Lecture 23: Metabolism الأيْض

1. Lecture 23:Metabolism الأيْض • Metabolism: is the set of chemical reactions that occur in living organisms to maintain life to grow and to reproduce. Metabolism is usually divided into two categories: • Catabolism;هدمbreaks down organic matter, for example to produce energy in cellular respiration (from large to small). • Anabolism;بناءconstructing بناء/تكوين components of cells such as proteins and nucleic acids (from small to large). • Enzymes are important to metabolism because they act as catalysts to allow chemical reactions to proceed quickly and efficiently.

2. Important biochemicals: 1- Proteins: • Proteins are made of amino acids arranged in a linear chain and joined together by peptide bonds. • Many proteins are the enzymes that catalyze the chemical reactions in metabolism. • Other proteins have structural تركيبيةor mechanical ميكانيكيةfunctions, such as the proteins that form the cytoskeleton. • Proteins are also important in cell signalling الإشارات الخلوية, immune responses الإستجابات المناعية, active transport across membranesالنقل النشط خلال الأغشية.

3. 2- Lipids: • Lipids composed of three fatty acids and glycerol molecule. • They construct تكوِّنpart of the cell membrane. • They are a source of energy. • Steroids such as cholesterol are another major class of lipids that are made in cells.

4. 3- Carbohydrates: • Carbohydrates are straight-chain with many hydroxyl groups that can exist as straight chains or rings. • Carbohydrates are the most abundant الأكثر توفراbiological molecules, and found as storage for producing energy (e.g. glycogen) and structural components (cellulose in plants, chitin in animals). • The basic carbohydrate units are called monosaccharides and include galactose, fructose, and glucose. • Monosaccharides can be linked together to form polysaccharides.

5. 4- Coenzymes إنزيمات مساعدة/مُعِينة • Metabolism involves chemical reactions, most involve metabolic intermediates وسطاء called coenzymes. • One central coenzyme is adenosine triphosphate (ATP), the energy source of cells. and used to transfer chemical energy between different chemical reactions. • ATP acts as a bridge between catabolism and anabolism, with catabolic reactions generating ATP and anabolic reactions consuming it.

6. 5- Vitamins: • Vitamin is an organic compound needed in small quantities that cannot be made in the cells. • In human nutrition, most vitamins function ascoenzymes after modification. 6- Minerals: • They are inorganic elements play important roles in metabolism; (e.g. sodium and potassium). • About 99% of mammals' mass وزن الجسم are the elements carbon, nitrogen, calcium, sodium, chlorine, potassium, hydrogen, phosphorus and oxygen.