Chemical Basis of Life 2.3

Transcription

1 Chemical Basis of Life 2.3 August 13, 212 Agenda General Housekeeping 2.3 Review Terminology Quiz Chapter 2 Assignments Stations Reading Building Molecules Review What is the significance of the valence shell of an atom? Compare the properties of ionic, covalent, and hydrogen bonds How do catalysts affect activation energy? 2.3 Chemical Constituents of Cells Objectives List the major groups of inorganic chemicals common in cells Describe the functions of various types of organic chemicals in cells Inorganic Compounds Inorganic compounds are structurally simple molecules that usually lack carbon - like the salt potassium chloride (KCl) Water Water is the most important and abundant inorganic compound in all living systems Water s most important property is polarity, the uneven sharing of valence electrons that enables reactants to collide to form products Sodium and Chloride ions dissolve in the polar water molecules Water as a Solvent In a solution, the solvent dissolves the solute Substances which contain polar covalent bonds and dissolve in water are hydrophilic, while substances which contain non-polar covalent bonds are hydrophobic The polarity of water and its bent shape allow it to interact with several neighboring ions or molecules Water s role as a solvent makes it essential for health and survival Properties of Water Water has a high heat capacity, meaning it can absorb or release a relatively large amount of heat with only a modest change in its own temperature This property is due to the large number of hydrogen ions in water Heat of vaporization (amount of heat needed to change from a liquid to a gas) is also high Evaporation of water from the skin removes large amounts of heat

2 Water serves as the medium for most chemical reactions in the body May participate as a reactant or product in some reactions Hydrolysis involves the addition of water to break large molecules down into smaller molecules In Dehydration Synthesis, water is produced as smaller molecules join to form a larger molecule Water is a major component of mucus and other lubricating fluids Oxygen Oxygen (O 2 ) enters the body via the respiratory organs and are transported throughout the body by blood Red blood cells bind and carry oxygen Cellular organelles use oxygen to release energy from glucose and other nutrients Drives metabolic activities Carbon Dioxide Carbon dioxide (CO 2 ) is produced as a waste product when certain metabolic processes release energy, and it is exhaled from the lungs Salts Is a compound composed of oppositely charged ions Abundant in tissue and fluids Important in metabolic processes, including transport of substances into and out of cells, muscle contraction, and nerve impulse conduction Organic Compounds Organic compounds always contain carbon and are usually large, complex molecules Usually contain hydrogen Always have covalent bonds The chain of carbon atoms in an organic molecule is called a carbon skeleton Hydrocarbons are carbons bonding to hydrogen Functional groups attach to the carbon skeleton Macromolecules Very large molecules are called macromolecules Polymers if all the monomer subunits are similar) Isomers have the same molecular formulas but different structures Glucose & galactose are both C 6 H 12 O 6 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 Carbohydrates are divided into three major groups based on their size: monosaccharides, disaccharides, and polysaccharides Monosaccharides are the simplest sugars 5 carbon sugars are used in nucleic acids 6 carbon sugars are the most easily recognizable in our diet Disaccharides are made by combining 2 monosaccharides by removing a water molecule (dehydration synthesis): - Glucose + Fructose = Sucrose - Glucose + Galactose = Lactose

3 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 Starches are polysaccharides formed from glucose by plants Cellulose is a polysaccharide formed from glucose by plants that cannot be digested by humans Lipids Like carbohydrates, they contain carbon, hydrogen, and oxygen Unlike carbohydrates, they do not have a 2:1 ratio of hydrogen to oxygen They have few polar covalent bonds, which makes them hydrophobic and mostly insoluble in water They combine with proteins (lipoproteins) for transport in blood The simplest lipids are the fatty acids Used to synthesize triglycerides and phospholipids, and can be catabolized to generate ATP Consists of a carboxyl group and a hydrocarbon chain Saturated fatty acids contain only single covalent bonds (saturated with H atoms) Unsaturated fatty acids contain one or more double covalent bonds and has a kink/bend at the site of the double bond Triglycerides are the most plentiful lipids in the body and provide protection, insulation, and energy (both immediate and stored) At room temperature, triglycerides may be either solid (fats) or liquid (oils) Triglyceride storage is virtually unlimited Excess dietary carbohydrates, proteins, fats, and oils are deposited in adipose tissue as triglycerides Triglycerides provide more than twice as much energy per gram as either carbohydrates or proteins Consists of a glycerol molecule and three fatty acid molecules Fat is a triglyceride that is a solid at room temperature Mostly saturated because the fatty acids lack double bonds in their hydrocarbon chains Oil is a triglyceride that is a liquid at room temperature Mostly unsaturated and can be either monounsaturated or polyunsaturated Phospholipids are important membrane components Both polar and nonpolar regions make them soluble in both water and fats This is called amphipathic, they are both hydrophilic and lipophilic They have a polar head formed from a phosphate group (PO 4-3 ) and a glycerol molecule (forms H-bonds with water), and 2 nonpolar fatty acid tails that interact only with lipids Phospholipids have a polar head and 2 non-polar tails Steroids are lipids molecules that have four rings of carbon atoms Sex hormones Bile salts Some vitamins Cholesterol, which serves as an important component of cell membranes and as starting material for synthesizing other steroids

4 Proteins Steroids are based on the lipid cholesterol molecule They include the molecules used as sex hormones, as well as other hormones used in coping with stress (cortisol) Proteins are constructed from combinations of different amino acids 2 human amino acids All amino acids (a.a.) have the same basic structure - only the R group changes Primary Structure is the unique sequence of a.a. that are linked by covalent peptide binds to form a polypeptide chain Secondary Structure is the repeated twisting or folding of neighboring a.a. in the polypeptide chain Tertiary Structure is the 3-D shape of a polypeptide chain and determines how it will function Quarternary Structure is the arrangement of individual polypeptide chains relative to one another Proteins are large molecules that contain carbon, hydrogen, oxygen, and nitrogen The normal adult body is 12-18% protein Dipeptides are formed from 2 amino acids joined by a covalent bond called a peptide bond This process involves dehydration synthesis Polypeptide chains contain 1 to 2 amino acids Fibrous proteins are insoluble in water and their polypeptide strands form long strands that are parallel to each other Structural function Globular proteins are more or less soluble in water and their polypeptide chains are spherical in shape Metabolic functions There are 4 levels at which proteins are structurally organized : Primary (1 ) Secondary (2 ) Tertiary (3 ) Quaternary (4 ) The resulting shape of the protein greatly influences its ability to recognize and bind to other molecules Denaturation (loss of protein structure) by a hostile environment causes loss of its characteristic shape and function An egg white turning solid white when exposed to high temperatures is an example of protein denaturation

5 Enzymes Enzymes are special proteins that catalyze (speed up) metabolic reaction in all living cells Some enzymes consist of two parts An apoenzyme protein portion A non-protein portion called a cofactor Metal ions or coenzymes The substrate is the substance upon which an enzyme has its effect In this regard, enzymes are highly specific Enzymes are subject to a variety of cellular controls Enzymes speed up chemical reactions by increasing frequency of collisions, lowering activation energy, and properly orienting colliding molecules Nucleic Acids Nucleic acids are huge organic molecules composed of monomeric nucleotides They contain carbon, hydrogen, oxygen, nitrogen, and phosphorus, and form the principle molecules that contain our genetic code DNA and RNA Nucleic acids are universal in living things These molecules carry genetic information as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) By controlling the formation of proteins, the genetic code regulates most of the activities that take place in our cells throughout a lifetime DNA molecules remain inside the nucleus of cells and are the master template of our genetic code RNA is a slightly different nucleic acid macromolecule that relays instructions from the nucleus to guide assembly of amino acids into proteins in the cytoplasm The basic units of nucleic acids are nucleotides, composed of a nitrogenous base, a pentose sugar, and a phosphate The nucleotides of DNA and RNA are joined to a sugarphosphate backbone to make a long chain There are 2 sugarphosphate strands of DNA, joined in the middle by hydrogen bonds from one nucleotide to another RNA structure differs from DNA in that it is single stranded (instead of double stranded), ribose replaces the sugar deoxyribose, and uracil is the nitrogenous base that replaces thymine There are 3 types of RNA within the cell, each with a specific function: Messenger RNA Ribosomal RNA Transfer RNA Nucleic acids are also used in making a very important energy-carrying molecule in the body called adenosine triphosphate (ATP) ATP is used as a temporary storage of energy that is being transferred from exergonic catabolic reactions to cellular activities Clinical Connections Fatty Acids in Health and Disease Essential Fatty Acis (EFAs) cannot be made by the human body and must be obtained from foods or supplements Omega-3 fatty acids, omega-6 fatty acids, and cis-fatty acids Omega-3 and omega-6 are polyunsaturated fatty acids that are believed to work together to promote health Lowers total cholesterol, raises HDL, lowers LDL, decreases bone loss by increasing calcium utilization, promotes wound healing, improves mental function Omega-3: flaxseed, fish oils, walnuts Omega-6: cereal, bread, white rice, eggs, liver

6 Cis-fatty acids are used by the body to produce hormonelike regulators and cell membranes However, when hydrogenated, they are changed to unhealthy trans-fatty acids The H atoms are on opposite sides of the double bond in an unsaturated fat Hydrogenation is used to make vegetable oils solid at room temperature and less likely to turn rancid Found in commercially baked goods, some margarines, and fried foods Increases total cholesterol, decreases HDL, increases LDL, increases triglycerides, increases the risk of heart disease and other cardiovascular diseases Artificial Sweeteners Aspartame (NutraSweet and Equal) Saccharin (Sweet N Low) Sucralose (Splenda) 1 s of times sweeter than sucrose Zero calories because they pass through the body without being metabolized Does not cause tooth decay Assignments Finish Chapter 2 Review WS (due next class) Read Sections Rank your top five choices for your Research Paper Mid-Term Assessment #1 in one week! On Chapters 1 & 2