translation and regulation of gene expression
Which statement(s) about inducible operons is/are correct? -In an inducible operon, the repressor is synthesized in an active form. -Inducible enzymes generally function in synthetic pathways that produce end products from raw materials. -In an inducible operon, an inducer inactivates the repressor
-In an inducible operon, the repressor is synthesized in an active form -In an inducible operon, an inducer inactivates the repressor
How are genes coordinately controlled in eukaryotic cells?
Coordinately controlled genes in eukaryotic cells are activated by the same chemical signals and share a set of control elements
RNA polymerase in a prokaryote is composed of several subunits. Most of these subunits are the same for the transcription of any gene, but one, known as sigma, varies considerably. Which of the following is the most probable advantage for the organism of such variability in RNA polymerase?
It might allow the polymerase to recognize different promoters under certain environmental conditions
During splicing, which molecular component of the spliceosome catalyzes the excision reaction?
RNA
repressor
a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter
operon
a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins usually making up an entire metabolic pathway
Amino acids are attached to tRNA by enzymes called
aminoacyl-tRNA synthetase
miRNAs can control gene expression by what action?
binding to mRNAs and degrading them or blocking their translation
regulatory gene
codes for a protein,such a repressor, that controls the transcription of another gene or group of genes
DNA methylation is a mechanism used by eukaryotes to do what?
inactivate genes
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
many noncoding stretches of nucleotides are present in eukaryotic DNA
Negative control
-When lactose is absent, the repressor protein is active, and transcription is turned off. -When lactose is present, the repressor protein is inactivated, and transcription is turned on.
tRNA has_________and contains______
-amino acids covalently attached -contains an anticodon
The enzyme polynucleotide phosphorylase randomly assembles nucleotides into a polynucleotide polymer. You add polynucleotide phosphorylase to a solution of ATP, GTP, and UTP. How many artificial mRNA 3 nucleotide codons would be possible?
27
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'
In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?
RNA polymerase II
It is possible for a cell to make proteins that last for months; hemoglobin in red blood cells is a good example. However, many proteins are not this long-lasting; they may be degraded in days, hours, or even minutes. What is the advantage of short-lived proteins?
Short-lived proteins enable the cells to control their activities precisely and efficiently
_____ of translation happens when the ribosome hits a stop codon on the mRNA
Termination
Positive control
When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present
You are given an experimental problem involving control of a gene's expression in the embryo of a particular species. One of your first questions is whether the gene's expression is controlled at the level of transcription or translation. Which of the following might best give you an answer?
You measure the quantity of the appropriate pre-mRNA in various cell types and find they are all the same
What does a mutagen cause?
a change in the sequence of DNA
Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?
a deletion of two nucleotides
Inducer
a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, this switching an operon on.
Which of the following nucleotide triplets best represents a codon?
a triplet in the same reading frame as an upstream AUG
When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
In eukaryotes, general transcription factors
bind to other proteins or to a sequence element within the promoter called the TATA box
Steroid hormones produce their effects in cells by
binding to intracellular receptors and promoting transcription of specific genes
the _________are arranged sequentially after the promoter
genes of an operon
In humans, the hormone testosterone enters cells and binds to specific proteins, which in turn bind to specific sites on the cells' DNA. These proteins probably act to do what?
help RNA polymerase transcribe certain genes
_____of translation always happens at the start codon of the mRNA
initiation
When DNA is compacted by histones into 10-nm and 30-nm fibers, the DNA is unable to interact with proteins required for gene expression. Therefore, to allow for these proteins to act, the chromatin must constantly alter its structure. Which processes contribute to this dynamic activity?
methylation and phosphorylation of histone tails
regulatory proteins bind to the _____to control expression of the operon
operator
Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding. In general, which of the following would you expect many of them to be able to bind?
other transcription factors
promoter
specific nucleotide sequence in DNA that binds RNA polymerase positioning it to start transcribing RNA at the appropriate place
the RNA that has an amino acid attached to it, and binds to the codon on the mRNA is called
tRNA
the process performed by the ribosome of reading mRNA and synthesizing a protein is called
trasnlation