Download Chapter 3 Molecules

CHAPTER 3
The Molecules of Cells
Key Terms
amino acids
amino group
anabolic steroids
carbohydrates
carbonyl group
carboxyl group
cellulose
chitin
cholesterol
dehydration reaction
denaturation
deoxyribonucleic acid (DNA)
disaccharides
double helix
enzymes
fat
functional groups
gene
glycogen
hydrocarbons
hydrolysis
hydrophilic
hydrophobic
hydroxyl group
isomers
lipids
macromolecules
methyl group
monomers
monosaccharides
nucleic acids
nucleotides
organic compound
peptide bond
phosphate group
phospholipids
polymers
polypeptide
polysaccharides
primary structure
protein
quaternary structure
ribonucleic acid (RNA)
saturated fatty acid
secondary structure
starch
steroids
tertiary structure
trans fat
unsaturated fatty acid
Lecture Outline
I. Introduction
A. Most of the world’s population cannot digest milk-based foods.
1. These people are lactose intolerant because they lack the enzyme lactase.
2. This illustrates the importance of biological molecules, such as lactase, in the daily
functions of living organisms.
II. Introduction to Organic Compounds
A. 3.1 Life’s molecular diversity is based on the properties of carbon
1. Diverse molecules found in cells are composed of carbon bonded to
a. other carbons and
b. atoms of other elements.
2. Carbon-based molecules are called organic compounds.
3. By sharing electrons, carbon can
a. bond to four other atoms and
b. branch in up to four directions.
4. Methane (CH4) is one of the simplest organic compounds.
a. Four covalent bonds link four hydrogen atoms to the carbon atom.
b. Each of the four lines in the formula for methane represents a pair of shared
electrons.
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5. Methane and other compounds composed of only carbon and hydrogen are called
hydrocarbons.
6. Carbon, with attached hydrogens, can bond together in chains of various lengths.
7. A carbon skeleton is a chain of carbon atoms that can be
a. straight,
b. branched, or
c. arranged in rings.
8. Compounds with the same formula but different structural arrangements are called
isomers.
B. 3.2 A few chemical groups are key to the functioning of biological molecules
1. The unique properties of an organic compound depend on
a. size and shape of its carbon skeleton and
b. the groups of atoms that are attached to that skeleton.
2. The sex hormones testosterone and estradiol (a type of estrogen) differ only in the groups of atoms
highlighted in Figure 3.2.
3. Table 3.2 illustrates six chemical groups important in the chemistry of life.
4. The first five groups are called functional groups; they affect a molecule’s function in a characteristic way.
5. These five groups are polar, so compounds containing them are typically hydrophilic (water-loving)
and soluble in water.
6. A sixth group, a methyl group,
a. consists of carbon bonded to three hydrogen atoms,
b. is nonpolar and not reactive, but
c. still affects molecular shape and thus function.
7. The functional groups are
a. hydroxyl group—a hydrogen bonded to an oxygen,
b. carbonyl group—a carbon linked by a double bond to an oxygen atom,
c. carboxyl group—a carbon double-bonded to both an oxygen and a
hydroxyl group,
d. amino group—a nitrogen bonded to two hydrogen atoms and the
carbon skeleton, and
e. phosphate group—a phosphorus atom bonded to four oxygen atoms.
C. 3.3 Cells make large molecules from a limited set of small molecules
1. There are four classes of molecules important to organisms:
a. carbohydrates,
b. proteins,
c. lipids, and
d. nucleic acids.
2. The four classes of biological molecules contain very large molecules.
a. They are often called macromolecules because of their large size.
b. They are also called polymers because they are made from identical building blocks strung together.
c. The building blocks of polymers are called monomers.
3. Monomers are linked together to form polymers through dehydration reactions, which remove water.
4. Polymers are broken apart by hydrolysis, the addition of water.
5. These reactions are mediated by enzymes, specialized macromolecules that speed up
chemical reactions in cells.
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6. A cell makes a large number of polymers from a small group of monomers. For
example,
a. proteins are made from only 20 different amino acids and
b. DNA is built from just four kinds of nucleotides.
7. The monomers used to make polymers are universal.
III. Carbohydrates
A. 3.4 Monosaccharides are the simplest carbohydrates
1. Carbohydrates range from small sugar molecules (monomers) to large
polysaccharides.
2. Sugar monomers are monosaccharides, such as those found in
a. fructose,
b. glucose, and
c. honey.
3. Monosaccharides can be hooked together by dehydration reactions to form
a. more complex sugars and
b. polysaccharides.
4. The carbon skeletons of monosaccharides vary in length.
a. Glucose and fructose are six carbons long.
b. Others have three to seven carbon atoms.
5. Monosaccharides are
a. the main fuels for cellular work and
b. used as raw materials to manufacture other organic molecules.
6. Many monosaccharides form rings.
7. The ring diagram may be
a. abbreviated by not showing the carbon atoms at the corners of the ring and
b. drawn with different thicknesses for the bonds to indicate that the ring is a
relatively flat structure with attached atoms extending above and below it.
B. 3.5 Two monosaccharides are linked to form a disaccharide
1. Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction.
2. The disaccharide sucrose is formed by combining
a. a glucose monomer and
b. a fructose monomer.
3. The disaccharide maltose is formed from two glucose monomers.
C. 3.6 CONNECTION: What is high-fructose corn syrup, and is it to blame for obesity?
1. Most sodas and fruit drinks contain high-fructose corn syrup (HFCS).
2. Fructose is sweeter than glucose.
3. To make HFCS, glucose atoms are rearranged to make the glucose isomer, fructose.
4. High-fructose corn syrup (HFCS)
a. is used to sweeten many beverages,
b. consists of about 55% fructose and 45% glucose, and
c. is a mixture with about the same proportions as in sucrose.
5. Although HFCS consumption has declined somewhat in recent years, obesity rates continue to rise,
with almost 36% of U.S. adults now considered obese.
6. Good health is promoted by
a. a diverse diet of proteins, fats, vitamins, minerals, and complex carbohydrates, and
b. exercise.
D. 3.7 Polysaccharides are long chains of sugar units
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1. Polysaccharides are
a. macromolecules,
b. polymers composed of thousands of monosaccharides.
2. Polysaccharides may function as
a. storage molecules or
b. as structural compounds.
3. Starch is
a. a polysaccharide,
b. composed of glucose monomers, and
c. used by plants for energy storage.
4. Glycogen is
a. a polysaccharide,
b. composed of glucose monomers, and
c. used by animals for energy storage.
5. Cellulose
a. is a polymer of glucose and
b. forms plant cell walls.
6. Chitin is
a. a polysaccharide,
b. used by insects and crustaceans to build an exoskeleton, and
c. found in the cell walls of fungi.
7. Polysaccharides are usually hydrophilic (water-loving).
8. Bath towels, for example, are often made of cotton, which is mostly cellulose, and, therefore, water
absorbent.
IV. Lipids
A. 3.8 Fats are lipids that are mostly energy-storage molecules
1. Lipids
a. are water insoluble (hydrophobic, or water-fearing) compounds,
b. are important in long-term energy storage,
c. contain twice as much energy as a polysaccharide, and
d. consist mainly of carbon and hydrogen atoms linked by nonpolar covalent bonds.
2. Lipids differ from carbohydrates, proteins, and nucleic acids in that they are
a. not huge molecules and
b. not built from monomers.
3. Lipids vary a great deal in structure and function.
4. We consider three types of lipids:
a. fats,
b. phospholipids, and
c. steroids.
5. A fat is a large lipid made from two kinds of smaller molecules:
a. glycerol and
b. fatty acids.
6. A fatty acid can link to glycerol by a dehydration reaction.
a. A fat contains one glycerol linked to three fatty acids.
b. Fats are often called triglycerides because of their structure.
7. Some fatty acids contain one or more double bonds, forming unsaturated fatty acids.
a. These have one fewer hydrogen atom on each carbon of the double bond.
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b. These double bonds cause kinks or bends in the carbon chain, preventing them from packing together tightly and solidifying at room temperature.
8. Fats with the maximum number of hydrogens are called saturated fatty acids.
9. Unsaturated fats are referred to as oils.
10. Most animal fats are saturated fats.
11. Hydrogenated vegetable oils are unsaturated fats that have been converted to saturated fats by adding
hydrogen.
12. This hydrogenation creates trans fats, which are associated with health risks.
B. 3.9 SCIENTIFIC THINKING: Scientific studies document the health risks of trans fats
1. In the 1890s, the process of adding hydrogen atoms to unsaturated oils was developed to
a. reduce spoilage of oils
b. help oils withstand repeated heating for frying, and
c. reduce consumption of animal fats, thought to be less healthy than partially hydrogenated vegetable oils.
2. By the 1990s, partially hydrogenated oils were common in cookies, crackers, snacks, baked goods,
and fried foods.
3. Recent research has shown that trans fats pose an even greater health risk than
saturated fats.
a. One study estimated that eliminating trans fats from the food supply could prevent up to one in
five heart attacks!
b. In 2006, the U.S. Food and Drug Administration required the listing of trans fat on food labels.
c. Many cities and states have passed laws to eliminate trans fats in unlabeled foods served in restaurants and schools.
d. An increasing number of countries have banned trans fats.
4. Experimental studies have tested the health risks of consuming trans fats.
a. In experimental controlled feeding trials, the diets of participants contained different proportions
of saturated, unsaturated, and partially hydrogenated fats.
b. For ethical and practical reasons, controlled feeding trials are usually fairly short in duration, involve only limited dietary changes, generally use healthy individuals, and measure intermediary
risk factors, such as changes in cholesterol levels, rather than actual disease outcomes.
5. Observational scientific studies on dietary health effects can
a. extend over a longer time period,
b. use a more representative population, and
c. measure disease outcomes and risk factors.
6. The Nurses’ Health Study
a. began in 1976 with more than 120,000 female nurses and
b. is an example of an observational study on dietary health.
7. The results indicate that
a. for each 5% increase in saturated fat, there was a 17% increase in the risk of heart disease and
b. for each 2% increase in trans fat, there is a 93% increase in risk.
8. Trans fats are indeed a greater health risk than saturated fats.
C. 3.10 Phospholipids and steroids are important lipids with a variety of functions
1. Phospholipids are the major component of all cell membranes.
2. Phospholipids are structurally similar to fats.
a. Fats contain three fatty acids attached to glycerol.
b. Phospholipids contain two fatty acids attached to glycerol.
3. Phospholipids cluster into a bilayer of phospholipids.
4. The hydrophilic heads are in contact with
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a. the water of the environment and
b. the internal part of the cell.
5. The hydrophobic tails band in the center of the bilayer.
6. Steroids are lipids in which the carbon skeleton contains four fused rings.
7. Cholesterol is
a. a common component in animal cell membranes and
b. a starting material for making steroids, including sex hormones.
D. 3.11 CONNECTION: Anabolic steroids pose health risks
1. Anabolic steroids are synthetic variants of the male hormone testosterone that are abused by some
athletes with serious consequences, including
a. violent mood swings,
b. depression,
c. liver damage,
d. cancer,
e. high cholesterol, and
f. high blood pressure.
V. Proteins
A. 3.12 Proteins have a wide range of functions and structures
1. Proteins are
a. involved in nearly every dynamic function in your body and
b. very diverse, with tens of thousands of different proteins, each with a specific
structure and function, in the human body.
2. Proteins are composed of differing arrangements of a common set of just 20 amino
acid monomers.
3. Probably the most important role for proteins is as enzymes, proteins that
a. serve as catalysts and
b. regulate virtually all chemical reactions within cells.
4. Other types of proteins include
a. transport proteins embedded in cell membranes, which move sugar molecules and other nutrients
into your cells,
b. defensive proteins, such as antibodies of the immune system,
c. signal proteins, such as many hormones and other chemical messengers that help coordinate body
activities,
d. receptor proteins, built into cell membranes, which receive and transmit signals into your cells,
e. contractile proteins found within muscle cells,
f. structural proteins, such as collagen, which form the long, strong fibers of connective tissues, and
g. storage proteins, which serve as a source of amino acids for developing embryos in eggs and seeds.
5. The functions of different types of proteins depend on their individual shapes.
6. A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds.
7. The amino acid sequence causes the polypeptide to assume a particular shape.
8. If a protein’s shape is altered, it can no longer function.
9. In the process of denaturation, a protein
a. unravels,
b. loses its specific shape, and
c. loses its function.
10. Proteins can be denatured by changes in salt concentration, changes in pH, or high heat.
B. 3.13 Proteins are made from amino acids linked by peptide bonds
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1. Amino acids have
a. an amino group and
b. a carboxyl group (which makes it an acid).
2. Also bonded to the central carbon is
a. a hydrogen atom and
b. a chemical group symbolized by R, which determines the specific properties of each of the 20
amino acids used to make proteins.
3. Amino acids are classified as either
a. hydrophobic or
b. hydrophilic.
4. Amino acid monomers are linked together in a dehydration reaction,
a. joining the carboxyl group of one amino acid to the amino group of the next amino acid, and
b. creating a peptide bond.
5. Additional amino acids can be added by the same process to create a chain of amino
acids called a polypeptide.
C. 3.14 VISUALIZING THE CONCEPT: A protein’s functional shape results from four levels of structure
1. A protein can have four levels of structure:
a. primary structure
b. secondary structure
c. tertiary structure
d. quaternary structure
VI. Nucleic Acids
A. 3.15 DNA and RNA are the two types of nucleic acids
1. The amino acid sequence of a polypeptide is programmed by a discrete unit of inheritance known as a
gene.
2. Genes consist of DNA (deoxyribonucleic acid), a type of nucleic acid.
3. DNA is inherited from an organism’s parents.
4. DNA provides directions for its own replication.
5. DNA programs a cell’s activities by directing the synthesis of proteins.
6. DNA does not build proteins directly.
7. DNA works through an intermediary, ribonucleic acid (RNA).
a. DNA is transcribed into RNA in a cell’s nucleus.
b. RNA is translated into proteins in the cytoplasm.
B. 3.16 Nucleic acids are polymers of nucleotides
1. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are composed of monomers called nucleotides.
2. Nucleotides have three parts:
a. a five-carbon sugar called ribose in RNA and deoxyribose in DNA,
b. a phosphate group, and
c. a nitrogenous base.
3. DNA nitrogenous bases are
a. adenine (A),
b. thymine (T),
c. cytosine (C), and
d. guanine (G).
4. RNA also has A, C, and G, but instead of T, it has uracil (U).
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5. A nucleic acid polymer, a polynucleotide, forms from the nucleotide monomers when the phosphate
of one nucleotide bonds to the sugar of the next nucleotide by dehydration reactions.
6. This produces a repeating sugar-phosphate backbone with protruding nitrogenous
bases.
7. RNA is usually a single polynucleotide strand.
8. DNA is a double helix, in which two polynucleotide strands wrap around each other.
a. The two strands are associated because particular bases always hydrogen-bond to one another.
b. A pairs with T, and C pairs with G, producing base pairs.
C. 3.17 EVOLUTION CONNECTION: Lactose tolerance is a recent event in human
evolution
1. The majority of people
a. stop producing the enzyme lactase in early childhood and
b. do not easily digest the milk sugar lactose.
2. Lactose tolerance represents
a. a relatively recent mutation in the human genome and
b. a survival advantage for human cultures with milk and dairy products available
year-round.
3. Researchers identified three mutations in 43 groups in East Africa that keep the lactase gene permanently turned on.
4. The mutations
a. are all different from each other and from European mutation,
b. appear to have occurred about 7,000 years ago, and
c. occurred about the same time as the domestication of cattle in these regions.
Word Roots
de- = without or remove; hydro- = water (dehydration reaction: a chemical process in which two molecules become covalently bonded to each other with the removal of a water molecule)
di- = two; -sacchar = sugar (disaccharide: a sugar molecule consisting of two monosaccharides linked by a dehydration reaction)
carb- = coal (carboxyl group: a functional group in an organic molecule, consisting of an oxygen atom doublebonded to a carbon atom that is also bonded to a hydroxyl group)
glyco- = sweet (glycogen: an extensively branched polysaccharide of many glucose monomers that serves as an
energy-storage molecule in animal liver and muscle cells)
hydro- = water (hydrocarbon: a chemical compound composed only of the elements carbon and hydrogen)
iso- = equal (isomer: one of several organic compounds with the same molecular formula but
different structures and, therefore, different properties)
-lyse = break (hydrolysis: a chemical process in which polymers are broken down by the chemical addition of water molecules to the bonds linking their monomers)
macro- = large (macromolecule: a giant molecule in a living organism formed by the joining of smaller molecules)
mono- = single; -mer = part (monomer: a chemical subunit that serves as a building block of a
polymer)
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-philos = loving (hydrophilic: “water-loving”: refers to polar, or charged, molecules [or parts of molecules] that
are soluble in water)
-phobos = fearing (hydrophobic: “water-fearing”: refers to nonpolar molecules [or parts of
molecules] that do not dissolve in water)
poly- = many (polymer: a large molecule consisting of many monomers covalently joined together in a chain;
polysaccharide: many monosaccharides joined together)
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