BB1720 DNA: structure and composition Flashcards
How was DNA discovered?
- analysis which showed that chromosomes in the dividing cells contain hereditary information
- the double helix was discovered using xray diffraction
What is the structure of DNA?
- contains a major and minor groove
- 10 bases per turn
- one full turn rises 3.4nm
- 2nm wide
- can have right of left handed helicase shape or original
function of major groove
- more exposed bases for proteins to bind and recognise the correct sequence
- transcription regulators bind
function of minor groove
helps binding to histones and wrapping DNA
chemical composition of DNA
- 2 polynucleotide chains, form double helix
- held together by hydrogen bonds between complementary base pairs
- nucleotides composed of deoxyribose sugar, phosphate group, base
what are purines
double ring structures
adenine
guanine
what are pyrimidines
single ring structure
cytosine
thymine
what is a phosphate group
forms phosphodiester bonds between nucleotides
What did the xray diffraction tell scientists about DNA?
- the cross represents the double helix
- the fundamental repeats of the helix are 0.34nm
- the spacing between the spots indicate the pitch is 3.4nm
- the missing layer line indicates there’s more than one strand and they are not symmetrically placed
DNA nomenclature
- strands are antiparallel
- 5’ phosphate 3’ OH
- two strands are complementary
- 5’ ACGT 3’ -> direction of synthesis of DNA strand
- 3’ TGCA 5’ -> DNA template
Which base is not found in DNA?
uracil
How many base pairs are there in one full turn of the DNA double helix in its B form?
10
The three major forms of the DNA double helix are A, B and Z form. Which is considered the normal form in the cell?
B
Which technique was used to determine the double-helical structure of DNA?
X-ray crystallography
The double-helical structure of DNA is formed by which forces?
a combination of hydrogen bonds and stacking interactions
