Chemistry of Life Unit 3

Matter  Everything is made of matter.  Chemical changes in matter are essential to all life processes.

Elements  Pure substances that cannot be broken down.  96% of the mass of living things is made of 6 elements:  Carbon (C)  Hydrogen (H)  Oxygen (O)  Nitrogen (N)  Phosphorus (P)  Sulfur (S) CHONPS

Atom  Parts of an atom: Nucleus – central core, contains protons and neutrons Proton – positively charged particles Neutron – no electric charge particles Electrons – negatively charged particles  An atom is the simplest particle of an element.  Too small to see, so scientists use models.

Molecule  Two or more atoms held together by chemical bonds.  Chemical bonds are attractions between two atoms.  Bonds contain chemical energy that can be released or absorbed in chemical reactions.

Covalent Bonds  Covalent bond forms when two atoms share electrons.  Very stable, strong bond.  Chemical Formula: O + 2H = H 2 0

Ionic Bonds  Ion: charged atom that has lost or gained an electron  Lost electron = positive ion (K +, Ca +, H +, Na + )  Gained electron = negative ion (Cl -, Br - )  Ionic bonds form when oppositely charged ions are attracted to each other.  Not as strong as covalent bonds.  Chemical Formula: Na + + Cl - =NaCl (salt)

Hydrogen Bonds  Attraction of weak charges between hydrogen and oxygen atoms.  Very important bond for organisms. Helps hold molecules together.  Chemical formula – H 2 O + H 2 O = 2H 2 O

Chemical Reactions  Reactants converted to products  Need energy input to begin – activation energy  May release energy (exothermic) or absorb energy (endothermic)  Most life processes are a series of chemical reactions. ReactantsProducts = making and breaking bonds

Enzymes  Enzymes control reactions that occur inside cells.  Catalysts – speed up reactions by lowering activation energy.  Each enzyme has an active site with a specific shape to interact with its substrate.  Made of protein.

Enzyme Action  Enzymes are not changed by the reaction.  Each enzyme controls one specific reaction.  Named for their reactions (eg. lactase breaks down lactose sugar in milk)

Factors Affecting Enzyme Activity  Every enzyme has optimal conditions for functioning  Affected by:  Temperature  pH  At extreme conditions, enzymes are denatured – structure changed so the enzyme no longer functions

Organic Compounds  Organic compounds are high energy biological molecules.  Composed of carbon and hydrogen  The importance of CARBON  Carbon forms 4 covalent bonds  Can easily bond to several other carbon atoms in chains and rings to form large complex molecules.

Macromolecules  Monomer – simple subunit of macromolecules  Polymer – many monomers linked together  Macromolecule – large organic polymers, essential to life processes 1. Carbohydrates – made of monosaccharides 2. Lipids – made of fatty acids 3. Proteins – made of amino acids 4. Nucleic Acids – made of nucleotides  Every cell has thousands of macromolecules forming specialized structures to carry out cell functions (energy, transport, waste, structure)

Carbohydrates  Monomer: monosaccharide  Structure: rings of carbon  Function: store energy  Examples: sugar, bread, potatoes  Monosaccharide – 1  Glucose, fructose  Disaccharide – 2  Sucrose, lactose  Polysaccharide – many  Starch, cellulose

Lipids  Monomer: fatty acids  Structure: long carbon chains  Hydrophobic - do not mix with water  Functions: energy, insulation, cell membrane  Example: butter, oil, wax, cholesterol, phospholipids  Saturated  Solid, ex: butter  Unsaturated  Liquid, ex: oil  Double bonds = kinked

Proteins  Monomer: amino acids (22 types)  Structure: complex folded shape  Amino acids linked by peptide bonds  Shape depends on sequence of amino acids  Sequence determined by genetic code  Functions: “workhorses” of the cell 1) Structure (hair, nails) 4) Movement (muscle fibers) 2) Transport (hemoglobin) 5) Defense (antibodies) 3) Regulation of cell functions (hormones, enzymes)

Nucleic Acids  Monomer: nucleotides  Structure: long strands  Function: carry genetic code for making proteins  Example: DNA and RNA

Water  Water is essential to life.  H 2 O – unique properties based on structure.  Water is a polar molecule  Electrons in covalent bond between H and O are shared unequally.  Oxygen is negative.  Hydrogens are positive. – + +

Hydrogen Bonds  Positive hydrogens of one H 2 O molecule are attracted to the negative oxygen of other H 2 O molecules. This attraction is a hydrogen bond.  Hydrogen bonds are relatively weak, but cause water to have unique properties.

Wringing out Water on the International Space Station Click for video

Properties of Water 1. Water molecules are cohesive and adhesive due to the nature of hydrogen bonding.  Cohesion – water molecules attracted to each other  Adhesion – water attracted to different materials 2. Water dissolves many substances (due to polarity): water in cells can carry nutrients in and wastes out. 3. Water absorbs heat when it evaporates: this allows organisms to release excess heat by sweating. 4. Ice floats: prevents lakes & oceans from freezing solid.

Effects of Cohesion  Capillary action- the ability of a liquid to flow in narrow spaces in opposition to external forces like gravity.  Surface tension- something denser than water can float or run across the surface. Click for video

pH Scale  pH measures the amount of H+ and OH- in a solution  The pH scale ranges from 0 to 14.  The pH of pure water is 7 (neutral).  A solution with a pH below 7 is acidic.  A solution with a pH above 7 is basic.  Organisms can tolerate only small changes in pH or proteins will denature, so they maintain constant pH.  Cells use buffers – solutions that resist changes in pH ACIDS NEUTRALBASES

Review questions 1. In what kind of bond are electrons shared? 2. In what kind of bond are electrons borrowed? 3. What type of charge does a proton have? 4. What is the weakest type of bond discussed today? 5. How many electrons are required in the outer energy level to provide stability?