Question

QUESTION 11 Chargaff's Rules state that: a. The amount of A.T.G, and C in DNA varies from species to species b. The amount of ATG and C in DNA stays the same from species to species c. The amount of GC and A=T d. a and care correct e. band care correct QUESTION 12 A PCR thermocycle is: a. Annealing. Denaturation, Extension b. Denaturation, Annealing. Extension c. Denaturation, Extension, Annealing d. Extension, Annealing. Denaturation Click Save and Submit to save and submit. Click Save All Answers to save all answers. 3677 20 ... F1 F2 80

Answer 1

1) Chargaff's rules are as follows:

1. The base composition of DNA varies in different species.
2. DNA from different tissues of the same species have the same base composition.
3. The base composition of DNA in a species doesn't undergo any change with the organism's age, nutritional status or changing environment.
4. In all species, the number of Adenine is equal to number of Thymine residues (A=T) and the number of Guanine is equal to number of Cytosine (G=C). Thus the sum of the purine residues equals the sum of pyrimidine residues (A+G=T+C).

Thus options A and C are correct. Thus option d is the answer.

2) PCR stands for Polymerase Chain Reaction. It is an in vitro procedure which generates large quantities of DNA segments. Each cycle occurs through three steps:

1. DENATURATION: The DNA is denatured by heating at 95 degree Celsius for 30 seconds to 2 minutes, separating the two strands.
2. ANNEALING (RENATURATION): The primers base pair with the complementary regions flanking the target DNA strands as the temperature cools down to 50 degrees celsius. Since the primers occur in large numbers the probability of there annealing with DNA strands is more than that of two DNA strands annealing with each other.
3. EXTENSION (POLYMERISATION/SYNTHESIS): the DNA synthesis begins at the 3'-OH end of each primer. The primers grow in length by joining the bases complementary to DNA strands. This is a comparable to that of DNA replication on a leading strand. An optimal temperature has to be maintained throughout the process as required by the enzyme DNA polymerase. The DNA polymerase used in PCR is derived from a bacteria called Thermus aquaticus which lives in hot water springs. Hence this enzyme is not denatured but active at high temperatures. The polymerase reaction is allowed to continue in the presence of dNTPs at 72 degree Celsius for 30 seconds. In this way in both strands of DNA are duplicated in three steps.

Therefore answer is Denaturation ---> Annealing----> Extension. Option B is the answer.