Terms in this set (62)
Which of the following statements is NOT true about the differences between liver cells and kidney cells in the same organism?
They contain different genes.
At any given time, a typical differentiated human cell will express how many of its approximately 21,000 protein-coding genes?
From 5000 to 15,000
A cell can change the expression of its genes in response to external signals
Different cell types that respond to the same hormone usually turn on the same sets of genes.
Although all of the steps involved in expressing a gene can in principle be regulated, for most genes the most important point of control is:
Which form of control directly influences which mRNAs are selected by ribosomes for the synthesis of proteins?
Intense exercise can change gene expression.
Once a cell has become specialized to produce the set of proteins that are responsible for its distinctive properties, its gene expression patterns remain fixed.
Which would be the best method for determining which genes are being transcribed in a particular cell type?
Which of the following is considered a housekeeping protein?
In eukaryotes, what must assemble at a promoter before RNA polymerase can transcribe a gene?
General transcription factors
The assembly of general transcription factors at a eukaryotic promoter typically begins at what site?
The TATA box
are transcribed and translated simultaneously.
are translated after they are exported from the nucleus.
Which of the following does not increase the stability of eukaryotic mRNAs?
In bacteria, most protein-coding genes lack introns.
Introns are removed by:
RNA splicing in the nucleus.
In eukaryotes, which parts of a gene are transcribed into RNA?
Introns and exons
Unlike the coding sequence of an exon, most of the nucleotide sequence of an intron is unimportant.
What structure is responsible for selecting and transporting into the cytoplasm only properly processed eukaryotic mRNAs?
The nuclear pore complex
Which of the following statements is NOT true?
In a eukaryotic mRNA, the poly-A tail promotes degradation of the molecule
All are true
Many eukaryotic mRNAs have a longer lifetime than bacterial mRNAs.
The lifetime of a eukaryotic mRNA is controlled in part by nucleotide sequences in the mRNA itself.
The longer the lifetime of an mRNA, the more protein can be produced from it.
Which of the following is widely accepted in the scientific community?
Neither—the evolution of introns is still a topic of debate.
RNA capping and polyadenylation take place:
as an RNA is being transcribed.
Splicing of pre-mRNAs takes place:
as the RNA is being transcribed.
Each nucleotide in an mRNA encodes one amino acid in a protein.
How many nucleotides are necessary to specify a single amino acid?
In principle, how many reading frames in an RNA molecule can potentially be translated into protein
What is NOT true about codons in mRNA molecules?
Some codons code for more than one amino acid.
Amino acids are attached to their tRNA molecules by:
An RNA message is decoded by:
Within the ribosome, the formation of peptide bonds is catalyzed by:
an RNA molecule in the large ribosomal subunit
What is the term for an RNA molecule that possesses catalytic activity?
Translation takes place in a series of four steps. Which of these best describes this four-step cycle?
An aminoacyl-tRNA binds to the vacant A site on the ribosome; a peptide bond is formed; the large subunit of the ribosome translocates, moving the bound tRNAs to the E and P sites; the small subunit of the ribosome translocates, ejecting the tRNA from the E site.
Most organisms have how many different aminoacyl-tRNA synthetases?
One for each amino acid
During translation, the growing peptide chain is always held by the tRNA in the P site of the ribosome.
Many antibiotics work by inhibiting bacterial protein synthesis. Investigators have isolated a promising new compound and wish to determine its mechanism of action. Using a cell-free translation system similar to the ones originally used to deduce the genetic code, the researchers incubate their drug with the synthetic polynucleotide 5'-AUGUUUUUUUUU.
In the absence of the drug, this polynucleotide directs the synthesis of the peptide Met-Phe-Phe-Phe. When the drug is added, only the peptide Met-Phe is produced. Based on this observation, which is most likely the mechanism of action of this potentially new antibiotic?
It blocks translocation of the large ribosomal subunit, preventing the movement of peptidyl-tRNA from the A site to the P site of the ribosome.
Because introns are largely genetic junk, they do not need to be removed with any degree of precision during RNA splicing.
The genetic code was originally deciphered, in part, by experiments in which synthetic polynucleotides with repeating sequences were used as mRNAs to direct protein synthesis in cell-free extracts. Under these conditions, ribosomes could be made to start translation anywhere within the RNA molecules, no start codon was necessary. What peptide would be made by translation from a synthetic mRNA made entirely of adenine—poly A?
A polymer of lysine: Lys-Lys-Lys
The genetic code was originally deciphered, in part, by experiments in which synthetic polynucleotides with repeating sequences were used as mRNAs to direct protein synthesis in cell-free extracts. Under these conditions, ribosomes could be made to start translation anywhere on the RNA molecule, with no start codon necessary. What peptide would be made by translation from a synthetic mRNA made of the repeating dinucleotide CGCG...?
A peptide containing alternating arginines and alanines
The genetic code was originally deciphered, in part, by experiments in which synthetic polynucleotides with repeating sequences were used as mRNAs to direct protein synthesis in cell-free extracts. Under these conditions, ribosomes could be made to start translation anywhere on the RNA molecule, with no start codon necessary. What peptide would be made by translation from a synthetic mRNA made of the repeating trinucleotide UCGUCG...?
A polymer of serine (Ser-Ser-Ser...) plus a polymer of arginine (Arg-Arg-Arg...) plus a polymer of valine (Val-Val-Val...)
Investigators treat cells with a chemical that introduces random mutations into the DNA, including single-nucleotide changes that turn one base into another. They then isolate two mutants: one produces a protein that carries an alanine at a site that normally contains a valine; the other produces a protein that carries a methionine instead of the valine.
When these mutant cells are subjected to the same mutagenic treatment, they both produce proteins that contain a threonine at the site of the original valine. Assuming that the mutations causing these alterations are single-nucleotide changes, what were the codons that specified each of the amino acids discussed?
Val, GUG; Ala, GCG; Met, AUG; Thr, ACG
n an experiment conducted in 1962, investigators took tRNAs bearing cysteine and chemically converted the charged amino acid to an alanine. They then introduced these "hybrid" alanine-bearing tRNAs into a cell-free translation system from which they removed all of the normal, cysteine-bearing tRNAs. How did this chemical manipulation affect the proteins produced by this altered system?
The proteins contained alanines where cysteines were supposed to be.
To which part of an mRNA molecule do ribosomal subunits first bind?
The 5' end
The translation of an mRNA begins at the start codon:
In eukaryotes, the initiator tRNA always carries which amino acid?
Which part of a protein is synthesized by a ribosome first?
At what site does the charged initiator tRNA first bind on the ribosome?
At what site do all charged tRNAs (with the exception of the initiator tRNA) first bind on the ribosome?
Which statement is false?
Stop codons are not recognized by a tRNA.
What is a polyribosome?
A cluster of ribosomes simultaneously translating the same mRNA, but positioned at different sites along the mRNA
Some antibiotics can be taken in high doses because they disrupt bacterial, but not eukaryotic, protein synthesis.
How do proteases act?
By hydrolyzing peptide bonds between amino acids in a protein
Where in a cell are most damaged proteins broken down?
Proteasomes act primarily on proteins that have been marked for destruction by the covalent attachment of which small protein?
All proteins are fully functional upon leaving the ribosome
Which type of molecule has the potential to perform the catalytic act of reproducing itself?
Which biochemical reaction is catalyzed by a ribozyme?
Peptide bond formation in protein synthesis
Which sugar is not readily made from formaldehyde in experiments simulating conditions on primitive Earth?
Which is NOT specifically targeted for destruction by the proteasome?
Which would be more deleterious: the loss of a single nucleotide from the protein-coding region of a gene or the loss of three nucleotides in that same region?
The loss of a single nucleotide