4 - Enzymes Flashcards
What are enzymes?
- they speed up chemical reactions by acting as biological catalysts.
- they catalyse metabolic reactions at cellular level and for organisms as a whole.
- They can affect structures and functions of an organism.
- enzyme action can be intracellular (inside cells) or extracellular (outside cells).
- globular proteins
- have an active site with a specific shape (determined by tertiary structure).
intracellular enzymes? example?
- they are enzymes that work within cells.
- e.g catalase
- catalyses the breakdown of hydrogen peroxide (toxic by product of metabolic reactions) into oxygen and water.
Extracellular enzymes? examples?
- enzymes that work outside cells.
- amylase
- found in saliva
- secreted by salivary glands in mouth.
- catalyses hydrolysis of starch into maltose.
- trypsin (a protease)
- catalyses digestion of proteins into smaller peptides. (further broken down into amino acids by other proteases).
- produced by cells in pancreas, secreted into small intestine.
What are the two models for enzyme action?
- lock and key hypothesis
- induced fit hypothesis
Lock and key hypothesis explained?
- substrate molecule binds to an enzyme with active site with complementary shape. Enzyme-substrate complex is formed.
- products are formed in an enzyme-product complex.
- products are released, enzyme is left unchanged.
Induced fit hypothesis explained?
- active site is flexible
- substrate binds to active site of enzyme with complementary shape. Enzyme-substrate complex formed.
- enzyme’s tertiary structure changes shape slightly to strengthen binding, putting strain on the substrate molecule. Destabilises (weakens) bonds in substrate, lowering activation energy for the reaction.
- products formed in enzyme-product complex
- products released and enzyme returns to original shape.
Enzymes reduce activation energy. How?
- they lower activation energy, increasing rate of reaction.
- substrate fitting into the active site destabilises the bonds in the substrate molecule, making it easier for the bonds to be broken.
effect of temperature on enzyme activity?
- increase in temperature increases enzyme activity (frequency of collisions of particles increases).
- enzyme activity is highest at the optimum temperature.
- If temperature is greater than the optimum temperature, enzymes are denatured.
- If increase in temperature is too great, enzymes are denatured. Shape of active site changes, so enzyme-substrate complexes cannot form. Enzyme will no longer function as a catalyst.
What is optimum temperature?
- temperature at which the enzyme has the highest rate of activity.
How to calculate Q10 (temperature coefficient)?
Q10 = rate at (x+10)C / rate at xC
Effect of pH on enzyme activity?
- all enzymes have an optimum pH value. Most human enzymes ph7. Pepsin pH2 found in stomach acid.
- above and below the optimum pH, H+ and OH- in acids and alkali can affect ionic and hydrogen bonds in enzyme tertiary structure. Enzyme is denatured (shape of active site is changed).
Effect of substrate concentration on enzyme activity?
- increases
- Higher collision rate between active sites of enzymes and substrate molecules.
- rate increases up to Vmax.
- at this point all the enzyme active sites are occupied
- only way to increase rate is to increasing temp, or increase enzyme conc.
Effect of substrate concentration on enzyme activity?
- Increase
- Higher collision rate between active sites of enzymes and substrate molecules.
- rate increases up to Vmax.
- at this point max amount of enzyme-substrate complexes have formed.
- only way to increase rate is to increase temp, increase substrate conc.
What are cofactors?
non-protein substances bound to enzymes.
- loosely /temporarily bound to the enzyme
What are coenzymes?
organic cofactors.
What are cofactors used for?
Some enzymes need cofactors in order to carry out their function as biological catalysts.
What is the cofactor for amylase?
Cl-
- inorganic ion.
- necessary for the formation of a correctly shaped active site.
What is a good source of coenzymes?
vitamins.
What are prosthetic groups
- they are cofactors which are tightly bound and are a permanent feature of some enzymes.
What is the prosthetic group for carbonic anhydrase?
Zn2+
competitive inhibition steps?
- competitive inhibitors are molecules with similar shapes to substrate molecules.
- they compete with substrate molecules to bind to the active site of the enzyme.
- when they bind, they prevent substrate molecules from binding to the active site.
- enzyme cannot carry out its function, inhibited.
How does competitive inhibition affect rate of enzyme action?
- increase in inhibitor conc decreases rate (less active sites available for substrate to bind to).
- however, increase in substrate conc will increases rate (higher chance for substrate to bind to active site first) up to Vmax.
Non-competitive inhibition steps?
- inhibitor binds to allosteric site of enzyme (different location to active site).
- causes tertiary structure to change, active site changes.
- active no longer has complementary shape to substrate molecules
- enzymes cannot carry out function, inhibited.
How does non-competitive inhibition affect rate of enzyme action?
- increase in conc of non-competitive inhibitors decreases rate.
- Vmax is reduced.
What is reversible inhibitors?
- inhibitors which can be removed from the enzyme (due to weak bonds between them (hydrogen and ionic)).
What is irreversible inhibitors?
- inhibitors which cannot be removed from the enzyme (due to strong bonds between them (covalent)).
What is end product inhibition?
- non competitive reversible inhibition
- occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it.
- controls the amount of end-product produced.
examples of medicinal drugs as enzyme inhibitors
- antiviral drugs
- antibiotics
- they can inhibit enzymes in pathogens which reduces their harm caused in the body.
examples of metabolic poisons as enzyme inhibitors
- cyanide
- arsenic
- malonate
- They interfere with metabolic reactions that can lead to damage, illness, death.
Example of end-product inhibition?
- ATP is produced by the breakdown of glucose, catalysed by enzyme PFK
- ATP inhibits action of PFK
- High ATP levels prevent more ATP from being made.
- ATP regulates its own production.
