DNA Structure

Largely work of Rosalind Franklin that led to this discovery

Francis Crick and James Watson are credited with discovering structure of DNA

X-ray photographof DNA crystal Model of DNA

DNA (deoxyribonucleic acid) - molecule that encodes genetic information of living thingsFrancis Crick and James Watson are credited for discovering the structure of DNA and ultimately how it works. However, it was largely the work of Franklin Rosalind that led to this important discovery.

Basic units that make up DNA (deoxyribonucleic acid) molecule are nucleotidesEach nucleotide is made up of 3 components:Nucleotides are made of 3 components:

five carbon sugar (deoxyribose)

phosphate group

nitrogenous base

DNA Structure

Nucleotides are different due to nitrogenous basesDNA contains 4 different nucleotidesWhat makes these nucleotides different from each other are their nitrogenous bases.

Adenine (A) and Guanine (G) - double-ringed structures known as purines

Thymine (T) and Cytosine (C) - single-ringed structures known as pyrimidines

Known as Chargaff's rule

Thymine is paired with Adenine (T-A)

Cytosine is paired with Guanine (C-G)

Base pairs held together by hydrogen bonds

Thymine is paired with Adenine (T-A)

Cytosine is paired with Guanine (C-G)

2 hydrogen bonds

3 hydrogen bonds

Fifth carbon in deoxyribose points upward in one strand and downward in the other

5´

5´

5’

3’3’

5’

5’

3’

5’5’

3’

3’

5’

P

3’

PP

P

G

C

T

A

C

G

5´

5´

Along each strand, sugars linked together by phosophate

group

Complimentary nitrogenous bases hold

strands to one another through hydrogen bonds

Base pairs joined by hydrogen bonds

5’

3’

Sugar-phosphate

“backbone” in 3’-5’

orientation

Sugar-phosphate

“backbone” in 5’-3’

orientation

5’

3’

3.4 nm

To fit this massive amount of information into each cell, DNA is coiled upon itself to form chromosomes

If DNA in one cell were laid end to end - 3m (6 billion base pairs long)

Histones (+ charged proteins) act as "spools" on which DNA molecule coils

histonenucleosome

Nucleosomes (coil) coiled upon themselves to form chromatin fibre

How does it all

fit?

histonenucleosome

Chromatin condenses during mitosis - seen as chromosome

chromatin fibre

centromere

chromosome