EuchromatinLoose to allow txn or replication

HeterochromatinWound tightly to preventLose of DNA during celldivision

telomere

Chromosomes have two key structures also:centromere- indented region-can be telocentric, acrocentric, metacentric…helps to id chromosomesunder a microscope

telomere- structured ends that help to prevent DNA ends breaking-off when it’s dragged around a cell

Both are constitutively heterochormatinizedand contain repeated NT sequences

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 helixIn 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 replicated-

A process called “replication”

The general scheme…There are many more proteins involvedWe 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 needs1) dNTPs2) template DNA3) available 3’ end

In transcription,RNA polymerase Also works in a 5’ to 3’ direction

Mutation Types:

Many types1) silent- substitutionthat causes no change in aminoAcid b/c of genetic code’s redundancy

2) substitution- change (chg) that chgsthe amino acid

3) Base deletion-Chgs the reading frame so chgs aminoacid sequence of protein

4) Base insertion-Chgs the reading frame (result as above)