DNA replication Flashcards
1
Q
Why is semi-conservative replication important?
A
ensures genetic continuity between generations of cells
2
Q
What is the process of semi-conservative DNA replication?
A
- DNA helicase breaks H bonds between complementary bases unwinding double helix
- both strands act as templates
- free nucleotides attracted to exposed bases & join their complementary base pairs
- H bonds form between complementary bases
- DNA polymerase joins adjacent nucleotides on new strand by condensation reactions forming phosphodiester bonds
3
Q
Why is DNA replication semi-conservative?
A
each new DNA molecule consists of one original strand & one new strand
4
Q
Why does DNA polymerase move in opposite directions along DNA strands?
A
- DNA has antiparallel strands so arrangements of nucleotides on 2 ends are different
- DNA polymerase has a specific shaped active site so only binds to substrate with a complementary shape (phosphate end of developing strand)
5
Q
What 2 scientists proposed models of the chemical structure of DNA & DNA replication?
A
Watson & Crick
6
Q
What was the work of Meselson & Stahl in validating the Watson- Crick model of semi-conservative DNA replication?
A
- bacteria grown in medium containing heavy nitrogen - when DNA extracted & centrifuged it settled near the bottom since molecules have 2 ‘heavy strands’
- bacteria transferred tp medium containing light nitrogen for 1 generation - when DNA extracted & centrifuged it settled near the middle since molecules have 1 ‘heavy’ strand & 1 new ‘light strand’
- bacteria in light nitrogen divided for a second time - when DNA extracted & centrifuged half settled in the middle (contains 1’heavy’ strand & 1 ‘light’ strand and the other half settles near the top ( contains 2 ‘light’ strand)
