Covers the four levels of protein organisation, from the amino acid sequence through local folding, overall 3-D shape and multi-chain assembly, with the side-chain interactions that stabilise each level. It then contrasts fibrous and globular proteins with examples, outlines the Edman method for sequencing from the N-terminus, compares X-ray crystallography, NMR, cryo-EM and homology modelling for tertiary structure, and ends with a short overview of proteomics.
Topic 33 of 42 in the MU Sofia syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 6 sections, about 746 words (5 min of reading), with 19 flashcards.
In this note
Structural organisation of proteins.
Structural elements of primary, secondary, tertiary and quaternary structure.
Structure-Function Relationship in Proteins
Edman method of protein sequencing.
Methods for establishing the tertiary structure of proteins.
Proteomics.
Structural organisation of proteins.
1. Primary Structure:
Linear sequence of amino acids in the polypeptide chain.
2. Secondary Structure:
Local folding patterns of the polypeptide chain.
Common secondary structures include α-helix and β-sheet stabilized by hydrogen bonds.
3. Tertiary Structure:
Overall 3-D folding of the entire polypeptide chain.
Determined by interactions between amino acid side chains (e.g., hydrophobic interactions, hydrogen bonds, disulfide bonds).
4. Quaternary Structure:
Involves multiple polypeptide chains, each with its own tertiary structure.
Interactions between different chains give rise to the quaternary structure.
Examples include hemoglobin (composed of four subunits) and collagen (composed of three polypeptide chains).
Structural elements of primary, secondary, tertiary and quaternary structure.
Primary Structure:
Specifies the amino acids and their order in the polypeptide chain.
Sequence progresses from N-terminus (left) to C-terminus (right).
Secondary Structure:
Involves hydrogen-bonded arrangements.
Common secondary structures include α-helix and β-sheet.
Tertiary Structure:
Three-dimensional arrangement of the polypeptide chain.
Interactions between amino acid side chains guide folding.
Interactions include:
1. Disulfide Bonds: Covalent bonds formed between two cysteine residues.
2. Hydrophobic Interactions: Non-polar amino acids tend to aggregate in the interior, away from water.
3. Hydrogen Bonds: Formed between side chains containing oxygen and hydrogen.
4. Ionic Interactions: Between positively and negatively charged groups in side chains.
Quaternary Structure:
Involves the association of two or more peptide chains.
Not all proteins have quaternary structure.
Example: Hemoglobin, consisting of four peptide chains arranged to form a globular protein, serves as an oxygen carrier in mammalian blood.
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