Ch. 28 DNA Replication

DNA is semi conservative, what does this mean ?

One of the two original strands is conserved in each progeny molecule

DNA replication requires…

Unwinding of the DNA helix (breaking H bonds)

DNA replication is semi discontinuous, what does this mean?

The lagging strand is formed from newly synthesized short segments (Okazaki fragments)

Biodirectional replication involves…

Two replication forks that move in opposite directions

What unwinds the double helix in DNA ?

Helicases and gyrases

The lagging strand is formed from…

Okazaki Fragments

Enzymes that replicate DNA

DNA Polymerases

Chain growth of DNA Polymerases

5’-3’ direction antiparallel to the template strand

DNA Polymerases CANNOT initiate DNA synthesis, they require..

A primer oligonucleotide with a free 3’-OH

The chief DNA replicating enzyme of E. Coli

DNA Polymerases 3

What functions in DNA repair ?

Polymerases 1, 2, and 5

A protein + coenzyme or cofactor

Holoenzyme

The core enzyme of DNA Polymerase 3 has three subunits, what are they?

1. Alpha (polymerase)

2. Epsilon (3’-exonuclease)

3. Theta (holoenzyme assembly and epsilon stabilization

Where does Polymerase 3 sit ?

At each replication fork

Helps DNAB unwind the DNA double helix

DNA gyrase (topoisomerase)

Seals the nicks between Okazaki fragments

DNA ligase

What are the different DNA Polymerase families ?

1. Family A- polymerases involved in DNA repair in bacteria

2. Family B-eukaryotic polymerases involved in replication of chromosomal DNA

3. Family C- bacterial chromosomal DNA replicating enzymes

4. Families X and Y- DNA pathways

5. RT- designates retrovirus polymerase

The DNA polymerase resembles a right hand with distinct domains. What does the palm, fingers, and thumb domains represent ?

Palm domain- active site lies in the crevice

Fingers- deoxynucleotide recognition and binding

Thumb- DNA binding