CEM 137 Chapter 13

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CEM 137Chapter 13

• Peptides, Proteins, and Enzymes

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a-Amino Acids

• -NH2 always attached to the a-carbon (the carbon
  attached to -COOH)

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• At physiological pH the amino acids exist as a
  bipolar ion known as a zwitterion.

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Peptide Bond
The peptide bond is an amide linkage.
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Proteins

• Natural polymers made up of a-amino acids
  (molecular weight from 6000 to gt1,000,000
  g/mol).

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Proteins

• Fibrous Proteins provide structural integrity
  and strength to muscle, hair and cartilage.
• Collagen

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Proteins(continued)

• Globular Proteins
• roughly spherical shape
• transport and store oxygen and nutrients
• act as catalysts
• fight invasion by foreign objects
• participate in the bodys regulatory system
• transport electrons in metabolism

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Bonding in a-Amino Acids

• 
  H2O
• A peptide linkage
• There are 20 amino acids commonly found in
  proteins.

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Levels of Structure

• Primary Sequence of amino acids in the protein
  chain.
• Secondary The arrangement of the protein chain
  in the long molecule (hydrogen bonding determines
  this).
• Tertiary The overall shape of the protein
  (determined by hydrogen-bonding, dipole-dipole
  interactions, ionic bonds, covalent bonds and
  London forces).

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Peptide Bond

• The sequence of amino acids is the primary
  structure of the protein.

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Bovine Insulin
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Alpha Helix (secondary structure)
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Beta Pleated Sheet (secondary structure)
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Sperm Whale Myoglobin (tertiary/quaternary
structure)
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• Noncovalent interactions maintain the tertiary
  structure.

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Denaturation

• Denaturation is the change in a proteins
  conformation and therefore its function.
• Denaturation can be caused by heat, changes in
  pH, and denaturating agents like soaps and
  detergents.

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Enzymes

• Proteins tailored to catalyze specific biologic
  reactions.

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Enzymes

• Substrate molecule on which enzyme acts.
• Active Site location on the enzyme where the
  substrate bonds and reaction occurs.

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• Biological enzymes exhibit an optimum pH and
  temperature.

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Enzyme Specificity

• Absolute specificity
• Relative specificity
• Stereospecificity

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Model for Enzyme Activity

• Lock and Key vs. Induced Fit Model

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Michaelis-Menton Model

• No inhibition
• Competitive inhibition
• Noncompetitive inhibition

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Inhibition

• Irreversible inhibition of the COX enzyme by
  aspirin.

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Allosteric Enzymes
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Zymogens

• Inactive enzyme precursors