Chapter 25 & 5: Translation, Mutations, and Amino Acids

Flashcards covering key concepts from lecture notes on Chapter 25 (Translation, mRNA decoding, Mutations) and Chapter 5 (Amino acids).

Translation

The process where the ribosome uses an mRNA template and aminoacyl-tRNAs to synthesize a polypeptide.

Ribosome

A cellular machine that uses an mRNA template and aminoacyl-tRNAs to synthesize a polypeptide during translation.

mRNA template

Messenger RNA used as a blueprint during translation, read in the 5' to 3' direction.

Polypeptide synthesis

The process of building a polypeptide chain, which occurs from the N-terminus to the C-terminus.

tRNA (transfer RNA)

A single-stranded RNA molecule, typically about 80 nucleotides long, that is responsible for carrying a specific amino acid to the ribosome during protein synthesis. It has a cloverleaf secondary structure.

Cloverleaf structure

The characteristic secondary structure of tRNA, formed by intra-chain hydrogen bonding.

3'-OH group (tRNA)

The free hydroxyl group on the terminal nucleotide of tRNA where the amino acid covalently binds.

Anticodon (tRNA)

A 3-base sequence on the tRNA that forms hydrogen bonds (is complementary) to a codon on mRNA.

tRNA Secondary Structure

Formed by intra-chain hydrogen bonding (A-U and G-C) to produce regions called stems with an α-helix, giving it a cloverleaf form.

tRNA Tertiary Structure

The L-shaped overall 3D structure of tRNA, maintained by long-range hydrogen bonds.

Charging the tRNA

The first step in protein synthesis where an amino acid is attached to its specific tRNA, requiring ATP and catalyzed by aminoacyl-tRNA synthetase.

Aminoacyl-tRNA synthetase

The enzyme family responsible for covalently binding the correct amino acid to its corresponding tRNA, a process also known as charging the tRNA.

Adenylylation

A step in the tRNA charging reaction where an amino acid is activated by ATP to form an aminoacyl adenylate intermediate.

A-site (ribosome)

The aminoacyl site on the ribosome where incoming aminoacyl-tRNAs bind.

P-site (ribosome)

The peptidyl site on the ribosome where the tRNA carrying the growing peptide chain is located.

E-site (ribosome)

The exit site on the ribosome where deacylated tRNAs leave after delivering their amino acid.

Nonsense codon

A three-base codon (UAG, UAA, or UGA) that signals the termination of translation; also known as a stop codon.

Initiation (translation)

The first stage of translation where all components (mRNA, small ribosomal subunit, methionine-carrying tRNA) assemble to begin polypeptide synthesis.

Elongation (translation)

The stage of translation where the polypeptide chain grows by the sequential addition of amino acids catalyzed by the ribosome, involving peptide bond formation and ribosome shifting.

Termination (translation)

The final stage of translation where a stop codon is reached, leading to the release of the polypeptide chain and dissociation of ribosomal subunits.

Post-translational modification

Processes that occur after a protein has been synthesized, including directed transport, chain folding, covalent modification, and proteolytic cleavage.

Bacterial ribosome (70S)

A prokaryotic ribosome composed of two subunits: 50S (23S RNA, 5S RNA, 34 proteins) and 30S (16S RNA, 21 proteins).

Eukaryotic ribosome (80S)

A eukaryotic ribosome composed of two subunits: 60S (28S RNA, 5.8S RNA, 5S RNA, ~49 proteins) and 40S (18S RNA, ~33 proteins).

pI (isoelectric point)

The specific pH at which a protein has a net charge of zero.

High pI of ribosomal proteins

Ribosomal proteins typically have a high isoelectric point, making them positively charged at physiological pH, which facilitates their binding to negatively charged rRNA, contributing to ribosome stability.

Antibiotics

Substances that inhibit bacterial protein synthesis (translation) by exploiting differences between bacterial and human translational machinery.

Genetic Code

The set of rules by which information encoded in mRNA sequences (codons) is translated into amino acid sequences during protein synthesis.

Degenerate (Genetic Code)

A property of the genetic code where more than one three-base codon can code for the same amino acid.

Specific (Genetic Code)

A property of the genetic code where each codon specifies a particular amino acid, with no ambiguity.

Non-overlapping (Genetic Code)

A property of the genetic code where none of the bases are shared between consecutive codons, and no noncoding bases appear in the sequence.

Universal (Genetic Code)

A property of the genetic code indicating that it is largely the same for all organisms.

Codon

A sequence of three bases on mRNA that specifies an amino acid or a stop signal during protein synthesis.

Stop signal codons

The three codons (UAG, UAA, UGA) that do not code for an amino acid but signal the termination of translation.

Mutation

Mistakes or changes introduced into the DNA sequence of an organism.

Mutagen

Chemicals or agents that cause a change in the DNA sequence, often also carcinogens.

Carcinogen

A substance or agent that causes cancer.

Point mutation

A type of mutation involving the substitution of a single nucleotide for another in the DNA sequence.

Nonsense mutation

A type of point mutation that changes an amino acid-coding codon into a stop codon, often leading to early termination of protein synthesis.

Missense mutation

A type of point mutation that results in a codon coding for a different amino acid.

Silent mutation

A type of point mutation that changes a nucleotide but does not result in a change in the amino acid sequence due to the degeneracy of the genetic code.

Deletion (mutation)

A type of mutation where one or more nucleotides are lost from the DNA sequence.

Insertion (mutation)

A type of mutation where one or more nucleotides are added to the DNA sequence.