Proteins

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Proteins
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Proteins Multipurpose molecules
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Proteins

• Most structurally functionally diverse group
  of biomolecules
• Function
• involved in almost everything
• enzymes
• structure (keratin, collagen)
• carriers transport (membrane channels)
• receptors binding (defense)
• contraction (muscle fibers)
• Hormones (insulin)

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Monomer amino acid
central carbon amino group carboxyl group
(acid) R group (side chain)
H C
R random group
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Polymer polypeptide

• amino acids chained into a polymer

• There are 20 different amino acids
• different R-groups
• different properties

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Building proteins

• What type of reaction?
• links NH2 of one amino acid to COOH of
  another
• What type of bonds? Peptide bonds
• C- N bond

condensation
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Protein structure function

• FUNCTION depends on SHAPE

pepsin
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Protein structure function

• FUNCTION DEPENDS ON STRUCTURE
• 4 levels
• 1 primary
• 2 secondary
• 3 tertiary
• 4 quaternary

pepsin
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Primary structure

• Sequence of amino acids
• determined by DNA
• slight change in amino acid sequence can affect
  proteins structure its function
• even just one amino acid change can make all the
  difference!

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Example Sickle cell anemiaresults from ONE
wrong amino acid
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Secondary (2) structure

• Local folding
• ?-helix
• ?-pleated sheet

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Protein Structure

• R GROUPS give amino acids their distinctive
  properties reactivity.

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Tertiary

• determined by interactions between R groups
• Polar and - attract
• Nonpolar hydrophobic (hide on inside)

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Quaternary (4) structure

• More than 1 polypeptide chain joined together
• only then is it a functional protein

collagen skin tendons
hemoglobin
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Protein structure (review)
Molecular folding
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Protein Shape

• Proteins only do their job correctly when their
  shape is right
• Environmental factors can change a proteins shape
  - called DENATURING
• Example cooking eggs

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Toobers A protein building activity

• Tacks represent the side chains (R-groups) of
  amino acids
• (2) Blue Tacks basic amino acids ( charge)
• (2) Red Tacks acidic amino acids (- charge)
• (6) Yellow Tacks nonpolar/hydrophobic amino acids
• (3) White Tacks hydrophilic aminio acids

• Instructions
• Distribute the 15 tacks randomly but evenly along
  the toober. By doing this, the tacked toober
  represents a protein made of 15 amino acids.

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• Instructions
• Fold your protein according to the laws of
  chemistry that drive protein folding.

• R-groups interact with one another
  based on the following principles
• Nonpolar/ Hydrophobic sidechains will be buried
  on the inside of the globular protein, where they
  are hidden from polar water molecules.
• Charged sidechains opposite charges attract one
  another
• Hydrophilic sidechains will be on the surface of
  the protein where they can hydrogen bond with
  water.

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Enzymes
A special class of proteins
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How important are enzymes?

• all chemical reactions in living organisms
  require enzymes to work
• building molecules
• digesting (breakdown) molecules
• enzymes speed up reactions catalysts
• Chemical reactions only occur when molecules
  collide with one another
• Life cannot wait for chance collisions
• Without enzymes there reactions would not occur
  fast enough to sustain life

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Enzyme Action

• Speed up reaction by stressing bonds between
  molecules
• Force molecules together to form bonds OR pull
  molecules apart to break bonds
• Lowers amount of energy needed to start a
  reaction - called ACTIVATION ENERGY
• Causes reaction to speed up

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Enzymes Reduce Activation Energy
energy of activation
Energy
Reactants
Products
Progress of the reaction
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Enzymes are specific

• Lock and Key model
• Every biochemical reaction uses a specific enzyme
• the lock the enzymes active site
• part of enzyme that reacting molecule(s) fit into
• the key the substrate molecule
• Molecule(s) that enzymes work on

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Its shape that matters!
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Enzymes are reusable

• Enzymes are not changed by the reaction
• used only temporarily
• re-used again for the same reaction with other
  molecules
• very little enzyme needed to help in many
  reactions

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Effect of Temperature on Reaction Rate
What affects enzyme action?
reaction rate
temperature
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Temperature

• Effect on rates of enzyme activity
• Optimum temperature
• greatest number of collisions between enzyme
  substrate
• Raise temperature
• denature protein lose shape
• Lower temperature T
• molecules move slower
• decrease collisions

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Effect of pH on Reaction Rate
What affects enzyme action?
stomachpepsin
intestinestrypsin
reaction rate
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pH
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pH

• Effect on rates of enzyme activity
• pH changes protein shape
• most human enzymes pH 6-8
• depends on where in body
• pepsin (stomach) pH 3
• trypsin (small intestines) pH 8

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• For enzymesWhat matters?

SHAPE!