BIOC 385 Exam 4
Which amino acids are: (1) represented more than once, and (2) what is the C-terminal amino acid? 5' - GGG - CCT - AAT - TTA - GTC - GCT - GGT - GCA - CCT - ATG - TGA 3'
(1) Pro, Ala, Gly;; (2) Met
Which sequence is MOST likely to be prenylated in the ER? (The ... represents additional amino acids N-terminal to those shown.)
...Leu-Phe-Leu-Cys-Ile-Phe
In the figure below, which structure is known as the acceptor stem?
1
Based on the figure below, cleavage followed by rejoining at which sites would lead to no recombination or loss of genetic information?
1 and 3
Nirenberg and colleagues determined a portion of the genetic code using filter binding assays that included ribosomes, trinucleotides and tRNA molecules charged with radioactively-labeled amino acids. Choose the answer below that correctly answers the following three questions in order: 1) If the trinucleotide sequence is CAG, which amino acid will be bound to the filter paper? 2) If the wobble position of the trinucleotide sequence is changed to a U, which amino acid will be bound to the filter paper? 3) True or False: Two distinct tRNA molecules with different anticodon sequences MUST be used to recognize the codons AGA and AGG.
1) Gln, 2) His, 3) False
What is the approximate angle that is induced within the double helix when the lac repressor is associated (assume that non-bound DNA contains a 0º bend)?
40 degrees
Francis Crick hypothesized that the Genetic Code must require 3 nucleotides in the mRNA to specify each amino acid based on a simple calculation. What was the logic behind this calculation? Choose the ONE best answer.
Based on the number of known amino acids and the number of known nucleotide bases.
In the figure below, which is the mode of action for tetracyclines?
C
Which of the following proteins is responsible for binding to oriC to initiate replication in E. coli?
DnaA
Gene regulation of the lactose operon in E. coli is controlled by two transcription factors, CRP and the lac repressor. Beta-galatosidase is one product of the lab operon. Why does adding glucose to a bacterial culture containing lactose inhibit beta-galactosidase expression? Choose the ONE best answer.
Even though lactose is present, there is no beta-galatosidase expression because the high levels of glucose mean that there are low levels of cAMP. If cAMP levels are low, CRP does not bind and activate transcription.
What function do HAT and HDAC perform in the chromatin-modifying process?
HAT activates the gene and HDAC represses the gene.
A newly translated protein that is N-glycosylated could theoretically end up in which of the following locations and orientations?
In the plasma membrane, with the glycan facing the extracellular space. In the lysosome, with the glycan facing the interior of the lysosome.
Order the following steps of treating macular degeneration with iPS cells.
Isolate cells from patients skin Cause expression of genes required for pluripotency Cause expression of genes required fro RPE differentiation Implant cells into patient's retina
Why is azidothymidine (AZT) an effective medication for HIV patients?
It is a nucleotide analog that cannot participate in nucleotide polymerization.
Assume that you have identified all the cis-acting sites in a prokaryotic genome for a particular A. 2, 5, 7 B. 3, 5, 7 C. 4, 6, 7 D. 2, 3, 4 E. 1, 3, 5 trans-acting transcription factor. What is the function of this transcription factor when binding to these sites?
It is not possible to predict the function from the sites since could activate or repress at different sites.
Assume that you have identified all the cis-acting sites in a prokaryotic genome for a particular trans-acting transcription factor. What is the function of this transcription factor when binding to these sites?
It is not possible to predict the function from the sites since could activate or repress at different sites.
Where are pioneer factors least likely to bind?
Linker DNA between nucleosomes
Cis-Acting Sites
Polyadenylation site Shine-Dalgamo sequence
Describe the biochemical mechanism by which RNA splicing occurs precisely at the exon-intron borders considering that a single nucleotide offset by a mistake in splicing will reset the open reading frame register for the encoded protein.
RNA splicing involves small nucleoprotein RNA (snRNP) complexes that contain 'guide' ribozyme type RNA molecules and proteins. Sequential loading of spliceosome complexes onto the RNA provide alignment and catalysis to form an excised lariat structure. Both U1 and U2 snRNA form specific base pairs with regions of the target intron to ensure specific splicing.
Which of the following best describe(s) this resolvase RuvC?
Resolvase contains α helices and antiparallel β sheets. Resolvase is considered to be a homodimer
Why does RNA contain uracil and DNA contain thymine? Choose the one BEST answer.
Spontaneous cytosine deamination generates uracil, which base pairs with adenine during replication, and thereby converts a C-G base pair to a T-A base pair
The Trp repressor protein is bound to double-stranded DNA in the presence of tryptophan.
The Trp repressor protein is bound to double-stranded DNA in the presence of tryptophan.
What is a Holliday Junction? Choose the one BEST answer below.
The location in a DNA recombination intermediate where DNA strands from different DNA molecules are crossed over, which links the two DNA molecules together.
Which of the following is not a mechanism that enables the binding of a pioneer factor to a cis-acting sequence?
The pioneer factor binds to the DNA with the help of the mediator complex.
Which of the following is NOT an event that occurs during prokaryotic transcription?
The σ factor departs when the closed complex forms at the promoter.
There are several similarities between the miRNA and RNAi pathways. Which of the following are common features of both pathways?
There are several similarities between the miRNA and RNAi pathways. Which of the following are common features of both pathways?
Considering the molecular structure, which of the following correctly describes the relationship among carbohydrate nutrition, cAMP levels, CRP, DNA binding, and gene expression?
When cytoplasmic glucose levels are low, cAMP levels will be high, and then the CRP will be activated to bind DNA to activate transcription at certain gene loci.
Nucleotide ligand binds to the CRP in an active site that is structurally comprised of which of the following?
a β sheet, one α helix, and disorganized turns
The initiation, elongation, and termination of eukaryotic transcription is controlled by the
extent of phosphorylation and dephosphorylation of the RNA polymerase CTD.
Examine the structure of the lac repressor/DNA complex protein in this region as well as the DNA. The lac repressor contains which of the following?
helix-turn-helix motif that interacts with the major groove of target DNA
What is the biochemical explanation for why adding glucose to a bacterial culture containing lactose significantly decreases production of beta-galactosidase, whereas adding lactose to a bacterial culture containing glucose leads to only a minimal increase in the production of beta-galactosidase?
it will shut down cAMP production by adenylate cyclase through the PTS system and thereby block cAMP-CRP stimulation of the lac operon, so transcription and beta-galactosidase levels decrease significantly
Which of the following RNAs is both used during protein synthesis and is NOT recycled?
mRNA
Which of these RNAs are a coding RNA if consider lncRNA as an example of noncoding RNA?
mRNA
What explains the observation that a single eukaryotic protein coding gene can give rise to multiple different proteins, i.e., why are there only ~25,000 human genes in the genome, but ~150,000 different proteins in the human "proteome?" Choose the TWO best correct answers.
mRNA transcripts from the same gene can be differentially spliced to include/exclude exons. Genes can contain more than one polyadenylation site, which alters the 3' of the mRNA transcript and the inclusion/exclusion of exons.
A number of different RNAs are required for protein synthesis. Which of the following RNAs are required for the complete process of assembling the protein synthesis machinery as well as translation in eukaryotes?
mRNA, tRNA, and rRNA snoRNA and snRNA
Briefly describe the structure and function of the one key 1) E. coli protein and the one key 2) human protein that are each needed for high fidelity termination of DNA replication.
1) Tus protein prevents fork replication past termination 2) Telomerase prevents lagging strand deletion
Given that (1) the rate of polymerization for E. coli DNA polymerase is ~1 x 103 nucleotides/sec and that of human DNA polymerase is ~5 x 102, (2) the diploid human genome is ~2 x 103 times larger than the haploid E. coli genome, and (3) it takes ~480 minutes to replicate the diploid human genome, but only ~40 minutes to replicate the haploid E. coli genome, which number best describes the number of replication origins needed in the human genome to complete genome duplication in ~8 hours?
10^4
The Shine-Dalgarno sequence of mRNA base pairs with the __________ rRNA within the prokaryote __________ ribosomal subunit.
16S; 30S
If the following mRNA was added to a cell-free translation system, how many unique protein sequences would be generated? ACCACCACCACCACCACCACCACCACCACCACCACCACCACC
3
The correct mRNA secondary structure of transcriptional termination is __________ stem-loop structure.
3-4
If the sequence of the mRNA in this figure is 5'-UAC-3', what is the sequence of the anticodon?
5'-GTA-3'
What accounts for the high fidelity of DNA polymerization? Choose the ONE best answer.
Active site geometry ensures that only correct sized nucleotide base pairs are formed, and 3' to 5' proofreading removes incorrect nucleotides.
An exciting potential application for induced pluripotent stem cells (iPS cells) is to replace cells that have been damaged by disease. One of the first human diseases doctors have tried to treat with iPS cells is macular degeneration, an age-related condition that causes death of a group of cells in the retina. Macular degeneration has been considered a useful test case for the use of iPS cells. In fact, protocols for reprogramming iPS cells into retinal pigment epithelial (RPE) cells are well established and the cells can be implanted into the patient's retina without invasive surgery.
An exciting potential application for induced pluripotent stem cells (iPS cells) is to replace cells that have been damaged by disease. One of the first human diseases doctors have tried to treat with iPS cells is macular degeneration, an age-related condition that causes death of a group of cells in the retina. Macular degeneration has been considered a useful test case for the use of iPS cells. In fact, protocols for reprogramming iPS cells into retinal pigment epithelial (RPE) cells are well established and the cells can be implanted into the patient's retina without invasive surgery.
Order the following events in the life cycle of bacteriophage λ starting with the initial infection of the host cell.
DNA is injected in a linear form DNA circularizes within the cell insertion into the host chromosome Replication of λ DNA by host cell polymerase
Why is it necessary for σ factor to dissociate from the RNA polymerase in order for elongation to occur efficiently?
Dissociation of σ factor increases the affinity of RNA polymerase for general DNA.
Which of the following is not a part of the miRNA pathway for mRNA degradation?
Double-stranded RNA initiates the pathway.
What explains the observation that a single eukaryotic protein coding gene can give rise to multiple different proteins, i.e., why are there only ~25,000 human genes in the genome, but ~150,000 different proteins in the human "proteome?" Choose the THREE best answers.
Genes can have alternative promoters that include or exclude the first exon when being transcribed, thereby generating proteins with different amino termini. Differentially spliced mRNA transcripts can be generated from the same gene to include or exclude one or more exons Genes can contain more than one polyadenylation site, which alters the 3' of the mRNA transcript and the inclusion/exclusion of exons.
In the figure show below of an E. coli replication fork, which protein is responsible for relieving torsional stress?
Gyrase Helicase is responsible for unwinding the DNA duplex for replication. This action leads to torsional strain upstream of the replication fork, which would inhibit forward movement of the fork. Gyrase, which is a type II topoisomerase, relieves this strain.
Identify the sugars present in the bacterial culture for conditions 1, 2, and 3 using the
High glucose and high lactose 2) Low glucose and high lactose 3) Low glucose and low lactose
This image shows the expression pattern of even-skipped (eve) in a Drosophila embryo in brown, and highlights stripe 2 of eve expression in blue.Which proteins are present in the cells of eve stripe 2?
Hunchback Ecen-skipped Bicoid
Would having 61 tRNAs, with each one binding to just one of the amino acid-encoding codons, improve or impair the efficiency of protein synthesis? Assume that the total amount of tRNA in a cell would be unchanged.
Impair, because the greater variety of tRNAs would make it harder to find the right one for a particular codon.
How high should the concentration of aminoacyl-tRNA synthetases be, compared to the concentration of tRNAs in a cell?
Low, because a single aminoacyl-tRNA synthetase can catalyze many reactions.
Which of the following statements is NOT correct concerning lysine methylation?
Methylated lysines bind to bromodomains of proteins.
Which of the following is correct concerning self-splicing introns?
None of these answers are correct
What is the function of the MutS-MutL-MutH protein complex?
None of these answers are correct.
Why does RNA contain uracil and DNA contain thymine? Choose the ONE best answer to this question.
None of these statements are correct.
Observe the ribbon structure of the CRP-cAMP complex. The protein component is a dimer and each of the subunits binds to one cAMP molecule(s).
Observe the ribbon structure of the CRP-cAMP complex. The protein component is a dimer and each of the subunits binds to one cAMP molecule(s).
Choose 3 reasons why RNA is a dynamic biomolecule, and in that way, distinct from DNA.
RNA tertiary structure is altered by the binding of protein and small molecule ligands. RNA is able to participate in transitory functional base pairing interactions with RNA or DNA. RNA is synthesized and degraded continuously to control biochemical processes
A ribosome waiting to bind the next charged tRNA will not release its elongating polypeptide, no matter how long it waits. However, a ribosome that binds a release factor will quickly release the polypeptide. Why?
Release of the polypeptide requires the breaking of a covalent bond, which is thermodynamically unfavorable.
Trans-acting factors
TFIID Spliceosome Transcriptional repressor
An experiment designed to map the protein sequences required for fully functional mitochondrial targeting 100% of the time. It was observed that adding the amino terminal 12 amino acids from a known mitochondrial protein on to a known cytosolic protein directed the cytosolic protein into mitochondria ~50% of the time. Moreover, deleting the amino terminal 12 amino acids from the same mitochondrial protein decreased its frequency of mitochondrial localization to ~50% of the time. What do you conclude about the importance of the 12 amino acid sequence in mitochondrial protein targeting?
The 12 amino acids are necessary but not sufficient for fully functional mitochondrial targeting.
What accounts for the high fidelity of DNA polymerization?
The 3' to 5' exonuclease activity is a proofreading function that removes incorrect nucleotides at the fork.
What effect is likely from the alteration of the sequence at the 5' end of the RNA component of the U1 snRNP from 5'AUACYYACCU3" to 5'AUACYYGCCU3'? (Note that Y in the sequence stands for the modified base "psi") Choose the ONE best choice from the list below.
The 5' splicing junction that will be recognized by this altered spliceosome will be 5'AGGCAGGU3' because the nucleotide sequence of the base pairing portion of U1 snRNP has changed.
How is the Ames test used to quantitate mutagenic potential of chemical compounds? Select the TWO best answers.
The Salmonella test strain used in the Ames test contains a mutation in the histidine biosynthetic pathway, which is used to identify compounds that induce back mutations to permit bacterial growth on histidine free plates. The chemical compound to be tested is added to a filter paper disk and placed on agar plates containing the tester Salmonella strain; potent mutagens result in MORE colonies forming on histidine free plates as compared to control plates.
Observe the nucleic acid to which the Trp repressor protein is bound. Based on your observation of the molecular structure, which statement best describes the interaction between the Trp repressor protein and nucleic acid?
The Trp repressor binds upstream of the first gene of the trp operon, and the protein interaction spans two major grooves and one minor groove along the longitudinal axis of the binding site.
Describe how iPS therapy could be used to treat Parkinson's Disease. Include in your answer 1) method used to generate patient-specific iPS cells, 2) method used to isolate differentiated cells with the necessary phenotype, 3) method used to introduce the differentiated cells into the patient, and 4) possible risks to this therapy.
The approach to treating Parkinson's disease by iPS cells therapy is to isolate patient cells, convert them to dopamine producing cells, and then introduce them back to the patient. Specifically, 1) remove fibroblast cells from the patient and convert them to iPS cells by using viral infection carrying the four needed transcription factor genes (Oct4, Sox2, Klf4, c-Myc) and isolate colonies, 2) grow the iPS cells in special media to induce neuronal differentiation; screen for dopamine producing differentiated cells, 3) inject the clonal dopamine producing cells into the brain of the patient, and 4) the biggest risk is that the reinjected iPS cells will transform and become cancerous.
The bacteriophage λ life cycle events outlined in Part 1 represent the lysogenic cycle of phage replication.
The bacteriophage λ life cycle events outlined in Part 1 represent the lysogenic cycle of phage replication.
The processes of DNA replication and RNA transcription in E. coli are similar in some respects and different in others. Select the THREE statements below that describe BOTH DNA replication and RNA transcription in E. coli.
The direction of enzyme movement on the template strand is 3' to 5' The direction of enzyme movement on the template strand is 3' to 5' A specific region of the DNA is recognized and bound by the polymerase.
The processes of DNA replication and RNA transcription in E. coli are similar in some respects and different in others. Select the THREE statements below that describe BOTH DNA replication and RNA transcription in E. coli.
The direction of polymerization is 5' to 3' A specific region of the DNA is recognized and bound by the polymerase. The direction of enzyme movement on the template strand is 3' to 5'
If the human genome is used as the source of DNA for a functional gene that is 150,000 nucleotides long to synthesize protein in a bacterial protein expression system, rather than using the fully processed mRNA that is converted to complementary DNA (cDNA) as a the source of gene sequence, what is the most likely explanation for the lack of expressed protein considering that a bacterial promoter was used and large amounts of human RNA are being synthesized in the bacterial system?
The human gene contains introns that are not processed out by enzymes in the bacterial system.
RNA is typically more susceptible to backbone hydrolysis than DNA because of a chemical property. Choose the one correct answer from the right.
The presence of a 2' OH group
Why is the trp operon regulated in this manner? In other words, why would a mechanism, like the one observed in this molecular structure, be evolutionarily favorable?
The production of the tryptophan biosynthetic enzymes is a waste of metabolic energy if tryptophan is available to the bacterial cell from the environment.
What happens during protein synthesis if a tRNA is charged with the wrong amino acid?
The protein will contain the wrong amino acid in the corresponding codon position or None of these answers are correct.
Which of the following statements is FALSE concerning translation initiation in eukaryotes?
The ribosome binding site is known as the Shine-Dalgarno sequence.
Considering that binding of the correct tRNA to the aminoacyl-tRNA synthetase is the critical first step (amino acid proofreading occurs after tRNA binding), how is specific tRNA recognition and binding accomplished?
The specificity for tRNA recognition by aminoacyl-tRNA synthetases is not limited to the anticodon sequence as it is insufficient (2 of 3 nucleotides). Instead, a number of modified nucleotide bases scattered throughout the tRNA structure provide a recognition signature, many of which are in the D loop and acceptor stem
An undergraduate working in a biochemistry lab wants to express the human protein encoded by the "canonical gene" shown in Figure 21.45 using a bacterial expression system to provide purified protein for study. He uses plasmid cloning to insert the entire canonical gene into the plasmid and then transfects E. coli. He does not observe any protein being expressed in the bacterial cells. Provide two explanations for why his approach was unlikely to work.
The two reasons it will not work are 1) the transcriptional machinery in bacterial cells (RNA polymerase, sigma factor, regulatory proteins) will not recognize the human promoter sequences to initiate transcription by RNA polymerase. 2) The human canonical gene contains introns that will not be removed by RNA splicing in bacterial cells since bacteria lack this function; this would lead to STOP codons in the intron even if transcription occurred.
Observe the ligand that is bound to each of the lac repressor polypeptides. Based on your observation of the molecular structure and your knowledge of the physiology of this protein, what is true of the ligands that bind each subunit?
They are identical and their binding to the complex will cause a conformational change within the protein that allows a DNA binding domain to become inactive.
This DNA binding protein associates with eukaryotic DNA sequence upstream of a protein-coding sequence of DNA. If the TATAAA sequence were altered to AGGCTA, then that change would likely result in a decrease in the rate of transcription at this gene locus.
This DNA binding protein associates with eukaryotic DNA sequence upstream of a protein-coding sequence of DNA. If the TATAAA sequence were altered to AGGCTA, then that change would likely result in a decrease in the rate of transcription at this gene locus.
Which of the following best describes how trans- and cis-acting factors operate?
Trans-acting factors can bind to specific DNA sequences whereas cis-acting sites are DNA sequences.
Choose the best answer that correctly identifies the labeled DNA and RNA sequences. 5' - .....GGCAUGUGCCAAUGCC.... - 3' (X) 3'-.....CCGTACACGGTTACGG.... - 5' (Y) 5'-.....GGCATGTGCCAATGCC.... - 3' (Z)
X is RNA, Z is DNA coding, Y is DNA template.
What two types of amino acid sequences are needed in a protein to mediate post-translational farnesylation?
a signal peptide sequence to target the ribosome to the endoplasmic reticulum to continue protein synthesis 2) the C terminal CaaX sequence where "C" is cystein, "a" is aliphatic amino acid and "X" is the C-terminal amino acid
a) How long would it take in minutes to replicate the E. coli chromosome if it used unidirectional rather than bidirectional replication? Explain how you calculated this answer. b) Not accounting for individual chromosomes and telomeres, i.e., use genome size, polymerization rate, and number of origins, how long should it take in hours to replicate the diploid human genome? Explain how you calculated this answer. Why is this calculated time less than the observed time?
a) Method 1: It takes 40 minutes for bi-directional replication, so it would take ~80 minutes for unidirectional. Method 2: If using the genome size and rate of polymerization, it would be 4.6 x 106 divided by 103 nucleotides/sec, which is 4.6 x 103 seconds or 76 minutes. b) The genome size is 3.3 x 109 and the replication rate is 50 nucleotides/sec, so with one origin, it would take 6.6 x 107 seconds, but there are 104 origins, so would take only 6.6 x 103, now divide by 60 seconds in a minute and total time with assumptions is 110 minutes for haploid and 220 minutes for diploid, which is 3 hours and 40 minutes. Since there ARE chromosomes and telomeres, it actually takes ~8 hours.
a) Considering how the Ames test is used to quantitate mutagenicity of a compound, why are there more bacterial colonies, not less bacterial colonies, the more potent of a mutagenic compound is tested? b) What is the biochemical explanation for why pre-incubating a suspected mutagenic compound in a rat liver extract results in more bacterial colonies formed as compared to no pre- incubation in a liver extract?
a) The Ames test measures DNA mutations that "rescue" the inability to synthesize the amino acid histidine. Therefore, when growing bacteria on a histidine-deficient plate, it requires a mutation to revert the phenotype and allow the bacteria to grow. This provides a positive readout, rather than a negative one. b) The increased level of mutagenicity is likely due to enzymatic modification of the compound by liver enzymes, probably p450 oxygenases, that further activate the compound by altering chemical bonds. This makes a more mutagenic compound compared to no liver extract pre-treatment.
Answer these three questions: a) What is the amino sequence of the tripeptide encoded by the mRNA sequence 5'-AUGACUGGU-3'? b) Write a different mRNA sequence that does not alter the amino acid sequence of the encoded tripeptide? c) Based on the Genetic Code, how many different mRNA sequences are possible that will all encode the same amino acid tripeptide sequence in part b?
a) The amino acid sequence of the tripeptide is Met-Thr-Gly. b) Any sequence that contains 5'-AUG-ACx-GGx-3' c) 1 x 4 x 4 = 16; this is because there are 4 possible sequences to encode Thr and 4 possible sequences to encode Gly, but only possible sequence to encode Met.
When lactose levels in the environment are low, transcription of the lac operon
decreases
Resolvase activity will act upon Holliday junctions and will generate which of the following?
either recombinant or nonrecombinant nucleic acid
Producing an iPS cell is remarkable because the pathway
for conversion is general, not specific.
What four amino acid side chains are integral to the DNA binding function of the TATA binding protein?
four phenylalanine residue side chains
Describe the structure and function of miRNA, snRNA, and lncRNA, which represent the three major types of noncoding RNAs; what are four mechanisms by which lncRNA molecules are thought to regulate cellular processes?
miRNA is ~18-32 nucleotides short noncoding RNA that functions in translational regulation; snRNA ~70- 200 nucleotide small noncoding RNA that functions in RNA splicing, and lncRNA is ~200-1000 nucleotide long noncoding RNA is that functions in gene expression (pg 1057). The four mechanisms by which lncRNA is thought to regulate cellular processes are 1) binding to mRNA to regulate protein synthesis, 2) binding to DNA to regulate transcription, 3) binding to proteins to regulate protein functions, and 4) ligand-induced riboswitches to regulate signaling pathways
Match the name of the DNA repair mechanism with the correct description.
mismatch-Functions with DNA replication to remove incorrect nucleotides from the nascent strand. base excision repair-Requires an endonuclease to remove an abasic nucleotide before DNA Pol I can replace a portion of the strand. nucleotide excision repair-Is needed to repair chemical damage in DNA effecting more than one nucleotide, such as cyclobutane pyrimidine dimers. direct repair-Repairs nucleotide bases without requiring DNA ligase.
If 15N DNA replicated using conservative replication in 14N media, the outcome would be that new DNA has
one high density and one low density strand
Which of the following are consistent with the secondary structures that are observed in the TATA binding protein?
one large β sheet and four α helices
Rank the following events from earliest to latest during the initiation of E. coli DNA replication.
oriC becomes separated Binding of the primosome Interaction of Pol III via the beta-clamp t subunit Two opposing replication forks collide Resolution of catenated DNA molecules
What kind of control mechanism is ligand-induced binding of an activator protein?
positive
AZT is such a good HIV drug because it
prevents new DNA from being replicated.
Negative autoregulation can best be described as when the expression of a protein
provides feedback that represses its own expression.
What is the biochemical explanation for why pre-incubating a suspected mutagenic compound in a rat liver extract results in more bacterial colonies formed as compared to no pre-incubation in a liver extract using the Ames test of mutagenicity?
rat liver enzymes chemical modify the compound to transform it into and even more potent mutagen.
The resolvase active site contains an amino acid with which of the following?
side-chain hydroxyl that reacts with a phosphate group of the substrate
What are the two main types of stem cells?
somatic and embryonic
What experiment needs to be done in the Ames test for mutagenicity to rule out that the rat liver extract is causing His genetic reversions, rather than enzymes in the extract modify the test compound?
the liver extract is incubated with bacteria in the absence of the compound and there are few colonies
