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Chapter 5- The Structure and Function of MacromoleculesCarbohydrates

AP BIOLOGY

Macromolecules

• Carbohydrates • Proteins• Lipids

• Nucleic Acids

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Carbohydrates

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Polymer Vs. Monomer

• Polymer: A large molecule made up of identical or similar building blocks– Ex. Polysaccaride

• Starches

• Monomer: the building block that is used to make polymers– Glucose

Carbohydrates• Carbohydrates are composed of C, H, O• Most names for sugars end in –ose• CH2O (Empirical Formula)

(CH2O) C6H12O6

• Contains a Carbonyl (C=O) & many Hydroxyl (OH)• Function: Energy & Storage • ex: sugars, starches, cellulose, chitin

C6H12O6(CH2O)x

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Monosaccharides

• Simple 1 monomer sugars• Ex’s:

– Glucose– Frucotose– Galactose

sugar sugar sugar sugar sugar sugar sugarsugar

Biological function of monosaccharides

• ENERGY!!!!

• Key parts of other molecules (e.g. nucleic acids, ATP)

• Monomers for Disaccharides & Polysaccharides.

• They form polymers in dehydration reactions.

Classifying Monosaccharides

• Monosaccharides are uniquely identified based on:– The location of the carbonyl carbon in the straight chain

form

– The number of carbons present

– The spatial arrangement of carbons

Sugar structure5C & 6C sugars form rings in solution

Where do you find solutionsin biology?In cells!

Identifying monosaccharides

• The arrangement of the –OH group on the #1 carbon does not matter when naming sugars.

• The location of the other groups on the 2,3,4, and 5 carbons does matter.

alpha-glucose beta-glucose

C

CC

C

CC

1'

2'3'

4'

5'6'

O

energy stored in C-C bonds

Carbons are numbered

Carbon Skeleton• 3-7 Carbons long • Classified by number of carbons

– 6C = hexose (glucose)– 5C = pentose (ribose)– 3C = triose (glyceraldehyde)

OH

OH

H

H

HO

CH2OH

HH

H

OH

O

Glucose

H

OH

HO

O H

HHO

H

Ribose

CH2OH

Glyceraldehyde

H

H

H

H

OH

OH

OC

C

C6 5 3

Functional groups determine function

Ketone

Carbonyl in middle

Aldehyde

Carbonyl at end

Forming Disaccharides glucose+ glucose= Disaccharide monomer monomer Polymer

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Disaccharides• 2 monomers• Held by glycosidic bonds • Ex’s

– Sucrose– Lactose– Maltose

Disaccharide Monosaccharides

Sucrose Glucose +

Fructose

Lactose Glucose +

Galactose

Maltose Glucose +

Glucose

Building sugars

|fructose

|glucose

monosaccharides

sucrose(table sugar)

disaccharide

H2O

Dehydration synthesis

Building sugars

glycosidic linkage

|glucose

|glucose

monosaccharides disaccharide

|maltose

H2O

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Lactose

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Glucose and Fructose

Glucose

Polysaccharides • Polymers of sugars

– costs little energy to build• Function:

– energy storage • starch (plants)• glycogen (animals)

–in liver & muscles– structure

• cellulose (plants)• chitin (arthropods & fungi)

Polysaccharides

• Polymers of sugars joined by glycosidic linkages.

• Serve two main functions– Storage- glycosidic linkages are hydrolyzed to obtain

monosaccharides as energy is needed.

– Structural- make up the materials that are used to protect the organism.

Glycosidic Bonds

• Chemical linkage between the monosaccharide units of disaccharides, and polysaccharides, which is formed by the removal of a molecule of water – Condensation reaction

• Bond forms between the carbon-1 on one sugar and the carbon-4 on the other.

Α & β Glycosidic Bonds• An α-glycosidic bond- formed when the –OH group on

carbon-1 is below the plane of the glucose ring • A β-glycosidic bond is formed when it is above the plane.

– Ex. Cellulose- formed of glucose molecules linked by 1-4 β-glycosidic bonds (Above plane)

– Ex. Starch- composed of 1-4 α-glycosidic bonds (Below plane )

in starch

in cellulose

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Polysaccharides- 100’s to 1000’s of monosaccharides

Storage Polysaccharides Structural Polysaccharides

StarchPlants

CellulosePlants

GlycogenAnimals

ChitinAnimals-Insects Fungi

Structural Polysaccharides

• Key in forming the structure of an organism.

• Most common structural polysaccharide is cellulose.– Makes up cell walls in plants– Used to make paper

• Chitin

• Polymer of glucose • Forms via 1-4 glycosidic linkage.

Cellulose • Most abundant organic

compound on Earth– herbivores have evolved a mechanism to digest

cellulose– most carnivores have not

• cellulose = undigestible roughage

But it tasteslike hay!Who can liveon this stuff?!

Cowcan digest cellulose well; no need to eat other sugars

Gorillacan’t digest cellulose well; must add another sugar source, like fruit to diet

Helpful bacteria• How can herbivores digest cellulose so well?

– BACTERIA live in their digestive systems & help digest cellulose-rich (grass) meals

Rumen-Upper part of stomach

Digesting starch vs. cellulose

starcheasy todigest enzyme

enzyme

cellulosehard todigest

Plant Storage Polysaccharides

• Starch is the main storage polysaccharide- Found in two forms.– Amylose- main storage polysaccharide found in plants.

– 1-4 glycosidic linkage found in glucose.

– Amylopectin- also in plants. – Like starch with branching. – Branch occurs with a 1-6 glycosidic link.

Storage Polysaccharide in Animals

• Glycogen is the main storage polysaccharide in animals.

• It is even more highly branched than amylopectin.

• Stored primarily in muscle and liver cells and is used when glucose stores are low.

Polysaccharide diversity

• Molecular structure determines function

isomers of glucose structure determines function…

in starch in cellulose

Linear vs. branched polysaccharides

starch(plant)

glycogen(animal)

energystorage

slow release

fast release

Fig. 5-6

GlycogenBranched

Starch

GlycogenAmylose

Chloroplast

StarchUnbranched

Amylopectin

Mitochondria Glycogen granules

0.5 µm

1 µm

Difference between starch and cellulose• Starch production involves 1-4 glycosidic

linkage of a-glucose monomers.– Helical shape

• Cellulose production involves 1-4 glycosidic linkage of b-glucose monomers– Never branched , straight

• a- Glycogen • b- Cellulose • Does this matter?

Fig. 5-7a

(a) a and b glucose ring structures

a Glucose b Glucose

Fig. 5-7bc

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

(c) Cellulose: 1–4 linkage of b glucose monomers

Chitin

• Chitin is the structural polysaccharide in arthropods – Ex. insects, spiders, crustaceans, and fungi.

• Similar to cellulose, but it has a slightly different monomer that is a derivative of glucose

Fig. 5-10

The structureof the chitinmonomer.

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

Chitin is used to makea strong and flexiblesurgical thread.

YES, It matters!• Cellulose has a much different structure than starch.

• In storage polysaccharides, the polymer hydrogen bonds mainly with itself to form helices (spirals)– Ex. Glycogen

• In structural polysaccharides, the polymer hydrogen bonds with other polymer strands to form a strands that form thread like structures– Ex. Chitin & Cellulose

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Starch vs. CelluloseHelix

Sheet

IT REALLY MATTERS

• Animals lack the enzymes (cellular machinery) to break down cellulose.

• Only a few bacteria and fungi can break down cellulose.