SBI4U- Molecular Genetics
Select theBEST answer to each of the following by filling in the appropriate bubble on the SCANTRON CARD provided.
1)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 imagesBonus: Name this guy
d) complementary wishing you luck!
e) single-strandedDR. JAMES WATSON
2)Which of the following is a correct representation of a segment of DNA?
1. / 5'ATTC3'3'ATTC5' / 4. / 5'ATAG3'
3'TATC5'
2. / 5'AUUC3'
3'UAAG5' / 5. / 5'ACGA3'
3'TGCT5'
3. / 5'CCGG3'
5'GGCC3'
a) 1d) 4 and 5
b) 1 and 3e) 5 and 1
c) 2 and 3
3)DNA becomes more stable because hydrogen bonds are formed between
a) thymine and uracild) guanine and adenine
b) cytosine and thyminee) 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 sugard) a phosphate group, a sugar, a base
b) a sugar, a base, a phosphate groupe) a sugar, a phosphate group, a base
c) a base, a sugar, a phosphate group
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)DNA replication proceeds via a semi-conservatism mechanism. True
12)DNA is only found in the nucleus of a eukaryotic cell.False, mitochondria/chloroplast
13)A glycosyl bond connects the sugar and the nitrogenous base of a nucleotide.True
14)Replication bubbles are much more common in eukaryotic DNA versus that of prokaryotes.True
15)The duplication of DNA occurs during the G2 phase of interphaseFalse, 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 - aleading strand - blagging strand - c
helicase – dRNA primer - eOkazaki 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.