Carbohydrates
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Carbohydrates. Carbohydrates. “Hydrates of carbon” (C, H, & O) Polyhydroxy aldehydes (ALDOSES) or ketones (KETOSES) Usually C x (H 2 O) y “Sugars” Single unit: Monosaccharide Two units: Disaccharide Three units: Trisaccharide, etc. Many units: Polysaccharide. Carbohydrates. Functions

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Carbohydrates

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Carbohydrates

Carbohydrates


Carbohydrates1

Carbohydrates

  • “Hydrates of carbon” (C, H, & O)

  • Polyhydroxy aldehydes (ALDOSES) or ketones (KETOSES)

  • Usually Cx(H2O)y

  • “Sugars”

  • Single unit: Monosaccharide

  • Two units: Disaccharide

  • Three units: Trisaccharide, etc.

  • Many units: Polysaccharide


Carbohydrates2

Carbohydrates

  • Functions

    • Energy stores, fuels, and metabolic intermediates

    • Ribose and deoxyribose serve as structural framework to RNA and DNA

    • Structural elements in the cell walls of bacteria and plants

    • Linked to lipids and proteins

      • Mediates interactions among cells

      • Mediates interactions between cells and other elements in the cellular environment


Monosaccharides

Monosaccharides

  • The simplest carbohydrates; aldehydes or ketones that have two or more hydroxyl groups


Monosaccharides1

Monosaccharides

  • Fischer projections of monosaccharides

  • D,L designation refers to the configuration of the highest-numbered asymmetric center

  • D,L only refers the stereocenter of interest back to D- and L-glyceraldehyde!

  • D,L do not specify the sign of rotation of plane-polarized light!


Glucose cyclizes into a hemiacetal

Glucose Cyclizes into a Hemiacetal


Fructose cyclizes into a hemiketal

Fructose Cyclizes into a Hemiketal


Ribose and deoxyribose

Ribose and Deoxyribose


Glycosidic bonds

Glycosidic Bonds


Modified monosaccharides

Modified Monosaccharides

  • Addition of substituents other than alcohols; often found on cell surfaces


Disaccharides

Disaccharides


Polysaccharides

Polysaccharides

  • Energy storage and structural roles

  • Are homopolymers if all of the monosaccharides are the same, heteropolymers if not.


Carbohydrates

Some Common Polysaccharides

  • Starch: glucose polymer (alpha)

    • Potato, rice, wheat, corn

  • Glycogen: branched glucose polymer

    • Animal storage

  • Cellulose: glucose polymer (beta)

    • Plant structures, paper, cotton, wood

  • Chitin: Modified glucose (N-Acetyl Glucose)

    • Fungi cell wall, insect exoskeleton


Polysaccharides1

Polysaccharides


Starch a plant storage polysaccharide

StarchA plant storage polysaccharide

  • Two forms: amylose and amylopectin

  • Most starch is 10-30% amylose and 70-90% amylopectin

  • Branches in amylopectin every 12-30 residues

  • Amylose has alpha(1,4) links, one reducing end


Starch

Starch

  • Amylose-unbranched


Starch1

Starch

  • Amylopectin-branched


Starch a plant storage polysaccharide1

StarchA plant storage polysaccharide

  • Amylose is poorly soluble in water, but forms micellar suspensions

  • In these suspensions, amylose is helical

    • iodine fits into the helices to produce a blue color


Why branching in starch

Why branching in Starch?

Consider the phosphorylase reaction...

  • Phosphorylase releases glucose-1-P products from the amylose or amylopectin chains

  • The more branches, the more sites for phosphorylase attack

  • Branches provide a mechanism for quickly releasing (or storing) glucose units for (or from) metabolism


Glycogen

Glycogen

The glucose storage device in animals

  • Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass

  • Glycogen is stored energy for the organism

  • Only difference from starch: number of branches

  • Alpha(1,6) branches every 8-12 residues

  • Like amylopectin, glycogen gives a red-violet color with iodine


Dextrans a small but significant difference from starch and glycogen

DextransA small but significant difference from starch and glycogen

  • If you change the main linkages between glucose from alpha(1,4) to alpha(1,6), you get a new family of polysaccharides - dextrans

  • Branches can be (1,2), (1,3), or (1,4)


Dextrans a small but significant difference from starch and glycogen1

DextransA small but significant difference from starch and glycogen

  • Dextrans formed by bacteria are components of dental plaque

  • Cross-linked dextrans are used as "Sephadex" gels in column chromatography

  • These gels are up to 98% water!


Carbohydrates

Structural Polysaccharides Composition similar to storage polysaccharides, but small structural differences greatly influence properties

  • Cellulose is the most abundant natural polymer on earth

  • Cellulose is the principal strength and support of trees and plants

  • Cellulose can also be soft and fuzzy - in cotton


Cellulose

Cellulose


Carbohydrates

Structural Polysaccharides Composition similar to storage polysaccharides, but small structural differences greatly influence properties

  • Beta(1,4) linkages make all the difference!

  • Strands of cellulose form extended ribbons


Other structural polysaccharides

Other Structural Polysaccharides

  • Chitin - exoskeletons of crustaceans, insects and spiders, and cell walls of fungi

    • similar to cellulose, but C-2s are N-acetyl

    • cellulose strands are parallel, chitins can be parallell or antiparallel


Other structural polysaccharides1

Other Structural Polysaccharides

  • Alginates - Ca-binding polymers in algae

    • Eg. CARAGEENAN

      • alternating 3-linked-α-D-galactopyranose and 4-linked-β-D-galactopyranose units

      • Sulfonated, uses cations to gel; Common types 

  • Agarose and agaropectin - galactose polymers

  • Glycosaminoglycans - repeating disaccharides with amino sugars and negative charges


Glycosaminoglycans

Glycosaminoglycans

  • Made of disaccharide repeating units containing a derivative of an amino sugar, either glucosamine or galactosamine


Glycosaminoglycans1

Glycosaminoglycans

  • Present in the animal cell surface or the extracellular matrix

  • Usually attached to proteins to form proteoglycans

  • Proteoglycans resemble polysaccharides more than proteins

  • Function as lubricants and structural components in connective tissue, mediate adhesion of cells to the extracellular matrix, and bind factors that stimulate cell proliferation


Glycoproteins

Glycoproteins

  • Carbohydrates attached to proteins

  • Carbohydrates are a much smaller percentage of the weight of glycoproteins than of proteoglycans

  • Present in cell membranes

    • Cell adhesion and the binding of sperm to eggs

  • Present in soluble proteins


Carbohydrates3

CARBOHYDRATES

  • Extra carbohydrates is stored in the liver and muscle tissues as glycogen

  • Carbohydrates supply 4 kcal of energy per gram

  • “Good” and “Bad” carbohydrates

  • Glycemic index


On the sugarfree phenomenon

On the “Sugarfree” Phenomenon

  • Saccharin

    • Oldest artificial sweetener

  • Aspartame and Acesulfame-K

    • Not carbohydrates

  • Sucralose

    • “Splenda”


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