2.1.4 enzymes Flashcards
What are enzymes?
Enzymes are biological catalysts, they increase the rate of reaction by lowering the activation energy of the reaction.
What are anabolic reactions?
‘Building up’ reactions.
What are catabolic reactions?
‘Breaking down’ reactions.
What is metabolism?
Metabolism is the sum of all the different reactions and reaction pathways happening in a cell or organism.
What is Vmax?
Maximum initial velocity or rate of enzyme-catalysed reaction.
What is activation energy?
The minimum amount of energy for a reaction to start.
What is the lock and key hypothesis?
-The active site on the enzyme is complementary, only specific enzymes will fit specific substrates.
-When the substrate is bound to the active site, an enzyme-substrate complex is formed.
-The substrate then reacts and forms a enzyme-product complex.
-Products are released, leaving the enzyme.
What is the induced-fit hypothesis?
-The active site of the enzyme changes shape slightly, induces changes to tertiary structure.
-Causes the substrate and enzyme to bind stronger, putting strain on the substrate.
-The bonds weaken within the substrate, lowering activation energy.
What are intracellular enzymes?
Intracellular enzymes are enzymes which act within cells.
What is an example of an intracellular enzyme?
Catalase: catalyses the decomposition of hydrogen peroxide (a toxic product of many metabolic pathways) into water + oxygen.
What are extracellular enzymes?
Extracellular enzymes work outside the cell that made them.
What are examples of extracellular enzymes?
Amylase: carbohydrates catalyses digestion of starch to maltose in saliva/small intestine lumen.
Trypsin: pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine lumen.
Why are extracellular enzymes so important?
Allow large molecules, essential for reactions, to be broken down into smaller components.
What four factors affect enzyme activity?
-Temperature
-pH
-Substrate concentration
-Enzyme concentration
How does temperature affect enzyme activity?
-Increasing temperature increases the kinetic energy of particles.
-The particles move faster and collide more frequently.
-Increased rate of reaction.
-Too high a temperature can denature an enzymes active site.
What is temperature coefficient Q10?
A measure of how much the rate of a reaction increases with a 10 degree rise in temperature.
What happens when the temperature of a reaction exceeds the enzyme’s optimum temperature?
-At higher temperatures the bonds holding the protein together vibrates more.
-Vibrations increase until bonds strain and break.
-Breaking of bonds results in a change in tertiary structure, enzyme becomes denatured.
How does pH affect enzyme activity?
-When the pH changes from the optimum pH, it alters the active site .
-When the pH changes more significantly the structure of the enzyme is irreversibly altered and active site is no longer complementary, reducing rate of reaction.
-Hydrogen ions interact with polar and charged R-groups, changing concentration of H+ ions changes the degree of this interaction.
What is renaturation?
When the pH changes from the optimum pH, and then returns to the optimum the protein will return to normal shape and catalyse the reaction again.
What is the optimum pH of saliva, gastric juice, and pancreatic juice?
Saliva: 7-8
Gastric juice: 1-2
Pancreatic juice: 8
How does substrate and enzyme concentration affect enzyme activity?
-Increased number of substrate particles leads to higher collision rate with active sites of enzymes, rate of reaction increases.
-Increased number of enzymes increases the amount of available active sites.
-Rate of reaction increases up to maximum (Vmax), no more products can be formed at that time due to limiting factors (either too little active sites or substrates).
What is the serial dilutions practical?
-add 1ml of stock solution to 9ml of distilled water water, gives 10ml of dilute solution.
-repeat procedure multiple times.
How could a desired concentration of solution from a stock solution be formed?
volume of stock solution = required concentration x final volume needed / concentration of stock solution.
volume of distilled water = final volume needed - volume of stock solution.
How do competitive inhibitors work?
-Molecule or part of molecule has a similar shape to substrate of an enzyme can fit into the active site.
-Blocks the substrate from entering the active site, prevents enzyme from catalysing reaction.
-The Vmax will still be reached just slower.
-Most only bind temporarily, so effect is reversible.
What are example of competitive inhibitors?
-Statins
-Aspirin
How do non-competitive inhibitors work?
-Inhibitor binds to the enzyme on the allosteric site (separate to active site).
-Binding of the inhibitor causes the tertiary structure if the enzyme to change, changing the shape of active site.
-Active site is no longer complementary so unable to bind.
-The Vmax is lowered and cannot be reached with increased substrate concentration.
What is end-product inhibition?
End-product inhibition is the term for enzyme inhibition that occurs when the product acts as an inhibitor to the enzyme.
This is a negative feedback control mechanism, excess products are not made and resources are not wasted.
What is an example of end-product inhibition?
Production of ATP:
ATP regulates its own production in respiration.
What are inactive precursors in metabolic pathways?
To prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors e.g. proteases.
One part of the precursor acts as an inhibitor.
How do some medicinal drugs act as inhibitors?
Penicillin: non-competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross-links in bacterial cell wall.
Ritonavir: inhibits HIV protease to prevent assembly of new virions.
What are some examples of metabolic poisons?
-Cyanide: non-competitive, irreversible, inhibits cytochrome c oxidase.
-Malonate: competitive, inhibits succinate dehydrogenase.
-Arsenic: competitive, inhibits pyruvate dehydrogenase.
What is a metabolic poison?
Substance that damages cells by interfering with metabolic reactions.
What are co-factors?
Non-protein compounds required for enzyme activity:
-coenzymes
-inorganic cofactors
-prosthetic groups
What are Inorganic cofactors?
Metal ions which change the charge in the active site which enables the enzyme substrate complex to form.
What are examples of inorganic cofactors?
-Amylase contains a chloride ion.
-Mg^2+ in phosphotransferases.
