DNA Replication

Question 1

What are the 3 different proposed DNA replication methods, and which one was determined to be true.

Answer 1

1) Conservative
•1 new molecule with nucleotides from original, 1 with nucleotides solely from nuclear environment
2) Dispersive
•both new molecules with mixture of old and new nucleotides
3) Semiconservative
•both new molecules contain 1 from original and 1 from nuclear environment
(Semiconservative determines to be right)

Question 2

1st step Replication
(Separating strands of nucleotides)
(3 things)

Answer 2

•HB between 2 strands are broken by DNA Helicase

(Eukaryotes have multiple origins of replication)
•SSBfrom proteins bind to 2 strands to prevent rejoining

•topoisomerase relieves tension by cutting strands near replication fork, allowing them to untangle, rejoining

Question 3

2nd step replication
(Building new strand of DNA)
(4 enzymes)

Answer 3

1) Primase
•lays down RNA primer that is used by DNA polymerase III to build new strand
2) DNA Polymerase III
•adds correct nucleotides to developing strand of DNA
3) DNA Polymerase I
•removes RNA primer and replaces with correct sequence of DNA nucleotides
4) DNA ligase
•repairs phosphodiester bonds

Question 4

Continuous strand

Leading

Answer 4

•as DNA is unwound, primase attaches an RNA primer to 3’ end of the original and then DNA polymerase III will start to build new strand 5’ to 3’

Question 5

Discontinuous

Lagging

Answer 5

• as molecule of DNA unwinds, primase attaches RNA primer to an exposed 3’ end of the original 5’ to 3’ strand
• then DNA polymerase III will build in 5’ to 3’
• after strands are formed DNA polymerase I removed RNA primer and replaces it w proper DNA nucleotides
• DNA ligase attaches Okazaki fragments
• very last primer not replaced, DNA is lost, TELOMERES

Question 6

Dealing with errors

Answer 6

•DNA POLYMERASE III usually backs up and replaces incorrect bases
•DNA POLYMERASE I and II
move slowly along strand, looking for distortions
•ligase fills in gaps