TedED We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

TedED

The Book of YOU!

Why do we study DNA?We study DNA for

many reasons, e.g., its central

importance to all life on Earth,

medical benefits such as cures for diseases,

better food crops.

A HISTORY OF DNA

Discovery of the DNA double helix

A. Frederick Griffith – Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria (1928)

B. Rosalind Franklin - X-ray photo of DNA.

(1952)

C. Watson and Crick - described the DNA molecule from

Franklin’s X-ray.(1953)

SEE p. 292-293

Watson & Crick proposed…•DNA had specific pairing between the nitrogen bases:

ADENINE – THYMINE

CYTOSINE - GUANINE

•DNA was made of 2 long stands of nucleotides arranged in a specific way called the “Complementary Rule”

Chromosomes and DNA

Our genes are on our chromosomes.

Chromosomes are made up of a chemical called DNA.

DNA Nucleotide

OO=P-O O

Phosphate Group

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

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

One Strand of DNA

One strand of DNA is a polymer of nucleotides.

One strand of DNA has many millions of nucleotides.

nucleotide

One Strand of DNAThe backbone of the molecule is alternating phosphate and deoxyribose, a sugar, parts.

The teeth are nitrogenous bases.

phosphate

deoxyribose

bases

The Shape of the Molecule

DNA is a very long polymer.

The basic shape is like a twisted ladder or zipper.

This is called a double helix.

DNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

PURINES1. Adenine (A)

2. Guanine (G)

PYRIMIDINES3. Thymine (T)

4. Cytosine (C)

Nitrogenous Bases

T or C

A or G

Adenine must pair with Thymine

Guanine must pair with Cytosine

Their amounts in a given DNA molecule will be about the same.

Chargaff’s Rule

G CT A

BASE-PAIRINGS

CG

H-bonds

T A

Genetic Diversity…Different

arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

The Code of Life…The “code” of the chromosome is the

SPECIFIC ORDER that bases occur.

A T C G T A T G C G G…

DNA is wrapped tightly around histones and coiled tightly to form chromosomes

See p. 297