Protein-Coding Genes and the Genetic Code

Vocabulary flashcards covering the link between genes and enzymes, the levels of protein structure, and the mechanisms of the genetic code.

One Gene, One Enzyme Hypothesis

A hypothesis stating that each gene specifically controls the production of a single, specific enzyme, which in turn catalyzes a single step in a metabolic pathway, proposed by Beadle and Tatum in 1941.

Neurospora crassa

The species of bread mold used by Beadle and Tatum in experiments involving X-rays to induce mutations and study the gene-enzyme relationship.

Auxotrophic mutations

Mutations that cause an organism to be unable to produce necessary nutrients, preventing growth on a minimal medium without specific supplements.

Arginine biochemical pathway

A metabolic pathway proposed to have at least three steps: $\text{Precursor} \rightarrow \text{ornithine} \rightarrow \text{citrulline} \rightarrow \text{arginine}$.

One gene-one polypeptide hypothesis

An updated version of the original gene-enzyme hypothesis reflecting that some enzymes are made of several polypeptides encoded by different genes.

Alternative splicing

A process that allows one gene to produce multiple different proteins, serving as an exception to the one gene-one polypeptide rule.

Proteins

Complex macromolecules built from amino acid chains that fold into specific 3D shapes which determine their cellular functions.

Peptide bonds

The chemical bonds that link long chains of $20$ different amino acids together to form proteins.

Primary Structure

The unique, linear sequence of amino acids in a polypeptide chain.

Secondary Structure

Local folding of the polypeptide chain into regular structures, such as helices and pleated sheets, stabilized by hydrogen bonds.

Tertiary Structure

The overall three-dimensional shape of a single protein molecule, determined by interactions between amino acid side chains (R groups).

Quaternary Structure

The assembly of multiple polypeptide chains (subunits) into a single, functional protein complex.

Codon

A set of $3$ nucleotides in mRNA that encodes a single amino acid.

Degeneracy of the code

The concept that since there are $4 \times 4 \times 4 = 64$ possible codons and only $20$ common amino acids, multiple codons can specify the same amino acid.

Start Codon

The sequence AUG, which codes for methionine and signals the beginning of a protein synthesis sequence.

Stop Codon

Nucleotide sequences such as UAA, UAG, or UGA that signal the end of the protein synthesis sequence.