DNA Structure and Function

What is DNA?

DeoxyriboNucleic Acid

DNA is a Nucleic Acid The main job of DNA

is to make PROTEINS.

What is the function of DNA?

It is your genetic material or “program.”

Passed from cell to cell.

DNA can give clues to ancient mysteries!

Where do you find DNA?

DNA is found in the nucleus of the cell.

Our genes are on our chromosomes.

Chromosomes are made up of a chemical called DNA.

“Building Blocks” of DNA

Each nucleotide consists ofDeoxyribose (5-carbon sugar) Phosphate groupA nitrogen-containing base (A, G, T, C)

Nucleotide Structure

CH2

O

CC

C C

Sugar(deoxyribose)

NNitrogenous base (A, G, C, or T)

O=P-O O

Phosphate Group

Nitrogen Bases

Adenine (A)

Guanine (G)

Thymine (T)

Cytosine (C)

A or G

T or C

DNA Structure Watson-Crick Model

DNA is also called: The Double Helix Strands are held together by hydrogen bonds

between bases

Bases: A matches with T and C matches with G The sides of the ladder are a sugar-phosphate

backbone, while the “rungs” of the ladder are the bases.

DNA is a double strand

The four bases of DNA are:

Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

Make a copy of the following DNA Sequence:

DNA(Original): A T C G C G A A T C C A G

Copy: T A G C G C T T A G G T C

Base-Pairing Rule

DNA replication

Before mitosis and meiosis, all of the DNA in the cell must be copied or replicated

How does this happen?

newnew old old

DNA Replication Half of the

replicated DNA strand is “old” and the other half is “new”

Basepairing During Replication

• Each old strand serves as a template for the new complementary strand

DNA Replication: Fast & Accurate!

It takes E. coli <1 hour to copy 5 million base pairs in its single chromosome & divide to form 2 identical daughter cells

Human cell copies its 6 billion bases & divide into daughter cells in only few hours

Remarkably accurateonly ~1 error per 100 million bases~30 errors per cell cycle

DNA Repair

Mistakes can occur during replication Proofreading enzymes correct any

mistakes that occur during replication. DNA studies have helped us solve major

problems in history and in health. Ex. The Czar’s family in Russia, crime

scene investigation, and paternity tests.