PPG EM BIOTECNOLOGIA AGRÍCOLA
DISCIPLINA DE BIOLOGIA MOLECULAR
PROF. ODIR A. DELLAGOSTIN
NOME:
Exercício 1
1. DNA sample A melts or denatures into 2 separate helices at a lower temperature than DNA sample B. Why is this so?
A.Sample A has a greater % of G-C base pairs (which are less heat stable than A-T base pairs) than does sample B.
B.Sample A has a greater % of A-T base pairs (which are less heat stable than G-C base pairs) than does sample B
C.Sample A DNA comes from an organism adapted to Arctic environments, while Sample B comes from a tropical organism.
D.Sample A is from a prokaryotic organism and sample B from a eukaryote.
E.None of the above is true
2. The DNA in species A is denser than the DNA in species B. Why is this so?
A.Species A has double stranded DNA while species B has the single-stranded form.
B.Species A is a eukaryote and species B is a prokaryote.
C.Species A has a greater % of A-T base pairs than species B and A-T base pairs are denser than G-C base pairs.
D.Species A has a greater % of C-G base pairs than species B and C-G base pairs are denser than A-T base pairs.
E.Species A lives in the deep ocean under high pressure, while species B is surface living.
3. The genetic material of a new life-form is found to have 20% A, 30% T, 20% G and 30% C. What is the simplest explanation for this data?
A.This species has a new form of DNA in which C pairs with T and A with G
B.This species has normal double-stranded DNA as its genetic material.
C.This species has single-stranded DNA as its genetic material
D.This species has double-stranded RNA as its genetic material
E.This species has single-stranded RNA as its genetic material
4. Which enzyme has the ability to join pieces of DNA into one long continuous stretch?
A. DNA polymerase
B. Topoisomerase
C. Reverse transcriptase
D. DNA ligase
E. DNA nuclease
5. In which order do the following enzymes function during the replication of a single Okazaki fragment - ligase, primase and DNA polymerase
A. primase, polymerase, ligase
B. polymerase, primase, ligase
C. ligase, primase, polymerase
D primase, ligase, polymerase
E. none of the above are correct.
6. Agarose gel electrophoresis can be used to separate DNA molecules on the basis of differences in:-
A. Density
B. Electrical charge
C. Length
D. GC content
E. none of the above
7. DNA replication is carried out in prokaryotes by DNA polymerase III. Which of the following statements correctly summarizes the properties of this enzyme ?
A. It cannot synthesize DNA bidirectionally (from 5' to 3' and from 3' to 5')
B. It cannot degrade DNA in a 3' to 5' direction
C. It is also used in excision repair to replace damaged or altered nucleotides.
D. It requires an existing nucleic acid chain to add on to ie it needs no primer
E. It causes chain growth by adding small pieces of DNA containing several nucleotides to the 3' end of an existing strand
8. Guanosine is an example of:-
A. a pyrimidine base
B. a purine base
C. a nucleotide triphosphate
D. a nucleotide
E. a nucleoside
9. Nucleic acids contain the following atoms:-
A. C, H, O, N, P
B. C, H, O, N, S
C. C, H, O, P, S
D. C, H, O, N, Cl
E. C, H, O, P, S, N
10. Which of the following DNA fragments would have the highest Tm (melting temperature) ?
A. 5' AAATGTTTTAAGTATA3'
3' TTTACAAAATTCATAT5'
B. 3' AAATGTTTTAAGTATA5'
5' TTTACAAAATTCATAT3'
C. 5' CGGCGCCCCGGGGCAG3'
3' GCCGCGGGGCCCCGTC5'
D. 5' AGGTTCCCCAAGGCGG3'
3' TCCAAGGGGTTCCGCC5
E. Both A and B above
11. Why are RNA primers required during DNA synthesis ?
A. DNA ligase can only join RNA - DNA ends to form a continuous stretch of nucleic acids
B. They produce the free 5' end required by DNA polymerase to begin chain elongation
C. RNA primers stabilize the fork following unwinding
D. RNA primers are the first products of DNA polymerase and are later converted to DNA
E. They produce the free 3' end required by DNA polymerase to begin chain elongation
12. If a prokaryotic mRNA has a G + C content of 42%, what G + C value would you expect for the corresponding coding region in the DNA ?
A. 58%
B. 42%
C. Cannot be determined as mRNA is single stranded
D. 21%
E. 84%
13. Bacterial replicons (eg as in E. coli) differ from eukaryotic ones in that:-
A. In E. coli the whole chromosome is one single circular replicon; in eukaryotes each linear chromosome contains many replicons
B. In E. coli, replication proceeds unidirectionally round the cicular chromosome; in eukaryotes replication proceeds bidirectionally
C. The rate of replication is much faster in prokaryotes than in eukaryotes, perhaps because of the lack of nucleosomes in prokaryotes
D. In E. coli replication is bidirectional and involves many independent replicons, just as in eukaryotes
E. Two of the above are correct
14. If the DNA polymerase of a galactic organism can initiate replication without an existing 3' end, which enzyme(s) might you expect to play a greatly reduced role in its replication process ?
A. DNA
B. helicase
C. primase
D. ligase
E. Two of the above (which ?)
15. If the DNA polymerase of a galactic organism can add to either 5' or 3' ends, which enzyme(s) might you expect to play a greatly reduced role in its replication process ?
A. helicase
B. topoisomerase
C. primase
D. ligase
E. Two of the above (which ?)
16. Assume that a 100-base pair DNA double helix contains 45 cytosines. How many adenines are there?
A. 45
B. 90
C. 55
D. 155
E. None of the above