The Molecules of Life

Chapter 3

The Simplest Hydrocarbon

• Methane = Carbon + Hydrogen

• 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

Biology and Society

Fig 3.1

A Sleep-Inducing Meal

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?

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

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)

Variations in Carbon Skeletons

• Simplest organic compounds are hydrocarbons• Hydrocarbons consist of carbon and hydrogen• Each C atom forms 4 bonds; each H atom forms 1 bond

Fig 3.2

Methane – Simplest Hydrocarbon

The 4 single bonds of C point to the corners of a hydrocarbon

Fig 3.3.

Tetrahedral = 4 triangular sides

Larger Hydrocarbons

• Main molecules in the gasoline we burn in our cars

• Hydrocarbons of fat molecules provide energy for our bodies

Fig 3.4

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

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

Dissolved in water 1 part of a glucose molecule can bond to

another part to form a ring – reversible process

Fig 3.9

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