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Molecules of Life
Chapter 3
Section 2 Molecules of Life
Carbohydrates
• Carbohydrates are organic compounds composed
of carbon, hydrogen, and oxygen in a ratio of
about one carbon to two hydrogen atoms to one
oxygen atom.
• Carbohydrates are a source of energy and are
used as structural materials in organisms.
Chapter 3
Section 2 Molecules of Life
Carbohydrates
• Monosaccharides
– Carbohydrates are made up of monomers
called monosaccharides.
• Disaccharides and Polysaccharides
– Two monosaccharides join to form a double
sugar called a disaccharide.
– A complex sugar, or polysaccharide, is made of
three or more monosaccharides.
Chapter 3
Section 2 Molecules of Life
Proteins
• Proteins are organic compounds composed
mainly of carbon, hydrogen, oxygen, and
nitrogen.
• Proteins have many functions including structural,
defensive, and catalytic roles.
Chapter 3
Section 2 Molecules of Life
Proteins
• Amino Acids
– Proteins are made up of monomers called
amino acids. The sequence of amino acids
determines a protein’s shape and function.
• Dipeptides and Polypeptides
– Two amino acids are joined by peptide bonds
to form a dipeptide.
– A long chain of amino acids is called a
polypeptide.
Chapter 3
Section 2 Molecules of Life
Structure of Proteins
Chapter 3
Section 2 Molecules of Life
Proteins
• Enzymes
– Enzymes speed up chemical reactions and bind
to specific substrates.
– The binding of a substrate with an enzyme
causes a change in the enzyme’s shape and
reduces the activation energy of the reaction.
Chapter 3
Section 2 Molecules of Life
Enzyme Activity
Chapter 3
Section 2 Molecules of Life
Lipids
• Lipids are nonpolar molecules that store energy
and are an important part of cell membranes.
Chapter 3
Section 2 Molecules of Life
Lipids
• Fatty Acids
– Most lipids contain fatty acids, unbranched
carbon molecules that have a hydrophilic end
and a hydrophobic end.
• Triglycerides
– Triglycerides consist of three fatty acids and
one molecule of glycerol.
Chapter 3
Section 2 Molecules of Life
Lipids
• Phospholipids
– Phospholipids, which make up cell membranes,
consist of two fatty acids and one glycerol
molecule.
• Waxes
– A wax is made of one long fatty acid chain joined to
one long alcohol.
• Steroids
– A steroid is composed of four fused carbon rings.
Chapter 3
Section 2 Molecules of Life
Nucleic Acids
• A nucleic acid is a large and complex organic
molecule that stores and transports information.
• The nucleic acid deoxyribonucleic acid (DNA)
contains genetic information for cell activities.
• Ribonucleic acid (RNA) molecules play many key
roles in building of proteins and can act as
enzymes.
Chapter 3
Section 2 Molecules of Life
Structure of Nucleic Acids
Chapter 3
Standardized Test Prep
Multiple Choice
1. Which of the following is not a function of
polysaccharides?
A. energy source
B. energy storage
C. structural support
D. storage of genetic information
Chapter 3
Standardized Test Prep
Multiple Choice, continued
2. Which of the following statements is
false?
A. A wax is a lipid.
B. Starch is a lipid.
C. Saturated fats are solid at room
temperature.
D. Unsaturated fats are liquid at room
temperature.
Chapter 3
Standardized Test Prep
Multiple Choice, continued
3. Which of the following molecules stores
hereditary information?
A. ATP
B. DNA
C. protein
D. carbohydrates
Chapter 3
Standardized Test Prep
Multiple Choice, continued
4. What is the name of the molecule in
plants that stores sugars?
A. starch
B. protein
C. cellulose
D. glycogen
Chapter 3
Standardized Test Prep
Multiple Choice, continued
The figure below illustrates
the basic structure of a cell
membrane. Use the
figure to answer the questions
that follow.
5. Which of the following
molecules make up the
basic structure of a cell
membrane?
A. waxes
B. steroids
C. fatty acids
D. phospholipids
Chapter 3
Standardized Test Prep
Multiple Choice, continued
The figure below illustrates
the basic structure of a cell
membrane. Use the
figure to answer the questions
that follow.
6. The “tails” of the molecules
in the figure orient away
from water. Which of the
following describes the
tail’s movement away from
water?
A. polar
B. adhesive
C. hydrophilic
D. hydrophobic
Chapter 3
Standardized Test Prep
Multiple Choice, continued
7. simple sugars : carbohydrates :: amino acids :
A. lipids
B. proteins
C. nucleic acids
D. amino acids
Chapter 3
Standardized Test Prep
Multiple Choice, continued
The figure below represents
the structural formula of a
molecule. Use the
figure to answer the question
that follows.
8. What is the name of the
functional group circled in
the structural formula?
A. amino
B. hydroxyl
C. phosphate
D. carboxyl