(this diagram is previous page in #3). 3. DNA replication involves many differen

Question

(this diagram is previous page in #3).

3. DNA replication involves many different types of enzymes. in the table below, fill in the enzyme functions and names based on the model on the previous page
4. nucleotides are added to the 3' end of a growing DNA polymer
a. in the space below draw 2 nucleotides in a polymer. draw a third nucleotide about to be added to the growing polymer
b. label the 5' and 3' ends of your growing polymer
c. what is energy source for the polymerization reaction ?

Explanation / Answer

3. 1. Enzyme name: Helicase

Function: The helicase is responsible for unwinding the DNA strand to form single stranded DNA. This unwinding is brought about by breaking the hydrogen bonds between the nucleotides of the two strands. The unwinding of the DNA strand to single strands is an essential step in replication. The helicase functions similar to a zipper unzipping a zip.

2. Enzyme name:DNA polymerase

Function: The DNA polymerase is an enzyme that replicates, proofreads and repairs the DNA. The main function of the DNA polymerase is to replicate the DNA. This is brought about by the enzyme by adding nucleotide bases to the primer and further elongation of the new DNA strand in the 5' to 3' direction. The DNA polymerase then proofreads the new DNA strand and errors in coupling is corrected by the DNA polymerase where the incorrect base pairs is excised and correct nucleotide is inserted.

3. Enzyme name:Ligase (Green box: You ave written it as primer which is wrong)

Function: The ligase is responsible for joining the Okazaki fragments on the lagging strand during DNA replication. It basically joins DNA strands by catalyzing the phosphodiester bond formation.

4. Enzyme name:Primase

Function: Primase is responsible for synthesis of short RNA strands called primers (18-20 nucleotides long) which are complementary to single stranded DNA.

5.. Enzyme name:Primer

Function: The DNA polymerase cannot initiate synthesis of a new strand de novo. Hence for synthesis of a new DNA strand a primer is required. The DNA polymerase adds nucleotides to the 3' end of this primer and then extends the new DNA strand. Hence the primer serves as a starting point for the DNA polymerase to initiate synthesis of a new DNA strand.

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