Amino acids � Building blocks
All amino acids incorporated into proteins by organisms
are in the L form. All amino acids have acidic and basic
functional groups. All amino acids except glycine have a
chiral center. The pka for a functional group is the pH
at which acidic or basic groups on 50 % of the molecules
in a solution are deprotonated.
3D structures and conformation
Proteins are complex structures. Average protein contains
300 amino acids. Average amino acid contains 8 heavy atoms.
Average structure contains 2400 atoms. X ray crystallography
and NMR spectroscopy are the techniques which allow getting
atomic resolution pictures of proteins.
Protein folding
Protein molecules fold by interacting between atoms within
the protein chains and by interacting between the protein
and the solvent. The forces involved are van der waals
forces, disulphide bonds, hydrogen bonds, electrostatic
attraction, and hydrophobic interactions. Defect in primary
structure of proteins may arise due to mutations. Sickle
cell anemia is a defect in the hemoglobin � a protein found
in RBCs. Change in primary sequence decreases protein
solubility and protein aggregates. For a protein of n
residues, there are 20n possible sequences. It can fold into
any pattern which is decided by its function.
Covalent backbone and sequence
Alpha helix is formed by hydrogen bonds. Backbone does not
follow any actual bonds. They are used for structural super
impositions. Peptide bond has a partial double bond
character
Protein functions
Proteins are divided based on their functions. Ex: Collagen,
fibrous protein is classified under structural proteins. The
globular proteins have a number of biologically important
roles. Myoglobulin is present in the muscle and hemoglobin
in the RBC. Proteins act as biocatalyst � enzymes. They
regulate metabolism too.
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