Biochemistry VI
Proteins & Enzymes
Proteins
Large, complex organic molecules
Made of smaller monomers: Amino Acids
Categories of proteins:
– Structural Proteins
– Storage Proteins
– Transport Proteins
– Defensive Proteins
– Enzymes
Structural Proteins
Used to provide structure and support for
certain parts of organisms
Examples:
– Keratin in hair/horns of animals
– Collagen in connective tissues
– Silk in spider webs
Storage Proteins
Used to store other molecules for later use
Examples:
– Casein in milk
– Ovalbumin in egg whites
– Zein in corn seeds
Transport Proteins
Used to assist in the transport of
molecules into and out of a cell or other
membrane
Examples:
– Hemoglobin (O2 carrier) in red blood cells
– Integral membrane proteins
Defensive Proteins
Used to protect cells and organisms
against foreign substances or life forms
Examples:
– Antibodies
– Cell surface recognition proteins
– Poisons made by plants, insects, snakes, etc.
Enzymes
Regulate the rate of chemical reactions
Examples:
– DNA polymerase and helicase
– Lactase
– Peroxidase
– Sucrase
Amino Acids
The building blocks of proteins
20 total amino acids
Some can be synthesized by humans,
others must be consumed
Carbon w/ 4 groups:
Amine
Carboxyl (acid)
Hydrogen
R group (varies)
Amino Acid R Groups
R Groups determine the physical and
chemical properties of the protein
They can be polar, nonpolar, acidic, or
basic
They can also be used for the attachment
of other inorganic groups that are essential
for the functioning of the protein
– Heme group on hemoglobin bonds to Fe2+
– Other organic co-enzymes from our diet
(vitamins)
Putting Amino Acids Together
To build a protein, the amino acids must
be connected by peptide bonds
Peptide bonds connect the amine group of
one amino acid to the carboxyl group of
the next
This bond is caused by a dehydration
reaction
A chain of connected amino acids is called
a polypeptide
Where Do A.A.s Come From?
Many foods contain amino acids in the
form of protein
When we digest protein, we recycle the
amino acids and re-assemble them into
our proteins
Types of Amino Acids
Structure of a Protein
The code in the DNA recipe is a sequence
of A’s, T’s, C’s and G’s
The corresponding RNA copy of the recipe
contains this code, which is read in 3’s
– AUG, GGC, CUA, AAU, GCC, etc…
Every 3 letter combination translates into 1
specific amino acid
The chain of amino acids has a specific
sequence
Structure of Protein
Primary Structure
– A unique sequence of amino acids in a polypeptide
chain
Secondary Structure
– Repeated folds and coils of a polypeptide chain
Tertiary Structure
– Irregular contortions from bonding of the side chains
of the various amino acids
Quaternary Structure
– overall protein structure that results from the
aggregation of tertiary subunits
Website Animation
http://www.learner.org/channel/courses/bio
logy/units/proteo/images.html
http://www.johnkyrk.com/aminoacid.html
Enzymes
Enzymes speed up metabolic reactions
Enzymes: catalytic proteins
Catalyst: reduces the activation energy
Activation energy (Ea): energy required to
start a reaction
Enzymes
Substrate: reactant an enzyme works on
Active site: pocket where substrate is
worked on
Induced fit: brings chemical groups into
positions that enhance their ability to work
between the enzyme and substrate
Effects of temperature and pH: enzymes
have an optimal temperature and pH they
work within
Enzymes
Cofactors: helpers bound into active site
Coenzyme: an organic cofactor
Competitive inhibitors: block the active site
Non-competitive inhibitors: bind to another
part of the enzyme, inhibiting work
Allosteric site: receptor site away from the
active site, where other molecules regulate
activity
Enzymes
Feedback Inhibition: metabolic pathway is
switched off by its end product
Website Animations
http://www.phschool.com/science/biology_
place/labbench/lab2/images/indfit.gif