Microbio Ch 14 and 16
Transposons
(jumping genes) short strands of DNA capable of moving from one location to another within a cell's genetic material
characteristics of transcriptional regulatory proteins
- Bind to DNA - Bind to palindromic DNA sequences
Characteristics of regulatory proteins
- Binds to palindromic sequences on DNA - Individual subunits associate to form dimers - Responsible for processes such as induction and repression
Transcription of the trp operon is controlled by
- Premature termination through attenuation - Repressor protein inhibits initiation
DNA-bound repressor proteins inhibit the initiation of transcription by either ___ or ___.
- Preventing the movement of RNA polymerase - Blocking the binding of RNA polymerase
Attenuator terminator loop
- Similar to factor-independent transcription terminators - Formed by the pairing of regions 3 and 4 - Immediately followed by a poly-U region
Attenuator pause loop
- Slows down RNA polymerase - Formed by the pairing of regions 1 and 2
Which two of the following statements about the inhibition of transcription by the lac repressor protein are true? - The lac repressor binds to the O2 and O3 lac operator sites. - The lac repressor binds and inhibits RNA polymerase. - The lac repressor degrades the polycistronic message. - The lac repressor binds to O1 and one additional lac operator site. - The lac repressor bends the DNA in the promoter region.
- The lac repressor binds to O1 and one additional lac operator site. - The lac repressor bends the DNA in the promoter region.
Under normal growth conditions, the rate of naturally-occurring mutant cells is one mutant cell out of approximately ___ cells.
10^7 to 10^11
Forward mutation
A mutation that causes the wild type strain to become a mutant strain.
conditional mutation
A mutation that results in a characteristic phenotype only under certain environmental conditions. Phenotype is only affected at high temperatures
transversion mutation
A point mutation in which a pyrimidine is substitued for a purine, or vice versa.
transition mutation
A point mutation in which a pyrimidine is susbstituted for a pyrimidine, or a purine is substituted for a purine.
Missense mutation
A point mutation that involves a single base substitution and results in a change to the amino acid encoded by that codon
Which three types of mutations are classified as reversion mutations? A second frameshift mutation that restores an original reading frame. A second mutation that restores the original wild-type sequence. A second mutation that creates a different codon that codes for the wild type amino acid. A mutation that causes the wild type strain to become a mutant strain. A second mutation creates a codon that replaces the wild type amino acid with a similar amino acid.
A second mutation that restores the original wild-type sequence. A second mutation that creates a different codon that codes for the wild type amino acid. A second mutation creates a codon that replaces the wild type amino acid with a similar amino acid.
A DNA-binding protein that promotes transcription initiation is termed a(n) ________ protein
Activator
When _______ proteins bind to their transcriptional regulatory sites they facilitate the binding of RNA polymerase.
Activator
A repressor protein synthesized in its inactive form is referred to as a(n) ____.
Aporepressor
Transcription of the trp operon is regulated at the level of initiation by the trp repressor, and at the level of elongation by a process called
Attenuation
In E.coli regulatory pathways, which molecule functions to ensure that glucose is used as the preferred carbon and energy source?
CAP
Base analogues, DNA-modifying agents, and intercalating agents are three types of ________ mutagens
Chemical
Which two of the following are characteristics of the lac repressor protein? Has an arabinose binding site Composed of two identical subunits Composed of four identical subunits Each monomer has a helix-turn-helix domain
Composed of four identical subunits Each monomer has a helix-turn-helix domain
A mutant strain of E. coli that grows normally at 30°C, but dies at 40°C, is a(n)_________ mutant. nonsense prototrophic conditional silent
Conditional
Which three of these statements about nonsense mutations are correct? Effects range from mild to complete loss of normal gene function. They involve a single base substitution that changes a codon for one amino acid to a codon for a different amino acid. They cause the early termination of translation. They are typically not as severe when they occur near the beginning of a gene. By definition, they always produce stop codons.
Effects range from mild to complete loss of normal gene function. They cause the early termination of translation. By definition, they always produce stop codons.
T/F The Ames test can determine whether a particular substance is carcinogenic.
False The Ames test determines mutagenicity. Although many mutagens are carcinogens, carcinogenicity can only be determined by testing in animals.
Riboswitches
Folded RNAs that act as switches that can turn protein synthesis on or off in response to certain environmental conditions based upon the binding of an effector molecule to the mRNA.
characteristics of the attenuator antiterminator loop
Formed by the pairing of regions 2 and 3 Prevents the generation of the terminator loop Located in the leader region Prevents the generation of the pause loop
Silent, missense, nonsense, and frameshift are all common types of ________ mutations.
Forward
Mutations that arise from the insertion or deletion of 1 or 2 base pairs within the coding region of a gene are called _________ mutations
Frameshift
inducible genes
Genes whose expression is turned on by the presence of some substance. Regulate catabolic pathways.
The catabolite activator protein (CAP) functions in a regulatory network that allows E. coli to preferentially use ________, over all other carbon and energy sources.
Glucose
The first processes that regulate gene expression to be understood in detail were
Induction and repression
What conditions must exist to fully induce the lac operon?
Lack of preferred carbon and energy source Lactose present in the medium
Point mutations in a single base that result in a change to the amino acid encoded are called _______ mutations
Missense
missense mutations
Most common type of mutation, a base pair mutation in which the new codon makes sense in that it still codes for an amino acid. - They are a single base substitution that changes a codon for one amino acid into a codon for a different amino acid. - Effects range from no change to complete loss of normal gene function
resistance mutations
Mutant is not affected by a particular pathogen, antibiotic, or chemical
Suppressor mutation
Mutation that hides or suppresses the effect of another mutation at a site that is distinct from the site of the original mutation. ex: A second frameshift mutation that restores an original reading frame.
When transcription initiation is inhibited by a repressor protein binding to DNA, it is termed ___________ transcriptional control
Negative
describe the lac operon in E. coli
Negative transcriptional control of inducible genes (i.e., turned "off" until turned "on")
A missense mutation that has little to no effect on the activity of a gene product is called a(n) ________ mutation
Neutral
Point mutations that create a stop codon within a reading frame are called ______ mutations
Nonsense
The lac operon is considered a negative control system because it is considered to be turned ___ until lactose is present.
OFF
In bacteria, repressor proteins bind to a specific DNA sequence called the ____.
Operator
MutS
Recognizes single base mismatches
Which example of a missense mutation in a protein-encoding gene would most likely be a neutral mutation?
Replacement of a polar amino acid with another polar amino acid at the protein's surface Even though the amino acids are similar, changes inside a protein's interior are more likely to affect functions than changes to the protein's outer surface.
A DNA-binding protein that inhibits transcription initiation by binding to an operator is termed a(n) _______
Repressor
Point mutations that change the nucleotide sequence of a codon but do not change the amino acid encoded by that codon are called _________ mutations
Silent
Which term is used to describe genes that encode the non-regulatory proteins (enzymes) in an operon? Multiple choice question.
Structural genes
T/F Lethal mutants can be recovered only if they are conditional mutants.
T because a microbe cannot be studied unless it is able to grow under certain conditions.
Ames test
Test in which special strains of bacteria are used to evaluate the potential of chemicals to cause cancer.
mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.
Mutation
The general term for heritable changes in DNA sequence
recombinational repair
The repair of damaged DNA by recombination with an undamaged homologous DNA molecule
Why are transversion mutations more rare than transition mutations?
There are steric problems with pairing purines with purines.
prototroph
They are chemoorganotrophs able to grow on a minimal medium containing only salts and a carbon source.
Which two of these statements are correct about frameshift mutations? They are typically not as severe when they occur near the beginning of a gene. They usually result in the synthesis of nonfunctional proteins. They usually yield mutant phenotypes. By definition, they always produce stop codons. They involve a single base substitution that changes a codon for one amino acid into another.
They usually result in the synthesis of nonfunctional proteins. They usually yield mutant phenotypes.
Which two of the following are components or regulatory sequences for the lac operon?
Three structural genes lacI
T/F The ara operon is an example of both a positive and negative control system.
True The AraC protein can act as both a repressor and activator.
T/F A mutation can prevent a gene from being expressed, even if the coding sequence is completely unchanged.
True This would be false if the mutation affects a regulatory gene
The most prevalent form of a gene, and its associated phenotype, is called the _______ type
Wild
A suppressor mutation, which returns a mutant back to its wild-type phenotype, occurs at ____________ the first mutation.
a different site from
mutations in regulatory sequences
a mutation in the lac operator so the lac repressor cannot bind a mutation in a promoter so that RNA polymerase cannot bind
lac operon inducer
allolactose
tautomeric forms
alternate chemical forms of nucleotides that allow pairing with non complementary bases
In the trp operon attenuator, the formation of the __________ loop prevents the formation of both the 1:2 pause and 3:4 terminator loops.
anti terminator
The trpL operon encodes the leader peptide and ___________ sequences
attenuator
The lac repressor protein inhibits transcription by ____.
bending DNA in the promoter region
induced mutations
caused by environmental agents (physical and chemical)
morphological mutation
change in DNA sequence that alters a structural feature of the cell Affects the appearance of colonies.
reverse mutation
changes a mutant phenotype back to the wild-type phenotype
Aporepressors are synthesized in an inactive form and are activated by the binding of small effector molecules called _________
corepressor
excision repair
corrects damage that causes distortions in double helix - nucleotide excision repair - base excision repair
Riboswitches are regulatory mRNAs that can fold into different patterns based upon ____.
direct binding of an effector molecule to mRNA
DNA proofreading occurs
during DNA replication, before the next nucleotide is added
trpL
encodes a short peptide called the leader peptide which functions in attenuation
MutH
endonuclease, nicks DNA near damaged base
Direct DNA repair
enzymatic removal of damage such as thymine dimers and alkylated bases
A suppressor mutation that occurs in a different gene from the first mutation is called a(n) ______ suppressor mutation.
extragenic
point mutation
gene mutation in which a single base pair in DNA has been changed
constitutive genes
housekeeping genes that are expressed continuously by the cell
Positive transcriptional control
indicates that the binding of an activator protein to DNA promotes transcription initiation
The lac operon is expressed at high levels when the sugar ________ is available and a preferred source of carbon and energy is lacking.
lactose
Photoreactivation
light repair Enzyme uses energy from light Breaks covalent bonds of thymine dimer Only found in bacteria Direct dna repair
auxotroph mutation
mutant cannot synthesize an essential molecule such as an amino acid They are unable to grow on medium lacking a particular molecule, where the wild-type strain could grow. They have a conditional phenotype.
The trp operon is best described as an example of the ______.
negative transcriptional control of repressible genes
A tautomeric form is an isomer of a nucleotide in which the _____ is changed.
nitrogenous base
extragenic suppressor mutation types
nonesense suppresor physiological suppressor
catabolite activator protein (CAP)
protein that complexes with cAMP to bind to the promoter sequences of operons that control sugar processing when glucose is not available
global regulatory systems
regulatory systems that affect many genes, operons, and pathways simultaneously
Which two of these missense mutations would be predicted to have the most severe effects on the function of the protein encoded by the mutated gene? replacement of a hydrophobic amino acid with a different hydrophobic amino acid replacement of a nonpolar amino acid with a polar amino acid substitution of an amino acid located at the active site of an enzyme replacement of an amino acid located in a surface loop of an enzyme
replacement of a nonpolar amino acid with a polar amino acid substitution of an amino acid located at the active site of an enzyme
Proteins that inhibit transcription initiation by binding to operator DNA are called ___.
repressor proteins
The bacterium Deinococcus radiodurans is best known for its ability to
resist damage by radiation
Possible causes of spontaneous mutation include Multiple select question.
spontaneous lesions in DNA transposons errors in DNA replication
The attenuator pause loop of the trp operon slows down RNA polymerase by forming what structure in the newly formed mRNA?
stem loop
intragenic suppressor mutation
suppresses the effect of an earlier mutation within the same gene
Spontaneous mutations can occur when a nitrogenous base shifts to a different isomer, also called a(n)
tautomeric form
attenuation of trp operon
termination of transcription occurs with higher levels of Trp-tRNA Termination of transcription elongation before RNA polymerase enters the first structural gene of an operon
trp operon
tryptophan binds to the repressor protein and enables it to repress gene transcription. Repressible operon
Which three of these factors contribute to the extreme radiation resistance of Deinococcus radiodurans? two homologous chromosomes thick cell wall blocks radiation radiation-resistant proteins complex, atypical electron transport chain proteins that quickly repair damage to genome several unique DNA repair mechanisms
two homologous chromosomes radiation-resistant proteins proteins that quickly repair damage to genome