The Structure and Function of Macromolecules of the tough wall of plant cells •Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Chapter 5

The Structure and Function of

Macromolecules

PowerPoint lectures are originally from Campbell / Reece

Media Manager and Instructor Resources for BIOLOGY,

7th & 8th Edition by N. A. Campbell & J. B. Reece

Copyright 2005 & 2008 Pearson Education, Inc. Publishing

as Benjamin Cummings


Overview: 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 composed of thousands of covalently connected atoms

• Molecular structure and function are inseparable

© 2011 Pearson Education, Inc.


The Molecules of Life

• The four classes of macromolecules that are

important to life are:

– Carbohydrates

– Lipids

– Proteins

– Nucleic acids


Most macromolecules are polymers, built from monomers

• Three of the four classes of life’s organic molecules are polymers:

– Carbohydrates

– Proteins

– Nucleic acids


Macromecules are made of monomers

• Carbohydrates, Proteins, and Nucleic Acids are all

polymers made from building blocks. Building blocks can

be called monomers

Macromolecule Type

Carbohydrate Protein Nucleic Acid (DNA and RNA)

Name of

Monomer

monosaccharide Amino acid nucleotides

monomer


The Synthesis of Polymers by DEHYDRATION REACTIONS

• Monomers form larger

molecules called polymers

by condensation reactions

called dehydration

reactions.

• A dehydration reaction

occurs when two monomers

bond together through the

loss of a water molecule


Dehydration removes a water molecule, forming a new bond

Short polymer Unlinked monomer

Longer polymer

Dehydration reaction in the synthesis of a polymer

HO

HO

HO

H2O

H

H H

4 3 2 1

1 2 3

(a)


The Breakdown of Polymers by HYDOLYSIS REACTIONS

• Polymers are disassembled to monomers

by hydrolysis, a reaction that is essentially

the reverse of the dehydration reaction.

• In hydrolysis, bonds are broken by the

addition of water molecules.


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)


Concept 5.2: Carbohydrates serve as fuel and building material

• Carbohydrates include single (simple) sugars and

their polymers

• Carbohydrates may be classified as:

– Monosaccharides (the simplest)

– Disaccharides

– Polysaccharides


Monosaccharides

• Monosaccharides have molecular formulas that

are usually multiples of CH2O

(CH2O)n where n ranges from 1-7

• Glucose (C6H12O6) is the most common

monosaccharide.


Monosaccharides

• Monosaccharides have two

functional groups:

1- One carbonyl group that is either:

– An aldehyde group OR

– a ketone group

2- Many hydroxyl groups.


Monosaccharides

• Monosaccharides are classified by:

– The specific type of the carbonyl group:

• Aldoses

• ketoses

– and the number of carbons in the carbon skeleton:

• Trioses (3 Carbons)

• Tetroses (4 Carbons)

• Pentoses (5 Carbons)

• Hexoses (6 Carbons)

• Heptoses (7 Carbons)

LE 5-3 Triose sugars

(C3H6O3)

Glyceraldehyde

Pentose sugars

(C5H10O5)

Ribose

Hexose sugars

(C5H12O6)

Glucose Galactose

Dihydroxyacetone

Ribulose

Fructose


Monosaccharides

• Functions of monosaccharides:

– major fuel (source of energy) for cells and

– raw material for building other molecules such

as fatty acids and amino acids.


Monosaccharides

• Though often drawn as a linear skeleton, in

aqueous solutions they form rings


alpha and Beta Forms of Glucose

• There are two interconvertible forms of glucose

that differ in the placement of the hydroxyl

group attached to the number 1 carbon in the

ring form of glucose.

• These forms are α-glucose and β-glucose.

α-Glucose β-Glucose

Glucose

Maltose

Fructose Sucrose

Glucose Glucose

Dehydration

reaction in the

synthesis of maltose

Dehydration

reaction in the

synthesis of sucrose

1–4 glycosidic

linkage

1–2 glycosidic

linkage

• A disaccharide is formed when a dehydration reaction joins

two monosaccharides

• The covalent bond joining two monosaccharides is called a

glycosidic linkage

Disaccharides


Polysaccharides

• Polymers of monosaccharides

• Based on their function, there are two types of

polysaccharides:

– Storage polysaccharides.

– Structural polysaccharides.


Storage Polysaccharides

• Store glucose and are hydrolyzed as needed to

provide sugar for cells.

• Examples on storage polysaccharides:

– Starch in Plants

– Glycogen in animals


Figure 5.6b

Mitochondria Glycogen granules

0.5 m


Starch (A Storage Polysaccharides in Plants)

• Starch is a carbohydrate polymer consists

entirely of α-glucose monomers.

• Starch is a storage polysaccharide in plants.

• Two types of starch:

– Amylose is the unbranched polymer.

– Amylopectin is the branched polymer.

LE 5-6a Chloroplast Starch

1 µm

Amylose

Starch: a plant polysaccharide

Amylopectin


Glycogen (A Storage Polysaccharides in Animals)

• Glycogen is a storage polysaccharide in

animals

• Humans and other vertebrates store

glycogen mainly in liver and muscle cells

Glycogen: an animal polysaccharide


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 ()



Cell wall

Microfibril

Cellulose microfibrils in a plant cell wall

Cellulose molecules

Glucose monomer

10 m

0.5 m

Figure 5.8


• Enzymes that digest starch by hydrolyzing alpha

linkages can’t hydrolyze beta linkages in cellulose

• Humans can’t digest 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

Cellulose Digestion


Chitin (A Structural Polysaccharides)

• Chitin is found in the

exoskeleton of

arthropods

• Chitin also provides structural support for the cell walls of many fungi

• Chitin can be used as

surgical thread


Figure 5.9b

Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals.


Concept 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 (Hydrophobic)

• Lipids are hydrophobic becausethey consist

mostly of hydrocarbons, which form nonpolar

covalent bonds



Lipids

• The most biologically important lipids are:

– fats

– Phospholipids

– steroids


Fats

• Fats are constructed from one glycerol

and three fatty acid molecules

• 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 hydrocarbon skeleton


Figure 5.10

(a) One of three dehydration reactions in the synthesis of a fat

(b) Fat molecule (triacylglycerol)

Fatty acid (in this case, palmitic acid)

Glycerol

Ester linkage


• 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

Fatty Acids

Alpha linolenic acid (ALA) An Omega-3

f.a. and the parent of other omega-3 f.as


Fats (Saturated fats)

• Fats made from saturated fatty acids are called saturated fats

• Most animal fats are saturated

• Saturated fats are solid at room temperature

• A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits


Fats (Unsaturated fats)

• Fats made from unsaturated fatty acids are called

unsaturated fats

• Plant fats and fish fats are usually unsaturated

• Plant fats and fish fats are liquid at room

temperature and are called oils


Fats

• Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats


Trans Fatty Acids

• 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


Major Functions of Fats

• 1- Good source of energy. One gram of fat

stores more than twice as much energy as one

gram of a polysaccharide, such as starch.

• 2- Adipose tissue (the tissue that stores fats in

the body) also functions to cushion vital organs

such as the kidneys, and a layer of fat beneath

the skin insulates the body. The subcutaneous

layer is especially thick in whales, seals, and

most other marine mammals.


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


Figure 5.12

Choline

Phosphate

Glycerol

Fatty acids

Hydrophilic head

Hydrophobic tails

(c) Phospholipid symbol (b) Space-filling model (a) Structural formula

Hyd

rop

hil

ic h

ead

H

yd

rop

ho

bic

tail

s


Phospholipids in water (a micelle formation)

WATER Hydrophilic

head

Hydrophobic

tails

WATER

Phospholipids in water (a bilayer formation)

The structure of phospholipids in water results also in a

bilayer arrangement found in cell membranes

Phospholipids are the major component of all cell membranes


Steroids

• Steroids are lipids characterized by a carbon

skeleton consisting of four fused rings

• Different steroids are created by varying functional

groups attached to the rings.

Estradiol

Testosterone

Female lion

Male lion


Cholerterol (A Steroid)

• 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


Lipid Summary

Type of Lipid Structure of Lipid Function of Lipid

Triglycerides

Made out of one glycerol

molecule (blue part below)

with three fatty acids

attached (black parts

below).

These are entirely

hydrophobic. The "tri"

prefix of the name comes

from having three fatty

acids.

These are the "fats" and

also the "oils." They are

used for long-term sugar

storage or for insulation of a

multicellular organism.

http://faculty.stcc.edu/BIOL102/sounds/triglycerides.wav


Lipid summary cont’d

Phospholipids

Phospholipids have the special

property of having both

hydrophobic and hydrophilic

parts, although they are still

mostly hydrophobic. A molecule

that is both hydrophilic and

hydrophobic is called amphipathic.

Phospholipids help to make up the

basis of cellular membranes-- you

will learn much more about these

when we study membranes.


http://faculty.stcc.edu/BIOL102/sounds/phospholipids.wav


Lipid summary cont’d

Steroids (a sterol derivative) They are entirely hydrophobic, and

have their own special structure that

does NOT include fatty acids.

These molecules are all ringed

structures, with 4 carbon rings.

This group includes cholesterol,

estrogen, testosterone, progesterone,

and cortisone. Most steroids are used

as hormones.



Concept 5.4: 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


Figure 5.15-a

Enzymatic proteins Defensive proteins

Storage proteins

Transport proteins

Enzyme Virus

Antibodies

Bacterium

Ovalbumin Amino acids for embryo

Transport protein

Cell membrane

Function: Selective acceleration of chemical reactions Example: Digestive enzymes catalyze the hydrolysis

of bonds in food molecules.

Function: Protection against disease

Example: Antibodies inactivate and help destroy

viruses and bacteria.

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 cell membranes.


Figure 5.15-b

Hormonal proteins Function: Coordination of an organism’s activities

Example: Insulin, a hormone secreted by the

pancreas, causes other tissues to take up glucose,

thus regulating blood sugar concentration

High blood sugar

Normal blood sugar

Insulin secreted

Signaling molecules

Receptor protein

Muscle tissue

Actin Myosin

100 m 60 m

Collagen

Connective tissue

Receptor proteins

Function: Response of cell to chemical stimuli

Example: Receptors built into the membrane of a

nerve cell detect signaling molecules released by

other nerve cells.

Contractile and motor proteins Function: Movement

Examples: Motor proteins are responsible for the

undulations of cilia and flagella. Actin and myosin

proteins are responsible for the contraction of

muscles.

Structural proteins Function: Support

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.


Polypeptides

• Polypeptides are unbranched polymers built

from the same set of 20 amino acids

• A protein is a biologically functional molecule

that consists of one or more polypeptides



Polypeptide vs Protein

Lysozyme: an

antibacterial

enzyme found

in human

tears. It is

made of one

polypeptide

chain which is

folded into the

functioning

lysozyme

protein.

Hemoglobin (folded

protein) is made of

four polypeptides

Unfolded polypeptide

http://upload.wikimedia.org/wikipedia/commons/c/c1/Protein-primary-structure.png


Figure 5.UN01

Side chain (R group)

Amino group

Carboxyl group

carbon

• Amino acids are

organic molecules

with carboxyl and

amino groups


Amino Acids

• Cells use 20 amino acids to make thousands of proteins

• Amino acids differ in their properties due to differing side

chains, called R groups.

• According to the properties of their side chains, amino

acids are grouped into:

– Nonpolar

– Polar

– Electrically charged.


Figure 5.16 Nonpolar side chains; hydrophobic

Side chain (R group)

Glycine (Gly or G)

Alanine (Ala or A)

Valine (Val or V)

Leucine (Leu or L)

Isoleucine (Ile or I)

Methionine (Met or M)

Phenylalanine (Phe or F)

Tryptophan (Trp or W)

Proline (Pro or P)

Polar side chains; hydrophilic

Serine (Ser or S)

Threonine (Thr or T)

Cysteine (Cys or C)

Tyrosine (Tyr or Y)

Asparagine (Asn or N)

Glutamine (Gln or Q)

Electrically charged side chains; hydrophilic

Acidic (negatively charged)

Basic (positively charged)

Aspartic acid (Asp or D)

Glutamic acid (Glu or E)

Lysine (Lys or K)

Arginine (Arg or R)

Histidine (His or H)


Figure 5.16a

Nonpolar side chains; hydrophobic

Side chain

Glycine (Gly or G)

Alanine (Ala or A)

Valine (Val or V)

Leucine (Leu or L)

Isoleucine (Ile or I)

Methionine (Met or M)

Phenylalanine (Phe or F)

Tryptophan (Trp or W)

Proline (Pro or P)


Figure 5.16b

Polar side chains; hydrophilic

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 5.16c

Electrically charged side chains; hydrophilic

Acidic (negatively charged)

Basic (positively charged)

Aspartic acid (Asp or D)

Glutamic acid (Glu or E)

Lysine (Lys or K)

Arginine (Arg or R)

Histidine (His or H)


Peptide

bond

Amino end (N-terminus)

Peptide

bond

Side chains

Backbone

Carboxyl end (C-terminus)

(a)

(b)

Amino acids are linked by peptide bonds formed by

dehydration reactions


Amino Acid Polymers

• A polypeptide is a polymer of amino acids

• Polypeptides range in length from a few

monomers to more than a thousand

• Each polypeptide has a unique linear sequence of

amino acids


Protein Conformation and Function

• A functional protein consists of one or more

polypeptides twisted, folded, and coiled into a

unique shape

• The sequence of amino acids determines a

protein’s three-dimensional conformation

• A protein’s conformation determines its function


Figure 5.18

(a) A ribbon model (b) A space-filling model

Groove

Groove


• The sequence of amino acids determines a

protein’s three-dimensional structure

• A protein’s structure determines its function



Figure 5.19

Antibody protein Protein from flu virus


Many proteins are globular ( semi-spherical ) in shape, while others are fibrous.


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

• Tertiary structure is determined by interactions

among various side chains (R groups)

• Quaternary structure results when a protein

consists of multiple polypeptide chains

LE 5-20

Amino acid subunits

pleated sheet

+H3N Amino end

helix


• Primary structure, the sequence of amino

acids in a protein, is like the order of letters in a

long word


• The coils and folds of secondary structure

result from hydrogen bonds between the repeating

constituents of the polypeptide backbone (NOT

the amino acid side chain).

• Typical secondary structures are a coil called an alpha helix and a folded structure called a beta pleated sheet.


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 protein

containing -pleated sheets.

The radiating strands, made

of dry silk fibers, maintain

the shape of the web.

The spiral strands (capture

strands) are elastic, stretching

in response to wind, rain,

and the touch of insects.


• Tertiary structure is determined by interactions

between R groups, rather than interactions

between backbone constituents

• These interactions between R groups include

hydrogen bonds, ionic bonds, hydrophobic

interactions, and van der Waals interactions

• Strong covalent bonds called disulfide bridges

may reinforce the protein’s conformation

LE 5-20d

Hydrophobic

interactions and

van der Waals

interactions

Polypeptide

backbone

Disulfide bridge

Ionic bond

Hydrogen

bond


Figure 5.20f

Hydrogen bond

Disulfide bridge

Polypeptide backbone

Ionic bond

Hydrophobic

interactions and

van der Waals

interactions


• Quaternary structure results when two or more

polypeptide chains form one macromolecule

• Collagen is a fibrous protein consisting of three

polypeptides coiled like a rope

• Hemoglobin is a globular protein consisting of four

polypeptides: two alpha and two beta chains


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



Figure 5.21

Primary Structure

Secondary and Tertiary Structures

Quaternary Structure

Function Red Blood Cell Shape

subunit

subunit

Exposed hydrophobic region

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

Molecules crystallize into a fiber; capacity to carry oxygen is reduced.

Sickle-cell hemoglobin

Normal hemoglobin

10 m

10 m

Sic

kle

-cell

he

mo

glo

bin

N

orm

al h

em

og

lob

in

1

2

3

4

5

6

7

1

2

3

4

5

6

7


Figure 5.21a

10 m


Figure 5.21b

10 m


What Determines Protein Conformation?

• In addition to primary structure, physical and

chemical conditions can affect conformation

• Alternations in pH, salt concentration,

temperature, or other environmental factors can

cause a protein to unravel

• This loss of a protein’s native conformation is

called denaturation

• A denatured protein is biologically inactive

Denaturation

Renaturation

Denatured protein Normal protein

Good for cake Not good for cake

Heat


Protein Folding in the Cell

• It is hard to predict a protein’s structure from

its primary structure

• Most proteins probably go through several

stages on their way to a stable structure

• Chaperonins are protein molecules that

assist the proper folding of other proteins

• Diseases such as Alzheimer’s, Parkinson’s,

and mad cow disease are associated with

misfolded proteins



Figure 5.23

The cap attaches, causing the cylinder to change shape in such a way that it creates a hydrophilic environment for the folding of the polypeptide.

Cap

Polypeptide

Correctly folded protein

Chaperonin (fully assembled)

Steps of Chaperonin Action:

An unfolded polypeptide enters the cylinder from one end.

Hollow cylinder

The cap comes off, and the properly folded protein is released.

1

2 3


• Scientists use X-ray crystallography to

determine a protein’s structure

• Another method is nuclear magnetic

resonance (NMR) spectroscopy, which does

not require protein crystallization

• Bioinformatics uses computer programs to

predict protein structure from amino acid

sequences



Figure 5.24a

Diffracted X-rays

X-ray source X-ray

beam

Crystal Digital detector X-ray diffraction pattern

EXPERIMENT


Figure 5.24b

RNA DNA

RNA polymerase II

RESULTS


Concept 5.5: 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


The Roles of Nucleic Acids

• There are two types of nucleic acids:

– Deoxyribonucleic acid (DNA)

– Ribonucleic acid (RNA)

• DNA replicates in order for the cells to divide

• DNA directs synthesis of messenger RNA (mRNA)

and, through mRNA, controls protein synthesis

• Protein synthesis occurs in ribosomes

LE 5-25

NUCLEUS

DNA

CYTOPLASM

mRNA

mRNA

Ribosome

Amino

acids

Synthesis of

mRNA in the nucleus

Movement of

mRNA into cytoplasm

via nuclear pore

Synthesis

of protein

Polypeptide


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

LE 5-26a 5 end

3 end

Nucleoside

Nitrogenous

base

Phosphate

group

Nucleotide

Polynucleotide, or

nucleic acid

Pentose

sugar


Nitrogenous bases

• There are two families of nitrogenous bases:

– Pyrimidines have a single six-membered ring

– Purines have a six-membered ring fused to a five-membered ring.

Nitrogenous bases

Pyrimidines

Purines

Cytosine

C

Thymine (in DNA)

T

Uracil (in RNA)

U

Adenine

A

Guanine

G


Pentose sugar

• In DNA, the sugar is deoxyribose

• In RNA, the sugar is ribose.

Pentose sugars

Deoxyribose (in DNA) Ribose (in RNA)


The DNA Double Helix

• A DNA molecule has two

polynucleotides spiraling around

an imaginary axis, forming a

double helix

• The nitrogenous bases in DNA

form hydrogen bonds in a

complementary fashion: A always

pairs with T, and G always pairs

with C

Sugar-phosphate

backbone

3 end 5 end

Base pair (joined by

hydrogen bonding)

Old strands

Nucleotide

about to be

added to a

new strand

5 end

New strands

3 end

5 end 3 end

5 end


RNA

• RNA is made of one

polynucleotide (one strand of

nucleotides)

• The nucleotide of RNA is made

of:

– A nitrogenous bases,

Adenine (A), Uracil (U),

Guanine (G), or Cytosine

(C).

– A ribose sugar.

– A phosphate group.


Differences between DNA and RNA

DNA RNA

Composed of two strands

of polynucleotides twisted

together helically to form a

double helix

Composed of one strand

of polynucleotides.

Contains the 5-carbon

sugar Deoxyribose

Contains the 5-carbon

sugar Ribose


Differences between DNA and RNA

DNA RNA

Contains the nitrogenous

bases Adenine (A),

Thymine (T), Guanine (G),

and Cytosine (C)

Adenine pairs with Thymine

and Guanine pairs with

Cytosine.

Contains the nitrogenous

bases Adenine (A),

Uracil (U), Guanine (G),

and Cytosine (C)

Larger molecule. Shorter than DNA


Figure 5.UN02

Documents

The Structure and Function of Macromolecules of the tough wall of plant cells •Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ