1.5.2 DNA replication Flashcards
1
Q
why is semi conservative replication important
A
because it ensures genetic continuity between generations of cells
2
Q
what is the process of semi conservative DNA replication
A
- DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
- both strands act as a template
- free DNA nucleotides attracted to exposed bases join by specific complementary base pairing
- hydrogen bonds form between adenine & thymine and guanine & cytosine
- DNA polymerase joins adjacent nucleotides on new strand by condensation reaction
- forming phosphodiester bonds
3
Q
what is meant by semi conservative replication
A
each new DNA molecule consists of one original/template strand and one new strand
4
Q
use your knowledge of enzyme action to suggest why DNA polymerase moves in opposite directions along DNA strands
A
- DNA has antiparallel strands so the arrangements of nucleotides on two ends are different
- DNA polymerase is an enzyme with a specific shaped active site so can only bind to substrate with complementary shape ( phosphate end of developing strand )
5
Q
name the two scientists who proposed models of the chemical structure of DNA and DNA replication
A
watson and crick
6
Q
describe the work of meselson and stahl in validating the watson-crick model of semi conservative DNA replication
A
- bacteria grown in medium containing heavy nitrogen which was incorporated into DNA bases - DNA extracted and centrifuged so settles near bottom as all DNA molecules contain 2 heavy strands
- bacteria transferred to medium containing light nitrogen and allowed to divide once - DNA extracted and centrifuged so settles in middle as all DNA molecules contain 1 original heavy and 1 new light strand
- bacteria in light nitrogen allowed to divide again - DNA extracted and centrifuged so half settles in middle as contains 1 original heavy and 1 new light strand; half settles near top as contains 2 light strands
