An Introduction to Carbohydrates

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An Introduction to Carbohydrates

• Chapter 5

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Structure

• Carbohydrates have the generalized chemical
  formula (CH2O)n
• Contain a carbonyl, several hydroxyl functional
  groups, and many carbon-hydrogen (CH) bonds.

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Monosaccharides

• Simple sugars
• Vary in the placement of the carbonyl group
• Aldehyde sugar (aldose)
• On the end
• Ketone sugar (ketose)
• In the middle

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Monosaccharides

• Number of carbon atoms varies
• Three (a triose), five (a pentose), and six (a
  hexose).
• Carbon atoms are numbered starting at the end
  closest to the carbonyl group
• Vary in the placement of hydroxyl group
• Have the same chemical formula but different
  structures
• Form ring structures in solution

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Monosaccharides
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Monosaccharides
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Polysaccharides

• Form from monosaccharides through a condensation
  reaction
• Glycosidic linkage between hydroxyls

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Polysaccharides

• Linkages can be the same or different
• Starch- plant storage material
• a-glucose monomers joined by a-1,4-glycosidic
  bonds
• Forms a helix
• Branches when an a-1,6-glycosidic bond forms,
  called amylopectin
• Unbranched form is amylose

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Starch
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Glycogen

• Animals store carbohydrates as glycogen
• Short term storage, a day

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Cellulose

• The primary component of the plant cell wall
• b-glucose linked by a-1,4-glycosidic bonds

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Storage Polysaccharides
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Chitin

• N-acetylglucosamine monomers
• Cell walls of fungi and algae
• Major component of insect and crustacean
  exoskeletons

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Peptidoglycan

• Bacterial cell walls are composed primarily of
  peptidoglycan
• Made of alternating N-acetyl-muramic acid (M) and
  N-acetyl-glucosamine (G) monosaccharides
• Joined by b-1,4-glycosidic linkages.
• M monomer is linked to a chain of amino acids,
  and peptide bonds link the amino acid chains of
  adjacent strands

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Peptidoglycan
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Role of Carbohydrates
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Role of Carbohydrates

• Building blocks in the synthesis of other
  molecules
• Indicate cell identity
• Store chemical energy
• Form fibrous structural materials that protect
  cells.

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Cell Identity

• Carbohydrates help identify a cell
• Display information on the outer surface of cells
  in the form of glycoproteinsproteins with
  covalent bonds to carbohydrates
• Key molecules in cell-cell recognition and
  cell-cell signaling.
• Also important in defense

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Cell Identity
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Energy Production and Storage

• Most carbohydrates are formed by photosynthesis
• Transforms the energy of sunlight into the
  chemical energy of CH bonds
• Converts CO2 to carbohydrate
• The electrons in CH bonds are shared more
  equally and held less tightly than they are in
  CO bonds

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Energy Production and Storage
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Energy Production and Storage

• Carbohydrates are electron donors in redox
  reactions that produce ATP
• CH2O O2 ADP ? CO2 H2O ATP.
• The free energy in ATP is used to drive
  endergonic reactions and perform cell work.

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Energy Production and Storage

• As CO2 molecules are reduced (gain electrons),
  they also gain protons (H), so that the
  resulting compounds contain many CH bonds
• Fatty acids have even more CH bonds, and
  consequently more free energy, than carbohydrates
• Better stores than carbohydrates

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How they store energy

• Starch and glycogen are good glucose stores
  because the enzymes amylase and phosphorylase,
  catalyze reactions that release glucose subunits,
  which can then be used in the production of ATP.

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Structural Carbohydrates

• Structural polysaccharides form long strands with
  bonds between adjacent strands
• Strands can be organized into fibers or layered
  in sheets
• Gives cells and organisms strength and elasticity

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Structural Carbohydrates