Exam 2 - Pt3

Front 1

DNA polymerase FACTS
(5 facts)

Back 1

-I, II, and III can elongate an existing DNA strand (called a primer) but cannot initiate DNA synthesis.
-All three possess 3' to 5' exonuclease activity.
-only polymerase I
demonstrates 5' to 3' exonuclease activity.
-DNA polymerase III is the enzyme responsible for the 5' to 3' polymerization essential in vivo.
-Its 3' to 5' exonuclease activity allows proofreading.

Front 2

Polymerase I is believed to be responsible for

Back 2

removing the primer
the synthesis that fills gaps produced during synthesis

Front 3

polymerases I, II, IV, and V are involved in

Back 3

various aspects of repair of damaged DNA

Front 4

DNA polymerase III is

Back 4

a holoenzyme composed of 10 subunits:

Front 5

STEP 1
To open and stabalize Helix:

Back 5

-DnaA binds to origin of replication and is responsible for initial steps in unwinding the helix.
-Subsequent binding of DnaB and DnaC further opens and destabilizes the helix.
-Single-stranded binding proteins (SSBPs) stabilize the open conformation.

Front 6

helicases

Back 6

Proteins which require the energy normally supplied by the hydrolysis of ATP to break hydrogen bonds and denature the double helix

Front 7

STEP 2
release tension created by unwinding

Back 7

Relieved by DNA gyrase, a member of a larger group of enzymes referred to as DNA topoisomerases.

Front 8

STEP 3
Primer synthesis

Back 8

DNA Polimerase 3 needs a primer with a free 3’ –OH to add bases too.
Primase directs the synthesis of a small 10-12nt primer

Front 9

STEP 4
P.3 synthesizes DNA

Back 9

-Synthesis occurs on both strands simultaneously. The net effect is that the P.3 holoenzyme moves away from the origin.
-DNA synthesis by P.3 occurs only in the 5’->3’ direction
Recall that the DNA strands are antiparallel – therefore synthesis must occur in one direction on one strand, and in the opposite direction on the other.

Front 10

As replication fork moves:

Back 10

Leading Strand:Continuous Synthesis
Lagging Strand:Undergoes dicontinuous synthesis as Okazaki fragements *each with its own primer*

Front 11

STEP 5 & 6
Primer removal and Gap repair

Back 11

DNA P1 removes the primers on the lagging strand and the fragments are joined by DNA ligase

Front 12

Concurrent synthesis of the leading and lagging strands.

Back 12

Both DNA strands are synthesized concurrently by looping the lagging strand to invert the physical but not biological direction of synthesis.

Front 13

Proof-reading and error correcton
(4)

Back 13

-Base addition is not perfect.
-All of the DNA polymerases have 3' to 5' exonuclease activity that allows proofreading.
-Mismatched bases can be detected and excised in the 3-5> direction. -Once removed, synthesis can proceed in the 5->3 direction.
-This proofreading increases fidelity by a factor of 100.

Front 14

Eukaryotic Cell Issues:

Back 14

-there is more DNA than prokaryotic cells
-the chromosomes are linear
-the DNA is complexed with proteins

Front 15

Eukaryotic DNA Synthesis Is Similar to Synthesis in Prokaryotes, but More Complex

Back 15

-Similar to bacterial process: dsDNA unwound at replication origin, replication forks formed, synthesis is bidirectional creating leading and lagging strands.

Front 16

E. DNA Synthesys

Back 16

-Is much Slower
-Genome is much Larger
-Contain multiple origin of replication for time saving.