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Questions and Answers

What type of mutation is described by the sequence 5'-ACTCGTGA-3' compared to 5'-ACTACGTGA-3'?

  • Base substitution mutation (correct)
  • Insertion mutation
  • Frameshift mutation (correct)
  • Deletion mutation

    • Which of the following mutations would most severely affect the protein coded for by a gene?

  • Missense mutation
  • Frameshift deletion at the beginning of the gene (correct)
  • Silent mutation
  • Point mutation

    • Why would a mutation in a somatic cell of a multicellular organism not necessarily result in a detectable phenotype?

    Because the somatic mutation first appears in a single cell, and the organism is unlikely to be sufficiently altered to respond to a screen as other cells will not have the mutation.

    Why are frameshift mutations likely to be more detrimental than point mutations?

    <p>Because they are likely to change more than one amino acid.</p> Signup and view all the answers

    What is a tautomeric shift and how may it lead to a mutation?

    <p>Tautomeric shifts allow hydrogen bonding between bases that are usually noncomplementary, resulting in point mutations during replication.</p> Signup and view all the answers

    What mutagen causes thymine dimers?

    <p>UV light.</p> Signup and view all the answers

    What mutagen donates a CH2CH3 group to nucleotides?

    <p>Ethylmethane sulfonate.</p> Signup and view all the answers

    What is the process of error correction of mismatched bases carried out by DNA polymerases called?

    <p>Proofreading.</p> Signup and view all the answers

    What hazardous materials can stable molecules be transformed into when X rays penetrate cells?

    <p>Free radicals and reactive ions.</p> Signup and view all the answers

    What human condition is caused by unrepaired UV-induced lesions?

    <p>Xeroderma pigmentosum.</p> Signup and view all the answers

    Which repair pathway focuses on double-strand break repair?

    <p>Nonhomologous end joining</p> Signup and view all the answers

    Which statement about mismatch repair is false?

    <p>No known human diseases are caused by mutations in genes required for mismatch repair.</p> Signup and view all the answers

    Which enzyme is responsible for proofreading during replication?

    <p>DNA polymerase.</p> Signup and view all the answers

    What are the consequences of having pyrimidine dimers in DNA?

    <p>They distort the DNA structure and result in errors during DNA replication.</p> Signup and view all the answers

    Thymine dimers can be repaired by Photoreactivation Repair or Nucleotide Excision Repair.

    <p>True</p> Signup and view all the answers

    Which of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true?

    <p>Both NER and BER involve the removal of damaged bases by a nuclease.</p> Signup and view all the answers

    X-rays are known to be mutagenic.

    <p>True</p> Signup and view all the answers

    What reasons justify the use of X rays in mammography as a medical screening technique?

    <p>Mammography significantly reduces breast cancer mortality.</p> Signup and view all the answers

    What mutation is represented by having one copy of the NF1 gene lost?

    <p>Haploinsufficiency.</p> Signup and view all the answers

    Most cases of breast cancer are heritable.

    <p>False</p> Signup and view all the answers

    The most damaging and mutagenic type of radiation is ultraviolet (UV) radiation.

    <p>False</p> Signup and view all the answers

    Harmful chemicals are detoxified by _____ enzymes in our liver.

    <p>cytochrome p450.</p> Signup and view all the answers

    What is the most dangerous form of DNA damage?

    <p>Double-strand break.</p> Signup and view all the answers

    If a base in DNA is alkylated, what type of mutations does it lead to?

    <p>Transitions.</p> Signup and view all the answers

    DNA polymerase possesses intrinsic 3' to 5' exonuclease activity that allows it to proofread newly synthesized DNA during replication.

    <p>True</p> Signup and view all the answers

    A type of DNA repair pathway that occurs during DNA replication and fixes mistakes not corrected by DNA polymerase is called?

    <p>Mismatch repair.</p> Signup and view all the answers

    What disorder is a person with mutations in mismatch repair genes at risk of developing?

    <p>Hereditary nonpolyposis colon cancer.</p> Signup and view all the answers

    What type of damage is most likely to be corrected by nucleotide excision repair?

    <p>Thymine dimers induced by UV light.</p> Signup and view all the answers

    Which enzyme removes the incorrect base during base excision repair?

    <p>DNA glycosylase.</p> Signup and view all the answers

    Which of the following is NOT true of non-homologous end joining?

    <p>It is primarily used to repair single-strand breaks in DNA.</p> Signup and view all the answers

    The total set of DNA in a cell or organism is called its?

    <p>Genome.</p> Signup and view all the answers

    What is an example of highly repetitive, satellite DNA?

    <p>The alphoid family of DNA sequences.</p> Signup and view all the answers

    In what way is a DNA transposon different from a retrotransposon?

    <p>DNA transposons encode a transposase enzyme, while retrotransposons encode reverse transcriptase and integrase enzymes.</p> Signup and view all the answers

    Transposable elements may 'jump' into which region of DNA?

    <p>All of the above</p> Signup and view all the answers

    Whole genome sequencing involves first digesting the genome with restriction enzymes and then lining up the pieces to make a series of overlapping sequences called?

    <p>Contiguous fragments.</p> Signup and view all the answers

    Why are STRs the most commonly used loci for forensic DNA profiling?

    <p>Because STRs are like VNTRs, but the repeat portion is shorter, making them more suitable for PCR.</p> Signup and view all the answers

    How does homologous recombination repair correct double-strand breaks?

    <p>The break is recognized and degraded, leaving 3' overhangs that invade the homologous DNA duplex on the sister chromatid for alignment and extension by DNA polymerase.</p> Signup and view all the answers

    What DNA repair pathway is disabled in individuals suffering from skin-related disorders due to UV exposure?

    <p>Nucleotide excision repair pathway.</p> Signup and view all the answers

    Describe one example of how a mutation in a noncoding region of DNA might lead to changes in gene expression.

    <p>A mutation could cause a protein to be produced in the wrong place or at the wrong time, or completely eliminate its production.</p> Signup and view all the answers

    How might it be determined whether the BRCA1 mutation is part of Laurie's germline or just a somatic mutation in her tumor?

    <p>Germline pathogenic variants are identified through a blood sample, while somatic variants are detected by testing the tumor directly.</p> Signup and view all the answers

    Which protein connects sister chromatids to one another?

    <p>Cohesion.</p> Signup and view all the answers

    Assume that an organism has a diploid number of 10. How many chromatids are visible at the end of mitotic prophase?

    <ol start="20"> <li></li> </ol> Signup and view all the answers

    In a cancer cell, _____ are over-activated versions of normal _____.

    <p>Oncogenes; proto-oncogenes.</p> Signup and view all the answers

    In what phase of meiosis do nonsister chromatids exchange genetic information via crossing over?

    <p>Prophase I.</p> Signup and view all the answers

    What is the phenotypic ratio for monohybrid crosses, if both parents are heterozygous and the trait being studied is Mendelian?

    <p>3 dominant: 1 recessive.</p> Signup and view all the answers

    During anaphase I of meiosis, sister chromatids are separated.

    <p>False</p> Signup and view all the answers

    The African elephant has 56 chromosomes! During the development of a male elephant's sperm, how many tetrads are visible during prophase I?

    <ol start="28"> <li></li> </ol> Signup and view all the answers

    During mitosis and meiosis, the separation of chromosomes is called _____.

    <p>Disjunction.</p> Signup and view all the answers

    When a cell exits the cell cycle and stops dividing, it enters a state of _____ known as G0.

    <p>Quiescence.</p> Signup and view all the answers

    Marfan syndrome results from a mutation in a single gene on chromosome 15, which encodes for the structural protein fibrillin. As a result, affected individuals have structural deficiencies in multiple tissue types. What concept does this illustrate?

    <p>Pleiotropy.</p> Signup and view all the answers

    Some women who carry the BRCA1 gene mutation develop breast cancer at 32, while others develop ovarian cancer at 54. What phenomenon does this situation describe?

    <p>Variable expressivity.</p> Signup and view all the answers

    A husband and wife have normal vision, although both of their fathers are red-green color-blind, inherited as an X-linked recessive condition. What is the probability that their daughter will be color-blind?

    <ol start="0"> <li></li> </ol> Signup and view all the answers

    Which of the following is NOT a major feature of the Watson and Crick DNA model?

    <p>A complete turn is 20 angstroms</p> Signup and view all the answers

    You have discovered a new organism! Its DNA consists of 20% thymine. Based on this, what percentage of the DNA will be guanine?

    <p>30%.</p> Signup and view all the answers

    If the dinucleotide was cleaved with an enzyme that breaks the covalent bond connecting the phosphate to the 5' carbon, to which nucleoside is the phosphate now attached?

    <p>The nucleoside that contains A (deoxyadenosine).</p> Signup and view all the answers

    What is the complementary DNA sequence to 5′-ATGCTTGACTG-3′?

    <p>5′-CAGTCAAGCAT-3′.</p> Signup and view all the answers

    If Avery, MacLeod, and McCarty had determined that the transforming molecule was a protein, what experimental results would have been observed?

    <p>Heat-killed cultures treated with protease would not have transformed the IIR cells.</p> Signup and view all the answers

    Which enzyme is responsible for elongating the lagging strand during eukaryotic DNA replication?

    <p>DNA polymerase delta.</p> Signup and view all the answers

    Which enzyme is NOT directly involved in joining Okazaki fragments from the lagging strand?

    <p>Primase</p> Signup and view all the answers

    What is the function of the protein component of the telomerase enzyme?

    <p>To catalyze the synthesis of telomeric DNA by reverse transcription.</p> Signup and view all the answers

    If the dispersive model of DNA replication were correct, how many bands would have been observed by Meselson and Stahl after two rounds of replication?

    <ol> <li></li> </ol> Signup and view all the answers

    What accounts for the overall rate of eukaryotic DNA replication being similar to prokaryotes, despite larger genomes?

    <p>There are more origins of replication in eukaryotic chromosomes.</p> Signup and view all the answers

    Consider the figure. What can you conclude?

    <p>Both A and B</p> Signup and view all the answers

    Chromatin that is organized around actively expressed genes is configured as heterochromatin.

    <p>False</p> Signup and view all the answers

    During DNA replication, the newly-synthesized daughter strand of DNA is elongated in the 5' to 3' direction.

    <p>True</p> Signup and view all the answers

    The sequence of a DNA molecule is written below. Which transcript would it produce if the coding strand is indicated in bold type?

    <p>5' AAAUGCCGU 3'.</p> Signup and view all the answers

    Selenocysteine is the '21st amino acid.' It is encoded by the codon UGA. To what 'rule' does this dual use of the genetic code serve as an exception?

    <p>Codons are unambiguous.</p> Signup and view all the answers

    RNA synthesis differs from DNA synthesis in several ways. In what way are they NOT different?

    <p>RNA synthesis proceeds in the 5' to 3' direction, not the 3' to 5' direction.</p> Signup and view all the answers

    Which RNA polymerase is responsible for transcribing mRNAs in eukaryotic cells?

    <p>RNA polymerase II.</p> Signup and view all the answers

    Study Notes

    DNA Replication and Mutations

    • A segment of replicated DNA can include mutations such as frameshift or base substitution, altering the nucleotide sequence.
    • Frameshift mutations, particularly deletions or insertions, have significant effects on protein coding, often changing multiple amino acids due to shifting the reading frame.
    • Point mutations involve a single nucleotide substitution, but are generally less disruptive than frameshift mutations.

    Mutation Impact and Detection

    • Mutations in somatic cells may not result in observable phenotypes due to their occurrence in isolated cells, making these changes undetectable in genetic screenings.
    • Tautomeric shifts can cause mutations by enabling non-complementary base pairings, leading to point mutations during DNA replication.

    DNA Damage and Repair Mechanisms

    • UV light is a mutagen that causes thymine dimers, which distort DNA and produce errors in replication.
    • Ethylmethane sulfonate donates a CH2CH3 group to nucleotides, leading to mutations.
    • DNA polymerase performs proofreading, correcting mismatched bases during DNA synthesis through intrinsic exonuclease activity.

    Repair Pathways

    • Double-strand breaks are primarily repaired through nonhomologous end joining.
    • Nucleotide excision repair (NER) and base excision repair (BER) both involve the removal of damaged bases but address different types of DNA damage.
    • Pyrimidine dimers can be repaired via Photoreactivation or NER.

    Genetic Conditions and Repair Implications

    • Xeroderma pigmentosum arises from unrepaired UV-induced lesions, highlighting the importance of proper DNA repair mechanisms.
    • Mismatch repair deficiencies are linked to hereditary nonpolyposis colon cancer, showcasing the consequences of repair pathway failures.

    Chromosomal Behavior in Cell Division

    • In mitotic prophase, a diploid organism displays twice the number of chromosomes, correlating with chromatid visibility.
    • Oncogenes, derived from proto-oncogenes, become over-activated in cancer cells, disrupting normal cellular regulation.
    • Genetic exchange during meiosis occurs in prophase I through crossing over between nonsister chromatids.

    Genetic Inheritance and Expression

    • The phenotypic ratio of a monohybrid cross with heterozygous parents reflects a 3:1 dominance in Mendelian traits.
    • Traits can exhibit variable expressivity whereby identical mutations lead to different phenotypic outcomes in individuals.

    Transposable Elements and Genomic Structure

    • Transposable elements may integrate into various DNA regions, including gene coding sequences and promoters, potentially disrupting gene function.
    • Satellite DNA, such as the alphoid family, illustrates highly repetitive sequences found within genomes.

    Genetic Code and Transcription

    • RNA polymerase II is responsible for mRNA transcription in eukaryotes; transcription involves synthesizing RNA in the 5' to 3' direction.
    • The genetic code features exceptions, as exemplified by selenocysteine encoded by UGA, which typically functions as a stop codon.

    Experimental Findings in Genetics

    • The discovery of DNA's transforming principle highlighted that if proteins had been the transformative agent, heat-killed cultures would not affect non-virulent strains.
    • Whole genome sequencing comprises digesting DNA with restriction enzymes to produce overlapping contiguous fragments necessary for assembly.

    Cellular Responses and Genetic Profiles

    • Blood samples identify germline mutations, whereas somatic mutations are tested directly from tumors, critical for understanding cancer genetics.
    • Methods like STR analysis provide robust tools for forensic DNA profiling, leveraging shorter variously repeated DNA segments.

    Summary of Key Concepts

    • Cohesion proteins connect sister chromatids, maintaining structure during cell division.
    • Disjunction denotes the separation of chromosomes during mitosis and meiosis, impacting genetic distribution to daughter cells.
    • Quiescence describes a state where cells exit the division cycle, crucial for cellular senescence and tissue homeostasis.

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