Enzymes Flashcards
What type of proteins are enzymes
Globular proteins
Enzyme definition
Protein molecule that acts as a biological catalyst and increases the rate of reactions inside an organism with a complex tertiary structure.
What is the active site of an enzyme
Part of the enzyme which binds to the substrate and catalyses the reaction.
Lock and key theory
Active site shape is complementary to shape of substrate. Substrate molecules form temporary bonds with AAs of active site (charged groups attract) to produce enzyme-substrate complex. Reaction complete-products released and enzyme unchanged. Enzyme only catalyse one specific reaction as active site only complementary with one specific substrate.
Induced fit theory
Substrate enters active site enzyme changes shape slightly to fit shape of substrate. Only specifically shaped substrate induces correct change in enzyme active site.
Activation energy
Minimum amount of energy required to break bonds and start the reaction and for products to be formed. The energy makes molecules unstable enough to react.
How do enzymes reduce activation energy
Reduce the stability of bonds in the reactants making it more reactive. Provide an alternative reaction pathway with lower AE.
Why are enzymes needed inside organisms
Without them reactions would be too slow, would need extremely high temperatures and pressures to reach activation energy which would kill body cells.
What is the metabolism of an organism
The sum of all the chemical reactions occurring within it.
Intracellular enzymes
Produced and function inside the cell
Extracellular enzymes
Secreted by cells and catalyse reactions outside cells
Example of intracellular enzyme
Catalase, converts hydrogen peroxide which is a harmful by product into water and oxygen
Example of extracellular enzyme
Amylase- extracellular as macromolecules being digested too big to enter cell, hydrolyses starch into simple sugars.
What is a catabolic reaction
When large substrate molecules are broken down into smaller molecules
What is an anabolic reaction
When smaller molecules are built up into bigger molecules
How does enzyme concentration affect rate
Increase concen=increases number of active sites available for substrate to collide with= more ES complexes. Rate stops increasing when amount of substrate becomes limiting factor.
How does substrate concentration affect enzyme action
Increases rate as there are more substrate molecules= more collisions so more ES complexes. Rate slows as enzyme concen becomes limiting factor , when all active sites occupied(saturation point) rate no longer increases
How does temperature affect enzyme action
As temp increases so does rate as more KE so molecules move faster so more freq collisions between enzymes and substrates= increases number of ES complexes. Once temp goes over optimum temp for enzyme the rate decreases, eventually denatured
How does an enzyme become denatured
At high temps enzyme molecules vibrate too much and bonds are broken which maintain tertiary structure, active site changes shape=no more ES complexes can be made as substrate no longer fits
How does pH affect enzyme action
Each enzyme has optimum pH, above and below this the H+ and OH- ions disrupt ionic and hydrogen bonds holding tertiary structure in place= active site changes shape and no more ES complexes can form as denatured
What are enzyme inhibitors
Molecules other than the substrate specific to the enzyme which bind to the enzyme and slow or prevent enzyme activity
What are competitive inhibitors and where do they bind
Have a similar shape to substrate so bind to active site of enzyme, block active site so substrate cannot bind=no ES complex formed
What are non-competitive inhibitors and where do they bind
Have a different shape to that of the substrate so do not bind to active site but to site away from this called allosteric site.
How do non-competitive inhibitors stop enzymes binding to substrates
Bind to allosteric site which causes the active site of the enzyme to change=no longer complimentary to substrate=no ES complexes can be formed.
Graph with competitive inhibitors
Gradient less steep but reaches same maximum rate of reaction as substrate concen increases so substrates can outcompete competitive inhibitors and bind more frequently than inhibitors
Graph with non-competitive inhibitors
Lower maximum rate because non competitive do not release and change active site meaning enzymes can no longer form ES complexes with substrates
