1. Euchromatin Loose to allow txn or replication Heterochromatin Wound tightly to prevent Lose of DNA during cell division telomere 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

2. 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….

3. 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)

4. Both of these processes (mitosis and meiosis) require DNA to be replicated- A process called “replication”

5. 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)

8. 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

9. Mutation Types: Many types 1) silent- substitution that causes no change in amino Acid b/c of genetic code’s redundancy 2) substitution- change (chg) that chgs the amino acid 3) Base deletion- Chgs the reading frame so chgs amino acid sequence of protein 4) Base insertion- Chgs the reading frame (result as above)