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Chpt7-Microbial Genetics-PTC- Professor Nelson


one of two alternate forms of a gene that can have the same locus on homologous chromosomes and are responsible for alternative traits


group of three bases on a tRNA molecule that are complementary to an mRNA codon


strands run in opposite direction in the arrangement of the sugar-phosphate backbones in a DNA double helix.


any substance that causes cancer


in a eukaryotic cell, one of the structures in the nucleus that are made up of DNA and protein; in a prokaryotic cell, the main ring of DNA.


a specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid

dark repair

Mechanism for repair of damaged DNA by several enzymes that do not require light for activation; they excise defective nucleotide sequences and replace them with DNA complementary to the unaltered DNA strand

deaminating agent

point mutation; chemical mutagen/agent that removes an amino group from base of normal DNA


Two adjacent pyrimidines bonded together in a DNA strand, usually as a result of exposure to ultraviolet rays

DNA polymerase

enzyme that moves along behind the replication fork to makes a long strand of DNA; attaches at the replication fork; "proofreads" new DNA strands

DNA replication

process of making a new strand of DNA by using an old strand as a template


sequence of DNA that codes information for protein synthesis in eukaryotic cells

feedback inhibitor

the inhibition of a enzyme in a metabolic pathway by the final product of that pathway

frameshift mutation

a mutation in which a single base is added to or deleted from DNA


functional unit within a chromosome or plasmid sequence of DNA

genetic code

codon to specific amino acid


the genetic makeup of an organism; mutations always change the genotype


the passing (transmission) of traits from parents to offspring

induced mutation

produced by mutagens (chemical agents or radiation); increases mutation rate above spontaneous mutation rate


A mutation involving the addition of one or more nucleotide pairs to a gene.


A noncoding, intervening sequence within a eukaryotic gene.

lagging strand

backward; new strand of DNA formed in short, discontinuous DNA setments during DNA replication

leading strand

new strand of DNA formed as a continuous strand during DNA replication; easier direction for polymerase to add neucleotides

alkylating agent

a chemical mutagen that can add alkyl groups to DNA bases, altering their shapes and causing errors in the base paring

Ames test

test used to determine whether a particular substance is mutagenic, based on its ability to induce jmutatjions in auxotrophic bacteria`


the weakening of the disease-producing ability of an organism


an organism that used carbon dioxide gas to synthesize organic molecules

base analog

a chemical mutagen similar in molecular structure to one of the nitrogenous bases found in DNA that causes point mutation

constitutive enzyme

an enzyme that is synthesized continuously regardless of the nutrients available to the organism

end-product inhibition

feedback inhibition

enzyme repression

mechanism by which the presence of a particular metabolite reppresses the genes coding for enzymes used in its synthesis

fluctuation test

a test used to determine that resistance to chemical substances occurs spontaineously rather than being induced


a substance that binds to and inactivates a repressor protein

inducible enzyme

an enzyme coded for by a gene that is sometimes active and sometimes inactive


an enzyme that joins together DNA segments

light repair

aka photoreactivation; repair of DNA dimers by a light-activated enzyme

messeger RNA (mRNA)

a type of RNA that carries the information from DNA to dictate the arrangement of amino acids in a protein


an agent that increases the rate of mutations


permanant alteration in an organism's DNA

nonsense codon

aka terminator codon; a set of three bases in a gene (or mRNA) that does not code for an amino acid

Okazaki fragment

one of the short, discontinuous DNA segments formed on the lagging strand during DNA replication


swapped for thymine and pairs with adenine in RNA


specific characteristics displayed by organism


aka light repair

point mutation

mutation that affect a single base

polymerase chain reaction

technique that produces a billion or more identical copies of a DNA fragment without needing a celel


long chain of ribosomes attached at different points along an mRNA molecule


a normal, nonmutant organism


light rays, such as X-rays and UV rays, that can act as mutagens

replication fork

points at which two strands of DNA separate to allow replication of DNA

restriction endonuclease

an enzyme that cuts DNA at precise base sequences

reverse transcription

an enzyme found in retroviruss that copies RNA to DNA

ribosomal RNA (rRNA)

site for protein synthesis; combines with specific proteins to form ribosomes;

RNA polymerase

an enzyme that binds to one strand of exposed DNA during transcription and catalyzes the synthesis to RNA from the DNA template

semiconservative replication

process in replication that ends up with a strand of old (parent) DNA and new DNA

sense codon

a set of three DNA bases that code for an amino acid

spontaneous mutation

arise during DNA replication; occur in the absence of any agent

start codon

the first codon in a molecule of mRNA which begins the sequence of amino acids in protein synthesis

stop codon

aka terminator codon; the last codon to be translated in a molecule of mRNA, causing the ribosome to release from the mRNA

structural gene

a gene that carries information for the synthesis of a specific polypeptide


DNA to RNA; newly formed RNA released from DNA

transfer RNA (tRNA)

function is to transfer amino acids from the cytoplasm to the ribosomes for placement in a protein molecule; link between the codons and corresponding amino acids; each has an anticodon


RNA to protein;


The study of of heredity

eukaryotic cell

a cell that has a distinct cell nucleus and other membrane-bound structures

prokaryotic cell

a cell that lacks a cell nucleus; bacteria; contains a single circular chromosome

thymine, cytosine, adenine, guanine

the four neuclotides that make up DNA


where all information is stored; the product of replication

hydrogen bonds

holds together the nucleotide base pairs

steps to transfer DNA to protein

replication (get DNA), transcription (get RNA), translation (get protein)

messenger RNA (mRNA)

carries information from DNA for synthesis of protein; has codons; attaches to ribosomes

frameshift mutation

mutation which can affect more than one base in DNA

chemical mutagens

base analogs, alkylating agents, deaminating agents, acridine derivatives

mustard gas

an alkylating agent

base analog

substitutes "look-alike" molecule for notmal nitrogenous base during DNA replication

deaminating agent

removes an amino acid group from a nitrogenous group; results to a point mutation; ex; nitrous acid that is added to hot dogs

alkylating agent

adds alkyl group which results in incorrect pairing; results to a point mutation; ex: mustard gas

acridine derivative

inserts DNA ladder between backbones to form a new rung; distorts helis; causes framshift mutation;

light repair (photoreactivation)

uses an enzyme that is activated by visivle light and breaks bonds between pyrimidines of a dimer

free radical

highly reactive molecule, atom or ion that in turn attackS other cell molecules, including DNA

dark repair

uses several enzymes that do not require light for activation; excise defective DNA replace it with DNA complementar to the normal strand

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