Module 12; From gene to protein

Use the following model of a eukaryotic transcript to answer the next few questions. 5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3' Which components of the previous molecule will also be found in mRNA in the cytosol? 5' UTR I1 I2 I3 UTR 3' 5' E1 E2 E3 E4 3' 5' UTR E1 E2 E3 E4 UTR 3' 5' I1 I2 I3 3' 5' E1 I1 E2 I2 E3 I3 E4 3'

5' UTR E1 E2 E3 E4 UTR 3'

Which of the following does not occur in prokaryotic eukaryotic gene expression, but does in eukaryotic gene expression? mRNA, tRNA, and rRNA are transcribed. RNA polymerase binds to the promoter. A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end. Transcription can begin as soon as translation has begun even a little. RNA polymerase requires a primer to elongate the molecule.

A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.

A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate? The sequence evolves very rapidly. The sequence does not mutate. Any mutation in the sequence is selected against. The sequence is found in many but not all promoters. The sequence is transcribed at the start of every gene.

Any mutation in the sequence is selected against.

Which of the following statements is true about protein synthesis in prokaryotes? Extensive RNA processing is required before prokaryotic transcripts can be translated. Translation can begin while transcription is still in progress. Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles. Translation requires antibiotic activity. Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

Translation can begin while transcription is still in progress.

The figure represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid? UGG GUG GUA UUC CAU

UUC

Which of the following is the first event to take place in translation in eukaryotes? elongation of the polypeptide base pairing of activated methionine-tRNA to AUG of the messenger RNA binding of the larger ribosomal subunit to smaller ribosomal subunits covalent bonding between the first two amino acids the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA

The following question refers to this figure of a simple metabolic pathway: According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway? 0 1 2 3 It cannot be determined from the pathway.

2

The nitrogenous base adenine is found in all members of which group? proteins, triglycerides, and testosterone proteins, ATP, and DNA ATP, RNA, and DNA glucose, ATP, and DNA proteins, carbohydrates, and ATP

ATP, RNA, and DNA

What is the function of GTP in translation? GTP energizes the formation of the initiation complex, using initiation factors. GTP hydrolyzes to provide phosphate groups for tRNA binding. GTP hydrolyzes to provide energy for making peptide bonds. GTP supplies phosphates and energy to make ATP from ADP. GTP separates the small and large subunits of the ribosome at the stop codon.

GTP energizes the formation of the initiation complex, using initiation factors.

The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true? If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only). If one stop codon, such as UGA, is found to have a different effect on translation than another stop codon, such as UAA. If prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same polypeptide. If several codons are found to translate to the same amino acid, such as serine. If a single mRNA molecule is found to translate to more than one polypeptide when there are two or more AUG sites.

If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).

Which of the following is not true of a codon? It consists of three nucleotides. It may code for the same amino acid as another codon. It never codes for more than one amino acid. It extends from one end of a tRNA molecule. It is the basic unit of the genetic code.

It extends from one end of a tRNA molecule.

Garrod's information about the enzyme alteration resulting in alkaptonuria led to further elucidation of the same pathway in humans. Phenylketonuria (PKU) occurs when another enzyme in the pathway is altered or missing, resulting in a failure of phenylalanine (phe) to be metabolized to another amino acid: tyrosine. Tyrosine is an earlier substrate in the pathway altered in alkaptonuria. How might PKU affect the presence or absence of alkaptonuria? It would have no effect, because PKU occurs several steps away in the pathway. It would have no effect, because tyrosine is also available from the diet. Anyone with PKU must also have alkaptonuria. Anyone with PKU is born with a predisposition to later alkaptonuria. Anyone with PKU has mild symptoms of alkaptonuria.

It would have no effect, because tyrosine is also available from the diet.

When the function of the newly made polypeptide is to be secreted from the cell where it has been made, what must occur? It must be translated by a ribosome that remains free of attachment to the ER. Its signal sequence must target it to the ER, from which it goes to the Golgi. It has a signal sequence that must be cleaved off before it can enter the ER. It has a signal sequence that targets it to the cell's plasma membrane where it causes exocytosis. Its signal sequence causes it to be encased in a vesicle as soon as it is translated.

Its signal sequence must target it to the ER, from which it goes to the Golgi.

An experimenter has altered the 3' end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3' AC. Which of the following hypotheses describes the most likely result? tRNA will not form a cloverleaf. The nearby stem end will pair improperly. The amino acid methionine will not bind. The anticodon will not bind with the mRNA codon. The aminoacylsynthetase will not be formed.

The amino acid methionine will not bind.

In comparing DNA replication with RNA transcription in the same cell, which of the following is true only of replication? It uses RNA polymerase. It makes a new molecule from its 5' end to its 3' end. The process is extremely fast once it is initiated. The process occurs in the nucleus of a eukaryotic cell. The entire template molecule is represented in the product.

The entire template molecule is represented in the product.

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is TTT. UUA. UUU. AAA. either UAA or TAA, depending on first base wobble.

UUU.

Of the following, which is the most current description of a gene? a unit of heredity that causes formation of a phenotypic characteristic a DNA subunit that codes for a single complete protein a DNA sequence that is expressed to form a functional product: either RNA or polypeptide a DNA-RNA sequence combination that results in an enzymatic product a discrete unit of hereditary information that consists of a sequence of amino acids

a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene? the introns eukaryotic polymerases a bacterial promoter sequence eukaryotic ribosomal subunits eukaryotic tRNAs

a bacterial promoter sequence

Which small-scale mutation would be most likely to have a catastrophic effect on the functioning of a protein? a base substitution a base deletion near the start of a gene a base deletion near the end of the coding sequence, but not in the terminator codon deletion of three bases near the start of the coding sequence, but not in the initiator codon a base insertion near the end of the coding sequence, but not in the terminator codon

a base deletion near the start of a gene

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by a specific characteristic of the ribosome itself, which distinguishes free ribosomes from bound ribosomes. a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane. moving through a specialized channel of the nucleus. a chemical signal given off by the ER. a signal sequence of RNA that precedes the start codon of the message.

a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

Which of the following nucleotide triplets best represents a codon? a triplet separated spatially from other triplets a triplet that has no corresponding amino acid a triplet at the opposite end of tRNA from the attachment site of the amino acid a triplet in the same reading frame as an upstream AUG a sequence in tRNA at the 3' end

a triplet in the same reading frame as an upstream AUG

A frameshift mutation could result from a base insertion only. a base deletion only. a base substitution only. deletion of three consecutive bases. either an insertion or a deletion of a base.

either an insertion or a deletion of a base.

Use the following model of a eukaryotic transcript to answer the next few questions. 5' UTR E1 I1 E2 I2 E3 I3 E4 UTR 3' Suppose that exposure to a chemical mutagen results in a change in the sequence that alters the 5' end of intron 1 (I1). What might occur? loss of the gene product loss of E1 premature stop to the mRNA inclusion of I1 in the mRNA exclusion of E2

inclusion of I1 in the mRNA

A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that many noncoding stretches of nucleotides are present in mRNA. there is redundancy and ambiguity in the genetic code. many nucleotides are needed to code for each amino acid. nucleotides break off and are lost during the transcription process. there are termination exons near the beginning of mRNA.

many noncoding stretches of nucleotides are present in mRNA

The following questions refer to this table of codons. What amino acid sequence will be generated, based on the following mRNA codon sequence? 5' AUG-UCU-UCG-UUA-UCC-UUG 3' met-arg-glu-arg-glu-arg met-glu-arg-arg-glu-leu met-ser-leu-ser-leu-ser met-ser-ser-leu-ser-leu met-leu-phe-arg-glu-glu

met-ser-ser-leu-ser-leu

If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on which of the following media? minimal medium minimal medium supplemented with nutrient A only minimal medium supplemented with nutrient B only minimal medium supplemented with nutrient C only minimal medium supplemented with nutrients A and C

minimal medium supplemented with nutrient B only

Use the following information to answer the next few questions. A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Which component of the complex described enters the exit tunnel through the large subunit of the ribosome? tRNA with attached lysine (#1) tRNA with polypeptide (#2) tRNA that no longer has attached amino acid newly formed polypeptide initiation and elongation factors

newly formed polypeptide

A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that none of the proteins in the cell will contain phenylalanine. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU. the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons. the ribosome will skip a codon every time a UUU is encountered. none of the options will occur; the cell will recognize the error and destroy the tRNA.

proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that some tRNAs have anticodons that recognize four or more different codons. the rules for base pairing between the third base of a codon and tRNA are flexible. many codons are never used, so the tRNAs that recognize them are dispensable. the DNA codes for all 61 tRNAs but some are then destroyed. competitive exclusion forces some tRNAs to be destroyed by nucleases.

the rules for base pairing between the third base of a codon and tRNA are flexible.

Use this representation to answer the following questions. DNA template strand 5' ____________________________ 3' DNA complementary strand 3' ____________________________ 5' In the transcription event of the previous DNA, where would the promoter be located? at the 3' end of the newly made RNA to the right of the template strand to the left of the template strand to the right of the sense strand to the left of the sense strand

to the right of the template strand