BIO 198 Lecture Notes - Lecture 12: Thymine, Nonsense Mutation, Ap Site
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GENETICS QUESTION: For this experiment we focused on forward genetics: First, his- mutants were identified and then complementation analysis was used in order to determine which of the 7 his genes was mutated. ( The exact data can be seen at the bottom). In this experiment we screened for his- mutants that were generated via a random mutation process resulting from errors in DNA replication or induced by EMS aka Ethyl methanesulfonate. We compared a mutagenized culture that was treated with EMS and an un-mutagenized culture that was not treated with EMS. However, both cultures went trhough an enrichment process to increase the frequency of his- mutants.
Point mutations involve the substitution of one type of base pair for another. If the substitution replaces a purine with a purine (or a pyrimidine with a pyrimidine), it is called a transition. If the substitution replaces a purine with a pyrimidine (or a pyrimidine with a purine), it is called a transversion. Many mutagenic chemicals cause this type of mutation by alkylation of a nucleotide base. The chemically altered base can then be misread during replication or repair. For example the mutagen, ethyl methanesulfonate (EMS), adds an ethyl (-CH2-CH3) group to both guanine or thymine bases causing the modified guanine to pair with thymine and the modified thymine to pair with guanine.
1. Why might one gene be more susceptible to EMS mutagenesis than another gene?
2. Why might we have expected to find a higher frequency of polar mutants (his4A-B-C-) in the unmutagenized culture compared to the mutagenized culture?
| Table 2. Experiment 1B class data summary (number of his-mutants by section) Unmutagenized | |||||||||||
| Section | 1 | 2 | 3 | 4ABC | 4A | 4B | 4C | 5 | 6 | 7 | Total his- mutants |
| Tuesday | 7 | 1 | 5 | 4 | 2 | 1 | 9 | 2 | 3 | 1 | 35 |
| Wednesday | 2 | 1 | 14 | 0 | 4 | 2 | 2 | 4 | 8 | 2 | 39 |
| Total | 9 | 2 | 19 | 4 | 6 | 3 | 11 | 6 | 11 | 3 | 74 |
| % each mutant | 12.1 | 2.7 | 25.7 | 5.4 | 8.1 | 4.1 | 14.9 | 8.1 | 14.9 | 4.1 | ~100% |
| Mutagenized | |||||||||||
| Section | 1 | 2 | 3 | 4ABC | 4A | 4B | 4C | 5 | 6 | 7 | Total his- mutants |
| Tuesday | 2 | 5 | 4 | 2 | 6 | 5 | 5 | 0 | 4 | 1 | 34 |
| Wednesday | 9 | 1 | 15 | 0 | 9 | 1 | 2 | 2 | 9 | 4 | 52 |
| Total | 11 | 6 | 19 | 2 | 15 | 6 | 7 | 2 | 13 | 5 | 86 |
| % each mutant | 12.8 | 7.0 | 22.1 | 2.3 | 17.4 | 7.0 | 8.1 | 2.3 | 15.1 | 5.8 | ~100% |
QUESTION 1
A mutation caused by exposure to gamma rays is called a spontaneous mutation
| a. | True | |
| b. | False | |
| c. | Sometimes, depending on the type of base change | |
| d. | Gamma rays do not cause mutations |
QUESTION 2
A recessive mutation affecting an essential biochemical pathway can be detected________
| a. | when the organism is heterozygous for that mutation. | |
| b. | when the organism is homozygous for that mutation. | |
| c. | in either homozygous or heterozygous conditions. | |
| d. | only by sequencing (recessive mutations never show a phenotype). |
QUESTION 3
During DNA replication, the newly synthesized chain grows by adding
| a. | nitrogenous bases | |
| b. | the sugar-phosphate backbone | |
| c. | nucleosides | |
| d. | dNTPs |
QUESTION 4
During replication, the DNA strand 5â- AAGTCTAGCCTAG -3â will serve as a template for the polymerization of:
| a. | 5â- CTAGGCTAGACTT -3â | |
| b. | 5â - TTCAGATCGGATC -3â | |
| c. | 5â - GATCCGATCTGAA -3â | |
| d. | 3â - AAGTCTAGCCTAG -5â |
QUESTIOn 5
Given the following DNA sequences, select which statement(s) is(are) correct.
Sequence 1:
5â-TGGACGCTAA-3â
3â-ACCTGCGATT-5â
Sequence 2:
5â-AATCGCAGGT-3â
3â-TTAGCGTCCA-5â
Sequence 3:
5â-ACCTGCGATT-3â
3â-TGGACGCTAA-5â
| a. | Sequences 1 and 2 are the same | |
| b. | Sequences 1 and 3 are the same | |
| c. | Sequences 2 and 3 are the same | |
| d. | Sequences 1, 2 and 3 are all different |
QUESTION 6
Repetitive sequences in the genome are hotspots for:
| a. | Deamination | |
| b. | Depurination | |
| c. | Thymine dimer formation | |
| d. | Replication errors |
QUESTION 7
Select which statement(s) about the Ames test is(are) correct
| a. | it has been designed to understand mutation repair systems in Salmonella typhimurium | |
| b. | it uses mammalian liver extract | |
| c. | it allows to study whether chemical compounds or their enzymatic breakdown products are mutagenic | |
| d. | it is based on whether a chemical compound causes reversion mutations from his+ to his- | |
| e. | two of the above are correct | |
| f. | three of the above are correct |
QUESTION 8
Select which statement(s) is(are) correct.
| a. | All DNA strands have a direction, and it is specified by the carbons in the sugar backbone. | |
| b. | All DNA strands have a direction, and it is specified by hydrogen bonds between nucleotides. | |
| c. | In order to form proper base pairs in a double stranded DNA molecule, the two strands must run in opposite directions. | |
| d. | A and C are correct. | |
| e. | B and C are correct. |
QUESTION 9
Studies of gene mutation frequencies have shown that:
| a. | mutations are rare, and genomes are generally stable. | |
| b. | mutation frequencies differ among organisms and also between genes, suggesting certain genes are more susceptible to mutation. | |
| c. | mutation frequencies are consistent between organisms, and each region of DNA is equally susceptible to random mutations. | |
| d. | Both A and B are correct. | |
| e. | Both A and C are correct. |
QUESTION 10
The compound 5-bromodeoxyuridine (BrdU) is a derivative of uracil, and if BrdU becomes incorporated during DNA replication, it pairs with adenine. This compound is best classified as which type of mutagen?
| a. | base analog | |
| b. | base inducer | |
| c. | intercalating agent | |
| d. | oxidative agent | |
| e. | alkylating agent |
QUESTION 11
The rate of mutation of the fruit fly is higher than the rate of mutation of Algae
True
False
QUESTION 12
Thymine dimers are most commonly caused by which of the following?
| a. | X-rays | |
| b. | Alkylating agents | |
| c. | U.V. irradiation | |
| d. | DNA intercalating agents |
QUESTION 13
What chemical group is found in the 3â end of a DNA strand?
| a. | an alcohol | |
| b. | a hydroxyl | |
| c. | a methyl | |
| d. | a phosphate |
QUESTION 14
What chemical group is found in the 5â end of a DNA strand?
| a. | an alcohol | |
| b. | a hydroxyl | |
| c. | a methyl | |
| d. | a phosphate |
QUESTION 15
Which is the correct order of molecules binding to DNA during DNA replication?
| a. | Helicase, SSB, primase, DNA pol III, DNA pol I, ligase | |
| b. | SSB, DNA pol I, ligase, helicase, DNA pol I, primase | |
| c. | primase, helicase, DNA pol III, ligase, DNA pol I, SSB | |
| d. | SSB, helicase, primase, DNA pol III, DNA pol I, ligase |
QUESTION 16
Which statement(s) is(are) correct about strand slippage?
| a. | It can cause disorders such as Huntingon disease. | |
| b. | It is a process that causes mutations altering the number of DNA repeats. | |
| c. | It is a process that incorporates nucleotide base analogs and trinucleotide repeats. | |
| d. | a and b are correct. | |
| e. | b and c are correct. | |
| f. | a, b and c are correct. |
help needed asap.
13. The arms of a human and the wing of a bat are _________________ structures, composed of the same bones that have been modified for different functions.
| a. | analogous |
| b. | vestigial |
| c. | homologous |
| d. | convergent |
14. Xeroderma pigmentosum is an autosomal recessive genetic disorder. People who are homozygous for the disease-causing allele have skin that is damaged by exposure to ultraviolet radiation; this can lead to skin cancer at an early age. The mutation that causes this disorder is in a gene that functions:
| a. | to repair DNA by excising (removing) nucleotides damaged by UV light. |
| b. | in lysosomes, to break down lipids that otherwise accumulate in the nervous system. |
| c. | to produce the UV blocking pigment melanin in the skin cells |
| d. | in red blood cells to carry oxygen to the skin. |
15. The Amish are a religious sect descended from a small group of colonists who came to the United States over 200 years ago. Their religious beliefs have kept them isolated from society. The Amish have a much higher than average incidence of both polydactyly (extra fingers and toes) and dwarfism in their communities. This is most likely explained by:
| a. | inheritance of acquired characters. |
| b. | the founder effect. |
| c. | disruptive selection. |
| d. | natural selection. |
16. In the structure of DNA that Watson and Crick proposed, the sides of the "ladder" of the DNA molecule are always the same distance apart, making the molecule a constant width. This occurs because when the bases hydrogen bond to form the rungs of the "ladder", a:
| a. | purine always pairs with a pyrimidine. |
| b. | purine always pairs with a purine. |
| c. | pyrimidine always pairs with a pyrmidine. |
| d. | The structure of the double helix is not determined by how the bases pair. |
17. The RNA transcript of DNA that travels to the cytoplasm, carrying the instructions to make a protein, is called:
| a. | rRNA. |
| b. | tRNA. |
| c. | mRNA. |
| d. | RNA polymerase. |
18. When DNA is replicated, the error rate is approximately one error for every 10,000 nucleotides copied. However, that error rate is reduced to only 1 error for every 1 billion nucleotides. The DNA sequence is "corrected" by:
| a. | repeating S phase to see if the error rate is lower the second time around. |
| b. | enzymes that proofread the DNA and repair errors. |
| c. | messenger RNA during the process of transcription. |
| d. | Any errors made during DNA replication cannot be corrected. If errors are detected after S phase, the cell is destroyed. |
19. Mendel's principle of segregation says that:
| a. | when gametes are formed, each gamete receives only one allele for a particular gene. |
| b. | some genes are dominant to others. |
| c. | a testcross must be used to determine the genotype of an organism with a dominant phenotype. |
| d. | all of the above |
20. Tay-Sachs disease is lethal before reproductive age, but the allele persists in Louisiana French Canadians because:
| a. | it is a dominant allele. |
| b. | new mutations causing this disease are common in that population. |
| c. | it is not expressed in the phenotype of heterozygous individuals. |
| d. | the disease is contagious and can be transmitted by nonheritable means. |
21. Physical features that are similar in organisms which are not closely related to each other are most likely a result of ____________. A good example of this is the similarities seen between some marsupial and placental mammals.
| a. | natural selection. |
| b. | adaptation to similar environments |
| c. | convergent evolution |
| d. | All of the above phrases can be used to correctly fill this blank. |
22. In humans, which of the following sex chromosome compliments could be found in males?
| a. | XY |
| b. | XX |
| c. | Y |
23. The proteins that are associated with eukaryotic chromosomes:
| a. | help to package the DNA within the nucleus. |
| b. | are involved in gene expression, through binding with the DNA. |
| c. | may be replicating or transcribing the DNA. |
| d. | All of these are true of proteins that are associated with eukaryotic chromosomes. |
24. A sequence of DNA nucleotides that contains the information to produce a single protein is a(n):
| a. | codon. |
| b. | gene. |
| c. | polypeptide. |
| d. | anticodon. |
