1. The Structure and Function of Large Biological Molecules
Chapter 5
AP Biology

2. 4 main classes Carbohydrates Proteins Nucleic acids Lipids
The first 3 are considered to be macromolecules and polymers

3. Synthesis and breakdown of polymers
Polymers: built through a condensation reaction-
two monomers are joined and a water is produced (facilitated by enzymes)

4. molecule, forming a new bond H2O
Fig. 5-2a HO 1 2 3 H HO H
Short polymer
Unlinked monomer
removes a water
molecule, forming a new bond
H2O
Figure 5.2 The synthesis and breakdown of polymers HO 1 2 3 4 H
Longer polymer
(a)
reaction in the synthesis of a polymer

5. Synthesis and breakdown of polymers
Polymers are broken down through hydrolysis-
the bond between monomers is broken, which requires the use of a water molecule.

6. HO 1 2 3 4 H H2O HO 1 2 3 H HO H (b) Hydrolysis adds a water
Fig. 5-2b HO 1 2 3 4 H
Hydrolysis adds a water
molecule, breaking a bond
H2O
Figure 5.2 The synthesis and breakdown of polymers HO 1 2 3 H HO H
(b)
Hydrolysis of a polymer

7. Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species
An immense variety of polymers can be built from a small set of monomers (depending on how you link them together)

8. Carbohydrates

9. Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or single sugars
Disaccharides are two sugar molecules linked together
Carbohydrate macromolecules are polysaccharides, polymers composed of 3 or more sugar building blocks

10. Glucose (C6H12O6) is the most common monosaccharide
Monosaccharides serve as a major fuel for cells and as raw material for building molecules

11. This covalent bond is called a glycosidic linkage
A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage
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12. (a) Dehydration reaction in the synthesis of maltose
Fig. 5-5
1–4
glycosidic
linkage
Glucose
Glucose
Maltose
(a) Dehydration reaction in the synthesis of maltose
1–2
glycosidic
linkage
Figure 5.5 Examples of disaccharide synthesis
Glucose
Fructose
Sucrose
(b) Dehydration reaction in the synthesis of sucrose

13. Starch, a storage polysaccharide of plants, consists entirely of glucose monomers (3 or more strung together)
Plants store surplus starch as granules within chloroplasts and other plastids
Glycogen is a storage polysaccharide in animals
Humans and other vertebrates store glycogen mainly in liver and muscle cells

14. Structural Polysaccharides
The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ
The difference is based on two ring forms for glucose: alpha () and beta ()
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15. (b) Starch: 1–4 linkage of alpha glucose monomers
Fig. 5-7
(a)  and  glucose
ring structures
alpha Glucose
beta Glucose
Figure 5.7 Starch and cellulose structures
(b) Starch: 1–4 linkage of alpha glucose monomers
(b) Cellulose: 1–4 linkage of beta glucose monomers

16. Cell walls Cellulose microfibrils in a plant cell wall Microfibril
Fig. 5-8
Cell walls
Cellulose
microfibrils
in a plant
cell wall
Microfibril
10 µm
0.5 µm
Cellulose
molecules
Figure 5.8 The arrangement of cellulose in plant cell walls
Glucose
monomer

17. Some microbes use enzymes to digest cellulose
Enzymes that digest starch by hydrolyzing  linkages can’t hydrolyze  linkages in cellulose
Cellulose in human food passes through the digestive tract as insoluble fiber
Some microbes use enzymes to digest cellulose
Many herbivores, from cows to termites, have symbiotic relationships with these microbes
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18. Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin also provides structural support for the cell walls of many fungi
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19. Lipids

20. 5.3: Lipids are a diverse group of hydrophobic molecules
Lipids are the one class of large biological molecules that do not form polymers
The unifying feature of lipids is having little or no affinity for water
Lipids are hydrophobic becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds
The most biologically important lipids are fats, phospholipids, and steroids
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21. Fats
Fats are constructed from two types of smaller molecules: glycerol and fatty acids
The major function of fats is energy storage
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22. Fatty acid (palmitic acid)
Fig. 5-11
Fatty acid
(palmitic acid)
Glycerol
(a) Dehydration reaction in the synthesis of a fat
Ester linkage
Figure 5.11 The synthesis and structure of a fat, or triacylglycerol
(b) Fat molecule (triacylglycerol)

23. Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats
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24. Fatty acids vary in length (number of carbons) and in the number and locations of double bonds
Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds
Unsaturated fatty acids have one or more double bonds

25. Structural formula of a saturated fat molecule Stearic acid, a
Fig. 5-12
Structural
formula of a
saturated fat
molecule
Stearic acid, a
saturated fatty
acid
(a) Saturated fat
Figure 5.12 Examples of saturated and unsaturated fats and fatty acids
Structural formula
of an unsaturated
fat molecule
Oleic acid, an
unsaturated
fatty acid
cis double
bond causes
bending
(b) Unsaturated fat

26. Phospholipids
In a phospholipid, two fatty acids and a phosphate group are attached to glycerol
The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head

27. Choline Phosphate Hydrophilic head Glycerol Fatty acids
Fig. 5-13ab
Choline
Phosphate
Hydrophilic head
Glycerol
Fatty acids
Hydrophobic tails
Figure 5.13 The structure of a phospholipid
(a)
Structural formula
(b)
Space-filling model

28. Phospholipids are the major component of all cell membranes
When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior
The structure of phospholipids results in a bilayer arrangement found in cell membranes
Phospholipids are the major component of all cell membranes
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29. Hydrophilic head Hydrophobic tail WATER WATER
Fig. 5-14
Hydrophilic
head
WATER
Figure 5.14 Bilayer structure formed by self-assembly of phospholipids in an aqueous environment
Hydrophobic
tail
WATER

30. Steroids
Steroids are lipids characterized by a carbon skeleton consisting of four fused rings
Cholesterol, an important steroid, is a component in animal cell membranes
Although cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease
For the Cell Biology Video Space Filling Model of Cholesterol, go to Animation and Video Files.
For the Cell Biology Video Stick Model of Cholesterol, go to Animation and Video Files.
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31. Proteins

32. Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances

33. Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions
Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

34. Polypeptides
Polypeptides are polymers built from the same set of 20 amino acids
A protein consists of one or more polypeptides
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35. Protein Structure and Function
A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

36. A ribbon model of lysozyme A space-filling model of lysozyme
Fig. 5-19
Groove
Groove
Figure 5.19 Structure of a protein, the enzyme lysozyme
(a)
A ribbon model of lysozyme
(b)
A space-filling model of lysozyme

37. Four Levels of Protein Structure
The primary structure of a protein is its unique sequence of amino acids
Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain attraction between chain elements
Tertiary structure is determined by interactions among various side chains (R groups)
Quaternary structure results when a protein consists of multiple polypeptide chains
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38. +H3N Primary Structure Amino end Amino acid subunits 1 5 10 15 20 25
Fig. 5-21a
Primary Structure 1 5
+H3N
Amino end 10
Amino acid
subunits 15
Figure 5.21 Levels of protein structure—primary structure 20 25

39. The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone
Typical secondary structures are a coil called an  helix and a folded structure called a  pleated sheet
For the Cell Biology Video An Idealized Alpha Helix: No Sidechains, go to Animation and Video Files.
For the Cell Biology Video An Idealized Alpha Helix, go to Animation and Video Files.
For the Cell Biology Video An Idealized Beta Pleated Sheet Cartoon, go to Animation and Video Files.
For the Cell Biology Video An Idealized Beta Pleated Sheet, go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

40. Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents
Strong covalent bonds called disulfide bridges may reinforce the protein’s structure
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41. Hydrophobic interactions and van der Waals interactions Polypeptide
Fig. 5-21f
Hydrophobic
interactions and
van der Waals
interactions
Polypeptide
backbone
Hydrogen
bond
Disulfide bridge
Figure 5.21 Levels of protein structure—tertiary and quaternary structures
Ionic bond

42. Figure 5.21 Levels of protein structure—primary structure
Secondary
Structure
Tertiary
Structure
Quaternary
Structure
 pleated sheet
+H3N
Amino end
Examples of
amino acid
subunits
 helix
Figure 5.21 Levels of protein structure—primary structure

43. Sickle-Cell Disease: A Change in Primary Structure
A slight change in primary structure can affect a protein’s structure and ability to function
Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin
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44. Nucleic Acids

45. The Roles of Nucleic Acids
There are two types of nucleic acids:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
DNA provides directions for its own replication
DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis
Protein synthesis occurs at ribosomes
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46. DNA 1 Synthesis of mRNA in the nucleus mRNA NUCLEUS CYTOPLASM mRNA 2
Fig
DNA 1
Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA 2
Movement of
mRNA into cytoplasm
via nuclear pore
Ribosome
Figure 5.26 DNA → RNA → protein 3
Synthesis
of protein
Amino
acids
Polypeptide

47. The Structure of Nucleic Acids
Nucleic acids are polymers called polynucleotides
Each polynucleotide is made of monomers called nucleotides
Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group
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48. (a) Polynucleotide, or nucleic acid (c) Nucleoside components: sugars
Fig. 5-27
5 end
Nitrogenous bases
Pyrimidines
5C
3C
Nucleoside
Nitrogenous
base
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Purines
Phosphate
group
Sugar
(pentose)
5C
Adenine (A)
Guanine (G)
3C
(b) Nucleotide
Sugars
3 end
Figure 5.27 Components of nucleic acids
(a) Polynucleotide, or nucleic acid
Deoxyribose (in DNA)
Ribose (in RNA)
(c) Nucleoside components: sugars

49. Nucleotide Monomers There are two families of nitrogenous bases:
Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring
Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring
In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose
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50. Nucleotide Polymers
Nucleotide polymers are linked together to build a polynucleotide
Adjacent nucleotides are joined by covalent bonds that form between the –OH group on the 3 carbon of one nucleotide and the phosphate on the 5 carbon on the next
DNA polymerase can add free nucleotides to only the 3' end of the newly-forming strand. This results in elongation of the new strand in a 5'-3' direction
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51. Nitrogenous base Phosphate group Sugar (pentose)
Fig. 5-27ab
5' end
5'C
3'C
Nucleoside
Nitrogenous
base
5'C
Phosphate
group
Figure 5.27 Components of nucleic acids
3'C
Sugar
(pentose)
5'C
3'C
(b) Nucleotide
3' end
(a) Polynucleotide, or nucleic acid

52. The DNA Double Helix
A DNA molecule has two polynucleotides spiraling around an imaginary axis, forming a double helix
In the DNA double helix, the two backbones run in opposite 5 → 3 directions from each other, an arrangement referred to as antiparallel
The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)

53. 5' end 3' end Sugar-phosphate backbones Base pair (joined by
Fig. 5-28
5' end
3' end
Sugar-phosphate
backbones
Base pair (joined by
hydrogen bonding)
Old strands
Nucleotide
about to be
added to a
new strand
3' end
Figure 5.28 The DNA double helix and its replication
5' end
New
strands
5' end
3' end
5' end
3' end