bio homework, on nucleotides and DNA?

Question

You are a graduate student in a biochemestry lab. The professor tells you to isolate the protein responsible for adding nucleotides to a replicating strand of DNA. What is the name of the protein you will isolate?

Answer 1

DNA polymerases. There are more than one and it depends which organism you are working with. In higher eukaryotes (such as mammals), the major DNA polymerase is DNA pol delta. However, the very first portion of DNA is synthesized by DNA pol alpha, after its subunit primase has added the small RNA primer. DNA pol epsilon helps the delta one along to increase the processivity of the polymerases (i.e. the time that the enzymes stay attached to the DNA).

However, this is a VERY simplistic view of the whole thing, as, if you try to purify the polymerases bound to the DNA during S-phase, you will end up by isolating a HUGE complex called the replisome, of which the polymerases are only a very small part. Other proteins that would be co-purified include: helicases MCMs, repl. factor cdc45; single strand protein RPA, PCNA (i.e. the "clamp" that binds the DNA to the polymerase), replication factor C (RF-C1 to RF-C5) - which works as clam loader, ligase FEN1, etc...

Answer 2

DNA polymerase

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html

Answer 3

DNA polymerase III