Molecular Biology

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Molecular Biology

• 2.4 Proteins

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PROTEINS

• Made of C, H, O and N
• Proteins are large molecules constructed of many
  amino acids
• Most abundant organic compound found in living
  cells

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Most important macromolecule in the body
Proteins Rule Everything!
PROTEINS

• Functions?
• Structural parts
• nails, hair, cell membrane, and cartilage
• Pigments
• skin, eyes, and chlorophyll
• Hormones and receptors
• Muscle contractions
• Immunity-Antibodies
• Enzymes

• Cytoskeleton
• Blood clotting
• Transport of nutrients/gases
• Cell adhesion
• Cell membrane transport
• Packing of DNA

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PROTEINS

• Total energy gain is 4 Calories/gram. (however,
  energy gain is not their main function).

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PROTEINS

• Amino acids are linked together by condensation
  reactions to form polypeptides.
• The building blocks of proteins are amino acids.

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PROTEINS

• Amino Acids
• Centre carbon atom
• Bonded to
• Hydrogen (H)
• Amine group (-NH2)
• Carboxyl group (-COOH)
• R- group (different in each amino acid)

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PROTEINS

• Amino acids are linked together by condensation
  reactions to form polypeptides.
• The amino acids are bonded together by peptide
  bonds to form proteins.

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PROTEINS

• The bond that is formed from the acid group
  (COOH) and the amino group (NH2)
• Water is eliminated condensation reaction
• Proteins are frequently called polypeptides (many
  peptide bonds).

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PROTEINS

• The smallest polypeptide consists of 20 amino
  acids (less than that called an oligopeptide)
• Insulin contains 2 polypeptides 21 amino acids
  and 30 amino acids
• Human titin has 34 350 amino acids

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PROTEINS

• There are 20 different amino acids used by
  ribosomes to make polypeptides

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PROTEINS

• Draw molecular diagrams to show the formation of
  a peptide bond
• Locate the Amine, Carboxyl, and R-groups
• Show the formation of a peptide bond between 2
  amino acid
• Try to draw an oligopeptide with all 4

Alanine
Serine
Glutamic acid
Glycine
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PROTEINS

• Did you notice?
• The amine and carboxyl are used in the peptide
  bonds
• Chain of atoms linked with single bonds form
  backbone
• H attached to N by single bond
• O attached to C by double bond
• The R-groups remain

Alanine
Serine
Glutamic acid
Glycine
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PROTEINS

• The amine and carboxyl group are used in the
  condensation reaction
• The R-groups give the polypeptide its character
• The R-groups provide an amazing range of proteins

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PROTEINS

• Some proteins contain amino acids not contained
  in the list of 20.
• This is due to modification after a polypeptide
  has been made. Example hydroxyproline in
  collagen

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PROTEINS

• Patterns, trends, discrepancies most but not all
  organisms assemble polypeptides from the same
  amino acids.
• We can exclude the possibility that this trend is
  due to chance
• What reasons would account for almost all
  organisms using the same 20 amino acids?
• These were the ones produced before life
• These are the ideal
• All life evolved from a single ancestral species

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PROTEINS

• Amino acids can be linked together in any
  sequence giving a huge range of possible
  polypeptides

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PROTEINS

• Calculate the possibilities

Number of Amino Acids in the Chain Number of possible sequences Number of possible sequences
1 201
2 202 400
3 8000
4
64 000 000
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PROTEINS

• Shapes
• primary (linear)
• secondary (ß-pleated sheets and a-helix)
• tertiary (bent-coiled)
• quaternary (compact with a specific structure).

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PROTEINS

• You can unfold a protein (de-nature) by exposing
  the protein to heat, radiation or a change in pH.
  (i.e. frying an egg, baking a cake, UV exposure,
  x-rays).

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Questions

1. What 2 functional groups do all amino acids have
   in common?
2. Draw a generic formation of a peptide bond.
   Identify the amino terminus, carboxyl terminus,
   and peptide bond.
3. Define primary structure.
4. Name the 2 types of secondary structure. What
   type of bond stabilizes this structure?
5. Distinguish between polypeptide and protein.
6. Why do proteins have more diverse functional
   roles than carbohydrates?