Genetics Problem Set #3

One form of deafness called CMT is caused by the absence of a single amino acid in the middle of the PMP22 protein: everything else about the protein is normal. You look at the sequence of the PMP22 gene in a normal person and a person with CMT. When you are comparing the two sequences, you would expect to find that the person with CMT has: a) Any of the above is possible b) A new termination codon c) An insertion d) A deletion e) either a deletion or a new termination codon

A deletion

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein. Use this information and Figure 13-7 to answer the questions. Wild Type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr Mutant 1: Met-Trp Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His Which of the following could be the ribonucleotide change that produced Mutant 1? (Use only the information for the wild-type and Mutant 1 sequence in answering this question.) Select all that apply. - A to G - A to U - C to A - C to G - C to U - U to C - U to G - U to A

C to A C to G U to G U to A

How do the three types of base substitution mutations differ?

See image.

DNA polymerase is very accurate and rarely makes a mistake in DNA replication. Occasionally, however, an error in replication, known as a point mutation, is introduced. There are two general categories of point mutations—frameshift mutations (also called base-pair insertions or base-pair deletions) and base substitution mutations. If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above. 5'-ACTTACGTGA-3' 5'-ACTAAGTGA-3' 5'-ACTCGTGA-3' 5'-ACTACGTGT-3'

See image. A base substitution mutation can occur if the DNA polymerase inserts the wrong nucleotide base as it synthesizes a new strand of DNA. Base substitution mutations will change the composition of the sequence but not the number of nucleotides. A frameshift mutation can occur if the DNA polymerase leaves out a nucleotide or adds an extra nucleotide to the sequence. Frameshift mutations will change the number of nucleotides in a sequence Certain forms of cancer occur because of mutations in DNA sequences that are located in so-called mutational hotspots. These hotspots are locations in the DNA sequence where mutations occur more often than in other places.

DNA polymerase is very accurate and rarely makes a mistake in DNA replication. Occasionally, however, an error in replication, known as a point mutation, is introduced. There are two general categories of point mutations—frameshift mutations (also called base-pair insertions or base-pair deletions) and base substitution mutations. When a base substitution mutation occurs, one nucleotide in a replicating DNA sequence is substituted for another, which results in the production of a mutant strand of DNA. The result of the mutation depends on how the substituted nucleotide base alters the string of amino acids coded by the mutant DNA. The three types of base substitution mutations are nonsense mutations, missense mutations, and silent mutations. Each type is defined by how it affects protein synthesis. Label the four mutated DNA segments shown below according to the type of point mutation each represents. Use the codon table above to determine how each mutation would affect the amino acid coding for each segment.

See image. Point mutations in DNA sequences can profoundly affect protein synthesis, or they can have no effect at all. Point mutations can be beneficial to an organism but are more commonly neutral or harmful. All base substitution mutations alter one base within the DNA sequence, causing a new base pair to form as the DNA replicates. This change in turn alters the mRNA sequence when the DNA is transcribed. The effect of this nucleotide substitution on the translation of the mRNA to a protein will depend on what amino acid is now coded for by the altered base sequence. There are three possible outcomes that can result: nonsense mutation: the new base changes an amino acid codon to a stop codon, ending protein synthesis and resulting in a shorter and usually nonfunctional protein. missense mutation: the new base leads to the insertion of a different amino acid than had been coded for, possibly altering the resulting protein's structure. silent mutation: the new base does not change the amino acid sequence coded for by the original DNA strand.

Mutations in the BRCA2 gene are implicated in breast cancer. Members of a particular family have a nonsense mutation in the middle of the BRCA2 gene. This type of mutation will...... a) Convert a codon that encodes one amino acid into a different amino acid b) Both A and B c) Stop translation of the RNA into amino acids at that site d) Stop transcription of the DNA into RNA at that site

Stop translation of the RNA into amino acids at that site

Of the mutations listed below, which one will likely change the amino acid sequence of the protein coded by the gene the least? a) a base substitution at the beginning of the gene b) a base substitution at the end of the gene' c) a frameshift deletion at the beginning of the gene d) a frameshift deletion at the end of the gene

a base substitution at the end of the gene

DNA polymerase is very accurate and rarely makes a mistake in DNA replication. Occasionally, however, an error in replication, known as a point mutation, is introduced. There are two general categories of point mutations—frameshift mutations (also called base-pair insertions or base-pair deletions) and base substitution mutations. Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene? a) a base substitution at the beginning of the gene b) a base substitution at the end of the gene c) a frameshift deletion at the beginning of the gene d) a frameshift deletion at the end of the gene

a frameshift deletion at the beginning of the gene A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein. Use this information and Figure 13-7 to answer the questions. Wild Type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr Mutant 1: Met-Trp Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His What type of mutation led to Mutant 1? a) missense b) nonsense c) silent d) sense e) frameshift

b) nonsense

Use the codon chart to predict the amino acid sequence produced during translation by the following short hypothetical mRNA sequences. Sequence 1: 5'-AUGCCGGAUUAUAGUUGA-3' Sequence 2: 5'-AUGCCGGAUUAAGUUGA-3' What type of mutation gave rise to Sequence 2? Enter your answer as frameshift, nonsense or missense.

frameshift

Use the codon chart to predict the amino acid sequence produced during translation by the following short hypothetical mRNA sequences. Sequence 1: 5'-AUGCCGGAUUAUAGUUGA-3' Sequence 2: 5'-AUGCCGGAUUAAGUUGA-3' Sequence 2: 5'-AUGCCGGAUUAAGUUGA-3'

met-pro-asp-(stop)

Use the codon chart to predict the amino acid sequence produced during translation by the following short hypothetical mRNA sequences. Sequence 1: 5'-AUGCCGGAUUAUAGUUGA-3' Sequence 2: 5'-AUGCCGGAUUAAGUUGA-3' Sequence 1: 5'-AUGCCGGAUUAUAGUUGA-3'

met-pro-asp-tyr-ser-(stop)

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein. Use this information and Figure 13-7 to answer the questions. Wild Type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr Mutant 1: Met-Trp Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His What type of mutation led to Mutant 2?

missense

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein. Use this information and Figure 13-7 to answer the questions. Wild Type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr Mutant 1: Met-Trp Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His At which codon position did the ribonucleotide change occur?

third position