Protein Function

1
Protein Function
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Enzymatic Proteins

• Function To catalyze covalent bond breakage or
  formation.
• Example trypsin

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Transport Proteins

• Function To carry small molecules and ions.
• Example hemoglobin

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Structural Proteins

• Function To provide mechanical support to cells
  and tissues.
• Example keratin

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Storage Proteins

• Function To store small molecules or ions.
• Example ovalbumin

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Signal Proteins

• Function To carry signals from cell to cell.
• Example insulin

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Receptor Proteins

• Function To detect extracellular signals and
  transmit them to the cells response machinery
  inside.
• Example rhodopsin

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Motor Proteins

• Function To generate movement in cells and
  tissues.
• Example myosin

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Defensive Proteins

• Function To protect the cell against diseases.
• Example antibodies

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Gene Regulatory Proteins

• Function To bind DNA in order to switch genes
  on and off.
• Example lac repressor

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Special Purpose Proteins

• Function variable
• Example green fluorescent protein

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Enzymes
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Enzyme Catalysis

• What is an enzyme?
• What is catalysis?
• Why is enzyme catalysis important?
• Many cellular functions require speed
• Examples DNA replication, amino acid synthesis,
  protein modification

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Molecule Associations

• When a protein molecule binds to a second
  molecule, the second molecule is referred to as a
  ligand.

The region of the protein that associates with
the ligand is referred to as the binding site or
active site.
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Molecule Associations and Catalysis

• The protein molecule is the enzyme E
• The ligand is called the substrate S
• The product resulting from the action the E has
  on S is referred to as P

E S
ES
E P
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Molecule Associations and Catalysis

• What does E S look like?

E
S
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Measuring the Catalytic Properties of Enzymes

• Kd Dissociation constant ES/ES
• Ka Association constant ES/ES

Ka
E S
ES
E P
Kd
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Measuring the Catalytic Properties of Enzymes
E S
ES
E P

• There is a limit to the amount of substrate a
  single enzyme molecule can process in a given
  time.
• An increase in substrate concentration results in
  an increase in product formation up to a maximum
  value.

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Maximum Rate of the Reaction

• The maximum rate of the reaction or Vmax is
  reached when substrate concentration exceeds
  enzyme concentration by some amount.

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Michaelis-Menten Equation
VmaxS
Vo
KM S

• This equation describes the rate of a reaction.

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Serine Proteases
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Serine Proteases

• Definition A general class of enzymes that
  cleaves covalent peptide bonds.
• They are called serine proteases because serine
  is the most prominent functional group in the
  active site of the enzyme.

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Substrate Specificity

• Cleave adjacent to positively charged amino acids.

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Laboratory Trypsin Digest

• Partial trypsin digestion of bovine serum albumin
  (BSA)
• Digestion products separated by gel
  electrophoresis and then visualized.