HMG - Week 11: Translation and Protein Synthesis

Comprehensive vocabulary flashcards covering mRNA export, protein structure, the genetic code, tRNA/ribosome functions, and the stages of translation.

Nuclear Pore Complex (NPC)

A large protein channel with eight-fold symmetry and a cylindrical structure that controls the movement of molecules between the nucleus and cytoplasm; approximately 3,000 occur in the nuclear envelope.

HnRNP A1 and HnRNP K

Specific export proteins that recognize export signals on mRNA and guide it through the nuclear pore complex.

Ran-Dependent Export

A process requiring an export receptor and RanGTP, where RanGTP helps the receptor bind mRNA before the complex passes through the NPC and dissociates upon conversion to RanGDP.

TAP/NXT1 exporter complex

The major pathway for Ran-independent mRNA export in eukaryotic cells that does not require RanGTP.

Amino Acid structure

Consists of an amino group ($-NH_2$), a carboxyl group ($-COOH$), a hydrogen atom, and a variable R-group (side chain).

Peptide Bond

A bond formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another, releasing water.

Primary Structure

The linear sequence of amino acids in a polypeptide, determined directly by the DNA sequence.

Secondary Structure

Local folding of a polypeptide caused by hydrogen bonds, typically forming \text{\alpha-helix} or \text{\beta-pleated sheet} patterns.

Tertiary Structure

The overall 3D folding of a polypeptide stabilized by hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bonds.

Quaternary Structure

The association of multiple polypeptide chains, such as the four subunits found in Haemoglobin.

Codon

A group of 3 RNA nucleotides that specifies one amino acid; for example, AUG specifies Methionine.

$$4^3 = 64$$

The calculation explaining why a triplet code provides enough combinations (64) to code for 20 amino acids plus start and stop signals.

Reading Frame

The way codons are grouped during translation; changing the starting point changes every subsequent codon.

Frameshift Mutation

The insertion or deletion of a nucleotide that changes the reading frame, often resulting in different amino acids and non-functional proteins.

Marshall Nirenberg

The scientist who helped crack the genetic code by demonstrating that the codon UUU specifies Phenylalanine.

Universal

A characteristic of the genetic code meaning almost all organisms, from bacteria to humans, use the same code.

Degenerate

A characteristic of the genetic code where more than one codon can specify the same amino acid, such as Leucine having six different codons.

Silent Mutation

A mutation that changes a codon (e.g., GAA to GAG) but results in the same amino acid (Glutamate), leaving the protein sequence unchanged.

Start Codon

The codon AUG, which codes for Methionine and signals the beginning of translation.

Stop Codons

The codons UAA, UAG, and UGA, which do not code for amino acids but signal the termination of translation and recruit release factors.

Wobble Hypothesis

Proposed by Francis Crick, it states that while the first two codon bases pair strictly, the third base can pair flexibly, allowing one tRNA to recognize multiple codons.

Transfer RNA (tRNA)

An adaptor molecule 74–95 nucleotides long containing an acceptor arm for amino acids and an anticodon arm for mRNA binding.

40S subunit

The small subunit of the eukaryotic ribosome which contains 18S rRNA.

60S subunit

The large subunit of the eukaryotic ribosome which contains 5S, 5.8S, and 28S rRNA.

A site (Aminoacyl-tRNA site)

The ribosomal site where the incoming aminoacyl-tRNA enters during translation elongation.

P site (Peptidyl-tRNA site)

The ribosomal site that holds the tRNA carrying the growing polypeptide chain.

E site (Exit site)

The ribosomal site where empty tRNAs exit the ribosome after their amino acid has been added to the chain.

Translocation

The step in elongation where the ribosome moves $5' \rightarrow 3'$ along the mRNA, shifting tRNAs from the A to P site and P to E site.

Translation Initiation

The process where the small ribosomal subunit binds mRNA, the initiator tRNA binds the AUG codon, and the large subunit joins to form the initiation complex.