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 Proteins account for more than 50% of the dry mass of
most cells
 Monomer: amino acids
20 amino acids used in cells
Central carbon atom
One hydrogen attached
Amine (NH2) and carboxylic acid (COOH) groups
attached to carbon
 Only thing different is side chain…R-group (side
 Responsible for 3D shape of protein
 Polymer: polypeptide chains (proteins)
 Link between monomers is called: polypeptide
bond or PEPTIDE bond
 Made by a dehydration reaction
 (between amine group of one aa and carboxyl group of
another aa)
Functions of Proteins
 Structural support/strengthening
 Catalysts (enzymes)
 Storage
 Transport
 Cellular communications
 Movement
 Defense against foreign substances
Some famous proteins…
 Essential components of cell membranes
 Oxygen-carrying pigment hemoglobin
 Antibodies which attack and destroy invading
 Enzymes!
 Collagen! (fibrous)
Amino Acids
 20 -23 major AA (others have been synthesized in labs)
 Amino group on one end (-NH2)
 Carboxylic acid group on one end (COOH)
 Hydrogen
 R-group/side chain (changes)
Peptide Bond
 When two amino acids (AA#1 and AA #2) join,…
 AA #1 loses a hydroxyl group (-OH) from its
carboxylic acid (-COOH) side
 AA #2 loses a hydrogen from its amine (NH2) group
 The Carbon atom in the carboxyl group of AA#1 is
now free to make ONE bond with the Nitrogen of the
amine group in AA#2
 This bond is called a PEPTIDE Bond
 H- and –OH removed…what is this???
 WATER!!!
 Another condensation reaction (dehydration)
 Dipeptide Molecule
 New molecule formed by joining 2 amino acids
 Polypeptide Molecule
 Molecule made up of many amino acids joined by
peptide bonds
 Polypeptide is the POLYMER (not protein)
 Complete protein may contain one polypeptide chain,
twisted and folded or two or more polypeptide chains
interacting with each other
Polypeptide bonds
Where are amino acids linked?
 In living cell Ribosomes!
 These reactions that occur on
the ribosomes are controlled
by ENZYMES (more on this
How are polypeptides broken?
 Hydrolysis Reactions
 Naturally occurs in stomach and
small intestine
 Protein in food is hydrolyzed into
amino acids prior to being absorbed
by the blood
 Once in the blood, these AA can be
restructured into polypeptides and
then twisted and folded into
functioning PROTEINS the cells in
you body needs
Protein Structure
 Primary structure 1’
 Order of amino acids in a polypeptide chain
 Secondary structure 2’
 Polypeptide chain folds because of interactions between
amino acids
 Tertiary Structure 3’
 Gives proteins 3-D shape
 VERY IMPORTANT to function of protein
 Beta pleated sheets and alpha helices fold based on
interactions between R-groups of a.a.
 Hydrogen bonds, polar/non-polar interactions, acid/base
interactions, disulfide bonds, van derWaals forces
 Quaternary Structure 4’
 the association of the polypeptide chains
 some proteins contain more than one polypeptide chain
 Each polypeptide chain in the protein is called a subunit
 Two or more subunits come together for a specific
 On Red blood cells
 Its shape allows RBCs to carry oxygen all around your body!
Practice Set 4
(6 MC and 1 SAQ)