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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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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!
modified monosaccharides
Modified Monosaccharides
  • Addition of substituents other than alcohols; often found on cell surfaces
polysaccharides
Polysaccharides
  • Energy storage and structural roles
  • Are homopolymers if all of the monosaccharides are the same, heteropolymers if not.
slide15

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
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!
slide29
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
slide32
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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