Module 2.1.4 - Enzymes Flashcards
What are enzymes?
Proteins that speed up the rate of a chemical reaction by acting as a biological catalyst
What do enzymes do?
- Catalyze metabolic reactions at a cellular level and for an organism as a whole
- can affect structures in an organism (involved in production of collagen)
- enzyme action can be intracellular or extracellular
What is an intracellular example?
Catalyze an enzyme that works inside cells to catalyze the breakdown of hydrogen peroxide to oxygen and water. Hydrogen peroxide is the toxic by-product of several cellular reactions (can kill cells)
What is the structure of enzymes?
- globular protein
- have an active site which the substrate binds to
- active site has a specific shape which is determined by the enzymes tertiary structure
What is an extracellular example?
- Amylase works outside cells in the human digestive system. Amylase is found in saliva and it catalyses the breakdown of starch into maltose in the mouth
- Trypsin catalyses the hydrolysis of peptide bonds (turns big polypeptides into smaller ones). Trypsin is produced by cells in the pancreas and secreted in the small intestine
What is the activation energy?
A certain amount of energy needed before a reaction will start
What do enzymes reduce?
The amount of energy that is needed to make reactions happen at a lower temperature. This speeds up the rate of reaction
What is formed when a substrate binds to an enzymes active site?
An enzymes substrate complex is formed. This lowers the activation energy
What are the reasons for the activation energy lowering?
- If 2 substrate molecules need to be joined, attaching tot the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily
- If enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. The strain means the substrate molecules breaks up more easily
What is the lock and key model?
Enzymes only work with substrates that fit their active site with complementary shape. When the enzyme substrate complex is formed, it changes shape slightly, this locks the substrate in more tightly to the enzyme
What is the induced fit model?
The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well
What happens to to the rate of reaction when temp increases?
Rate of reaction increases
What factors affect enzyme activity?
- Temperature
- pH
- Enzyme concentration
- Substrate concentration
How does the rate of reaction increase?
More heat = more kinetic energy = molecules move faster
This makes the substrate molecules more likely to collide with the active site of an enzyme
What does the energy of the collisions increasing do?
Each collision is more likely to result in a reaction
What is the optimum temperature for most reactions
37 degrees
What happens if the temperature gets too high?
Reaction will stop because the increase in temp causes the enzyme molecule to vibrate. If they vibrate too much it can cause the bonds to hold the enzyme in shape to break/denatured
When does the rate of reaction continue increase until?
The enzyme reaches optimum temperature
What does the Q10 value for a reaction show?
How much the rate of reaction changes when the temperature is raised by 10 degrees
What is the Q10 equation?
Q10 = R2 (rate at high temp) / R1 (rate at lower temp)
What does the pH of an enzyme do?
Is the pH that the enzyme controlled reaction works fastest
What happens if the pH goes above or bellow the optimum?
The H+ and OH- ions can break the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. This would change the active site of the enzyme and would become denatured
What do most human enzymes work best at?
pH 7
The higher the substrate concentration…?
The faster the reaction
What happens due to the more enzyme molecules there are in a solution?
The more likely a substrate molecule will collide into one of them to form an enzyme substrate complex. This will increase the rate of reaction
What happens if the substrate is limited?
There is no point adding more enzymes as it will have no further affect
What does more substrate molecules mean?
More collisions between enzymes and a substrate. This is only true up until saturation point (all the active sites of enzymes are full) and adding more substrate will make no difference
What is the limiting factor?
Enzyme concentration
What do inorganic cofactors do?
- Work by helping the enzyme and substrate bind together
- don’t directly participate in the reaction so aren’t used up or changed in any way
What are the 2 types of cofactors and coenzymes?
organic and inorganic
What do organic cofactors (coenzymes) do?
- Participate in reactions and are changed by it
- often act as carriers moving chemical groups between different enzymes
What is a prosthetic group?
A cofactor is closely bound to the enzyme
What are enzyme inhibitors/what do they do?
Enzymes can be prevented by enzyme inhibitors (molecules that bind to the enzyme that they inhibit). There are 2 types of inhibitors: competitive and non-competitive
What are competitive inhibitors?
- have similar shape to that of a substrate molecule
- compete with the substrate molecule to bind to the active site but no reaction takes place
- block the active site
- if increase conc of inhibitors, will take up most of the active sites and hardly any substrate will get to the enzyme
- increasing conc of substrate increases the ROR up to a point
What are non-competitive inhibitors?
- bind to the enzyme away from the active site called the enzymes allosteric site
- causes enzyme to change shape so the substrate molecules can no longer bind to it
- don’t compete with a substrate so increase in conc of substrate will not make any difference (enzyme activity will be inhibited0
What are reversible and non-reversible inhibition?
Inhibitors can be reversible (not bind permanently to an enzyme) or non-reversible (bind permanently to an enzyme). Which one they are depends on the strength of the bonds between the enzymes and the inhibitors
What bonds does non-reversible inhibition have?
Strong covalent bonds so inhibitor can’t be removed easily so its non-reversible
What bonds does reversible inhibition have?
Weak hydrogen bonds/ weak ionic bonds so the inhibitor can be removed so its reversible
What can some medical drugs be used as?
Inhibitors
What do metabolic poisons do?
Interfere with metabolic reactions (reactions that occur in cells), causing damage, illness or death
Give examples of medical drugs
Antiviral drugs
Antibiotics
Give examples of metabolic poisons
Cyanide
Malonate
Arsenic
What is product inhibition?
- metabolic pathways are regulated by end-product inhibition
- metabolic pathway is a series of connected metabolic reactions
- product of the 1st reaction takes part in the 2nd and so on…
- each reaction is catalyzed by a different enzyme
What is a metabolic pathway?
A series of connected metabolic reactions
What is end-product inhibition?
- when final product in metabolic pathway inhibits an enzyme that acts earlier on in the pathway
- regulated the pathway and controls amount of end-product made
Are product and end-product inhibition reversible or non-reversible?
Both are reversible
What happens when the level of product starts to drop?
The level of inhibition will start to fall and the enzyme can start to function again (more product can be made)
