LECTURE 18 Flashcards
Double stranded (dsDNA) is the genetic material in
All organisms on earth
Single stranded (ssDNA) is the genetic material in some
viruses.
RNA is the genetic material for these viruses
RNA has the same structure as DNA except :
1) its single, not doubles stranded
2) sugars is ribose, not deoxyribose
2) urical instead of thymine
General requirements for DNA replication
1) enzyme that can catalyze DNA synthesis form deoxyribose
2) Mg++ ions (required for enzyme function)
3) deoxyribose (dNTPs)
enzyme that can catalyze DNA synthesis form deoxyribose
- called DNA polymerase
- all organisms contain many different DNA pools (with different roles in replication or repair of DNA)
In dsDNA, the two strands are
Antiparallel and complementary
The enzyme that replicates DNA is
DNA polymerase
DNA polymerase will only attach nucleotides to an
Existing nucleotides free 3’-OH
This means that DNA polymerase cannot initiate synthesis of polynucleotide
A new DNA polymer is formed by adding monomer nucleotides to the end, via a _________
3’-OH. Dehydration reaction
DNA polymerase lll catalyzes formation of
Phosphodiester bond
What determines which bases are chosen and how?
The templates determines it
loss of phosphates is an __________ reaction that powers __________
Exergonic reaction
Polymerization
Coupling of the exergonic reactions to synthesis is necessary because
Order is being created (individual nucleotides put into an ordered structure)
A new DNA polymer is formed by adding
Monomer to the 3’-OH end, via dehydration reactions
Replication proceeds in
Both directions from each origin, until the entire molecule is copied
Parental dsDNA molecule is
2 complementary, antiparallel strands
The DNA helix is unwound by a _____ that acts at the origins as of replication
Helicase
Topiosomerase
Moves in front of the fork, to help relive strain due to twisting caused by helicase
How does topiosomerase work?
(it cuts one strand, lets the DNA unwind by one turn, and then it “mends” the cut)
Single strand biding proteins
- prevents singles strand from coming back together
- easily displaced by DNA pol
How many replication forks are there in a bubble?
2, one at each end
Primate
Synthesizes a 5-10 net RNA primer, complementary to DNA
Does primate needs 3’-OH
NO
Sliding clamp
Keeps DNA pol on the template
Where does the new DNA strand start from
3’OH of the RNA
Synthesis off the leading strand is
Continuous (stops at the end, or when it reaches another fork form a different origin (in eukaryotes) )
Lagging strand is synthesized
Discontinuously
As more ssDNA is made available at the fork,
Primase makes a primer
Okazaki fragments
The lagging stand contains many short segments of the newly synthesized DNA
Okazaki fragments must be converted into a
Single continuous strand
DNA pol l
Removed one RNA, one nucleotide at a time, from the 5’ end, and replace it with DNA (adding to the 3’ end of the adjacent DNA)
Is there a DNA pol that can join an existing 3’ end to an existing 5’ end ?
NO
DNA ligand
Seals the gaps between the sugar-phosphates of the adjoining pieces of DNA
At each replication bubble, there will be
Two leading strands and two lagging strands
