The Structure and Function of Macromolecules

Part 2 Chapter 5

Emergent properties of macromolecules from smaller subunits

• Within cells, small organic molecules are joined together to form larger molecules.

• These large macromolecules may consist of thousands of covalently bonded atoms and weigh more than 100,000 daltons

In this chapter we’ll study the structure and function of these macromolecules and their place in living organisms.

Four major classes of macromolecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Most macromolecules are polymers, built from monomers

• Carbohydrates, proteins, and nucleic acids are made of polymers, repeating subunits of smaller molecules called monomers.

• Lipids are not polymers but they are macromolecules

• Macromolecules - very large• Polymers - many (repeating) parts

– Monomer - one unit

Carbohydrate polymers

Monomer of glucose

Polymers of glucose

Synthesis and digestion

• Condensation/Dehydration reaction – synthesis - to build

– Bonds monomers together– Release water molecule

• Hydrolysis/Digestion – breaks down– hydrolysis (water breaking)– Adds water ions to the broken ends

Condensation or dehydration reactions

• Reaction that builds polymers from monomers by removing one molecule of water.

• The cell uses energy to build polymers with the help of enzymes

Fig. 5-2a

Dehydration removes a watermolecule, forming a new bond

Short polymer Unlinked monomer

Longer polymer

Dehydration reaction in the synthesis of a polymer

HO

HO

HO

H2O

H

HH

4321

1 2 3

(a)

Hydrolysis/Digestion• Reverse reaction of Condensation

• Enzymes help to speed up the reaction

• Polymers are split by addition of water molecule

• OH (Hydroxyl) is added to one monomer and a Hydrogen to the adjacent monomer.

• Ex. In digestion large polymers are broken down and monomers are used to build new polymers needed by the body.

Fig. 5-2b

Hydrolysis adds a watermolecule, breaking a bond

Hydrolysis of a polymer

HO

HO HO

H2O

H

H

H321

1 2 3 4

(b)

Carbohydrates……Sugars

Monosaccharides have the molecular formula

in multiples of CH2O

• Glucose (C6H12O6) is the most common monosaccharide

Monosaccharides are classified by

1. location of the carbonyl group – Aldose –carbonyl is on the last carbon in the chain– Ketose Carbonyl is located between two carbons

2. Number of carbons in the carbon skeleton

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Fig. 5-3

Dihydroxyacetone

Ribulose

Ket

ose

sA

ldo

ses

Fructose

Glyceraldehyde

Ribose

Glucose Galactose

Hexoses (C6H12O6)Pentoses (C5H10O5)Trioses (C3H6O3)

Examples of Disaccharides

Disaccharide Sources

Monosaccharide units

Maltose Germinating grains

Used in brewing beer

glucose + glucose

Lactose Milk, yogurt, ice cream

glucose + galactose

Sucrose Sugar cane, sugar beets

glucose + fructose

Polysaccharides

• Made of many monosaccharides joined by glycosidic linkages

• The structure and function of a polysaccharide is determined by the monomers and the position of the glycosidic linkage

Three important polysaccharides made of repeating units of glucose

• Complex sugars - many sugar units• Starch

– Glucose chain molecules– Energy storage in plants

• Glycogen– Glucose chain molecule– Energy storage in animals

• Cellulose– Glucose chain molecule– Structural molecule in plant cell walls

Fig. 5-10

The structureof the chitinmonomer.

(a) (b) (c)Chitin forms theexoskeleton ofarthropods.

Chitin is used to makea strong and flexiblesurgical thread.

Chitin hard, insoluble... and yet somehow flexible

Chitin is polysaccharide N-acetylglucosamine (a natural derivative of glucose).

Carbohydrate structural Isomers molecular formula C6H12O6

Lipids• Not polymers made of Glycerol molecule

and 3 fatty acids called a triglyceride

• Hydrophobic - Water fearing

• Fats and steroids

• Fats functions– Store twice as much energy as carbs– Protection, Cushion and insulate internal

organs– Fats are stored in adipose cells– Examples include waxes, oils, fats and

steroids

Fig. 3.14

Saturated versus Unsaturated fats

• Saturated fats– No double bonds between carbons– All possible Hydrogens attached to carbons– Solid at room temperature commonly

produced by animals– Examples lard, butter, bacon grease– Linked to cardiovascular disease

Unsaturated Fats

• Have carbon=carbon double bonds

• In place of attached Hydrogens

• Liquid at room temperature

• Commonly produced by plants

• Examples are vegetable, corn and olive oils

Phospholipids• Two regions with opposite properties• Forms plasma membrane• Phosphate ‘head’ is polar

– Hydrophillic water loving– Phosphate group faces out– Towards Watery environment inside and

outside cell• Fatty acid tails are non-polar

– Hydrophobic - water fearing– Tails face each other– Forms a barrier

Fig. 5-14

Hydrophilichead

Hydrophobictail WATER

WATER

Steroids• Lipids because they are hydrophobic

• Carbon chains form 4 fused rings

• Cholesterol– Component of cell membranes– Forms other steroids from it– Make into sex hormones

• Estrogen • Testosterone

Fig. 3.15

Anabolic steroids• Mimic testosterone

• First used for anemia / muscle disease

• Abused by athletes

• Misuse can cause– Facial bloating/acne– Violent mood swings– Liver damage– Increase cholesterol levels– Reduce sex drive and fertility

Proteins have many structures, resulting in a wide range of functions

• Proteins are polymers made of amino acid monomers

• Amino acid general structure- central carbon is bonded to a a carboxyl group, amine group, a Hydrogen and an R group which varies.

• Peptide bonds link amino acids by dehydration synthesis

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Fig. 5-UN1

Aminogroup

Carboxylgroup

carbonGeneral structure of an amino acid

Proteins• Amino acids linked by peptide bonds• The function of a protein depends on the

order and number of amino acids. Polypeptide (protein) formationPrimary structure

– Unique sequence of amino acids– There are 20 different amino acids– Change in order can cause disease

• Sickle cell anemia• One amino acid changed

Fig. 5-21a

Amino acidsubunits

+H3N

Amino end

25

20

15

10

5

1

Primary Structure

Secondary Structure

• Secondary structure, found in most proteins refers to one of two three-dimensional shapes as a result of Hydrogen bonding

• Alpha helix is a coiled shape

• Beta pleated sheet is an accordion shape

Fig. 5-21c

Secondary Structure

pleated sheet

Examples ofamino acidsubunits

helix

• Tertiary structure results in a complex globular shape due to interactions between R groups,

• Interactions include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions

• Strong covalent bonds called disulfide bridges may reinforce the protein’s structure

Animation: Tertiary Protein StructureAnimation: Tertiary Protein Structure

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

Tertiary Structure

Fig. 5-21e

Tertiary Structure Quaternary Structure

Quaternary Structure

• Quaternary structure – Interaction between two or more

polypeptide chains linked together to form one large protein.

– Example: hemoglobin is a globular protein with quaternary structure composed of four chains

– Single amino acid substitution causes sickle cell anemia

Fig. 5-21g

Polypeptidechain

Chains

HemeIron

Chains

CollagenHemoglobin

Fig. 3.21

Fig. 5-22c

Normal red bloodcells are full ofindividualhemoglobinmolecules, each carrying oxygen.

Fibers of abnormalhemoglobin deformred blood cell intosickle shape.

10 µm 10 µm

How is structure determined?• Order of amino acids specified by a gene -

recipe for a polypeptide

• Proteins include– Structural– Storage– Contractile– Transport– Defensive– Signal proteins– ENZYMES!

Chaperonins

• Chaperonins are protein molecules that assist in the proper folding of proteins within cells.

• It provides protection against other particles in the cytoplasm while the protein folds.

ADD

Denaturation of Proteins• The function of a protein is determined by

the sequence and spontaneous folding of the polypeptide chain.

• Certain physical and chemical conditions– pH, salt concentration, temperature

• Denaturation occurs when a protein unfolds, loses its shape and ability to function properly.

• Can you think of a way we denature proteins?

ADD

• The white (albumen) turns opaque during cooking because denatured proteins solidify.

• This is why high fevers can be fatal

• Proteins in the blood can become denatured from high body temperatures

Table 5-1

Fig. 5-21d

Abdominal glands of thespider secrete silk fibers

made of a structural proteincontaining pleated sheets.

The radiating strands, madeof dry silk fibers, maintain

the shape of the web.

The spiral strands (capturestrands) are elastic, stretching

in response to wind, rain,and the touch of insects.

Nucleic acids

• DeoxyriboNucleic Acid - DNA• DNA is a recipe book for proteins• Genes direct the order of amino acids• Two types of nucleic acids

– DNA– RNA - RiboNucleic Acid

• Chemical code– Nucleic acid to protein language– RNA helps with this process

Fig. 5-26-2

mRNA

Synthesis ofmRNA in thenucleus

DNA

NUCLEUS

mRNA

CYTOPLASM

Movement ofmRNA into cytoplasmvia nuclear pore

1

2

Nucleic Acids: DNA and RNA

• DNA and RNA are polynucleotides made up of monomers called nucleotides

• Each Nucleotide has three parts:– Nitrogenous base (adenine, thymine, guanine,

cytosine and uracil (RNA only)– Pentose - five carbon sugar, deoxyribose in

DNA and ribose in RNA– Phosphate group

Fig. 5-27ab5' end

5'C

3'C

5'C

3'C

3' end

(a) Polynucleotide, or nucleic acid

(b) Nucleotide

Nucleoside

Nitrogenousbase

3'C

5'C

Phosphategroup Sugar

(pentose)

Nitrogenous bases

• Pyrimidines-six membered ring of carbon and nitrogen– Cytosine C (DNA &RNA)– Thymine T (DNA)– Uracil U (RNA)

• Purines-six membered ring fused to a five membered ring of carbon and nitrogen– Adenine A (DNA & RNA)– Guanine G (DNA & RNA)

Fig. 3.26

Sugar –phosphate backbone

The backbone• Adjacent nucleotides

are connected by phosphodiester linkages between the OH group on the sugar and phosphate group of the next nucleotide

Double helix strands run anti-parallell

The Roles of nucleic acids DNA RNA

• DNA is the genetic material organisms inherit from their parents

• Each chromosome contains one long DNA molecule containing from several hundred to more than a thousand genes.

• DNA programs all the cells activities by producing proteins as needed

• DNA directs the synthesis of mRNA which then directs the production of amino acids

Which of the following molecules would contain a polar covalent

bond?

A. Cl2B. NaCl

C. H2O

D. CH4

E. C6H12O6