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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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