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Euchromatin
Loose to allow txn or
replication
Chromosomes have two key structures
also:
centromere- indented region
-can be telocentric, acrocentric,
metacentric…helps to id chromosomes
under a microscope
telomere- structured ends that help to
prevent DNA ends breaking-off when it’s
dragged around a cell
Both are constitutively heterochormatinized
and contain repeated NT sequences
telomere
Heterochromatin
Wound tightly to prevent
Lose of DNA during cell
division
Dispelling some myths…so what is a chromosome really?
-Each chromosome is really a DNA db helix….not the X-shaped structure you
normally think of….
When DNA is replicated (doubled) in a cell, you make another DNA helix
In mitosis both helices attach to each other at the centromere forming sister
chromatids….which makes the X-shaped chromosome you normally think of when
thinking about chromosomes.
The kinetochore is a complex of proteins formed at the centromere to binds the mitotic
spindle….thus allowing sister chromatids to move to be pulled to cell poles during
mitosis
When cells divide
by mitosis, each
daughter cell
receives one helix
(not one strand)
Both of these processes (mitosis and meiosis)
require DNA to be replicatedA process called “replication”
The general scheme…
There are many more proteins involved
We will discuss some but not all…
BUT THERE IS A LOT MORE GOING ON!!!
All replication needs:
DNA Polymerase (an enzyme)
And DNA Polymerase needs 3 substrates:
dNTP’s
Template
Available 3’-end (e.g. primer in PCR)
Synthesis occurs in
a 5’ to 3’ direction…
in replication
DNA polymerase needs
1) dNTPs
2) template DNA
3) available 3’ end
In transcription,
RNA polymerase
Also works in a
5’ to 3’ direction
Mutation Types:
Many types
1) silent- substitution
that causes
no change in amino
Acid b/c of genetic
code’s redundancy
2) substitutionchange (chg)
that chgs
the amino acid
3) Base deletionChgs the reading
frame so chgs amino
acid sequence of
protein
4) Base insertionChgs the reading
frame
(result as above)