INTRODUCTION. Chapter 2. Basic Principles. Chapter Overview

Transcription

1 INTRODUCTION Chapter 2 The Chemical Level of Organization Since chemicals compose your body and all body activities are chemical in nature, it is important to become familiar with the language and fundamental concepts of chemistry. 1 2 Chapter Overview Matter Chemical bonds Chemical energy Chemical reactions Inorganic compounds Organic compounds Basic Principles Chemistry is the science of the structure and interactions of matter Matter is anything that occupies space and has mass Mass is the amount of matter a substance contains Weight is the force of gravity acting on a mass Describe two ways that you could change your weight 3 4

2 How is Matter Organized Matter is made up of atoms An element is a quantity of matter composed of atoms of the same type Atoms join together to form chemicals with different characteristics Chemical characteristics determine physiology at the molecular and cellular level 5 6 Atomic Particles Proton: positive, 1 mass unit Neutron: neutral, 1 mass unit Electron: negative, low mass Electron Shells Most likely region of the electron cloud in which to find electrons Each electron shell can hold only a limited number of electrons first shell can hold only 2 electrons 2nd shell can hold 8 electrons Number of electrons = number of protons Each atom is electrically neutral; charge = 0 PLAY The Structure of Atoms 7 8

3 Atomic number: number of protons Mass number: Particles and Mass number of protons plus neutrons Atomic weight: exact mass of all particles (daltons) PLAY Chemical Properties of Atoms Isotopes 2 or more elements with equal numbers of protons but different numbers of neutrons Certain isotopes called radioactive isotopes are unstable because their nuclei decay to form a simpler and thus more stable configuration Radioactive isotopes can be used to study both the structure and function of particular tissues 9 10 Atomic Number & Mass Number Atomic number is number of protons in the nucleus. Mass number is the sum of its protons and neutrons. Ions If an atom either gives up or gains electrons, it becomes an ion an atom that has a positive or negative charge due to having unequal numbers of protons and electrons. written with its chemical symbol and (+) or (-) (e.g., Na +, Cl - ) cations are positive anions are negative 11 12

4 Free Radicals A free radical is an electrically charged atom or group of atoms with an unpaired electron in its outermost shell Unstable and highly reactive; can become stable by giving up an electron taking an electron from another molecule can break apart important body molecules in the process Antioxidants are substances that inactivate oxygenderived free radicals Free Radicals & Your Health Produced in your body by absorption of energy in ultraviolet light in sunlight, x-rays, by breakdown of harmful substances, & during normal metabolic reactions Linked to many diseases -- cancer, diabetes, Alzheimer s, atherosclerosis and arthritis Damage may be slowed with antioxidants such as vitamins C and E, selenium & betacarotene (precursor to vitamin A) Chemical Bonds The atoms of a molecule are held together by forces of attraction called chemical bonds. The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost (valence) shell. Atoms with incompletely filled outer shells tend to combine with each other in chemical reactions to produce a chemically stable arrangement of filled outer shells for each atom. Ionic bonds: Chemical Bonds attraction between cations and anions Covalent bonds: strong electron bonds Hydrogen bonds: weak polar bonds 15 16

5 The Ionic Bond in Sodium Chloride Sodium loses an electron to become Na+ (cation) Chlorine gains an electron to become Cl- (anion) Na+ and Cl- are attracted to each other to form the compound sodium chloride (NaCl) -- table salt Ionic compounds generally exist as solids Some may dissociate into positive and negative ions in solution. Such a compound is called an electrolyte. 17 Covalent Bonds Atoms share electrons to form covalent bonds Electrons spend most of the time between the 2 atomic nuclei single bond = share 1 pair double bond = share 2 pair triple bond = share 3 pair Covalent bonds are common and are the strongest chemical bonds in the body. PLAY Covalent Bonds 18 Polar Covalent Bonds Unequal sharing of electrons between atoms. In a water molecule, oxygen attracts the hydrogen electrons more strongly Oxygen has greater electronegativity as indicated by the negative Greek delta sign. Hydrogen Bonds Approximately 5% as strong as covalent bonds Useful in establishing links between molecules or between distant parts of a very large molecule Help determine 3-D shape of large molecules (e.g., proteins). Give water considerable cohesion which creates a very high surface tension 19 20

6 Chemical Reactions New bonds form and/or old bonds are broken. Metabolism is the sum of all the chemical reactions in the body. Law of conservation of mass The total mass of reactants equals the total mass of the products. 21 Forms of Energy Energy is the capacity to do work. Kinetic energy is the energy associated with matter in motion. Temperature is an indirect measure of molecular motion. Potential energy is energy stored by matter due to its position. Chemical energy is a form of potential energy stored in the bonds of compounds or molecules. The total amount of energy present at the beginning and end of a chemical reaction is the same; energy can neither be created nor destroyed although it may be converted from one form to another (law of conservation of energy). 22 Energy Transfer in Chemical Reactions An exergonic reaction is one in which the bond being broken has more energy than the one formed so that extra energy is released, usually as heat (occurs during catabolism of food molecules). An endergonic reaction is just the opposite and thus requires that energy be added, usually from a molecule called ATP, to form a bond, as in bonding amino acid molecules together to form proteins. Energy Transfer in Chemical Reactions Reactions in living systems usually involve both kinds of reactions occurring together. exergonic reactions release energy endergonic reactions absorb energy You will learn of many examples in human metabolism that involve coupled exergonic and endergonic reactions; the energy released from one reaction will drive the other. Glucose breakdown releases energy, which is used to build ATP molecules (that store the energy for later use in other reactions.) 23 24

7 Activation energy is the energy needed to initiate a reaction. Increases in concentration or temperature can help achieve activation energy. Activation Energy Catalysts Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur. A catalyst does not alter the difference in potential energy between the reactants and products. It only lowers the amount of energy needed to get the reaction started. A catalyst helps to properly orient the reactants to favor formation of products. The catalyst itself is unchanged at the end of the reaction; it is often re-used many times Effectiveness of Catalysts Catalysts speed up chemical reactions by lowering the activation energy. Catalysts or Enzymes Normal body temperatures and concentrations are low enough that many chemical reactions are effectively blocked by the activation energy barrier. Most chemical reactions that sustain life cannot occur unless the right enzymes are present Enzymes are biological catalysts that carry out specific chemical reactions in the body. e.g., lactase breaks down lactose into glucose and galactose

8 Types of Chemical Reactions Decomposition reaction (catabolism): AB! A + B Synthesis reaction (anabolism): A + B! AB Exchange reaction: AB + CD! AC + BD Reversible reaction: AB " A + B Hydrolysis: A B C D + H 2 O! A B H + HO C D Dehydration synthesis (condensation): A B H + HO C D! A B C D + H 2 O Organic and Inorganic Molecules Organic: molecules based on carbon and hydrogen Inorganic: molecules not based on carbon and hydrogen Nutrients: Essential Molecules essential molecules obtained from food Metabolites: molecules made or broken down in the body Water Water is the most important and abundant inorganic compound in all living systems. Most of our body weight is water. An important property of water is its polarity, the uneven sharing of valence electrons that confers a partial negative charge near the one oxygen atom and partial positive charges near the two hydrogen atoms in the water molecule

9 Solubility: Properties of Water water s ability to dissolve a solute in a solvent to make a solution Reactivity: most body chemistry uses or occurs in water High heat capacity: water s ability to absorb and retain heat Lubrication: to moisten and reduce friction Aqueous Solutions Polar water molecules form hydration spheres around ions and small polar molecules to keep them in solution Electrolytes Inorganic ions which conduct electricity in solution Electrolyte imbalance seriously disturbs vital body functions Hydrophilic: Molecules and Water hydro = water, philos = loving reacts with water Hydrophobic: phobos = fear does not react with water 35 36

10 ph ph: the concentration of hydrogen ions (H + ) in a solution Neutral ph: a balance of H + and OH pure water = 7.0 Acid (acidic): ph lower than 7.0 high H + concentration, low OH concentration Base (basic): ph higher than 7.0 low H + concentration, high OH concentration ph Scale Has an inverse relationship with H + concentration: more H + ions mean lower ph ph is a logarithmic scale ph of 1 contains 100 times more H+ than ph of Control of ph Acidosis: excess H + in body fluid (low ph) damages cells and tissues alters proteins interferes with normal physiological functions Alkalosis: excess OH in body fluid (high ph) also cause problems, but rarely Buffers: control ph weak acid/salt compounds (e.g., sodium bicarbonate) neutralizes either strong acid or strong base biochemical reactions are very sensitive to even small changes in acidity or alkalinity Organic Compounds Usually large and contain carbon, hydrogen, and oxygen atoms 4 major classes - carbohydrates - lipids - proteins - nucleic acids 39 40

11 Carbon Functional Groups The carbon that organic compounds always contain has several properties that make it particularly useful to living organisms. It can react with one to several hundred other carbon atoms forms large molecules of many different shapes. Many carbon compounds do not dissolve easily in water useful materials for building body structures. Carbon compounds are mostly or entirely held together by covalent bonds and tend to decompose easily organic compounds are a good source of energy. 41 Molecular groups which allow molecules to interact with other molecules 42 Carbohydrates Carbohydrates provide most of the energy needed for life and include sugars, starches, glycogen, and cellulose. Some carbohydrates are converted to other substances which are used to build structures and to generate ATP. Other carbohydrates function as food reserves. About 2-3% of total human body weight Carbohydrates are divided into three major groups based on their size: monosaccharides, disaccharides, and polysaccharides Monosaccharides Monosaccharides contain from three to seven carbon atoms and include glucose, a hexose that is the main energy-supplying compound of the body. Humans absorb only 3 simple sugars without further digestion in our small intestine glucose found in syrup or honey fructose found in fruit galactose found in dairy products 43 44

12 Disaccharides Disaccharides are formed from two monosaccharides by dehydration synthesis; they can be split back into simple sugars by hydrolysis. sucrose = glucose & fructose maltose = glucose & glucose lactose = glucose & galactose (lactose intolerance) Clinical Application: Lactose intolerance is a deficiency of the enzyme lactase. As a result undigested lactose remains in the feces and bacterial fermentation of lactose produces gas Polysaccharides Polysaccharides are the largest carbohydrates and may contain hundreds of monosaccharides. The principal polysaccharide in the human body is glycogen, which is stored in the liver or skeletal muscles. When blood sugar level drops, the liver hydrolyzes glycogen to yield glucose which is released from the liver into the blood Lipids = fats Formed from C, H and O Hydrophobic: mostly insoluble in polar solvents such as water Types of lipids triglycerides phospholipids steroids eicosanoids lipoproteins some vitamins 18-25% of body weight 47 48

13 Triglycerides Triglycerides Triglycerides are the most plentiful lipids in the body and provide protection, insulation, and energy At room temperature, triglycerides may be either solid (fats) or liquid (oils). Triglycerides provide more than twice as much energy per gram as either carbohydrates or proteins. Triglyceride storage is virtually unlimited. Excess dietary carbohydrates, proteins, fats, and oils will be deposited in adipose tissue as triglycerides Saturation of Triglycerides Determined by the number of single or double covalent bonds Saturated fats contain single covalent bonds and are saturated with hydrogen atoms: lard Monounsaturated are not completely saturated with hydrogen: olive and peanut oil Polyunsaturated fats contain even less hydrogen atoms: safflower oil, corn oil Clinical Application Essential fatty acids (EFA s) are essential to human health and cannot be made by the human body. They must be obtained from foods or supplements. Omega-3 and omega-6 fatty acids 51 52

14 Chemical Nature of Phospholipids head tails Phospholipids Phospholipids are important membrane components. They are amphipathic, with both polar and nonpolar regions. a polar head a phosphate group (PO 4 3- ) & glycerol molecule forms hydrogen bonds with water 2 nonpolar fatty acid tails interact only with lipids Steroids Four Ring Structure of Steroids Steroids have four rings of carbon atoms Steroids include sex hormone bile salts some vitamins cholesterol, with cholesterol serving as an important component of cell membranes and as starting material for synthesizing other steroids 55 56

15 Other Lipids Eicosanoids include prostaglandins and leukotrienes. Lipid type derived from a fatty acid called arachidonic acid prostaglandins = wide variety of functions modify responses to hormones contribute to inflammatory response prevent stomach ulcers dilate airways regulate body temperature influence formation of blood clots leukotrienes = allergy & inflammatory responses Body lipids also include fatty acids; fat-soluble vitamins such as beta-carotenes, vitamins D, E, Proteins Proteins are the most abundant and important organic molecules Basic elements: carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) Basic building blocks: 20 amino acids Proteins and K; and lipoproteins PLAY Protein Functions Support: structural proteins Movement: contractile proteins Transport: transport proteins Buffering: regulation of ph Metabolic regulation: enzymes Coordination and control: hormones Defense: antibodies Proteins: KEY CONCEPT control anatomical structure and physiological function determine cell shape and tissue properties perform almost all cell functions 59 60

16 Amino Acids Peptides Polypeptide: Primary Structure a long chain of amino acids Secondary Structure Hydrogen bonds form spirals or pleats 63 64

17 Tertiary Structure Secondary structure folds into a unique shape Quaternary Structure Final protein shape: several tertiary structures together Enzymes How Enzymes Work Enzymes are catalysts: proteins that lower the activation energy of a chemical reaction are not changed or used up in the reaction Highly specific Very efficient speed up reaction up to 10 billion times faster PLAY Enzymes 67 68

18 Protein Denaturation The function of a protein depends on its ability to bind to another molecule Hostile environments such as heat, acid or salts will change a protein s 3-D shape and destroy its ability to function raw egg white when cooked is vastly different Nucleic Acids: DNA and RNA Nucleic acids are large organic molecules, which store and process genetic information at the molecular level Deoxyribonucleic acid (DNA) forms the genetic code inside each cell and thereby regulates most of the activities that take place in our cells throughout a lifetime. Ribonucleic acid (RNA) relays instructions from the genes in the cell s nucleus to guide each cell s assembly of amino acids into proteins by the ribosomes Each gene of our genetic material is a piece of DNA that controls the synthesis of a specific protein. A molecule of DNA is a chain of nucleotides. A nucleotide includes: nitrogenous base (A-G-T- C) pentose sugar phosphate group DNA Structure Differs from DNA RNA Structure single stranded ribose sugar not deoxyribose sugar uracil nitrogenous base replaces thymine Types of RNA within the cell, each with a specific function messenger RNA ribosomal RNA transfer RNA 71 72

19 Adenosine Triphosphate (ATP) Temporary molecular storage of energy for use in cellular activities muscle contraction, transport of substances across cell membranes, movement of structures within cells and movement of organelles Consists of 3 phosphate groups attached to adenine & 5-carbon sugar (ribose) Formation & Usage of ATP Synthesis of ATP enzyme ATP synthase catalyzes the addition of the terminal phosphate group to ADP energy from 1 glucose molecule is used during both anaerobic and aerobic respiration to create 36 to 38 molecules of ATP Hydrolysis of ATP (removal of terminal phosphate group by enzyme -- ATPase) releases energy for cellular processes leaves ADP (adenosine diphosphate) 73 74