BioSc 231
General Genetics
Exam 3
Name __________________________________
Multiple Choice. (1 point each)
_____The base cytosine is always paired with ___.
A.
B.
C.
D.
Adenine
Guanine
Cytosine
Thymine
_____ The presence of a ___ with a free 3'-OH group is essential for DNA polymerase to synthesize DNA since no known DNA
polymerase is able to initiate chains.
A.
B.
C.
D.
E.
origin of replication
restriction endonuclease
palindrome
primer
promoter
_____ ___ is an enzyme that links Okazaki fragments together after the RNA primers have been replaced by DNA.
A.
B.
C.
D.
E.
origin of replication
convertase
primase
ligase
topoisomerase
_____ The process of producing a RNA polymer from a DNA template is called __.
A.
B.
C.
D.
replication
transcription
translation
duplication
_____ The process of producing an amino acid polymer (polypeptide) from a RNA template is called __.
A.
B.
C.
D.
replication
transcription
translation
duplication
_____ The chemical bond in a polypeptide by which the carboxyl group of one amino acid is linked to the amino group of the adjacent
amino acid is called a(n) ____ bond.
A.
B.
C.
D.
E.
phosphodiester
peptide
hydrogen
hydrophobic
hydrophilic
_____ During the process or translation, as the ribosome moves down the mRNA and exposes the codon for the next amino acid in the
chain, an acylated tRNA with the appropriate anti-codon enters the ___ of the large ribosomal subunit.
A.
B.
C.
D.
A site
P site
E site
S site
_____ E. coli genomic DNA differs from a eukaryotic chromosome in that E. coli DNA
A.
B.
C.
D.
has a single centromere.
is circular.
has telomeres.
does not undergo supercoiling.
_____ The RNA polymerase that produces the primer necessary for DNA synthesis is called the ___.
A.
B.
C.
D.
E.
origin of replication
convertase
primase
ligase
topoisomerase
_____ Which of the following is true regarding RNA processing?
A.
B.
C.
D.
Involves removal of exons
Involves removal of one or more introns.
Occurs in prokaryotes
Occurs in the cytoplasm
_____ In prokaryotic organisms, normal self-termination of transcription occurs due to the presence of
A.
B.
C.
D.
stem-loop sequences at the 3’ end of the mRNA
multiple stop codons
multiple RNA polymerase molecules
histones
_____ The four ribonucleotide triphosphates incorporated into mRNA are
A.
B.
C.
D.
Thymine, Uracil, Guanine, Cytosine
Inosine, Guanine, Uracil, Thymine
Adenine, Guanine, Cytosine, Thymine
Cytosine, Uracil, Adenine, Guanine
_____ Which of the following is not a modification of eukaryotic mRNA?
A.
B.
C.
D.
Intron removal
Coupling of transcription and translation
3' polyadenylation
mRNA capping
_____ Which of the following is true for histones?
A.
B.
C.
D.
They are rich in acidic amino acids
They are associated with the nucleosome..
They are found in the endoplasmic reticulum.
They form the scaffolding structure.
Short Answer. (variable points)
If the GC content of a DNA molecule is 62 percent, what are the percentages of the four bases (A,T,C and G)? (2 points)
What is the function of transcription factors in eukaryotic transcription (2 points)
Give an example of a type of polypeptide secondary structure (2 points).
What is the function of histones? (1 point)
The photograph to the right is an electron
micrograph that shows the process of active
transcription of several genes. The location of
one gene is indicated with a bar. Draw an
arrow on the picture to indicate the direction of
transcription of the indicated gene. Briefly
explain how you know the direction of
transcription. (4 points)
Three unknown samples of bacteria were found in Griffith’s lab. The samples were injected individually and in all possible
combinations into mice to figure out what is in each sample. Based on the results of this experiment, which are shown in the table to
the right, what is in each sample? (6 points)
Sample A
Sample B
Sample C
Sample Response Cells recovered
A
None
Live R cells
B
None
None
C
Dead
Live S cells
A+B
Dead
Live S cells
A+C
Dead
Live R&S cells
B+C
Dead
Live S cells
A+B+C Dead
Live S cells
The following 5 questions refer to the numbers on this figure. (5 points)
A. What end (5' or 3') of the molecule is indicated by arrow number 8?
B. Is arrow 7 pointing to the template for the leading or lagging strand?
C. What kind of nucleic acid is indicated by arrow number 4?
D. What do you call the short DNA fragments indicated by arrow number 5?
E. What enzyme (indicated by arrow 2) deals with supercoiling ahead of the replication fork?
Translate the following mRNA using the single letter amino acid code (5 points)
5’ GAGGCCGACGUGCCGACGUCAGAUGGAAAAUGAUGAAUUGCAUGCAACG
GAGAGCCCAGAAGCAUCGUAACCAAAGGCUCCUUUUGGAGCUUUUUUUU 3’
Meselson and Stahl used a heavy form of nitrogen to demonstrate semi-conservative DNA replication. Bacterial cells were grown in
the presence of heavy nitrogen until all the DNA contained the heavy form. The bacteria were then transferred to a medium that only
contained the light form of nitrogen. At different time points, DNA was isolated from the bacteria and subjected to density gradient
ultracentrifugation. Use the following test tube pictures to indicate the location of the DNA band(s) at the beginning of the
experiment, after 1 generation, after 2 generations and after 4 generations. (4 points)
Beginning
1 Generation
2 Generations
4 Generations
Complete the structure of the nucleotide below by filling in the boxes with the letter of the appropriate functional group. (3 points)
Short Essay (8 points) Answer one of the following two questions.
1. List the enzymes and proteins involved in DNA replication. Briefly describe the function of each.
2. Using boxes or lines as a schematic representation of template DNA, mRNA and protein, diagram the parts indicated below (from a
prokaryote).
A) Promoter (-10 and -35)
B) AUG
C) Ribosome binding site
D) Coding sequence
E) Transcriptional terminator
F) Amino and carboxyl ends of the resulting protein.
Below is a segment of a double stranded DNA molecule containing a promoter sequence. Write the sequence of the RNA molecule
that would be produced by the RNA polymerase binding to this promoter (up to the end of the molecule). (4 points)
-35
-10
+1
5’-CGTTCGGATCGATGCCGATCAGCGGGTAGCGGGTGATCTCGGCCGCCGACACCTGCTTGCGGCCGGCCAGCTCGTGGCC–3’
3’-GCAAGCCTAGCTACGGCTAGTCGCCCATCGCCCACTAGAGCCGGCGGCTGTGGACGAACGCCGGCCGGTCGAGCACCGG-5’
Bonus question. (4 pts)
One of the earliest drugs used to treat patients with HIV infections was the nucleotide analog AZT. A nucleotide analog has a
structure and function similar to a nucleotide. Some of the nucleotide analogs being used to treat HIV infections are called dideoxy
nucleotides. Dideoxy nucleotides include a ribose sugar that lacks both a 2’ and 3’ hydroxyl group. Based on what you know about
nucleic acid synthesis, what effect do you think these analogs have on viral nucleic acid synthesis?