The Molecules of Life Chapter 3 The Simplest

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 to be an effective sleep aid Fig 3. 1

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 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 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 CO 2 as waste • Monosaccharides also provide cells with carbon skeletons that can be used as raw material