PROTEINS

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PROTEINS

• THE MOLECULAR TOOLS OF THE CELL

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Proteins

• account for more than 50 of the dry weight of
  cells
• used for
• support (hair, horns, feathers, spider webs)
• storage ( a.a.s in seeds, egg white, milk)
• transport (hemoglobin, cell membranes)
• movement (muscle fibers, cilia, flagella)
• defense (antibodies)
• regulate metabolism (enzymes)

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Structural Proteins

• keratin
• hair
• nails
• fur
• skin
• horns
• Collagen (most abundant protein in vertebrates)
• tendons
• cornea
• bones
• ligaments

• fibrous
• insoluble
• strong

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Functional Proteins

• globular
• soluble

• enzymes
• regulate metabolism
• hemoglobin
• transports oxygen
• hormones
• regulate metabolism

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Structurally Sophisticated

• Each has a unique three dimensional shape
• all are peptides (polymers of amino acids)
• 20 amino acids
• central carbon
• partnered with an amino grp, carboxyl grp,
  hydrogen atom and R grp

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PROTEIN FUNCTION

• depends on structure
• globular or fibrous
• example - antibody shape determines what antigen
  (foreign protein) it recognizes

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SIDE CHAINS OF AMINO ACIDS

• physical and chemical properties of side chain
  determines characteristics
• grouped by properties of side chains
• hydrophobic - non polar side chains
• hydrophilic -polar side chains
• acidic - negatively charged side chain
• basic - positively charged side chains

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The 20 Amino Acids
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POLYPEPTIDE BONDS

• results from dehydration synthesis
• OH from carboxyl group and H from amino group

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PRIMARY STRUCTURE OF LYSOZYME
A.A. sequence is determined through genetic
information.
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SECONDARY STRUCTURE OF A LYSOZYME
An alpha helix is held together by H bonds
between every fourth a.a. Pleated sheets are
regions of the polypeptide chain that are
parallel and are held by H bonds.
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TERTIARY STRUCTURE OF A PROTEIN
Hydrophobic bonds are initiated by water. Water
molecules H bond to each other and to hydrophilic
side chains of the protein. H bonds form between
polar side chains and ionic bonds between pos and
neg side chains.
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QUATERNARY STRUCTURE OF HEMOGLOBIN
Notice that this protein is made of four
polypeptide chains.
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DENATURATION OF PROTEIN

• pH, salt concentration, temperature and other
  conditions of the environment affect protein
  shape.
• Extremes that change protein shape cause the
  protein to be unable to function

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DENATURATION OF PROTEIN

• pH, salt concentration, temperature and other
  conditions of the environment affect protein
  shape.
• Extremes that change protein shape cause the
  protein to be unable to function

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STUDYING PROTEIN STRUCTURE

• Originally models were made of wood, wire and
  plastic.
• Now models are computerized
• first crystallize a protein use x-ray
  crystallography
• atoms defract the x-rays into a regular pattern
• second photograph diffraction pattern

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- third computer generate map of
successive slices - fourth Create picture
showing position of each atom