Chapter 16 + 17
The following question refers to this table of codons. A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence Phe-Leu-Ile-Val would be ________.
3' AAA-GAA-TAA-CAA 5'
A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is _____.
3' UCA 5'
Use this representation to answer the following question. DNA template strand 5' ___________________________ 3'DNA nontemplate strand 3' ___________________________ 5' Given the locally unwound double strand above, in which direction does the RNA polymerase move while transcribing DNA?
3' → 5' along the template DNA strand
Which model shows the correct polarity of double-stranded DNA?
3'<---------------------5' AGACTGGT TCTGACCA 5'--------------------->3'
Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms?
5 bases
Use this model of a eukaryotic transcript to answer the following question. E = exon and I = intron 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 E1 E2 E3 E4 UTR 3'
The direction of synthesis of an RNA transcript is _____.
5' —> 3'
Which model shows the correct polarity between mRNA and the DNA template during transcription?
5'----------->3' AGACU TCTGACCA 3'<-----------------5'
After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?
A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
Which of the following contradicts the one-gene, one-enzyme hypothesis?
A single antibody gene can code for different related proteins, depending on the splicing that takes place posttranscriptionally.
Transcription begins at a promoter. What is a promoter?
A site in DNA that recruits the RNA Polymerase
When a base substitution mutation occurs, one nucleotide in a replicating DNA sequence is substituted for another, which results in the production of a mutant strand of DNA. The result of the mutation depends on how the substituted nucleotide base alters the string of amino acids coded by the mutant DNA. The three types of base substitution mutations are nonsense mutations, missense mutations, and silent mutations. Each type is defined by how it affects protein synthesis. Label the four mutated DNA segments shown below according to the type of point mutation each represents. Use the codon table above to determine how each mutation would affect the amino acid coding for each segment. Drag the labels to their appropriate locations to identify the type of point mutation shown.
A) silent mutation B) nonsense mutation C) missense mutation D) frameshift mutation
At which site do new aminoacyl tRNAs enter the ribosome during elongation?
A-site
Which of these is a tRNA?
B
What determines which base is to be added to an RNA strand during transcription?
Base pairing between the DNA template strand and the RNA nucleotides
The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.
CUG
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?
Complementary
Which of the following occurs in prokaryotes but not in eukaryotes?
Concurrent transcription and translation
In the diagram below, the two blue strands represent _____.
DNA
Genotype is to _____ as phenotype is to _____.
DNA base sequence; physical traits that are products of the proteins produced
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.
False
Which of these correctly illustrates the pairing of DNA and RNA nucleotides?
GTTACG CAAUGC
What happens to RNA polymerase II after it has completed transcription of a gene?
It is free to bind to another promoter and begin transcription.
Consider the following section of mRNA: UCUGAUGGGCUUU Beginning with the start codon, which amino acids, in order, are coded for by this section of mRNA? Consult the codon table if necessary.
Methionine, glycine, and phenylalanine
What does it mean when we say the genetic code is redundant?
More than one codon can specify the addition of the same amino acid.
DNA does not store the information to synthesize which of the following?
Organelles
The initiator tRNA attaches at the ribosome's _____ site.
P
The DNA in a cell's nucleus encodes proteins that are eventually targeted to every membrane and compartment in the cell, as well as proteins that are targeted for secretion from the cell. For example, consider these two proteins: 1) Phosphofructokinase (PFK) is an enzyme that functions in the cytoplasm during glycolysis. 2) Insulin, a protein that regulates blood sugar levels, is secreted from specialized pancreatic cells. Assume that you can track the cellular locations of these two proteins from the time that translation is complete until the proteins reach their final destinations.For each protein, identify its targeting pathway: the sequence of cellular locations in which the protein is found from when translation is complete until it reaches its final (functional) destination. (Note that if an organelle is listed in a pathway, the location implied is inside the organelle, not in the membrane that surrounds the organelle.)
PFK = cytoplasm only inslin = ER -> Golgi -> outside cell
Which of the following processes is an example of a post-translational modification?
Phosphorylation
In the process of transcription, _____.
RNA is synthesized
In the diagram below, the gray unit represents _____.
RNA polymerase
The enzyme complex associated with DNA in the associated figure is ________.
RNA polymerase
Where does translation take place?
Ribosome
Which one of the following statements about RNA processing is TRUE?
Ribozymes may function in RNA splicing.
Interpret this model of transcription
The 5' labels refer to the end of the strand with a nitrogenous base. (False) The model shows the correct polarity between the orange and red strands. (False) The model correctly shows an arrowhead on the 3' ends of the strands. (True) The red lines represent DNA. (True) The 3' labels refer to the end of the strand with a phosphate group. (False) Hydrogen bonds between the orange and red strands are not shown but are implied by the model. (True) The orange line represents RNA. (True)
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex.
Which of the following statements best describes the promoter of a protein-coding gene?
The promoter is a nontranscribed region of a gene.
What is meant by translocation?
The ribosome slides one codon down the mRNA.
How can a molecule with these characteristics hold the information required to build and maintain a cell?
The sequence of bases codes the information needed to create proteins.
What is the process called that converts the genetic information stored in DNA to an RNA copy?
Transcription
Compared with mRNAsmRNAs that have a cap and tail, predict what will be observed if a eukaryotic mRNAmRNA lacked a cap and poly(A) tail.
Translation would occurs inefficiently.
Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced? Enter the sequence of bases as capital letters with no spaces and no punctuation. Begin with the first base added to the growing RNA strand, and end with the last base added.
UGAGCC
Which small-scale mutation would be most likely to have a catastrophic effect on the functioning of a protein?
a base deletion near the start of a gene
Which of the following DNA mutations is most likely to damage the protein it specifies?
a base-pair deletion
Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?
a frameshift deletion at the beginning of the gene
During RNA processing a(n) _____ is added to the 3' end of the RNA.
a long string of adenine nucleotides
The diagram below shows an mRNA molecule that encodes a protein with 202 amino acids. The start and stop codons are highlighted, and a portion of the nucleotide sequence in the early part of the molecule is shown in detail. At position 35, a single base-pair substitution in the DNA has changed what would have been a uracil (U) in the mRNA to an adenine (A).
a nonsense mutation resulting in early termination of translation
What is responsible for termination of transcription in eukaryotic protein-coding genes?
a polyadenylation, or poly(A), signal
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in _____.
a polypeptide missing an amino acid
Which of the following mutations is likely to cause the most dramatic phenotypic change?
a single nucleotide deletion in an exon coding for an active site
Which of the following nucleotide triplets best represents a codon?
a triplet in the same reading frame as an upstream AUG
Which of the following is NOT synthesized from a DNA template?
amino acids
What enzyme catalyzes the attachment of an amino acid to tRNA?
aminoacyl-tRNA synthetase
Splicing begins:
as transcription occurs.
Ribosomes can attach to prokaryotic messenger RNA ________.
before transcription is complete
The anticodon of a particular tRNA molecule is _____.
complementary to the corresponding mRNA codon
Translation occurs in the _____.
cytoplasm
A frameshift mutation could result from _____.
either an insertion or a deletion of a base
The RNA segments joined to one another by spliceosomes are _____.
exons
If a segment of DNA were replicated without any errors, the replicated strand would have the following sequence of nucleotides: 5' - ACTACGTGA - 3' Sort the following replicated DNA sequences by the type of point mutation each contains (frameshift, base substitution, or neither), as compared to the correct sequence shown above. Sort the items into the appropriate bins.
frameshift mutation = 5'-ACTTACGTGA-3' 5'-ACTCGTGA-3' base substitution mutation = 5'-ACTAAGTGA-3' 5'-ACTACGTGT-3'
In comparing DNA replication with RNA transcription in the same eukaryotic cell, only DNA replication _____.
incorporates the entire template molecule in the product
What is the name of the process shown in the diagram?
initiation (of translation)
A nonsense mutation in a gene _____.
introduces a premature stop codon into the mRNA
Codons are part of the molecular structure of _____.
mRNA
Which nucleic acid is translated to make a protein?
mRNA
During RNA processing a(n) _____ is added to the 5' end of the RNA.
modified guanine nucleotide
As a result of alternative splicing, most protein-coding genes can encode ______ protein.
more than one
Spliceosomes are composed of _____.
small RNAs and proteins
During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand?
the base sequence of the gene's promoter
In the diagram below, the green unit represents _____.
the promoter
Which of the following is directly related to a single amino acid?
the three-base sequence of mRNA
In order to initiate transcription in eukaryotes, _______.
transcription factors bind to the promoter, and RNA polymerase is then recruited to begin transcribing the gene
RNA plays important roles in many cellular processes, particularly those associated with protein synthesis: transcription, RNA processing, and translation. Drag the labels to the appropriate bins to identify the step in protein synthesis where each type of RNA first plays a role. If an RNA does not play a role in protein synthesis, drag it to the "not used in protein synthesis" bin.
transcription/RNA processing = pre-mRNA, mRNA, snRNA translation = rRNA, tRNA not used in protein synthesis = RNA primers
Beadle and Tatum discovered that metabolic pathways are studied most effectively using which of the following techniques?
using single gene mutations resulting in nonfunctional enzymes specific to a metabolic pathway