DNA Flashcards
Composition of nucleotides
- Cyclic nitrogenous bases
- Pentose sugars
- Phosphate groups
Structural difference between Uracil and Thymine
CH3 on C3 of Thymine
Structural differences between Thymine and Cytosine
- Cytosine has NH2 instead of O on C4
- 2 double bonds 1 between C4 and C5 in Cytosine
- C5 has N instead of HN on cytosine
Structural differences between Adenine and Guanine
- Adenine has double bond between C7 and C8
- Adenine has NH2 instead of O on C7
- Guanine has NH2 instead of H on C = CN across from O/ NH2 group
Structural differences between ribose and deoxy ribose sugar
Ribose - OH OH
Deoxyribose - OH H
Bases are connected to sugars by
Beta - N glycosidic bonds
How are successive deoxyribose resides joined?
By phosphate group between 3’ of one sugar and 5’ of next -> one end (left) free 5’ end and the other is 3’ end
B-form DNA characteristics
- Wide + deep major groove, narrow + less deep minor groove
- bp/ turn : 10.4
- av. rise/ bp : 0.34 nm
- helical diameter: 2.4nm
- pitch: 3.5 nm
Nucleases cleave ______ which contribute to _____ with products X and Y
Phosphodiester bond , 5’ and 3’C polarity
X = 5’phosphate + 3’hydroxyl group
Y = 3’ Phosphate + 5’ hydroxyl group
Types of nucleases:
- DNAses + RNAses
- Endo + exonucleases
- Specific for ds DNA/ ssDNA
- Restriction endonucleases cleave both strands of dsDNA at specific sequences
type 2 : palindromic
Ligase
catalyse formation of ppd between 5’ and 3’ end
Chargraff principle
purine : pyrimidine 1:1
Packing ratio
Length B-form DNA / actual length
Nucleosome characteristics
30nm fiber : DNA xomplexed with histones
-> 8 histones each wrapped by DNA 1.65 times
Histone
Basic repeating unit of 11nm chromatic fibre