A.P. Bio Chapter 18 Vocabulary

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activator

A protein that binds to DNA and stimulates transcription of a specific gene.

AIDS (acquired immunodeficiency syndrome)

The name of the late stages of HIV infection, defined by a specified reduction of T cells and the appearance of characteristic secondary infections.

bacteriophage

A virus that infects bacteria; also called a phage.

capsid

The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.

conjugation

In prokaryotes, the direct transfer of DNA between two cells that are temporarily joined. In ciliates, a sexual process in which two cells exchange haploid micronuclei.

corepressor

A small molecule that cooperates with a repressor protein to switch an operon off.

cyclic AMP (cAMP)

Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells (for example, in vertebrate endocrine cells). It is also a regulator of some bacterial operons.

episome

A genetic element that can exist either as a plasmid or as part of the bacterial chromosome.

F factor

A fertility factor in bacteria; a DNA segment that confers the ability to form pili for conjugation and associated functions required for the transfer of DNA from donor to recipient. It may exist as a plasmid or be integrated into the bacterial chromosome.

F plasmid

The plasmid form of the F factor.

HIV (human immunodeficiency virus)

The infectious agent that causes AIDS. HIV is a retrovirus.

host range

The limited range of host cells that each type of virus can infect and parasitize.

inducer

A specific small molecule that inactivates the repressor in an operon.

insertion sequence

The simplest kind of transposable element, consisting of inverted repeats of DNA flanking a gene for transposase, the enzyme that catalyzes transposition.

lysogenic cycle

A phage replication cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage and does not kill the host.

lytic cycle

A type of viral (phage) replication cycle resulting in the release of new phages by lysis (and death) of the host cell.

nucleoid

A dense region of DNA in a prokaryotic cell.

operator

In prokaryotic DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.

operon

A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.

plasmid

A small ring of DNA that carries accessory genes separate from those of a bacterial chromosome; also found in some eukaryotes, such as yeast.

prion

An infectious form of protein that may increase in number by converting related proteins to more prions.

prophage

A phage genome that has been inserted into a specific site on the bacterial chromosome.

R plasmid

A bacterial plasmid carrying genes that confer resistance to certain antibiotics.

regulatory gene

A gene that codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes.

repressor

A protein that suppresses the transcription of a gene.

retrovirus

An RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome; an important class of cancer-causing viruses.

reverse transcriptase

An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.

temperate phage

A phage that is capable of reproducing by either the lytic or lysogenic cycle.

transduction

(1) A DNA transfer process in which phages carry bacterial genes from one host cell to another. (2) In cellular communication, the conversion of a signal from outside the cell to a form that can bring about a specific cellular response.

transformation

1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell.

transposable genetic element

A segment of DNA that can move within the genome of a cell by means of a DNA or RNA intermediate; also called a transposable element.

transposon

A transposable element that moves within a genome by means of a DNA intermediate.

vaccine

A harmless variant or derivative of a pathogen that stimulates a host's immune system to mount defenses against the pathogen.

viral envelope

A membrane that cloaks the capsid that in turn encloses a viral genome.

viroid

A plant pathogen composed of molecules of naked circular RNA only several hundred nucleotides long.

virulent phage

A phage that reproduces only by a lytic cycle.

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