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

2. Overview: The Molecules of Life
All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids
Within cells, small organic molecules are joined together to form larger molecules
Macromolecules are large molecules composed of thousands of covalently connected atoms
Molecular structure and function are inseparable
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3. Macromolecules are polymers, built from monomers
A polymer is a long molecule consisting of many similar building blocks
These small building-block molecules are called monomers
Three of the four classes of life’s organic molecules are polymers:
Carbohydrates
Proteins
Nucleic acids
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4. Reaction to build or breakdown
Fig. 5-2a
Reaction to build or breakdown HO 1 2 3 H HO H
Short polymer
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
H2O
Synthesis
Figure 5.2 The synthesis and breakdown of polymers HO 1 2 3 4 H
Longer polymer
(a)
Dehydration reaction in the synthesis of a polymer

5. HO 1 2 3 4 H H2O HO 1 2 3 H HO H (b) Reaction to build or breakdown
Fig. 5-2b
Reaction to build or breakdown HO 1 2 3 4 H
Hydrolysis adds a water
molecule, breaking a bond
H2O
Breakdown/degredation
Figure 5.2 The synthesis and breakdown of polymers HO 1 2 3 H HO H
(b)
Hydrolysis of a polymer

6. Carbohydrates serve as fuel and building material
Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or single sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
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7. Glucose (C6H12O6) is the most common monosaccharide
Sugars
Monosaccharides have molecular formulas that are usually multiples of CH2O
Glucose (C6H12O6) is the most common monosaccharide
Monosaccharides are classified by
The location of the carbonyl group (as aldose or ketose)
The number of carbons in the carbon skeleton
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8. Examples of Monosaccharides
Fig. 5-3
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Aldoses
Glyceraldehyde
Examples of Monosaccharides
Ribose
Glucose
Galactose
Figure 5.3 The structure and classification of some monosaccharides
Ketoses
Dihydroxyacetone
Ribulose
Fructose

9. Various ways to present macromolecules
Fig. 5-4
Various ways to present macromolecules
(a) Linear and ring forms
Figure 5.4 Linear and ring forms of glucose
(b) Abbreviated ring structure

10. Examples of synthesis Glucose Glucose Maltose
Fig. 5-5
Examples of synthesis
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

11. Polysaccharides
Polysaccharides, the polymers of sugars, have storage and structural roles
The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages
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12. Two examples of Polysaccharides
Fig. 5-6
Two examples of Polysaccharides
Chloroplast
Starch
Mitochondria
Glycogen granules
0.5 µm
1 µm
Figure 5.6 Storage polysaccharides of plants and animals
Amylose
Glycogen
Amylopectin
(a) Starch: a plant polysaccharide
(b) Glycogen: an animal polysaccharide

13. Chemistry of bond directs processing of Molecule
Fig. 5-7
Chemistry of bond directs processing of Molecule
(a)  and  glucose
ring structures
 Glucose
 Glucose
Figure 5.7 Starch and cellulose structures
(b) Starch: 1–4 linkage of  glucose monomers
(b) Cellulose: 1–4 linkage of  glucose monomers

14. 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

15. (a) The structure of the chitin monomer. (b) (c) Chitin forms the
Fig. 5-10
(a)
The structure
of the chitin
monomer.
(b)
Chitin forms the
exoskeleton of
arthropods.
(c)
Chitin is used to make
a strong and flexible
surgical thread.
Figure 5.10 Chitin, a structural polysaccharide

16. 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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17. Fats
Fats are constructed from two types of smaller molecules: glycerol and fatty acids
Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon
A fatty acid consists of a carboxyl group attached to a long carbon skeleton
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18. Fatty acid (palmitic acid) Glycerol
Fig. 5-11a
Fatty acid
(palmitic acid)
Glycerol
Figure 5.11 The synthesis and structure of a fat, or triacylglycerol
(a)
Dehydration reaction in the synthesis of a fat

19. Fat molecule (triacylglycerol)
Fig. 5-11b
Ester linkage
Figure 5.11 The synthesis and structure of a fat, or triacylglycerol
(b)
Fat molecule (triacylglycerol)

20. Structural formula of a saturated fat molecule Stearic acid, a
Fig. 5-12a
Structural
formula of a
saturated fat
molecule
Figure 5.12 Examples of saturated and unsaturated fats and fatty acids
Stearic acid, a
saturated fatty
acid
(a)
Saturated fat

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

22. 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
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23. Choline Hydrophilic head Phosphate Glycerol Fatty acids
Fig. 5-13
Choline
Hydrophilic head
Phosphate
Glycerol
Fatty acids
Hydrophobic tails
Hydrophilic
head
Figure 5.13 The structure of a phospholipid
Hydrophobic
tails
(a)
Structural formula
(b)
Space-filling model
(c)
Phospholipid symbol

24. Hydrophilic head Hydrophobic tail WATER WATER Fig. 5-14
Figure 5.14 Bilayer structure formed by self-assembly of phospholipids in an aqueous environment
Hydrophobic
tail
WATER

25. 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

26. Fig. 5-15
Figure 5.15 Cholesterol, a steroid

27. Proteins have many structures, resulting in a wide range of functions
Proteins account for more than 50% of the dry mass of most cells
Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances
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28. Table 5-1
Table 5-1

29. 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
Animation: Enzymes
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30. Breakdown of a Disaccharide
Fig. 5-16
Breakdown of a Disaccharide
Substrate
(sucrose)
Glucose
Enzyme
(sucrase) OH
H2O
Fructose
Figure 5.16 The catalytic cycle of an enzyme H O

31. Polypeptides are polymers built from the same set of 20 amino acids
A protein consists of one or more polypeptides
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32. Amino acids are organic molecules with carboxyl and amino groups
Amino Acid Monomers
Amino acids are organic molecules with carboxyl and amino groups
Amino acids differ in their properties due to differing side chains, called R groups
Amino
group
Carboxyl
group
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33. Fig. 5-UN5

34. Nonpolar Glycine (Gly or G) Alanine (Ala or A) Valine (Val or V)
Fig. 5-17a
Nonpolar
Glycine
(Gly or G)
Alanine
(Ala or A)
Valine
(Val or V)
Leucine
(Leu or L)
Isoleucine
(Ile or I)
Figure 5.17 The 20 amino acids of proteins
Methionine
(Met or M)
Phenylalanine
(Phe or F)
Tryptophan
(Trp or W)
Proline
(Pro or P)

35. Polar Serine (Ser or S) Threonine (Thr or T) Cysteine (Cys or C)
Fig. 5-17b
Polar
Serine
(Ser or S)
Threonine
(Thr or T)
Cysteine
(Cys or C)
Tyrosine
(Tyr or Y)
Asparagine
(Asn or N)
Glutamine
(Gln or Q)
Figure 5.17 The 20 amino acids of proteins

36. Electrically charged Acidic Basic Aspartic acid (Asp or D)
Fig. 5-17c
Electrically
charged
Acidic
Basic
Figure 5.17 The 20 amino acids of proteins
Aspartic acid
(Asp or D)
Glutamic acid
(Glu or E)
Lysine
(Lys or K)
Arginine
(Arg or R)
Histidine
(His or H)

37. Amino acids are linked by peptide bonds
Amino Acid Polymers
Amino acids are linked by peptide bonds
A polypeptide is a polymer of amino acids
Polypeptides range in length from a few to more than a thousand monomers
Each polypeptide has a unique linear sequence of amino acids
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38. Amino end (N-terminus) Carboxyl end (C-terminus)
Fig. 5-18
Peptide
bond
(a)
Side chains
Peptide
bond
Figure 5.18 Making a polypeptide chain
Backbone
Amino end
(N-terminus)
Carboxyl end
(C-terminus)
(b)

39. Protein Structure and Function
Fig. 5-20
Protein from flu virus
Antibody protein
Protein Structure and Function
Figure 5.20 An antibody binding to a protein from a flu virus
The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s structure determines its function

40. Animation: Primary Protein Structure
Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word
Primary structure is determined by inherited genetic information
Animation: Primary Protein Structure
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41. Four Levels of Protein Structure
Fig. 5-21
Four 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

42. Abdominal glands of the spider secrete silk fibers
Fig. 5-21d
Abdominal glands of the
spider secrete silk fibers
made of a structural protein
containing  pleated sheets.
The radiating strands, made
of dry silk fibers, maintain
the shape of the web.
Figure 5.21 Levels of protein structure—secondary structure
The spiral strands (capture
strands) are elastic, stretching
in response to wind, rain,
and the touch of insects.

43. Tertiary Structure Quaternary Structure
Fig. 5-21e
Tertiary Structure
Quaternary Structure
Figure 5.21 Levels of protein structure—tertiary and quaternary structures

44. 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

45. Polypeptide  Chains chain Iron Heme  Chains Hemoglobin Collagen
Fig. 5-21g
Polypeptide
chain
 Chains
Iron
Figure 5.21 Levels of protein structure—tertiary and quaternary structures
Heme
 Chains
Hemoglobin
Collagen

46. 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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47. Normal hemoglobin Primary structure 1 2 3 4 5 6 7 Secondary
Fig. 5-22a
Normal hemoglobin
Primary
structure
Val
His
Leu
Thr
Pro
Glu
Glu 1 2 3 4 5 6 7
Secondary
and tertiary
structures
 subunit  
Quaternary
structure
Normal
hemoglobin
(top view)  
Figure 5.22 A single amino acid substitution in a protein causes sickle-cell disease
Function
Molecules do
not associate
with one
another; each
carries oxygen.

48. Sickle-cell hemoglobin Primary structure 1 2 3 4 5 6 7
Fig. 5-22b
Sickle-cell hemoglobin
Primary
structure
Val
His
Leu
Thr
Pro
Val
Glu 1 2 3 4 5 6 7
Exposed
hydrophobic
region
Secondary
and tertiary
structures
 subunit  
Quaternary
structure
Sickle-cell
hemoglobin  
Figure 5.22 A single amino acid substitution in a protein causes sickle-cell disease
Function
Molecules
interact with
one another and
crystallize into
a fiber; capacity
to carry oxygen
is greatly reduced.

49. 10 µm 10 µm Normal red blood cells are full of individual hemoglobin
Fig. 5-22c
10 µm
10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.
Figure 5.22 A single amino acid substitution in a protein causes sickle-cell disease

50. What Determines Protein Structure?
In addition to primary structure, physical and chemical conditions can affect structure
Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel
This loss of a protein’s native structure is called denaturation
A denatured protein is biologically inactive
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51. Denaturation Normal protein Denatured protein Renaturation Fig. 5-23
Figure 5.23 Denaturation and renaturation of a protein
Normal protein
Denatured protein
Renaturation

52. Nucleic acids store and transmit hereditary information
The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene
Genes are made of DNA, a nucleic acid
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53. 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 in ribosomes
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54. 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

55. The Structure of Nucleic Acids
Fig. 5-27ab
5' end
The Structure of Nucleic Acids
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

56. (c) Nucleoside components: nitrogenous bases
Fig. 5-27c-1
Nitrogenous bases
Pyrimidines
Cytosine (C)
Thymine (T, in DNA)
Uracil (U, in RNA)
Purines
Figure 5.27 Components of nucleic acids
Adenine (A)
Guanine (G)
(c) Nucleoside components: nitrogenous bases

57. Fig. 5-UN6

58. (c) Nucleoside components: sugars
Fig. 5-27c-2
Sugars
Deoxyribose (in DNA)
Ribose (in RNA)
Figure 5.27 Components of nucleic acids
(c) Nucleoside components: sugars

59. Nucleoside = nitrogenous base + sugar
Nucleotide Monomers
Nucleoside = nitrogenous base + sugar
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
Nucleotide = nucleoside + phosphate group
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60. 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
These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages
The sequence of bases along a DNA or mRNA polymer is unique for each gene
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61. 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
One DNA molecule includes many genes
The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C)
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62. 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

63. Fig. 5-UN10

64. Fig. 5-UN8

65. Fig. 5-UN2a

66. Fig. 5-UN2b

67. Fig. 5-UN9