Protein Structure and Enzyme Function

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Protein Structure and Enzyme Function

• How Protein Activity Depends on Proper Folding

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Four Levels of Protein Structure
Tertiary(Folding by R-group interactions)
Primary(Sequence)
Quaternary(Two or more chains associating)
Secondary(Coiling by Hydrogen Bonding)
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Proteins Structure

• Primary structure chain of amino acids
• Amino acids have common features

Carboxylic AcidGroup
AminoGroup    
R
CentralCarbon
The R GroupDiffers for Each Amino Acid
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Proteins Structure Forming the Protein Chain
Phenylalanine
Leucine
Dehydration Synthesis between COOH NH2
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Proteins Structure Forming the Protein Chain
The Peptide Bond
Water
Phenylalanine-Leucine Dipeptide
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Four Levels of Protein Structure

• Secondary Structure
• Folded structure due to hydrogen bonds between
  the amino and acid groups of amino acids

C
N
C
N
H
O
H
O
or
O
H
O
H
N
C
N
C
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Four Levels of Protein Structure

• Tertiary Structure
• Three dimensional folded structure due to
  attractions and repulsions between R groups
• Can involve
• covalent bonding hydrogen bonding ionic
  interactions hydrophilic and hydrophobic
  interactions

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Four Levels of Protein Structure

• Quaternary Structure
• Association of two or more protein chains

eg. Hemoglobin is composed of 4 protein
chains 2 are called alpha
hemoglobin 2 are called beta
hemoglobin
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Applying Your Knowledge

• Primary
• Secondary
• Tertiary
• Quaternary

• Which structure results from hydrogen bonding?
• Which structure involves an association of two or
  more protein chains?
• Which structure describes the linear sequence of
  amino acids?
• Which structure depends upon interactions between
  the R groups of the amino acids?

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Enzymes Assist in Biological Reactions

• Enzymes are biological catalysts.
• biological composed of protein
• or, rarely, RNA
• catalyst speeds up a reaction
• without being changed
• by the reaction

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Properties of Enzymes

• Most enzymes are proteins.
• All enzymes are SPECIFIC for the reactants
  (substrates) in the reactions that they catalyze.
  
• Enzymes speed up biological reactions by lowering
  the activation energy for the reaction.

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Enzyme-Substrate Interactions
Substrate
Substrate
1 Substrates enter active site
ActiveSite
2 Shape change promotes reaction
Enzyme

• Product releasedenzyme ready again

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Activation Energy Controls Rate of Reaction
Activationenergy withoutcatalyst
Activationenergy withcatalyst
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Properties of Enzymes

• Three dimensional structure of an enzyme
  preserves its ACTIVE SITE
• active site region on enzyme where
• reactants bind
• Conditions that can affect three dimensional
  structure include heat, pH (acid/base balance)
  and other chemicals (salt, charged ions)

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Effects of Temperature and pH on Enzymatic
Activity
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Applying Your Knowledge

• Active Site
• Activation Energy
• Enzyme
• Catalyst

• A biological catalyst is a(n) __________ .
• The region on an enzyme where reactants bind is
  the _________.
• Enzymes (raise or lower) the (1, 2, 3 or 4) of a
  reaction.