The Molecules of Life Chapter 3

The Simplest Hydrocarbon Methane = Carbon + Hydrogen

Biology and Society Thanksgiving dinner: carbohydrates (mashed potatoes); fats (butter/gravy); proteins (meat) After finishing a huge Thanksgiving dinner many people feel especially lethargic - many think that turkey makes you sleepy - is there a biological basis to this claim? Turkey meat is high in trytophan - it is converted to serotonin, a chemical that can act on the brain to promote sleep

A Sleep-Inducing Meal Tryptophan must be taken on an empty stomach Fig 3.1 Tryptophan must be taken on an empty stomach to be an effective sleep aid

Organic Molecules A cell is mostly water but the rest consists mainly of carbon based molecules Compounds that contain carbon are called organic compounds Carbon has the ability to form the large, complex diverse, molecules necessary for life functions Why are carbon atoms so versatile as molecular ingredients?

Carbon Chemistry Carbon a versatile atom has 4 electrons in an outer shell that holds 8 - carbon can share its electrons with other atoms to form up to 4 covalent bonds Carbon can use its bonds to attach to other carbons to form an endless diversity of carbon skeletons - each carbon in an organic molecule can branch off in up to 4 directions Carbon atoms of organic molecules can also bond with other elements (hydrogen, oxygen, nitrogen) Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Variations in Carbon Skeletons Fig 3.2 Simplest organic compounds are hydrocarbons Hydrocarbons consist of carbon and hydrogen Each C atom forms 4 bonds; each H atom forms 1 bond

Methane – Simplest Hydrocarbon Tetrahedral = 4 triangular sides Fig 3.3. The 4 single bonds of C point to the corners of a hydrocarbon

Larger Hydrocarbons Main molecules in the gasoline we burn in our cars Fig 3.4 Main molecules in the gasoline we burn in our cars Hydrocarbons of fat molecules provide energy for our bodies

Functional Groups Each type of organic molecule has a unique 3-dimensional shape that defines its function in an organism - the molecules of your body recognize one another based on their shapes The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton - these atoms are called functional groups Functional groups behave consistently from one organic molecule to another

4 Important Functional Groups Many biological molecules have 2 or more functional groups How do cells make large molecules out of smaller organic molecules

Building Blocks On a molecular scale, many of life’s molecules are gigantic - biologists call them macromolecules (macro = ‘big’) such as DNA, carbohydrates, proteins Most macromolecules are polymers - polymers are made by stringing together many smaller molecules called monomers - cells link monomers together through a dehydration reaction (removes a molecule of water) Organisms break down macromolecules (digestion) - cells do this by a process called hydrolysis (hydro = ‘water’ lyse = ‘break’; to break with water)

Dehydration Reaction Synthesis – a polymer grows in length when an incoming monomer and the monomer at the end of the existing chain contribute to the formation of a water molecule, the monomers then replace their lost covalent bonds with a bond to each other

Hydrolysis Breaking a polymer chain – hydrolysis reverses the process by breaking down the polymer with the addition of water molecules, which break the bonds between monomers

Biological Molecules There are 4 categories of large molecules in cells: Carbohydrates Lipids Proteins Nucleic Acids

Carbohydrates ‘Carbs’ - from small sugar molecules in soft drinks to long starch molecules in pasta and potatoes - serve as a primary source of dietary energy - used as building material to form the body of a plant Monosaccharides (mono = ‘one’, and sacchar = ‘sugar’) are simple sugars: - glucose found in sports drinks - fructose found in fruits Monosaccharides glucose and fructose are isomers - they have the same molecular formula, but their atoms are arranged differently

Isomers 2 trademarks of sugars: hydroxyl groups and a carbonyl group Fig 3.8 2 trademarks of sugars: hydroxyl groups and a carbonyl group

Isomers Molecules that have the same molecular formula but different structures - because shape is so important minor differences in the arrangement of atoms give isomers different properties - shape difference gives fructose a taste considerably sweeter than glucose In aqueous solutions, monosaccharides form rings

Ring Structure of Glucose Fig 3.9 Dissolved in water 1 part of a glucose molecule can bond to another part to form a ring – reversible process

Glucose Monosaccharides, particularly glucose, are the main fuel that cells use for cellular work Cells break down glucose molecules and extract their stored energy - give off CO2 as waste Monosaccharides also provide cells with carbon skeletons that can be used as raw material