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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