Theme 2 Module 3: Translation and Gene Function

Vocabulary flashcards covering the components, steps, and regulatory mechanisms of translation, as well as the experimental history of gene-protein relationships.

Translation

The cellular process in which molecular components read the genetic message in a messenger RNA (mRNA) sequence and translate it into the specific primary amino acid sequence of a protein.

Transfer RNA (tRNA)

A single RNA strand ranging between $70\text{--}90$ nucleotides in length that folds into four double-helical segments and three characteristic loops (a 2D clover-leaf and 3D L-shape) to transfer amino acids from the cytoplasm to a growing polypeptide on a ribosome.

Anticodon

A specific nucleotide triplet located on a tRNA molecule, conventionally written in the 3' to 5' direction, that forms complementary base pairs with a specific mRNA codon written in the 5' to 3' direction.

Amino Acid Attachment Site

A single-stranded CCA nucleotide sequence at the 3' end of a tRNA molecule where the terminal adenine (A) serves as the point of covalent attachment for a specific amino acid.

Aminoacyl tRNA Synthetase

A family of $20$ distinct enzymes (one for each amino acid) that recognizes the anticodon and attachment site of a tRNA to catalyze its covalent attachment to its corresponding amino acid using energy from ATP hydrolysis.

Aminoacyl tRNA (Charged tRNA)

A tRNA molecule that has been activated by being covalently bound to its specific amino acid, allowing it to deliver that amino acid to a growing polypeptide chain on a ribosome.

Wobble

The flexibility in complementary base pairing between the third nucleotide of an mRNA codon and the corresponding base of a tRNA anticodon, explaining why approximately $45$ tRNA molecules can translate all $64$ possible codons.

Shine-Dalgarno Sequences

Prokaryotic ribosome-binding sites located a few bases upstream of the AUG start codon where the translation initiation complex assembles in the absence of a 5' cap.

Polycistronic mRNA

A single prokaryotic mRNA transcript containing multiple open reading frames coding for more than one protein, transcribed from a single promoter regulating functionally related genes.

Peptidyl (P) Site

The site on the ribosome where the initiator methionine-charged tRNA binds during initiation, and where the tRNA holding the growing polypeptide chain resides during elongation.

Aminoacyl (A) Site

The ribosomal site where incoming charged tRNAs, delivered in association with GTP-bound elongation factors, bind prior to peptide bond formation.

Exit (E) Site

The ribosomal site to which a deacylated tRNA translocates following peptide bond formation before being released from the ribosome upon entry of the next aminoacyl-tRNA into the A site.

Peptidyl-Transferase Reaction

A ribosomal RNA-catalyzed condensation reaction that forms a peptide bond and transfers the growing polypeptide chain from the tRNA in the P site to the amino acid on the tRNA in the A site.

Release Factors

GTP-bound proteins that bind to the ribosomal A site upon reaching a stop codon, catalyzing the hydrolysis of the bond between the polypeptide and the tRNA in the P site and promoting dissociation of the translation complex.

One-Gene-One-Enzyme Hypothesis

The concept proposed in the 1940s by George Beadle and Edward Tatum stating that each gene produces a specific enzyme responsible for catalyzing a specific step in a metabolic pathway.

Neurospora crassa

The filamentous bread mold fungus used by Beadle and Tatum, as well as Srb and Horowitz, to establish the relationship between genetic mutations and enzymatic defects in arginine synthesis.

Minimal Medium

A growth medium consisting solely of simple sugars, inorganic salts, and essential growth vitamins, used to demonstrate that wild-type organisms can synthesize all necessary amino acids on their own.

arg1, arg2, and arg3 Mutants

Three radiation-induced mutant strains of Neurospora crassa isolated by Adrian Srb and Norman Horowitz that had mutations in the genes encoding Enzyme 1, Enzyme 2, and Enzyme 3, respectively, in the arginine biosynthetic pathway.

One-Gene-One-Polypeptide Hypothesis

The refined version of Beadle and Tatum's hypothesis recognizing that genes dictate the primary structure of all individual proteins and polypeptides, not strictly metabolic enzymes.

Human Proteome

The complete set of proteins expressed by the human genome, which exceeds the number of protein-encoding genes ($20{,}000\text{--}25{,}000$) due to mechanisms like alternative splicing and post-translational modifications.