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Macromolecules Part 3
Proteins
Proteins!
Functions of Proteins
– Structural support
– Storage
– Transport
– Cellular communications
– Movement
– Defense against foreign substances
Proteins
• Monomer: amino acids
– 20 amino acids
– Amine (NH2) and carboxyl (COOH) groups
attached to carbon
– Only thing different is side chain…R-group
• Polymer: polypeptide chains (proteins)
• Link between monomers is called:
polypeptide bond
– Made by a dehydration reaction
– (between amine group of one aa and carboxyl
group of another aa)
• STRUCTURE of A.A.
– Amino group on one end (-NH2)
– Carboxyl group on one end (COOH)
– Hydrogen
– R-group/side chain (changes)-------- ALANINE
• Proteins account for more than 50% of the dry
mass of most cells
Polypeptide bonds
Some famous proteins…
– Essential components of cell
membranes
– Oxygen-carrying pigment
hemoglobin (hemoglobin)
– Antibodies which attack and
destroy invading
microorganisms
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
– HYDROGEN BONDING
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 der Waals 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
function
–
HEMOGLOBIN
• On Red blood cells
• Its shape allows RBCs to carry oxygen all around your
body!
Primary Structure
• Sequence of AA in a long
polypeptide chain
• AA= letters of alphabet
• Sequence of AA= arrangement
of letters to make words
• HUGE amount of different
primary structures
• Changing ONE AA is polypeptide
chain GREATLY changes the
properties of the polypeptide
chain and PROTEIN
Secondary Structure
• The order of AA in
polypeptide chain
determine interactions
between functional
groups of AA
• Functional groups
interact via HYDROGEN
BONDS
– Attraction between oxygen
in the –CO end of one AA
and the hydrogen in the –
NH end of another AA
– H-bond easily broken
• Change pH and change
Temperature
– Three possible 2o
structures
• Determined by order Rgroups
– No particular arrangement
– Alpha helix
• Polypeptide chains that coil
tightly
– Beta pleated sheet
• Looser, straighter shape
created by hydrogen bonds
Tertiary Structure
• Secondary structure gets coiled
and folded
• Precise 3D shape
• Folding is determined by
interactions between R-groups
– Hydrogen bonds
• Tryptophan
• Arginine
• Asparigine
– Disulphide bonds
• Between 2 cystine molecules
– Ionic bonds
• b/t R groups containing amine
and carboxyl groups
– Hydrophobic interactions
• b/t R groups that are non-polar
(hydrophobic)
Quaternary Structure
• Proteins are made up of multiple polypeptide
chains, sometimes with an inorganic
component (for example, a haem group in
haemoglogin)
– Prosthetic Group (inorganic component of
protein)
• These proteins will only be able to function if
all subunits are present
• Made by same bonds found in tertiary
structure
• Interactions between R-groups
– Hydrogen bonds
• Tryptophan
• Arginine
• Asparigine
– Disulphide bonds
• Between 2 cystine molecules
– Ionic bonds
• b/t R groups containing amine and carboxyl
groups
– Hydrophobic interactions
• b/t R groups that are non-polar (hydrophobic)
Denaturation
• Unraveling/unfolding of protein
• Why would this be a problem?
• When protein loses its 3-D shape and thus its specific
function
• Caused by:
– Unfavorable changes in pH, temperature or other
environmental condition
– Disrupts the interactions between side chains and causes
loss of shape
• Examples:
– Frying an egg
– Straightening your hair
Enzymes!
ENZYMES!!!
• A special type of protein…???
• In order for a protein to work at its
SPECIFIC JOB, it must have….???
• Because an enzyme is a protein, it
MUST have….???
• Can any key unlock the door to
your house???
• Can any substrate/reactant fit into
a specific enzyme?
• How many different enzymes do
we have???
ENZYMES!!!
• Proteins
• Biological catalysts that
speed up the rate of
chemical reactions
• They help make
products faster!
• Never used up!
• “Matchmaker”
•
•
•
Enzymes
Enzyme
– Catalyst
• Anything that speeds up the rate of a
reaction by lowering the ACTIVATION
ENERGY
– Activ. E: energy required for a chem.
Rxn to start making products
– used to regulate the rate (speed) of chemical
reactions
– Protein that helps speed up a reaction that
occurs in a biological system
– Name of enzymes end in –ASE
each chemical reaction in an organism requires
its own specific enzyme
enzymes are never changed by their reactions!
Substrate
Molecule/compound that attaches to
enzyme
Active Site
Specific location on enzyme for substrate
to attach
Where the enzymatic reaction occurs
Enzyme-substrate complex
When substrate binds to active site of
enzyme
Products
molecules produced at the end of
an enzymatic reaction
Lock and Key
Model
Enzymes in Action
• Enzymes speed up
chemical reactions
that take place in cells
• They DECREASE
ACTIVATION ENRGY
– The energy needed to
get the reaction
started (or energy
needed to start
making product)
Proteins: Enzymes
• What is a chemical reaction?
• Do they happen on their own?
– If we stare at the piece of paper, are we going to
be able to make the oxygen molecules in the air
collide with the cellulose in the paper?
– What do we need to do?
• What are reactants?
• What are products?
Factors that Effect the
Rate of Reactions
•
Temperature
– Hot
•
Breaks bonds that give proteins its tertiary structure
DENATURES
– Cold
•
•
Slow down chemical reaction (formation of enzyme
substrate complex)
pH
– Acids and bases produce OH- and H+ ions
•
•
too many ions are present, the enzyme may be
denatured (twisted and pulled so out of shape that it
can no longer function)
Inhibitors
– Non-competitive
•
•
react with portions of the active site, changing of its
shape
Allosteric Inhibitors
–
–
Change shape of the enzyme
Attach to regulatory site (not active site) and change the
shape of the entire enzyme (specifically the active site)
– Competitive
•
look like substrate, bind to active site, but do not make
the intended product
Examples of endothermic
reactions:
Melting of ice absorbs energy
Dissolving ammonium nitrate
in water( the essence of
commercial cold packs)
PHOTOSYNTHESIS
Examples of exothermic
reactions:
Digestion of food releases
energy (CELL RESPIRATION)
All combustion reactions (fires)
C + O2 CO2 + E
Adding an alkali metal to water
2 Na + 2 H2O 2 NaOH + H2 + E
Condensation of water
Explosion of bombs
Endothermic Reactions
the reactants have less potential energy than
do the products. Energy must be input in order
to raise the particles up to the higher energy
level.
Energy + A + B --> AB
Exothermic Reactions
the reactants have more potential energy than
the products have. The extra energy is released
to the surroundings.
A + B --> AB + Energy
• Acetylcholinesterase
– catalyzes the breakdown of the neurotransmitter
acetylcholine at several types of synapses as well
as at the neuromuscular junction — the
specialized synapse that triggers the contraction
of skeletal muscle.
– One molecule of acetylcholinesterase breaks
down 25,000 molecules of acetylcholine each
second
– makes possible the rapid "resetting" of the
synapse for transmission of another nerve
impulse.
Class work! Label Each box!
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