Question

what are the building blocks that make up proteins

Answer 1

Proteins are made from small building blocks called amino acids.

Key points:
- Each amino acid has a central (alpha) carbon bonded to:
- an amino group (—NH2),
- a carboxyl group (—COOH),
- a hydrogen atom,
- and a variable side chain (R group) that gives each amino acid its chemical properties.
- Amino acids link together by peptide bonds (a condensation reaction between the carboxyl of one and the amino of the next), forming a polypeptide chain. A folded polypeptide that performs a biological function is called a protein.
- There are 20 standard (canonical) amino acids encoded by the genetic code; they differ in size, polarity, and charge. Cells use mostly the L‑stereoisomers (glycine is achiral).
- Two additional amino acids (selenocysteine and pyrrolysine) are sometimes incorporated in specific proteins.
- Protein structure is described at four levels:
- Primary: amino acid sequence.
- Secondary: local structures (alpha-helices, beta-sheets).
- Tertiary: overall 3D fold.
- Quaternary: assembly of multiple polypeptide subunits.
- Side-chain chemistry and sequence determine a protein’s shape and function (enzymes, structural proteins, transporters, signaling molecules, etc.). Post‑translational modifications (phosphorylation, glycosylation, etc.) further diversify function.