BIOL 201 Lecture Notes - Lecture 5: Meiosis, Superoxide Dismutase, Outer Perimeter
Mitochondria are not rugby balls: form complex tubular networks
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Most are fused together in cells and undergo fusion and fission events during mitosis (facilitates transmission)
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Most eukaryotic cells contain many mitochondria, which may be fused to one another and may collectively
occupy as much as 25 percent of the volume of the cytoplasm.
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The numbers of mitochondria in a cell are regulated to match the cell’s requirements for ATP
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Participate in a wide variety of cellular processes, not just ATP production
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Outer membrane = smooth outer perimeter
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boundary membrane (flat membrane immediately adjacent to outer)
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Cristae: invaginations that extend from boundary towards interior
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Connections between them are cristae junctions
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Inner membrane has 3 domains
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MICOS ( mitochondrial contact site and cristae
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organizing system) are diffusion barrier preventing mixing of proteins and lipids in boundary and cristae
invaginating cristae expand the surface area of the inner membrane, hence the mitochondrion’s capacity
to synthesize ATP.
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Each mitochondrion has two distinct, concentric membranes: the inner and outer mitochondrial membranes.
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Composed of intermembrane space (between the outer and inner membranes) and the matrix (lumen within the
inner membrane)
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Behold! The Mitochondria
Aerobic respiration as the putative drive for endosymbiosis
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Engulfment of aerobic bacteria (capable of oxidative phosphorylation, eg. Creb's cycle
and ETC) by anaerobic cell
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Behave like independent organisms, but is that proof of anything?
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Mitochondria make their own ribosomes, segregate their own DNA, etc
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"Origin of Mitosing Cells" rejected by 15 papers before publishing
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Endosymbiosis was controversial
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Aerobic proto-eukaryote with cristae like surface that enlarged and engulfed its
respiratory surfaces
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Central counter: host was already aerobic, what would be the benefit
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We now know that the ancestor knew how to perform aerobic respiration,
but ate the prokaryote anyway?
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What was the alternative hypothesis to endosymbiosis?
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Sequence of superoxide dismutase (mitochondrial enzyme)
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Conservation of sequence between mitochondrial enzyme and that of bacterial
E.coli enzyme
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1981: complete sequence of human mitochondrial genome, showed that it
clearly had prokaryotic origin
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Sequence analysis carried the day for Endosymbiosis
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Mitochondria were bacteria once
Energetics of genome complexity: number of genes carried by an organism
has energy cost associated with it, to produce more proteins, etc.
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Eukaryote has much larger number of watts per haploid genome
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Prokaryotes have very small genomes, much smaller than that of
eukaryotes
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Evolutionary advantage gained by endosymbiosis
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Hypothesis: Mitochondria increased Power per gene, enabled explosion in
genome complexity and had enough power to become sophisticated
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Evolution of metabolism much more complex than that of recent evolution
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Can be used to determine whether a gene encodes mitochondrial or
cytoplasmic protein
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Mitochondria have their own genetic code: codons read differently than in
standard genetic code
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Most mitochondrial components are encoded by the nucleus (blue);
those highlighted in pink are encoded by mtDNA in some eukaryotes
but by the nuclear genome in other eukaryotes, whereas a small
portion are invariably
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specified by mtDNA (purple).
Most genes in mitochondrial genome have transitioned into nucleus
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Nuclear genes translated by cytoplasmic ribosomes, but are
transported back into mitos
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Mitochondrial proteins are built from a combination of nuclear and mtDNA
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So why did endosymbiosis occur?
The petite mutation in yeast is a model for mtDNA inheritance
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When mutations in mtDNA are found, cells contain mixtures of wild-
type and mutant mtDNAs (heteroplasmy)
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Petite cells occur by chance due to the random segregation of
mtDNA
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Creates different mode of inheritance
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When cells propagate petite is lost due to dominance of
normal phenotype
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Mitos who DNA is carrying a mutation will mix with normal
mitochondria when haploid cells mated
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Mutations in mtDNA segregate differently
Lecture 5: Mitochondria
January 19, 2018
10:30 AM
Section 1 Page 1
Document Summary
Mitochondria are not rugby balls: form complex tubular networks. Most are fused together in cells and undergo fusion and fission events during mitosis (facilitates transmission) Most eukaryotic cells contain many mitochondria, which may be fused to one another and may collectively occupy as much as 25 percent of the volume of the cytoplasm. The (cid:374)u(cid:373)(cid:271)e(cid:396)s of (cid:373)ito(cid:272)ho(cid:374)d(cid:396)ia i(cid:374) a (cid:272)ell a(cid:396)e (cid:396)egulated to (cid:373)at(cid:272)h the (cid:272)ell"s (cid:396)e(cid:395)ui(cid:396)e(cid:373)e(cid:374)ts fo(cid:396) atp. Participate in a wide variety of cellular processes, not just atp production. Each mitochondrion has two distinct, concentric membranes: the inner and outer mitochondrial membranes. Inner membrane has 3 domains boundary membrane (flat membrane immediately adjacent to outer) Cristae: invaginations that extend from boundary towards interior. Micos ( mitochondrial contact site and cristae organizing system) are diffusion barrier preventing mixing of proteins and lipids in boundary and cristae i(cid:374)vagi(cid:374)ati(cid:374)g (cid:272)(cid:396)istae e(cid:454)pa(cid:374)d the su(cid:396)fa(cid:272)e a(cid:396)ea of the i(cid:374)(cid:374)e(cid:396) (cid:373)e(cid:373)(cid:271)(cid:396)a(cid:374)e, he(cid:374)(cid:272)e the (cid:373)ito(cid:272)ho(cid:374)d(cid:396)io(cid:374)"s (cid:272)apa(cid:272)it(cid:455) to synthesize atp.
