3. Quaternary structure

What is quaternary structure?

Structure formed by the assembly of multiple polypeptide chains (subunits), e.g., hemoglobin (Hb) with 4 subunits or DNA polymerase with 10 subunits.

What type of bonds hold quaternary structure together?

Weak non-covalent bonds.

How can one protein serve 2 functions in hemoglobin?

One binds oxygen, the other binds carbon dioxide.

What are holoenzymes?

Enzymes composed of multiple protein subunits.

What causes loss of protein function?

Loss of protein structure (denaturation or proteolysis).

What is denaturation?

Process where proteins lose structure (not completely); caused by heat (affecting H+ bonds) or pH (e.g., detergents, solvents).

What interactions stabilize globular proteins?

Hydrophobic interactions in the protein core.

How is protein structure linked to function?

Proteins' 3D structure determines shape, internal organization, and functions in cellular life and communication.

What is familial hypercholesterolemia?

Defect in LDL receptor or its binding region on apolipoprotein B (apoB), leading to high LDL and heart disease.

What causes diabetes insipidus?

Mutations in AQP2 (V2 receptors); insensitivity to ADH → Nephrogenic DI or low ADH → Hypothalamic DI.

What is a prion disease?

Disorder where PrP^C converts to misfolded PrP^Sc (β-sheet form); causes fatal brain degeneration.

What causes Alzheimer's disease?

Misfolding/refolding of amyloid-β protein; forms plaques in the brain.

What mutation causes sickle cell anemia?

Point mutation in β-chain of hemoglobin → valine replaces glutamic acid.

What causes scurvy?

Defective collagen post-transcription due to Vitamin C (ascorbic acid) deficiency.