DNA Flashcards
Structure of DNA
- deoxyribose sugar ( one less oxygen than RNA)
- phosphate group
- nitrogen containing bases A,T,G,C
How is dinucleotide formed ?
- 2 mononuceotides joined through condensation reac.
How does phosphodiester bond formed ?
- between deoxyribose sugar of 1st mononucleotide and phosphate of 2nd
Base pairing in DNA
Adenine - thymine
Guanine - cytosine
All bases are in equal proportion
What bond forms between bases in pairs ?
Hydrogen bonds
A-T 2 hydrogen bonds
G-C 3 hydrogen bonds
The double helix
- as anti parallel
- uprights composed of deoxyribose sugar and phosphate ( backbone of DNA)
- base pairs in the middle
Adaptations of DNA (5)
- a very stable structure
- hydrogen bonds between 2 nucleotides
- large molecule
- position of base pairs
- base pairs
Functions of adaptations of DNA (5)
- stable SO can passes info from generation to next without changes, rarely mutate
- H bonds SO allow nucleotides to be separated during DNA replication and protein synthesis
- Large molecule SO can carry large amount of genetic information
- B.P positioned inside backbones SO can be protected from the effect of outside chemical / physical forces
- B.P SO DNA able to replicate and transfer information as mRNA
Why is DNA a stable molecule ?
- H bonds link B.P = the more G-C ratio= more stable the DNA
- base stacking interactive forces = hold them as a molecule
Purpose DNA replication
- ensure all daughter cells have the same genetic informations to produce enzymes and other proteins that they need
Semi- conservative replication
- because one of the parental strand is conserved into a template plus a newly synthesised strand to form a complete DNA molecule
1st stage of DNA replication
- DNA helicase breaks H bonds between bases in pairs between 2 strand of double helix = causes DNA to unwind
2nd stage of DNA replication
- parental DNA as a template and free floating nucleotides attracted to complementary base pairs on the template strands of parental dna
3rd stage of dna replication
- adjacent nucleotides joined, DNA polymerase catalyse to form phosphodiester bond
4th stage
- 2 sets of daughter DNA forms = contains one parental and one new synthesised DNA
Meselsohn and stahl semi- con experiment
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E.g. explain why and how DNA helicase is important in DNA replication (2)
M1 it hydrolyse hydrogen bonds to unwind double helix
M2 so nucleotides can attach with adjacent ones
E.g. how does drug that inhibits DNA polymerase effective against cancer ? (2)
- slows or prevent DNA replication
- newly synthesised strand won’t form
