Polypeptides {protein, peptide}| {polypeptide} are 50% of body solids. Polypeptide has 5 to 4000 amino acids.
nitrogen
Protein is the only nitrogen source in diet. Nitrogen leaves body as urea in urine.
metabolism
Conjugated protein can bind to another molecule. Peptide-bond breaking, phosphorylation, dephosphorylation, amidation, methylation, and glycosylation alter protein structure and function.
structure
Protein has four structure levels: primary, secondary, tertiary, and quaternary.
functions
Most proteins are enzymes. Proteins are also for transport, structure, storage, hormones, movement, toxins, protection, and clotting. Proteins maintain water balance, because soluble cell proteins cause higher water pressure inside cell, by osmosis. Proteins buffer water solution inside cells, because soluble proteins have weak acid and weak base groups.
functions: storage
Proteins {storage protein} can be for storage. Ferritin stores iron. Casein stores carbohydrate. Ovalbumin stores fat and carbohydrate.
functions: structures
Fibrous proteins {structural protein} are for body structure.
Alpha-keratin is in skin, hair, wool, horn, and nails. Alpha-keratin has three to seven amino acid chains in bundle, cross-linked by disulfide bonds, which then bundle again.
Scales, claws, beaks, silk, and feathers have beta-keratin. Beta-keratin is mostly glycine, alanine, and serine.
Collagen covers organs and bones. Collagen has three amino-acid chains twisted into left-handed helix. It is mostly glycine, alanine, proline, and hydroxyproline. It has lysine-bond cross-links. Boiled collagen is gelatin.
Elastin is in ligaments and stretchable connective tissue such as blood vessel walls.
Resilin is in flea-leg ligaments, fly-wing ligaments, and cicada-song vibrating tissue.
Glycoprotein is in membranes and cell walls.
Mucoprotein is in membranes and cell walls.
Wing joints have resilen, which is elastic.
Insect skeletons have sclerotin.
Viruses have protein coats.
functions: transport
Proteins {transport protein} can transport small molecules {protein transport}.
Ceruloplasmin carries copper.
Ferritin carries iron.
Hemoglobin carries oxygen and carbon dioxide.
Lipoprotein carries fats and cholesterol.
Myoglobin carries oxygen and carbon dioxide.
Serum albumin carries fatty acids and many other substances.
Proteins can also carry calcium and heavy metals.
Physical Sciences>Chemistry>Biochemistry>Protein
5-Chemistry-Biochemistry-Protein
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Date Modified: 2022.0224