1. The Molecules of Life Figures 3.1 – 3.7
CHAPTER 3
The Molecules of Life
Figures 3.1 – 3.7

2. Americans consume an average of 140 pounds of sugar per person per year
Cellulose, found in plant cell walls, is the most abundant organic compound on Earth

3. A typical cell in your body has about 2 meters of DNA
A typical cow produces over 200 pounds of methane gas each year

4. BIOLOGY AND SOCIETY: GOT LACTOSE?
Milk is among the healthier foods you can eat
It is rich in many nutrients
But milk-containing foods make some people ill
This is called lactose intolerance

5. Lactose intolerance can be managed by
People who are lactose intolerant do not produce enough of the enzyme lactase
Their cells cannot break down and absorb lactose
Lactose intolerance can be managed by
Eating lactose-free foods
Ingesting lactase in pill form
Figure 3.1

6. ORGANIC MOLECULES A cell is mostly water
The rest of the cell consists mostly of carbon-based molecules
Organic chemistry is the study of carbon compounds

7. Carbon is a versatile atom
Carbon Chemistry
Carbon is a versatile atom
It has four electrons in an outer shell that holds eight
Carbon can share its electrons with other atoms to form up to four covalent bonds

8. Carbon can use its bonds to
Carbon skeletons vary in length
Attach to other carbons
Form an endless diversity of carbon skeletons
Carbon skeletons may be unbranched or branched
Carbon skeletons may have double bonds,
which can vary in location
Figure 3.2
Carbon skeletons may be arranged in rings

9. The simplest organic compounds are hydrocarbons
These are organic molecules containing only carbon and hydrogen atoms
The simplest hydrocarbon is methane
Structural
formula
Ball-and-stick
model
Space-filling
model
Figure 3.3

10. The hydrocarbons of fat molecules provide energy for our bodies
Larger hydrocarbons
Are the main molecules in the gasoline we burn in our cars
The hydrocarbons of fat molecules provide energy for our bodies
Figure 3.4

11. Each type of organic molecule has a unique three-dimensional shape that defines its function in an organism
The molecules of your body recognize one another based on their shapes
Receptor
molecule
Transmitting
cell
Receiving
cell
Signal
molecule
Figure 3.5

12. 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

13. Some common functional groups
Hydroxyl group
Carbonyl group
Amino group
Carboxyl group
Found in alcohols
and sugars
Found in amino acids
and urea in urine (from
protein breakdown)
Found in amino acids,
fatty acids, and some
vitamins
Found in sugars
Figure 3.6

14. Giant Molecules from Smaller Building Blocks
On a molecular scale, many of life’s molecules are gigantic
Biologists call them macromolecules
Examples: proteins, DNA

15. Most macromolecules are polymers
Polymers are made by stringing together many smaller molecules called monomers
Cells link monomers by a process called dehydration synthesis
Short polymer
Monomer
Longer polymer
(a) Dehydration synthesis of a polymer
Figure 3.7A

16. Organisms also have to break down macromolecules
Cells do this by a process called hydrolysis
(b) Hydrolysis of a polymer
Figure 3.7B