Freeman Chapter 5 Carbohydrate Presentation

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Chapter 5 _An

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Key Concepts

• _{Sugars and other carbohydrates are highly variable in structure}

• Monosaccharides are monomers that polymerize to form

polymers called polysaccharides, via different types of glycosidic linkages.

• _{Carbohydrates perform a wide variety of functions in cells,}

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Monosaccharides Vary in Structure

(1) Location of the carbonyl group.

• _{Aldose: The carbonyl is at the end of the monosaccharide.}

• Ketose: The carbonyl is in the middle of the sugar’s carbon chain.

(2) Number of carbon atoms present.

• _{Triose: three}

• Pentose: five

• _{Hexose: six}

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Carbonyl Group Configurations

Carbonyl group at end of carbon chain

An aldose A ketose

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Linear and Ring Forms

Linear form of glucose Ring forms of glucose

-Glucose

-Glucose

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The Structure of Polysaccharides

• _{Polysaccharides}_{are polymers that form from monosaccharides}

through a condensation reaction between two hydroxyl groups to

create a glycosidic linkage.

(1) The monomers joined by glycosidic linkages can be identical or different.

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What Do Carbohydrates Do?

• _{Carbohydrates are important building blocks in the synthesis of}

other molecules.

• _{They indicate cell identity.}

• They store chemical energy.

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Glycoproteins: Cell Identity

• _{Although polysaccharides are unable to}_store_{information, they}

do display information on the outer surface of cells in the form of

glycoproteins—proteins joined to carbohydrates by covalent

bonds.

• Glycoproteins are key molecules in cell recognition and

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Glycoproteins: Identification Badge for Cells

Outside of cell

Inside of cell

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Starch and Glycogen: Storage Polysaccharides

• _{Plants store sugars as}_starch_, _{which is made of many α-glucose}

monomers joined by α-1,4-glycosidic linkages. This causes the monomer chain to form a helix. Animals store sugars as

glycogen.

• Starch can be branched (amylose) or unbranched (amylopectin).

Glycogen is highly branched.

• Branching occurs when glycosidic linkages form between carbon

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Carbohydrates and Free Energy

• _{In chemical evolution, the kinetic energy of sunlight and heat}

were converted into chemical energy stored in the bonds of H₂CO

and HCN.

• Today, most sugars are produced via photosynthesis [CO₂ + H₂O

+ sunlight  (CH₂O)n + O₂], a key process that transforms the

energy of sunlight into the chemical energy of C–H bonds in carbohydrates.

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Carbohydrates Have High Free Energy

Carbon dioxide Water (CH2O)n

(Carbohydrate)

Oxygen

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Carbohydrates and Energy Storage

• _{Carbohydrates participate in exergonic reactions that synthesize}

ATP:

CH₂O + O₂ + ADP + P_i  CO₂ + H₂O + ATP.

The free energy in ATP is used to drive endergonic reactions and perform cell work.

• _{Carbohydrates contain a large number C–H bonds, which have}

high free energy.

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How Do Carbohydrates Store Energy?

• _{Starch and glycogen are efficient energy storage molecules}

because the α-linkages are readily hydrolyzed, whereas the

β-linkages of structural carbohydrates resist enzymatic degradation.

• _{The enzymes amylase and phosphorylase catalyze the hydrolysis}

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Structural Polysaccharides: Cellulose, Chitin, Peptidoglycan

• _Cellulose_{: A polymer of β-glucose monomers linked by}

β-1,4-glycosidic linkages. (Component of plant cell walls)

• _Chitin_{: A polymer of N-acetylglucosamine monomers linked by}

β-1,4-glycosidic linkages. (Component of cell walls of fungi and algae, and insect and crustacean exoskeletons).

• _{Peptidoglycan:}_{Two types of monosaccharides linked by}

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Polysaccharides and Chemical Evolution

• _{Although polysaccharides are important to organisms today, they}