Carbohydrates

1
Carbohydrates

• Chapter 20

2
Goals

• Understand classification of carbohydrates
• Become familiar with stereoisomerism.
• Draw the structure of several hexoses
• Compare structures of di- and poly- saccharides.

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Why are carbs important?

• Glucose is the only energy source for brain.
• Carbohydrates line outside of cell walls. Our
  immune system recognizes these after vaccine.
• Structural components of plants, cofactors of
  enzymes
• Monosaccharides coat the outside of red blood
  cells to determine blood type.

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Carbohydrates

• Contain C, H and O
• Monosaccharides
• When added to water they dont break down into
  simpler sugars.
• Disaccharides
• Give two monosaccharides when added to water.
• Polysaccharides

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General Structures

• Aldose - contain aldehyde group
• Glucose dextrose blood sugar
• Ketose - contain ketone group
• Fructose fruit sugar
• Be able to draw the general structure of an
  aldose and a ketose.

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Naming sugars

• All have the suffix ose, the stem is the number
  of C
• Example triose, pentose, hexose
• D- or R- rotate light to the right
• L- or S- rotate light to the left
• Look at C farthest away from carbonyl
• alpha - the single OH next to the O inside the
  ring is down
• Beta - the single OH next to the O inside the
  ring is up.

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Optical Isomers

• L- carvone D-carvone

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Where do they come from?

• Monosaccharides from photosynthesis
• CO2 H2O -gt C6H12O6 O2 (balanced?)
• Di- and poly- saccharides from polymerization
  reactions.
• If ABC is a chemical, then ABCABCABC
• is a polymer of it.
• Starch is a polymer of glucose.
• All carbohydrates come from plants.

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Starch vs. cellulose

• Starch
• cellulose

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Oxygen Carbon Dioxide Cycle

• photosynthesis
• CO2 H2O C6H12O6
• metabolism

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Stereoisomers- specifically diasteriomers

• Occur when 4 different atoms or groups connected
  to the same C- single bond
• Have no plane of symmetry.
• Mirror images, not superimposable.
• Only one enantiomer biologically active.
• D sugars, L- amino acids, drugs ibuprofen,
  methamphetamine, etc.
• Chiral
• Enatiomers
• 
  H

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Monosaccharides again

• Cant be broken down into simpler sugars
• Can be drawn as a ring (Haworth projection) or
  straight chain (Fischer proj.)
• Categorized by number of C
• Triose, tetrose, pentose, hexose
• Hexoses most common
• Differences between monosaccharides with same C
  is which side OH groups are on.

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Tests for monosaccharides

• Fermentation
• Glucose/fructose yeast -gt CO2 CH3CH2OH
• Pentoses will not ferment
• Oxidation
• Hexose Cu2 -gt Cu2O water
• blue yellow, green, orange or red

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Disaccharides

• Isomers of C12H22O11
• Sucrose glucose fructose
• Table sugar, cane sugar
• Maltose glucose glucose
• Germinating wheat
• Lactose glucose galactose
• milk

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Sugar Substitutes

• Sweeter than sucrose, so need less.
• Reduces calories because need less or because the
  body doesnt break it down.

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Polysaccharides

• Starch is a polymer of
• glucose
• Cellulose (wood, cotton, paper) is a polymer of
  glucose
• We cant digest cellulose because the glucose is
  beta- linked, we dont have the enzyme to break
  beta linkages.
• Heparin blood thinner, polymer of glucuronic
  acid and glucosamine