The Biochemical Basis of Heredity Practice Problems (page 2)

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By — McGraw-Hill Professional
Updated on Aug 19, 2011

Practice 5

Using the information in Table 3-2, convert the following mRNA segment (shown in register as triplets) into a polypeptide chain. Does the number of codons equal the number of amino acids?

    …5'   AUG   GAA   GCA   UCA   CCC   UAG   3'…

Solution 5

    met – glu – ala – ser – pro – (stop)

The number of codons does not equal the number of amino acids because the final codon is a stop codon and does not specify an amino acid.

Practice 6

In the DNA replication fork diagrammed below, the old (template) strands are shown. The two strands on the left are not yet unwound, but the DNA is unwinding in this direction. Using arrows, draw in the new strands that will be synthesized. Which strand will be the leading strand, the upper or lower strand? Indicate the presence of an RNA primer with the letter "P."

Solved Problems

Solution 6

Solved Problems

The upper strand will be the leading strand, as its synthesis can occur from 5' to 3' continuously in the direction that the replication fork is moving. The lower strands are Okazaki fragments that will be joined together to form the lagging strand.

Practice 7

If 54 mutations are detected among 723 progeny of males that received a gamma ray dosage of 2500 roentgen (r) units and 78 mutations among 649 progeny of males that received 4000 roentgens, how many mutants would be expected to appear among 1000 progeny of males that received 6000 roentgens?

Solution 7

The number of mutations induced by ionizing radiation is directly proportional to the dosage.

    78/649s       = 12:02% mutations at 4000 roentgens
    54/723        = 7:47%mutations at 2500 roentgens
    Difference    = 4:55%mutations for 1500 roentgens

Among 1000 progeny at 6000 roentgens we expect 1000(6000/1500) (0:0455) = 182 mutants.

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