The Molecules of Cells

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The Molecules of Cells

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



2. Carbon-based molecules are called 3. By sharing electrons, carbon can

a. bond to four other atoms b. branch in up to

4. Methane (CH4) is one of the simplest organic compounds.

a. Four covalent bonds

b. Each of the four lines in the formula for methane represents a pair of shared electrons.

5. Methane and other compounds composed of only carbon and hydrogen

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. branched

b. unbranched

8. Compounds with the same formula but

B. 3.2 A few chemical groups are key to the functioning of biological molecules 1. An organic compound has unique properties that depend upon the



2. A functional group affects a biological molecule’s function in a characteristic way.

3. Compounds containing functional groups are 4. The functional groups are

a. hydroxyl group—consists of a hydrogen bonded to an oxygen

b. carbonyl group—a carbon linked by a double bond to an oxygen atom

c. carboxyl group—consists of a carbon double-bonded to both an oxygen and a hydroxyl group


e. phosphate group—consists of a

5. An example of similar compounds that differ only in functional groups is sex hormones.

a. Male and female sex hormones differ only in functional groups.

b. The result is distinguishable features of males and females.

C. 3.3 Cells make a huge number of large molecules from a limited set of small molecules 1. There are four classes of molecules important to organisms:

a. carbohydrates b.

c. lipids d.

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

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. All biological reactions of this sort are mediated by enzymes, which

6. A cell makes a large number of polymers from a small group of monomers. For example, a. proteins are made from only

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 honey a. glucose

b. fructose

3. Monosaccharides can be hooked together to form a. more complex sugars (ex.

b. polysaccharides (ex. starch and cellulose)

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

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

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 (table sugar) is formed by combining a glucose monomer and a fructose monomer.

3. The disaccharide maltose is formed from two glucose monomers.

C. 3.7 Polysaccharides are long chains of sugar units 1. Polysaccharides are

a. macromolecules

b. polymers composed of thousands of 2. Polysaccharides may function as

a. storage molecules or b. as structural compounds.

3. Starch is

a. a polysaccharide, composed of glucose monomers b. used by plants for energy storage.

4. Glycogen is

a. a polysaccharide, composed of glucose monomers b. used by

5. Cellulose

a. is a polymer of glucose b. forms plant cell walls 6. Chitin is

a. a polysaccharide

b. used by insects and crustaceans to build an 7. Polysaccharides are usually hydrophilic ( 8. Bath towels are

a. often made of cotton, which is mostly cellulose b. water absorbent

IV. Lipids

A. 3.8 Fats are lipids that are mostly energy-storage molecules 1. Lipids

a. are water insoluble (hydrophobic, or ) compounds b. are important in long-term energy storage

c. contain twice as much energy as a polysaccharide

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 b. not built from monomers 3. Lipids vary a great deal in


4. We will consider three types of lipids:

a. fats

b. phospholipids c. steroids

5. A fat is a large lipid made from two kinds of smaller molecules, a. glycerol

b. fatty acids

6. A fatty acid can link to glycerol by a dehydration reaction.

a. A fat contains one glycerol linked to

b. Fats are often called triglycerides because of their structure.

7. Some fatty acids contain one or more double bonds, forming unsaturated fatty acids that a. cause kinks or bends in the carbon chain

b. prevent them from packing together tightly and solidifying at room temperature 8. Fats with single bonds only are called saturated fatty acids.

9. Unsaturated fats include 10. Most animal fats are

B. 3.9 Phospholipids and steroids are important lipids with a variety of functions 1. Phospholipids are

a. structurally similar to fats and

b. 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 and a 3. Phospholipids cluster into a bilayer of phospholipids 4. The hydrophilic heads are in contact with

a. the water of the environment 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

b. starting material for making steroids, including sex hormones V. Proteins

A. 3.11 Proteins are made from amino acids linked by peptide bonds 1. Proteins are

a. involved in nearly every dynamic function in your body

b. very diverse, with ten 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 3. Amino acids have

a. an amino group

b. a carboxyl group (which makes it an acid)


4. Also bonded to the central carbon is a. a hydrogen atom

b. a chemical group symbolized by R, which determines the specific properties of each of the 20 amino acids used to make proteins

5. Amino acids are classified as either hydrophobic or 6. Amino acid monomers are linked together

a. in a dehydration reaction

b. joining carboxyl group of one amino acid to the amino group of the next amino acid c. creates a peptide bond

7. Additional amino acids can be added by the same process to create a chain of amino acids called a

B. 3.12 A protein’s specific shape determines its function

1. Probably the most important role for proteins is as enzymes, proteins that a. serve as metabolic catalysts

b. regulate the chemical reactions within cells.\

2. Other proteins are also important:

a. Structural proteins provide associations between body parts b. Contractile proteins are found within

c. Defensive proteins include antibodies of the immune system

d. Signal proteins are best exemplified by hormones and other chemical messengers e. Receptor proteins transmit signals into cells

f. Transport proteins carry

g. Storage proteins serve as a source of amino acids for developing embryos

3. A polypeptide chain contains of hundreds or thousands of amino acids linked by peptide bonds.

4. The amino acid sequence causes the polypeptide to assume a particular shape 5. The shape of a protein determines its specific function

6. If a protein’s shape is altered, it can no longer function 7. In the process of denaturation, a polypeptide chain

a. unravels b. loses its shape c.

8. Proteins can be denatured by changes in salt concentration, pH, or by C. 3.13 A protein’s shape depends on 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

2. The primary structure of a protein is its unique amino acid sequence

a. The correct amino acid sequence is determined by the cell’s genetic information b. The slightest change in this sequence may affect the protein’s ability to function 3. Protein secondary structure results from coiling or folding of the polypeptide

a. Coiling results in a helical structure called an alpha helix


4. The overall three-dimensional shape of a polypeptide is called its tertiary structure a. Tertiary structure generally results from interactions between the R groups of the various

amino acids

b. Disulfide bridges may further strengthen the protein’s shape

5. Two or more polypeptide chains (subunits) associate providing quaternary structure a. Collagen is an example of a protein with quaternary structure

b. Collagen’s triple helix gives great strength to connective tissue, bone, VI. Nucleic Acids

A. 3.14 DNA and RNA are the two types of nucleic acids

1. In 1952, Alfred Hershey and Martha Chase used bacteriophages (viruses that infect bacteria) to show that DNA, not proteins, is the genetic material of living things

2. The amino acid sequence of proteins is programmed by a discrete unit of inheritance called a gene

3. Genes consist of segments of DNA (deoxyribonucleic acid), a type of nucleic acid.

4. Genes are

5. DNA is inherited from an organism’s parents 6. DNA provides directions for its own replication 7. DNA programs a cell’s activities by

8. DNA does not build proteins directly

9. DNA works through an intermediary, ribonucleic acid (RNA) a. DNA is transcribed into RNA

b. RNA is translated into proteins

10. The “Central Dogma of biology refers to:

a. the flow of genetic information in cells

b. genetic information passing from DNA to RNA by transcription c. genetic information passing from

B. 3.15 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

c. a nitrogenous base 3. DNA nitrogenous bases are

a. adenine (A) b. thymine (T) c. cytosine (C) d. guanine (G)

4. Edwin Chargaff showed that DNA contains equal amounts of the nitrogenous bases of adenine and thymine, and equal amounts of cytosine and guanine

5. Chargaff’s Rule lead to the discovery that in a DNA molecule, adenine always pairs with thymine and cytosine always pairs with guanine

6. RNA

a. also has A, C, and G, b. but instead of T,


7. A nucleic acid polymer, a polynucleotide, forms a. from the nucleotide monomers

b. when the phosphate of one nucleotide bonds to the sugar of the next nucleotide c. by dehydration reactions

d. by producing a repeating sugar-phosphate backbone with

8. Two polynucleotide strands wrap around each other to form a DNA double helix a. The two strands are associated because particular bases always hydrogen bond to one


b. A pairs with T, and C pairs with G, 9. RNA is usually a single nucleotide strand

10. By the mid 1950s, the following facts were known about DNA:

a. It was b. It was c. It was




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