2 & 3) Proteins

• The spatial arrangement of atoms in a protein is referred to as its conformation.
• The conformations of a protein include any structural state that can be achieved without breaking covalent bonds.
• The three-dimensional structure of a protein reflects its function.
• The primary structure of proteins is stabilized by peptide bond.
• The peptide C-N bond is shorter and appears to be partial double bond in comparison to the C-N bond in a simple amine due to the resonance or partial sharing of two pairs of electrons between the carbonyl oxygen and the amide nitrogen.
• The oxygen of the peptide bond has a partial negative charge and the nitrogen a partial positive charge, setting up a small electric dipole.
• The peptide bond is planar, meaning the 6 atoms associated with the peptide group are coplanar and lie in a single plane.
• Restricted rotation around C-N bond in peptide bond due to trans localization of the oxygen atom of the carbonyl group and the hydrogen atom of the amide nitrogen and of the R-groups of the AAs.
• A protein’s conformation is stabilized largely by weak Interactions.
• Hydrogen bonding is a type of weak interaction that occurs within and between polypeptide chains and with the surrounding aqueous medium.
• The deficiency of Vitamin C leads to impairment of post- translational modification of collagens, which are proteins of the extracellular matrix.
• The maturation of collagen involves oxidation of Proline.
• Scurvy is a deficiency disease characterized by general degeneration of connective tissue.
• Hydrophobic forces are a type of weak interaction that play the major role in shaping protein structure.
• Manifestations of advanced scurvy include numerous small hemorrhages caused by fragile blood vessels, tooth loss, poor wound healing and the reopening of old wounds, bone pain and degeneration, and eventually heart failure.
• The cell has ruptured and haemoglobin fibers are spilling out.
• Electrostatic forces are mainly of three types: charge-charge, charge-dipole and dipole-dipole.
• Typical charge-charge interactions that favor protein folding are those between oppositely charged R-groups.
• Substantial for protein folding are the charge-dipole interactions, which refer to the interaction of ionized R-groups of amino acids with the dipole of the water molecule.
• The majority of the amino acids found on the exterior surfaces of globular proteins contain charged or polar R-groups.
• There are both attractive and repulsive van der Waals forces that control protein folding.
• Collagen is organized into tropocollagen (a right-handed triple helix), protofibril (binding N-end to C-end), and microfibril.
• In a-keratins, the cross-links stabilizing tertiary structure are disulfide bonds.
• Some proteins contain two or more separate polypeptide chains, or subunits, which may be identical or different, and the arrangement of these protein subunits in three-dimensional complexes constitutes quaternary structure.
• The tertiary structure of myoglobin is a good example of globular protein structure.
• Diabetes insipidus, the nephrogenic form, is a disorder of water balance where patients produce too much urine (polyuria) which causes them to be excessively thirsty (polydipsia).
• Fibrous proteins usually consist of a single type of secondary structure and are involved in forming structures that provide support, shape, and external protection to vertebrates.
• Globular proteins have polypeptide chains folded into a spherical or globular shape.
• Fibrous proteins share properties that give strength and/or flexibility to the structures in which they occur.
• Tertiary structure includes longer-range aspects of amino acid sequence, including interactions between amino acids that are far apart in the polypeptide sequence and are in different types of secondary structure, to fold the structure of a protein.
• Globular proteins often contain several types of secondary structure and most enzymes and regulatory proteins are globular proteins.
• Fibrous and globular proteins can be divided into two major groups based on their higher level of structure.
• Many coiled coils can be assembled into large supramolecular complexes, protofilaments and then protofibril.
• All fibrous proteins are insoluble in water due to a high concentration of hydrophobic amino acid residues both in the interior of the protein and on its surface.
• Proteins with quaternary structure insert their function when the complex is assembled.
• The tetramer formed by 2 a-type subunits (a and ζ) and 4 non-a-type (b, δ, γ, ε) is an example of quaternary structure.
• The association of the subunits in the quaternary structure occurs through weak non-covalent bonds.
• Fibrous proteins have polypeptide chains arranged in long strands or sheets.
• Fibrous proteins include keratin, collagen, elastin, and silk fibroin.
• The a-keratin helix is a right-handed a-helix and two strands of a-keratin, oriented in parallel (with their amino termini at the same end), are wrapped about each other to form a super twisted coiled coil, making a strong rope.