Vocabulary
- 5’ Cap
- The 5’ end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.
- A Site
- One of a ribosome’s three binding sites for tRNA during translation. The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA.)
- Alternative RNA Splicing
- A type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.
- Aminoacyl-tRNA Synthetase
- An enzyme that joins each amino acid to the correct tRNA.
- Anticodon
- A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.
- Base-Bair Substitution
- A type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides.
- Codon
- A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
- Deletion
- (1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.
- Domain
- An independently folding part of a protein.
- E Site
- One of a ribosome’s three binding sites for tRNA during translation. The E site is the place where discharged tRNAs leave the ribosome. (E stands for exit.)
- Exon
- A coding region of a eukaryotic gene. Exons, which are expressed, are separated from each other by introns.
- Frameshift Mutation
- A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the following nucleotides into codons.
- Insertion
- A mutation involving the addition of one or more nucleotide pairs to a gene.
- Intron
- A noncoding, intervening sequence within a eukaryotic gene.
- 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.
- Missense Mutation
- The most common type of mutation, a base-pair substitution in which the new codon makes sense in that it still codes for an amino acid.
- Mutagen
- A chemical or physical agent that interacts with DNA and causes a mutation.
- Mutation
- A rare change in the DNA of a gene, ultimately creating genetic diversity.
- Nonsense Mutation
- A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.
- One Gene–One Polypeptide Hypothesis
- The premise that a gene is a segment of DNA that codes for one polypeptide.
- P Site
- One of a ribosome’s three binding sites for tRNA during translation. The P site holds the tRNA carrying the growing polypeptide chain. (P stands for peptidyl tRNA.)
- Point Mutation
- A change in a gene at a single nucleotide pair.
- Poly-A Tail
- The modified end of the 3’ end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.
- Polyribosome (Polysome)
- An aggregation of several ribosomes attached to one messenger RNA molecule.
- Primary Transcript
- An initial RNA transcript; also called pre-mRNA when transcribed from a protein-coding gene.
- Promoter
- A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA.
- Reading Frame
- The way a cell’s mRNA-translating machinery groups the mRNA nucleotides into codons.
- 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.
- Ribosome
- A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits.
- Ribozyme
- An enzymatic RNA molecule that catalyzes reactions during RNA splicing.
- RNA Polymerase
- An enzyme that links together the growing chain of ribonucleotides during transcription.
- RNA Processing
- Modification of RNA before it leaves the nucleus, a process unique to eukaryotes.
- RNA Splicing
- The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.
- Signal Peptide
- A stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.
- Signal-Recognition Particle (SRP)
- A protein-RNA complex that recognizes a signal peptide as it emerges from the ribosome.
- Spliceosome
- A complex assembly that interacts with the ends of an RNA intron in splicing RNA, releasing the intron and joining the two adjacent exons.
- TATA Box
- A promoter DNA sequence crucial in forming the transcription initiation complex.
- Template Strand
- The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript.
- Terminator
- In prokaryotes, 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.
- Transcription
- The synthesis of RNA on a DNA template.
- Transcription Factor
- A regulatory protein that binds to DNA and stimulates transcription of specific genes.
- Transcription Initiation Complex
- The completed assembly of transcription factors and RNA polymerase bound to the promoter.
- Transcription Unit
- A region of a DNA molecule that is transcribed into an RNA molecule.
- 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.
- Translation
- The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of languagefrom nucleotides to amino acids.
- Triplet Code
- A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.
- Wobble
- A violation of the base-pairing rules in that the third nucleotide (5’ end) of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3’ end) of a codon.
