DNA replication and structure Flashcards
primary structure of DNa
sequence of nucleotides = order of mononucleotides which are linked by
phosphodiester bonds
-3’ end of the strand : free 3-OH-group
5’end of the strand : free 5-phosphate group
sugar-phosphate backbone
composed of pentoses and phosphate groups linking them
secondary DNA
Doublestrandedstructuretwostrandsrun antiparallelly (3’ end of one strand meets 5’ end of the other strand)
A-T - 2 H bonds
G-C - 3 H bonds
denaturation of dna
due to heating ( 70-80 deg)
break H bonds
renaturation of dna
cooling , the double stranded structure of dna rearranges
tertiary structure of dna
such a double helix, where the two strands are wrapped around each other, and the sugar- phosphate backbone faces outside, while bases inside
minor groove
distance between 2 strands
major groove
distance between 2 turns
types of double helix
B-DNA : right-handed, 10 base pairs per turn
A-DNA:decreased humidity/increased salt concentration -> frequent turns (right-handed, 11 base pairs per turn)
Z-DNA: zig-zag form, abnormal type, induces immune reaction (left-handed)
quaternary structure of DNA of prokaryotes : superhelix
relaxed form : double helix is loose
positive superhelix :double helix is spirally
twisted (transcriptionally less active)
negatively superhelix:double helix is twisted in an opposite direction (transcriptionally more active)
Topoisomerases
are enzymes responsible for the formation of relaxed form from superhelix
Topoisomerase I
- Splits then ligates one DNA strand
* No energy is needed for its operation (no ATP)
Topoisomerase II. = DNA gyrase
- Splits then ligates both DNA strands
* Requires energy (hydrolysis of ATP)
number of chromosomes possessed by a prokaryote
1 which is free in the cytosol
histone
DNA is wrapped around histones
histones are alkaline protein withhigh proportion of alkaline amino acid Arg and Lys
- high isoelectric point
positive charge on the pH of nucleus
