Chem Unit 3
many noncoding stretches of nucleotides are present in eukaryotic DNA.
A eukaryotic 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
UUU
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is
bonding of the anticodon to the codon and the attachment of amino acids to tRNAs
Accuracy in the translation of mRNA into the sequence of amino acids in a polypeptide depends on specificity in which of the following?
A-site
At which site do new aminoacyl tRNAs enter the ribosome during elongation?
a long string of adenine nucleotides
During RNA processing a(n) _____ is added to the 3' end of the RNA.
modified guanine nucleotide
During RNA processing a(n) _____ is added to the 5' end of the RNA.
a frameshift deletion at the beginning of the gene
Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?
It might substitute a different amino acid in the active site.
In what way might a point mutation in DNA make a difference in the function of a protein?
small RNAs and proteins
Spliceosomes are composed of _____.
exons
The RNA segments joined to one another by spliceosomes are _____.
P
The initiator tRNA attaches at the ribosome's _____ site.
a polypeptide missing an amino acid
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. What is the most likely result of this mutation in the protein product?
CUG
The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____.
The mutation introduces a stop codon.
The template strand of a gene contains this sequence: 3'-TAC TAG GCT AGT TGA-5'. A mutation occurs that changes the gene sequence to 3'-TAC TAG ACT AGT TGA-5'. How does this mutation affect the resulting amino acid sequence?
the rules for base pairing between the third base of a codon and tRNA are flexible.
There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that
cytoplasm
Translation occurs in the _____.
False
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.
a change in the sequence of DNA
What does a mutagen cause?
aminoacyl-tRNA synthetase
What enzyme catalyzes the attachment of an amino acid to tRNA?
an RNA with enzymatic activity
What is a ribozyme?
The ribosome slides one codon down the mRNA.
What is meant by translocation?
It introduces a premature stop codon into the mRNA.
What is the effect of a nucleotide-pair substitution that results in a nonsense mutation in a gene?
GTP provides the energy for the formation of the initiation complex, using initiation factors.
What is the function of GTP in translation?
It binds to the stop codon in the A site in place of a tRNA.
What is the function of the release factor in translation?
initiation (of translation)
What is the name of the process shown in the diagram?
Its signal sequence must target it to the ER, after which it goes to the Golgi.
What must happen to a newly made polypeptide before it can be secreted from a cell?
hydrogen bonding between base pairs
What type of bonding is responsible for maintaining the shape of the tRNA molecule in the figure?
a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.
When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by
ribosome
Where does translation take place?
mRNA
Which nucleic acid is translated to make a protein?
a base-pair deletion
Which of the following DNA mutations is likely to have the most negative effect on the protein it specifies?
It helps protect the mRNA from degradation by hydrolytic enzymes.
Which of the following is a function of a poly-A tail in mRNA?
Phosphorylation
Which of the following processes is an example of a post-translational modification?
It can allow the production of proteins of different sizes and functions from a single mRNA.
Which of the following statements correctly describes alternative RNA splicing?
Translation can begin while transcription is still in progress
Which of the following statements is true about protein synthesis in prokaryotes?
The large ribosomal subunit joins the complex.
Which of the following steps occurs last in the initiation phase of translation?
a deletion of two nucleotides
Which of the following types of mutation, resulting in an error in the mRNA just after the 3 AUG start codon, is likely to have the most serious effect on the polypeptide product?
either an insertion or a deletion of a base
Which of the following types of mutations could result in a frameshift mutation?
B (looks like a translator stick)
Which of these is a tRNA?
A gene codes for either a polypeptide or an RNA molecule.
Which of these is currently considered the best definition of a gene?
UUC
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?
