BIOL 200 Lecture Notes - Ancient Dna, Field Guide, Cytochrome C Oxidase Subunit I
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Naveen Sooknanan McGill Fall 2011
1
Organellar Chromosomes and DNA Barcoding:
DNA can not only be found in the nucleus of a cell, but also in specific organelles. In animals,
DNA can be found in the mitochondria (called mitochondrial DNA or mtDNA) whereas plant
cells contain DNA within their chloroplasts (cpDNA).
Theses chromosomes are important for respiration within the mitochondria or
photosynthesis within the chloroplasts
These genes are originally free floating and were endocytosed into the cell and
incorporated into their respective organelles
These genomes resemble prokaryotic genomes in many ways
o They are circular
o They typically lack introns
o Their genetic products resemble those of prokaryotes
There are many mitochondria or chloroplasts in one cell, and each of these organelles
may contain multiple genomes
Both organelles may have been formed from an ancestral cell which endocytosed a bacterium
capable of either respiration or photosynthesis.
We are not sure if this happened once or multiple times
Some animals, like seas slugs, eat specific algae types whose chloroplasts are endocytosed by the
slug’s epidermal cells.
As a result, the slug is able to undergo photosynthesis due to the algae it consumes
Gene exchange may also occur between the mitochondrion/chloroplast and the nucleus
Nucleus genome is much larger than Organellar DNA
Gene elimination may occur, which transports genes from the nucleus to the respective
organelles
The mitochondrion and chloroplasts may also transfer genes to the nucleus
The mitochondrion has many functions, including those listed
here. Many proteins needed in these functions are produced by
the nucleus DNA and the translated products are transferred to
the mitochondrion.
Human mitochondrial DNA (mtDNA) is a circular piece of
chromosomal DNA measuring 16,569 bp in length, which is tiny
compared to a gene within the nucleus.
Proteins can be synthesised using moving in either direction by
using each strand as a template
It only contains 37 genes because most of the genes in mtDNA
underwent gene elimination and were moved to the nucleus
o As a comparison, the e. coli chromosome contains over
5000 genes
Many encode components are needed for translation
There are no introns in mtDNA (like prokaryotes)