1. The Molecules of Life
Chapter 3

3. The Simplest Hydrocarbon
Methane = Carbon + Hydrogen

4. 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

5. 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

6. 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?

7. 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

8. 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

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

10. 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

11. 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

12. 4 Important Functional Groups
Many biological molecules have 2 or more functional groups
How do cells make large molecules out of smaller organic molecules

13. 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)

14. 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

15. 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

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

17. 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

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

19. 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

20. 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

21. 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