Enzymes Flashcards
(37 cards)
What are catalysts?
Catalysts are substances that reduce the activation energy of a chemical reaction, facilitating it or making it energetically viable. The catalyst increases the speed of the chemical reaction.
What amount of catalyst is consumed in the reaction it catalyzes?
None. Catalysts are not consumed in the reactions they catalyze.
Is there a difference between the initial and the final energy levels in catalyzed and non-catalyzed reactions?
The catalysis does not alter the state of the energy of the reagents and products of a chemical reaction. Only the energy necessary for the reaction to occur, the activation energy, is altered.
What is the importance of enzymes for living beings?
They are of vital importance for life because most of the chemical reactions in cells and tissues are catalyzed by enzymes. Without enzyme action, those reactions would not occur due to the temperature being too low or would not happen with the required speed.
What are the main theoretical models that try to explain the formation of the enzyme-substrate complex?
There are two main models that explain the formation of the enzyme-substrate complex: the lock and key model and the induced fit model.
In the lock and key model, the enzyme has an active site complementary for the binding of the substrate. In the induced fit model, the binding of the substrate induces a change in the active site of the enzyme to make the substrate fit.
On what structural level of the enzyme (primary, secondary, tertiary or Quaternary) does the enzyme-substrate interaction depend?
The substrate binds to the enzyme at the active sites. These are specific three-dimensional sites and therefore they depend on the protein’s tertiary and Quaternary structures.
Why is enzyme action considered highly specific?
Enzyme action is highly specific because only the specific substrates of an enzyme bind to the activation center of that enzyme. Each enzyme generally catalyzes only one specific chemical reaction.
What are the main factors that alter the speed of enzymatic reactions?
The main factors that change the speed of enzymatic reactions are temperature, pH, enzyme and substrate concentrations
How does substrate concentration affect the speed of enzyme reactions?
Initially, as substrate concentration increases, the speed of the reaction increases. This happens because free active sites of the enzyme bind to free substrates. Once all of the active sites of the available enzymes are bound to their substrates, new increases in the substrate concentration will have no effect on the speed of the reaction.
If other conditions were to remain constant, which one of the following changes would explain a reduced rate of activity in an enzyme-controlled reaction?
A increase in concentration of end-product
B increase in substrate concentration
C increase in enzyme concentration
D increase in temperature towards the optimum
Correct answer is A. This is called end-product inhibition and is an example of a feedback mechanism.
When an enzyme is subjected to temperatures above the optimum, it denatures. Which of the following bonds are the first to be disrupted by high temperatures?
A. Disulfide
B. Hydrogen
C. Ionic
D. Peptide
Correct answer is B because hydrogen bonds are the weakest.
What is an enzyme inhibitor?
A substance or molecule which slows down the rate of an enzyme controlled reaction.
Explain how a non-competitive inhibitor affects the rate of an enzyme related reaction.
It reduces rate of reaction by fitting into allosteric site of the enzyme. It attaches to tertiary structure of enzyme and changes shape of the active site, which means that the substrate can no longer bind with active site. This can be permanent.
What are the advantages of using immobilized enzymes?
It means that you can keep and reuse the enzymes which is much cheaper, the product is enzyme free and immobilized enzymes are more tolerant of temperature and pH changes.
Explain how a competitive inhibitor affects the rate of an enzyme catalyzed reaction?
A competitive inhibitor reduces the rate of reaction at a low substrate concentration as it has a similar shape to the active site of the enzyme, therefore it binds to the active site of the enzyme preventing enzyme-substrate-complexes forming.
What is an example of a competitive and non-competitive inhibitor?
Non-competitive= cyanide Competitive= Malonic Acid
Explain the mode of action of an enzyme.
The shape of the enzymes active site complementary to the shape of the substrate molecule, therefore the enzyme and substrate can bind together forming an enzyme-substrate-molecule. This temporary bond lowers the activation energy of the enzyme as the substrate is held closer so it can react more easily which increases the rate of reaction.
What is the difference between intracellular and extracellular enzymes and give examples of each?
Intracellular enzymes operate within cells e.g. hydrolytic enzymes.
Extracelluar enzymes are secreted by cells and catalyse reactions outside cells e.g. digestive enzymes.
Explain how end-product-inhibition controls metabolic reactions.
The end-product of a chain of reactions is used as a non-competitive reversible inhibitor which creates a feedback mechanism. When the level of product 3 rises there is an increasing inhibition of enzyme 1. So, there is less product 1,2 and 3 being formed. However, when level of product 3 falls the enzyme loses its attachment to enzyme 1.
How can you investigate pH on enzyme activity?
You can use buffer solutions which each have a particular pH and maintain it even if the reaction taking place would cause the pH to change.
Explain how pH affects an enzyme controlled reaction.
pH is a measure of the concentration of hydrogen ions in a solution. With a low pH there is a high hydrogen ion concentration and with a high pH there is a high hydroxide ion concentration so the enzyme becomes denatured. This is because the hydrogen and hydroxide ions interact with the R groups of the amino acids affecting the ionization, which affects the ionic bonding. This will affect the 3D arrangement of the enzyme molecule which will cause the shape of the active site to be changed, therefore the enzyme can no longer bind to the substrate.
What is meant by the turnover rate of an enzyme?
The number of reactions an enzyme can catalyze per second.
What is meant by the Vmax for an enzyme?
The theoretical maximum rate of an enzyme-controlled reaction, obtained when all the active sites are occupied.
What is meant by the Km for an enzyme?
The substrate concentration at which an enzyme works at half its maximum rate (1/2 Vmax) , used as a measure of the affinity of an enzyme.
