1. Section 2 Molecules of Life
Chapter 3
Objectives
• Distinguish between monosaccharides, disaccharides,and
polysaccharides.
• Explain the relationship between amino acids and protein
structure.
• Describe the induced fit model of enzyme action.
• Compare the structure and function of each of the different
types of lipids.
• Compare the nucleic acids DNA and RNA.

2. Section 2 Molecules of Life
Chapter 3
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 (1C:2H:1O)
• Carbohydrates are a source of energy and are used
as structural materials in organisms.

3. Section 2 Molecules of Life
Chapter 3
Carbohydrates
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4. Section 2 Molecules of Life
Chapter 3
Carbohydrates, continued
• Monosaccharides
– Carbohydrates are made up of monomers called
monosaccharides (or simple sugars).
– Contains carbon, hydrogen, and oxygen in a ratio
of 1:2:1
– General formula is (CH20)n

5. Monosaccharides
• The most common monosaccharides:
– Glucose – the main source of energy for cells
– Fructose – found in fruits and is the sweetest
monosaccharide
– Galactose – found in milk

6. Monosaccharides
• Glucose, fructose, and galactose have the same
molecular formula (C6H1206), but differing structures
• The different structures determine the slightly
different properties of the three compounds
• Isomers are compounds with the same chemical
formula but different structural forms

7. Section 2 Molecules of Life
Chapter 3
Carbohydrates, continued
• Disaccharides and Polysaccharides
– Two monosaccharides join in a condensation
reaction to form a double sugar called a
disaccharide.
– A complex sugar, or polysaccharide, is made of
three or more monosaccharides.

8. Polysaccharides
• Animals store • Plants store glucose
glucose as the as the
polysaccharide polysaccharide
glycogen starch
• Plants also make
the polysaccharide
cellulose (gives
strength and rigidity
to plant cells)

9. Section 2 Molecules of Life
Chapter 3
Disaccharides
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10. Section 2 Molecules of Life
Chapter 3
Proteins
• Proteins are organic compounds composed mainly
of carbon, hydrogen, oxygen, and nitrogen.
• Proteins have many functions including structural,
defensive, and catalytic roles.

11. Section 2 Molecules of Life
Chapter 3
Proteins, continued
• Amino Acids
– Proteins are made up of monomers called amino
acids. The sequence of amino acids determines a
protein’s shape and function.

12. Amino Acids
• There are 20 amino acids that all share a basic
structure
• Each amino acid contains a central carbon atom
covalently bonded to four other atoms or functional
groups
– A single hydrogen atom
– A carboxyl group
– An amino group
– R group

13. Section 2 Molecules of Life
Chapter 3
Amino Acids
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14. Section 2 Molecules of Life
Chapter 3
Proteins, continued
• Dipeptides and Polypeptides
– Two amino acids are joined by peptide bonds
through a condensation reaction to form a
dipeptide.
– A long chain of amino acids is called a
polypeptide.

15. Section 2 Molecules of Life
Chapter 3
Structure of Proteins

16. Section 2 Molecules of Life
Chapter 3
Proteins, continued
• 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.

17. Section 2 Molecules of Life
Chapter 3
Enzyme Activity

18. Enzymes
• To learn more about the function of enzymes, you are
going to do a virtual experiment
• PHSchool.com
• cbp-1024

19. Section 2 Molecules of Life
Chapter 3
Lipids
• Lipids are nonpolar molecules that store energy and
are an important part of cell membranes.

20. Section 2 Molecules of Life
Chapter 3
Lipids, continued
• Fatty Acids
– Most lipids contain fatty acids, unbranched
carbon molecules that have a hydrophilic end and
a hydrophobic end.

21. Section 2 Molecules of Life
Chapter 3
Fatty Acids
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22. Section 2 Molecules of Life
Chapter 3
Lipids, continued
• Triglycerides
– Triglycerides consist of three fatty acids and one
molecule of glycerol.

23. Section 2 Molecules of Life
Chapter 3
Lipids, continued
• Phospholipids
– Phospholipids, which make up cell membranes,
consist of two fatty acids and one glycerol
molecule.

24. Section 2 Molecules of Life
Chapter 3
Lipids, continued
• 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.

25. Section 2 Molecules of Life
Chapter 3
Nucleic Acids
• A nucleic acid is a large and complex organic
molecule that stores and transports information.

26. Section 2 Molecules of Life
Chapter 3
Structure of Nucleic Acids

27. Section 2 Molecules of Life
Chapter 3
Nucleic Acids
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28. Section 2 Molecules of Life
Chapter 3
Nucleic Acids, continued
• 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.