Macromolecules & Carbohydrates

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Macromolecules Carbohydrates

• Lecture 3
• Dr. Mamoun Ahram

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Cell's weight
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Subunits

• Subunits the small building blocks (precursors)
  used to make macromolecules
• Macromolecules large molecules made of subunits

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Macromolecules

• Carbohydrates (monosaccharides)
• Proteins (amino acids)
• Nucleic acids (nucleotides)
• Lipids (fatty acids)
• Except for lipids, these macromolecules are also
  considered polymers

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Relationship (monomers and polymers)
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How water is removed?

• Mechanism 1 One subunit contributes an H and
  the other subunit contributes an OH
• Mechanism 2 One subunit contributes 2 H the
  other subunit contributes an O

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Carbohydrates
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What are they?

• Carbohydrates are polyhydroxy aldehydes or
  ketones
• Saccharide is another name for a carbohydrate

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Functions

• Source of energy
• Structure (cellulose and chitin)
• Building blocks
• Cellular recognition

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Classification I

• Monosaccharides
• Disaccharides
• Oligosaccharides
• Polysaccharides

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Monosaccharides

• Basic chemical formula (CH2O)n
• They contain two or more hydroxyl groups

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Drawing sugars

• Fisher projections or perspective structural
  formulas

Forward Backward Top (C1) Most highly
oxidized C
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Numbering carbonsagain
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Classification 2

• By the number of carbon atoms they contain

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Trioses
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Glyceraldehyde
Chiral carbon
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Mirror images and non-superimposable,
thenstereoisomers
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Stereoisomers
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This is different than structural isomers
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Sugar enantiomers (D- vs. L-)
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Which chiral carbon?
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Number of possible stereoisomers

• 2n (n is the number of chiral carbons in a sugar
  molecule)

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Isomers of glucose
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Diastereomers
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Epimers
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Formation of a ring structure
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Hemiacetal vs. hemiketal
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Haworth vs. Fischer projections
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Ring structures
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Example
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Anomers
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?- vs. ?-glucopyranose
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Cyclic fructose
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Galactose
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Fischer vs. HaworthLeft-right vs. up-down
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Cyclic aldohexoses
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Cyclic ribofuranose
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Modified sugars
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Sugar esters (esterification)

• What is the reacting functional group? Where does
  it react? What are the end products? Where are
  they used?

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Sugar acids (oxidation)

• Where is it oxidized? What does it form?

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Example 1
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Example 2
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Example 3
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Note

• Oxidation of ketoses to carboxylic acids does not
  occur

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Sugar alcohols (reduction)

• What does it form?
• Examples include sorbitol, mannitol, and xylitol,
  which are used to sweeten food products

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Deoxy sugars

• One or more hydroxyl groups are replaced by
  hydrogens
• An example is 2-deoxy-2-ribose, which is a
  constituent of DNA

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N-glycosides

• What is the reacting functional group? Where does
  it react? What are the end products? Where are
  they used?
• Examples nucleotides (DNA and RNA)

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Amino sugars

• What is the reacting functional group? Where does
  it react? What are the end products? Where are
  they used?
• Further modification by acetylation

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O-Glycosides

• What is the reacting functional group? Where does
  it react? What are the end products? Where are
  they used?

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Formation of full acetal
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Disaccharides

• What are disaccharide? Oligosaccharides? Hetero-
  vs. homo-?
• What is the type of reaction?
• What is a residue?
• Synthesizing enzymes are glycosyltransferases
• Do they undergo mutarotation?
• Are products stable?

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Distinctions of disaccharides

• The 2 specific sugar monomers involved and their
  stereoconfigurations (D- or L-)
• The carbons involved in the linkage (C-1, C-2,
  C-4, or C-6)
• The order of the two monomer units, if different
  (example galactose followed by glucose)
• The anomeric configuration of the OH group on
  carbon 1 of each residue (a or ß)

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Abundant disaccharides

• Configuration
• Designation
• Naming (common vs. systematic)
• Reducing vs. non-reducing

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Raffinose

• What are oligosaccharide?
• Example raffinose
• It is found in peas and beans

• Homework
• What are the names of monosaccharides that make
  up raffinose?
• What is the monosaccharide that is attached to
  what disaccharide?

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Oligosaccharides as drugs

• Streptomycin and erythromycin (antibiotics)
• Doxorubicin (cancer chemotherapy)
• Digoxin (cardiovascular disease)

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Polysaccharides

• What are polysaccharides?
• Homopolysaccharide (homoglycan) vs.
  heteropolysaccharides

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Features of polysaccharides

• Monosaccharides
• Length
• Branching

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Storage polysaccharides

• Glycogen
• Starch
• Dextran

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Glycogen

• Which organisms? Which organs?

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Structure
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Starch

• Which organisms?
• Forms
• amylase (10-20)
• amylopectin (80-90)

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Dextran

• A storage polysaccharide
• Yeast and bacteria
• ?-(1-6)-D-glucose with branched chains
• Branches 1-2, 1-3, or 1-4

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Structural polysaccharides
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Cellulose

• Which organism?
• Degradation?

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Structural features? Why?
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Glycosaminoglycans

• What are they? Where are they located?
• Derivatives of an amino sugar, either glucosamine
  or galactosamine
• At least one of the sugars in the repeating unit
  has a negatively charged carboxylate or sulfate
  group

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Localization and function of GAG
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Bond orientation

• Glycosidic bonds in chondroitin 4-sulfate,
  hyaluronate, dermatan sulfate, and keratan
  sulfate are alternating ? (1?3) and ?(1?4)
  linkages
• Exception is heparin

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Proteoglycans

• Lubricants
• Structural components in connective tissue
• Mediate adhesion of cells to the extracellular
  matrix
• Bind factors that stimulate cell proliferation

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Bacterial cell wall
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Glycoproteins

• Soluble proteins as well as membrane proteins
• Purpose
• Protein folding
• Protein targeting
• prolonging protein half-life
• Cell-cell communication
• Signaling

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Blood typing

• Three different structures
• A, B, and O
• The difference
• N-acetylgalactosamine (for A)
• Galactose (for B)
• None (for O)

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Sialic acid

• N-acetylneuraminate, (N-acetylneuraminic acid,
  also called sialic acid) is derived from the
  amino sugar, neuraminic acid and is often found
  as a terminal residue of oligosaccharide chains
  of glycoproteins giving glycoproteins negative