Ch 3

Term Definition
bacteriophage a virus that infects bacteria
nucleotide an organic compound that consists of a sugar, a phosphate, and a nitrogenous base; the basic building block of a nucleic-acid chain
double helix the spiral-staircase structure characteristic of the DNA molecule
base pairing rules the rules stating that DNA cytosine pairs with guanine and adenine pairs with thymine and that in RNA cytosine pairs with a guanine and adenine pairs with uracil
replication process by which DNA is copied
DNA polymerase an enzyme that catalyzes the formation of the DNA molecule
central dogma theory that states that, in cells, information only flows from DNA to RNA to proteins
RNA ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis
transcription the process of forming a nucleic acid by using another molecule as a template
RNA polymerase an enzyme that starts the formation of RNA by using a strand of DNA molecule as a template
messenger RNA form of RNA that carries genetic information from the nucleus to the cytoplasm, where it serves as a template for protein synthesis
ribosomal RNA RNA that is in the ribosome and guides the translation of mRNA into a protein; also used as a molecular clock
transfer RNA form of RNA that brings amino acids to ribosomes during protein synthesis
translation the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains
codon in DNA and mRNA, a three-nucleotide sequence that encodes an amino acid or signifies a start signal or a stop signal
stop codon codon that signals to ribosomes to stop translation
start codon codon that signals to ribosomes to begin translation; codes for the first amino acid in a protein
anticodon a region of tRNA molecule that consists of a sequence of three bases that is complementary to an mRNA codon
promoter a nucleotide sequence on a DNA molecule to which an RNA polymerase molecule binds, which initiates the transcription of a specific gene
operon a unit of adjacent genes that consists of functionally related structural genes and their associated regulatory genes; common in prokaryotes and phages
exon one of several nonadjacent nucleotide sequences that are part of one gene and that are transcribed, joined together, and then translated
intron a nucleotide sequence that is part of a gene and that is transcribed from DNA into mRNA but not translated into amino acids
mutation a change in the structure or amount of the genetic material of an organism
point mutation a mutation in which only one nucleotide or nitrogenous base in a gene is changed
frameshift mutation a mutation, such as the insertion or deletion of a nucleotide in a coding sequence, that results in the misreading of the code during translation because of a change in the reading frame
mutagen agent that can induce or increase the frequency of mutation in organisms

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