Euchromatin Loose to allow txn or replication Heterochromatin Wound tightly to preve Lose of DNA during cel 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
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Euchromatin Loose to allow txn or replication Heterochromatin Wound tightly to prevent Lose of DNA during cell division telomere Chromosomes have two key.
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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)