Unit 2 Chemical Constituents of Cells and Metabolism Anatomy and Physiology http://www.hopkinsmedicine.org/Press_releases/2006/Images/CellMetabolismArt.jpg

2.3 Chemical Constituents of Cells Organic compounds contain both hydrogen and carbon. All other compounds are considered inorganic. Water Most abundant compound in living things and 2/3 of the weight of adults. An important solvent - most metabolic reactions occur in water. Important in transporting materials in the body - a major component of blood. Carries waste materials and can absorb and transport heat.

2.3 Chemical Constituents of Cells Oxygen Needed to release energy from nutrients and is used to drive the cell's metabolism. Carbon Dioxide Released as a waste product during energy-releasing metabolic reactions. Inorganic Salts Provide necessary ions - sodium, chloride, potassium, calcium, magnesium, phosphate, carbonate, bicarbonate, and sulfate. Electrolytes play important roles in many of the body's metabolic processes.

2.3 Chemical Constituents of Cells Organic Substances: Carbohydrates Provide energy for cellular activities - composed of carbon, hydrogen, and oxygen. Made from monosaccharides (simple sugars-glucose); disaccharides (two monosaccharides joined together-sucrose); and polysaccharides (complex sugars) e.g. starch - built of many sugars . Humans synthesize the polysaccharide glycogen.

2.3 Chemical Constituents of Cells Lipids: function-protection, insulation and storage Organic substances that are insoluble in water and include fats, phospholipids, and steroids. Fats supply energy for cellular function, and are built from glycerol and three fatty acids. Fats have a smaller proportion of oxygen atoms than carbohydrates. Fatty acids with hydrogen at every position along the carbon chain are saturated; those with one or more double bonds are called unsaturated fats. A lean person has 18-25% of their body mass of fat Triglycerides- don’t dissolve in bloodstream and any excess carbs, proteins, fats and oils is deposited in adipose tissue

2.3 Chemical Constituents of Cells Phospholipids: Contain glycerol, two fatty acids, and a phosphate group – for cell structure. Steroids: Complex ring structures, and include cholesterol, which is used to synthesize the sex hormones.

2.3 Chemical Constituents of Cells Proteins: Have a great variety of functions in the body--as structural materials, energy sources, hormones, receptors on cell membranes, antibodies, and enzymes to catalyze metabolic reactions (enzymes). Contain C, O, H, and nitrogen atoms; some also contain sulfur. Building blocks are the amino acids, each of which has a carboxyl group, an amino group and a side chain called the R group.

2.3 Chemical Constituents of Cells Proteins have complex shapes held together by hydrogen bonds. Protein shapes, which determine how proteins function, can be altered (denatured) by pH, temperature, radiation, or chemicals.

2.3 Chemical Constituents of Cells Nucleic Acids: Form genes and take part in protein synthesis. Contain carbon, hydrogen, oxygen, nitrogen, and phosphorus - bound into building blocks called nucleotides. Two major types: DNA (with deoxyribose) and RNA (with ribose). RNA (ribonucleic acid) functions in protein synthesis; DNA (deoxyribonucleic acid) stores the molecular code in genes.

DNA vs. RNA DNA RNA Doulbe Helix Sugar is Deoxyribose Stores Genetic Info Nitrogenous Bases Thymine Adenine Guanine Cytosine RNA Single Strand 3 kinds of RNA mRNA, rRNA, tRNA Sugar is Ribose Makes proteins Nitrogenous Bases Uracil Adenine Guanine Cytosine

4.2 Metabolic Reactions Introduction Metabolic reactions are of two types: Anabolic reactions - Larger molecules are constructed from smaller ones, requires energy Catabolic reactions - Larger molecules are broken down, releases energy. The reactions of metabolism are often reversible.

4.3 Control of Metabolic Processes Enzymes control the rates of all the metabolic reactions of the cell. Enzyme Action Complex proteins that lower the activation energy of a reaction so it may begin and proceed more rapidly. Enzymes are called catalysts. Work in small quantities and are recycled by the cell. Each is specific, acting on only one kind of substrate. Active sites on the enzyme combine with the substrate and a reaction occurs. The speed of enzymatic reactions depends on the number of enzyme and substrate molecules available.

4.3 Control of Metabolic Processes Factors That Alter Enzymes Enzymes (proteins) can be denatured by heat, pH extremes, chemicals, electricity, radiation, and by other causes.

4.4 Energy for Metabolic Reactions Energy is the capacity to do work. Common forms of energy include heat, light, sound, electrical energy, mechanical energy, and chemical energy. Release of Chemical Energy - Cellular Respiration Often occurs through the oxidation of glucose. Burning glucose requires energy to begin the process. The end-products of these reactions are heat as well as stored energy. This stored energy is called ATP which has a chain of three phosphates.

4.4 Energy for Metabolic Reactions ATP Molecules Up to 38 molecules of ATP are produced for each molecule of glucose oxidized. ATP molecules contain three phosphates in a chain.

4.4 Energy for Metabolic Reactions Energy is stored in the last phosphate bond. Energy is stored while converting ADP to ATP; when energy is released, ATP becomes ADP, ready to be regenerated into ATP.

4.4 Energy for Metabolic Reactions Anaerobic Respiration The first part of cellular respiration is the splitting of 6-C glucose that occurs through a series of enzyme-catalyzed steps called glycolysis. The result is two 3-C molecules of pyruvate. Glycolysis occurs in the cytosol and does not require oxygen (is anaerobic). Energy from ATP is used to start the process but there is a net gain of energy as a result.

4.4 Energy for Metabolic Reactions Aerobic Respiration Oxygen is needed for aerobic respiration, which occurs within the mitochondria. There is a much greater gain of ATP molecules from aerobic respiration. The final products of glucose oxidation are carbon dioxide, water, and energy.

4.5 Metabolic Pathways The enzymes controlling either an anabolic or catabolic sequence of reactions must act in a specific order. A sequence of enzyme-controlled reactions is called a metabolic pathway.

4.5 Metabolic Pathways Regulation of Metabolic Pathways Determined by a regulatory enzyme responsible for one of its steps. A rate-limiting enzyme is the first step in a series.