Bio Exam 4 Simpson
The lack of organelles in bacteria impacts transcription and translation in which way?
Transcription and translation can occur simultaneously.
What would be the consequence of a mutation that eliminated the function of a sigma protein?
Transcription from certain bacterial genes would be reduced or eliminated.
Which eukaryotic protein binds to the promoter-proximal region of only some genes?
Transcriptional activators
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is _____.
UUU
Which of the following statements is true of proto-oncogenes?
When mutated, they become oncogenes, driving the cell cycle forward and promoting cancer.
What is responsible for termination of transcription in eukaryotic protein-coding genes?
a polyadenylation signal or poly(A)
An enhancer is __________.
a region of DNA that may be located more than 100,000 bases away
A promoter is ______.
a sequence in DNA that brings RNA polymerase near the site for transcription
Alternative RNA splicing _____.
can allow the production of proteins of different sizes and functions from a single mRNA
The addition of acetyl groups to histones is associated with ______.
chromatin decondensation and higher levels of gene expression
In eukaryotes, the first step in the control of gene expression is ______.
chromatin remodeling
MicroRNAs work to ______.
destroy mRNA or block its translation
A mechanism of inheritance that does not depend on differences in DNA sequence is ______.
epigenetic inheritance
The poly(A) tail on one end of eukaryotic mRNA __________.
helps protect the mRNA from degradation by enzymes in the cytoplasm
Regulatory transcription factors _____.
influence the assembly of the basal transcription complex
What molecule carries a genetic message from DNA to the protein-synthesizing components of the cell?
mRNA
According to the wobble hypothesis, __________.
more than one codon codes for an amino acid and they all have the same nucleotides in the first two positions
What is recognized by an aminoacyl tRNA synthetase?
one amino acid and the set of tRNAs that are coupled to that amino acid
Why are loss-of-function mutations in p53 observed in over half of all human cancers?
p53 normally functions as a tumor suppressor to stop the cell cycle after DNA damage occurs.
Refer to the figure above. The mRNA is smaller than the length of the DNA that codes for it because _____.
post-transcriptional modification removes the introns
To label amino acids within cells, researchers "pulsed" E. coli with radioactive sulfate and "chased" with a large excess of nonradioactive sulfate. They observed that radioactivity was first associated with ribosomes and then later with completed proteins. The biologists concluded that __________.
proteins are synthesized by ribosomes and are subsequently released
Alternative RNA splicing allows for the number of different _________ to exceed the number of different __________.
proteins; genes
Differential gene expression is the result of different cells containing different ______.
regulatory proteins
If RNA polymerase is missing in E coli _____, then transcription initiation would not occur at the appropriate initiation sites.
sigma
How is a mature mRNA that lacks introns produced in eukaryotic cells?
snRNPs bind to the primary transcript and form the spliceosome, which removes introns.
During mRNA splicing ______.
snRNPs that make up the spliceosome recognize and remove introns
The life span of an mRNA molecule can be controlled by the activities of __________.
the RISC protein complex
The wobble hypothesis explains ______.
the ability of some tRNAs to read more than one codon
Death cap mushrooms produce a substance called alpha-amanitin. Alpha-amanitin efficiently blocks synthesis of mRNA, but not of tRNA or rRNA in eukaryotic organisms. This is possible because alpha-amanitin efficiently interferes with _____.
the action of RNA polymerase II, but not RNA polymerase I or III
Compared to bacteria, eukaryotic transcription is more complex because __________.
the promoters are more diverse and the primary RNA transcript must be extensively processed
Which of the following is the first event to take place in translation in eukaryotes?
the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA
In what direction is RNA synthesized during transcription?
5' to 3'
Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?
A cap is added to the 5′ end of the mRNA.
If there were a mutation in a ribosome that prevented tRNA molecules from moving into the E site, how many amino acids would be found in the resulting peptide chain formed on this ribosome?
A maximum of two
Which of the following statements about translational initiation in bacteria is true?
A specific sequence on the small ribosomal subunit binds a complementary sequence on the mRNA.
How does termination of translation take place?
A stop codon is reached.
Which of the following will speed up the rate of transcription?
Activators
What is the most likely way that humans can produce at least 50,000 different proteins (with different amino acid sequences) from around 20,000 genes?
Alternative splicing
During the elongation phase of translation, individual tRNAs move through the three sites of the ribosome in the following sequence _____.
A—>P—>E
Which of the following statements about transcription in bacteria and eukaryotes is true?
Bacteria and eukaryotes rely on proteins that recognize specific DNA sequences in the promoter to initiate transcription.
Which of the following statements about transcription in bacteria and eukaryotes is true?
Bacteria use only one RNA polymerase to transcribe RNA, whereas eukaryotes use three.
Which of the following is true about the initiation of transcription of mRNA in eukaryotes?
Basal transcription factors that bind the promoter and regulatory transcription factors that bind the enhancer are connected by mediators to initiate transcription.
Which statement is most accurate concerning the function(s) of the 5' cap and the 3' poly(A) tail of eukaryotic mRNAs?
Both structures are important for initiating translation and extending the lifespan of the mRNA.
Which of the following statements is generally true of cancer?
Cancer occurs when mutations disable genes that stop the cell cycle or those that activate it.
Which of the following is the tightly coiled DNA-protein complex?
Chromatin
How can 2 meters of DNA found in a typical human cell be packed into a nucleus that is only a few micrometers in diameter?
DNA is associated tightly with histone proteins in nucleosomes, which pack the DNA compactly.
In studies of chromatin and nucleosomes, how was DNase used to show that open chromatin structures are transcriptionally active?
DNA wrapped around histones is not transcribed and is protected from degradation by nucleases.
If cells of an individual contain the same set of genes, how do these cells become different from each other during development?
Differences in extracellular signals received by each cell lead to differences in the types of regulatory proteins present in each cell.
What are two mechanisms used for turning genes off in eukaryotic cells?
Genes are turned off when chromatin remains condensed or a regulatory protein binds to a silencer.
What are histones?
Histones are proteins associated with DNA to form chromatin.
Which of the following events would most likely increase production of a growth hormone protein?
Increased mRNA transcription
How is a mutation in a bacterial cell that deletes three base pairs 10 base pairs upstream from the +1 site likely to affect transcription and why?
Initiation will be inhibited because sigma cannot bind to the promoter.
Which of the following statements about the p53 protein is true?
It activates genes that induce apoptosis in cells with extensively damaged DNA.
Which of the following statements best describes a eukaryotic promoter?
It is found upstream of the gene and contains the TATA box.
Which of the following statements about the DNA in one of your brain cells is true?
It is the same as the DNA in one of your heart cells.
In a eukaryotic cell, which of the following statements about post-translational modification of proteins is true?
Many proteins are modified chemically after they are synthesized.
Are histone deacetylases (HDACs) associated with negative or positive control of gene expression? Why?
Negative control, because they make DNA less accessible for transcription
Just prior to the formation of a new peptide bond, the tRNA attached to the polypeptide chain occupies the _______ site of the ribosome.
P
Which of the following statements about peptide bond formation is true?
RNA catalyzes the formation of peptide bonds.
Transcription normally stops when the __________.
RNA polymerase reaches a termination signal on the DNA that leads to the formation of a hairpin loop in the mRNA
Which of the following statements best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
Which is the best description of the loops in a tRNA molecule?
Regions of the molecules that remain as single-stranded RNA due to the absence of complementary base pairs
Which of the following will decrease the rate of transcription?
Repressors
How many copies of a protein can be produced from a single ribosome/mRNA interaction?
Several ribosomes can bind and translate one mRNA transcript at the same time, following each other along the mRNA.
Which of the following statements is true about protein production in eukaryotes?
Splicing patterns in mRNA are critical to protein formation.
Which of the following molecules is a basal transcription factor?
TATA-binding protein (TBP)
What would be the effect of a mutation in the Trp aminoacyl tRNA synthetase that eliminated the tRNA binding site?
The aminoacyl Trp tRNA would not be produced.
If cells carrying a mutant form of p53 that cannot activate transcription are exposed to UV radiation, what is the most likely immediate outcome?
The cells will fail to repair DNA damage prior to the next cell division.
How can gene expression change in an individual cell in a multicellular eukaryotic organism?
The expression of specific genes is turned on or off by signal pathways activated by molecules secreted by nearby or distant cells.
Which of the following experiments best supports the idea that a transcriptional regulatory sequence can be located in an intron of a gene?
The intron of a gene is deleted, the gene is introduced into mouse cells, and the mRNA levels are measured. These mRNA levels are compared to a normal gene that is also introduced into mouse cells. The mutated gene shows no mRNA transcription, whereas the normal one does.
In smooth and striated muscle cells, the DNA for tropomyosin is the same, yet the mRNAs produced are different. Which of the following statements explains this phenomenon?
The presence of cell-type-specific molecules influences the splicing patterns of the mRNA.
Which of the following is true of the sequence called the TATA box?
The sequence is located 30 base pairs upstream of the transcription site and is important for recognition by RNA polymerase.
Which of the following statements about eukaryotic regulatory sequences is true?
They can function if their 5' to 3' orientation is reversed.
Which answer best explains how certain patterns of histone acetylation or DNA methylation could influence whether a cell became a muscle cell or a brain cell?
They could affect which sets of genes are transcribed in different cell types.
How do histone deacetylases impact chromatin structure?
They deacetylate histones, making them more positively charged and condenses the chromatin.
Which statement correctly explains one factor that contributes to the phenotypic difference between muscle cells and brain cells?
They inherited different types of modified histones from their parental cells.
