Chapter 5: The Molecules of Life

Organic Compounds Compounds in the natural world that contain the element carbon bonded to hydrogen. Hydrocarbons – contain only C & H (ex. CH4) Most organic compounds also include oxygen and some also have nitrogen, phosphorus and sulfur. Carbon can form thousands of different compounds because it can form 4 strong covalent bonds

Inorganic Compounds & Functional Groups Inorganic compounds do not contain carbon Ex) H2O, O2 A group of atoms within a molecule that interacts in predictable ways with other molecules is called a functional group Functional groups determine the properties of organic molecules. For example, hydrophilic groups (such as –OH) attract water and hydrophobic groups repel.

Polymerization During polymerization, building-block molecules called monomers (small compounds) are joined to become polymers (complex compounds) Macromolecules are very large polymers Polymer Monomers

Dehydration Synthesis & Hydrolysis Dehydration Synthesis: water is removed (-H from one molecule, -OH from another) so that a bond can form between molecules. Hydrolysis: water is added (-H to one molecule, -OH to another) so that a bond can be broken to separate molecules.

Self-Assessment Draw a molecule that has a 3-C (carbon) skeleton and a hydroxyl group on the middle carbon. (Hint: formula is C3H8O) Explain the connection between monomers and polymers. What molecule is released during the construction of a polymer? What is this process called? Draw at least three ways in which five carbon atoms can be drawn to make different carbon skeletons.

Compounds of Life (Biomolecules) There are four groups of organic compounds that are found in living things. Carbohydrates Proteins Lipids Nucleic Acids These compounds all come from our foods and are needed by our bodies.

DO NOW: The diagram below shows two amino acids, the monomers of a protein. Draw these amino acids in your notes. What has to happen for these two molecules to combine? (What must be done for bonds to be made in biological systems?) Represent this process by redrawing the amino acids bonded together and drawing the bi-product formed.

Dehydration Synthesis In living systems, bonds are made by removing water. An –OH from one molecule and an –H from the other combine to form water. The removal of these atoms provides “space” for the new bond to form, by leaving atoms with unfilled valence shells.

Carbohydrates

Carbohydrates: Monosaccharides Sugars Made of C, H, and O Can contain 2-7 carbons – most have 5 (pentoses) or 6 (hexoses) Breaking of their covalent bonds releases energy (food for cells) Monosaccharides (single sugars) Glucose (sugar green plants produce) Galactose (found in milk) Fructose (found in fruits)

Isomers The formula for all three monosaccharides glucose, fructose and galactose is C6H12O6 Although they contain the atoms in the same proportion, their structural arrangement differs. In aqueous solutions, most monosaccharides form ring structures as shown for glucose Also note the trademark functional groups of sugars, multiple hydroxyl groups and a carbonyl group

Disaccharides Formed when two monosaccharides are joined by dehydration synthesis (condensation) Examples: Sucrose Lactose Maltose

Carbohydrates: Polysaccharides Polysaccharides: complex sugars made up of many monosaccharides (polymer) Takes a long time to digest and break down polysaccharides into glucose through hydrolysis Taste is not sweet Starch: used in plants as an energy storage molecule Cellulose: makes up cell walls of plants; most abundant compound on Earth Glycogen: used by animals to store excess sugar

Self-Assessment Explain the difference between a monosaccharide and a disaccharide. Give an example of each. Compare and contrast starch, glycogen and cellulose. How do animals store excess glucose molecules? (two steps)

Lipids Non-polar; hydrophobic Triglycerides (Waxes, oils, fats), phospholipids and steroids Contain C, H & O, but lower proportion of oxygen than carbs Lipids store more energy than carbohydrates because they have twice as many energy rich (C-H) bonds than carbohydrates. (9 cal/g v. 4cal/g)

Categories of Lipids Trigylcerides (Neutral Fats) Phospholipids Glycerol & 3 fatty acids “tails” Fatty tissue – insulation & reserve energy Phospholipids Polar phosphate “head” and non-polar fatty-acid “tails” Amphiphilic (amphipathic) Make up plasma membranes Steroids 4 ring structure Found in cell membranes Base of steroid hormones; bile salts & vitamin D

Categories of Triglycerides Saturated -carbons are joined by all single bonds (not healthy) Unsaturated -2 carbons are joined by a double bond Polyunsaturated -carbons have many double bonds (most healthy)

Self-Assessment What property do all lipids share? What are the parts of a fat (triglyceride) molecule? Describe two ways that steroids differ from fats. What does the term “unsaturated fat” on a food label mean?

Proteins : Peptides A peptide bond is the covalent bond that joins amino acids A Polypeptide is a long chain of amino acids Note the water molecule lost when a peptide bond is formed –(dehydration synthesis) To break a bond, water would be added (hydrolysis)

Proteins Contains N,H,C, and O Proteins come from animal foods Proteins are polymers of Amino Acids All 20 amino acids are similar except for an “R” group A proteins amino acid sequence determines it’s shape which determines its function. If shape changes, function is disrupted, denaturing

Enzymes 1000’s of chemical reactions occur in the body (ex: digestion) Theses reactions need to be sped up Catalysts speed up chemical reactions by lowering the activation energy required to start the reaction. Enzymes, a type of protein, are biological catalysts

Self-Assessment State two “everyday examples of proteins. What are their functions? How are amino acids, polypeptides and proteins related? What parts of amino acids are the same between the 20 different amino acids? What part is the same? Heat can alter the shape of a protein. What affect will this probably have?

Types of Chemical Reactions Endothermic Exothermic Energy is absorbed (endo = enter) Energy is released (exo = exit)

Enzymes – A Closer Look Enzymes bind to a substrate at an “active site” Each enzyme is specific to a certain reaction (induced-fit hypothesis) Ex: Lactase only works on lactose to break it down into glucose and galactose. Lactase added to sucrose would not break it down into it’s monosaccharide monomers

Enzymes

Self-Assessment Explain the role of activation energy in a reaction. How does an enzyme affect activation energy? Describe how a substrate interacts with an enzyme.

Nucleic Acids Large molecules composed of C,H,O, N and P. The monomers are called nucleotides Two types of nucleic acids are RNA and DNA DNA: Hereditary info: Directions for making proteins Controls cellular activities RNA: Carries out the instructions of DNA to make proteins

DNA & RNA Structure

Self-Assessment What is the monomer of nucleic acids? Draw and label the three parts of a nucleotide. How are the functions of DNA and RNA related?

Summary Assessment Some food labels list the ingredient “partially hydrogenated vegetable oil.” This means that hydrogens have been added to some of the double bonds (creating single bonds instead) in the oil’s fatty acid chains. Does this make the food more or less healthy? Many humans are lactose-intolerant, meaning they cannot digest milk products containing the disaccharide lactose. Use the information learned in this chapter to hypothesize a cause of lactose intolerance. Which of the three polysaccharides you learned about in this chapter are most likely found in paper? Explain.