CHAPTER 7
Metabolism: All chemical reactions within organisms that enable them to maintain life. * Two main categories: Catabolism and anabolism * Most active metabolism sites include your liver, muscle, and brain cells. * Body needs energy even during sleep * Our cells get their energy from * Chemical energy: Energy contained in the bonds between atoms of molecules. * Chemical energy in foods and beverages come from the sun. * Green plants use light energy to make carbohydrates in a process called photosynthesis. * Carbon dioxide from the air + Water Glucose and Oxygen * Plants store glucose as starch and release oxygen * Plants with high amount of starch: Corn, peas, squash, turnips, potatoes, and rice. * We lose more than half of the total food energy at heat. * Law of thermodynamics: We never lose or gain energy. Just change form and location. * 3 stages of extracting energy from food: * Digestion, absorption, and transportation. * Breaks food down (Simple sugars, fatty acids, monoglycerides) * System transports these nutrients to tissue throughout the body * Breakdown of many small molecules to a few key metabolites. * Inside cells, chemical reactions convert simple sugars, fatty acids, glycerol, and amino acids into a few key metabolites: * Any substance produced during metabolism. * This process liberates a small amount of energy. * Transfer of energy to a form that cells can use. * Complete breakdown of metabolites into carbon dioxide and water liberates LARGE amounts of energy. * Responsible for converting more than 90% of the available food energy. * Metabolism is a general term that encompasses all chemical changes occurring in living organisms. * Metabolic Pathway: A series of chemical reactions that either break down a large compound into smaller units (CATABOLISM) or synthesize more complex molecules from smaller ones (ANABOLISM) * GI tract breaks down starch into glucose units * Cells further catabolise glucose units to release energy (muscle contractions) * Anabolic reactions take available glucose assembling them into glycogen for storage * Metabolic pathways are never completely inactive
The Cell is the Metabolic Processing Center * Cells: “work centers” of metabolism (basic structural units of all living tissues) * 2 major parts: nucleus and cytoplasm * Most cells have similar structure * Nucleus: primary site of genetic information in the cell, enclosed in a double-layered membrane * Cytoplasm: material of the cell, excluding the cell nucleus and cell membranes, includes the semifluid cytosol, the organelles and other particles * Cytosol: semifluid inside the cell membrane, excluding the organelles. The site of glycolysis and fatty acid synthesis * Organelles: various membrane-bound structures that form part of the cytoplasm, include mitochondria, lysosomes, perfom specialized metabolic functions * Mitochondria: sites of aerobic production of ATP, where most of the energy from carbohydrate, protein, and fat is captured * Human cell contains about 2000 mitochondria * Enzymes, which are catalytic proteins, speed up chemical reactions in metabolic pathways * Cofactors: compounds required for an enzyme to be active (usually vitamin or mineral, Fe, Cu, Mg) * Coenzymes: organic compounds, often B vitamin derivatives that combine with an inactive enzyme to form an active enzyme in metabolic reactions
Who are the Key Energy Players? * Adenosine triphosphate (ATP): readily usable form of energy * Making large molecules from smaller ones require energy * ATP molecule has 3 phosphate groups attached to adenosine (organic compound) * Cells can use this energy to power biological work * When a metabolic reaction breaks the first