Bio Unit 6

Amino group, Carboxyl group, R group

(or side chain), Peptide bond, Amino end,

Carboxyl end, Polypeptide, Primary

structure, Secondary structure, Tertiary

structure, Quaternary structure, α (alpha)

helix, β (beta) sheet, Denaturation,

Chaperone

Translation

The biochemical process by which the sequence of nucleotide triplets in an mRNA molecule directs the synthesis of a specific polypeptide chain at a ribosome.

Messenger RNA (mRNA)

A single-stranded transcript synthesized from a DNA template that carries coding sequences specifying the primary structure of a protein to the site of synthesis.

Ribosome

A complex macromolecular ribonucleoprotein machine composed of ribosomal RNA and proteins that coordinates translation and catalyzes peptide bond formation.

Aminoacyl (A) site

The ribosomal binding pocket that accommodates an incoming charged tRNA carrying the next amino acid to be added to the growing peptide chain.

Peptidyl (P) site

The ribosomal cavity that holds the tRNA attached to the growing polypeptide chain during translation.

Exit (E) site

The ribosomal binding location where an uncharged tRNA is positioned immediately prior to release from the translational machinery.

Codon

A contiguous sequence of three consecutive nucleotides in mRNA that specifies a particular amino acid or a termination signal.

Reading frame

The non-overlapping, triplet-based grouping of nucleotides established by the positioning of the start codon during translation.

Anticodon

A three-nucleotide sequence on a transfer RNA molecule that base-pairs in an antiparallel orientation with a complementary mRNA triplet.

Aminoacyl tRNA synthetase

An enzyme that couples a specific amino acid to its corresponding tRNA molecule through an ATP-dependent esterification reaction.

Genetic code

The set of universal and degenerate rules that dictates how nucleotide triplets are translated into specific amino acid residues in proteins.

Initiation

The primary stage of translation involving the recruitment and assembly of the small ribosomal subunit, initiation factors, initiator tRNA, and mRNA at the start codon before large subunit association.

Elongation

The cycle in translation during which tRNA selection, peptide bond formation, and ribosomal translocation add successive amino acids to the nascent chain.

Termination

The concluding stage of translation triggered when a stop codon enters the A site, resulting in the hydrolysis and dissociation of the completed polypeptide.

Initiation factor

A regulatory protein that coordinates the assembly of ribosomal subunits, mRNA, and the initial charged tRNA at the translation start site.

Elongation factor

A protein cofactor, often a GTPase, that facilitates the delivery of aminoacyl-tRNA to the A site and promotes ribosomal translocation.

Release factor

A protein that recognizes a stop codon within the ribosomal A site and catalyzes the hydrolysis of the ester bond connecting the polypeptide to the P-site tRNA.

Gene regulation

The collective mechanisms used by cells to control the timing, location, and level of expression of specific functional gene products.

Posttranslational modification

A covalent chemical change made to a polypeptide after synthesis, such as phosphorylation, glycosylation, or proteolytic cleavage.

Protein sorting (or targeting)

The cellular process by which newly translated polypeptides are recognized, directed, and transported to their designated subcellular locations or secretory pathways.

Signal sequence

A short hydrophobic amino acid motif, typically located at the N-terminus of a nascent polypeptide, that directs the translation complex to the endoplasmic reticulum membrane.

Nuclear localization signal

A specific sequence of basic amino acid residues that targets a folded protein for transport across the nuclear envelope via importins.

Signal-recognition particle (SRP)

A cytosolic ribonucleoprotein complex that identifies and binds an emerging N-terminal signal sequence, temporarily halting translation to dock the ribosome onto the ER membrane.

Signal-anchor sequence

An internal hydrophobic segment of a nascent polypeptide that directs insertion into the ER membrane and permanently integrates to form a transmembrane $\alpha$-helix.