Enzymes Flashcards
State the characteristics of enzymes
Enzymes are biological catalysts that increase the rate of reaction and remain chemically
Unaltered at the end of the reaction, and can be reused. Effective in small amounts.
Operate at milder reaction conditions
Exhibit specificity (Absolute and Group)
Describe the active sites of enzymes
A precise 3D groove in enzymes that are complementary to their intended substrate.
Contact AAs int reversibly w sub via weak H and I bonds.
R grps of catalytic AAs catalyse rxn
Rest provides a structural framework that maintain confirm of AS
How can 2 amino acid that are far apart along the polypeptide chain end up next to each other in
the active site?
Folding of polypeptide chain during synthesis (describe primary -> tertiary -> globular structure)
Describe the “Lock and Key” and “Induced Fit” hypotheses
Lock and Key:
Active site of enzyme is fixed in shape and complementary to substrate. It binds reversibly
To the substrate and an enzyme-substrate complex is formed. After catalysis has completed
The products no longer fit in the active site and are released. The active site is available
To take in the next substrate
Induced Fit:
Substrate binding induces a confmational change in enz and AS moulds into a more precise
Fit for the substrate
Describe the 5 mechanisms which contribute to the lowering of activation energy
Proximity- temp binding of rxts next to each other to facilitate catalysis
Orientation- Rxts held in such a way that they are exposed to chemical attack
Strain- distorts the substrate with physical pressure to break hydrogen bonds
Microenvironment effects- Hphobic AAs create water-free zone for non-polar rxts
Acid-base catalysis.
Describe enzyme cofactors
May be inorganic ions that bind to the enzyme and aid in its substrate catalysis by making
Enzyme active site more complementary to its substrate, increases rate of reaction.
Or coenzymes or prosthetic group
How to measure product formation and the disappearance of substrate over time
Gas syringe and plot a graph of change in mass.
Explain how temperature affects rate of enzyme-catalysed reactions
As temperature increases, kinetic energy of substrate molecules and enzymes increases.
Faster, frequency of collisions between enzymes and substrates increases, thermal agitation
Breaks bonds in substrates easily. Proportion of
Substrate molecules with energy higher than or equal to activation energy increases so freq
Of effective collisions increases. Saturation at optimum temperature where enzymes are comp
To substrate and max E-S complexes are formed. Beyond optimum temp, high kinetic energy of
Enzyme molecules causes high intramolecular vibrations which breaks hydrogen bonds that keep
The enzyme in specific 3D conformation. Hence shape of active site changes and is no longer
Comp to substrate. No enzyme-substrate complexes can be formed, so enzymes have denatured
And lost catalytic function
Describe and explain competitive and non-competitive inhibition
Competitive inhibitors have similar conformation to the substrate. They bind to the enzyme active site, which is also complementary to them, preventing substrates from binding and forming E-S complexes. Hence they lower rate of reaction by decreasing availability of enzyme active sites. Inhibition can be overcome by increasing concentration of substrate.
Non-competitive inhibitors have dissimilar conformation to substrate. They bind to a site on yhe enzyme other than the active site which forms an inactive inhibitor-enzyme complex which prevents substrates from binding and forming enzyme-substrate complexes. This reduces availability of enzyme active sites and lowers rate of reaction. Cannot be overcome.
Describe and explain allosteric regulation
Allosteric enzymes are regulated by inhibitors and activators. They have two or more subunits where each subunit have their own active site for substrate binding and allosteric site for activator and inhibitor binding. They exist in two conformational states, allowing them to exhibit cooperativity.
Binding of substrate to first subunit changes confirm of other subunits such that it becomes easier to accept subsequent substrates
