Dna Structure Flashcards
What is a nucleotide
A repeating unit that makes up DNA made of nitrogenous base, sugar, phosphate
What are purines
The two purines are Adenine and Guanine
What are Pyrimidines
The two pyrimidines are Thymine and Cytosine
Difference between RNA bases and DNA bases
Instead of Thymine Rna contains Uracil
What type of sugar is in the bases
2’- deoxyribose in cyclic hemiacetal form
How are bases connected
They are connected via phosphordiester bonds, created by removing oxygen from the phosphate and replacing it with the oxygen from the ribose, releasing h2o
Deoxiribonucleoside nomenclature
Base + 2’ deoxyribose
Eg: deoxyadenosine, deoxyguanosine, deoxycitidine, deoxythimidine
deoxyribonucleotide nomenclature
base + 2 ‘deoxyribose + 1 phosphate
Eg: deoxyadenosine monophosphate (dAMP)
deoxyribonucleoside diphosphate nomenclature
Base + 2’ deoxyribose + 2 phosphate
Eg deoxyadenosine diphosphate (dADP)
Deoxyribonucleoside triphosphate nomenclature
Base + 2’ deoxyribose + 3 phosphate
Eg deoxyadenosine triphosphate (dATP)
Chargaffs rules
- Bases are not equally represented
- Dna from an organism or same species have the same base composition in every cell
- Dna in different species can vary
- A=T, C=G
(A+G)/(T+C) =
= 1
watson crick model
- Consists of antiparallel strands,
- Bases are inside the helix
- Held together through hydrogen bonds
- Strict pairing between the bases
- Complementary strands
- Right-handed double helix
- Minor and major grooves
- Hydrophobic interactions between horizontally stacked basepairs stabilise the dna making it rigid
B from dna
Watson and crick model
How many base pairs in 1 b form turn
10 base pairs = 3.4 nm
What are the measurements of dna
Width = 2nm
Height between bases = 0.34nm
Height between one turn = 3.4nm
Methylation of bases
Most commonly in cytosin in eukaryotes
CH3 binds to another molecule physically and chemically altering its properties
Typically acts to repress gene transcription
How does dna fit into cells
Dna is supercoiled and packaged with proteins, making chromatin
Supercoiling
Turns are added or removed
Positive supercoiling = coiling in the Sam direction as the helix
Negative supercoiling = helix twists in on itself in the other direction
Packaging of dna
Dna is wrapped around histones to take up less space and then is further coiled until it’s tightly packed and present as chromatin
