Biology 207 - Practice questions 1 - Answers
Question 1 Suppose one was provided with an actively dividing culture of E. coli bacteria to
which radioactive thymine had been added. What would happen if a cell replicated once in
the presence of this radioactive base?
E. DNA in both daughter cells would be radioactive
Question 2 The chromosome of E. coli O157:H7 is 5 498 450 bp long and has a G+C
content of 52%. How many of each of the four DNA nucleotides are present in this
If G+C is 52% then the relative amount of G must be 26%, C is 26%, A is 24%, and T is 24%.
This chromosome contains 10 996 900 nucleotides of which approximately 2 859 194 are G,
2 859 194 are C, 2 639 256 are A, and 2 639 256 are T.
Question 3 Explain why each of my rules governing nucleic acid synthesis holds true for the
process of DNA replication. Recall that the rules are that nucleic acids are (i) made using a
ssDNA template, (ii) made 5’ to 3’, (iii) pair antiparallel, and (iv) pair with complementary base
(i) made using a ssDNA template - The Helicase separates the dsDNA into two ssDNA
(ii) made 5’ to 3’ - DNA Polymerase adds nucleotides onto the 3' hydroxyl of both the leading
strand and the Okazaki fragments on the lagging strand.
(iii) pair antiparallel - DNA Polymerase travels down the template DNA strand from 3' to 5'.
(iv) pair with complementary base pairing - DNA Polymerase chooses the nucleotide that can
fit opposite the nucleotide in the template strand.
Question 4 Below is a diagram of a DNA molecule that is undergoing bi-directional
replication. Question 5 Complete the following statements:
a) DNA replication begins at the origins of replication (oris) on the chromosome
and ends when two replication forks meet and annihilate each other or when a
replication forks runs to the end of a linear chromosome.
b) Synthesis of a eukaryotic mRNA begins at the promoter on the DNA and ends
when the RNA is cleaved 10 to 35 nucleotides after the termination signal,
c) Protein synthesis begins at the start codon on the mRNA and ends when the
ribosome reaches the stop codon.
Question 6 Below is a typical eukaryotic gene, its pre-mRNA, and its mature mRNA. The
direction of transcription is from left to right. Label the diagram with the following structures:
start codon(s), stop codon(s), 3'UTR(s), 5'UTR(s), 5'cap(s), open reading frame(s),
promoter(s), poly(A)tail(s), transcription termination signal(s), intron(s), and exon(s).