Unit 3 Genetics – DNA
1.
Key
What are the building blocks of DNA? Nucleotides
2. Arrange the following in order from largest to smallest in size?
Nucleus, DNA, Chromosome, nucleotide, cell
The Order: Cell, Nucleus,
Chromosome, DNA, nucleotide.
3. What are the purine bases and what are the pyrimidine bases for DNA:
a) Purine bases = adenine and guanine.
b) Pyrimidine bases = thymine and cytosine
4. A particular sequence of parent DNA has four purine bases and two pyrimidine bases. According to basepairing rules what are the possible sequences formed during replication:
Representing Purine as Pu and Pyrimidine as Py then a parent strand might read:
Pu Pu Pu Pu Py Py. If that is the strand to replicate that means that the new strand
that will base pair will read:
Py Py Py Py Pu Pu. because
Adenine (purine) base pairs with Thymine (pyrmidine) and
Guanine (purine) base pairs with Cytosine (pyrimidine).
Therefore: the replicate new strand will have 4 pyrimidines and 2 purines.
5. In which part of the cell does this process shown above take place? On the ribosomes in the cytoplasm
6. Structure I in the figure above represents a(n) anticodon.
7. Structure II in the figure above represents a(n) messenger RNA.
8. Structure III in the figure above represents a(n) amino acid sequence - protein
9. Structure IV in the figure above represents a(n) transfer RNA.
10. Structure V in the figure above represents a(n) amino acid.
11. The process illustrated in the figure above is called Translation is the process by which the mRNA
“template” is used to form polypeptides.
12. Which of the structures in the figure above are composed of RNA?
The II is mRNA “template” and the IV tRNA molecule which includes I which is an anticodon composed
of nucleotide bases. III is a polypeptide, and V is an amino acid that are not RNA.
13. X-ray evidence was used to discover that the shape of DNA was a double helix
14. In 1962 a Nobel Prize for Medicine/Physiology was awarded to whom?
Francis Crick, James Watson and Maurice Wilkins
15. The information that directs replication, transcription and translation is found in DNA’s nitrogenous bases
which are: adenine, guanine, cytosine, and thymine.
16. What is Chargaff’s Rule and how was it important for determining DNA’s structure? The Base pairing in
DNA was determined from Chargaff’s Rule which showed, the percentage of pyrimidines in DNA is
about equal to the percentage of purines resulting in the following base pairing rules A binds with T;
C binds with G used to determine the structure of DNA.
17. This segment of DNA has undergone a mutation in which six
nucleotides have been deleted. A repair enzyme would replace
them. Which series of bases will complete the strand of DNA?
GTAGGC
The messenger RNA codes for six different amino acids are shown in the table below.
18. In one type of mutated gene for hemoglobin, CAC has replaced the
normal CTC in the DNA code. What amino acid substitution has
taken place in the mutated hemoglobin?
Original DNA = CTC
Original mRNA = GAG code for amino acid glutamic acid
Mutated DNA = CAC; Mutated mRNA = GUG which codes for
amino acid valine
Valine replaced Glutamic acid
19. Process 1 in the diagram above is known as Replication
20. Process 2 in the diagram above is known as Transcription
21. Process 3 in the diagram above is known as Translation
22. What is the product of process 3 as shown in the diagram above? Protein
23. Which process in the diagram above occurs in the nucleus? Replication and Transcription
24. Which process in the diagram above occurs in the cytoplasm? Translation
25. How many bases are needed to specify four amino acids?
3 bases/codon x 1 codon/amino acid x 4 amino acids = 12 bases
26. What is the difference between the lagging strand and the leading strand?
Lagging strand replicated discontinuously forming Okasaki fragments. The Leading strand is replicated
continuously.
27. A DNA segment is changed from-AAGTAG- to -AAATAG-. This is a point substation mutation because a G
was replaced with a A.
28. A DNA segment is changed from -AATTAGAAATAG- to -ATTAGAAATAG-. This is a(n) frameshift
mutation due to the deletion of adenine from the beginning of the sequence.
29. Here are two related mRNA sequences: 5'UUUAGCGAGCAU3' and 5'UUUAGCCAUAAAAAAAA3'. How was
the second sequence formed? Intron (GAG) removed and a poly A tail was added to form the second
sequence.
30. Use the amino acid code chart to sequence the following messenger RNA strand into an amino acid strand.
AUGUUACCCCAAUUU –
AUG – UUA – CCC – CAA - UUU –
Met – Leu – Pro – Gln - Phe
Help Wanted
Positions Available in the genetics industry. Hundreds of entry-level openings for tireless workers. No
previous experience necessary. Must be able to transcribe code in a nuclear environment.
Accuracy and Speed vital for this job in the field of translation. Applicants must demonstrate skills in
transporting and positioning amino acids. Salary commensurate with experience.
Executive Position available. Must be able to maintain genetic continuity through replication and control
cellular activity by regulation of enzyme production. Limited number of openings. All benefits.
Supervisor of production of proteins—all shifts. Must be able to follow exact directions from doublestranded template. Travel from nucleus to the cytoplasm is additional job benefit.
31. Applicants for the first job of the Help Wanted ad in the table above "Position Available," could qualify if
they were RNA Polymerase.
32. Applicants for the second job of the Help Wanted ad in the table above "Accuracy and Speed vital," could
qualify if they were transfer RNA.
33. Applicants for the third job of the Help Wanted ad in table above "Executive Position," could qualify if they
were DNA is the genetic material that replicates and is passed along when a cell divides. DNA
controls the production of enzymes and other proteins.
34. Applicants for the fourth job of the Help Wanted ad in the table above "Supervisor," could qualify if they
were mRNA which is formed from the template strand of DNA, and it carries the “code” from the
nucleus to the ribosomes.
35. What is the mRNA sequence for a strand of DNA reading CACGTAC? GUGCAUG
36. The template strand of a piece of DNA being replicated reads: 5'-ATAGGCCGT-3'. A partially synthesized
Okazaki fragment is 5'CCTA3'. If the next fragment is four bases long, what is its first base?
5’ATAGG CCGT 3’
3’ _ATCC
A (3’ RNA Primer)5’
The next fragment will replicate CCGT and the first base in the replicate fragment is A.
37. What type of mutation has occurred in the figure?
Deletion of the nucleotide U caused a frameshift
mutation since the codons following the deletion will code
for a different amino acid.
38. What will be the result of the mutation in the figure
above?
Nearly every amino acid in the protein will change.
39. This is a template DNA sequence: 3'AATCGCA5'. This is a partially-completed mRNA strand transcribed
from the DNA template: 3'GCGA5'. What is the next nucleotide that RNA polymerase will attach?
3'AATCGCA 5'. DNA
5' AGCGU 3' mRNA
The RNA polymerase proceeds down one strand of DNA moving in the 3′ to 5′ direction.
Synthesis of the RNA proceeds in the 5′ to 3′ direction
40. Using DNA sequencing, you discover that a bacterium has experienced a deletion mutation that removed
three nucleotides. The bacterium appears completely unaffected in all its functions. Where is the mostly
likely location for the mutation?
Introns, or intervening sequences, which get processed out of the mRNA before it leaves the nucleus,
so removal of an intron would probably have little effect on bacterial functions such as enzyme
synthesis.
41. Three samples of DNA contain the
percentages of nitrogenous bases listed in
Table 12-2. According to Chargaff’s law,
which two samples probably belong to the
same species?
Though the numbers do not match exactly, 1 and 3 have similar percentages of adenine and
cytosine
42. You have a building toy set consisting of parts that can be connected together. You are going to use it to
model a piece of DNA. You have decided that each part of DNA will be represented by a different type of toy piece. You have chosen
the following four pieces so far: adenine = large red cube; guanine = large green cube, thymine = small orange cube; cytosine = small blue
cube. How many other types of pieces do you need to represent the remaining parts both the 3-prime and the 5prime strands of a section of DNA?
The only pieces still needed represent a sugar and a phosphate—the order of those pieces determines
the direction of the strand.
43. Describe the parts which are found in each nucleotide found in DNA?
a. Deoxyribose + phosphate + cytosine
b. Deoxyribose + phosphate + guanine
c.
Deoxyribose + phosphate + thymine
d. Deoxyribose + phosphate + adenine
44. Because of base pairing in DNA, the percentage of pyrimidines in DNA is about equal to the percentage of
purines.
45. DNA is copied during a process called replication - Semi- conservative replication because each copy has
one new strand and one original strand.
46. How is RNA different from DNA?
RNA has ribose sugar, single stranded, uracil no thymine
DNA has deoxyribose sugar, double stranded, thymine no uracil
47. Which type(s) of RNA is(are) involved in protein synthesis? messenger RNA, ribosomal RNA, and transfer
RNA
48. What is produced during transcription? RNA including: mRNA, tRNA, and rRNA inside the nucleus.
49. During transcription, an RNA molecule is formed:
a. Inside the nucleus
b. Is _single-stranded
c. Is complementary to one of the strands of DNA
50. Why is it possible for an amino acid to be specified by more than one kind of codon? There are 64
different kinds of codons (4x4x4) but only 20 amino acids.
51. Which type of RNA functions as a blueprint of the genetic code? mRNA
52. What happens during the process of translation?
The cell uses information from messenger RNA to produce proteins.
53. The cell uses information from messenger RNA to produce proteins.
54. During translation, the type of amino acid that is added to the growing polypeptide depends on the codon on
the mRNA and the anti-codon on the tRNA to which the amino acid is attached.
55. Explain the following types of gene mutations:
a) Insertion – addition of an extra nucleotide – results in a frameshift mutation
b) Deletion - removal of an original nucleotide – results in a frameshift mutation
c) Substitution – change of a nucleotide to another – results in a point mutation
d) Point mutation – mutation affecting one or a few nucleotides
e) Frame-shift mutation – mutation causing a change in the reading frame of codons which in turn
can change the amino acid sequence after the mutation.
56. What is a promoter? Binding site for RNA polymerase.
57. RNA polymerase is used to transcribe RNA from DNA, regulate RNA synthesis, binds to a specific
section where mRNA will be synthesized. As the DNA strand unwinds the RNA polymerase initiates
mRNA synthesizing by moving along the DNA strand in the 3- to 5’ direction. The DNA strand that
is read by the RNA polymerase is called the template strand. Once the mRNA is complete the RNA
polymerase detaches.
58. An expressed gene is turned on.
59. Proteins that bind to Regulatory Sites on DNA determine whether a gene is expressed.
60. If a specific kind of protein is not continually used by a cell, the gene for that protein is turned on and off
at different times as needed by the cell.
61. A bacterium that was once able survive in a tryptophan-free environment is now unable to synthesize its own
tryptophan. The bacterium is otherwise unaffected. Where is the most likely location for the mutation
causing the change?
The trp promoter is the most likely location for the mutation because if it cannot operate,
transcription of the tryptophan-synthesizing enzymes does not take place.
62. What can result when a mutation to DNA occurs?
Cancer (mutation affecting body cell/somatic cell), decreased functioning, birth defects (mutation
affecting sex cell), or no observable problem within the cell.
63. Under
a)
b)
c)
certain conditions RNA can perform additional functions which include?
catalyzing chemical reactions
processing messenger RNA after transcription
helping DNA replicate
64. Describe the following enzymes:
a. DNA helicase – unwinds and unzips the DNA double helix
b. DNA ligase – binds Okasaki fragments together
c.
DNA polymerase – catalyzes the addition of DNA nucleotides to make replicates adding to the 3’ end of
new strand.
d. RNA primase – adds short pieces of RNA to each strand of DNA to help keep the helix open and to as
a starter piece with a 3’ end.
e.
RNA polymerase - catalyzes the addition of RNA nucleotides to transcribe DNA into RNA adding to the
3’ end of new strand.
65. What are introns and exons? Introns and Exons are DNA sequences that are transcribed into RNA, but
introns (intervening sequences) are removed during RNA processing and exons are the coding sequences
that are translated into proteins.
66. Compare and contrast the trp operon and the lac operon
CHARACTERISTICS
TRP OPERON
Responds to the presence of:
Tryptophan – an amino
acid
Transcription is turned on when:
No tryptophan is present
The repressor is active when:
Tryptophan binds to the
repressor
When the operon is turned on, the cell can:
Synthesize tryptophan
LAC OPERON
Allolactose (indicates presence of
lactose – milk sugar)
Allolactose is present
No allolactose is bound to the
repressor
Digest Lactose