Biochemistry 1 Lecture 4 PDF

Proteins are organic compounds with a high  molecular weight. Twenty different amino acids are commonly required for synthesis of proteins. Amino acids have both acidic and basic  centers so when they react with an acid behave just like a base (accept the hydrogen ion) and when rea...

Proteins are organic compounds with a high  molecular weight. Twenty different amino acids are commonly required for synthesis of proteins. Amino acids have both acidic and basic  centers so when they react with an acid behave just like a base (accept the hydrogen ion) and when react with a base behave as an acid (proton donor), so amino acids show dual nature ,such compounds are known as amphoteric compounds. 1-According to R group(chemical classification). 2-According to polarity of side chain. 3- According to nutritional value(nutritional classification). Essential amino acids: These are amino acids which cannot be synthesized in the body and must be supplied by diet. This group includes 8 a.a :Valine – Leucine – Isoleucine – Threonine – Methionine – Lysine – Phenylalanine – Tryptophan. Semi essential amino acids: These are amino acids which are synthesized in the body in amounts that are sufficient for adults but not sufficient for growing children. This group includes 2a.a - Arginine and Histidine Non essential amino acids: These are amino acids which (those which be synthesized in the body in sufficient amounts. - This group includes the remaining amino acids. Peptide bond is a covalent bond that is formed when the carboxyl group of one amino acid reacts with the amino group of the another amino acid, releasing a molecule of water. This is a condensation reaction and the resulting CO- NH bond is called a peptide bond. N.B: Oligopeptides contain from 2 to 10 amino acids. Polypeptides contain from 11 to 49 amino acids, Protein molecule is formed of 50 or more amino acids. Glutathione: - Tripeptide formed of 3 amino acids (glycine, glutamate and cysteine). - Functions: antioxidant, coenzyme and plays an important role in amino acid transport. Glucagon - Peptide hormone formed of 29 amino acids produced by the pancreas. -Functions- Increases plasma glucose level (hyperglycemic agent). Insulin - Protein hormone formed of 51 amino acids produced by the pancreas. Functions - Decreases plasma glucose level (hypoglycemic agent).