Structural Carbohydrates

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Structural Carbohydrates

• Cellulose
• Most abundant organic compound on earth
• Plants use cellulose as structural component of
  cell walls
• Most animals cannot digest
• Certain bacteria can degrade cellulose
• Cows and termites have symbiotic relationship w/
  bacteria
• Fiber in your diet usually means cellulose
• Not digested so acts as a mechanical cleansing
  mechanism as it passes through the intestines
• Comprises polymerized units of glucose

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Lipids

• Hydrophobic molecules
• Carbons bound to hydrogens are not polar
• Most often found as fatty-acid
• Carboxyl group at one end
• Carbon/hydrogen chain
• Chain may be saturated or unsaturated
• Saturated means that each carbon (except the
  carboxyl carbon) is bound to the maximum number
  of hydrogens

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Fats

• Used primarily as a long term method of energy
  storage
• Animal fats tend to contain saturated lipids
• Plant fats contain unsaturated fat
• Saturated fats are linear molecules and thus able
  to pack in more tightly and are solid at room
  temp
• Unsaturated fats have angles and do not pack in
  tightly. They are liquid at room temp.
• Fats that are liquid at room temp are called oils

4
Structure of fats

• Three fatty acid chains bound to a glycerol
  backbone
• Also called triaclyglycerol
• Formed by dehydration reaction
• Fatty acids are bound to glycerol by ester linkage

5
Phospholipids

• Major component of cell membranes
• Contain hydrophilic domain that contains
  phosphate (and other hydrophilic structure)
• Contains hydrophobic domain of lipid chains

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Amphipathic Molecules

• Contain both hydrophobic and hydrophilic domains
• Tend to aggregate with hydrophobic domains turned
  together and hydrophilic domais turned outward
• Can for bilayers or micelle structures
• Bilayers are essential for membrane structure

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Hormones

• Derived from cholesterol molecules
• Used as global regulators in biology
• Send signals to distant cells to affect behavior
• Are complicated ring structures
• Are essential for homeostasis

8
Lipids Summary

• Non-polar molecules that are hydrophobic
• Typically found as fatty acids
• Contain carboxyl group at end of a hydrocarbon
  chain
• Can be saturated or unsaturated
• Are used for long-term energy storage
• Phospholipids are amphipathic molecules that are
  essential for membrane structure
• Are the basis for hormone structure

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Protein Functions

• Most versatile of the macromolecules
• Structural collagen, keratin, silk, tubulin
• Storage casein, ovalbumin
• Transport hemoglobin
• Hormones insulin
• Receptor ASGPR
• Contractile actin
• Defensive antibodies
• Enzymaticlysozyme and many others

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Amino acids

• Monomeric subunit of polypeptides
• Have amino group and carboxyl group
• 20 natural amino acids
• Each has different R group
• Differences in R group makes amino acids react
  differently

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Functional Groups of Amino Acids

• Based on the chemical properties of the R side
  group
• Nonpolar (hydrophobic)glycine, alanine, valine,
  leucine, isoleucine, methionine, phenylalanine,
  tryptophan and proline
• Polar (hydrophilic) serine, threonine, cysteine,
  tyrosine, asparagine and glutamine
• Electrically charged
• Acidic aspartic acid, glutamic acid
• Basic lysine, arginine and histidines

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Synthesis of Polypeptides

• Polypeptide is synthesized by dehydration
  reaction
• Chain grows from amino terminus to carboxy
  terminus
• Chain has a repetitive backbone with variable
  side groups
• R groups frequently interact with others

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Four Levels of Protein Structure

• Biological activity of protein is determined by
  these levels
• Primary structure is the sequence of amino acids
  in a polypeptide (Usually read N-C)
• Secondary structures are localized folds or
  helices that form within a region of a
  polypeptide
• Tertiary structures are larger folding events
  that are stabilized by interactions between R
  groups
• Quaternary structure is the interaction of
  multiple polypeptides within one active proteins

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Primary Structure

• Sequence of amino acids within a single
  polypeptide
• Are often similar among proteins of similar
  function
• Usually written from amino terminus to carboxy
  terminus
• Can also provide some insight into additional
  structures by the position of particular groups
  of amino acids

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Secondary Structure

• Localized within regions of polypeptide
• Stabilized by hydrogen bonding
• a helix-stabilized by frequent polar groups
• Right handed helices
• b-pleated sheets are formed by consecutive polar
  groups on two regions of polypeptide

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Tertiary Structure

• Large folding events that are stabilized by
  interactions between amino acids
• Hydrophobic interactions
• Nonpolar regions generally internalize in
  structure
• Disulfide bridge
• Very stable bond formed between two distant
  cysteine residues
• Ionic interactions
• Strong bond between oppositely charged side groups

-Hydrogen bonds form between polar groups
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Quaternary Structure

• Only seen in compound proteins
• Interactions are maintained between polypeptide
  chains by bonds similar to tertiary structure
• Function is often unique to quaternary structure
• Individual components are unable to accomplish
  task alone

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Protein Structure Revisited
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Protein Conformation

• The 3D structure in which the protein is
  biologically active is called the active
  conformation
• Denatured protein has lost its active
  conformation
• Shape of a protein is consistent under identical
  conditions
• Proteins will attempt to find the lowest energy
  form under conditions
• Conditions that affect conformation
• Solvent (polar versus non-polar),pH, temperature
  and chemical agents (2-mercaptoethanol)

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Protein summary

• Very important biological macromolecules that
  perform a wide array of functions
• Polymers of amino acids
• 20 natural amino acids that have distinct R side
  groups
• The side groups determines the shape and function
  of a polypeptide
• There are four levels of structural organization
  of proteins