atp immediate source of energy that drives cellular work adenosine triphosphate nucleotide with...
TRANSCRIPT
ATP
Immediate source of energy that drives cellular work
Adenosine triphosphate Nucleotide with unstable phosphate
bonds Phosphate bonds easily hydrolyzed Nucleoside: adenine joined to ribose 3 phosphates attached to ribose
Hydrolysis of unstable bonds between phosphates Terminal phosphate bonds
unstable Products of hydrolysis more stable Exergonic (spontaneous) Produces ADP + P G = -7.3kcal/mole in lab In living cell –13kcal/mol
ATP performs workrequires enzymes Exergonic hydrolysis coupled
with endergonic phosphorylation Phosphorylation – transfer of P
to another molecule Molecule receiving P becomes
more active Page 95
Regeneration of ATP
Continual rapid process 107 molecules used and
made/sec/cell ADP + P ATP Requires energy --- how much? Endergonic
Enzymes
Biological catalysts: Most are proteins
Some are ribozymes-RNASpeed up rxns by lowering
energy barriers
Even if a reaction is spontaneous, it may take a really long time to get enough energy to start. (example digestion)
Enzymes LOWER the amount of energy, helping spontaneous reactions to occur faster.
Free energy of activation EA
activation energy Energy required to start a reaction (heat) Needed to get molecules to their transition
state, unstable condition to break bonds Spontaneous reactions can be slow Heat can catalyze reactions, but heat is not
good for all parts of the cell/body SO, we have enzymes to catalyze reactions (Exergonic, spontaneous reactions)
Example of a spontaneous reaction Urea + H2O CO2 + NH3
(Ammonia)
Bacteria in air breakdown urea At room temperature and pH 8 Time required 3 million years With enzyme urease – 30 000
molecules/s
Specificity of enzymes
Determined by protein conformation Specific to a substrate Substrate: Substance an enzyme acts
on Active site – restricted region of an
enzyme which binds to substrate Pocket or groove
Changes shape in response to substrate
Induced fit – change in shape of active site
Occurs as enzyme joins to substrate
Specific to a substrate Induced fit animation
Steps in Catalytic Cycle
Formation of enzyme-substrate complex
Induced fit (like clasping handshake) Side chains of a few amino acids
catalyze conversion of substrate to product
Product departs Enzyme emerges in its original form
Mechanisms that lowerEA (Activation energy) Hold two or more reactants in
proper position to react Induced fit may distort substrate’s
bond Active site might provide a micro-
environment for reaction Side chains may participate directly
in the reaction
Rate of Reaction
Higher the substrate concentration the faster the reaction
Up to a limit Enzyme can become saturated with
substrate molecules If saturated – rate depends upon how
fast the active sites can convert substrates
If saturated – to speed up, add enzyme
Conditions that favor enzyme activity Optimal temperature Optimal pH Cofactors
Small non-protein molecules May bind to active site and substrate Inorganic (zinc, iron, copper) Organic (vitamins), called coenzymes
Enzyme Inhibitors
Competitive inhibitors Resemble substrate Compete for active site and block active site
from substrate If reversible (weak bonds) – overcome by
increased concentration of substrate CO binds to hemoglobin Sarin, a nerve gas (binds to an enzyme in
the nervous system)
Noncompetitive inhibitors
Bind to another part of enzyme Causes change in shape Substrate can not bind to active site Metabolic poisons DDT, many antibiotics Selective inhibition is necessary in
cell to regulate metabolism
Metabolic control: Allosteric regulation
Allosteric site Specific receptor site on some part of
the enzyme Two receptor sites: active and
allosteric Enzymes with these have two or
more polypeptide chains Each chain has active site Allosteric site where subunits join
Allosteric enzymes have 2 conformations
One conformation is active The other is inactive Activator binds to allosteric to
stabilize active site conformation Inhibitor (noncompetitive) binds to
allosteric site to stabilize the inactive conformation
Cooperativity
Substrate binds to active site of one subunit
Induces a conformational change in other subunits
Stabilizes active site in subunits More substrate can bind to other
active sites EX: Hemoglobin (4 active sites)
Feedback Inhibition
Regulation of metabolic pathway
End product inhibits enzyme within the pathway
Prevents cell from wasting chemical resources
If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?
A. additional product will form B. additional substrate will form C. the reaction will change from
endergonic to exergonic D. Nothing, the reaction will stay at
equilibrium
Describe what allosteric regulation is.
Allosteric activation would stabilize the _____________ form of the enzyme. Which means……?