BCH3021 Lecture Notes - Lecture 9: Mendelian Inheritance, Cycloheximide, Nuclear Dna
Lecture 9 – Molecular Biology of Mitochondria
Origin o Mitochondrion
• Endosymbiotic Theory
o Originated from anaerobic cell derived from an archaeon
o Cell engulfs aerobic bacterium (atmospheric O2 increases)
▪ Loss of membrane from archael cell → mitochondria with
double membranes
Cooperative Synthesis of Mitochondria
• Cooperation with nuclear encoded genes
• Mitochondria contains 1000 different types of protein
o ~2% of proteins (13) are encoded within
mitochondrial – protein synthesis
▪ Encoded in human mtDNA
▪ Mitochondria has DNA and apparatus
for replication transcription and protein
synthesis
o Remaining 98% undergo cytosolic protein
synthesis
▪ Imported from cytosol
• Nucleus: genomic DNA → RNA
• Protein import is unidirectional
• Antibiotics
o Chloramphenicol – inhibits translational apparatus of ribosomes for
mitochondria
o Cycloheximide – inhibits cytosolic ribosome apparatus
• Genetic Evidence Supporting Idea of co-operative synthesis
o Genetic evidence
▪ Cytoplasmic inheritance:
• Studies in yeast: extra-nuclear modes of inheritance of
mutations affecting OXPHOS activities
• Yeast cells deficient for Oxphos (form petite colonoies)
• Can’t grow using ethanol as carbon source – can use
glucose
• Mating by cell fusion to form diploid zygote (from
haploid) is followed by meiotic division (sporulation) to
form only Oxphos competent cells
▪ Mendelian inheritance of nuclear chromosomal mutations that
affect mitochondrial function
• Indicates wild type mtDNA and mutant mtDNA can
complement one another when in same cell
o Biochemical evidence
▪ Mitochondrial DNA not isolated until 1960s
▪ DNA detected in isolated mitochondria
• Small circular DNA molecules (mammals)
• Replicative forms observed
▪ RNA synthesis detected in isolated mitochondria
▪ Protein synthesis detected in isolated mitochondria (in vitro)
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Document Summary
Origin o mitochondrion: endosymbiotic theory, originated from anaerobic cell derived from an archaeon, cell engulfs aerobic bacterium (atmospheric o2 increases, loss of membrane from archael cell mitochondria with double membranes. Random segregation: mitochondrial dna segregates randomly, cells bearing both normal and mutant mtdna, random distribution of mitochondria and mtdna indicates non-mendelian genetics. Visualisation of mtdna in euglena cell: cells treated with two dyes, ethidium bromide (red dna binding dye, nucleus fluoresces red, dioc6 (green dye) presence of mtdna, yellow dots (overlay of red and green) mitochondrial dna. Number of mtdna molecules per mitochondrion varies due to fusion and fission of. Organelles: each mitochondria must have its own mtdna, mtdna exists as cllusers in nucleoids, replicates throughout cell cycle (unlike nuclear dna, particular genome replicated is random, total mtdna doulbes before cell dividsion. Coding of mitochondrial gene products: products of human mtdna: all directed towards formation or function of.
