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what is an enzyme
mainly proteins that function as biological catalysts
what is a catalyst
a substance that speeds up the rate of a chemical reaction, catalysts are effective in small amounts and remain unchanged at the end of the reaction
what allows reactions to occur at relatively high rates in cells
enzymes
in general, catalysts
are effective in small amounts, remain unchanged at the end of the reaction
what can cells do by making some enzymes and not others
cells can control what chemical reactions happen in the cytoplasm
what are metabolites
Include all the molecules synthesized or broken down by chemical reactions inside our bodies
what is anabolism
the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions
what is catabolism
the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
how many substrates can fit into each enzyme
usually only one
how are enzymes usually classified
according to the type of reaction they catalyse and they can be named according to their substrate
what does metabolism consist of
chains and cycles of enzyme-catalysed reactions, such as we seen in respiration, photosynthesis and protein synthesis and in many other pathways
what are some examples of anabolism
the synthesis of proteins from amino acids, the synthesis of polysaccharides from simple sugars, photosynthesis
what are some examples of catabolism
hydrolysis of macromolecules into monomers in digestion, oxidation of substrates in respiration
what is a substrate
the starting substance in a reaction catalysed by an enzyme it is the molecule that the enzyme reacts with
what is the product
what the substrate is converted to in a reaction catalysed by an enzyme
what is the active site
the region of an enzyme molecule where the substrate molecule binds and catalysis occurs
what is the enzyme-substrate complex
a temporary structure formed when a substrate binds to the active site of an enzyme
what type of molecules are enzymes typically
large, globular protein molecules where the tertiary structure has given the molecule a generally rounded shape
how do enzymes work
by binding to the substrate molecule at a specially formed pocket in the enzyme, here the enzyme and substrate from an enzyme-substrate complex, the substrate is raised to a high energy transition state, this complex has the briefest of existences before the substrate molecule is formed into another molecule or broken down into others by the catalytic properties of the active site, then the products are released, together with the unchanged enzyme, the enzyme is available for reuse
how is it ensured that the active site has the necessary properties for catalysis
the interactions between the amino acids within the overall 3D structure of amino acids, including binding to the substrate molecule, holding onto it while the chemical reaction takes place and lowering the energy of the transition state
what is the size of most substrate molecules compared to the enzyme
quite small
what is induced fit
the binding of the substrate to the enzyme causes a change in the shape of the enzyme and the substrate, resulting in the proper alignment of the catalytic groups on its surface, which enables catalysis to take place
why are enzymes specific
because of the way they bind with their substrate at the active site
what happens as the substrate binds to the enzyme
a slight change of shape is induced in the enzyme and substrate molecules
what does the enzyme hexokinase catalyse
glucose + ATP -> glucose-6-phosphate + ADP
what is an immobilized enzyme
an enzyme attached to an inert, insoluble material, enabling recovery, reuse and improved enzyme stability
what is needed for a substrate molecule and an active site to come together
movement, the greater the kinetic energy of enzyme and substrate the greater the chance of collisions between molecules and the formation of enzyme substrate complexes
what method of enzyme use is widely used in food processing, pharmaceuticals and wastewater treatment
Enzymes immobilized on (or in) a membrane
what does the EIM system facilitate
recycling of the enzymes and also, often enhanced enzyme properties,
what does enzyme immobilization involve
the attachment of enzymes to insoluble materials which then provide support
what are the different enzyme immobilization techniques
entrapment, adsorption, covalent bonding, cross-linking, affinity
what are the advantages of using an immobilized enzyme in industrial processes
it permits reuse of the enzyme preparation, the product is enzyme free, the enzyme may be much more stable and long lasting due to protection by the inert matrix
when does denaturation occur
when the weak intramolecular interactions within a globular protein, formed between different amino acid, residues, break, this changes the 3D shape of the active sites
what bonds are not hydrolyzed during denaturation
peptide bonds
what happens when starch is hydrolyzed by the enzyme amylase
maltose is produced
is it sufficient to say when explaining the increase in the reaction rate of an enzyme, because there are more collisions with the enzyme
no, a better answer is, because there are more frequent collisions between the substrate and the active sites
do all enzymes have the same optimum temperature
no, bacteria in thermal springs can have enzymes with optimum temperatures closer to 0C
what is the optimum pH of enzymes often close to
pH 7, the point of neutrality
why does the effect of pH on enzymes occur
because the structure of a protein, and therefore the shape of the active site is maintained by various bonds and weaker intermolecular forces within the proteins structure, a change in pH from the optimum value alters the bonding patterns, progressively changing the 3D shape of the molecule, the active site may quickly be rendered inactive
are the effects of pH on the active sites normally reversible
yes, if the change in pH wasn't too extreme
why do some digestive enzymes have different optimum pH values from most other enzymes
some parts of the digestive system are very acidic so the enzymes must have a lower optimum pH
what do we do when measuring the rate of enzyme catalysed reactions
we measure the amount of substrate that has disappeared from a reaction mixture or the amount of product that has accumulated in a unit of time
what is convenient to measure when investigating the rate of enzyme activity of catalase
the rate at which oxygen accumulates
what is the relationship between the substrate concentration and the rate of reaction
at lower concentrations, the rate increases in direct proportion to the substrate concentration, at higher substrate concentrations, the rate of reaction becomes constant and shows no increase
what is the result of increased concentrations of substrate in terms of collisions
increased concentrations of substrate mean there are more frequent collisions between substrate and the enzyme with a higher likelihood of the substance binding with the active site of the enzyme and enzyme-substrate complexes forming, causing the reaction to take place
what happens when there is more substrate than enzyme
substrate molecules must queue up for access to an active site so there is no increase in the rate of reaction as the substrate concentration is further increased
what is activation energy
the energy required by a substrate molecule before it can undergo a chemical change
how do we represent the reaction between an enzyme and substrate including the transition state
E + S -> [ES] -> ES -> P + E
what happens in terms of energy when the substrate becomes the product
energy is released
how do enzymes work in terms of activation energy
they lower the amount of energy required to activate the reacting molecules by providing a new alternative reaction pathway
do enzymes remove the activation energy barriers
no, they just make it significantly smaller
what is an extracellular enzyme
an enzyme secreted by a cell that functions outside the cell
what is an intracellular enzyme
an enzyme that functions within the cell in which it was produced
what is an example of a type of enzyme that is exported from cells
digestive enzymes
how do extracellular enzymes leave the cell
through endocytosis
what are two of the main metabolic processes in respiration
glycolysis and the Krebs cycle
what happens in terms of energy when glucose is oxidized to carbon dioxide and water in aerobic cell respiration
energy is transferred from the store of chemical potential energy to heat energy
what is free energy
energy available to do work
what are exergonic reactions
reactions that release free energy
give an example of an exergonic reaction
the oxidation of glucose
what is inevitable in metabolic reactions
heat generation
what are endotherms
animals that depend on the release of heat from metabolic reactions for the maintenance of a constant body temperature
what are ectotherms
animals that cannot use metabolic heat to maintain a constant body temperature
what are endergonic reactions
reactions that require energy
what is an example of an endergonic reaction
the synthesis of a protein from amino acids
what is a linear metabolic pathway
a series of enzyme catalysed reactions that run in one direction, from reactant to product
what is a cyclical metabolic pathway
a circular series of enzyme catalysed reactions where there is no end to the series, one reaction leads to the next and eventually back to the starting point
what is a metabolic pathway
a sequence of enzyme catalysed biochemical reactions in cells and tissues
give an example of a linear metabolic pathway
glycolysis
give an example of a cyclical metabolic pathway
the Krebs cycle
what are the two sets of reactions in photosynthesis
the light dependent reactions and the light independent reactions
which cycle drives the light independent reactions in photosynthesis
the Calvin cycle
what is an enzyme inhibitor
a substance that slows or blocks enzyme action
what is a competitive inhibitor
a substance that binds to the active site of an enzyme, slowing or blocking enzyme action
what is a non-competitive inhibitor
a substance that does not bind to the active site but to another part of the enzyme, slowing or blocking enzyme action
what is the enzyme that catalyses the reaction between carbon dioxide and the acceptor molecule in photosynthesis
ribulose biphosphate carboxylase
what is ribulose biphosphate carboxylase competitively inhibited by
oxygen
what is an allosteric regulator
molecules that change the shape and activity of an enzyme by reversibly binding at a site on the enzyme
what does the binding of an allosteric activator do
temporarily stabilize the enzyme shape as an active an effective catalyst
what does the binding of an allosteric inhibitor do
change the enzyme shape into an inactive form
what is allosteric regulation a form of
reversible non-competitive inhibition or activation of an enzyme
what can subtle fluctuations in the concentration of activators and inhibitors do
fine tune the activity of a critical pathway as constantly changing conditions or requirements of cell metabolism demands
what is the name given to the specific substances that can bind to an allosteric site
effectors
what is the rate of an enzyme-catalysed reaction
the amount of substrate that has disappeared from a reaction mixture or the amount of product that has accumulated in a period of time
what is a statin
any class of drugs that lower the level of low density lipoproteins in the blood by inhibiting the activity of an enzyme involved in the production of cholesterol in the liver
what is competitive inhibition a consequence of
an inhibitor binding reversibly to an active site
what type of inhibitor are statins
competitive inhibitors
what do statins competitively inhibit
HMG-CoA reductase
what are statins similar in structure to
the substrate of HMG-CoA reductase
what are the two forms of cholesterol in the blood
low-density lipoproteins, high-density lipoproteins
what can result from excess blood cholesterol, present as LDLs
atherosclerosis
what is atherosclerosis
the progressive degeneration of the artery walls, a direct consequence of this is an increased likelihood of the formation and circulation of blood clots
what are statins taken for
to reduce LDLs in the blood and therefore reduce the risk of coronary heart disease
what is end-product inhibition
when the product of the last reaction in a metabolic pathway inhibits the enzyme that catalyses the first reaction of the pathway
how can individual pathways in metabolism by switched off
by the final product acting as a reversible inhibitor of the enzyme that catalyses the first step in the pathway
what can bacteria synthesize isoleucine from
threonine
explain the metabolic pathway for the synthesis of isoleucine
isoleucine acts as a non-competitive inhibitor by binding to the allosteric site of the enzyme threonine deaminase, threonine deaminase is an essential enzyme in the first stage of the metabolic pathway, its inhibition turns off isoleucine production, this regulates the production of isoleucine, initially, when isoleucine concentration is still low, the metabolic pathway can proceed as non competitive inhibition is low, as isoleucine concentration increases, non-competitive inhibition takes place and the metabolic pathway is regulated, as isoleucine is used in the cell for protein synthesis, its concentration falls and the allosteric sites of threonine deaminase are no longer occupied, so the enzyme can once again act in the conversion of threonine to isoleucine
what is mechanism based inhibition
a process that occurs when unreactive molecules are transformed into an active form through catalytic reactions, these active forms inhibit the enzyme, typically through covalent modification of the active site, it is an irreversible form of enzyme inhibition
what is a substrate analogue
a molecule that has a similar structure to the substrate
describe mechanism-based inhibition
a substrate analogue binds to the active site of the enzyme covalently, the substrate analogue is modified by the enzyme to produce a reactive group, which reacts irreversibly to form a stable inhibitor-enzyme complex
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