DNA History

and StructureEssential Question:

What is the overall structure of DNA

Where is DNA located in the Cell?

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DNA

• DNA is often called the blueprint of life.

• DNA contains the instructions for making proteins within the cell.

DNA(deoxyribonucleic acid)

Functions

1. Storage of genetic information2. Expression of the genetic message (information). 3. Self-duplicate (replicates itself)

DNA’s major function is to code for proteins.

• By the early 1900’s it was known that the chromosomes carry the genetic information

• Chromosomes consist of DNA (deoxyribonucleic acid)

Discovery of DNA

Discovery of DNA

- Watson & Crick proposed a model of DNA shape

- won Nobel Prize in 1962

Discovery of DNA- Rosalind Franklin produced X ray

photographs of DNA

- helped Watson and Crick develop their model

- Did NOT win Nobel Prize for her work

Watson and Crick’s Double Helix Model explained:

1. How replication of DNA during mitosis produces exact copies for the daughter cells.

2. The double helix structure, two nucleotide strands are antiparallel (complementary).

3. How DNA acts as a code, specifying how proteins are made by the cell.

Structure of DNA

Structure of DNA

• DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.

• A molecule of DNA is made up of millions of tiny subunits (monomers) called Nucleotides.

• Each nucleotide consists of:1. Phosphate group2. Pentose sugar3. Nitrogenous base

Nucleotides

Phosphate

Deoxy-Ribose sugar

NitrogenBase

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The Double Helix Molecule

• The DNA double helix has two strands twisted together.

Four Nucleotides

A

Adenine

T

Thymine

G

Guanine

C

Cytosine

Structure of DNA

- 4 different nucleotides are used to make the DNA molecule

- Adenine (A)

- Guanine (G)

- Cytosine (C)

- Thymine (T)

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Types of Bases

• Double ring PURINESAdenine (A)Guanine (G)

• Single ring PYRIMIDINESThymine (T)Cytosine (C)

T or C

A or G

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Structure of DNA

- held together by hydrogen bonds

- pairing rules:

A binds with T

G binds with C

Chargaff’s Rule:

• Adenine and Thymine always join together, base pairing

A T• Cytosine and Guanine always join

together, base pairingC G

Base-Pairings• Purines only pair with

Pyrimidines• Guanine & Cytosine

CG

3 H-bonds

T A

Adenine & Thymine

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One Strand of DNA• The backbone of

the molecule is alternating phosphates and deoxyribose sugars

• The nitrogenous bases are inside of the double helix.

phosphate

deoxyribose

bases

G

G

A

T

T

A

A

C

T

G

C

A

T

C

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Complementary Base Pairing

• the order of the bases in one strand determines the order of the bases in the other strand.

• DNA has two strands that fit together like a zipper.