2.4 proteins

basics (structure)

ncc backbone w r group/side chain/residual group(polar/np), h, amine group, carboxyl cooh group

elements: CHON, sulfure, some phosphorus

proteins = folded polypeptides

folding + modification gives it function

multiple peptides

oligopeptides: <20 aa

dipeptides: 2 aa, condensation rxn bw nh2 and cooh

eg. insulin

small p, only 2 polypeptides

originally has 3 regions, but middle section is removed during modification → disulphide bonds created to connect strands

number of combinations

infinite

P=20^n

n = number of aa residues in the polypeptide

sequence of aas

determined by sequence of dna bases

• impt because it determine the 3d conformation of the P which gives it its function

• slight change can cause drastic alternations: eg. sickle cell anemia — glu → val.

dna → transcription → mrna codon → translation at ribosome → polypeptide

primary structure

peptide bonds

sequence of aas

secondary structure

folding of the polypeptide

h bonds

alpha helix: ribbon like structure, used in keratin (hair, nails, feathers, hooves). most common

beta pleated sheets: exist as stable sheets with high tensile strength, eg. spider silk. adjacent portions of polypeptides run in opposite directions to each other. common in insoluble Ps.

tertiary structure

h, ionic, disulphide bonds, van der waal forces, hydrophobic interactions

the folding that gives it a 3d conformation

essential for protein to function

quaternary structure

>2 polypeptide chains tgt

h, ionic bonds, hydrophobic interactions

eg. hemoglobins: 4 polypeptide subunits

fibrous vs globular

fibrous: long, narrow strands. secondary structure. structural role. parallel poly chains, cross-linked at regular intervals → form sheets. insoluble in water, tough. eg. myosin in muscle, collagen.

globular: complex & rounded shape. functional roles (eg. antibodies, hormones). tertiary structure. soluble in water.

eg. insulin

hormone: signals (liver) cells to absorb glucose → reduce blood glucose conc

affected cells have insulin receptors eg.

eg. spider silk

tough, high tensile strength, extensible

eg. rhodopsin

aka visual purple

a pigment that absorbs light

a membrane protein in the rod cells of the retina

consists of the opsin polypeptide surrounding a retinal prosthetic group