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Chapter 2
The Chemical Composition of Cells
CHAPTER OUTLINE
An introduction to basic chemistry
Atoms are the smallest particles of elements
Each atom has an atomic number and an atomic mass
Electrons move around the nucleus, but their exact positions are uncertain
Chemical bonds hold atoms together
Atoms gain and lose electrons to form ionic bonds
Atoms share electrons to form covalent bonds
Hydrogen bonds are attractions between adjacent molecules
Inorganic compounds
Water, an inorganic compound, is essential to plants
Water’s polarity causes many of its properties
Acids and bases
Acids and bases dissociate when dissolved in water
A solution’s acidity or alkalinity is expressed in terms of pH
Organic compounds
Sugars, starches, and cellulose are examples of carbohydrates
Fats and oils are examples of lipids
Proteins are large organic molecules composed of amino acids
Enzymes are proteins that accelerate chemical reactions
DNA and RNA are nucleic acids
Energy is temporarily stored in ATP
Energy and biological work
The laws of thermodynamics govern energy transformations
Focus On: How Did Life Begin?
Process of Science: Miller and Urey’s experiment in chemical evolution
Plants and the Environment: Acid Rain
Plants and People: Phytochemicals and Human Health
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CHAPTER OBJECTIVES
1. Describe the basic structure of an atom and explain ionic, covalent, and hydrogen
bonds.
2. Discuss the properties of water, and explain the importance of water to life.
3. Distinguish between acids and bases, and describe the pH scale.
4. Describe the chemical compositions and functions of carbohydrates, lipids, proteins, and
nucleic acids.
5. Discuss the role of enzymes in cells.
6. State the first and second laws of thermodynamics, and describe how each applies to plants
and other organisms.
LECTURE OUTLINE
I. What is an element?
A.
How many naturally occurring elements are on Earth?
B.
What system do chemists use to write abbreviations of the element names?
II. What are atoms?
A.
Where (specifically) are protons, electrons, and neutrons found? What is the charge
of each one?
B.
What is the relationship between the number of protons and the number of electrons
in an atom?
C.
How is the atomic number determined?
D.
How is the atomic mass number determined?
E.
What are isotopes?
F.
How are electrons arranged in energy levels? What is the relationship between an
electron’s energy level and its distance from the atomic nucleus?
III. What are chemical compounds?
A. What are chemical bonds? What determines the number of bonds that a particular atom
can form?
B. Ionic bonds
1. What are ions and how are they formed from neutral atoms?
2. How do you define an ionic bond?
3. Give an example of an ionic substance.
C. Covalent bonds
1. How are covalent bonds formed?
2. How are double bonds formed?
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3. What are some examples of compounds with covalent bonds?
4. Distinguish between nonpolar and polar covalent bonds.
D. What is a hydrogen bond?
IV. What is the difference between inorganic and organic substances?
V. Describe the biological importance of water.
A. Why should you suspect that water is important to life?
B. What are three distinct functions water has in living systems?
C. The biological properties of water are due to its polarity.
1. Water can exist in all three phases (solid, liquid, and vapor) on the earth,
depending on the temperature.
2. Why does evaporating water have a cooling effect?
3. Water is a good solvent for ionic and polar compounds.
4. What is cohesion? What is adhesion?
5. How does hydrogen bonding contribute to the unique properties of ice?
VI. What are acids and bases?
A. Give examples of strong and weak acids and bases.
B.
Describe what happens when acids and bases dissolve in water.
C.
Describe how acids and bases react with each other.
D. How does the pH scale express the relative acidity or alkalinity of a solution?
VII. Carbohydrates are sugars or macromolecules made from sugars.
A.
Give some examples of carbohydrates.
B.
What is the basic chemical composition of all carbohydrates?
C.
What are monosaccharides? How are they used in cells?
D. What are disaccharides? Describe a condensation reaction.
E.
What are polysaccharides?
1.
What monosaccharide makes up starches and cellulose?
2.
How do starches and cellulose differ in structure and function in plants?
3.
How do humans use starches and cellulose?
VIII. Lipids are nonpolar compounds.
A.
Give some examples of lipids.
B. How are fats and oils used in cells?
C.
What is the basic structure of fats and oils?
1.
What is glycerol?
2.
What are fatty acids?
3.
Distinguish between saturated vs. unsaturated fats and oils.
4.
How are phospholipids different from fats and oils?
D.
Waxes are also lipids. What are waxes used for?
IX. Proteins are large molecules.
A.
What is the importance of proteins?
B.
What is the structure of proteins?
C. What are amino acids? What is the typical structure of an amino acid?
1.
What are peptide bonds? How and where are they formed?
2. What are “essential amino acids”?
3. What are enzymes?
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4.
5.
What is a catalyst?
What is the energy of activation for a reaction?
C. Why are enzymes important?
1. How do enzymes work? How fast? Are they used up in the reaction?
2. What is the substrate?
3. What is the active site?
X. Nucleic acids
What are nucleic acids?
A.
How are nucleic acids used in the cell?
B.
What are the building blocks of nucleic acids?
1.
What are nucleotides?
2.
What are the components of nucleotides?
C.
ATP is a nucleotide that is not used to build nucleic acids; instead it’s used to
temporarily store energy to be used for cellular reactions.
XI. What is energy?
A. What is the difference between potential energy and kinetic energy?
B. What is thermodynamics?
C. What is the first law of thermodynamics? Give an example of the conversion of
energy into different forms.
D. What is the second law of thermodynamics?
1. What is entropy? What is the expected eventual outcome of the increase of
entropy in the universe?
2. How do organisms maintain their complex organization?
KEY TERMS
acid, p. 30
adhesion, p. 29
atom, p. 24
activation energy, p. 37
active site, p. 37
adenosine triphosphate
(ATP), p. 38
amino acid, p. 36
atomic mass, p. 24
atomic number, p. 24
base, p. 30
carbohydrate, p. 32
chemical bond, p. 25
cohesion, p. 29
compound, p. 25
condensation reaction, p. 34
covalent bond, p. 26
deoxyribonucleic acid
(DNA), p. 38
disaccharide, p. 33
electron configuration, p. 25
element, p. 24
entropy, p. 41
enzyme, p. 37
fatty acid, p. 35
first law of thermodynamics,
p. 40
gene, p. 38
glycerol, p. 35
hydrogen bond, p. 27
inorganic compounds, p. 27
ion, p. 26
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ionic bond, p. 26
isotope, p. 24
kinetic energy, p. 39
lipid, p. 34
molecule, p. 26
monosaccharide, p. 32
nonpolar covalent bond,
p. 27
nucleic acid, p. 38
nucleotide, p. 38
organic compound, p. 27
peptide bond, p. 37
pH scale, p. 30
phospholipid, p. 35
polar covalent bond, p. 27
polysaccharide, p. 34
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potential energy, p. 39
protein, p. 36
ribonucleic acid (RNA),
p. 38
saturated fatty acid, p. 35
second law of
thermodynamics, p. 40
substrate, p. 37
thermodynamics, p. 40
unsaturated fatty acid, p. 35
TEACHING TIPS
1. There are six elements found in biomolecules that form the word CHNOPS. Carbon, hydrogen,
and oxygen are in all biomolecules, nitrogen and phosphorous are in nucleic acids, and
nitrogen and sulfur are in proteins. For discussion, ask the question, “What three features do
these elements share which contribute to their importance to organic molecules?” They are all
small atoms, and small atoms are stable atoms. They all form covalent bonds, which are strong
bonds. Except for hydrogen, they all form multiple bonds. These three characteristics allow for
the formation of large, complex, branched, stable molecules, which make up the matter of life
and are durable.
2. Capillary action: for a lab activity or for a lecture demonstration, use three glass or plastic
tubes of different diameter and colored water. Place the tubes in a beaker with the colored
water about 5 mm deep and observe the water climb up the tubes to different heights. This will
lead to a discussion of adhesion and cohesion, the collective strength of hydrogen bonds, and
the use of capillary tubes for such things as taking a hematocrit sample. For a second
demonstration, place two glass slides together and dip the ends in the water. Capillary action
will draw the water between the slides and make them difficult to pull apart. Relate this to the
reason wood swells when it gets wet, and imbibition of water by seeds.
3.
Define hydrophilic and hydrophobic and describe how dissolved ions and polar
compounds are surrounded by a hydration layer, which keeps them separate and
suspended in solution.
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