Chapter 3Carbohydrates and

Lipids

You Must Know• The cellular functions of carbohydrates and

lipids.

• How the sequence and subcomponents of carbohydrates and lipids determine their properties.

• (You are not going to be asked about nucleic acids on the Chapter 3 Test.)

Concept 3.3: Carbohydrates serve as fuel and building material

• Carbohydrates include sugars and the polymers of sugars

• Monosaccharides – serve as a major fuel for cells and as raw material

for building molecules.

– have molecular formulas that are usually multiples of CH2O

– classified by the number of carbons in the carbon skeleton and the placement of the carbonyl group

Figure 3.7c

6-carbon sugars (C6H12O6)

Glucose Fructose

Carbonyl

Aldehyde – because the carbonyl group is at the end of the carbon skeleton.

Ketone – because the carbonyl group is within the carbon skeleton.

Figure 3.9-2

Glucose Fructose

Sucrose

glycosidic linkage

Polysaccharides

• Polysaccharides, the polymers of sugars, have storage and structural roles

• The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages.

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Storage Polysaccharides

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

• Plants store surplus starch as granules• The simplest form of starch is amylose

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Starch granulesin a potato tuber cell Starch (amylose)

Glucosemonomer

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

mainly in liver and muscle cells

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Glycogen granulesin muscletissue

Glucose!

Figure 3.11(a) and glucose

ring structures

Glucose Glucose

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

Hydroxyl Hydroxyl

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

Starch (and glycogen) are largely helical

Cellulose molecules are relatively straight.

Figure 3.10c

Cellulose microfibrilsin a plant cell wall

Cellulosemolecules

Hydrogen bondsbetween —OH groups oncarbons 3 and 6

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Chitin: another structural polysaccharide

Concept 3.4: Lipids are a diverse group of molecules

• What do these molecules have in common?

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fat Steroid

phospholipid

Fats

OH

OH

OH

Glycerol

Hydroxyl

HO

HO

HO

Fatty Acid

carboxyl

triglyceride

Ester linkage

• Fatty acids vary in length (number of carbons) and in the number and locations of double bonds

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(a) Saturated fat

Structuralformula of asaturated fatmolecule

Space-fillingmodel ofstearic acid,a saturatedfatty acid

Saturated fatty acids have the maximum number of hydrogen atoms possible and no carbon carbon double bonds.

(b) Unsaturated fat

Structuralformula of anunsaturated fat molecule

Space-fillingmodel of oleic acid, an unsaturatedfatty acid Double bond

causes bending.

Unsaturated fatty acids have one or more carbon carbon double bonds.

• The major function of fats is energy storage• Fat is a compact way for animals to carry their

energy stores with them

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Figure 3.14ab

(a) Structural formula (b) Space-filling model

Choline

Phosphate

Glycerol

Fatty acids

Hyd

rop

hili

c h

ead

Hyd

rop

ho

bic

tai

ls

Phospholipids

Figure 3.14cd

Hydrophilichead

Phospholipid bilayer

Phospholipid

Hydrophobictails

Steroids