Genetics
What is the role of DNA helicase in DNA replication?
It uses the energy created by 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?
They hold the separated strands apart and prevent their degredation.
The replication fork moves ___________.
ahead of the newly synthesized DNA.
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 known 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 for DNA replication?
each of the original DNA strands
Which enzyme(s) 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 polymerase 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.
How many RNA primers are required for the leading strand of DNA replication?
How many for the lagging strand of DNA?
One RNA primer
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.
Okazaki fragments are typically ____ nucleotides in length and are found on the ______ strand of DNA replication.
1000 and Lagging
Name the 4 steps of lagging strand DNA replication.
1. Primase adds an RNA primer
2. DNA polymerase synthesizes new DNA strand in the
5' to 3' direction.
3. RNAse removes the RNA Primer.
4. Okazaki fragments are joined together.
Name the three products of transcription
mRNA, rRNA, tRNA
The role of transcription is ___________________.
to copy the information stored in DNA into RNA.
_______ is used to make ribosomes
rRNA
_______ is involved in bringing amino acids to the ribosomes
tRNA
_______ is a copy of a DNA sequence used to make protein
mRNA
In general, higher levels of transcription lead to ______________________.
higher amounts of protein.
Name three functions of RNA polymerase
It binds to the promoter region of the gene prior to starting RNA synthesis, adds nucleotides to the 3' end of the growing RNA molecule, and reads the template strand of DNA.
How does protein-dependent termination differ from protein-independent termination?
Protein-dependent termination involves the use of a protein to end transcription.
Translation
the process of making protein from RNA.
Ribosomes move along the mRNA in which direction?
5' to 3'
Name three things involved in translation
ribosomes, amino acids, and mRNA
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.
mRNA is not a part of the initiation process.
T or F?
True
Release factors _______________________and ________________________.
bind to the A site
are coded by stop codons
Name 3 genetic elements found in an operon
operator region, structural genes, and promoter
Where does the activation and repression of an operon occur?
operator region
Inducible operons are transcribed only ____________________.
when they are activated.
Repressible operons are always transcribed unless
_________________________________.
they are deactivated by a repressor
The structural genes of an operon typically have the same biochemical function in the cell.
T or F?
True
What does the inducer bind to in the lac operon system?
repressor proteins
Which genetic element codes for the repressor protein?
the regulatory gene
___________ _______ bind to the operator, preventing RNA polymerase from transcribing the structural genes.
Repressor proteins
When is the regulatory gene transcribed?
Always
What ceases when lactose is absent from the system.
Induction of the operon
The inducer acts by ________?
turning off the repressor
Allolactose serves as ___________?
an inducer
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?
The structural genes are used to make tryptophan, which would not be needed if tryptophan is available.
What is the target of the activated repressor protein?
the operator region of the operon
The repressor gene is always _____________.
transcribed
Activated repressor proteins bind to the operator region, preventing ______________________________.
RNA polymerase from transcribing the structural genes
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?
fragment mutation
A chemical that can increase the rate of mutations.
mutagen
Base pair substitutions that can result in what 3 types of mutations
silent, nonsense, and missense
How frequently does an error occur in DNA replication in the absence of a mutagen?
one error for every 1,000,000,000 nucleotides copied
What is a potential source of mutations from ionizing radiation?
The resulting Ions and free radicals 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
5-bromouracil is an example of a ___________ _______.
nucleoside analog
Enzymes known as 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.
Name the 2 repair mechanisms that require assistance from DNA polymerase to make the correction?
excision-repair mechanism AND mismatch-repair mechanism
Light repair mechanism does not involve the removal of nucleotides?
T or F
True
Name 2 repair mechanisms that might be involved in repairing a mutation that results from exposure to UV light
light-repair mechanism AND
excision-repair mechanism
The transfer of DNA from one bacterium to another is an example of ______________ _________ _____________.
Horizontal gene transfer
Transcription is NOT a type of horizontal gene transfer.
T or F
True
Name 3 types of horizontal gene transfer.
conjugation, transformation, and transduction
Recombinant
A cell that has incorporated new DNA as part of its own
Cells that are naturally able to take up DNA from their environment
competent
Why do S strains escape killing by host phagocytes?
They are encapsulated.
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.
T or F?
S strains are capable of causing disease in mice.
True
___________ are unable to cause disease in mice.
R strains
R strains do not produce a _________.
capsule
Generalized transduction is initiated by ___________.
the lytic cycle of viral replication
Transduction
the transfer of bacterial DNA from one host to another via a bacteriophage
What would be a fate of a bacterium infected by a generalized transducing bacteriophage?
integration of the packaged DNA into the host chromosome
The process of generalized transduction requires a _______ ______________.
lytic bacteriophage
The process of generalized transduction utilizes any fragment of the bacterial chromosome.
T or F?
True
Generalized transduction is the result of ________________________?
Sloppy packaging of the DNA by bacteriophage
What 2 things initiate specialized phage transduction?
Prophage integrates into the host genome
AND
bacteriophage enters lysogeny
Two terms that could describe the newly infected host of a specialized transducing bacteriophage
recipient cell AND
recombinant cell
What is packaged by the bacteriophage during induction?
the phage DNA with some of the host DNA
What is 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.
T or F?
After conjugation, each cell involved has a copy of the shared DNA.
True
What is unique about the DNA transferred between two cells during conjugation?
It is transferred by a single strand
3 chronological events of conjugation
Pulling of donor and recipient cells together,
Fusion of the cell membranes, Transfer of the DNA
What characteristics do F+ and F- cells share?
each contain a chromosome
Following conjugation between a donor and a recipient, what cell types are present?
two F+ cells
F plasmid
fertility factor
What DNA molecule is transferred between cells during conjugation between an F+ and an F- cell?
a single stranded F plasmid
The 4 chronological events of conjugation
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.
Name 3 characteristics of an F- cell
Cannot synthesize a sex pili
absence of fertility factor
Cannot mate with another F- cell
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 gene 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 transfer.
Transposons
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
inverted repeat
3 functions of the enzyme transposase
cuts the DNA so the transposon can leave its current position, cuts the DNA at the new site for a transposon, and covalently links the transposon to the new DNA site.
How does replicative transposition differ from cut-and-paste transposition?
Replicative transposition results in multiple copies of the transposon in the 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 a 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.