Molecular Components of Cells PDF

Chapter 2 Molecular Components of cells Inorganic and Organic Compounds  I. Proteins 7. Structures of Proteins a. Primary Structure b. Secondary Structure c. Tertiary Structure d. Quaternary Structure  I. Proteins a. Primary Structure ✓...

Chapter 2 Molecular Components of cells Inorganic and Organic Compounds  I. Proteins 7. Structures of Proteins a. Primary Structure b. Secondary Structure c. Tertiary Structure d. Quaternary Structure  I. Proteins a. Primary Structure ✓ Linear aa sequence ✓ Determined by: nucleotide sequence in DNA ✓ Stabilized by: covalent bonds between aa ✓ Determines all of the other structures → its alteration impairs protein functions ✓ All copies of the same protein have identical primary structures  I. Proteins b. Secondary Structure ✓ Folding of aa portions into: helices & β-pleated sheets (+ turns & irregular random coiling) ✓ Stabilized by hydrogen bonds (except for supercoiling: covalent bonds) ✓ A specific aa sequence will acquire the same folding wherever it is found  I. Proteins c. Tertiary Structure ✓ Helical & non-helical regions are folded back in precise positions ✓ Determined by secondary structures ✓ Hides hydrophobic aa in core & exposes charged aa ✓ Brings distant segments together → active domains ✓ Stabilized by: - hydrogen bonds - ionic bonds - hydrophobic interactions - salt bridges - disulfide bridges  I. Proteins c. Tertiary Structure ▪ Protein Denaturation ✓ Unfolding + segment separation of proteins ✓ By: physical agents (low pH, high temp) & chemical agents (detergents, urea) ✓ Protein loses its activity ✓ Irreversible unless mild  I. Proteins d. Quaternary Structure ✓ Some proteins need it ✓ Assembly of ≥2 subunits (identical or different) → forms active domains ✓ Stabilized by: weak bonds (+ sometimes covalent) ✓ Protein activation / deactivation: by changing its 3D conformation: by: - Phosphorylation / dephosphorylating - Allosteric transition (ligand binding / dissociation)  I. Proteins 8. Classification of Proteins ✓ By composition - Holoproteins / apoproteins: only aa - Heteroproteins: aa + other molecules ex: lipoproteins, glycoproteins, nucleoproteins, hemoproteins (ion) ✓ By structure - Fibrous: insoluble in water (keratin, collagen) - Globular: soluble in water (globulin, albumin, histones) ✓ By function Structural – defense – regulatory – transporter – catalytic – contraction…  FS.I Partial 2020 7)c 8)b 18)b 21)d