Lecture 23: Animal physiology Metabolism الأيْض Metabolism: is the set of chemical reactions that occur in living organisms to maintain life يحافظ على الحياة . These processes allow organisms to grow and reproduce يتناسل , maintain their structures, and respond to their environments. Metabolism is usually divided into two categories: Catabolism; هدمbreaks down organic matter, for example to produce energy in cellular respiration. Anabolism; بناءconstructing بناء/تكوين components of cells such as proteins and nucleic acids. Enzymes are important to metabolism because they act as catalysts to allow chemical reactions to proceed quickly and efficiently.

Key Biomolecules In Metabolism الجزيئات الحيوية الأساسية في الأيض Most of the structures that make up animals, plants and microbes are made from three basic types of molecule: proteins, carbohydrates and lipids (often called fats). As these molecules are important for life, metabolism focuses on utilizing these molecules in two ways: in the construction of cells and tissues تكوين الخلايا والأنسجة, or breaking them down and using them as a source of energy كمصدر للطاقة . These macromolecules are essential parts of all living organisms.

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 تُسهِّـل the chemical reactions in metabolism. Other proteins have structural تركيبيةor mechanical ميكانيكية functions, such as the proteins that form the cytoskeleton. Proteins are also important in cell signalling الإشارات الخلوية, immune responses الإستجابات المناعية, active transport across membranes النقل النشط خلال الأغشية.

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.

3- Carbohydrates Carbohydrates are straight-chain aldehydes or ketones 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.

4- Coenzymes إنزيمات مساعدة/مُعِينة Metabolism involves chemical reactions, most involve metabolic intermediates وسطاء called coenzymes. Coenzymes are therefore continuously being made تتكون باستمرار, consumed وتستهلكand then recycled ويعاد تكوينها . 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. It also serves as a carrier of phosphate groups in phosphorylation تفاعلات الفسفرة reactions.

5- Vitamines Vitamin is an organic compound needed in small quantities that cannot be made in the cells. In human nutrition, most vitamins function as coenzymes after modification. Nicotinamide adenine dinucleotide (NADH), a derivative مشتق من of vitamin B3 (niacin), is an important coenzyme that acts as a hydrogen acceptor مستقبل للهيدروجين. NAD+ exists in two related forms in the cell, NADH and NADPH. The NAD+/NADH form is more important in catabolic reactions, while NADP+/NADPH is used in anabolic reactions.

6- Minerals & Cofactors a)- elements b)- ions: 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, oxygen and sulfur. The organic compounds (proteins, lipids and carbohydrates) contain the majority of the carbon and nitrogen and most of the oxygen and hydrogen is present as water. b)- ions: The most important inorganic ions are sodium, potassium, calcium, magnesium, chloride, phosphate, and the organic ion bicarbonate. These Ions are also critical for nerves and muscles.

Catabolism الهدم & Anabolism البناء a)- Catabolism: It is the metabolic processes that break down large molecules. The purpose الهدف of the catabolic reactions is to provide the energy and components needed by cell. In animals these reactions involve complex organic molecules being broken down to simpler molecules, such as carbon dioxide and water. b)- Anabolism: It is the constructive البنائية metabolic processes where the energy released by catabolism is used to synthesize لتكوينcomplex molecules from small and simple components. Anabolism involves three basic stages. the production of components such as amino acids, monosaccharides, and fatty acids, their activation into reactive forms using energy from ATP, the assembly تركيب/تشكيل of these components into complex molecules such as proteins, polysaccharides and lipids.

Catabolismالهدم Anabolismالبناء Metabolism الأيض (Metabolism is the chemical reactions that occur in living organisms to maintain their life, to grow and to reproduce). Catabolismالهدم Anabolismالبناء Is the break down of large molecules to provide energy and components needed for anabolic reactions. Is the constructive processes that uses energy formed by catabolism to synthesize complex molecules for make up cellular structures.