Translation – The Central Phase of Protein Synthesis (Lecture Notes)

Vocabulary flashcards covering key terms related to translation, genetic code, ribosome function, mutations, clinical relevance, and antibiotics.

Translation

The process by which the ribosome reads mRNA codons to assemble amino acids into a polypeptide chain; occurs in the cytoplasm or on the rough endoplasmic reticulum in eukaryotes.

Ribosome

Molecular machine consisting of small (40S) and large (60S) subunits that coordinates decoding of mRNA and synthesis of protein.

mRNA

Messenger RNA; template carrying codons that dictate the amino acid sequence of a protein.

tRNA

Transfer RNA; carries specific amino acids and recognizes codons via anticodons.

Aminoacyl-tRNA synthetase

Enzyme that charges tRNAs with the correct amino acids (aminoacylation).

Initiation factors (eIFs)

Proteins that regulate translation initiation and promote ribosome assembly on mRNA.

GTP/ATP

Energy sources used to drive initiation, elongation, and termination steps of translation.

Genetic code

Code that maps 3-nucleotide codons in mRNA to specific amino acids; includes start codon AUG and stop codons UAG, UGA, UAA.

Codon

Three-nucleotide sequence in mRNA that codes for a specific amino acid or a stop signal.

Anticodon

Three-nucleotide sequence in tRNA that base-pairs with its complementary mRNA codon.

Start codon AUG

Codon that signals the beginning of translation and codes for methionine.

Stop codons UAG, UGA, UAA

Codons that signal termination of translation.

Unambiguous

Each codon specifies a single amino acid.

Universality of the genetic code

Conservation of codon-to-amino-acid mapping across organisms (with minor exceptions).

Degeneracy

More than one codon can code for the same amino acid.

A-site

Ribosomal site where aminoacyl-tRNA enters.

P-site

Ribosomal site where the growing polypeptide chain is held during elongation.

E-site

Ribosomal site where discharged tRNA exits the ribosome.

Initiation

First phase of translation: 40S binds the 5' cap with initiation factors, scans for AUG, Met-tRNA pairs with AUG, 60S joins to form the 80S ribosome.

Elongation

Phase where a charged tRNA enters the A-site; a peptide bond forms; ribosome translocates A→P→E with EF proteins and GTP hydrolysis.

Termination

Phase when a stop codon is in the A-site; release factors promote hydrolysis and the polypeptide is released and the ribosome dissociates.

RER-bound ribosomes

Ribosomes on the rough endoplasmic reticulum that synthesize secreted, membrane, or lysosomal proteins.

Free ribosomes

Ribosomes in the cytosol that synthesize cytosolic, nuclear, mitochondrial, or peroxisomal proteins.

Aminoacyl-tRNA

A tRNA that is bound to its specific amino acid (charged tRNA).

Silent mutation

DNA change that alters a codon without changing the encoded amino acid.

Missense mutation

DNA change that results in a different amino acid being incorporated.

Nonsense mutation

DNA change that creates a premature stop codon, truncating the protein.

Splice site mutation

Mutation at splice sites that alters mRNA splicing.

Frameshift mutation

Insertion or deletion that shifts the reading frame of the codons, altering downstream amino acid sequence.

β-thalassemia start codon mutation

Mutations at the start codon that can impair translation initiation and contribute to β-thalassemia.

Diphtheria toxin

Inhibits elongation by inactivating elongation factor EF-2, blocking protein synthesis.

Ricin

Ribosome-inactivating protein that inhibits elongation by depurinating rRNA.

Chaperone defects

Misfolded proteins leading to disorders such as Alzheimer’s and Parkinson’s disease.

Impaired ubiquitination

Defects in tagging proteins for degradation, linked to neurodegenerative diseases.

Overactive mTOR

Hyperactive mTOR signaling associated with cancer, tuberous sclerosis, and epilepsy.

Amyloidosis

Disease caused by extracellular deposition of misfolded amyloid proteins in organs.

Ehlers-Danlos syndrome (EDS)

Hereditary connective tissue disorders with skin hyperextensibility, joint hypermobility, and collagen defects; many subtypes; often autosomal dominant in classic type.

COL5A1

Gene encoding type V collagen; mutations contribute to some forms of EDS.

COL1A1

Gene encoding type I collagen; mutations contribute to some forms of EDS.

Streptomycin

Antibiotic that inhibits initiation and causes misreading by binding the 30S ribosomal subunit and blocking aminoacyl-tRNA binding.

Tetracycline

Antibiotic that binds the 30S subunit and inhibits binding of aminoacyl-tRNA to the A-site.

Erythromycin

Antibiotic that binds the 50S subunit and inhibits translocation during elongation.