Microbial Genetics (ch 9)

Transposons

DNA segment with an insertion sequence at each end, enabling it to migrate to another plasmid, to the bacterial chromosome, or to a bacteriophage

Operon

a genetic operational unit that regulates metabolism by controlling mRNA production; in sequence the unit consists of a regulatory gene, inducer or repressor control sites, and structural genes

Back-mutation

a mutation which contracts an earlier mutation, resulting in the restoration of the original DNA sequence

Mutations

a permanent inheritable alteration in the DNA sequence or content of a cell

Nitrogen base

a ringed compound of which pyrimidines and purines are types

Gene

a site on a chromosome that provides information for certain cell function; a specific segment of DNA that contains the necessary code to make a protein or RNA molecule

Exons

a stretch of eukaryotic DNA coding for a corresponding portion of mRNA that is translated into peptides; during transcription are separated from introns and spliced together into continuous mRNA transcript

tRNA

a transcript of DNA that specializes in converting RNA language into protein language

Induced

any alteration in DNA that occurs as a consequence of exposure to chemical or physical mutagens

Double helix

cellular DNA is in the form of double-stranded DNA twisted around each other

Point mutations

change that involves the loss, substitution, or addition of one of a few nucleotides

RNA genes

code for ribosomal and transfer RNA molecules

Structural Genes

code for the proteins of the cell

Regulatory genes

control the expression of structural and RNA genes

Chromosome

discrete cellular structure composed of neatly packaged DNA

RNA polymerase

enzyme that translates the code of DNA to RNA

Phenotype

expression of the genotype, which creates traits or certain structures and metabolic functions

Semiconservative

in DNA replication, the synthesis of paired daughter strands, each retaining a parent strand template

Replication

in DNA synthesis, the semiconservative mechanisms that ensure precise duplication of the parent DNA strands

Conjugation

in bacteria, the contact between donor and recipient cells associated with the transfer of genetic material such as plasmids; can involve special(sex) pili; also a form of sexual recombination in ciliated protozoans

Transformation

in microbial genetics, the transfer of genetic material contained in "naked" DNA fragments from a donor cell to a competent recipient cell

Transcription

mRNA synthesis; the process by which a strand of RNA is produced against a DNA template

Ames test

method of detecting mutagenic and potentially carcinogenic agents based upon the genetic alteration of nutritionally defective bacteria

Spontaneous

mutation in DNA caused by random mistakes in replication and not known to be influenced by any mutagenic agent; these mutations give rise to an organism's natural, or background, rate of mutation

Missense mutation

mutation in which a change in the DNA sequence results in a different amino acid being incorporated into a protein, with varying results

Nonsense mutation

mutation that changes an amino acid-producing codon into a stop codon, leading to premature termination of a protein

Silent mutation

mutation that, because of the degeneracy of the genetic code, results in a nucleotide change in both DNA and mRNA but not the resultant amino acid and thus, not the protein

Translation

protein synthesis; the process of decoding the messengerRNA code into a polypeptide

mRNA

single-stranded transcript that is a copy of the DNA template that corresponds to a gene

Codons

specific sequence of three nucleotides in mRNA (or sense strand of DNA) that constitutes the genetic code for a particular amino acid

Antiparallel

strands run opposite direction; one 5'-3' other 3'-5'

Genotype

sum of all three types of genes and constitute an organism's distinctive genetic make-up

Nucleotides

the basic structural unit of DNA and RNA; each nucleotide consists of a phosphate, a sugar, and nitrogenous base such as adenine, guanine, cytosine, thymine or uracil

Introns

the segments on split genes of eukaryotes that do not code for polypeptide; they can have regulatory functions

Anticodons

the trinucleotide sequence of transfer RNA that is complementary to the trinucleotide sequence of messenger RNA (the codon)

Gene expression

transcribed into mRNA and then translated into protein

Transduction

transfer of genetic material from one bacterium to another by a bacteriophage vector

Hydrogen Bonding

two strands adhere to one another by hydrogen bonds that connect base-base