Proteins Use after doing Activity: Chemistry of Amino Acids and Proteins

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Proteins Use after doing Activity Chemistry of
Amino Acids and Proteins

• Function
• Structure

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Function of Proteins

• Serve as
• structural molecules
• may serve as storage molecules
• chemical messengers-hormones
• transport molecules
• defense mechanisms-antibodies, lysozymes
• enzymes or biological catalysts

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Chemical Composition

• Proteins are macromolecules composed of one or
  more polypeptide
• Polypeptides are linear chains of amino acids
  linked together by peptide bonds and formed by
  enzyme controlled dehydration synthesis
• A polypeptide can contain hundreds of amino
  acids. Most proteins consist of two or more
  polypeptides

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The amino acid structure

• There are 20 different amino acids, each w/
  different characteristics that determine the role
  of each protein
• Central (alpha) Carbon
• Amino group (NH2) attached to alpha
• A carboxyl group
• R (alkyl) group (it is here where amino acids
  differ)

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The Amino Acid Structure

• H R O
• Amino N C C Carboxyl
• H H OH
• R is the variable group
• Refer to list of amino acids in textbook

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Four levels of structure in proteins

• The correlation between form and function in
  proteins results from the levels of structure in
  proteins
• Primary
• Unique sequence of AA in a protein
• Determined by genes
• Changes in this sequence alter the proteins
  configuration (e.g. sickle-cell shape of
  hemoglobin
• Determination of AA sequence using Sangers Method

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• Secondary
• Regular, repeating folding of a proteins
  polypeptide backbone
• Stabilized by hydrogen between peptide linkages
  in the proteins backbone (carbonyl and amino
  groups)
• Two types of secondary structure are alpha (a )
  and beta (b) pleated sheet
• alpha (a) helical coil stabilized by hydrogen
  bonding betwee every fourth peptide bond. Found
  in fibrous protein (keratin and collagen) and in
  some sections of globular proteins
• beta (b ) Secondary protein structure which is a
  sheet of anitparallel chains folded into
  accordion pleats. Held together by H-bonds. Make
  up a dense core of many globular proteins (e.g
  lysozyme) and the major portion of some fibrous
  proteins (fibroin, the structural protein of
  silk)

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• Tertiary Structure
• Irregular contortions of a protein due to bonding
  between side chains (R-groups) superimposed upon
  primary and secondary structure
• Covalent linkage
• Disulfide bridges form between two cysteine
  monomers brought together by folding of the
  protein.
• Weak interactions
• Hydrogen bonding
• Ionic bonds between charged side chains
• Hydrophobic interactions between nonpolar side
  chains in proteins interior

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Cysteine

• H O
• H3N C C
• CH2 O-
• SH
• Disulfide bridges form between two cysteine
  monomers bought together by folding of the
  protein. This is a strong bond that reinforces
  conformation

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• Quaternary
• Structure that results from the interaction among
  several polypeptides (subunits) in a single
  protein
• For example collagen, a fibrous protein with
  three helical polypeptides super-coiled into a
  triple helix. Found in animal connective tissue,
  collagenss super-coiled quaternary structure
  gives it strength.
• Some globular proteins have subunits that fit
  tightly together. For example hemoglobin, a
  globular protein that has four subunits (two a
  and two b chains)