Introduction
- Self assembly of macromolecules
- Macromolecules spontaneously bind to form supramolecular complexes.
- Recognition based on spatial affinity, correspondence, shape, and surface charges.
- Complexes held together by non-covalent forces: ionic bonds, hydrogen bonds, van der Waals forces, hydrophobic forces.
- Classifications
- Nucleic acids
- Proteins X Proteins (quaternary structures)
- Proteins X Nucleic acids (Nucleoproteins)
- Proteins X lipids (lipoproteins)
Proteins X Proteins (quaternary structures)
- Proteins recognize and bind to each other, forming quaternary structures.
- Small complexes like hemoglobin consist of fixed subunits.
- Many enzymes have quaternary structures, including CDKs with cyclin subunits.
- Large complexes include cytoskeletal structures, extracellular matrix fibers, and viral capsids.
- Example: Collagen.
Proteins X Nucleic acids (Nucleoproteins)
- Nucleosome: It's a DNA-protein complex and the basic unit of chromatin in somatic cells.
- Structure:
- Diameter: 10nm.
- Composition: DNA wrapped around histones (H2A, H2B, H3, H4).
- Separated by several dozens of base pairs (linker DNA).
- Structure of a nucleosome
- Sperm Chromatin: During sperm differentiation, histones are replaced by protamines, tightly packaging DNA into toroid-shaped structures.
- Ribosome Assembly: Involves a multistep process including synthesis, folding, and binding of 3 rRNAs and about 50 ribosomal proteins.
- Tobacco Mosaic Virus: Protein capsids initially form a two-layer disk, followed by RNA joining, forcing protein molecules to rearrange into a helix.
- Phage Assembly Pathway:
- Capsid-coated proteins bind to a scaffold protein, forming the procapsid.
- Scaffold proteins are then ejected.
- DNA is packed into the procapsid.
- Portal and stopper proteins bind to the portal protein to prevent DNA leakage.
- Proteins bind to the capsid and tail, completing assembly.
Proteins X lipids (lipoproteins)
- membrane proteins
- In 1972, Singer and Nicolson proposed the fluid mosaic model, describing the membrane as a fluid combination of phospholipids, cholesterol (which helps regulate fluidity), and proteins.
- functions and structures
- lipoproteins
- Description: Lipoproteins are complexes of proteins and lipids essential for the transport and metabolism of fats throughout the body.
- LDL (Low Density Lipoproteins): LDLs transport cholesterol from the liver to tissues, contributing to the buildup of excess cholesterol in arterial walls, a hallmark of atherosclerosis.
- HDL (High Density Lipoproteins): HDLs, in contrast, remove excess cholesterol from tissues and transport it back to the liver for excretion, helping to prevent atherosclerosis and maintaining cardiovascular health.
- Honeybee toxin and membrane disruption:
- The active molecule in bee venom called mellitin disrupts the self-assembly of membranes.
- When it binds to membranes, mellitin causes the formation of toroid-shaped pores.
- This pore formation leads to the release of pro-inflammatory cytokines.
THE CYTOSKELTON