Question

Why were Meselson and Stahl unable to distinguish between the dispersive and the semiconservative models following only one round of DNA replication?

2. Describe in order, the four repeating steps that repeat over and over on the discontinuous lagging strand of DNA replication and name the major proteins required to carry out each of these steps in E. coli. The first function is given

. I. Function:

Create RNA primer Enzyme:

II. Function:

Enzyme:

III. Function:

Enzyme:

IV. Function:

Enzyme:

3. Which bacterial enzyme is responsible for removing the RNA primer of an Okazaki fragment and replacing it with DNA nucleotides during lagging strand replication?

4. Which E. coli enzyme is the main replicative polymerase in bacteria that synthesizes the genome?

5. DNA ligase seals the “nick” between two Okazaki fragments using energy from which of the following? a. ATP or NAD b. GTP c. pyrophosphate released from the last nucleotide in the strand d. 3’OH on the last nucleotide in the strand

6. Which enzyme replicates DNA at a faster rate, E. coli DNA Pol III or mammalian DNA Pol δ? Also explain why this difference occurs.

7. What enzymatic activity is used to remove RNA primers at the end of DNA replication? Be specific and name the direction! (Hint: I am looking for an enzymatic activity, not the enzyme name in E. coli)

8. Polymerases add nucleotides to the __________ end of a strand of nucleic acid.

9. What is the function of the single strand binding proteins during DNA replication?

10. Why do human germ cells (cells that undergo meiosis to produce gametes) express the enzyme telomerase?

11. Why do adult human cells (other than germ cells and stem cells) NOT express the enzyme telomerase? In other words what benefit does not having telomerase provide to these cells?

Answer 1

3.In the replication process, RNase H removes the RNA primer (created by primase) from the lagging strand and then polymerase I fills in the necessary nucleotides between the Okazaki fragments (see DNA replication) in a 5'→3' direction, proofreading for mistakes as it goes.

8.DNA polymerases add nucleotides to the 3′ end of a polynucleotide chain. The polymerase catalyzes the nucleophilic attack of the 3′-hydroxyl group terminus of the polynucleotide chain on the α-phosphate group of the nucleoside triphosphate to be added.

9.Single-strand DNA-binding protein.Single-stranded DNA is produced during all aspects of DNA metabolism: replication, recombination, and repair. As well as stabilizing this single-stranded DNA, SSB proteins bind to and modulate thefunction of numerous proteins involved in all of these processes.

10.Telomerase is found in fetal tissues, adult germ cells, and also tumor cells.Telomerase activity is regulated during development and has a very low, almost undetectable activity in somatic (body) cells. Because these somatic cells do not regularly use telomerase, they age. The result of aging cells is an aging body.