Terminology

30S - A name for the small prokaryotic ribosomal subunit. The name arises from its size -S is a unit of centrifugal force related to size. This subunit contains 21 unique proteins and the 16S rRNA.
50S - A name for the large prokaryotic ribosomal subunit. The name arises from its size -S is a unit of centrifugal force related to size. This subunit contains 32 unique proteins and the 23S and 5S rRNAs.
A site - A tRNA binding site found on the 50S ribosomal subunit. During translation it holds the incoming tRNA with the amino acid to be added to the growing peptide chain. Figure 27.22
Acceptor Stem - The portion of a tRNA where the amino acid is covalently attached. Figure 27.6
Aminoacyl-tRNA Synthetases - A group of enzymes that catalyze attachment of a specific amino acid to each tRNA molecule.
Anticodon - A three nucleotide base sequence in the anticodon loop of a tRNA complementary to the codon of a messenger RNA. During translation, this structure base pairs with the codon to bring the appropiate amino acid into the place where protein synthesis is occurring.
Anticodon Loop - The part of the tRNA where the anticodon is located. Figure 27.6
Codon - A sequence in a messenger RNA of three nucleotide bases that specify either an amino acid for incorporation into a protein or a stop signal to terminate protein synthesis at that point.
D-Loop - The loop of a tRNA nearest the 5' end. Figure 27.6.
Deformylase - A prokaryotic enzyme that removes the formyl group from the N-formyl-methionine at the end of bacterial polypeptides.
E site - A tRNA binding site found on the 50S ribosomal subunit. During translation, the tRNA that has just transferred its peptide to the next tRNA moves to this site briefly before exiting. Figure 27.22
EF-G - A translational elongation factor that is necessary for translocation. Table 27.4
EF-TS - A translational elongation factor that participates in recharging EF-Tu with GTP. Table 27.4
EF-Tu - A translational elongation factor that carries tRNA into the A site. Table 27.4.
Frame Shift Mutation - A mutation in the region of a gene coding for protein that results in insertion or deletion ofa number of bases not divisible by three.
Genetic Code - The code by which the nucleotide sequence of a DNA or RNA molecule specifies the amino acid sequence of a polypeptide. It consists of three-nucleotide codons that either specify a particular amino acid or tell the ribosome to stop translating and release the polypeptide. With a few minor exceptions, all living things use the same code. Figure 27.3
IF1 - A translational initiation factor that promotes dissociation of the 70S ribosome Table 27.4
IF2 - A translational initiation factor that helps attach initiator tRNA to the initiation complex. Table 27.4
IF3 - A translational initiation factor that promotes dissociation of the 70S ribosome. Table 27.4
Intergenic Mutation - A suppressor mutation that occurs in a second gene apart from the original mutation. Fiugre 27.22
Missense Mutation - A mutation in the region of a gene coding for protein that results in a change of amino acid inserted at a particular point.
N-formylmethionine - A modified form of methionine used by prokaryotic organisms as the first amino acid in a polypeptide. It is the only place the amino acid is used in a polypeptide. Everywhere else that the AUG codon appears, methionine is used.
Nonsense Mutation - A mutation that converts a codon for an amino acid to a stop codon.
Operon - A set of contiguous prokaryotic structural genes that are transcribed as a unit, along with the adjacent regulatory elements that control their expression.
P site - A tRNA binding site found on the 50S ribosomal subunit. During translation it holds the tRNA that is attached to the growing peptide chain. The initiator tRNA also occupies this site at the initiation of translation. Figure 27.22
Peptide Bond - The bond that links successive amino acids in a peptide; it consists of an amide bond between the -carboxyl group of one amino acid and the -amino group of the next.
Peptidyltransferase - An enzymatic activity that is an integral part of the 50S ribosomal subunit. It catalyzes formation of a peptide bond as the growing peptide chain is transferred to the amino acid on the tRNA in the A site of the ribosomal subunit.
Polycistronic Messages - The form by which messages are often carried in prokaryotic organisms- multiple polypeptide coding sequences located on a single mRNA.
Resistance Gene - A term for a gene in a cell that enables it to grow in the presence of an antibiotic designed to kill it.
RF1 - A translational release factor for UAA, UAG. Table 27.4.
RF2 - A translational release factor for UAA, UGA. Table 27.4.
RF3 - A GTPase that promotes release of the polypeptide chain. Table 27.4.
Ribosome - The multiprotein-RNA complex on which translation occurs in the cell. Figure 27.13
Ribozyme - An RNA that catalyzes a reaction. In the 50S ribosomal subunit, the rRNA in it acts this way.
SecA - An ATPase involved in secretion of E. coli proteins. It binds to the secretory pore and uses both ATP hydrolysis and the electrochemical potential gradient across the membrane to drive translocation of the protein out of the cell.
SecB Protein - A molecular chaperone involved in secretion of prokaryotic polypeptides. Figure 27.30.
Selenocysteine - A rare amino acid that occasionally is incorporated into proteins according to the UGA codon, which normally specifies STOP.
Shine-Dalgarno Sequence - A common, conserved sequence in prokaryotic mRNAs that helps orient the ribosome to begin translation. The sequence is located just before the AUG start codon and is complementary to the 3' end of the 16S rRNA in the ribosome.
Signal Sequence - A stretch of highly hydrophobic amino acids at the amino terminus of bacterial genes that target the polypeptide for secretion (export across the cell membrane). Figure 27.30.
Start Codon - The first codon that is translated in making a protein. It is almost always AUG, which codes for methionine. Figure 27.3
Stop Codon - A codon that, when encountered by the ribosome during translation of an mRNA, causes translation to stop. In the universal code, this is specified by UAA, UAG, and UGA. Figure 27.3
Suppressor Mutation - A mutation occurring elsewhere in the genome that overcomes the effect of a primary mutation. For example, if a nonsense mutation occurs, it can be suppressed by a mutation in another gene that causes the gene containing the premature stop codon to still make full length proteins. Figure 27.27
TC Loop - The loop of a tRNA nearest the 3' end. Figure 27.6
Transfer RNA - The form of RNA that provides translation between the three base codon sequence in the mRNA and amino acid corresponding to it.
Transformylase - An enzyme that catalyzes transfer of a formyl group to methionine after the methionine is linked to the tRNA.
Translation - A process carried out by the ribosomes in which the genetic code in mRNA is converted to amino acids in polypeptide. The process of making polypeptides in a cell.
Universal Genetic Code - The version of the genetic code that is used by almost all organisms.
Variable Loop - A tiny loop that varies considerably from one tRNA to another. Figure 27.6
Wobble Position - In a codon, the third nucleotide is often referred to as this because the first two bases are the most important ones in specifying an amino acid and the third position can vary (in many cases) to some extent. In an anticodon, the wobble position is the first nucleotide, due to the antiparallel nature of base pairing of nucleic acids. Figure 27.4