Chapter 15 (Genes and Proteins)

5'-cap

modification added to the 5' end of pre-mRNAs to protect mRNA from degradation and assist translation

anticodon

three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon

central dogma

states that genes specify the sequence of mRNAs, which in turn specify the sequence of proteins

codon

three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation

downstream

nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3' end relative to a site on the mRNA

exon

sequence present in protein-coding mRNA after completion of pre-mRNA splicing

intron

non-protein-coding intervening sequences that are spliced from mRNA during processing

nonsense codon

one of the three mRNA codons that specifies termination of translation

non template strand

strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

modification added to the 3' end of pre-mRNAs to protect mRNA from degradation and assist mRNA export from the nucleus

promoter

DNA sequence to which RNA polymerase and associated factors bind and initiate transcription

reading frame

sequence of triplet codons in mRNA that specify a particular protein; a ribosome shift of one or two nucleotides in either direction completely abolishes synthesis of that protein

RNA editing

direct alteration of one or more nucleotides in an mRNA that has already been synthesized

splicing

process of removing introns and reconnecting exons in a pre-mRNA

start codon

AUG (or rarely, GUG) on an mRNA from which translation begins; always specifies methionine

stop codon

mRNA nucleotides at which translation stops; does not code for an amino acid.

template strand

strand of DNA that specifies the complementary mRNA molecule

upstream

nucleotides preceding the initiation site; in general, sequences toward the 5' end relative to a site on the mRNA