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4 MOLECULES OF LIFE
CHAPTER OUTLINE
LEARNING OBJECTIVES
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List the four major categories of organic molecules found in living things.
Describe how dehydration synthesis and hydrolysis are used to make and break macromolecule.
Describe the structure of protein, name the building block molecules that compose proteins, and
list some functions of protein molecules in living organisms.
Describe the structure of nucleic acids, name the building block molecules that compose them, and
list some functions of DNA and RNA in living organisms.
Describe the structure of carbohydrates, name the building block molecules that compose them,
and list some functions of carbohydrates in living organisms.
Describe the structure of lipids, name the building block molecules that compose them, and list
some functions of lipid molecules in living organisms.
Forming Macromolecules (p. 60)
4.1
Polymers Are Built of Monomers (p. 60; Figs. 4.1, 4.2; Table 4.1)
A. Organic molecules are based on long chains of carbon with functional groups on the ends that
give the molecules their unique properties.
B. Four major categories of organic molecules are found in living things; proteins, lipids,
carbohydrates, and nucleic acids.
C. Large organic molecules are called macromolecules because of their size and complexity.
D. A macromolecule is a polymer built from repeating subunits called monomers.
E. Making (and Breaking) Macromolecules
1. Subunits of macromolecules are joined together using enzymes and dehydration
synthesis.
2. Adding water to macromolecules to break them into subunits is called hydrolysis.
Types of Macromolecules (p. 62)
4.2
Proteins (p. 62; Figs. 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9; Table 4.2)
A. Proteins can serve as enzymes, play structural roles, and act as chemical messengers.
B. Proteins are polypeptides made up of amino acids joined together by peptide bonds.
C. Protein Structure
1. The sequence of amino acids within a protein is called the primary structure.
2. The secondary structure is any folding of the primary chain.
3. Globular shapes are the tertiary structure of a protein.
4. When more than one polypeptide chain composes the protein, it is said to have quaternary
structure.
D. How Proteins Fold into Their Functional Shape
1. The shape of a protein can be denatured, which prevents it from functioning properly.
2. Many proteins serve as enzymes, which function as catalysts in chemical reactions.
E. Chaperone Proteins
1. Chaperone proteins help newly produced proteins to fold properly.
F. Protein Folding and Disease
1. Chaperone protein deficiencies may be involved in causing diseases such as cystic
fibrosis and Alzheimer’s disease by failing to facilitate folding of key proteins.
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4.3
4.4
4.5
Nucleic Acids (p. 67; Figs. 4.10, 4.11, 4.12)
A. Nucleic acids (polynucleotides) store information for cells and are made up of subunits called
nucleotides.
1. Each nucleotide has a five-carbon sugar and a phosphate group.
2. Each nucleotide has a nitrogen base that can be either adenine, guanine, cytosine,
thymine, or uracil.
B. DNA and RNA
1. Deoxyribonucleic acid (DNA) exists as a double helix of polynucleotides, exhibiting base
pairing within the helix.
a. DNA nucleotides contain the five-carbon sugar deoxyribose
b. DNA encodes genetic instructions for the cell
2. Ribonucleic acid (RNA) is involved in protein synthesis
a. RNA nucleotides contain the five-carbon sugar ribose
b. RNA is single-stranded
c. RNA uses the nitrogen base uracil instead of thymine
C. The Double Helix
1. The reason for DNA to assume its double helix is because only two base pairs are
possible.
a. Adenine pairs with thymine and cytosine pairs with guanine with a specific pattern of
hydrogen bonds.
2. The advantage of the double helix is that it contains two copies of the information —
one the mirror image of the other.
Carbohydrates (p. 70; Figs. 4.13, 4.14, 4.15; Table 4.3)
A. Carbohydrates are used as energy sources and are made up of polymers of simple
carbohydrates.
B. Simple Carbohydrates
1. The simple sugars, or monosaccharides, consist of one subunit.
2. Another simple carbohydrate is a disaccharide, built of two subunits.
C. Complex Carbohydrates
1. Animals and plants store energy in polysaccharides formed from glucose.
2. Examples of complex carbohydrates include glycogen, chitin, cellulose, and starch.
Lipids (p. 72; Figs. 4.16, 4.17, 4.18)
A. Fats and all other biological molecules that are not soluble in water but are soluble in oil are
lipids.
B. Fats are employed for long-term storage of energy.
C. Fats
1. Triacylglycerol molecules (triglycerides) are made up of glycerol and three fatty acids.
2. The fatty acids may be saturated or unsaturated with hydrogen along the carbon chain.
D. Other Types of Lipids
1. Phospholipids are used to build biological membranes.
2. A third type of lipid, steroids, serve a number of functions within the cell.
KEY TERMS
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macromolecules (p. 60) A macromolecule is any large organic molecule, such as a polysaccharide, a
protein, a lipid, or a nucleic acid.
proteins (p. 62)
nucleic acids (p. 67) The “building blocks” of nucleic acids are the nucleotides. Because the building
blocks of proteins are amino acids, students often mistakenly think nucleic acids are the building blocks
of nucleotides.
 carbohydrates (p. 70)
 lipids (p. 72)
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LECTURE SUGGESTIONS AND ENRICHMENT TIPS
1. Demonstrate denaturing of proteins. Using a hot plate or bunsen burner, fry an egg in a beaker. Heating
denatures the protein in egg whites, causing them to turn from clear to white in appearance. Heating the
proteins of the egg causes them to unfold. When newly exposed amino acids are chemically attracted to
other newly exposed amino acids, new peptide and new hydrogen bonds form.
2. Demonstrate the curdling of milk to show structural properties of proteins. Milk contains two kinds of
proteins, whey and casein proteins. The casein proteins are involved in the curdling of milk. These proteins
normally exist as negatively charged groups that repel each other, and are thus distributed evenly
throughout the milk. When vinegar or lemon juice, both acids, are added to milk, this causes the groups of
casein proteins to lose their negative charges, and then lose their ability to repel each other. They then bond
with each other, causing coagulation, or curdling (souring) of the milk.
CRITICAL THINKING QUESTION
1. Based on what you know about how macromolecules are synthesized and degraded, why is adequate
water in the diet necessary to aid digestion and cell metabolic reactions?
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