The Structure and Function of Large Biological Molecules

Overview: The Molecules of Life

All living things are made up of

Fig. 5-1

Concept 5.1: Macromolecules are polymers, built from monomers

A polymer is a

A condensation reaction or more specifically a dehydration reaction occurs when

Fig. 5-2

Short polymer

HO

1

2

3

H

HO

H

Unlinked monomer

Dehydration removes a water
molecule, forming a new bond

HO

H2O

H

1

2

3

4

Longer

Fig. 5-2a

Dehydration removes a water
molecule, forming a new bond

Short polymer

Unlinked monomer

Longer

Fig. 5-2b

Hydrolysis adds a water
molecule, breaking a bond

Hydrolysis of a polymer

HO

HO

HO

H2O

H

H

H

3

2

1

1

2

3

4

(b)

The Diversity of Polymers

Each cell has thousands of different kinds of

Concept 5.2: Carbohydrates serve as fuel and building material

Carbohydrates include sugars

Sugars

Monosaccharides have molecular formulas that are usually multiples of CH2O
Glucose (C6H12O6)

Fig. 5-3

Dihydroxyacetone

Ribulose

Ketoses

Aldoses

Fructose

Glyceraldehyde

Ribose

Glucose

Galactose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

Fig. 5-3a

Aldoses

Glyceraldehyde

Ribose

Glucose

Galactose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

Fig. 5-3b

Ketoses

Dihydroxyacetone

Ribulose

Fructose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

Though often drawn as linear skeletons, in aqueous solutions many sugars

Fig. 5-4

(a) Linear and ring forms

(b) Abbreviated ring structure

Fig. 5-4a

(a) Linear and ring forms

Fig. 5-4b

(b) Abbreviated ring structure

A disaccharide is formed when a dehydration reaction joins two monosaccharides

Fig. 5-5

(b) Dehydration reaction in the synthesis of sucrose

Glucose

Fructose

Sucrose

Maltose

Glucose

Glucose

(a) Dehydration reaction

Polysaccharides

Polysaccharides, the polymers of sugars, have storage and structural roles
The structure

Storage Polysaccharides

Starch, a storage polysaccharide of plants, consists entirely of glucose

Fig. 5-6

(b) Glycogen: an animal polysaccharide

Starch

Glycogen

Amylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria

Glycogen granules

0.5

Glycogen is a storage polysaccharide in animals
Humans and other vertebrates store

Structural Polysaccharides

The polysaccharide cellulose is a major component of the tough

Fig. 5-7

(a)  and  glucose
ring structures

 Glucose

 Glucose

(b) Starch:

Fig. 5-7a

(a)  and  glucose ring structures

 Glucose



Fig. 5-7bc

(b) Starch: 1–4 linkage of  glucose monomers

(c) Cellulose: 1–4

Polymers with α glucose are helical
Polymers with β glucose are straight
In

Fig. 5-8

Glucose
monomer

Cellulose
molecules

Microfibril

Cellulose
microfibrils
in a plant
cell wall

0.5 µm

10 µm

Cell walls

Enzymes that digest starch by hydrolyzing α linkages can’t hydrolyze β

Fig. 5-9

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin

Fig. 5-10

The structure
of the chitin
monomer.

(a)

(b)

(c)

Chitin forms the
exoskeleton of
arthropods.

Chitin is used to

Concept 5.3: Lipids are a diverse group of hydrophobic molecules

Lipids are

Fats

Fats are constructed from two types of smaller molecules: glycerol and

Fig. 5-11

Fatty acid
(palmitic acid)

Glycerol

(a) Dehydration reaction in the synthesis of a

Fig. 5-11a

Fatty acid
(palmitic acid)

(a)

Dehydration reaction in the synthesis of a fat

Glycerol

Fig. 5-11b

(b)

Fat molecule (triacylglycerol)

Ester linkage

Fats separate from water because water molecules form hydrogen bonds with

Fatty acids vary in length (number of carbons) and in the

Fig. 5-12

Structural
formula of a
saturated fat
molecule

Stearic acid, a
saturated fatty
acid

(a) Saturated fat

Structural formula
of

Fig. 5-12a

(a)

Saturated fat

Structural
formula of a
saturated fat
molecule

Stearic acid, a
saturated fatty
acid

Fig. 5-12b

(b)

Unsaturated fat

Structural formula
of an unsaturated
fat molecule

Oleic acid, an
unsaturated
fatty acid

cis double
bond

Fats made from saturated fatty acids are called saturated fats, and

A diet rich in saturated fats may contribute to cardiovascular disease

The major function of fats is energy storage
Humans and other mammals

Phospholipids

In a phospholipid, two fatty acids and a phosphate group are

Fig. 5-13

(b)

Space-filling model

(a)

(c)

Structural formula

Phospholipid symbol

Fatty acids

Hydrophilic
head

Hydrophobic
tails

Choline

Phosphate

Glycerol

Hydrophobic tails

Hydrophilic head

Fig. 5-13ab

(b)

Space-filling model

(a)

Structural formula

Fatty acids

Choline

Phosphate

Glycerol

Hydrophobic tails

Hydrophilic head

When phospholipids are added to water, they self-assemble into a bilayer,

Fig. 5-14

Hydrophilic
head

Hydrophobic
tail

WATER

WATER

Steroids

Steroids are lipids characterized by a carbon skeleton consisting of four

Fig. 5-15

Concept 5.4: Proteins have many structures, resulting in a wide range

Table 5-1

Animation: Structural Proteins

Animation: Storage Proteins

Animation: Transport Proteins

Animation: Receptor Proteins

Animation: Contractile Proteins

Animation:

Enzymes are a type of protein that acts as a catalyst

Fig. 5-16

Enzyme
(sucrase)

Substrate
(sucrose)

Fructose

Glucose

OH

H

O

H2O

Polypeptides

Polypeptides are polymers built from the same set of 20 amino

Amino Acid Monomers

Amino acids are organic molecules with carboxyl and amino

Fig. 5-UN1

Amino
group

Carboxyl
group

 carbon

Fig. 5-17

Nonpolar

Glycine
(Gly or G)

Alanine
(Ala or A)

Valine
(Val or V)

Leucine
(Leu or L)

Isoleucine
(Ile or

Fig. 5-17a

Nonpolar

Glycine
(Gly or G)

Alanine
(Ala or A)

Valine
(Val or V)

Leucine

Fig. 5-17b

Polar

Asparagine
(Asn or N)

Glutamine
(Gln or Q)

Serine
(Ser or S)

Threonine

Fig. 5-17c

Acidic

Arginine
(Arg or R)

Histidine
(His or H)

Aspartic acid
(Asp or

Amino Acid Polymers

Amino acids are linked by peptide bonds
A polypeptide is

Peptide
bond

Fig. 5-18

Amino end
(N-terminus)

Peptide
bond

Side chains

Backbone

Carboxyl end
(C-terminus)

(a)

(b)

Protein Structure and Function

A functional protein consists of one or more

Fig. 5-19

A ribbon model of lysozyme

(a)

(b)

A space-filling model of lysozyme

Groove

Groove

Fig. 5-19a

A ribbon model of lysozyme

(a)

Groove

Fig. 5-19b

(b)

A space-filling model of lysozyme

Groove

The sequence of amino acids determines a protein’s three-dimensional structure
A protein’s

Fig. 5-20

Antibody protein

Protein from flu virus

Four Levels of Protein Structure

The primary structure of a protein is

Primary structure, the sequence of amino acids in a protein, is

Fig. 5-21

Primary
Structure

Secondary
Structure

Tertiary
Structure

 pleated sheet

Examples of
amino acid
subunits

+H3N
Amino end

 helix

Quaternary
Structure

Fig. 5-21a

Amino acid
subunits

+H3N
Amino end

25

20

15

10

5

1

Primary Structure

Fig. 5-21b

Amino acid
subunits

+H3N
Amino end

Carboxyl end

125

120

115

110

105

100

95

90

85

80

75

20

25

15

10

5

1

The coils and folds of secondary structure result from hydrogen bonds

Fig. 5-21c

Secondary Structure

 pleated sheet

Examples of
amino acid
subunits

 helix

Fig. 5-21d

Abdominal glands of the
spider secrete silk fibers
made of a structural

Tertiary structure is determined by interactions between R groups, rather than

Fig. 5-21e

Tertiary Structure

Quaternary Structure

Fig. 5-21f

Polypeptide
backbone

Hydrophobic
interactions and
van der Waals
interactions

Disulfide bridge

Ionic bond

Hydrogen
bond

Fig. 5-21g

Polypeptide
chain

 Chains

Heme

Iron

 Chains

Collagen

Hemoglobin

Quaternary structure results when two or more polypeptide chains form one

Sickle-Cell Disease: A Change in Primary Structure

A slight change in primary

Fig. 5-22

Primary
structure

Secondary
and tertiary
structures

Quaternary
structure

Normal
hemoglobin
(top view)

Primary
structure

Secondary
and tertiary
structures

Quaternary
structure

Function

Function

 subunit

Molecules do
not associate
with one
another; each
carries oxygen.

Red

Fig. 5-22a

Primary
structure

Secondary
and tertiary
structures

Function

Quaternary
structure

Molecules do
not associate
with one
another; each
carries oxygen.

Normal
hemoglobin
(top view)

 subunit

Normal hemoglobin

7

6

5

4

3

2

1









Glu

Val

His

Leu

Thr

Pro

Glu

Fig. 5-22b

Primary
structure

Secondary
and tertiary
structures

Function

Quaternary
structure

Molecules
interact with
one another and
crystallize into
a fiber;

Fig. 5-22c

Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.

Fibers of

What Determines Protein Structure?

In addition to primary structure, physical and chemical

Fig. 5-23

Normal protein

Denatured protein

Denaturation

Renaturation

Protein Folding in the Cell

It is hard to predict a protein’s

Fig. 5-24

Hollow
cylinder

Cap

Chaperonin
(fully assembled)

Polypeptide

Steps of Chaperonin
Action:

An unfolded poly-
peptide enters the
cylinder from one

Fig. 5-24a

Hollow
cylinder

Chaperonin
(fully assembled)

Cap

Fig. 5-24b

Correctly
folded
protein

Polypeptide

Steps of Chaperonin
Action:

1

2

An unfolded poly-
peptide enters the
cylinder from one end.

The

Scientists use X-ray crystallography to determine a protein’s structure
Another method is

Fig. 5-25

EXPERIMENT

RESULTS

X-ray
source

X-ray
beam

Diffracted
X-rays

Crystal

Digital detector

X-ray diffraction
pattern

RNA
polymerase II

RNA

DNA

Fig. 5-25a

Diffracted
X-rays

EXPERIMENT

X-ray
source

X-ray
beam

Crystal

Digital detector

X-ray diffraction
pattern

Fig. 5-25b

RESULTS

RNA

RNA
polymerase II

DNA

Concept 5.5: Nucleic acids store and transmit hereditary information

The amino acid

The Roles of Nucleic Acids

There are two types of nucleic acids:
Deoxyribonucleic

Fig. 5-26-1

mRNA

Synthesis of
mRNA in the
nucleus

DNA

NUCLEUS

CYTOPLASM

1

Fig. 5-26-2

mRNA

Synthesis of
mRNA in the
nucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement of
mRNA into cytoplasm
via nuclear pore

1

2

Fig. 5-26-3

mRNA

Synthesis of
mRNA in the
nucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement of
mRNA into cytoplasm
via nuclear pore

Ribosome

Amino
acids

Polypeptide

Synthesis
of protein

1

2

3

The Structure of Nucleic Acids

Nucleic acids are polymers called polynucleotides
Each polynucleotide

Fig. 5-27

5 end

Nucleoside

Nitrogenous
base

Phosphate
group

Sugar
(pentose)

(b) Nucleotide

(a) Polynucleotide, or nucleic acid

3 end

3C

3C

5C

5C

Nitrogenous bases
Pyrimidines

Cytosine (C)

Thymine

Fig. 5-27ab

5' end

5'C

3'C

5'C

3'C

3' end

(a) Polynucleotide, or nucleic acid

(b) Nucleotide

Nucleoside

Nitrogenous
base

3'C

5'C

Phosphate
group

Sugar
(pentose)

Fig. 5-27c-1

(c) Nucleoside components: nitrogenous bases

Purines

Guanine (G)

Adenine (A)

Cytosine (C)

Thymine (T, in

Fig. 5-27c-2

Ribose (in RNA)

Deoxyribose (in DNA)

Sugars

(c) Nucleoside components: sugars

Nucleotide Monomers

Nucleoside = nitrogenous base + sugar
There are two families of

Nucleotide Polymers

Nucleotide polymers are linked together to build a polynucleotide
Adjacent nucleotides

The DNA Double Helix

A DNA molecule has two polynucleotides spiraling around

Fig. 5-28

Sugar-phosphate
backbones

3' end

3' end

3' end

3' end

5' end

5' end

5' end

5' end

Base pair

DNA and Proteins as Tape Measures of Evolution

The linear sequences of

The Theme of Emergent Properties in the Chemistry of Life: A

Fig. 5-UN2

Fig. 5-UN2a

Fig. 5-UN2b

Fig. 5-UN3

% of glycosidic
linkages broken

100

50

0

Time

Fig. 5-UN4

Fig. 5-UN5

Fig. 5-UN6

Fig. 5-UN7

Fig. 5-UN8

Fig. 5-UN9

Fig. 5-UN10

You should now be able to:

List and describe the four major