| A | B |
|---|
| reading frame | The way a cell's mRNA translating machinery groups the mRNA nucleotides into codons. |
| RNA ploymerase | A enzyme that links together the growing chain of ribonucleotides during transcription. |
| transcription unit | A region of a DNA molecule that is transcribed into an RNA molecule. |
| Transcription factors | A regulatory protein that binds to DNA and stimulates transcription of specific genes. |
| Transcription initiation complex | The completed assembly of transcription factors and RNA ploymerase bound to the promoter. |
| TATA box | A promoter DNA sequence crucial in forming the transcription initiation complex. |
| 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. |
| 5' cap | A modified form of a guanine nucleotide added on to the 5' end of a pre-mRNA molecule after transcription of the first 20 to 40 nucleotides. |
| 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. |
| RNA splicing | The removal of noncoding portions (introns) of the RNA molecule after initial synthesis. |
| intron | A noncoding, intervening sequence within a eukaryotic gene. |
| exon | A coding region of a eukaryotic gene which is expressed and seperated from one another by introns. |
| 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. |
| domain | An independently folding part of a protein. |
| auxotroph | An organism, such as a strain of bacteria, that has lost the ability to synthesize certain substances required for its growth and metabolism as the result of mutational changes. |
| one gene--one polypeptide | discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses) |
| transcription | synthesis of RNA on a DNA template |
| mRNA | messenger RNA, the key intermediary in gene expression, translating the DNA's genetic code into the amino acids that make up proteins |
| translation | synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of "language" from nucleotides to amino acids |
| RNA processing | modification of RNA before it leaves the nucleus, a process unique to eukaryotes |
| primary transcript | an initial RNA transcript, also called pre-mRNA when transcribed from a protein-coding gene |
| triplet code | A set of three-nucleotide-long words that specify the amino acids for polypeptide chains |
| template strand | DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript |
| codon | three-nucleotides sequence of DNA or mRNA that specifies a particular amino acid or termination signal; basic unit of genetic code |
| Point mutation | A change in a gene at a single nucleotide pair |
| Base-pair substiution | A type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides |
| Missense mutation | The most common type of mutation, a base-pair substitution in which the new codon makes sense in that it stil codes for an amino acid |
| Nonsense mutation | A mutation that chagnes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein |
| Insertion | A mutation involving the addition of one more nucleotide pairs to a gene |
| Deletion | A mutational loss of one or more nucleotide pairs from a gene |
| Frameshift mutation | A mutation occuring 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 |
| Mutagens | A chemical or physical agent that interacts with DNA and causes a mutation |
| Ames test | Test used to assess the mutagenic potential of chemical compounds |
| tRNA | An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing that appropriate codons in the mRNA |
| anticodon | A specialized base triplet at one end a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule |
| Wobble | A violation of the base-pairing rules in that the third nucleotide(5' end) of a tRNA anticodon can form hydrogen with more than one kind of base in the third position(3' end) of a codon |
| Aminoacyl-tRNA | An enzyme that joins each amino acid to the correct tRNA |
| rRNA | Ribosomal RNA. The most abundent type of RNA, which together with proteins forms the structure ribosomes. |
| P site | One of a ribosomes threee binding sites for tRNA during translation. THe P site holds the tRNA carrying the growing polypeptide chain. |
| A site | One of a ribosomes's three binding sites for tRNA during translation. The A site hold the tRNA carrying the next amino acid to be added to the polypeptide chain |
| E Site | One of the ribosomes three binding sites for tRNA translation . The E siteis the place where discharged tRNAs leace the ribosome. |
| Polyribosome | An aggregation of several ribosomses attached to one messenger RNA molecule |
| 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 complelx that recognizes a signal peptide as it emerges from the ribosome |
| Mutation | A change in the DNA of a gene, ultimately creating genetic diversity. |
