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67 Cards in this Set
- Front
- Back
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What are the 3 mechanisms to regulate gene expression?
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Repression
Induction Attenuation |
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Why does the cell want to regulate its gene expression?
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because gene expression is an energy costly process.
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What are constitutive enzymes?
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Enzymes that are present at all times in a cell.
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What is repression?
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Regulatory mechanism which inhibits gene expression and decreases the synthesis of enzymes.
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What are the regulatory proteins which mediate repression called and what do they do?
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Repressors: block the ability of RNA polymerase to initiate transcription.
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What is induction?
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Process that turns on the transcription of a gene or genes.
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What is an inducer?
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A substance that acts to induce transcription (induction).
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What are inducible enzymes?
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Enzymes that are synthesized in the presence of inducers.
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Explain everything about the operon model.
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A. Explain everything about the operon model.
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What is an operon?
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Genes clustered together on the same chromosome
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How ware the genes arranged in an operon?
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Regulatory Gene
Promoter Operator Structural Genes The genes contained in the operon are either expressed together or not at all. |
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What is the promoter and where is it located?
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Where RNA polymerase binds to the DNA, located after the regulatory gene and before the operator.
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How many promoters are there in one operon?
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One
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What is an operator?
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Usually adjacent to the promoter; binding site for the repressor; repressor protein binds to the Operator sequence on DNA, and blocks progression of RNA polymerase.
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What is a regulator gene? Where is it found?
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Encodes the repressor protein. Before the promoter.
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Be able to draw a typical operon, the lac operon, and the trp operon.
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A. Be able to draw a typical operon, the lac operon, and the trp operon.
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What is the lac operon?
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Lactose operon: responsible for lactose metabolism in E.coli .
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What are the structural genes in the lac operon?
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Lac Z - B-galactosidase: hydrolyzes lactose to glucose & galactose
Lac Y - lactose permease: transports lactose into the cell Lac A - transacetylase: |
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Be able to explain what happens to the expression of the structural genes in E. coli under different environmental conditions. (+ glucose, - lactose; + glucose, + lactose; -glucose, + lactose).
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A. Be able to explain what happens to the expression of the structural genes in E. coli under different environmental conditions. (+ glucose, - lactose; + glucose, + lactose; -glucose, + lactose).
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What is CAP?
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Catabolic activator protein.
When glucose is no longer available, cAMP accumulates in the cell. The cAMP binds to the allosteric site of CAP. CAP then binds to the lac promoter, which initiates transcription by making it easier for RNA polymerase to bind to the promoter. |
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What is allolactose?
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When cells are grown in the presence of lactose, however, a lactose metabolite called allolactose, which is a combination of glucose and galactose, binds to the repressor, causing a change in its shape. Thus altered, the repressor is unable to bind to the operator, allowing RNAP to transcribe the lac genes and thereby leading to high levels of the encoded proteins.
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Why is the lac operon an example of an inducible operon?
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Because it can be turned on or induced when needed. In this case when lactose is present it is induced. Off by default.
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What is the inducer in the lac operon?
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The presence of allactose.
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What is catabolite repression or the glucose effect?
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the inhibition of the metabolism of alternative Carbon sources by glucose. When glucose is available, the level of cAMP in the cell is low, and consequently CAP is not bound.
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Why is the trp operon an example of a repressible operon?
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Because it is on by default and repressible or able to be turned off.
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What is the repressor in trp and when does it become active? What happens when it is active?
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Tryptophan repressor: becomes active when it binds with it's corepressor Tryptophan. The activated repressor binds with the operator, preventing transcription from the operon. Transcription of Tryptophan stops.
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Where does the repressor bind and when is it active?
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It binds to the operator. Only active when repressor is activated by corepressor. In this example, when theres too much Tryptophan.
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How many structural genes are present in trp opteron?
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5 Genes
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What is attenuation?
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a control mechanism that allows mRNA synthesis to begin but then prematurely terminates it.
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Give an example of attenuation?
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When E. coli grows in a medium with no amino acids, the cell will contain the enzymes necessary for the synthesis of all 20 amino acids.
- If the amino acid tryptophan is added to the medium, it will result in a decrease in the synthesis of enzymes needed to make that tryptophan. - This response conserves resources because the enzymes for the tryptophan synthesis are not needed when tryptophan is available to the cell. |
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What is mutation?
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a change in the base sequence of DNA
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What are the 2 major categories of mutation?
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Spontaneous mutation: arises naturally within the cell and are rare, random events. Are not caused by known mutagens. Ex. Error in DNA replication or repari; base substitution or point mutation, frameshift (deletion or addition)
Induced mutation: arises through treatment with mutagens (agents/chemicals known to increase the rate of mutations). Ex. high-energy radiation; specific chemicals |
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What is base substitution or point mutation?
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A single base at one point in the DNA is replaced with a different one; can occur during DNA replication
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What is missense mutation?
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change in base pair results in chane in Amino Acid. AAA (Lys) to AGA (Arg)
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What is nonsense mutation?
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base change results in a stop codon in the middle of an mRNA molecule. Will result in a truncated Amino acid chain.
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What is silent mutation?
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change in base pair does not change amino acid encoded (due to degeneracy) AGG (Arg) to CGG (Arg)
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What is a frameshift mutation?
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One or a few mucleotides are deleted or inserted in the DNA.
Inserting or deleting one nucleotide in the middle of a gene causes many amino acids downstream from the site to change. Will almost always result in a long stretch of missense and an inactive protein. |
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What are mutagens?
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Agents in the environment such as chemicals or radiation that brings about mutations.
1) Chemical mutagens 2) Radiation |
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What does nitrous acid do to DNA and what type of mutagen is it?
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converts Adenine to a form which no longer pairs with Thymine but instead pairs with Cytosine.
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What are base analogues? Give 2 Examples and tell what they do to DNA.
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molecules are structurally similar to the normal nitrogenous bases, but they have slightly altered base-pairing properties.
Ex.: 2-aminopurine replaced Adenine and can pair with Citosine. Ex: 5-bromouracil replaces Thymine and can pair with Guanine. Some antiviral and anti tumor drugs are base analogues. |
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What are the forms of ionizing radiation?
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X-Rays, Gamma Rays.
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What does ionizing radiation cause?
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Causes the electrons to pop out of their usual shells. These electrons then bombard other molecules and causes damage, generating ions and free radicals that are very reactive.
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What are examples of ionizing radiation?
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Base substitutions
Can break covalent bonds in the sugar-phosphate backbone of DNA and thus cause physical breaks in chromosomes. |
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UV light is an example of what type of radiation?
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Nonionizing radiation
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What does ultraviolet light do to the DNA?
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UV light forms harmful covalent bonds among the bases.
Adjecent pyrimidines in a DNA strand can crosslink to form pyrimidine dimers (T-T, T-C, C-C) In the presence of these pyrimidine dimers, the cell cannot properly transcribe or replicate. |
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How do bacteria repair UV radiation damage?
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Bacteria and other organisms can repair radiation damage with enzymes.
1) Endonuclease cuts out the region containing the pyrimidine dimer. 2) DNA polymerase synthesizes new DNA to replace the thymine dimer. 3) DNA ligase seals the new strand to the old strand. |
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What is the mutation rate and how do you calculate it?
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the probability that a gene will mutate when a cell divides.
Ex. If there is a 1 chance in 10,000 that a gene will mutate when the cell divides, the mutation rate is 1/10,000. |
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How do you identify mutants by positive or direct selection?
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involves the detection of mutant cells by rejection of the unmutated parent cells.
Ex. Want to find mutant bacteria that are resistant to ampicillin (Amp) Slide 30. Lecture 07. |
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Be able to design an expirement to detect a mutant using Positive (direct) Selection.
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A. Be able to design an expirement to detect a mutant using Positive (direct) Selection.
Slide 30 |
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Why is it easy to detect mutations in bacteria?
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because bacteria multiplies so quickly that very rare mutations will be easier to find.
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Explain how to identify mutants using negative or indirect selection? Be able to design an experiment to detect a mutant using this method. Be able to distinguish this method from positive selection.
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A. Explain how to identify mutants using negative or indirect selection? Be able to design an experiment to detect a mutant using this method. Be able to distinguish this method from positive selection.
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What is replica-plating?
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is a technique in which one or more secondary Petri plates containing different solid (agar-based) selective growth media (lacking nutrients or containing chemical growth inhibitors such as antibiotics) are inoculated with the same colonies of microorganisms from a primary plate (or master dish), reproducing the original spatial pattern of colonies. The technique involves pressing a velvet-covered disk, nitrocellulose membrane, or filter paper to a primary plate, and then imprinting secondary plates with cells in colonies removed from the original plate by the material.
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What is the master plate?
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an agar plate containing a rich, nonselective medium on which all cells will grow.
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What is minimal medium/media?
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contains the basic elements necessary for life on agar plate, with glucose as a carbon and energy source.
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What is auxotropAh?
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Any mutant microorganism possessing a nutritional requirements not possessed by the parent.
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Can a histidine auxotroph produce all the amino acids? Can it produce histidine?
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???
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What is a carcinogen?
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a substance that causes cancer in animals, including humans
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Explain how the Ames test identifies possible carcinogens.
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See slide 35
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What are reversions or back-mutations?
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based on the observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effects of the original mutation.
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What is genetic recombination?
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The exchange of genes between two DNA molecules to form new combinations of genes on a chromosome.
Contributes to a population's genetic diversity. |
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What does genetic recombination contribute to?
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to a population's genetic diversity
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When does genetic recombination occur in eukaryotes?
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Sexual reproduction.
Crossing over of homologuous pairs of chromosomes during prophase I of meiosis. (process of which sperm and egg are produced) |
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What percentage of the bacterial population does genetic recombination occurs?
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1% or less
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What is a recombinant?
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the recipient cell that incorporates the donor DNA into it's own DNA.
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What is a donor cell?
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Donor cell gives a portion of its total DNA to a recipient cell.
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What is horizontal gene transfer?
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passing genes latrally to other microbes that may not be its direct offspring.
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What are the different types of genetic transfers in prokaryotes?
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Transformation
Genetic Recombination Conjugation Transduction |
