DNA and Replication

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Helix

Most DNA has a right-hand twist with 10 base pairs in a complete turn

Left twisted DNA is called Z-DNA or southpaw DNA

Hot spots occur where right and left twisted DNA meet producing mutations

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DNA

Stands for Deoxyribonucleic acid

Made up of subunits called nucleotides

Nucleotide made of:

1. Phosphate group

2. 5-carbon sugar

3. Nitrogenous base

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DNA Nucleotide

O

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Pentose Sugar

Carbons are numbered clockwise 1’ to 5’

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DNA

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Antiparallel Strands

One strand of DNA goes from 5’ to 3’ (sugars)

The other strand is opposite in direction going 3’ to 5’ (sugars)

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Nitrogenous Bases

Double ring PURINES

Adenine (A)

Guanine (G)

Single ring PYRIMIDINES

Thymine (T)

Cytosine (C)

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Base-Pairings

Purines only pair with Pyrimidines

Three hydrogen bonds required to bond Guanine & Cytosine

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Two hydrogen bonds are required to bond Adenine & Thymine

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Question:

If there is 30% Adenine, how much Cytosine is present?

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Answer:

There would be 20% Cytosine

Adenine (30%) = Thymine (30%)

Guanine (20%) = Cytosine (20%)

Therefore, 60% A-T and 40% C-G

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DNA Replication

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Replication Facts

DNA has to be copied before a cell divides

DNA is copied during the S or synthesis phase of interphase

New cells will need identical DNA strands

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Synthesis Phase (S phase)

S phase during interphase of the cell cycle

Nucleus of eukaryotes

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DNA Replication

Begins at Origins of Replication

Two strands open forming Replication Forks (Y-shaped region)