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

ATP

nucleoside

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)

Activation energy change

Activation energy:With and without enzymes

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

Review of enzymes

Composition Lower EA

Do not change Very selective

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

Enzyme, substrates, and active site

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)

Competitive inhibitor

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

Competitive or noncompetitive inhibitor?

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

Feedback Inhibition

True or False. Enzymes change the direction of the reaction.

Describe the relationship between activation energy and enzymes.

Describe the relationship between active sites and substrates.

What is the difference between competitive inhibitors and noncompetitive inhibitors?

True or False. All protein enzymes work at the same optimal pH.

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……?

True or False. The types of inhibition with

enzyme-catalyzed reactions always have negative impacts on the organism.