B1.2 HL Globular vs Fibrous Proteins
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How does protein structure relate to function?
Shape and properties of proteins determine biological role.
Properties of globular proteins?
Water soluble, spherical, folded polypeptide chains, tertiary structure critical.
Functions of globular proteins?
Catalytic (enzymes e.g., Rubisco). Regulatory (hormones e.g., insulin). Transport (haemoglobin). Protective (immunoglobulins). Structural (rare) (actin, tubulin monomers).
Example of a globular protein hormone?
Insulin – regulates blood glucose.
Example of a globular protein enzyme?
RuBisCO – catalyzes carbon fixation in photosynthesis.
How would a change in tertiary structure affect function of globular protein?
Alters active/binding sites → loss of function.
Example of a globular protein transport molecule?
Haemoglobin – transports oxygen.
Properties of fibrous proteins?
Water insoluble, elongated/fibrous or sheet-like, tough, parallel polypeptides, strong structural roles.
Collagen structure?
Three polypeptides wound in a triple helix → hydrogen bonding + covalent cross-links → fibrils → fibres.
Functions of fibrous proteins?
Structural (collagen in skin/tendons). Contractile (actin, myosin). Protective (keratin in hair, nails, feathers). Elastic (elastin in arteries).
Keratin structure?
α-keratins (vertebrates), β-keratins (reptiles, birds). High sulfur content → many disulfide bridges → strong & rigid.
Elastin structure?
Many hydrophobic amino acids + covalent cross-links between lysine → stretch & recoil.
What common feature gives collagen, keratin, and elastin strength?
Covalent cross-linkages between molecules.
Shape and solubility of fibrous proteins?
Long, repetitive chains, insoluble, structural role.
Properties of fibrous proteins?
Water-insoluble, tough, strong, may be stretchy, often cross-linked.
Functions of fibrous proteins?
Structural (collagen, keratin), Contractile (actin, myosin), Elastic (elastin).
Example of a fibrous protein with tensile strength.
Collagen – triple helix, covalent cross-links, connective tissue.
Example of a fibrous protein with rigidity.
Keratin – high sulfur content, disulfide bridges, hair/nails.
Example of a fibrous protein with elasticity.
Elastin – hydrophobic regions allow stretch/recoil (arteries, skin).
What feature contributes to the strength of collagen, keratin, and elastin?
Cross-links (disulfide bridges or covalent bonds).
What is the monomer of proteins?
Amino acids.
What bond links amino acids?
Peptide bonds (condensation).
What are the 4 levels of protein structure?
Primary, secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multiple chains).
What determines protein function?
Shape (conformation), esp. tertiary structure.