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(A) A double-ring nitrogenous base found in DNA and RNA


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


A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule


A virus that infects bacteria; also called a phage.


A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code


(C) A single-ring nitrogenous base found in DNA and RNA

DNA ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain

DNA polymerase

An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain

double helix

The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape


A coding region of a eukaryotic gene.


(G) A double-ring nitrogenous base found in DNA and RNA


(human immunodeficiency virus)The infectious agent that causes AIDS


A noncoding, intervening sequence within a eukaryotic gene

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 replication cycle resulting in the release of new phages by death or lysis of the host cell

messenger RNA

(mRNA)A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein

molecular biology

The study of the molecular basis of genes and gene expression


A chemical or physical agent that interacts with DNA and causes a mutation


The creation of mutations


A rare change in the DNA of a gene ultimately creating genetic diversity


The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group


A virus that infects bacteria; also called a bacteriophage


A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA


A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA


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

reading frame

The way a cell's mRNA-translating machinery groups the mRNA nucleotides into codons


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 RNA viruses that uses RNA as a template for DNA synthesis

ribosomal RNA

(rRNA)The most abundant type of RNA, which together with proteins, forms the structure of ribosomes. Ribosomes coordinate the sequential coupling of tRNA molecules to mRNA codons

RNA polymerase

An enzyme that links together the growing chain of ribonucleotides during transcription

RNA splicing

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis

start codon

On mRNA, the specific three-nucleotide sequence (AUG) to which an initiator tRNA molecule binds, starting translation of genetic information

stop codon

In mRNA, one of three triplets (UAG, UAA, UGA) that signal gene translation to stop

sugar-phosphate backbone

The alternating chain of sugar and phosphate to which the DNA and RNA nitrogenous bases are attached


A special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene


(T) A single-ring nitrogenous base found in DNA


The synthesis of RNA on a DNA template

transfer RNA

(tRNA)An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA


The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of "language" from nucleotides to amino acids


An aberration in chromosome structure resulting from an error in meiosis or from mutagens; specifically, attachment of a chromosomal fragment to a nonhomologous chromosome.

triplet code

A set of three-nucleotide-long words that specify the amino acids for polypeptide chains


(U) A single-ring nitrogenous base found in RNA

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