BIO130H1 : BIO130 Section One Guide (5)

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26 Apr 2011

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Mutation rate rate at which observable changes occur in dna sequences: a single genes that encodes an average-sized protein ( 103 nucleotide pairs) accumulates a mutation about once in about 106 bacterial cell generations. Comparing amino acid sequences of the same protein in several species can provide an estimate of mutation rates in mammals; because natural selection causes mutations to vanish from the population, these tend to be underestimates. Luckily, the sequence of one family of protein fragments (fibrinopeptides) does not seem to matter, allowing the encoding genes to accumulate mutations without being selected against. Fibrinopeptides fragments 20 aa long that are discarded when the protein fibrinogen is activated to form fibrin during blood clotting: because the function of fibrinopeptides doesn"t depend on its aa sequence, it can tolerate almost any mutation. Another way to estimate mutation rates is to compare dna sequences between related species. Low mutation rates are necessary for life as we know it.

Related Questions

1) Explain how the Ames test can be used to detect potential mutagens? What are the limitations of this test?

2) The base pair sequence of a region of a gene coding for a polypeptide is:

Strand A: 5â C A C C T A A C T T A C T C A G* C T T A C G A A G T C T A C C C A G C G 3â

Strand B: 3â G T G G A T T G A A T G A G T C* G A A T G C T T C A G A T G G G T C G C 5â

A.) If this gene codes for a polypeptide that contains three Tyrosines (Tyr), which strand is transcribed? (1 pt)

B). What is the nucleotide of the mRNA transcribed from this DNA? (Note: there is no âstartâ codon. Simply start from the âappropriateâ end). You MUST label the appropriate 5 â and 3â ends.

C.) What is the polypeptide sequence of the protein translated from this mRNA?

D.) Hydroxylamine (HA) affects the bold-faced (*) base pair and causes a mutation during DNA replication. What is the amino acid sequence of the polypeptide coded by the mutant gene?

The effect of base-pair substitution mutations on protein function varies widely from no detectable effect to the complete loss of protein function (null allele).

Part A Why do the functional consequences of base-pair substitution vary so widely? Select the four correct answers.

1. Nucleotide substitutions might not cause changes in the amino acid sequence of the protein.

2. The reading frame of the gene could be affected by base-pair substitution mutations, which almost always leads to lack of function.

3. Nucleotide substitutions in exons always lead to changes of amino acids in the protein.

4. The reading frame of the gene could be affected by base-pair substitution mutations, which rarely leads to lack of function.

5. Missense mutations create amino acid substitutions, which might affect protein functionality.

6. Mutations that occur in the intron sequences generally do not affect protein functionality.

bluelion973

Histone proteins areamong the most highly conserved proteins in eukaryotes. Histone H4proteins from a pea and a cow, for example, differ in only 2 of 102amino acids. Comparison of the gene sequences shows many moredifferences at the nucleotide level, but only two of these changeencoded amino acids. These observations indicate that mutationsthat change amino acids must be selected against. Why do yousuppose that amino acid-altering mutations in histone genes aredeleterious?

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BIO130H1 : BIO130 Section One Guide (5)

BIO130H1 Full Course Notes

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