Question

2. If 28% of the bases in a DNA strand are guanine, what percentage are thymine?

3. DNA replication is semi-conservative. What does this mean?
4. Match the DNA replication enzyme with Its correct function:
1.__ Helicase
2.__ primase
3.__ DNA polymerase
a. Adds new DNA nucleotides
B. Unwinds the DNA strand
C. Add an RNA primer to signal where replication should begin

Answer 1

2) According to Erwin Chargaff's rule:

* Purine adenine is equimolar with pyrimidine thymine

* Purine guanine is equimolar with pyrimidine cytosine

i.e. A = T & G = C

So, If G = 28% then C = 28%

Total bases = 100%

A + T + G + C = 100%

2T + 2G = 100%

2T + 56% = 100%

2T = 100% - 56%

2T = 44%

T = 22%

Percentage of thymine = 22%

3) Watson and Crick proposed a scheme for DNA replication that suggest that the two stands of DNA would separate and act as template for the synthesis of complementary strands. After the completion of replication, each DNA molecule would have one parental and one newly synthesized strand. This scheme was termed as semi-conservative DNA replication.

4) 1. Helicase - B. Unwinds the DNA strand

2. Primase - C. Add an RNA primer to signal where replication should begin

3. DNA polymerase - A. Adds new DNA nucleotides