Chapter 4 Chemical Basis of Life Everything consists of matter (biotic and abiotic) Matter is anything that occupies space and has mass Matter is composed of elements Elements – a pure substance that can’t be broken down into simpler substances

4.1 - Life requires about 25 elements. What is an element? element – a pure substance that cannot be broken down into simpler substances There are 25 essential elements to life. 96% of our body is made oxygen, carbon, hydrogen and nitrogen The other elements in our bodies are called trace elements – elements critical to our health even though they are found in small amounts

4.1 - continued How are elements and compounds related? compound – a substance that consists of two or more elements - A compound contains elements in a fixed ratio. - The properties of a compound are different than those of its elements.

4.2 – Chemical Properties are based on the structure of atoms. atom - a specific type of element Identify the 3 parts of an atom. Each atom contains 3 particles: - proton – positive charge; located in nucleus - neutron – neutral charge; located in nucleus - electron – negative charge; located in electron cloud Most of the area of an atom is the electron cloud and most of the mass is in the nucleus.

ATOMIC PICTURE

4.2 - continued What does the atomic number tell us about an atom? Each atom is unique because of its: - atomic number – the number of protons in an atom - mass number – the number of protons and neutrons in an atom

4.2 - continued Each element can have several variations called isotopes. An isotope is when an atom has the same number of protons as other atoms of the same element but has a different number of neutrons. Each element contains different numbers of isotopes. radioactive isotopes – occur when the nucleus decays over time and gives off radiation (energy); these are used in medicine and research

4.2 - continued Electrons are held in energy levels around the nucleus. The electrons in the outer most energy level determines how atoms react, these are called valence electrons. Energy levels and electrons they can hold 1 ST LEVEL= 2 ELECTRONS (MAX) 2 ND LEVEL= 8 ELECTRONS (MAX) 3 RD LEVEL= 18 ELECTRONS (MAX) 4 TH LEVEL= 32 ELECTRONS (MAX)

PICTURE OF ENERGY LEVELS

4.3 – Chemical bonds join atoms to one another. Atoms may gain, lose, or share electrons with other elements in order to create compounds. Identify 2 types of chemical bonds. Types of bonds: 1. ionic bonding – occurs when atoms gain or lose electrons in order to form a compound - When atoms gain or lose electrons, they create a charged particle – this is called an ion - Types of ions: A. cations – positive charge B. anions – negative charge

4.3 - continued 2. covalent bonding – this is where 2 or more atoms share electrons - There are no ions involved. - Two or more atoms held together by covalent bonds form molecules.

PICTURE OF COVALENT BONDING

WATER MOLECULE

4.3 – continued chemical reaction – breaking of old chemical bonds and the formation of new bonds to form new substance - chemical equation – an expression that is used to describe a chemical reaction A. reactants – the starting materials for a chemical reaction (left side) B. products – the ending materials in a chemical reaction (right side)

4.3 - continued Chemical equations must have the same number of atoms of each element on both sides of the equation. The atoms in a compound are not created or destroyed during a chemical reaction – they are simply rearranged ---- this is the Law of Conservation of Mass.

4.4 – Life depends on the unique properties of water. 3. hydrogen bonding – a weak attraction between the hydrogen atom of one molecule and the slightly negative atom in another molecule - This is called a “polar” molecule and is seen in water (hydrogen has a + charge and oxygen a – charge). - Hydrogen bonding causes water to have unique properties.

4.4 - continued Unique properties of water: 1. Most liquids when cooled get smaller, water expands when cooled. 2. Most objects have a higher density when they are a solid; water has a higher density when it’s a liquid. 3. cohesion – the ability of water molecules to stick together

4.4 - continued 4. adhesion – the ability of water molecules to stick to other items 5. Water loses/gains temperature slower than other substances.

4.4 - continued In an aqueous solution, a small amount of particles break apart into ions (H+ and OH-). Explain the difference between and acid and a base. - acid – a compound that donates H+ ions to a solution - base – a compound that removes H+ ions from a solution (done by donating OH- ions)

4.4 - continued pH (potential hydrogen) refers to the amount of hydrogen ions in a solution. The “pH” is measured by the pH scale acids neutral bases The pH of our body allows most chemical processes to work correctly (if the pH changes we will be harmed).

5.1 – Carbon is the main ingredient of organic molecules. What is the difference between an organic compound and an inorganic compound? Types of molecules: 1. organic molecules – contain carbon (called carbon skeletons) like glucose 2. inorganic molecules – lack carbon (no carbon skeleton) like water and ` oxygen

5.1 - continued Two terms are used to describe the size of a molecule: 1. monomer – small, simple units of molecules 2. polymer – complex chain of many monomers

5.1 - continued Polymer chains are made by adding monomers – this involves removing water and is called a dehydration reaction. Polymer chains are broken down by adding water and is called a hydrolysis reaction.

5.2 – Carbohydrates provide fuel and building material. Describe a carbohydrate. carbohydrates (sugars) – contain carbon, oxygen and hydrogen in the ratio of 1 carbon, 2 hydrogen and 1 oxygen Function: - Carbohydrates provide energy for us and serve as building materials for cells.

5.2 - continued Types of carbohydrates: 1. monosaccharides – small sugars – glucose and fructose – example is honey 2. disaccharides – 2 monosaccharides– sucrose and maltose 3. polysaccharides – large chains of sugars– starch, glycogen and cellulose (in plants)

5.3 – Lipids include fats and steroids. lipid – hydrophobic molecules that include fats, oils, phospholipids, and steroids Types of lipids: 1. fats – consist of a 3-carbon backbone called glycerol attached to three fatty acids, store energy, provide your body with insulation, and protect organs

5.3 - continued Describe two types of fats. A. saturated – all three fatty acid chains contain the maximum number of hydrogen atoms - Diets high in saturated fats are unhealthy because they promote the buildup of deposits called plaques in the walls of blood vessels that contribute to heart disease.

5.3 - continued B. unsaturated fats – contain less than the maximum number of hydrogen atoms in one or more of the fatty acid chains - Fats in fruits vegetables and fish are generally unsaturated. 2. steroid – lipid molecule in which the carbon skeleton forms four fused rings (ex. estrogen, testosterone, and cholesterol)

5.4 – Proteins perform most functions in cells. Identify 2 functions of proteins. proteins – large molecules that have the following functions: 1. Serve as building materials for cells. 2. Carry out chemical reactions. 3. Pump small molecules. 4. Aid in cell defense. PROTEINS ARE THE BASIC BUILDING BLOCKS OF THE HUMAN BODY

5.4 - continued The monomers of proteins are called amino acids – consist of a central carbon atom bonded to four partners (hydrogen, carboxyl group, amino group, and a side group). Several amino acids form polypeptides. Several polypeptides form proteins. Each protein is different because of the sequence of amino acids.

5.5 – Enzymes are proteins that speed up specific reactions in cells. What is an enzyme? enzyme - special protein that: 1. causes a specific type of reaction. 2. have a special shape, called the active site. 3. reacts on specific reactants called substrates. 4. are affected by temperature and pH.

5.5 - continued Enzymes control the speed of chemical reactions by lowering the activation energy - energy needed for reaction to occur. Thus – they speed up reactions – so they are called catalysts. Explain the effects of pH and temperature on enzymes. When enzymes are exposed to extreme temperatures or pH, they become denatured – which means the enzyme loses its shape and effectiveness.