BackWhich of the following is not true of a codon?
a. It may code for the same amino acid as another codon.
b. It never codes for more than one amino acid.
c. It extends from one end of a tRNA molecule.
d. It is the basic unit of the genetic code.
Which of the following correctly ranks the structures in order of size, from largest to smallest?
a. Gene–Chromosome–Nucleotide–Codon
b. Chromosome–Gene–Codon–Nucleotide
c. Nucleotide–Chromosome–Gene–Codon
d. Chromosome–Nucleotide–Gene–Codon
Using the genetic code (Table 10.1), list the order of amino acids encoded by the following mRNA nucleotides: CAACGCAUUUUG.
Which of the following describes the experimental strategy that was used to decipher the genetic code?
a. Comparing the amino acid sequences of proteins with the base sequence of their genes
b. Analyzing the sequence of RNAs produced from known DNA sequences
c. Analyzing mutants that changed the code
d. Examining the polypeptides produced when RNAs with particular sequences were translated
A minimal genetic code requires only 21 codons—one for each amino acid, and one for a stop signal. Given this, what advantage might be offered by having a code with 64 codons?
Using Figure 17.6, identify a 5′→3′ sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys.
a. 5′-UUUCCCAAA-3′
b. 5′-GAACCCCTT-3′
c. 5′-CTTCGGGAA-3′
d. 5′-AAACCCUUU-3′
Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.)
(b) Suppose a mutant strain can survive if substrate 5 is added to the growth medium, but it cannot grow if substrates 1, 2, 3, or 4 are added. Which enzyme in the pathway is affected in this mutant?
Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.)
(a) Suppose a mutation made the gene for enzyme C nonfunctional. What molecule would accumulate in the affected cells?
One of the possibilities considered about the genetic code was that the code was overlapping, meaning that a single base could be part of up to three codons. How many amino acids would be encoded in the sequence 5′-AUGUUACGGAAU-3′ by a non-overlapping and a maximally overlapping triplet code?
a. 4 (non-overlapping) and 16 (overlapping)
b. 4 and 12
c. 4 and 10
d. 12 and 4