Chapter 4 Enzymes Flashcards
What are enzymes?
Biological catalysts. The speed up the rate of reaction by reducing activation energy, without being used up
Why are enzymes important?
Chemical reactions which sustain life need high rates of reaction
Needs harsh conditions such as high temperatures and pressures which are dangerous/ not feasible in cells
Enzymes can be used to enable these reactions to occur at high enough rates
Are needed within cells and outside of cells for the whole organism
What are the two type of reactions enzymes are involved in?
Anabolic- building up
Catabolic- breaking down
Define metabolism
The sum of all the different reactions and reaction pathways happening in a cell, which are controlled by enzymes
How far can enzymes speed up the rate of reaction?
Vmax
Maximum initial velocity
State the two explanations of enzyme action
Lock and Key hypothesis
Induced Fit Hypothesis
What is the active site of an enzyme?
An area within the tertiary structure of an enzyme which is complimentary to the shape of a specific substrate molecule
According to the lock and key hypothesis, what happens between the enzyme and substrate?
The correct substrate collides with the active site of an enzyme, forming an enzyme substrate complex
The substrate reacts to form the products, forming a enzyme product complex
The products are then released
What does the lock and key hypothesis state?
Only a very specific substrate, with a shape complementary to the active site, will be able to fit in the active site of an enzyme
An enzyme will only be able to catalyse one type of very specific reaction
According to the induced fit hypothesis, what happens between the enzyme and substrate?
As the substrate approaches the active site of the enzyme, hydrogen bonds will form between the two, causing a change in the tertiary structure of the enzyme= catalytic conformation
This strengthened binding weakens bonds in the reactants
The active site is now active, forming E.S.C and E.P.C releasing the products
The active site then changes back to its original inactive form
How do enzymes reduce the activation energy?
May hold atoms in the substrate close enough to react together
R groups in the active site may interact with the substrate, weakening the bonds within the substrate itself
What does catalase do?
Catalyses the break down of H2O2 which is a toxic product of many metabolic pathways- intracellular
What does amylase and trypsin do?
Amylase digests starch (saliva, pancreas) into maltose then maltase breaks it down to glucose
Trypsin is a protease which helps break down proteins to small peptides, produced in pancreas in juice to the intestines.
How does temperature affect enzymes?
Higher temperatures increases the kinetic energy of particles, making move faster so increasing collision frequency of substrate and enzyme, increasing successful collisions
More E.S.C, increased rate
If too high, bonds holding protein together vibrate more, eventually break causing change in tertiary structure=denaturing, no E.S.C
What is Q10?
The temperature coefficient
A measure of how much the rate of reaction increases with a 10 degree increase, usually 2 x2 rate in enzymes
How does pH affect enzyme activity?
Disrupt the ionic/hydrogen/polar bonds present in the tertiary structure of the enzyme, interact too little , therefore changing the shape of the active site (also H bonds when substrate approach disrupted)
Narrow range of pH, can renature if H+ change removed
How does substrate concentration affect enzyme activity?
Increases until a point. More crowded, increase collision rate, increases number of successful collisions , more E.S.C formed, greater rate
However, at Vmax, not enough enzymes as all being used up so cannot go higher
How does enzyme concentration affect enzyme activity?
Increases until a point. More crowded, increase collision rate, more E.S.C formed, greater rate
However, at Vmax, no more substrate as all being used up so cannot go higher
What are inhibitors and what are the 2 main types?
Molecules which prevent enzymes from carrying out their normal function
Competitive and Non-competitive
How does competitive inhibition work?
The inhibitor, a molecule which has a similar shape to the substrate, binds to active site of the enzyme , blocking the substrate from entering
Prevents catalysis, reduces the number of E.S.C in a given time
Can be permanent but usually temporary
How does non competitive inhibition work?
Inhibitor binds to the enzyme not at the active site but at the allosteric site
This binding causes a change in the tertiary structure of the enzyme, active site no longer complimentary to the substrate so no E.S.C
Can be permanent or temporary
What is an example of competitive inhibition?
Statins, bind to enzyme which produces cholesterol, reversible
Aspirin, binds to COX enzymes, preventing formation of chemicals which give fevers and pain, irreversible
What is an example of non competitive inhibition?
Organophosphates bind to acetyl cholinesterase, prevent nerve impulses, irreversible
Used in pesticides
Proton Pump Inhibitors PPIs, block H+ in stomach, irreversible
How do competitive and non competitive inhibitors effect vmax?
As substrate concentration increases:
Co. Reach original vmax but later (so much substrate is overcomes it)
Non-co. Does not reach Vmax, lower
