Genetics Mock Exam 3 Answers
- What causes cAMP levels to rise and does an increase in cAMP increase transcription of the lac operon?
- Decrease in glucose, no
- Increase in glucose, no
- Decrease in glucose, yes
- Increase in glucose, yes
When glucose is low, cAMP levels are high and the CAP-cAMP complex binds to the promoter of the lac operon and increases transcription. Page 458
- True/False- B-Galactosidase transforms allolactose into lactose which acts as the substrate that binds to the repressor and causes transcription to occur.
False- While the presence of lactose does cause transcription to turn on in the lac operon, allolactose acts as the substrate that binds to the repressor protein. This is because the enzyme B-Galactosidase converts lactose to allolactose. Unless specified like in this question, assume that the presence of lactose causes transcription to turn on in the lac operon. Page 451-453
- Which of the following is not a product of transcription from the lac operon?
Galactose is a product made by B-Galactosidase converting lactose into galactose (and also glucose) page 452
- What makes Taq polymerase special in PCR compared to other DNA polymerases?
- It can withstand temperatures of up to 90oF
- It can be made quickly, cheaply, and collected in large quantities
- It is not denatured in the strand-separation step of PCR
- It amplifies the DNA
In PCR, first DNA is separated at 90-100oC. Taq polymerase is a DNA polymerase found naturally in the boiling springs of Yellowstone. It is stable at these high temperatures and doesn’t denature. Because of this, it can synthesize DNA over and over again, without being denatured. Page 548
- True/False- Genetic testing is very accurate and rarely gives false negative results.
False- Genetic testing can give false negative results and some genetic diseases can be caused by hundreds of different mutations, which questions the accuracy of genetic testing. Also, some question if it is ethical to test for genetic diseases that have no cure. Page 571
- Which of the following is true for the GAL4 protein?
- Binds to GAL3 in the absence of galactose
- Activates the transcription of yeast genes needed for metabolizing galactose
- Interacts with the basal transcription apparatus to inhibit transcription
- All of the above
Transcription of yeast genes whose products metabolize galactose occurs when galactose is present and the GAL4 activator binds to the gene on the UASG site. Page 480
- True/False- Real-time PCR is used to accurately determine the amount of DNA that is present in a solution after each PCR cycle.
The amount of DNA amplified is measured as the reaction proceeds. Page 548
- Which of the following is true about orthologs and paralogs
- Orthologs are homologous genes found in a different species that evolved from the same gene
- Paralogs are homologous genes in the same organism that arose by duplication of a single gene
- Orthologs and paralogs often have the same or related function
- A and B
- All of the above
- True/False- Detailed genetic and physical maps of the genome must first be created before they can be used in map-based sequencing.
Page 584 Shotgun sequencing is quicker than map-based sequencing, but causes the genome to be sequenced multiple times.
- Which of the following is true of insulators?
- They block the effect of enhancers
- They always lie in between an enhancer and promoter
- They can be found in prokaryotes
- A and C
- All of the above
An insulator can be found outside the region between the enhancer and promoter, but it won’t block the effect of the enhancer. Insulators only work when placed in between and enhancer and promoter page 481
- Which of the following is NOT true for SNPs?
- An SNP close to a disease causing locus will be inherited with the disease causing allele
- People with a certain disease have different SNPs than healthy people
- The location of a disease causing gene can be determined from the location of an SNP
- SNPs usually produce phenotypic differences page
- What unmethylated nucleotide does sodium bisulfite convert to uracil?
Uracils are detected as thymine during sequencing. Sequencing DNA with and without this technique can determine the locations of all copies of 5-methylcytosine page 627
- Which of the following is NOT true of genomic imprinting?
- Some genes are imprinted in certain tissues
- Some genes are imprinted at certain types of development
- Imprinting is due to different degrees of methylation
- Both A and B
- All of the above are true
- Which of the following is true regarding chromatin and histones?
- Proteins can bind to DNA and reposition nucleosomes
- Acetylation of histones decreases transcription
- Altering the chromatin structure only comes by altering the structure of histones
- All of the above are false
- Which of the following are true regarding RNA degradation?
- Eukaryotic mRNA are more stable than bacterial mRNA
- Cellular RNA is degraded by ribonucleases
- The amount of mRNA depends on rate of synthesis and rate of degradation
- B and C
- All of the above
- Which of the following is NOT true of RNA interference?
- Dicer enzymes cut double stranded RNA to make siRNA and miRNA
- siRNA and miRNA cleave mRNA to regulate gene expression
- siRNA and miRNA can degrade mRNA
- siRNA and miRNA are normally 200-250 nucleotides long
- True/False- Genes are not organized into operons in Eukaryotes.
True, each structural gene has its own promoter and is transcribed separately.
- Which of the following does NOT affect gene regulation by altering chromatin structure?
- Chromatin remodeling
- Modification of histones
- DNA methylation
- Transcriptional silencing
- What is true about genes when they become transcriptionally active?
- They are prone to be replicated by RNA polymerase
- They become sensitive to the action of DNase 1
- More acyl groups are being added to the template strand
- Methyl groups are added to cytosine making CpG islands
- True/False- 5-methylcytosine is chemically altered by treatment with bisulfite and is not detected during sequencing. This helps when researchers try to determine the locations of 5-methylcytosine.
False- 5-methylcytosine is not chemically altered and is detected as cytosine during sequencing. Page 627
- Does the presence of lactose affect the amount of CAP protein in a bacterial cell and does lactose increase or decrease the rate of transcription in the lac operon?
- No, Increase
- No, decrease
- Yes, increase
- Yes, decrease
Page 454 and 458 CAP is not affected by levels of lactose. Glucose, on the other hand, does affect the amount of cAMP in the cell, but does not affect CAP levels. However, cAMP binds to CAP forming the CAP-cAMP complex. Since there is more cAMP when glucose is low, there will be more CAP-cAMP complex. This complex binds to the operon and increases transcription. In short, low glucose levels increase transcription and high levels of glucose decrease transcription for the lac operon gene.
- True/False- DNA methylation and deacetylation of histones both repress transcription.
- What is the complementary strand on the following dideoxy reaction?
Here’s the best way to solve this kind of problem. Start at the top, put 3’ and then go down and put the letter that corresponds to the band and after the last letter, put 5’. If we do this for the example, we get 3’-CGTAGTCAT-5’. This is the COMPLIMENTARY strand. For the template strand, simply write the strand complimentary and antiparallel to the strand we just wrote. This would be 5’-GCATCAGTA-3’ which is the template strand and the original sequence given.
- Which man is most likely the father from the following gel?
Mom Jim Joe Child
- Neither is the father
- Both could be the father
These questions are fairly easy. Pick the man with the most bands that are the same as the child, and you have the father. Here Jim only has one band that is the same as the child, where Joe has 3.
- Question 24 is a practical use of DNA fingerprinting. Which of the following is NOT true about DNA fingerprinting?
- DNA fingerprinting done by using microsatellites or STRs.
- A person with more repeats in an STR produces a longer segment than a person with fewer repeats.
- Longer segments are further down the gel than shorter segments
- Two random people having the same DNA profile is less than 1 in a billion
- How are genetic maps constructed and what are some limitations of genetic maps?
Genetic maps are based genetic function of recombination. They use frequencies of recombination between loci to be made. Some limitations is that genetic maps lack detail. They also don’t accurately correspond to physical distances between genes. Also, distances between genes on a genetic map are only approximations to the real physical distances. Page 580
- List the steps it would take to engineer a tobacco plant that can produce its own insecticide. Use Bt toxin as the foreign DNA and a Ti plasmid as the vector and A. tumefaciens as the bacteria used to infect the plants.
First, cut foreign DNA and Ti plasmid with the same restriction enzyme. Then insert foreign DNA (Bt toxin) into the Ti plasmid. Then transfer the plasmid into the A. tumefaciens bacteria. After bacteria goes through recombination, infect the tobacco plants with the bacteria. Page 545-546
- What are CpG islands and what is their function?
CpG is where methylation occurs on cytosines adjacent to guanines. DNA regions with many CpG sequences are called CpG islands. CpG islands are often methylated while the genes aren’t being transcribed. This methylation also attracts deacetylases which removes acetyl groups and also causes transcription to be repressed. CpG methylation is also associated with long-term gene repression, such as on the inactivated X chromosome on female mammals
- What is the difference between DNA methylation and histone methylation and what are the effects of both.
Histone methylation is the addition of methyl groups to histone proteins. This can either activate or repress transcription.
DNA methylation is like CpG islands where methyl groups are added to cytosines. Heavily methylated DNA is associated with the repression of transcription in vertebrates and plants, whereas transcriptionally active DNA is usually unmethylated. Page 475-476
- What is the difference between a DNA library, a genomic library and a cDNA library?
A DNA library is a collection of clones containing all the DNA fragments from one source.
A genomic library is a set of bacterial colonies containing all the DNA sequences from the human genome. Must contain a large number of clones to ensure that all DNA sequences in the genome are represented in the library.
A cDNA library is a genomic library consisting of DNA sequences transcribed into mRNA. An advantage of a cDNA library is that it has fragments from actively transcribed genes.