energy barrier
Prokaryotic cells made enormous amounts of ATP through mitochondrion
o High plasma membrane surface area to support volume of cell
Energy supplied by plasma membrane supports volume of cell
Transporters also need enormous PM
o Don't have a lot of energy
Make less protein
o Low plasma membrane surface area to volume ratio
o ETC is in mitochondrion membrane
o More ATP = greater function
o Complexity
Processes (Proteins are linked to function)
Tissue development
Endomembrane system
Energy Required
Maintaining DNA & DNA replication
o 2% of cell energy budget
Protein Synthesis
o 75% of cell energy budget
o Lots of ATP = lots of protein = greater function & bigger genome (genes code protein)
Lateral Gene Transfer
Million years after endosymbiosis
Lots genes in both mitochondria and nucleus
Lateral Gene Transfer
o Some genes in chloroplastic genome and mitochondrion genome
have relocated into nucleus
Ex. Southern Blot (see picture)
o Species B lateral gene transfer has occurred
o Species C lateral gene transfer is occurring
o Species A lateral gene transfer has not occurred
Earliest Eukaryotes
o Very primitive eukaryotes
o Contains nucleus but lack mitochondria
o Question: did it have them and then lost them or did it not
have them at all?
o Ex. Giardia
Giardia & cpn60
cpn60 gene
o Chaperone
o Other Eukaryotes
Found in nucleus
Imported and functions in mitochondria (helps proteins fold)
o Diplomonads (Giardia)
Found in nucleus
Not in mitochondrio
o Ancestral Eukaryote
Had mitochondrion
Lateral gene transferred occur cpn60 imported into nucleus
Evidence that mitochondrion were present in diplomonads but they lost them
Rubisco Assemply
Mitochondrion & chloroplasts
o Need 3,000 genes
o Most proteins are coded by genes now in nucleus
o Some proteins are coded by both genomes
Some coded by mitochondria genome
Some coded by nuclear genome
Ex. Rubisco Assembly
8 Large Subunits (LSU)
8 Small Subunits
o Coded by different genomes
o Requires elaborate control
o Only large subunits are coded
by chloroplast genome in
o Small subunits are coded by
nuclear genome in nucleus
Imported into
o Combine to make functional protein
Evidence very strong
o Ex. Rubisco
o Has chloroplasts from Vaucheria
o Contains Rubisco
o Nuclear genome
Does it have small subunits to make Rubisco?
No evidence of nuclear genome genes of Vaucheria in the nucleus of Elysia
Unclear as to how it maintains functional chloroplasts
Reason for Lateral Gene Transfer
Can’t have free living (uncontrollable) cell in another cell
o Nuclear genome has to control overall cellular function
o Has to transfer genes to shift control
Reactive molecules (REDOX)
o Energy-transducing organelles lots of high energy electrons, powerful reductants & oxidants
o DNA sensitive to oxidation (induce
o Mitochondrion and chloroplasts can
create reactive oxygen species
Toxic molecules
Hydrogen peroxide
o Shift DNA to nucleus better protected from reactive environments
Sexual Recombination
o Only occurs in nucleus
o Chromosomes can get rid of mutations genomes can be repaired
Bacterial Genome
Why hasn't the entire genome relocated?
Bacterial genome 5, 144 genes & 4,639,625 base pairs