Question

1.) Cytosine makes up 20% of the nucleotides in a sample of DNA from an organism. What percent of the nucleotides in this sample will be thymine?

A. 20

B. 30

C. 40

D. 80

E. it cannot be determined from the information given

2.) Which one of the following statements about DNA is incorrect?

A. The amount of A in double stranded DNA is equal to the amount of G.

B. The amount of purines in double stranded DNA is equal to the amount of pyrimidines.

C. The amount of thymine can differ in the DNA of various species.

D. The ratio of thymine to adenine is the same in the DNA of all species.

E. All of the above statements about DNA are correct.

3.) All of the following are characteristics of telomerase EXCEPT

A. produces repeated DNA sequences on the ends of chromosomes

B. can cause cells to divide uncontrollably

C. function reduces with age of cell

D. is found in prokaryotes and eukaryotes

E. has an RNA region that can be used to produce DNA

Answer 1

1. Option B 30
In any DNA the amount of cytosine is always equal to amount of guanine and amount of adenine is equal to the amount of thymine.
We know that C= 20% , C = G and A=T ……………equation 1
from this we know that amount of guanine is 20%
A+T+G+C = 100%
A+A+20+20 =100 ……………from equation 1
2A+ 40 =100
A = 100-40/2
A=30
therefore the amount of thymine is 30%

2. Option A The amount of A in double stranded DNA is equal to the amount of G.
The amount of A in double stranded DNA is always equal to T that is Thymine and not to G.
The amount of purines in double stranded DNA is equal to the amount of pyrimidines. The two-carbon nitrogen ring bases adenine and guanine are purines, while the one-carbon nitrogen ring bases thymine and cytosine are pyrimidines where A is always equal to T and G is always equal to C.
The amount of thymine can differ in the DNA of various species but the ratio of thymine to adenine is the same in the DNA of all species.

3. Option C function reduces with age of cell.
The function does not reduce with the age of the cell whereas the decrease in telomere causes loss of division in cells which may result in the aging of the cell and eventually to the death. Age is a result of shortening of telomere but reduced function is not a result of aging.
It produces repeated DNA sequences or nucleotide sequences on the ends of chromosomes in order to protect them from DNA damage.
Telomerase allows each offspring to replace the lost bit of DNA, allowing the cell line to divide without ever reaching the limit.
It is found in both prokaryotes and eukaryotes
Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule to make cDNA