Unit 6 Exam
The AUC and AUA codons in mRNA both specify isoleucine. What feature of the genetic code explains this?
Degeneracy
In the figure, which deletion is in a repressor involved in regulating the gene?
Deletion 1
The level of transcription of a gene is tested by creating deletions in the gene as shown in the illustration. These modified genes are tested for their level of transcription: (++) normal transcription levels; (+) low transcription levels; (+++) high transcription levels.
Deletion 3
How many nucleotides are in 12 mRNA codons?
36
Imagine if there were 200 commonly occurring amino acids instead of 20. Given what you know about the genetic code, what would be the shortest possible codon length?
4
If the rate of replication in a particular prokaryote is 900 nucleotides per second, how long would it take to make two copies of a 1.2 million base pair genome?
44.4 min
What will result from the binding of a transcription factor to an enhancer region?
Increased transcription of a distant gene
Which type of point mutation would result in the substitution of a stop codon for an amino acid?
Nonsense
What type of nucleic acid material is analyzed the most frequently in forensics cases?
Nuclear chromosomal DNA
Where are the RNA components of ribosomes synthesized?
Nucleolus
What are Okazaki fragments, and how they are formed?
Okazaki fragments are short stretches of DNA on the lagging strand, which is synthesized in the direction away from the replication fork.
Targeted therapies are used in patients with a certain gene expression pattern. A targeted therapy that prevents the activation of the estrogen receptor in breast cancer would be beneficial to what type of patient?
Patients with over-expression of ER alpha in their tumor cells
What is personalized medicine? How can it be used to treat cancer?
Personalized medicines would vary based on the type of mutations and the gene's expression pattern.
The ends of the linear chromosomes are maintained by what?
Telomerase
Where is uracil found?
mRNA
A poly-A sequence is added at the —
3' end of a transcript in the nucleus
What is involved in post-transcriptional control?
Control of RNA splicing
What procedure uses information obtained by microscopic analysis of stained chromosomes?
Cytogenetic mapping
What is an example of a genomic mapping method?
Cytogenetic mapping obtains information from microscopic analysis of stained chromosomes. It can estimate the approximate distance between markers.
Which cell structure does NOT contain heritable information?
Cytoplasmic membrane
Which enzyme is only found in prokaryotic organisms?
DNA gyrase
If the sequence of the 5' to 3' strand is AATGCTAC, then the complementary sequence has which sequence?
3'-TTACGATG-5'
In which direction does DNA replication take place?
5' to 3'
A drug designed to switch silenced genes back on in cancer cells would result in what?
Methylation of DNA and deacetylation of histones
What would be the consequence of a mutation in a mismatch repair enzyme? How would this affect the function of a gene?
Mismatch repair corrects the errors after the replication is completed by excising the incorrectly added nucleotide and adding the correct base. Any mutation in a mismatch repair enzyme would lead to more permanent damage.
A mutation within the promoter region can alter gene transcription. How can this happen?
Mutated promoters alter the binding site for transcription factors to increase or decrease the rate of transcription.
A mutation results in the formation of the mutated mature-mRNA as indicated in the diagram. What type of mutation occurred, and what is the likely outcome of the mutation?
Mutation in the GU-AG sites of introns produced a nonfunctional protein.
What does the enzyme primase synthesize?
RNA primer
How can external stimuli alter post-transcriptional control of gene expression?
RNA-binding proteins are modified through phosphorylation.
The experiments by Hershey and Chase helped confirm that DNA was the hereditary material on the basis of the finding of what?
Radioactive phosphorus was found in the cell.
What are regions 1 through 5 in the diagram?
Regions 1, 3, and 5 are exons; regions 2 and 4 are introns.
What process transfers heritable material to the next generation?
Replication
How would you describe the difference between rho-dependent and -independent termination of transcription in prokaryotes?
Rho-dependent termination is controlled by the rho protein, and the polymerase stalls near the end of the gene at a run of G nucleotides on the DNA template. In rho-independent termination, when the polymerase encounters a region rich in C-G nucleotides, the mRNA folds into a hairpin loop that causes the polymerase to stall.
What is the main structure that differentiates rho-dependent and -independent termination in prokaryotes?
Rho-independent termination involves the formation of a hairpin.
Meselson and Stahl's experiments proved that DNA replicates by which mode?
Semiconservative
What is the percentage of single gene defects causing disease in developed countries?
0.2 (WRONG)
In any given species, there are at least how many types of aminoacyl tRNA synthetases?
20
If DNA of a particular species was analyzed and it was found that it contains 27 percent A, what would be the percentage of T?
27%
What is a purine?
A double-ring structure with a six-membered ring fused to a five-membered ring
Which pre-mRNA processing step is important for initiating translation?
Adding the 7-methylguanosine cap
What are epigenetic modifications?
Addition of reversible changes to histone proteins and DNA
What are Autonomously Replicating Sequences (ARS)?
Areas of eukaryotic chromosomes that are equivalent to the origin of replication in E. coli
What processing step enhances the stability of pre-tRNAs and pre-rRNAs?
Methylation
What can post-translational modifications of proteins affect?
Chemical modifications
Describe the structure and complementary base pairing of DNA.
DNA is made up of two strands that are twisted around each other to form a helix. Adenine pairs up with thymine and cytosine pairs with guanine. The two strands are antiparallel in nature; that is, the 3' end of one strand faces the 5' end of the other strand. Sugar, phosphate, and nitrogenous bases contribute to the DNA structure.
Which enzyme is most directly responsible for the main process of producing a new DNA strand?
DNA pol III
What is the initial mechanism for repairing nucleotide errors in DNA?
DNA polymerase proofreading
What would be the outcome of a mutation that prevented DNA-binding proteins from being produced?
Decreased transcription because enhancers would not be able to bind to transcription factors
Cystic fibrosis (CF) is a progressive genetic disease that causes persistent lung infections and affects the ability to breathe. CF is inherited in an autosomal recessive manner, caused by the presence of mutations in both copies of the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Partial nucleotide sequences and the corresponding amino acid sequences for an unaffected individual and an affected individual are modeled in Figure 1.
Deletion, because a thymine is missing, which changes the reading frame.
Cystic fibrosis (CF) is a progressive genetic disease that causes persistent lung infections and affects the ability to breathe. CF is inherited in an autosomal recessive manner, caused by the presence of mutations in both copies of the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Partial nucleotide sequences and the corresponding amino acid sequences for an unaffected individual and an affected individual are modeled in Figure 1. Based on the information in Figure 1, which type of mutation explains the nature of the change in DNA that resulted in cystic fibrosis in the affected individual?
Deletion, because a thymine is missing, which changes the reading frame.
Scientists conducted a transformation experiment using E. coli bacteria and the pTru plasmid. Samples of the pTru plasmid (lane A) and the chromosomal DNA from two different E. coli strains that the scientists attempted to transform (lane B and lane C) were compared using gel electrophoresis. The results are shown in Figure 1. Which of the following statements best explains the experimental results observed in Figure 1 ?
E. coli in lane C have been successfully transformed and contain additional genetic information.
Binding of an RNA-binding protein will change the stability of the RNA molecule inwhat way?
Either increase or decrease
Control of gene expression in eukaryotic cells occurs at which level(s)?
Epigenetic, transcriptional, translational, and post-translational levels
What best distinguishes prokaryotic and eukaryotic cells?
Eukaryotic cells contain a nucleus whereas prokaryotes do not, and eukaryotes show greater compartmentalization that allows for greater regulation of gene expression.
What is the major challenge in the production of RNA in eukaryotes compared to prokaryotes?
Exporting the mRNA across the nuclear membrane
Which answer provides a brief summary of the Sanger sequencing method?
Frederick Sanger's sequencing is a chain termination method that is used to generate DNA fragments that terminate at different points using dye-labeled dideoxynucleotides. DNA is separated by electrophoresis on the basis of size. The DNA sequence can be read out on an electropherogram generated by a laser scanner.
Who was the first person to isolate the material that came to be known as nucleic acids?
Friedrich Miescher
A mutation in the promoter region of the gene for beta-globin can cause beta-thalassemia, a hereditary condition that causes anemia. Why would mutations in the promoter region lead to low levels of hemoglobin?
Globin chains do not fold properly and are nonfunctional.
Which statement about epigenetic regulation is false?
Histone protein charge becomes more positive when acetyl groups are added.
Nucleotide base pairing in DNA is universal across organisms. Each pair (T−A; C−G) consists of a purine and a pyrimidine. Which of the following best explains how the base pairs form?
Hydrogen bonds join two single-ringed structures in each pair. (Wrong)
Flowering Locus C (FLC) is a gene that is responsible for flowering in certain plants.FLC is expressed in new seedlings, which prevents flowering. Upon exposure to cold temperatures, FLC expression decreases and the plant flowers. FLC is regulatedthrough epigenetic modifications.What type of epigenetic modifications is present in new seedlings and after cold exposure?
In new seedlings, histone acetylations are present; upon cold exposure, methylation occurs.
Explain the initiation of transcription in prokaryotes. Include all proteins involved.
In prokaryotes, the polymerase comprises five polypeptide subunits, two of which are identical. Four of these subunits, denoted and compose the polymerase core enzyme. The fifth subunit, is involved only in the initiation of transcription. The polymerase, which comprises all five subunits, is called the holoenzyme.
What would happen if the operator sequence of the lac operon contained a mutation that prevented the repressor protein from binding the operator?
In the absence of lactose, the lac operon will be transcribed.
What would happen if the operator sequence of the trp operon contained a mutation that prevented the repressor protein from binding to the operator?
In the presence of tryptophan, the genes trpA-E will be transcribed.
All cells must transcribe rRNA in order to construct a functioning ribosome. Scientists have isolated and identified rRNA genes that contribute to ribosomal structure for both prokaryotes and eukaryotes. Figure 1 compares the transcription and processing of prokaryotic and eukaryotic rRNA. Which of the following statements provides the best explanation of the processes illustrated in Figure 1 ?
Introns are removed from the pre- rRNA , and the mature rRNA molecules are joined and then translated to produce the protein portion of the ribosome. (WRONG)
If the protein is missing, will a prokaryotic gene be terminated?
It depends on the gene.
What is true about linkage analysis?
It is based on the natural recombination process.
Suppose a gene has the sequence ATGCGTTATCGGGAGTAG. A point mutation changes the gene to read ATGCGTTATGGGGAGTAG. How would the polypeptide product of this gene change?
It would change from MRYRE to MRYGE.
What does the chain termination method of DNA sequencing use to terminate polynucleotide elongation?
Labeled dideoxynucleotides
Which portion of a chromosome contains Okazaki fragments?
Lagging strand
What does the addition of an ubiquitin group to a protein do?
Marks the protein for degradation
What is often the first amino acid added to a polypeptide chain?
Methionine
What is the name of the method developed by Fred Sanger to sequence DNA?
NOT Double helix determination, NOT Polymer gel electrophoresis
Exposure to ultraviolet (UV) radiation is the leading cause of skin cancer in humans. Figure 1 shows a model of how UV exposure damages DNA.
Naturally occurring dimers are removed by the UV photons, causing misshapen DNA , which results in replication errors.
Should she be worried?
No, the mutations causing the cancer are in somatic cells, not reproductive germ cells.
If mRNA is complementary to the DNA template strand and the DNA template stand is complementary to the DNA non-template strand, why are the base sequences of mRNA and the DNA non-template strand not identical? Could they ever be?
No, they cannot be identical because the T nucleotide in DNA is replaced by the U nucleotide in RNA, and AUG is the start codon.
What are positive cell-cycle regulators that can cause cancer when mutated called?
Oncogenes
Which polymerase is responsible for the synthesis of 5S rRNA?
Polymerase III
What transcripts will be most affected by low levels of -amanitin?
Pre-mRNAs
What is the difference in the rate of replication of nucleotides between prokaryotes and eukaryotes?
Prokaryotes are 10 times faster.
Which statement is correct regarding the distinction between prokaryotic and eukaryotic gene expression?
Prokaryotes regulate gene expression at the level of transcription, whereas eukaryotes regulate at multiple levels including epigenetic, transcriptional, and translational. (WRONG)
What are two ways in which gene regulation differs and two ways in which it is similar in prokaryotes and eukaryotes?
Prokaryotes show co-transcriptional translation, whereas eukaryotes perform transcription prior to translation; in both cell types, regulation occurs through the binding of transcription factors, activators, and repressors.
Which of the following best explains how the pattern of DNA arrangement in chromosomes could be used, in most cases, to determine if an organism was a prokaryote or a eukaryote?
Prokaryotic- Single circular chromosome Eukaryotic DNA- Multiple linear chromosome
Which molecule does NOT contain genetic information?
Protein
Which answer best explains why radioactive sulfur and phosphorus were used to label bacteriophages in the Hershey and Chase experiments?
Protein was labeled with radioactive sulfur and DNA was labeled with radioactive phosphorus. Phosphorus is found in DNA, so it will be tagged by radioactive phosphorus.
Nucleotide excision repair often is employed when UV exposure causes the formation of what?
Pyrimidine dimers
How can RBPs prevent miRNAs from degrading an RNA molecule?
RBPs can bind first to the RNA, thus preventing the binding of miRNA, which degrades RNA.
The binding of what is required for transcription start?
RNA polymerase
Huntington's disease, an autosomal dominant disorder, is caused by a mutation in the HTT gene. The HTT gene contains multiple repeats of the nucleotide sequence CAG. A person with fewer than 35 CAG repeats in the HTT gene is unlikely to show the neurological symptoms of Huntington's disease. A person with 40 or more CAG repeats almost always becomes symptomatic. Due to errors in meiosis, an individual without symptoms of Huntington's disease can produce gametes with a larger number of CAG repeats than there are in their somatic cells. A woman develops Huntington's disease. Her father had the disorder. Her mother did not, and there is no history of the disorder in the mother's family. Which of the following best explains how the woman inherited Huntington's disease?
She inherited an allele with more than 40 CAG repeats in the HTT gene from her father.
Which option is associated with the docking of mRNA on a ribosome in eukaryotic cells?
Shine-Dalgarno sequence (WRONG)
Which type of point mutation would have no effect on gene expression?
Silent
What type of modification might be observed in the GR gene in all newborn rats?
The DNA will have many methyl molecules.
Which step in the transcription of eukaryotic RNA differs the most from its prokaryotic counterpart?
The initiation step in eukaryotes requires an initiation complex with enhancers and transcription factors. Also, the separation of the DNA strand is different, as histones are involved.
When comparing transcription of heritable information in prokaryotes and eukaryotes, which events are the same?
The transcription by polymerase, the recognition of a consensus sequence in the promoter, and the termination by a hairpin loop are conserved.
How can Chargaff's rules be used to identify different species?
The amount of adenine, thymine, guanine, and cytosine varies from species to species and is not found in equal quantities. They do not vary between individuals of the same species and can be used to identify different species.
Lactose digestion in E. coli begins with its hydrolysis by the enzyme galactosidase. The gene encoding galactosidase, lacZ, is part of a coordinately regulated operon containing other genes required for lactose utilization. Which figure correctly depicts the interactions at the lac operon when lactose is NOT being utilized?
The answer is the picture with the Repressor under the Operator with nothing in it.
A tRNA is chemically modified so that the bound amino acid is different than the one specified by its anticodon. Which codon in the mRNA would the tRNA recognize: the one specified by its anticodon or the one that matches the modified amino acid it carries?
The anticodon will match the codon in mRNA.
A researcher wants to study cancer cells from a patient with breast cancer. Is cloning the cancer cells an option?
The cancer cells, being the clones of each other already, should directly be grown in a culture media and then studied.
What happens when a dideoxynucleotide is added to a developing DNA strand?
The chain is not extended any further.
In the Avery, Macleod, and McCarty experiments, what conclusion would the scientists have drawn if the use of proteases prevented the transformation of R strain bacteria?
The conclusion would be that proteins are the heritable material in cells instead of nucleic acids.
How do the linear chromosomes in eukaryotes ensure that their ends are replicated completely?
The ends of the linear chromosomes are maintained by the activity of the telomerase enzyme.
How does the enzyme reverse transcriptase violate the central dogma of molecular biology in HIV?
The enzyme reverse transcriptase reverse-transcribes the RNA in the genome of HIV into DNA.
What part of the central dogma is NOT always followed in viruses?
The flow of information in HIV is from RNA to DNA, then back to RNA to protein. Influenza viruses never go through DNA.
What characteristic of the genetic code points to a common ancestry for all organisms?
The genetic code is almost universal.
How should the following DNA sequence (non-template strand) be transcribed and translated?5'-ATGGCCGGTTATTAAGCA-3'
The mRNA would be 5'-AUGGCCGGUUAUUAAGCA-3' and the protein will be MAGY.
Whole-genome sequencing can be used for advances in what field?
The medical field
In a new cancer treatment, a cold virus is genetically modified so that it binds to, enters, and is replicated in cells, causing them to burst. The modified cold virus cannot replicate when wildtype p53 protein is present in the cell. How does this treatment treat cancer without harming healthy cells?
The modified virus replicates only in cancer cells.
A mutation is found in eIF-2, which impairs the initiation of translation. The mutation could affect all but one of the following functions of eIF-2.Which function would NOT be affected?
The mutation prevents eIF-2 from being phosphorylated.
Which set of results was found in Meselson and Stahl's experiments?
The original chromosome was split and half went to each duplicate.
You sequence a gene of interest and isolate the matching mRNA. You find that the mRNA is considerably shorter than the DNA sequence. Why is that?
The processed mRNA is shorter because introns were removed.
What would be the result of a mutation in the repressor protein that prevented it from binding lactose?
The repressor will bind the operator in the presence of lactose.
What would happen if the 5' methyl guanosine was not added to an mRNA?
The transcript would degrade when the mRNA moves out of the nucleus to the cytoplasm.
What could happen if a cell had too much of an activating transcription factor present?
The transcription rate would increase, altering cell function.
New drugs are being developed that decrease DNA methylation and prevent the removal of acetyl groups from histone proteins. How could these drugs affect gene expression to help kill tumor cells?
These drugs maintain the demethylated and the acetylated forms of the DNA to keep transcription of necessary genes on.
What is true of epigenetic changes?
They allow movement of histones.
Why are the -10 and -35 regions of prokaryotic promoters called consensus sequences?
They are similar in all bacterial species.
What do Figures X and Y in the figure illustrate?
Transcription and translation in a prokaryotic cell (Figure X) and a eukaryotic cell (Figure Y)
The lac operon consists of regulatory regions such as the promoter as well as the structural genes lacZ, lacY, and lacA, which code for proteins involved in lactose metabolism. What would be the outcome of a mutation in one of the structural genes of the lac operon?
Transcription will continue but lactose will not be metabolized properly.
What is bacterial transformation?
Transformation is a process in which external DNA is taken up by a cell, thereby changing morphology and physiology.
Explain Griffith's transformation experiments. What did he conclude from them?
Two strains of S. pneumoniae were used for the experiment. Griffith injected a mouse with heat-inactivated S strain (pathogenic) and R strain (nonpathogenic). The mouse died and S strain was recovered from the dead mouse. He concluded that external DNA is taken up by a cell that changed morphology and physiology.
Changes in epigenetic modifications alter the accessibility and transcription of DNA. How could environmental stimuli, such as ultraviolet light exposure, modify gene expression?
UV rays could cause methylation and deacetylation of the genes that could alter the accessibility and transcription of DNA.
How can understanding the gene expression pattern in a cancer cell tell you something about that specific form of cancer?
Understanding gene expression patterns in cancer cells will identify the faulty genes, which is helpful in providing the relevant drug treatment.
What are introns?
Untranslated DNA sequences in a gene
What do regions 1 and 5 correspond to?
Untranslated regions
The DNA double helix does NOT have what?
Uracil
The trp operon in E. coli is an example of a repressible operon that consists of genes coding for enzymes used to synthesize tryptophan. When tryptophan levels are high, the operon is turned off and these genes are not transcribed. However, it is also known that tryptophan does not bind directly to the operator DNA sequence. A regulatory gene called trpR has also been discovered although it is not part of the trp operon. The proposed model of how tryptophan acts as a corepressor is shown in Figure 1. Which of the following evidence best supports a claim that tryptophan functions as a corepressor?
When trpR is mutated, the trp operon is transcribed regardless of tryptophan levels.
Would you be able to determine which RNA polymerase you isolated from a eukaryotic cell without analyzing its products?
Yes, they can be determined as they differ in -amanitin sensitivity.
In prokaryotic cells, ribosomes are found in/on the —
cytoplasm
The enzyme polyadenylate polymerase catalyzes the addition of adenosine monophosphate to the 3' ends of mRNAs to form a poly-A tail. If the enzyme were blocked so that it could not function, the result would be
decreased mRNA stability in eukaryotes and no effect in prokaryotes
Individual genetic maps in a given species are —
genetically similar
A mutation in the 5'UTR that prevents any proteins from binding to the region will
increase or decrease the stability of the RNA molecule
Which molecule in the central dogma can be compared to a disposable photocopy of a book kept on reserve in the library?
mRNA
Which subunit of the E. coli polymerase confers specificity to transcription?
o
What are cancer-causing genes called?
oncogenes
