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227 Cards in this Set

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  • Back
Describe components of DNA & explain its functional relationship to RNA & protein.
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 & 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, C-G. The information held in the sequence of nucleotides in DNA is the basis for synthesis of RNA and proteins in a cell.
A mutagen that is incorporated into DNA in place of a normal base.
Nucleoside analog
A mutagen 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 causes insertions
frameshift mutagen
a mutagen that causes the formation of pyrimidine dimers
nonionizing radiation
Transfer of DNA from a donor to a recipient cell by a bacteriophage
transduction
Transfer of DNA from a donor to a recipient as naked DNA in solution
transformation
Feedback inhibition differs from repression because feedback inhibition
stops the action of preexisting enzymes
Bacteria can acquire antibiotic resistance by all of the following except
snRNP's
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 B-galactosidase. Which flask(s) do you predict will have this enzyme?
C
Plamids differ from transponsons because plasmids
are self-replicated outside the chromosomes
Mechanism by which the presence of glucose inhibits the lac operon
catabolite repression
The mechanism by which lactose controls the lac operon
induction
Two daughter cells are most likely to inherit which one of the following from the parent cell
a change in a nucleotide in DNA
Which of the following is not a method of horizontal gene transfer
binary fission
Genetics
the study of what genes are, how they carry information, how their information is expressed, and how they are replicated and passed to subsequent generations or other organisms
DNA in cells exists as double-stranded helix; held together by
hydrogen bods between specific nitrogenous base pairs: AT & CG
A Gene
is a segment of DNA, a sequence of nucleotides, that codes for a functional product, usually a protein
The DNA in a cell is duplicated before
the cell divides, so each daughter cell receives the same genetic information
Genotype
is the genetic composition of an organism, its entire complement of DNA
Phenotype
is the expression of the genes; the proteins of the cell and the properties they confer on the organism
The DNA in a chromosome exists as
one long double helix associated with various proteins that regulate genetic activity
Bacterial DNA is
circular
the chromosome of E. coli, for example, contains about 4 million base pairs and is approximately 1000 timex longer than the cell
Genomics
is the molecular characterization of genomes
Information contained in the DNA is transcribed into
RNA and translated into proteins
During DNA replication
the two strands of the double helix separate at the replication fork, and each strand is used as a template by DNA ploymerases to synthesize two new strands of DNA according to the rules of nitrogenous base pairing
The result of DNA replication is two new strands of DNA, each having
a base sequence complementary to one of the original strands.
Because each double-stranded DNA molecule contains
one original and one new strand, the replication process is called semiconservative.
DNA is synthesized in one direction designated 5'--3'. At the replication fork,
the leading strand is synthesized continuously and the lagging strand discontinuously
DNA ploymerase proofreads new molecules of DNA and
removes mismatched bases before continuing DNA synthesis
Each daughter bacterium receives a chromosome that is
virtually identical to the parent's
During transcription, the enzyme RNA polymerase synthesizes
a strand of RNA from one strand of double-stranded DNA, which serves as a template
RNA is synthesized from
nucleotides containing the bases A, C, G, and U, which pair with the bases of the DNA strand being transcribed
RNA polymerase binds the promoter; transcription begins at AUG; the region of DNA that is end point of transcription is the
terminator; RNA is synthesized in the 5'--3' direction
Translation
is the process in which the information in the nucleotide base sequence of mRNA is used to dictate the amino acid sequence of a protein
the mRNA associates with ribosomes, which consists of
rRNA and protein
Three-base segments of mRNA that specify amino acids are called
codons
the genetic code refers to
the relationship among the nucleotide base sequence of DNA, the corresponding codons of mRNA, and the amino acids for which the codons code.
the gentic code is
degenerate; that is, most amino acids are coded for by more than one codon.
of the 64 codons, 61 are sense condons (which code for amino acids), and
3 are nonsense codons (which do not code for amino acids and are stop signals for translation).
the start codon
AUG, codes for methionine
specific amino acids are attached to
molecules of tRNA. Another portion of the tRNA has a base triplet called an anticodon
the base pairing of codon and anticodon at the ribosome results in
specific amino acids being brought to the site of protein synthesis
the ribosome moves along the mRNA strand, as amino acids are joined to form
a growing polypeptide; mRNA is read in the 5'--3' direction
Translation ends when
the ribosome reaches a stop codon on the mRNA.
Regulating protein synthesis at the gene level is energy-efficient because
proteins are synthesized only as they are needed.
Constitutive enzymes
produce products at a fixed rate. Examples are genes for the enzymes in glycolysis.
For these gene regulatory mechanisms, the control is
aimed at mRNA synthesis
Repression
controls the synthesis of one or several (repressible) enzymes
When cells are exposed to a particular end-product,
the synthesis of enzymes related to that product decreases.
In the presence of certain chemicals (inducers),
cells synthesize more enzymes. This process is called induction.
An example of induction
is the production of B-galactosidase by E. coli in the presence of lactose; lactose can then be metabolized.
The formation of enzymes is determined by
structural genes.
In bacteria, a group of coordinately regulate structural genes with related metabolic functions, plus
the promoter and operator sites that control their transcription, are called an operon.
In the operon model for an inducible system, a regulatory gene codes for
the repressor protein.
When the inducer is absent, the repressor binds to the
operator, and no mRNA is synthesized.
When the inducer is present, it bind to the
repressor so that it cannot bind to the operator; thus, mRNA is made, and enzyme synthesis is induced.
In repressible systems, the repressor requires
a corepressor in order to bind to the operator site; thus, the corepressor controls enzyme synthesis.
Transcription of structural genes for catabolic enzymes (such as B-galactosidase) is induced by the absence of
glucose. Cyclic AMP and CRP must bind to a promoter in the presence of an alternative carbohydrate.
The presence of glucose inhibits
the metabolism of alternative carbon sources by catabolite repression.
A mutation
is a change in the nitrogenous base sequence of DNA; that change causes a change in the product coded for by the mutated gene.
Many mutations are
neutral, some are disadvantageous, and others are beneficial.
Types of Mutation:
A base substitution occurs when
one base pair in DNA is replaced with a different base pair.
Alterations in DNA can result in
missense mutations (which cause amino acid substitutions) or nonsense mutations (which create stop codons).
In a frameshift mutation, one or a few base pairs are
deleted or added to DNA.
Mutagens are
agents in the environment that cause permanent changes in DNA.
Spontaneous mutations
occur without the presence of any mutagen.
Chemical mutagens include
base-pair mutagens, nucleoside analogs, and frameshift mutagens.
Ionizing radiation causes
the formation of ions and free radicals that react with DNA; base substitutions or breakage of the sugar phosphate backbone results.
Ultraviolet (UV) radiation
is nonionizing; it causes bonding between adjacent thymines.
Damage to DNA caused by UV radiation can be repaired by
enzymes that cut out and replace the damaged portion of DNA.
Light-repair enzymes repair
thymine dimers in the presence of visible light.
Frequency of Mutation:
Mutation Rate is
the probability that a gene will mutate when a cell divides; the rate is expressed as 10 to a negative power.
Mutations usually occur randomly along a
chromosome.
A low rate of spontaneous mutations is beneficial in
providing the genetic diversity needed for evolution.
Identifying Mutants:
Mutants can be detected by
selecting or testing for an altered phenotype.
Positive selection involves
the selection of mutant cells and rejection of nonmutated cells.
Replica planting
is used for negative selection--to detect, for example, auxotrophs that have nutritional requirements not possessed by the parent (nonmutated) cell.
Identifying Chemical Carcinogens:
The Ames test
is a a relatively inexpensive and rapid test for identifying possible chemical carcinogens
The test assumes
that a mutant cell can revert to a normal cell in the presence of a mutagen and that may mutagens are carcinogens.
Genetic Transfer & Recombination:
Genetic Recombination
the rearrangement of genes from separate groups of genes, usually involves DNA from different organisms; it contributes to genetic diversity.
In crossing over, genes from two chromosomes are
recombined into one chromosome containing some genes from each original chromosome.
Vertical gene transfer
occurs during reproduction when genes are passed from an organism in its offspring.
Horizontal gene transfer in bacteria
involves a portion of the cell's DNA being transferred from donor to recipient.
When some of the donor's DNA has been integrated into the recipient's DNA,
the resultant cell is call a recombinant.
Transformation in Bacteria:
During this process, genes are transferred from
one bacterium to another as "naked" DNA in solution.
This process occurs naturally among
a few genera of bacteria.
Conjugation in Bacteria:
This process requires
contact between living cells.
One type of genetic donor cell is an F+;
recipient cells are F-. F cells contain plasmids called F factors; these are transferred to the F- cells during conjugation.
When the plasmid becomes incorporated into the chromosome, the cell is called
an Hfr (high frequency of recombination) cell.
During conjugation,
an Hfr cell can transfer chromosomal DNA to an F- cell. Usually, the Hfr chromosome breaks before it is fully transferred.
Transduction in Bacteria:
In this process, DNA is passed
from one bacterium to another in a bacteriophage and is then incorporated into the recipient's DNA.
In generalized transduction, any bacterial genes can be
transferred.
Plasmids & Transposons:

Plasmids
are self-replicating circular molecules of DNA carrying genes that are not usually essential for the cell's survival.
There are several types of plasmids, including
conjugative plasmids, dissimilation plasmids, plasmids carry genes for toxins or bacteriocins, and resistance factors.
Transposons
are small segments of DNA that can move from one region to another region of the same chromosome or to a different chromosome or a plasmid.
Transposons are found
in chromosomes, in plasmids, and in the genetic material of viruses. They vary from simple (insertion sequences) to complex.
Complex transposons can carry
any type of gene, including antibiotic-resistance genes and are thus a natural mechanism for moving genes from one chromosome to another
Genes & Evolution:
Diversity is the
precondition for evolution.
Genetic mutation and recombination provide
a diversity of organisms, and the process of natural selection allows the growth of those best adapted to a given environment.
What must occur for an organism to pass its genetic information on to its offspring?
The parent must copy its own DNA and provide a copy to its offspring.
The process of copying DNA prior to cell replication is know as
DNA replication
What is meant by semiconservative replication?
the new copies of DNA contain one original strand of DNA and one new strand of DNA
What serves as the template fro DNA replication
each of the original DNA strands
What is the role of DNA helicase in DNA replication?
DNA helicase uses the energy from ATP to break the hydrogen bonds between two DNA strands, thereby "unzipping" the molecule
The replication fork
is the point where DNA helicase is "unzipping" the double-stranded DNA molecule.
What is the function of stabilizing proteins?
The hold the separated strands apart and prevent their degredation.
The replication fork moves
ahead of the newly synthesized DNA
Which enzyme can synthesize new strands of DNA?
DNA polymerase
Why is primase essential for DNA replication?
It provides a 3' end of the newly synthesized strand, allowing DNA polyerase to begin copying DNA
DNA synthesis occurs in which direction?
From 5' to 3' on both the leading and lagging strands
How does the DNA polymerase know which nucleotide triphosphate to add to the growing strand?
It hydrogen-bonds the nucleotide to the parental strand, pairing adenines to thymines and guanines to cytosines
What might happen if the cell does not have RNAse?
The newly made chromosome would consist of DNA and RNA molecules
Which of the following statements concerning DNA replication is true?
The leading strand of DNA replication requires only one RNA primer. The lagging strand of DNA replications requires multiple RNA primers
What is the function of the connector proteins?
They link the leading strand DNA polymerase and the lagging strand DNA polymerase together
Which of the following statements regarding Okazaki fragments are true?
They are typically 1000 nucleotides in length. They are found on the lagging strand of DNA replication.
Place the following events of lagging strand DNA synthesis in order
Primase adds an RNA primer.
DNA polymerase synthesizes new DNA strand in the 5' - 3' direction.
RNAse removes the RNA primer.
Okazaki fragments are joined together.
Which mutation is the least likely to be harmful to a cell?
silent mutation
A mutation that results in the presence of a stop codon in the middle of the genetic code is a
nonsense mutation
What type of mutation can change all subsequent amino acids following it?
frameshift mutation
A chemical that can increase the rate of mutations is called a
mutagen
Base pair substitutions can result in what type of mutation?
silent, nonsense, and missense
How frequently does an error occur in DNA replication in the absence of a mutagen?
one error for every one billion nucleotides copied
What is a potential source of mutations from ionizing radiation?
Ions and free radicals resulting from ionizing radiation can break chromosomes.
Ethidium bromide can result in
frameshift mutations via insertion or deletion of nucleotides
x-rays would be considered which type of mutagen
ionizing radiation
which of the following is an example of a nucleoside analog?
5-bromouracil
Enzymes known a photolyases are involved in which type of repair?
light-repair mechanism
How can a mismatch repair enzyme detect which strand contains the correct DNA sequence?
The original strand will likely have a methyl group attached, while the newly mutated strand will not.
Which of the repair mechanism requires assistance from DNA polymerase to make the correction?
excision-repair mechanism AND mismatch-repair mechanism
Which of the following repair mechanism does not involve the removal of nucleotides
light-repair mechanism
Which of the following repair mechanisms might be involved in repairing a mutation that results from exposure to UV light?
light-repair mechanism AND excision-repair mechanism
which of the following is a product of transcription
all of the above
?
The role of transcription is
to copy the information stored in DNA into RNA
which of the following is used to make ribosomes
rRNA
which of the following is involved in bringing amino acids to the ribosomes
tRNA
which of the following is the copy of DNA sequence used to make protein
mRNA
in general, higher levels of transcription lead to
higher amounts of protein
how does protein-dependent termination differ from protein-independent termination
protein-dependent termination involves the use of a protein to end transcription
translation is
the process of making protein from RNA
which of the following is involved in translation
all of the above
?
ribosomes move along the mRNA in which direction
5' to 3'
how many codons code for the termination of transcription
3
AUG codes for
methionine
CAU codes for
histidine
which of the following codes for leucine
all of the above
according to the chart, how many amino acids are coded for by codons
20
what is the order of ribosomal sites that a charged tRNA molecule passes through
A site, P site, E site
the anticodon sequence is found on the
tRNA
an amino acid is considered charged
when it is bound to its correct tRNA
which of the following is not a part of the initiation complex
mRNA
release factors
bind to the A site AND are coded by stop codons
which of the following are genetic elements found in an operon
all of the above
which of the following statements regarding operons is true
all of the above
according to the animation, where does the activation and repression of an operon occur
at the operator region
what does the inducer bind to in the lac operon system
repressor proteins
which genetic element codes for the repressor protein
the regulatory gene
which of the following statements regarding the lac operon is true?
the repressor proteins bind to the operator, preventing RNA polymerase from transcribing the structural genes
when is the regulatory gene transcribed?
it is always transcribed
whch of the following statements regarding the trp operon is true
the trp operon is always activated unless deactivated by a repressor
what is the role of tryptophan in the trp operon
it activates the repressor proteins
which of the following are genetic elements found in an operon
all of the above
which of the following statements regarding operons is true
all of the above
according to the animation, where does the activation and repression of an operon occur
at the operator region
what does the inducer bind to in the lac operon system
repressor proteins
which genetic element codes for the repressor protein
the regulatory gene
which of the following statements regarding the lac operon is true?
the repressor proteins bind to the operator, preventing RNA polymerase from transcribing the structural genes
when is the regulatory gene transcribed?
it is always transcribed
whch of the following statements regarding the trp operon is true
the trp operon is always activated unless deactivated by a repressor
what is the role of tryptophan in the trp operon
it activates the repressor proteins
why is the transcription of structural genes of the trp operon turned off in the presence of tryptophan
?
what is the target of the activated repressor protein
the operator region of the operon
which of the following statements is false regarding the trp operon
the structural genes of the trp operon are transcribed only in the presence of tryptophan
would be an example of horizontal gene transfer
the transfer of DNA from one bacterium to another
is NOT a type of horizontal gene transfer
transcription
a cell that has incorporated new DNA as part of its own is termed a
recombinant
cells that are naturally able to take up DNA from their environment are said to be
competent
why do S strains escape killing by host phagocytes?
?
what reason most likely explains the recovery of S strain from a mouse injected with heat-killed S strain mixed with living R strain
the R strain picked up the S-strain DNA, enabling it to produce capsules
generalized transduction is initiated by
the lytic cycle of viral replication
transduction is
the transfer of bacterial DNA from one host to another via a bacteriophage
the process of generalized transduction
all of the above
?
fate of a bacterium infected by a generalized transducing bacteriophage
integration of the packaged DNA into the host chromosome
the following happens to initiate specialized phage transduction
prophage integrates into the host genome AND bacteriophage enters lysogeny
the following is packaged by the bacteriophage during
the phage DNA with some of the host DNA
the following terms could describe the newly infected host of a specialized transducing bacteriophage
recipient cell
recombinant cell
the purpose of bacterial conjugation
to transfer DNA between two living cells
why is E. coli considered the model of bacterial conjugation
the process of conjugation is best characterized in E. coli
which statement about conjugation is true
after conjugation, each cell involved has a copy of the shared DNA
what is unique about the DNA transferred between two cells during conjugation
it is transferred as a single strand
conjugation order
recipient cells together;
pulling of the donor;
transfer of the DNA Fusion of the cell membranes
what characteristics do F+ and F- share
they each contain a chromosome
following conjugation between a donor and a recipient, what cell types are present
two F+ cells
the fertility factor is also known as
an F plasmid
what DNA molecule is transferred between cells during conjugation between an F+ and an F- cell
a single-stranded F plasmid
put the following events of conjugation in order
attachment of the sex pilus;
pulling of donor and recipient cells together;
fusion of the cell membranes;
transfer of the F factor
how does an F+ cell become an Hfr cell
by integrating the F plasmid into the chromosome
what typically results from conjugation between an Hfr cell and an F- cell
one Hfr cell and one F- cell
what does Hfr stand for
high frequency of recombination
why are F- cells unable to spread the fertility factor
F- cells rarely receive a complete copy of the fertility factor during conjugation
how long does it take an Hfr strain of E. Coli to transfer its complete chromosome
100 minutes
approximately how long would it take for the serA gene to transfer
62 minutes
if conjugation was allowed to be carried out for 42 minutes, which genes would be transferred to the recipient strain?
trp
which gene would transfer quickest during conjugation for this Hfr strain?
fertility factor
if gen X transferred at 99 minutes, what conclusion could you make about gene X
Gene X is close to the fertility factor on the Hfr chromosome, but it is near the end of the chromosome
transposons are
DNA fragments that can move from one location in the DNA to another
which type of transposon would contain an antibiotic resistance gene
complex transposons
insertion sequences are composed of
a transposase gene flanked by inverted repeats
a region of DNA in which the sequence of nucleotides is identical to an inverted sequence on the complementary strand is known as a(n)
inverted repeat
what is the function of the enzyme transposase
all of the above
?
how does replicative transposition differ from cut-and-paste transposition
replicative transposition results in multiple copies of the transposon in DNA; cut and paste transposition has only one copy
what is unique about complex transposons
they have two simple transposons with another DNA sequence between them
why is complex transposon containing an antibiotic resistance gene more likely to be copied than a simple insertion sequence when the host reproduces?
they confer a survival advantage for the host
PCR
rapidly increases the number of copies of a piece of DNA
what is/are the role of dNTPs in a PCR
both of the above answers apply
which of the following is not a constituent of PCR
dUTP
what is unique about the DNA polymerase in PCR
it can withstand the high temperatures needed for PCR
place the following steps of PCR in order:
separation of strands;
annealing of primers;
synthesis of new DNA
the device used to achieve the varying temperatures required for PCR is called a(n)
thermocycler
why is a temperature of 94 degrees C required during PCR
it allows for the strands of the target DNA to separate
which of the following statements about PCR is true
the number of DNA double after each cycle
event order PCR
denature at 94 C;
prime at 60 C;
extend at 72 C;
repeat 30+ times
what is the ultimate goal of recombinant DNA technology
to improve the organism
which of the following cuts DNA at specific sequences
restriction enzyme
why must the recipient plasmid be cut with the same restriction enzyme
to allow for a site in the plasmid for the donor DNA to attach
which of the following can result once the recombinant DNA molecule has been made?
all of the above
?