SBI4U- Molecular Genetics
Select the BEST answer to each of the following by filling in the
appropriate bubble on the SCANTRON CARD provided.
1)
2)
Total:
The paired bases of a DNA molecule are best described as
a) covalently linked across the width of the double helix
b) identical
c) mirror images
Bonus: Name this guy
d) complementary
wishing you luck!
e) single-stranded
DR. JAMES WATSON
/27
Good
luck!
Which of the following is a correct representation of a segment of DNA?
1.
2.
3.
a) 1
b) 1 and 3
c) 2 and 3
5'ATTC3'
3'ATTC5'
5'AUUC3'
3'UAAG5'
5'CCGG3'
5'GGCC3'
4.
5.
5'ATAG3'
3'TATC5'
5'ACGA3'
3'TGCT5'
d) 4 and 5
e) 5 and 1
3)
DNA becomes more stable because hydrogen bonds are formed between
a) thymine and uracil
d) guanine and adenine
b) cytosine and thymine
e) purines and pyrimidines
c) adenine and uracil
4)
Telomeric DNA
a) is found towards the centromere of a chromosome
b) is special coding DNA that make protein products needed for growth
c) is likely added to chromosomes as one ages
d) is likely present because of faults associated with DNA replication
e) all of the above
5)
If Hershey and Chase’s experiment with radioactive phosphorous and sulfur had shown that
sulfur entered the cells and not phosphorous then
a) DNA would have been solidified as the molecule of heredity
b) RNA would have been a prospect as the molecule of heredity
c) protein would have been prospect as the molecule of heredity
d) sulfate would have been confirmed as being in DNA structure
e) they would have changed careers into making chocolate and enforcing highway traffic laws
6)
When DNA helicase is active, the result is
a) annealing of RNA primers to the DNA
b) formation of phosphodiester bonds
c) formation of hydrogen bonds
d) separation of the two strands of the double helix
e) swivelling of the single separated strands of DNA
7)
During DNA replication, one of the new strands of DNA is synthesized continuously, while the
other is synthesized as a number of separate fragments of DNA that are subsequently linked
by DNA ligase. This is because
a) replication starts at many points on the chromosome
b) RNA primers only anneal to one of the parental strands of DNA
c) DNA polymerase III only synthesizes DNA in the 3' - 5' direction
d) one of the parental strands is unwound slower than the other by helicase
e) DNA polymerase III only synthesizes DNA in the 5' - 3' direction
8)
A DNA nucleotide contains
1. a cyclic nitrogen-containing part
2. a single ring containing five carbons
3. a part which contains four oxygen atoms surrounding a central atom.
In order, 1, 2 and 3 are
a) a base, a phosphate group, a sugar
b) a sugar, a base, a phosphate group
c) a base, a sugar, a phosphate group
d) a phosphate group, a sugar, a base
e) a sugar, a phosphate group, a base
9)
The main support to the DNA molecule is provided by two backbones which run along the two
sides of the double helix. These backbones consist of
a) sugars joined by ester links
b) phosphates joined by ester links
c) sugars and phosphates linked together
d) phosphates and bases linked together
e) sugars and bases linked together
10)
If a free phosphate is found at the 5' end of a DNA strand, what is found at the other end of
the same strand?
a) a hydroxyl group on the 5' carbon of a deoxyribose sugar
b) a hydroxyl group on the 3' carbon of a deoxyribose sugar
c) a phosphate group on the 5' carbon of a deoxyribose sugar
d) a phosphate group on the 3' carbon of a deoxyribose sugar
e) a base attached to the 3' carbon of a deoxyribose sugar
True/False – Indicate whether the following statements are true or false. If the statement is true, fill
in letter A on the SCANTRON CARD; if the statement is false, fill in the letter B.
11)
12)
13)
14)
15)
DNA replication proceeds via a semi-conservatism mechanism. True
DNA is only found in the nucleus of a eukaryotic cell. False, mitochondria/chloroplast
A glycosyl bond connects the sugar and the nitrogenous base of a nucleotide. True
Replication bubbles are much more common in eukaryotic DNA versus that of
prokaryotes. True
The duplication of DNA occurs during the G2 phase of interphase False, S phase
Short Answer (12 marks) Answer the following.
1) a) An active replication fork is shown below. Match the list of items to the appropriate letters
on the diagram. Label f corresponds to the name of the piece of DNA (of equivalent length)
found in the larger diagram. (3 marks)
template strand - a
helicase – d
leading strand - b
RNA primer - e
lagging strand - c
Okazaki fragment - f
b) Generally speaking, which enzyme would be located at the spots where you see the arrow
heads and what is its job? (2 marks) DNA polymerase
c) Based upon b), what is exposed at this site such that the enzyme works here?
(1 mark) 3’ OH of the deoxyribose in the nucleotide
2) a) You have isolated a sample of DNA from a eukaryotic cell and found that the % of guanine
in the sample is approximately 33%. How could you use this information to deduce the
percentage of the other bases? Show these remaining percentages. (3 marks) (T/I)
Because of complementary base-pairing, the % of cytosine is 33%. This means that
the remaining 34% would comprise the Adenine-Thymine pairing. 17% would be
thymine while 17% would be adenine.
b) Why are these calculations an approximation? (1 mark) (T/I)
Mutations can alter these figures
c) Would you expect this sample of DNA to boil at a higher or lower temperature compared to
another sample of DNA (from a different species) that was 33% adenine? Explain. (2 marks)
(T/I)
Higher since guanine and cytosine form 3 hydrogen bonds as opposed to adenine and
thymine which form only 2. It would take more energy to break apart the extra
hydrogen bonds.