What does a bacterial RNA polymerase produce when it transcribes a protein-coding gene? a. rRNA b. tRNA c. mRNA d. snRNA

If a base-pair change occurs in DNA, this a. is a mutation. b. would be a mutation only if it falls in a protein-coding part of a gene. c. would be a mutation only if it falls in a transcribed part of the genome. d. is not a mutation, because only one base pair has been altered.

Which of the following is an important exception to the central dogma of molecular biology? a. Many genes code for RNAs that function directly in the cell. b. DNA is the repository of genetic information in all cells. c. Messenger RNA is a short-lived 'information carrier.' d. Proteins are responsible for most aspects of the phenotype.

Where is the start codon located? a. at the start (5′ end) of the mRNA b. in the DNA just upstream of where transcription starts c. at the downstream end of the 5′ untranslated region (UTR) d. at the upstream end of the 3′ untranslated region (UTR)

Splicing begins: a. as transcription occurs. b. after transcription is complete. c. as translation occurs. d. after translation is complete.

DNA's primary structure is made up of just four different bases, and its secondary structure is regular and highly stable. How can a molecule with these characteristics hold the information required to build and maintain a cell?

Compared with mRNAs that have a cap and tail, predict what will be observed if a eukaryotic mRNA lacked a cap and poly(A) tail. a. The primary transcript would not be processed properly. b. Translation would occur inefficiently. c. Enzymes on the ribosome would add a cap and poly(A) tail. d. tRNAs would become more resistant to degradation.

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 friend says, 'Geneticists spend all their time talking about DNA, but that's silly because DNA really isn't that important in the functions of a cell.' In what ways is she right, and in what ways might she be wrong?

RNases and proteases are enzymes that destroy RNAs and proteins, respectively. Which of the following enzymes, if added to a spliceosome, would be predicted to prevent recognition of pre-mRNA regions critical for splicing? a. an RNase specific for tRNAs b. an RNase specific for snRNAs c. a protease specific for initiation factors d. a protease specific for a release factor

For each of these statements about the genetic code, select True or False. a. T/F Wobble pairing accounts for the redundancy of the genetic code. b. T/F There are 64 different tRNAs that read the 64 possible codons. c. T/F All possible codons are used, but not all codons specify an amino acid. d. T/F Some codons are recognized by proteins, not by tRNAs.

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?

Imagine discovering a loss-of-function mutation in a eukaryotic gene. You determine the gene's nucleotide sequence from the start site for transcription to the termination point of transcription and find no differences from the wild-type sequence. Explain where you think the mutation might be and how the mutation might be acting.

Which of the following describes mutations? Select True or False for each statement. T/F Point mutations can occur in any DNA sequence. T/F Frameshift mutations can occur in any DNA sequence. T/F Neutral mutations depend on the degeneracy of the genetic code. T/F Deleterious mutations occur only in protein-coding sequences of DNA.

In a particular bacterial species, temperature-sensitive conditional mutations cause expression of a wild-type phenotype at one growth temperature and a mutant phenotype at another—typically higher—temperature. Imagine that when a bacterial cell carrying such a mutation is shifted from low to high growth temperatures, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects: a. the terminator sequence b. the start codon c. sigma d. one of the polypeptides of the core RNA polymerase

Explain what's wrong with this statement: All point mutations change the genotype and the phenotype.

In what ways are a promoter and a start codon similar? In what ways are they different?

The nucleotide shown here is called cordycepin triphosphate. It is a natural product of a fungus that is used in traditional medicines. If cordycepin triphosphate is added to a cell-free transcription reaction, the nucleotide is added onto the growing RNA chain but then no more nucleotides can be added. Examine the structure of cordycepin and explain why it ends transcription.

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?

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?

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

Controlling the rates of transcription and translation is important in bacteria to avoid collisions between ribosomes and RNA polymerases. Calculate what the maximum rate of translation by a ribosome in a bacterial cell would have to be, in units of amino acids per second, so as not to overtake an RNA polymerase that is synthesizing mRNA at a rate of 60 nucleotides per second. How long would it take for this bacterial cell to translate an mRNA containing 1800 codons?

Skin color is often one of the first traits people notice in each other. Studies in zebrafish uncovered a mutation that altered a transport protein and resulted in light-colored fish. This discovery led to the finding that the same gene in humans has a strong influence on skin pigmentation in many populations. The zebrafish 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. a missense mutation b. a frameshift mutation c. a neutral mutation d. a silent mutation

Eating even a single death cap mushroom (Amanita phalloides) can be fatal due to a compound called αα-amanitin, a toxin that inhibits transcription.What would you predict to be the immediate outcome of adding αα-amanitin to a cell? a. reduced DNA synthesis b. reduced production of one or more types of RNA c. reduced binding of tRNAs to anticodons d. reduced rate of translocation of ribosomes translating mRNA

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

α-Amanitin inhibits transcription by binding inside an RNA polymerase to a region other than the active site that catalyzes addition of a nucleotide to the RNA chain. Based on the model of RNA polymerase shown in Figure 17.3, predict how the toxin might function to inhibit transcription.

Toxins like αα-amanitin are used for research in much the same way as null mutants (Chapter 16)—to disrupt a process and see what happens when it no longer works. Researchers examined the ability of αα-amanitin to inhibit different RNA polymerases. They purified RNA polymerases I, II, and III from rat liver, incubated the enzymes with different concentrations of αα-amanitin, and then tested their activity. The results of this experiment are shown here. These findings suggest that cells treated with αα-amanitin will have a reduced level of: a. tRNAs b. rRNAs c. snRNAs d. mRNAs

A small portion of the human transport protein amino acid sequence is shown here. 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?

Researchers compared the amino acid sequences of the transport protein in zebrafish, puffer fish, mice, and humans. They found many stretches with identical sequences in all four species. Does this mean that the corresponding mRNA base sequences are also the same in these four species? Explain why or why not.

If you wanted to use αα-amanitin to shut down 95 percent of transcription by RNA polymerase II, roughly what concentration of αα-amanitin would you use? Note that the scale on the x-axis of the graph in Question 13 is logarithmic rather than linear, so that each tick mark shows a tenfold higher concentration.