Microbiology unit 8
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* * * To summarize, genes are the units of biological information encoded by the sequence of nucleotide bases in DNA. A gene is expressed, or turned into a product within the cell, through the processes of transcription and translation. The genetic information carried in DNA is transferred to a temporary mRNA molecule by transcription. Then, during translation, the mRNA directs the assembly of amino acids into a polypeptide chain: a ribosome attaches to mRNA, tRNAs deliver the amino acids to the ribosome as directed by the mRNA codon sequence, and the ribosome assembles the amino acids into the chain that will be the newly synthesized protein.
Describe how DNA serves as genetic information.
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Describe protein synthesis, including transcription, RNA processing, and translation.
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Discuss the role of plasmids, resistance factors (R factors), and transposons in the development of antibiotic resistance.
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What is competence
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If enzyme a is inducible and is not being synthesized at present, a ______ protein must be bound tightly to the _____ site.
1) repressor protein 2) operator site
Assume a cell is grown in a culture medium containing radioactively labeled thymidine. After three cell divisions, what percentage of the cells would contain the radioactive label?
100%
3.Human herpesvirus-8 (HHV-8) is common in parts of Africa, the Middle East, and the Mediterranean, but is rare elsewhere except in AIDS patients. Genetic analyses indicate that the African strain is not changing, whereas the Western strain is accumulating changes. Using the portions of the HHV-8 genomes (shown below) that encode one of the viral proteins, how similar are these two viruses? What mechanism can account for the changes? What disease does HHV-8 cause? Western 3′-ATGGAGTTCTTCTGGACAAGA Africsn 3′-ATAAACTTTTTCTTGACAACG
6. Human Herpescirus-8 (HHV-*) causes Kaposi sarcoma, systemic skin lesions (AIDS patients). Treatment is HAART which stands for reverse transcriptase inhibitors plus protease inhibitors. These are the cocktail of drugs given in the western world by combining the two interrupts it in two different phases of its cycle. It has helped with the incidence of viral drug resistance because the virus would have to undergo three separate mutations separately at nearly impossible odds. The African strain is the original strain since they don't have the resources to treat it and thus the virus doesn't mutate. The western strain is mutated due to medications we throw at it. The mechanisms that account for these mutations are insertions, deletions, and frameshifts. They have 4 out of 7 amino acids created based on codons in common and 3 out of 7 different.
Which of the following statements about eukaryotic mRNA is TRUE?
A cap is added to their 5' end, A poly-A tail is added to their 3' end, each usually specify only a single protein.
Which of the following can cause changes in a sequence of several amino acids
A frameshift mutation
Corepressor
A molecule that binds to a repressor protein, enabling the repressor to bind to an operator.
Use the genetic code in your textbook to solve this problem: The mRNA copied from a given gene is as follows: UACAAAGAAAUU. If base 2 were changed to U, what effect would this have?
A missense mutation will occur
Which of these statements is true of translation?
A molecule of tRNA can bind to both an mRNA molecule and an amino acid. The "language" of nucleotides is changed to the "language" of amino acids. Three different nonsense codons code for termination of protein synthesis. A single mRNA may have several ribosomes attached.
What is the difference between plasmid and bacterial chromosomes
The genes that plasmid carries carry are usually not essential for the growth of the cell under normal conditions. The plasmids responsible for conjugation are transmissible between cells during conjugation.
genome,
The genetic information in a cell. It includes its chromosomes and plasmids.
Silent mutations commonly occur
when one nucleotide is substituted for another in the DNA, especially at a location corresponding to the third position of the mRNA codon.
Auxotrophs
will not grow on a plate that lacks the growth factor, but will grow on a complete medium that contains the growth factor
Match the following examples of mutagens.
A mutagen that is incorporated into DNA in place of a normal base= Nucleoside analog A mutaaen that causes the formation of highly reactive ions=Ionizing radiation A mutagen that alters adenine so that it base-pairs with cytosine=Base-pair mutagen A mutagen that cause insertion=Frameshift mutagen A mutagen that causes the formation of pyrimidine dimers=Nonionizing radiation
Auxotroph
A mutant microorganism with a nutritional requirement that is absent in the parent.
F factor (fertility factor)
A plasmid found in the donor cell in bacterial conjugation.
Inducer
A substance that acts to induce transcription of a gene is called an
Which of these statements is true about transduction?
A virus is required for transfer of genetic material. In this process, bacterial DNA is transferred from a donor cell to a recipient cell inside a virus that infects bacteria, called a bacteriophage,
Which of the following is not a method of horizontal gene transfer? a.binary fission b.conjugation c.integration of a transposon d.transduction e.transformation
A) binary fission
Which one of the following nucleotide sequences is most likely affected by ultraviolet light?
AGTTTC
Methylase
Adds methyl group to selected bases in newly made DNA
RNA primase
An RNA polymerase that makes RNA primers from a DNA template
Plasmids differ from transposons in that plasmids a.become inserted into chromosomes. b.are self-replicated outside the chromosome. c.move from chromosome to chromosome. d.carry genes for antibiotic resistance. e.none of the above
B
Which of these events occur as a prokaryotic mRNA is being transcribed?
Binding of ribosomes
Nucleoside analogs and ionizing radiation are used in treating cancer. These mutagens can cause cancer, so why do you suppose they are used to treat the disease?
Both of these methods of inducing mutation cause breaks in replicating DNA. This will especially effect cells undergoing mitosis - one of the characteristics of cancer cells. These breaks, in large enough quantities, will cause the cell to undergo apoptosis and die. This is a method of using a characteristic of cancer cells (frequent mitoses) to kill them without as much damage to non-cancerous cells.
Suppose you inoculate three flasks of minimal salts broth with E. coli. Flask A contains glucose. Flask B contains glucose and lactose. Flask C contains lactose. After a few hours of incubation, you test the flasks for the presence of (β-galactosidase. Which flask(s) do you predict will have this enzyme? a.A b.B c.C d.A and B e.B and C
C
Feedback inhibition differs from repression because feedback inhibition a.is less precise. b.is slower acting. c.stops the action of preexisting enzymes. d.stops the synthesis of new enzymes. e.all of the above
C) stop the action of preexisting enzymes
Which sequence is the best target for damage by UV radiation: AGGCAA, CTTTGA, or GUAAAU? Why aren't all bacteria killed when they are exposed to sunlight?
CTTTGA. Endospores and pigments offer protection against UV radiation. Additionally, repair mechanisms can remove and replace thymine polymers.
Mechanism by which the presence of glucose inhibits the lac operon
Catalase repression
Which one of the following is a method of vertical gene transmission?
Cell division
Transfer of DNA from a donor to a recipient cell by a bacteriophage.
Conjugaison
RNA polymerase
Copies RNA from a DNA template
If enzyme a is repressible, end-product C, called a (1) ______, causes the (2) ______ to bind to the (3) _______
Corepressor, Repressor protein, Operator
Endonucleases
Cut DNA backbone in a strand of DNA; facilitate repair and insertions
Exonucleases
Cut DNA from an exposed end of DNA; facilitate repair
Tranposase
Cuts DNA backbone, leaving single-stranded "sticky ends"
Two offspring cells are most likely to inherit which one of the following from the parent cell? a.a change in a nucleotide in mRNA b.a change in a nucleotide in tRNA c.a change in a nucleotide in rRNA d.a change in a nucleotide in DNA e.a change in a protein
D
Bacteria can acquire antibiotic resistance by all of the following except a.mutation. b.insertion of transposons. c.conjugation. d.snRNPs. e.transformation.
D) snRNPs
Briefly describe the components of DNA, and explain its functional relationship to RNA and protein.
DNA consists of a strand of alternating sugars (deoxyribose) and phosphate groups with a nitrogenous base attached to each sugar. The bases are adenine, thymine, cytosine, and guanine. DNA exists in a cell as two strands twisted together to form a double helix. The two strands are held together by hydrogen bonds between their nitrogenous bases. The bases are paired in a specific, complementary way: A-T and C-G. The information held in the sequence of nucleotides in DNA is the basis for synthesis of RNA and proteins in a cell.
Which of the following hypotheses was developed following Griffith's 1928 experiment
DNA from dead encapsulated bacteria can transform living nonencapsulated bacteria into living encapsulated bacteria.
enzymes and their functio
DNA helicase: unwinds two strands of DNA DNA ligase: joins pieces of DNA together DNA polymerase: synthesizes DNA and proofreads
In which direction is DNA synthesized?
DNA is synthesized in the 5′ to 3′ direction.
Of the choices below, which is the LAST to happen during DNA replication?
DNA ligase joins all the new pieces together.
All of these statements are true about DNA replication
DNA ligase joins the small DNA fragments of the lagging strand. DNA polymerase is required to add new nucleotides to the growing ends of the DNA strands. RNA polymerase synthesizes the primers.
Normally a commensal in the human intestine, this bacterium became pathogenic after acquiring a toxin gene from a Shigella bacterium.
Escherichia coli
Which one of the following would be the most likely to yield a recombinant cell after mating? Which of these statements is true of translation?
F+ cell and F- cell Three different nonsense codons code for termination of protein synthesis. Hfr cell and F+ cell The "language" of nucleotides is changed to the "language" of amino acids. A molecule of tRNA can bind to both an mRNA molecule and an amino acid. F- cell and F+ cell A single mRNA may have several ribosomes attached.
For the peptide with the amino acid sequence, proline-alanine-glycine (pro-ala-gly), the DNA template strand could have the sequence
GGC CGA CCG
The mechanism by which lactose controls the lac operon.
Induction
Which of these answers is true for positive (direct) selection?
It enables detection of a rare mutant from a population containing an extremely large number of bacteria. An example would be the detection of bacteria resistant to ampicillin by incorporation of ampicillin into the plating medium. The mutant will grow on the selective medium, so there is no need for replica plating. The selective medium is designed so that only the mutant cells grow on that medium.
Which of the following correctly describes the lac operon?
It is an inducible operon that is turned on if lactose is present and glucose is absent.
DNA Ligase
Makes Covalent bonds to join DNA strands; joins Okazaki fragments and new segments in excision repair
The major source of the genetic diversity among microorganisms upon which natural selection operates is
Mutation
Why are mutation and recombination important in the process of natural selection and the evolution of organisms?
Mutation and recombination provide genetic diversity. Environmental factors select for the survival of organisms through natural selection. Genetic diversity is necessary for the survival of some organisms through the processes of natural selection. Organisms that survive may undergo further genetic change, resulting in the evolution of the species.
statements about DNA replication
Primase synthesizes the primers. DNA ligase joins the small DNA fragments of the lagging strand. DNA polymerase is required to add new nucleotides to the growing ends of the DNA strands..
Compare protein synthesis in prokaryotes and eukaryotes
Prokaryotes: Coupled transcription- translation = translation can begin before transcription finishes. Do not contain introns and exons. Ribosomes are small and they recognizes a purine rich area on mRNA. Uses operons for genes regulation. Contain 1 circular chromosome. Eukaryotes: Transcription must finish before translation begins, Contain introns and exons, Ribosomes are large and they recognize Guanine cap at the 5' end of mRNA transcript, don't have operons, made of many chromosomes
The antibiotic kasugamycin blocks binding of tRNA-Fmet (the bacterial tRNA that carries formylmethionine) to a ribosome. From this information, you can conclude that kasugamycin prevents
Protein synthesis
During conjugation, DNA is transferred from one bacterium to another. Often, it is plasmid DNA that is transferred. Which of the following plasmid names correctly matches the information that it carries?
R factors: antibiotic-resistance genes
Ribozyme
RNA enzyme that removes introns and splices exons together
snRPN
RNA-protein complex that removes introns and splices exons together
Degeneracy
Redundancy of the genetic code; that is, most amino acids are encoded by several codons.
DNA Gyrase
Relaxes supercoiling ahead of the replication fork
Topoisomerase
Relaxes supercoiling ahead of the replication fork; separates DNA circles at the end of DNA replication
The tryptophan operon contains genes that encode the enzymes involved in tryptophan biosynthesis. An abundance of tryptophan will "turn off" the operon. This operon is an example of a
Repressible operon
When the inducer is present, it will bind to the (3) ______ so that (4) _____ can occur.
Repressor Transcription
DNA Polymerase
Synthesizes DNA; proofreads and repairs DNA
Replication of the E. coli chromosome takes 40 to 45 minutes, but the organism has a generation time of 26 minutes. How does the cell have time to make complete chromosomes for each offspring cell?
The cell does not regulate the rate at which DNA is synthesized, but it regulates the rate at which replication forks on the chromosome are initiated. The cell initiates multiple forks so that a daughter cell will inherit a complete chromosome plus additional portions from multiple replication forks. Chromosome replication begins during or immediately after division
Pseudomonas has a plasmid containing the mer operon, which includes the gene for mercuric reductase. This enzyme catalyzes the reduction of the mercuric ion Hg2+ to the uncharged form of mercury, Hg°. Hg2+ is quite toxic to cells; Hg° is not. a.What do you suppose is the inducer for this operon? b.The protein encoded by one of the mer genes binds Hg2+ in the periplasm and brings it into the cell. Why would a cell bring in a toxin? c.What is the value of the mer operon to Pseudomonas?
The inducer for the operon is probably mercury ions. The process of converting mercuric ion to mercury may have some benefits to Pseudomonas and that is probably why it brings it in. This operon helps Pseudomonas survive in mercury rich environments.
Translation
The ribosome stops protein synthesis when it reaches a nonsense codon in the mRNA.
Which of the following statements concerning translation is correct?
The ribosome stops protein synthesis when it reaches a nonsense codon in the mRNA.
genomics.
The sequencing and molecular characterization of genomes is called
Terminator
The site on a DNA strand at which transcription ends.
Promoter
The starting site on a DNA strand for transcription of RNA by RNA polymerase.
Anticodon
The three nucleotides by which a tRNA recognizes an mRNA codon.
Conjugaison
The transfer of genetic material from one cell to another involving cell-to-cell contact.
Consider the polypeptide sequence encoded by the following DNA: TAC AAA GAA ATT. If base number 6 is changed to G, how will this affect the polypeptide?
There will be no change in the polypeptide.
Why can translation begin before transcription is complete in prokaryotes but not in eukaryotes?
There's ribosomes right there waiting in prokaryotes! In eukaryotes the primary transcript undergoes post-transcriptional processing -- removal of introns; alternate splicing; addition of 5' G cap; addition of 3' poly-A tail. Ribosomes outside the nucleus, nowhere near the DNA
Plasmids are readily transferred between bacterial cells
They are responsible for the emergence of methicillin-resistant Staphylococcus aureus and the recent emergence of carbapenem-resistant Klebsiella pneumoniae.
All of these statements are true of plasmids
They can be transferred between bacteria during conjugation. they may encode genes that enhance the pathogenicity of an organism. they are small, circular molecules of DNA that can carry genes for heavy metal resistance. they may contain antibiotic resistance genes.
What is the purpose of DNA replication?
To make an identical copy of DNA
Overall goal of translation
To produce protein using mRNAs as the source of biological information
Which means of genetic transfer among bacteria involves a virus?
Transduction
Your lab partner has mixed a dead tryptophan+ strain of Bacillus subtilis with a live tryptophan- strain and observes that her B. subtilis culture is now tryptophan+. The most likely explanation for this is _
Transformation
Transfer of DNA from a donor to a recipient as naked DNA in solution.
Translation
Splicing joins together
Two exons
Helicase
Unwinds double-stranded DNA
Photolyase
Uses visible light energy to separate UV-induced pyrimidine dimers
When does translation stop?
When a stop codon is reached
When iron is not available, E. coli can stop synthesis of all proteins, such as superoxide dismutase and succinate dehydrogenase, that require iron. Describe a mechanism for this regulation.
When iron is not available, E. coli can stop synthesis of all proteins, such as superoxide dismutase and succinate dehydrogenase, that require iron. Describe a mechanism for this regulation.
You are analyzing a segment of DNA and observe an area of sequence that appears to act as a promoter element. Based on this, what can you conclude?
You have found the beginning of a gene.
All of these statements are true of base substitutions
a base substitution can result in the production of a shortened protein a base substitution may be beneficial if the affected gene encodes an enzyme with enhanced activity base substitutions may be caused by radiation or chemical mutagens a base substitution may cause no change in the protein encoded by the affected gene
A mutation occurs that results in a codon change from UGU to UGA. UGU encodes a cysteine amino acid, and UGA is a stop codon. Therefore, this is an example of
a nonsense mutation
Ciprofloxacin, erythromycin, and acyclovir are used to treat microbial infections. Ciprofloxacin inhibits DNA gyrase. Erythromycin binds in front of the A site on the 5°S subunit of a ribosome. Acyclovir is a guanine analog. a.What steps in protein synthesis are inhibited by each drug? b.Which drug is more effective against bacteria? Why? c.Which drugs will have effects on the host's cells? Why? d.Use the index to identify the disease for which acyclovir is primarily used. Why is it more effective than erythromycin for treating this disease?
a) ciprofloxacin inhibits transcription > helicase grinds to a halt > can't make mRNA (need to relieve torsional strain resulting from unravelling DNA strands) > no template for protein synthesis erythromycin inhibits translation > EF-tu-tRNA-aa complex can't enter A site of ribosome > initiation/elongation can't occur > mRNA cannot be translated acyclovir inhibits transcription > acyclovir incorporated into mRNA strand > no phosphate group available on acyclovir to perform attack on incoming nucleotide (in other words no elongation for transcription) b) Erythromycin is best against bacteria because it targets bacterial ribosomal subunits (odd numbered) and not eukaryotic ribosomal subunits (even numbered) c) Acyclovir is probably best against viruses to prevent transcription of needed proteins. Some viruses have ssDNA so they don't need to unwind it. Also, other viruses have ssRNA, so they already have the mRNA needed to make proteins. However, vacyclovir isn't useful in all cases. But I would say it is generally the most effective for the most cases. d) Acyclovir because I don't think the Ciprofloxacin drug is able to get into the cell's nucleus, so it won't affect production of mRNA (in eukaryotes, transcription is in nucleus, not cytosol).
Define antiparallel and explain why continuous synthesis of both DNA strands is not possible.
a. DNA strands' sugar-phosphate backbones run in opposite directions b. Continuous synthesis of both DNA strands is not possible because the two strands run in opposite direction, and DNA polymerases add nucleotides only to free 3' end not 5'
Compare where transcription and translation occur in prokaryotes and in eukaryotes
a. In prokaryotic cell, mRNA produced by transcription is immediately translated without additional processing b. In eukaryotic cell, the nucleus provides a separate compartment for transcription. The original RNA transcript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA
The following is a code for a strand of DNA. a.Using the genetic code provided in Figure 8.8, fill in the blanks to complete the segment of DNA shown. b.Fill in the blanks to complete the sequence of amino acids coded for by this strand of DNA. c.Write the code for the complementary strand of DNA completed in part (a). d.What would be the effect if C were substituted for T at base 10? e.What would be the effect if A were substituted for G at base 11? f.What would be the effect if G were substituted for T at base 14? g.What would be the effect if C were inserted between bases 9 and 10? h.How would UV radiation affect this strand of DNA? i.Identify a nonsense sequence in this strand of DNA.
a.ATATTACTTTGCATGGACT. b.met-lys-arg-thr-(end). c.TATAATGAAACGTTCCTGA. d.No change. e.Cysteine substituted for arginine. f.Proline substituted for threonine (missense mutation). g.Frameshift mutation. h.Adjacent thymines might polymerize. i.ACT.
Identify when (before transcription, after transcription but before translation, after translation) each of the following regulatory mechanisms functions. a.ATP combines with an enzyme, altering its shape. b.A short RNA is synthesized that is complementary to mRNA. c.Methylation of DNA occurs. d.An inducer combines with a repressor.
a.After translation. b.After transcription. c.Before transcription. d.Before transcription.
You are provided with cultures with the following characteristics: Culture 1: F+, genotype A+ B+ C+ Culture 2: F-, genotype A- B- C- a.Indicate the possible genotypes of a recombinant cell resulting from the conjugation of cultures 1 and 2. b.Indicate the possible genotypes of a recombinant cell resulting from conjugation of the two cultures after the F+ has become an Hfr cell.
a.Culture 1 will remain the same. Culture 2 will convert to F+ but will have its original genotype. b.The donor and recipient cells' DNA can recombine to form combinations of A+B+C+ and A−B−C−. If the F plasmid also is transferred, the recipient cell may become F+.
Describe the process of DNA replication.
aReplication begins at specific sites, origins, where two parental strands separate to form replication bubbles b. Bubbles expand laterally as DNA replication proceeds in both direction; end of bubbles are called replication forks (Y-shaped region) c. Replication bubbles fuse, and synthesis of daughter strands is completed
Actions of Messenger RNA
acts as an intermediate between the permanent storage form, DNA, and the process that uses the information, translation.
gene
are segments of DNA (except in some viruses, in which they are made of RNA) that code for functional products.
chromosome
are structures containing DNA that physically carry hereditary information; contain the genes.
Transposons
because they may be carried between cells on plasmids or viruses, they can also spread from one organism—or even species—to another. For example, vancomycin resistance was transferred from Enterococcus faecalis to Staphylococcus aureus via a transposon called Tn1546. Transposons are thus a potentially powerful mediator of evolution in organisms.
In E. coli, Hfr cells
can pass main chromosome genes to a recipient cell
Cirpofloxacin, erythromycin, and acyclovir are used to treat microbial infections. Cirpofloxacin inhibits DNA gyrase. Erythromycin binds in front of the A site on the 50S subunit of a ribosome. Acyclovir is a guanine analog. What steps in protein synthesis are inhibited by each drug? Which drug is more effective against bacteria? Why? Which drug will have effects on the host's cells? Why? Use the index to identify the disease for which acyclovir is primarily used. Why is it more effective than erythromycin for treating this disease?
ciprofloxacin inhibits transcription > helicase grinds to a halt > can't make mRNA (need to relieve torsional strain resulting from unravelling DNA strands) > no template for protein synthesis erythromycin inhibits translation > EF-tu-tRNA-aa complex can't enter A site of ribosome > initiation/elongation can't occur > mRNA cannot be translated acyclovir inhibits transcription > acyclovir incorporated into mRNA strand > no phosphate group available on acyclovir to perform attack on incoming nucleotide (in other words no elongation for transcription) b) Erythromycin is best against bacteria because it targets bacterial ribosomal subunits (odd numbered) and not eukaryotic ribosomal subunits (even numbered) c) Acyclovir is probably best against viruses to prevent transcription of needed proteins. Some viruses have ssDNA so they don't need to unwind it. Also, other viruses have ssRNA, so they already have the mRNA needed to make proteins. However, vacyclovir isn't useful in all cases. But I would say it is generally the most effective for the most cases. d) Acyclovir because I don't think the Ciprofloxacin drug is able to get into the cell's nucleus, so it won't affect production of mRNA (in eukaryotes, transcription is in nucleus, not cytosol).
Conjugation differs from transformation in two major ways.
conjugation requires direct cell-to-cell contact. The conjugating cells must generally be of opposite mating type; donor cells must carry the plasmid, and recipient cells usually do not.
New diseases are the results of genetic changes in some existing organism;
for example, E. coli O157:H7 acquired the genes for Shiga toxin from Shigella.
How does mRNA production in eukaryotes differ from the process in prokaryotes
have variations in the number of chromosomes between species genes contain introns E
Operon
is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter.
DNA
is a macromolecule composed of repeating units called nucleotides. Recall that each nucleotide consists of a nucleobase (adenine, thymine, cytosine, or guanine), deoxyribose (a pentose sugar), and a phosphate group
Cyclic AMP
is an example of an alarmone, a chemical alarm signal that promotes a cell's response to environmental or nutritional stress. (In this case, the stress is the lack of glucose.)
The chemical 5-bromouracil is a mutagen because it
is similar in structure but not base-pairing ability to thymine
genetics,
is the science of heredity; it includes the study of what genes are, how they carry information, how they are replicated and passed to subsequent generations of cells or passed between organisms, and how the expression of their information within an organism determines the particular characteristics of that organism.
Transcription
is the synthesis of a complementary strand of RNA from a DNA template.
Using the genetic code in your textbook, determine the polypeptide encoded by the RNA sequence AUGUUUCUUUAA.
met-phe-leu
genotype
of an organism is its genetic makeup, the information that codes for all the particular characteristics of the organism. Represents potential properties, but not the properties themselves. Collection of gene
phenotype
refers to actual, expressed properties, such as the organism's ability to perform a particular chemical reaction. Phenotype, then, is the manifestation of genotype. Collection of protein
Two genetic control mechanisms known as repression and induction
regulate the transcription of mRNA and consequently the synthesis of enzymes from them. These mechanisms control the formation and amounts of enzymes in the cell, not the activities of the enzymes.
A frameshift mutation in a gene encoding a protein usually
results in the production of a nonfunctional peptide........in which one or a few nucleotide pairs are deleted or inserted in the DNA
Which of the following processes is involved in the production of diphtheria toxin by C. diphtheria or erythrogenic toxin by Streptococcus pyogenes?
specialized transduction
When the antibiotic chloramphenicol binds to the 50S portion of the ribosome, the effect is to
stop the ribosome from moving along the mRNA strand
Plasmid
that plasmids are self-replicating, gene-containing circular pieces of DNA about 1-5% the size of the bacterial chromosome
In the lac operon of E. coli,
the repressor protein binds to the operator in the absence of lactose
For the amino acid aspartic acid (asp)
the sequence of the DNA template would be CTG
genetic code
the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein
The Ames test is used to
to determine if a chemical is mutagenic and possibly carcinogenic
Why mutagens are used experimentally
to enhance the production of mutant cells for research on the genetic properties of microorganisms and for commercial purposes.
step in translation?
transport of amino acids by tRNA's pairing of codons with anticodons initiation at the AUG start codon peptide bond formation
