Download (most also have sulfur) The monomers of proteins are amino acids.

Proteins and Enzymes
Proteins have many functions
• They provide structural
support in bones and
muscles
• They form parts of cell
membranes
• They function as
hormones to regulate the
body
Proteins have many functions
• They form antibodies to
protect against infection
• They increase the
rate of chemical
reactions
Proteins are macromolecules.
• They contain nitrogen, carbon, hydrogen,
and oxygen (most also have sulfur)
• The monomers of proteins are amino acids.
Proteins are macromolecules.
• Amino acids contain an amino group, a
carboxyl group, and a variable R-group.
• When the amino acids join, they form a polymer
called a polypeptide. The monomers are held
together by peptide bonds.
• 20 different amino acids are found in nature.
• Since the R-group varies, it allows for much
variety. That is why proteins have so many
functions.
Proteins have four levels of organization.
• This allows for the
unique shape of
proteins.
• Shape is very important; if a protein is not the
right shape, it will not work.
Primary structure
• A sequence of
amino acids
Secondary structure
• α helix – coil held together by hydrogen bonding
• β sheet – two or more regions of the polypeptide chain
are parallel
Tertiary Structure
• Ionic bonding
• Hydrophobic
interactions
• Disulfide bonding
• Hydrogen bonding
Hydrogen Bonding
• http://programs.northlandcollege.edu/biology
/Biology1111/animations/hydrogenbonds.htm
l
• This animation shows hydrogen bonding in water – but it is
the same type of bonding in other molecules
Quaternary Structure
• Combination of two or more polypeptide
chains
– Ex: Hemoglobin consists of 2 alpha chains and 2
beta chains
Enzymes – a special type of protein
• Enzymes are biological catalysts, which work to
speed up a chemical reaction.
• Without enzymes, several reactions in cells would
never occur or happen to slowly to be useful.
Enzymes lower activation energy.
• Activation energy is
the energy needed to
get a chemical
reaction started.
Effect of Enzymes
• When activation
energy is
lowered, the
reaction speeds
up.
Enzyme Action
• Enzymes provide a site where
reactants can be brought
together to react.
• This is site is called the active
site.
• The reactants are called the
substrates.
Enzyme Action
• The shape of an enzyme is so specific that generally only
one enzyme will work for one substrate.
• Therefore, enzymes are said to fit together like a “lock and
key.”
Enzyme Action
Since only the
substrate
changes
during the
reaction, the
enzyme can be
reused again
and again.
• Enzymes work best at specific temperatures
and pH.
• Heating can change the enzyme shape
(denaturing)
• The wrong pH affects the binding of the
substrate to the enzyme.
• Most enzymes in our body work best at 37°C
(98.6°F) and at a pH between 6.5 to 7.5.
High Salinity also disrupts the
enzyme’s shape
Induced-Fit Model
• Says that enzymes and substrates don’t quite fit
together perfectly
• Enzyme conforms slightly to substrate, which aids
the enzyme in changing the substrate’s structure
Cofactors
• Metal ions or coenzymes (often vitamins)
• Shift electron arrangement in enzymesubstrate complex
Enzyme Regulation
• Most cells contain proteins that turn enzymes
on or off.
Allosteric Control
• Molecule binds to enzyme (not at active site)
and changes active site structure
Allosteric Control
Affect of substrate concentration
Affect of enzyme concentration
• Assumes unlimited amount of substrate
• Eventually enzymes will run out of substrate
to bind with, lowering the reaction rate