Micro 201, Exam #2
Do prokaryotes, eukaryotes, or both have 70s ribosomes inside their cells?
- BOTH - 70s ribosomes are typically found in prokaryotes but also eukaryotic mitochondria and chloroplasts, if they have chloroplasts.
Transformation
- Bacterial uptake of small fragment of DNA from the surrounding environment. - Usually nonspecific-- any DNA fragment can be taken up. - Cells that are capable of being transformed are called "competent." - DNA fragment is incorporated into the bacterial chromosome.
What is saving energy?
- Control of enzyme synthesis at the transcription level is particularly beneficial for this. - Transcription and translation are very costly energetically
Meiosis
- Diploid cell undergoes two sequential divisions resulting in 4 cells, each with a single set of chromosomes. - Homologous chromosomes (members of a pair) pair up and crossing-over may occur. - Sexual reproduction and meiosis result in increased genetic recombination. - Crossing over happens in Meiosis 1
Which of the following factors contribute to problems with antibiotic resistant pathogen
- Doctors prescribing antibiotics to treat viral infections. - Use of antibiotics in animal feed. - Overuse of antibiotics in hospitals. - Patients that stop their antibiotic therapy prematurely. *all of the above*
DNA
- Double Stranded - Double Helix - A-T & G-C base pairs - Base pairs are hydrogen bonded
What are chloroplasts?
- Eukaryotic cells could have DNA in their nuclei, mitochondria, and this other organelle. - Not all the genes needed to make chloroplasts are maintained in the chloroplast, many chloroplast genes have moved to the chromosomes in the cell nucleus during the course of evolution.
Enzymes
- Facilitate each step in a metabolic pathway - biological catalyst (speeds up rxn by lowering activation energy) - Physically bind to reactants/substrates for a brief period - Enzyme is released when product is formed - Control metabolic pathways
What is transformation?
- Fredrick Griffith first demonstrated genetic material could be exchanged from dead to living bacteria through this process. -Genetic material can be transferred from dead bacteria to live bacteria, hence the observation that the cells were "transformed."
lac Operon with both glucose and lactose
- Glucose is the preferred sugar source, so cells utilize glucose completely before utilizing lactose from the media. - With glucose levels high, cAMP is low and no CAP/cAMP complex forms. No binding to activator and RNA polymerase is not bound to the activator binding site. - Lactose is blocked from entering the cells, so no allolactose can be made and the regulator binds to the operator, further blocking any potential for lac operon transcription. *same as only glucose* *No transcription of the lac operon!*
lac Operon with only Lactose
- Glucose levels are low so cAMP levels are high, cAMP binds to the activator and the resulting CAP/cAMP complex can now bind the activator site, now bringing RNA polymerase to the promoter. - Since lactose is being utilized, B-galactosidase can cleave lactose into glucose and also makes the inducer allolactose, which binds the regulator and keeps the regulator/allolactose complex from binding to the operator, allowing transcription. AKA- no regulator/allolactose *Transcription of the lac operon*
What is DNA?
- Its bases are A,T,G,C nucleotides - Also notice that DNA is double stranded while RNA is single stranded
CAP Protein
- Needs cAMP (allosteric inducer of CAP) bound to it to be in the active state, otherwise CAP is inactive and doesn't bind the activator binding site. - Levels of cAMP and glucose are opposite (cAMP high when glucose low and vise versa) - Without CAP/cAMP complex bound to activator site, RNA polymerase will not be brought to the promoter.
Genes for antibiotic resistance can be found:
- On the chromosomal DNA of the bacterium. - On transposons - On plasmids *all the above*
Prokaryotes
- Polycistronic mRNA - Transcription and translation coupled which both occur in the cytoplasm - A,U,G,C - mRNA - operons - RNA polymerase - polyribosomes
What is the cytoplasm?
- Prokaryotes and eukaryotes both have polyribosomes that make proteins in this cellular compartment - See the multiple ribosomes on each message = polyribosomes
What is the sequence of amino acids in a protein?
- The codons in mRNA specify this. - Don't forget about start and stop codons as well. The start codon is an amino acid but the stop codons do not code for amino acids, they help stop translation.
What are induced mutations?
Caused by exposure to mutagens such as radiation (X-rays, UV light) or chemical agents that damage DNA
What are spontaneous mutations?
Caused by mistakes in DNA replication.
Penicillin Derivatives
Changes in the penicillin side chain changes the solubility, half life, and oral bioavailability of the antibiotic NOT its mechanism of action
What is Hfr in one cell and F- in the other cell?
Conjugation from an integrated F+ plasmid ultimately leads to two cells with this recombination status.
Types of Horizontal Gene Transfer
Conjugation: transfer of a plasmid from a donor to a recipient bacterium Transducation: transfer of genes from one bacterium to another mediated by bacteriophage Transformation: uptake and incorporation of free DNA into a recipient bacterium
Transctiption
Copies the information in DNA into RNA via RNA polymerase Steps: Initiation- RNA polymerase binds to the promoter and melts a short stretch of DNA Elongation- Sigma factor dissociates from RNA polymerase, leaving the core enzyme to complete transciption Termination- RNA polymerase encounters a terminator it falls off the template and releases the newly synthesized RNA
Which is NOT a mechanism of horizontal gene transfer?
Cross-incorporation
A fungistatic agent would be one that kills fungi
False
An antibiotic with a low therapeutic index would be less toxic to the patient than an antibiotic with a high therapeutic index
False
Broad spectrum antibiotics attack multiple process in a given microbe
False
Point Mutations
Silent- changes 3rd letter "wobble position" Nonsense- changes 1st letter and creates a stop codon Missense- changes 2nd letter
What is feedback inhibition?
The type of enzymatic activity regulation where the end product is an allosteric inhibitor.
What are enzymes?
These molecules catalyze each step in metabolic pathways.
Which is NOT true about the chemical derivatives of penicillin, such as methicillin and ampicillin, which have altered side chains?
They have changed their mechanism of action
What is the Ames test?
This method tests for potential mutagenic chemicals.
What is RNA?
This molecule has a pentose sugar which is ribose.
What is crossing over?
This process during meiosis in sexual reproduction results in genetic recombination.
What is the genetic makeup of an organism?
This statement defines a genotype.
What is a mutant refers to an organism with a mutation and a mutation is a genetic inheritable change to the genetic information of an organism?
This statement describes the difference between a mutant and a mutation.
What is RNA from DNA?
Transcription is the process that produces this type of molecule from this other type of molecule.
What is the cytoplasm?
Translation always occurs in this cellular compartment in eukaryotic cells.
What is inverted repeats at each end of a transposase gene?
Transposons contain this type of sequence at each end of this type of gene.
Acquired resistance is due to mutation or acquisition of new genes.
True
Food poisoning outbreaks in the U.S. are widespread across many industries
True
The Ames test is used to assess whether a given chemical compound acts as a mutagen.
True
What is conjugation?
Type of gene transfer where transfer of F plasmid leads to both cells being F+
What is off? (Lac Operon)
When lactose is absent the operon is in this state of activity.
Antibiotic
a chemical substance from one microorganism that inhibits or kills another microorganism - place selection pressure on bacteria - Antibiotics do not induce mutations, simply select for advantageous mutations spontaneously arising in the population
Polycistronic
ability to make multiple proteins *in prokaryotes*
Insertions
addition of bases shifts the reading frame of the mRNA so the codons are not read correctly
Inversion
adjacent bases switch positions resulting in a change in one or more codons.
The new guidelines developed by the FDA will:
all the above
The repressor protein that plays a critical role in the functioning of the lac operon:
all the above
T/F The "direct selection" method will always produce mutants with a colony size phenotype when plated on media without antibiotic selection.
false
Minimum bactericidal concentration (MBC)
lowest concentration of a drug that will kill 99.9% of the population of a particular bacterium.
Therapeutic Index
lowest dose toxic to the patient divided by the dose used to treat the disease. The higher the therapeutic index, the less toxic the drug.
Selective Toxicity
meaning that they kill microbial cells but not the host's own cells
Which of the following is not a type of gene transfer: Transposition, Transduction, Sensitization, Transformation, Conjugation.
sensitization
This type of point mutation does not change the resulting amino acid:
silent mutation
this transduction mechanism begins as a lysogenic infection...
specialized transduction
Enzymes do this to the rate of chemical reactions?
speed them up
What is an amino acid?
tRNA molecules add this to the growing polypeptide chain during translation.
Ames Test
tests for potential mutagenic chemicals
Minimun Inhibitory Concentration (MIC)
the lowest concentration of a drug that will inhibit the microorganism from growing.
Phenotype
the observable characteristics or traits (physical or physiological) of an organism
Which is an example of intrinsic resistance:
the outer membrane of gram negative bacteria blocking entry of a large antibiotic like Vancomycin
Transposons capable of jumping from one position to another always have:
the transposase gene
Fungal diseases are hard to treat because:
their cells are structurally and functionally very similar to mammalian cells.
"wobble position"
third letter in the genetic code
The genetic element that can move from one place in the bacterial genome to another is called a(n):
transposon
It is MOST likely that a mutation resulting from the deletion of one base pair:
will cause a shift in the reading frame during translation.
A mutation that changes a codon specifying tyrosine into a stop codon:
will create a short or truncated version of the protein.
Substitution
wrong base is inserted resulting in a change in one codon.
What are prokaryotes?
Introns are not found in mRNA messages of this domain of organisms. (prokaryotes or eukaryotes?)
Transposons
"Jumping Gene" - Transposable elements can move from one location in the genome to another. - Contain inverted repeat sequences at the ends of a transposase gene. - Can create genetic recombination. - Can cause mutations in genes where they are inserted.
What are sugar phosphate backbones and nitrogenous bases?
- The structure of DNA, the double-helix, is composed of these. - Adenine pairs with thymine and glycine pairs with cytosine through hydrogen bonding
What is the nucleus?
- Transcription in eukaryotes takes place in this cellular compartment. - Prokaryotes don't have membrane bound organelles so transcription occurs in the cytoplasm
What is a sigma factor?
- Transcription of RNA from a DNA template in prokaryotes requires RNA polymerase and this other protein factor. - Sigma factors are utilized to express classes of genes in response to certain conditions. For example, heat stress induces a sigma factor to help RNA polymerase bind promoters for genes needed to cope with heat stress.
lac Operon only Glucose
- With glucose high, cAMP levels are low, so cAMP is in insufficient amounts to complex with CAP, thus no binding of a CAP/cAMP complex to the activator site and no subsequent RNA polymerase brought to the promoter. - With no lactose, there is no production of allolactose from B-galactosidase activity and no regulator/allolactose complex, so the regulator binds the operator. AKA- only regulator binds *No transcription of the lac operon!*
lac Operon with NO glucose of lactose
- With no glucose, cAMP levels are high so the CAP/cAMP complex forms and binds to the activator, recruiting RNA polymerase - With no lactose, there is no conversion of lactose to allolactose, so the regulator remains tightly bound to the operator, blocking RNA polymerase from transcribing the lac operon. AKA- everything binds BUT allolactose *No transcription of the lac operon!*
RNA polymerase binds to a site on the DNA called:
- a regulator - a histone - an intron - an anticodon *none of the above*
Eukaryotes
- poly a tail - 5' cap - 70s & 80s ribosomes - Monocistronic mRNA - A,T,G,C - Alternative Splicing - tRNA -mRNA - Transcription in nucleus, translation in cytoplasm - introns and extrons - RNA polymerase - nuclear envelope export - polyribosomes
RNA
- ribose sugar - single stranded - A-U and G-C base pairs - can exhibit intra-strand base pairing creating a secondary and tertiary structure
In E. coli, the genes for lactose utilization are found within an inducible operon. This means that: Answer transcription occurs when lactose binds to the RNA polymerase molecule.
- the genes are located on a plasmid. - the genes are transcribed during the process of transduction. - the genes are transcribed at any time the cell is actively growing. *none of the above*
Transduction
2 Types: 1. Generalized- 2. Specialized- starts with lysogenic infection
Conjugation
2 types: 1. Transfer of F plasmid 2. Transfer of chromosomal DNA
What is two separate IS elements often with an antibiotic resistance gene in between? (they also move as one complete unit)
A composite transposon has these features in its sequence.
What is the wobble position?
A mutation to a gene here "can" lead to a silent mutation.
What is generalized transduction?
A phage packaging mistake from a bacterial genome which was cut up by phage encoded enzymes is typical for transduction of this type.
What are insertions?
Addition of bases into the genetic code.
What are inversions?
Adjacent bases switch positions resulting in a potential change in one or more codons.
This test is designed to identify potential mutagenic chemicals
Ames test
What is a mutation?
Any permanent, inheritable change in the genetic information of the cell.
lacZ
B-galactosidase can cleave the disaccharide sugar lactose into glucose and galactose. It also can convert a little bit of lactose into allolactose.
What is extremely short generation time?
Because of this feature of bacterial growth and division, a rare individual mutant bacterium with an adaptive advantage can quickly become the dominant strain within the population.
Regulator Protein
Binds the operator and blocks RNA polymerase (if bound to promoter) from initiating transcription.
Allolactose
Binds the regulator and blocks the regulator/allolactose complex from binding the operator, thereby permitting transcription if RNA polymerase has bound the promoter sequence.
High Arginine Concentration
Binds to the repressor protein, changes its shape, and allows it to bind to the operator. This turns off the genes for arginine synthesis when they are not needed.
Central Dogma of Microbiology
DNA --> (transctiption) --> RNA --> (translation) --> Protein *Protein synthesis takes a lot of energy* *In prokaryotes transcription and translation are coupled* *much simpler in prokaryotes*
What is growing an overnight culture of media in nutrient agar without antibiotics and then plating on antibiotic selection plates and looking for rare colonies?
Direct selection of mutants is carried out by this method.
DNA Replication
Duplicates the DNA molecule so its encoded information can be passed on to the next generation
What is lactose?
E. coli cells growing in media with glucose and lactose will utilize this sugar source last.
Constitutive Gene Expression
Gene is always expressed (mRNA transcription always occurs)
What is high cAMP (inducer) binding the activator (CAP protein), leading to activator/inducer complex binding to the activator binding site and subsequent RNA pol binding to the promoter, leading to transcription of the lac operon?
In catabolite repression of the lac operon, the absence of glucose leads to this.
Vancomycin
Interferes with peptidoglycan by binding to the amino acid side chain of NAM molecules, blocking peptidoglycan synthesis
Beta-lactam Antibiotics
Interferes with peptidoglycan by completely inhibiting enzymes that form the peptide bond and glycan chains
Bacitracin
Interferes with peptidoglycan by interfering with the transport of peptidoglycan precursors across the cytoplasmic membrane
Translation
Interprets the information carried by RNA to synthesize the encoded protein
The test most commonly used to determine antibiotic susceptibility is:
Kirby-Bauer test
What is a repressible operon?
Normally 'on' until a co-repressor binds a repressor is this type of operon.
Low Arginine Concentration
Operon is on and the enzymes for arginine synthesis are produced.
What are eukaryotes?
Organisms in this domain have processed mRNA messages with a 5'-CAP and a Poly-A tail.
In 1910, _________________ discovered a drug to treat syphillus. This drug, called salversan, was the first chemotherapeutic agent used to successfully treat an infectious disease.
Paul Ehrlich
What is transformation?
Picking up DNA from the environment and incorporating it into the genome of a competent cell is indicative of this type of gene transfer.
Resistance (R) Factor
Plasmid carrying one or more genes for antibiotic resistance
What is a nonsense mutation?
Point mutation the results in a stop codon.
Which is Eukaryotic specific, ie not in Prokaryotes
Poly-A-tail
lac Operon
RNA polymerase transcribes lacZ, lacY, lacA when lactose is being utilized by the cell.
Repressible operons are important in regulating prokaryotic _____
RNA transcription
What are auxotrophic mutants?
Replica plating can be used to search for this class of mutants using nutrient agar vs glucose salt agar.
Intrinsic Resistance
Resistance due to an inherent characteristic of the microbe
Acquired Resistance
Resistance due to mutation or acquisition of new genes
Genetic Recombination
The production of offspring that combine the traits of two different individuals.
What is Histidine auxotroph revertants on glucose salt media in high colony numbers compared to control plates?
The Ames test functions by selecting for what?
What is allolactose binds the repressor and changes its conformation, thereby blocking its ability to bind the operator and inhibit transcription?
The lac operon is turned on when this happens to the repressor.
lacY
The lacY gene codes for a permease protein which becomes embedded in the cytoplasmic membrane to enable transport of lactose into the cell.
Mutation
any permanent, inheritable change in the genetic information of the cell
When both glucose and lactose are present in the media, the genes of the lac operon in an E. coli cell:
are not expressed because lactose is blocked from entering cells, thus no allolactose can be made
A broad-spectrum antibiotic will:
be effective against a wide range of microbes
An antibiotic that disrupts the normal flora:
can lead to an overgrowth of antibiotic resistant microbes.
tRNA
carries AA, translation
Spontaneous Mutation
caused by a mistake in the DNA, low frequency of occurring, important source of genetic variation
Induced Mutation
caused by exposure to mutagens such as radiation or chemical agents that damage DNA
Antimicrobial Drug
chemical that inhibits a microbe, includes antibiotics and synthetic drugs
mRNA
codes for proteins
Bacterial cell-to-cell contact is essential for the gene transfer to occur in the process of:
conjugation
Narrow Spectrum
effective against a limited range of microbes *one mechanism of action*
Broad Spectrum
effective against a wide range of microbes *one mechanism of action*
Inducible Gene Expression
gene is only expressed under certain conditions (transcription of mRNA only occurs under these conditions)
Repressible Gene Expression
gene is usually expressed, but transcription is blocked under certain conditions
Genotype
genetic makeup of an organism
The beta-lactam antibiotics such as penicillin:
inhibit cell wall formation in susceptible bacteria
Bacteriostatic Drug
inhibits growth but does not kill bacteria
Which is NOT a common mechanism of gene transfer in bacteria
introns - Conjugation, Transformation, Transduction, Transposons are all forms of gene transfer
Bactericidal Drug
kills bacteria
lacA
lacA encodes the acetylase galactoside Oacetyltransferase, its non-essential for lactose utilization and its function is still be explored today
Deletions
loss of one or two bases will shift the "reading frame" of the mRNA so that codons are not read in the correct register. (frameshift)
What is a deletion?
loss of one or two bases will shift the "reading frame" of the mRNA so that codons are not read in the correct register. (frameshift)
Enzymes do this to the activation energy required for a reaction.
lower it
Introns
non-coding regions *in eukaryotes these must be spliced out before the mature mRNA can function in protein synthesis, a poly-A-tail is added to help this process*
Alternative Splicing
one gene but there are many different protein possibilities that can be made Transcription --> alternative splicing --> translation --> protein
Monocistronic
only one protein can be made *in eukaryotes*
Mutant
organism that beats a mutation and may exhibit an altered phenotype
Wild type
organism that exhibits the normal (non-mutated) phenotype
rRNA
part of ribosome
the observable characteristics or traits (physical and physiological) of an organism is termed:
phenotype