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MEDS2003
Molecular Biology
The Eukaryotic Genome
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Madi Smith
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The human genome has
22
pairs of autosomes and 1 pair of
sex
chromosomes
The X chromosome is
bigger
than the Y chromosome
Eukaryotes have a huge
genome
, but only a small proportion of it codes for
proteins
centromeres and
telomeres
have highly
repetitive
sequences
We can look at the variable number tandem
repeats
in a repetitive sequence through
PCR
Most protein-coding genes only have
one
copy
Gene families come from
duplication
of a
single
gene
Gene families
have
similar
sequence and function
the
globin family is a
gene
family
DNA is wound around proteins called
histones
to form
nucleosomes
Histone
tails have lots of
arginine
and lysine, which are positively charged at physiological pH
histones can form electrostatic interactions with the
negative
phosphate backbone of DNA,
independent
of its sequence
Histones shield the
negative
charges of the
phosphates
, allowing DNA to bend and wrap
The ends of chromosomes contain
telomeres
to
protect
the information at the ends
Histone
restricts
transcription
The centromere
is the region where the
sister chromatids
attach
The
p arm
is the short arm of the chromosome
The
q arm
is the
long
arm of the chromosome
Chromatin
is the complex of DNA and
proteins
Condensed DNA is harder for
proteins
such as
transcription
factors to access
Heterochromatin
: More condensed, so less
transcription
is occurring
Euchromatin
: Less condensed, so more
transcription
is occurring
DNA isn't always
packed tightly
into chromosomes
Modifying
histone
tails can remove the charge, enabling
proteins
to bind
Some
proteins
can recognise modifications and interact with
histones
HATs
acetylate
lysine to remove the positive charge of the
histone
tail
HAT =
histone acetyltransferase
Acetylation
of histones causes DNA to be wound less tightly, meaning that is more accessible to initiate
transcription
Some proteins can also bind to
acetylated
lysine
HDACs reverse the
acetylation
of
histone
tails, reducing transcription
HDAC =
histone deacetylases
HMTs methylate lysine
or
arginine
on the histone tail
HMT =
histone methyltransferases
Some proteins can bind to these
methylated
residues
Histone
demethylases remove the
methyl
group from the histone tail
In specific cells, regions of the chromosome that aren't required will be
packaged tightly
and not
accessed
The packaging of
chromosomes
affects the expression of
proteins
Cells only express
proteins
relevant to their
functions
Induced
pluripotent stem cells
Modify
histones
Introduce
transcription
factors
Expression of genes required for
pluripotency