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Zoology – The Chemical Basis of Animal Life I. Attributes of Living Organisms A. It would seem a simple thing to define life, but it actually isn’t. Many of the characteristics of life can be found in nonliving things. 1. It is easier to describe the characteristics of life. B. Composition and Structure 1. The hierarchy of life. An ascending order of complexity: a. Cells – the smallest unit of life (e.g. a heart muscle cell) b. Tissues – cells that have a similar appearance and are organized together to perform a common function (e.g. the heart muscle) c. Organs – 2 or more tissues that combine to perform a common function (e.g. the heart – including muscle, epithelial, nervous, and connective tissues) d. Organ systems – 2 or more organs that share a common function (e.g. the cardiovascular system – the heart & its blood vessels) e. Organism – there are 11 organ systems in a human being. C. Growth – changes in size and shape a plant undergoes from origin to adult 1. Growth usually results from the production of new cells. 2. Cell lineages differentiate and become adult tissues. 3. Growth is influenced both by genetics and the environment D. Reproduction - Organisms produce offspring, which resemble the parents 1. Reproduction can occur sexually or asexually E. Response to Environmental Stimuli – adapting to their environment F. Homeostasis – the tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, despite outside changing conditions. G. Metabolism– all of the biochemical reactions taking place in an organism. 1. Respiration – releasing the energy of carbohydrate (C6H12O6) bonds to produce carbon dioxide (CO2) and water (H2O). This energy is caught and used to form ATP (the energy currency of cells). H. Complexity of Organization 1. Living organisms are made up of far more complex molecules than nonliving matter. 2. These complex molecules are called macromolecules and include… a. Carbohydrates which are chains of simple sugars b. Lipids, which include triglycerides and cholesterol c. Proteins, which in turn are made up of chains of amino acids d. Nucleic acids which include DNA and RNA II. Chemical Basis of Life A. The Elements – units of matter 1. Matter occupies space, has mass, and is composed of elements. 2. Matter exists in 4 states: solid, liquid, gas, and plasma B. The Atom: Smallest stable subdivision of an element 1. Atoms have a nucleus where you find the protons and neutrons. a. Each proton has a positive charge. 2. Circling around the nucleus are electrons. a. Each electron has a negative charge. b. The electrons occupy electron (or valence) shells. c. The shells can only hold a specific number of electrons. 3. Atoms and molecules try to be as electrically stable as possible. Two ways they can achieve this stability include… a. Remaining electrically neutral (i.e. the number of electrons must equal the number of protons). Any atom or molecule with a charge is an ion. 1) If an atom or molecule has more electrons than protons, it will become negative. a) This is an anion. Important anions in biology are chlorine (Cl-) and bicarbonate (HCO3-). 2) If an atom or molecule has more protons than electrons, it will become positive. a) This is a cation. Important cations in biology are potassium (K+), sodium (Na+), and calcium (Ca++). b. Filling their outermost electron shells (known as valence shells). C. Elements can combine to form molecules through chemical bonds. 1. There are 3 types of chemical bonds: a. Ionic bonds – A bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion. (An example is table salt, Na+Cl-) b. Covalent bonds - a chemical bond that involves sharing a pair of electrons between atoms in a molecule. (An example is the phosphoanhydride bonds in ATP which store potential energy.) c. Hydrogen bonds – A hydrogen atom of one molecule is attracted to an electronegative atom (especially a nitrogen, oxygen, or fluorine atom) of another molecule. (An example is the hydrogen bonds holding complementary base pairs together in DNA.) D. Acids, Bases, Buffers, and Salts 1. The concentration of ions is commonly expressed in terms of the pH scale. a.The pH scale is measured from 0 to 14. 1) Pure water pH = 7 (neutral) 2) Anything with a pH below 7 is acidic 3) Anything with a pH above 7 is alkaline (basic) b. The pH scale is a negative logarithmic scale with a base number of ten. 1) Thus, a solution with a pH of 2 is 10 times more acidic than a solution with pH of 3 2. Acids - release hydrogen (H+) ions when dissolved in water 3. Bases - release negatively charged hydroxyl (OH-) ions when dissolved in water 4. Buffers - Substances that enable solutions to resist pH changes when an acid or base is added. c. Buffers are very important in helping organisms maintain a relatively constant pH. 5. Salts – usually crystalline solid compounds that formed, or can be regarded to have formed, from an acid and a base by replacement of one or more hydrogen atoms in the acid molecules by positive ions from the base d. e.g. Table salt, Na+ClIII. The Molecules of Animals A. The chemicals that enter into, or are produced by, metabolic reactions are divided into 2 large groups: 1. Inorganic molecules – lack carbon atoms 2. Organic molecules – contain carbon atoms – we are carbon-based life forms. The important groups of organic molecules in animals include: a. Carbohydrates b. Lipids c. Proteins d. Nucleotides e. Nucleic acids B. Living organisms are made up of far more complex molecules than nonliving matter. Polymers (macromolecules) are formed when 2 or more small monomers bond together. 1. Bonding between monomers occurs by dehydration synthesis and is controlled by enzymes. a.Dehydration synthesis – removal of water in the formation of a bond 1) e.g. Amino acids joining to become a polypeptide (protein). 2) e.g. Monosaccharides joining to form a polysaccharide (starch). 2. Bonds between monomers are broken by hydrolysis a.Hydrolysis – occurs when a hydrogen becomes attached to one monomer and a hydroxyl group to the other. 1) e.g. Table salt dissolving in water 2) e.g. ATP ADP + Pi b. Energy is released C. Carbohydrates – animal’s major source of energy, the most abundant organic compounds in nature. Most animals use mitochondria to release energy stored in carbon-hydrogen bonds of sugar and starches. This process is called cellular respiraiton. 1. Carbohydrates are composed of C, H, and O in a ratio of [CH2O]n or 1:2:1 a.e.g. Glucose is C6H12O6. Deoxyribose is C5H10O5. b. Sugars end with the suffix –ose. 2. There are 3 basic kinds of carbohydrates: monosaccharides, disaccharides, and polysaccharides. 3. Monosaccharides – simple sugars with backbones of 3 to 7 carbon atoms a.e.g. Glucose and fructose 4. Disaccharides – formed when two monosaccharides bond together by dehydration synthesis. a.e.g. Sucrose (table sugar) = glucose + fructose; maltose (malt sugar - building block of starch) = glucose + glucose; lactose (milk sugar) = glucose + galactose 5. Polysaccharides – formed when several to many monosaccharides bond together. SUGAR IS ENERGY. WITHOUT ENERGY, CELLS DIE. PROBLEM: SUGARS CRYSTALLIZE & POP CELLS. CELLS DIE. POLYSACCHARIDES ARE CHAINS OF SUGARS THAT CANNOT CRYSTALLIZE. ANIMALS STORE SUGARS IN A CHAIN CALLED GLYCOGEN. D. Lipids - fatty or oily substances that are insoluble in water. The most common lipids in animals are fats. 1. Typically store twice as much energy as carbohydrates a.Important as long term energy reserves and as structural components of cells. e.g. chloesterol 2. Contain carbon, hydrogen, and oxygen, but have proportionately less oxygen than carbohydrates 3. Fats and oils are produced from one molecule of glycerol & 3 fatty acid molecules. a.Most fatty acids consist of a chain with 16 to 18 carbon atoms. 1) Saturated fats - with hydrogen atoms attached to every available bonding site on carbons of fatty acid, and with no double bonds (Solid at room temperature) 2) Unsaturated fats - with fewer hydrogen atoms and with at least one double bond between carbon atoms (Liquid at room temperature) 4. Phospholipids – constructed like fats, but one of the fatty acids is usually replaced by a phosphate group a.Important components of plasma membranes & other cellular membranes E.Proteins, polypeptides, and amino acids 1. Proteins are structural material, energy sources, and regulate chemical reactions (as enzymes) in cells. 2. Proteins are long chains of amino acids. a.The amino acids are joined by peptide bonds. Hence, proteins are also referred to as polypeptides. b. Each amino acid is composed of: 1) Amino group (-NH2) 2) Carboxyl group (-COOH) 3) R group - can vary from one hydrogen to a complex ring a) R groups are distinctive for each of the 20 amino acids found in living cells. 3. Proteins have complex structures. a.Primary Structure - Sequence of amino acids fastened together by peptide bonds b. Secondary Structure - Formation of an alpha helix or of pleated sheets due to hydrogen bonding between amino acids c. Tertiary Structure - Further coiling or folding maintained by interactions among R groups (3 dimensional shape) d. Quaternary Structure - Association of more than one polypeptide to form a single functional protein 4. Enzymes – mostly large, complex proteins that function as biological catalysts under specific conditions. (A special type of RNA can also function as an enzyme.) a.Enzymes do the following: 1) Break bonds and allow new bonds to form, facilitating chemical reactions 2) Speed up reaction times (similar to stirring or heating sugar to get it to dissolve faster in tea.) 3) Lower the energy of activation (the minimal amount of energy needed to cause molecules to react with one another) b. Enzymes temporarily bond with a substrate. 1) Substrates fit into the active sites of enzymes. a) The reaction occurs rapidly & products are released c. Enzymes remain unchanged in the reaction & usually go on to catalyze further reactions. d. Enzyme names end in -ase, e.g., maltase, lactase F. Nucleic Acids – very large, complex polymers that are vital to internal cellular communication and cell functioning. 1. There are two types: a.DNA – deoxyribonucleic acid b. RNA – ribonucleic acid 2. DNA consists of a double helix of repeating subunits of nucleotides. a.Nucleotides are composed of a nitrogenous base, a five-carbon sugar and a phosphate. 3. Nucleotides include one of 4 different nitrogenous bases. The bases pair with hydrogen bonds. a.Cytosine always pairs with Guanine. b. Adenine always pairs with Thymine. 4. DNA forms a double helix. 5. DNA contains genes that code the information that determines the form and structure of an organism. a.DNA can be passed on from generation to generation without change. 6. RNA occurs as a single strand and is involved in protein synthesis. a.The sugar is ribose (as opposed to deoxyribose in DNA) b. The nitrogenous base Uracil replaces the Thymine found in DNA