2. The Structure and Function of Large Biological Molecules5
The Structure and Function of Large Biological Molecules
Lecture Presentation by Nicole Tunbridge and
Kathleen Fitzpatrick

3. The Molecules of Life
All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids
Macromolecules are large molecules and are complex
Large biological molecules have unique properties that arise from the orderly arrangement of their atoms

4. Concept 5.1: Macromolecules are polymers, built from monomers
A polymer is a long molecule consisting of many similar building blocks
Three of the four classes of life’s organic molecules are polymers
Carbohydrates
Proteins
Nucleic acids
The repeating units that serve as building blocks are called monomers

5. The Synthesis and Breakdown of Polymers
Enzymes are specialized macromolecules that speed up chemical reactions such as those that make or break down polymers
A dehydration reaction occurs when two monomers bond together through the loss of a water molecule
Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction

6. (a) Dehydration reaction: synthesizing a polymer
Figure 5.2
(a) Dehydration reaction: synthesizing a polymer 1 2 3
Short polymer
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond.
H2O 1 2 3 4
Longer polymer
(b) Hydrolysis: breaking down a polymer
Figure 5.2 The synthesis and breakdown of polymers 1 2 3 4
H2O
Hydrolysis adds a water
molecule, breaking a bond. 1 2 3

7. Animation: Polymers

8. The Diversity of Polymers
Each cell has thousands of different macromolecules
Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species
A huge variety of polymers can be built from a small set of monomers

9. Concept 5.2: Carbohydrates serve as fuel and building material
Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or simple sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks

10. 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

11. Aldoses (Aldehyde Sugars) Ketoses (Ketone Sugars)
Figure 5.3
Aldoses (Aldehyde Sugars)
Ketoses (Ketone Sugars)
Trioses: 3-carbon sugars (C3H6O3)
Glyceraldehyde
Dihydroxyacetone
Pentoses: 5-carbon sugars (C5H10O5)
Ribose
Ribulose
Hexoses: 6-carbon sugars (C6H12O6)
Figure 5.3 The structure and classification of some monosaccharides
Glucose
Galactose
Fructose

12. Though often drawn as linear skeletons, in aqueous solutions many sugars form rings
Monosaccharides serve as a major fuel for cells and as raw material for building molecules

13. (a) Linear and ring forms
Figure 5.4
(a) Linear and ring forms
Figure 5.4 Linear and ring forms of glucose
(b) Abbreviated ring structure

14. A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage

15. Glucose Glucose Maltose Glucose Fructose Sucrose
Figure 5.5
(a) Dehydration reaction in the synthesis of maltose
1−4
glycosidic
linkage
H2O
Glucose
Glucose
Maltose
(b) Dehydration reaction in the synthesis of sucrose
1−2
glycosidic
linkage
Figure 5.5 Examples of disaccharide synthesis
H2O
Glucose
Fructose
Sucrose

16. Polysaccharides
Polysaccharides, the polymers of sugars, have storage and structural roles
The architecture and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages

17. Storage Polysaccharides
Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
Plants store surplus starch as granules within chloroplasts and other plastids
The simplest form of starch is amylose

18. Glucose monomer 50 µm 1 µm 10 µm 0.5 µm
Figure 5.6
Storage structures
(plastids)
containing starch
granules in a potato
tuber cell
Amylose (unbranched)
Amylopectin
(somewhat
branched)
Glucose
monomer
50 µm
(a) Starch
Glycogen
granules in
muscle
tissue
Glycogen (branched)
Cell
wall
1 µm
(b) Glycogen
Figure 5.6 Polysaccharides of plants and animals
Cellulose microfibrils
in a plant cell wall
Cellulose molecule (unbranched)
Plant cell,
surrounded
by cell wall
10 µm
Microfibril
Hydrogen bonds
0.5 µm
(c) Cellulose

19. Glycogen is a storage polysaccharide in animals
Glycogen is stored mainly in liver and muscle cells
Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases

20. 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 ()

21. (a) 𝛂 and 𝛃 glucose ring structures
Figure 5.7a
𝛂 Glucose
𝛃 Glucose
Figure 5.7a Starch and cellulose structures (part 1: ring structures)
(a) 𝛂 and 𝛃 glucose ring structures

22. Starch (a configuration) is largely helical
Cellulose molecules (b configuration) are straight and unbranched
Some hydroxyl groups on the monomers of cellulose can hydrogen bond with hydroxyls of parallel cellulose molecules

23. (b) Starch: 1–4 linkage of 𝛂 glucose monomer
Figure 5.7b
(b) Starch: 1–4 linkage of 𝛂 glucose monomer
Figure 5.7b Starch and cellulose structures (part 2: linkages)
(c) Cellulose: 1–4 linkage of 𝛃 glucose monomers

24. Enzymes that digest starch by hydrolyzing  linkages can’t hydrolyze  linkages in cellulose
The 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

25. Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin also provides structural support for the cell walls of many fungi

26. Chitin, embedded in proteins, forms the exoskeleton of arthropods.
Figure 5.8 ►
The structure
of the chitin
monomer ►
Chitin, embedded in proteins,
forms the exoskeleton of
arthropods. ►
Chitin is used to
make a strong
and flexible
surgical
thread.
Figure 5.8 Chitin, a structural polysaccharide

27. Concept 5.3: Lipids are a diverse group of hydrophobic molecules
Lipids are the one class of large biological molecules that does not include true polymers
The unifying feature of lipids is that they mix poorly, if at all, with 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

28. 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

29. (in this case, palmitic acid)
Figure 5.9
H2O
Fatty acid
(in this case, palmitic acid)
Glycerol
(a) One of three dehydration reactions in the synthesis of a fat
Ester linkage
Figure 5.9 The synthesis and structure of a fat, or triacylglycerol
(b) Fat molecule (triacylglycerol)

30. Animation: Fats

31. Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats
In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride
The fatty acids in a fat can be all the same or of two or three different kinds

32. 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

33. (a) Saturated fat (b) Unsaturated fat Structural formula
Figure 5.10
(a) Saturated fat
(b) Unsaturated fat
Structural
formula
of a saturated
fat molecule
Structural
formula of an
unsaturated
fat molecule
Space-filling
model of
stearic acid,
a saturated
fatty acid
Figure 5.10 Saturated and unsaturated fats and fatty acids
Space-filling
model of oleic
acid, an
unsaturated
fatty acid
Cis double
bond causes
bending.

34. Fats made from saturated fatty acids are called saturated fats and are solid at room temperature
Most animal fats are saturated
Fats made from unsaturated fatty acids are called unsaturated fats or oils and are liquid at room temperature
Plant fats and fish fats are usually unsaturated

35. A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits
Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen
Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds
These trans fats may contribute more than saturated fats to cardiovascular disease

36. Certain unsaturated fatty acids are not synthesized in the human body
These must be supplied in the diet
These essential fatty acids include the omega-3 fatty acids, which are required for normal growth and are thought to provide protection against cardiovascular disease

37. The major function of fats is energy storage
Humans and other mammals store their long-term food reserves in adipose cells
Adipose tissue also cushions vital organs and insulates the body

38. 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

39. (c) Phospholipid symbol
Figure 5.11
Choline
Hydrophilic
head
Hydrophilic head
Phosphate
Hydrophobic
tails
Glycerol
(c) Phospholipid symbol
Fatty acids
Hydrophobic tails
Kink due to cis
double bond
Figure 5.11 The structure of a phospholipid
(a) Structural formula
(b) Space-filling model
(d) Phospholipid bilayer

40. When phospholipids are added to water, they self-assemble into double-layered structures called bilayers
At the surface of a cell, phospholipids are also arranged in a bilayer, with the hydrophobic tails pointing toward the interior
The structure of phospholipids results in a bilayer arrangement found in cell membranes
The existence of cells depends on phospholipids

41. Steroids
Steroids are lipids characterized by a carbon skeleton consisting of four fused rings
Cholesterol, a type of steroid, is a component in animal cell membranes and a precursor from which other steroids are synthesized
A high level of cholesterol in the blood may contribute to cardiovascular disease

42. Figure 5.12
Figure 5.12 Cholesterol, a steroid

43. Concept 5.4: Proteins include a diversity of structures, resulting in a wide range of functions
Proteins account for more than 50% of the dry mass of most cells
Some proteins speed up chemical reactions (catalytic enzymes)
Other protein functions include defense, storage, transport, cellular communication, movement, or structural support

44. Enzymatic proteins Defensive proteins Storage proteins
Figure 5.13a
Enzymatic proteins
Defensive proteins
Function: Selective acceleration of
chemical reactions
Function: Protection against disease
Example: Antibodies inactivate and help
destroy viruses and bacteria.
Example: Digestive enzymes catalyze the
hydrolysis of bonds in food molecules.
Antibodies
Enzyme
Bacterium
Virus
Storage proteins
Transport proteins
Function: Storage of amino acids
Function: Transport of substances
Examples: Casein, the protein of milk, is the
major source of amino acids for baby
mammals. Plants have storage proteins in
their seeds. Ovalbumin is the protein of egg
white, used as an amino acid source for the
developing embryo.
Examples: Hemoglobin, the iron-containing
protein of vertebrate blood, transports
oxygen from the lungs to other parts of the
body. Other proteins transport molecules
across membranes, as shown here.
Figure 5.13a An overview of protein functions (part 1)
Transport
protein
Ovalbumin
Amino acids
for embryo
Cell membrane

45. Contractile and motor proteins Structural proteins
Figure 5.13b
Hormonal proteins
Receptor proteins
Function: Coordination of an organism’s
activities
Function: Response of cell to chemical
stimuli
Example: Insulin, a hormone secreted by the
pancreas, causes other tissues to take up
glucose, thus regulating blood sugar,
concentration.
Example: Receptors built into the
membrane of a nerve cell detect
signaling molecules released by other
nerve cells.
Receptor
protein
Insulin
secreted
High
blood sugar
Normal
blood sugar
Signaling
molecules
Contractile and motor proteins
Structural proteins
Function: Movement
Function: Support
Examples: Motor proteins are responsible
for the undulations of cilia and flagella.
Actin and myosin proteins are responsible
for the contraction of muscles.
Examples: Keratin is the protein of hair,
horns, feathers, and other skin
appendages. Insects and spiders use silk
fibers to make their cocoons and webs,
respectively. Collagen and elastin proteins
provide a fibrous framework in animal
connective tissues.
Figure 5.13b An overview of protein functions (part 2)
Actin
Actin
Myosin
Collagen
Muscle
tissue
30 µm
Connective
tissue
60 µm

46. Enzymes are proteins that act as catalysts to speed up chemical reactions
Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life

47. Proteins are all constructed from the same set of 20 amino acids
Polypeptides are unbranched polymers built from these amino acids
A protein is a biologically functional molecule that consists of one or more polypeptides

48. Amino Acid Monomers
Amino acids are organic molecules with amino and carboxyl groups
Amino acids differ in their properties due to differing side chains, called R groups

49. Side chain (R group) 𝛂 carbon Amino group Carboxyl group Figure 5.UN01
Figure 5.UN01 In-text figure, amino acid monomer, p. 75
Amino
group
Carboxyl
group