DNA Replication

Question 1

why is semi conservative replication important

Answer 1

-ensures genetic continuity between generations of cells

Question 2

describe the process of semi conservative DNA replication

Answer 2

-DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
-both strands act as templates
-free DNA nucleotides are attracted to exposed bases and join by specific complementary base pairing
-hydrogen bonds form between a-t and g-c
-dna polymerase joins adjacent nucleotides on new strand by condensation reactions
-forming phosphodiester bonds

Question 3

what does semi conservative dna mean

Answer 3

each new dna molecule consists of
-one original/template strand -one new strand

Question 4

suggest why dna polymerase moves in opposite directions along DNA strands based on enzyme action

Answer 4

-dna has antiparallel strands
-so shapes/arrangements of nucleotides on two ends are different
-dna polymerase is an enzyme with a specific shaped active site
-so can only bind to a substrate with a complementary shape (the phosphate end of developing strand)

Question 5

name the two scientists who proposed models of the chemical structure of dna and dna replication

Answer 5

watson and crick

Question 6

describe the work of meselson and stahl in validating the watson crick model of semi conservative dna replication

Answer 6

1. bacteria grown in medium containing heavy nitrogen (15N) so nitrogen is incorporated into dna bases
   -dna is extracted and centrifuged, settles near the bottom as all dna molecules contain 2 heavy strands
2. bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once
   -dna is extracted and centrifuged, settles in middle, as all DNA molecules contain 1 original heavy, and 1 new light strand
3. bacteria in light nitrogen allowed to divide again
   -dna extracted and centrifuged, half settles in middle, as contains 1 heavy and 1 light strand; half settles near top as contains 2 light strands

Question 7

why are models other than semi conservative replication (dispersive, conservative) not supported

Answer 7

-bands would be in different places to semi conservative replication