Lecture 10

______ repair is activated by extensive DNA damage and uses a polymerase that lacks proofreading ability, ultimately resulting in mutations.

SOS

Considering that mutations are rare events, why are they significant?

They are fundamental forces of evolution because they fuel the variability in populations and thus enable evolutionary change.

A bacterium spontaneously developing resistance to 2 different types of antibacterial medications is ______ it developing resistance to just one of them

BLANK: Much less likely

Organisms most fit to survive in a given environment will predominate because they can reproduce more rapidly than others. This phenomenon is called

natural selection

The process by which organisms best adapted to a given environment will predominate in that environment is called

natural selection

If a base substitution changes an amino acid-encoding codon to a stop codon what would it be called?

nonsense mutation

Which of the following are possible outcomes of a base substitution?

nonsense mutation, missense mutation, synonymous mutation

The native or wild type strain describes the typical phenotype of strains isolated from nature (i.e. carry non-mutated DNA)

True

Mutants that can grow under conditions in which the parent (wild type) cells cannot are easily isolated by Blank 1 selection

Blank 1: direct or positive

A(n) Blank 1 mutation results from an insertion or deletion of nucleotides, leading to a shift of the reading frame from the point of mutation downstream.

Blank 1: frameshift

Ultraviolet rays are chemical mutagens.

False (Reason: Ultraviolet rays are a form of radiation that is commonly used to induce mutations.)

How is mutation different from horizontal gene transfer?

Mutation is a change in nucleotide sequence in a single gene whereas horizontal gene transfer involves the transfer of many genes to a cell.

Errors by DNA polymerase that incorporate the wrong nucleotide into replicating DNA can be repaired quickly by which two mechanisms?

Proofreading by DNA polymerase Mismatch repair

Which of the following types of radiation are mutagenic?

Ultraviolet rays X-rays

Segments of DNA that can move to new positions within the genome of a single cell are called BLANK

Blank 1: transposons

Chemical mutagens that modify ______ increase the odds of incorrect nucleotide incorporation during DNA replication.

nucleobases

Which type of DNA repair is shown in this figure?

nucleotide excision repair

Vertical gene transfer is the transfer of genes from one organism to another in a population, while horizontal gene transfer is the transfer of genes from parent cell to progeny.

False => Vertical transfer is from parent to offspring, while horizontal transfer is from one organism to another in a population.

Can the phenotype change without a change in genotype?

No

This figure illustrates the potential outcomes of base substitution mutations. The column labeled with a zero (far left) indicates the wild type. Match each Arabic numeral to its correct designation.

1=>synonymous substitution 2 => missense mutation 3=> nonsense mutation

The BLANK is the nucleotide sequence in the DNA of a cell or an organism.

Blank: genotype or genome

Explain how intercalating agents cause mutations.

Insertion of these agents distorts the DNA double helix, thereby interfering with DNA replication, transcription, and repair.

Can the genotype change without a change in phenotype?

Yes

The type of DNA damage repair illustrated here is _______.

base excision repair (Reason: This illustrates DNA with oxidation damage that must be removed and replaced. The process is called base excision repair.)

Which of the following are caused by chemical mutagens?

base substitutions frameshift mutations

Spontaneous mutations are important because

they allow populations of bacteria to adapt to a changing environment

The majority of transposons contain _______ terminators.

transcriptional

When treating tuberculosis, two or more antimicrobial medications are often prescribed because

taking only one type of medication greatly increases the mutation rate of the bacteria

Chemicals that cause cancer are known as ______, and most of them are ______.

carcinogens; mutagens

Selecting penicillin-resistant mutants by plating them on a medium containing penicillin is an example of ______ selection.

direct

Two methods used to identify mutants in a culture are ______ and ______ selection.

direct; indirect

Replica plating _______.

employs a medium on which the mutant will not grow but the parental cell type will, and so is useful for identifying auxotrophs

Which of the following terms describes the sequence of nucleotides (genetic makeup) of an organism or a cell?

genotype

Genes into which transposons "jump" are usually ______ by the event.

inactivated

In the Ames test, it is expected that a mutagen would ______ the reversion rate of of a histidine-requiring auxotroph of Salmonella.

increase

Replica plating is used in ______ selection to transfer an identical pattern of bacterial cells to both a nutrient agar and a glucose-salts agar plate.

indirect

Mutations that are caused by external influences such as radiation or chemicals are called ______ mutations.

induced

Chemical mutagens that squeeze between base pairs and induce frameshift mutations are called ______.

intercalating agents

Describe the difference between a prototroph and an auxotroph.

Auxotrophs are organisms that lose the ability to produce specific organic substances needed for their survival, while prototrophs are organisms that are capable of producing all organic substances essential for their growth from inorganic compounds

A(n) Blank 1 mutation occurs if a single base pair is changed during DNA synthesis.

BLANK: point

Blank 1 are DNA segments that increase the rate of mutations by inserting themselves into genes and inactivating them.

Blank 1: Transposons

Blank 1 agents insert themselves between adjacent base pairs in a DNA strand, increasing the rate of frameshift mutations.

Blank 1: Intercalating

Mutagens that modify nucleobases change their Blank 1 Blank 1- Blank 2 properties.

Blank 1: base Blank 2: pairing

Sometimes DNA polymerase adds the wrong nucleotide to the growing chain. If proofreading does not fix the error, then it is usually fixed by a mechanism called Blank 1 repair.

Blank 1: mismatch

Repair of nucleotide incorporation errors during the process of DNA replication is accomplished by Blank 1 by DNA polymerase and by Blank 2 repair.

Blank 1: proofreading Blank 2: mismatch

A(n) BLANK is a change in the nucleotide sequence of DNA that is passed on to daughter cells.

Blank: mutation

Why is replica plating required to isolate an auxotroph from a prototrophic strain, but not the reverse?

Prototrophic strains will grow on the nutrient rich agar and the glucose salt agar (minimal) while the auxotroph will only grow on the nutrient rich agar. You can then identify the auxotroph on the master plate.

Why is proofreading more important for DNA polymerase than RNA polymerase?

RNA polymerase has higher levels of errors in transcription compared with DNA replication. Generally, proofreading prevents or corrects errors in DNA replication, so the absence of proofreading in transcription will lead to more errors that go uncorrected

Chemical mutagens can cause two types of mutations: Blank 1 substitutions and Blank 2 mutations.

Blank 1: base, base pair, or nucleobase Blank 2: frameshift

Mutant cells in bacterial cultures can be isolated by Blank 1 selection and Blank 2 selection methods.

Blank 1: direct Blank 2: indirect

During DNA replication, the template strand can be distinguished from the newly synthesized strand by the presence of Blank 1 groups on certain nucleobases. This is very important for mismatch repair

Blank 1: methyl or CH3

Many DNA polymerases have the ability to detect and repair their own errors in nucleotide incorporation. This ability is called ______

Blank 1: proofreading or editing

Thymine dimers can kill cells if left unrepaired, as they cause kinks in DNA that interfere with the processes of Blank 1 and Blank 2.

Blank 1: replication Blank 2: transcription

Ultraviolet radiation causes covalent bonds to specifically form between adjacent Blank 1 molecules on a DNA molecule.

Blank 1: thymine or pyrimidine

A base substitution in a protein-encoding gene results in one of three possible mutation outcomes: Blank 1 mutation, Blank 2 mutation, or Blank 3 mutation

Blank 1: silent or synonymous Blank 2: missense Blank 3: nonsense

Which type of DNA repair is shown in this illustration?

mismatch repair (has methyl groups)

A base substitution that leads to the creation of a stop codon is called a(n) Blank 1 mutation.

BLANK: nonsense

The consequences of not repairing damaged DNA in cells include ______.

cancer (in animals) cell death

A mutant that requires a growth factor is a(n)

Auxotroph

During repair of oxidized guanine, which enzyme removes the damaged nucleobase from the sugar-phosphate backbone?

DNA glycosylase

______ sometimes incorporates the incorrect nucleotide when generating a new strand of DNA during DNA ______; this leads to a detectable distortion in the DNA helix.

DNA polymerase; replication

In humans, two of the genes associated with the development breast cancer encode enzymes involved in ______.

DNA repair

A point mutation always leads to a shift of the reading frame from the point of mutation downstream.

False (Reason: A frameshift mutation involves a shift of the triplet sequence from the point of mutation downstream. A point mutation is a substitution of bases, not a shift in the reading frame.)

Which of the following mutations frequently results in the production of a shortened and non-functional protein because a different set of codons is translated?

Frameshift

______ is used to fix nucleotide incorporation errors that are missed by the proofreading function of DNA polymerase.

Mismatch repair

What is the difference between a mutagen and a carcinogen?

Mutagen can change the DNA structural form and carcinogens just affect uncontrolled cell divisions making too much of something

Which term refers to an organism that has a mutation?

Mutant

How is a missense mutation different from a nonsense mutation?

Non-sense mutations create a stop codon, which can prevent the protein from being produced entirely, while missense mutations result in the substitution of one amino acid for another

Which process requires visible light to repair DNA damage caused by ultraviolet light?

Photoreactivation

A base substitution that results in a codon that still codes for the wild type amino acid is called a(n) ______ mutation.

Synonymous

______ are segments of DNA that can move from one location to another in a cell's genome.

Transposons

What is a transposon? How does it cause mutations?

Transposons are a group of mobile genetic elements that are defined as a DNA sequence. Transposons can jump into different places of the genome

A point mutation involves any substitution of a single nucleotide. (i.e.A point mutation involves any substitution of a single nucleotide that does not change the DNA reading frame.)

True

Incorporation of an incorrect nucleotide in a molecule of DNA results in a distortion of the DNA helix that can be detected by repair enzymes.

True

How does UV light cause mutations?

Ultraviolet light is absorbed by a double bond in thymine and cytosine bases in DNA. This added energy opens up the bond and allows it to react with a neighboring base. If the neighbor is another thymine or cytosine base, it can form a covalent bond between the two bases

Genetic change in bacteria occurs through which two mechanisms?

mutation and horizontal gene transfer

Which of the following describes an organism's observable characteristics?

phenotype

The repair of thymine dimers by enzymes that break the covalent bonds between the dimers is called ______ repair.

photoreactivation

This figure shows the steps of ______, a process that repairs thymine dimers by breaking the covalent bonds that have formed between adjacent thymines.

photoreactivation

Mutagens that are DNA segments that can insert into genes and thereby inactivate them are called ______.

transposons

The distortion of DNA by thymine dimers directly blocks which of the following cellular processes?

Transcription Replication

Ultraviolet radiation causes a very specific type of DNA damage called ______.

thymine dimers

BLANK is the change of a mutated genetic sequence back to its original, non-mutated form.

BLANK: Reversion

Consider a population of bacteria susceptible to an antimicrobial. If a bacterium acquires a spontaneous mutation that gives resistance to the antimicrobial, this bacterium will ______ if the population is exposed to the antimicrobial

BLANK: grow without competition

A(n) Blank 1 mutation is a base substitution that changes the codon to one that specifies a different amino acid.

BLANK: missense

Base ______ structurally resemble nucleobases and can be mistakenly incorporated into nucleotides and then into DNA.

analogs

A mutant which needs a particular nutrient to grow which the normal strain does not is called a(n)

auxotroph

In replica plating, colonies from the master plate that grow on the nutrient agar plate but not on the glucose-salts plate are ______.

auxotrophs

Mutations that arise naturally during cellular metabolism, and not as a result of exposure to mutation-causing agents, are called BLANK mutations.

spontaneous

Random genetic changes that result from normal cellular processes are

spontaneous mutations

Base ______ mutations occur when an incorrect nucleotide is incorporated in place of another during DNA synthesis.

BLANK: substitution

The most common type of mutation is base BLANK where an incorrect nucleotide is incorporated during DNA replication.

BLANK: substitution

A base substitution that results in a codon that still codes for the wild type amino acid is called a(n) ______ mutation.

BLANK; synonymous

Blank 1 Blank 2 structurally resemble nucleobases and can be mistakenly used when cells make nucleotides, which are then incorporated by DNA polymerase into DNA.

Blank 1: Base or Nucleobase Blank 2: analogs

BLANK mutations are generally the most harmful to cells because they change all of the codons downstream of the mutation.

Blank 1: Frameshift

Blank 1 selection is used to isolate an auxotroph from a prototrophic parent strain, because no selective medium exists to inhibit the parent.

Blank 1: Indirect or Negative

BLANK mutations are genetic changes caused by factors from outside of the cell such as radiation or chemicals.

Blank 1: Induced

Extensively damaged DNA activates the Blank 1 repair mechanism, which cannot always determine the correct nucleotide sequence, thus introducing mutations resulting from the repair process itself.

Blank 1: SOS

Consider a base substitution mutation that occurs in a codon that specifies the amino acid tryptophan. If it leads to a different amino acid, the mutation is called Blank 1 mutation, and if the resultant codon is a stop codon, then the mutation is termed a(n) Blank 2 mutation

Blank 1: missense Blank 2: nonsense

Consider a base substitution mutation that occurs in a codon that specifies the amino acid tryptophan. If it leads to a different amino acid, the mutation is called Blank 1 mutation, and if the resultant codon is a stop codon, then the mutation is termed a(n) Blank 2 mutation.

Blank 1: missense Blank 2: nonsense

A(n) Blank 1 mutation is a base substitution that does not change the encoded amino acid

BLANK: silent or synonymous

What would the consequence be to a cell if it didn't have an SOS system?

It would compromise its ability to repair DNA damage, induce mutagenesis, and respond effectively to stressors such as DNA-damaging agents. This could have significant consequences for the cell's survival, growth, and adaptation.