chapter 16 hw

Mutant N. crassa cells that cannot make arginine on their own must be supplied with arginine to grow. For the metabolic pathway shown in Figure 16.1, if a mutant lacked enzyme 2, would it still be able to grow if it were provided with (a) ornithine or (b) citrulline in its diet?

(a) No; (b) Yes

Given this, what advantage might be offered by having a code with 64 codons?

An advantage of having more than the minimum number of codons is error tolerance. Because of the redundancy in an expanded code, not every base pair change will change the meaning of a codon.

Which of the following is an important exception to the central dogma of molecular biology?

Many genes code for RNAs that function directly in the cell.

A frameshift mutation that occurs very early in a protein sequence would have what effect on the protein's structure?

Primary, secondary, and tertiary structures would be altered.

Why is a single base-pair deletion mutation within a protein-coding sequence more likely to be harmful than a single base-pair change mutation?

Single base-pair deletions shift the reading frame and jumble the message at all points after the mutation. A single base-pair change may not even change the amino acid, and if it does, it's possible the single amino acid change within a protein can be tolerated.

Identify the start and stop codons in the mRNA sequence 5'-UAUCCAUGGCACUUUAAAC-3'. What is the resulting amino acid sequence?

Start codon: AUG; stop codon: UAA; protein: Met-Ala-Leu-stop

A small portion of the human transport protein amino acid sequence is shown below. The upper sequence is associated with darker skin, and the lower sequence is associated with lighter skin. What DNA base-pair change created the light-skin form of the human protein from the gene that coded for the dark-skin form?

The base-pair change must have been from a GC to an AC in the first position of the codon.

The zebra fish mutation that reduced coloration created a null allele of the transport protein gene. Which of the following types of mutation would be most likely to create this null allele?

a frameshift mutation

Investigators examined the expression of transporter mRNA and protein produced in zebrafish homozygous for each of the alleles and found the results summarized below (+ = present, − = absent). Does the allele associated with light color appear to be altering transcription or translation? Why?

transcription This is because the end product of transcription is RNA, and no RNA is produced in individuals homozygous for the light-color allele.

Beginning within the nucleus, the first step leading to the synthesis of a polypeptide is _____.

transferring of information from DNA to messenger RNA