1.4: Enzymes Flashcards
What is the definition of enzymes?
Enzymes are globular proteins with a specific tertiary structure which act as biological catalysts and increase the rate of reaction by lowering the activation energy
What is the amino acid sequence of enzymes?
Irregular
What is the stability of enzymes?
Relatively unstable
What are the functions of enzymes?
Metabolism
Is polypeptide folding compact or non compact in enzymes?
Compact
What is the solubility of enzymes?
Soluble
What are catalyst and their characteristics?
They speed up chemical reactions but remain unchanged at the end and can be reused
What are anabolic reactions?
They build up complex molecules from simple ones e.g. making a disaccharide
What are catabolic reactions?
Breaking down complex molecules into smaller ones e.g. breaking down a disaccharide
What are intracellular enzymes and give an example?
Enzymes which act inside cells e.g. hydrolases inside lysosomes
What are extracellular proteins and give an example?
Enzymes which act outside cells e.g. digestive enzymes
Where does the name of enzymes usually come from?
Derived from the name of the substrate and ends in -ase
What reaction does lactase catalyse?
Lactose which breaks down into glucose and galactose
What reaction does glycogen synthase catalyse?
creating glycogen by joining together glucose molecules
What are enzymes made from?
Globular proteins made of amino acids
How are the enzymes structured?
Coiled into a precise 3D shape
Why are enzymes soluble?
Because they have hydrophilic R groups on the outside and hydrophobic R groups on the inside to help maintain its specific shape
What is an active site on an enzyme?
Groove or depression on the surface of an enzyme to which specific substrate binds.
The shape of the site is —- to the shape of the substrate
complementary
What is the turnover number?
The rate at which substrate molecules can bind to an enzyme’s active site be converted into product(s) and leave the active site
What is the catalase turnover no?
10⁷ molecules second -¹
What are the two ideas of how enzymes work?
- the lock and key hypothesis
- the induced fit hypothesis
Describe this…
- Enzyme, substrate and active site
- Enzyme substrate complex
- enzyme product complex
- Enzyme and products
Draw the lock and key hypothesis
What is the function of the substrate?
It fits perfectly into the active site, because they are complementary to the shape of the active site
How is the substrate held in the active site?
By temporary bonds formed between the substrate and the R groups in the active site
What is the enzyme substrate complex?
When the active site and substrate fits together
What is the substrate converted into and what is it called?
The substrate is converted into products on the active sire to from the enzyme product complex.
What does the lock and key hypothesis explain?
why enzymes are specific and reversible
What makes the product release?
Because the R groups do not interact with the product
Draw the induced fit model?
In the induced fit model what happens when the substrate collides with the enzyme?
The enzyme molecule changes shape slightly which causes the active site to fit more closely around the substrate
How is the substrate held in position in the induced fit theory?
By oppositely charged groups on the substrate and active site.
What does the oppositely charged groups do to the substrate?
Puts a strain on the substrate and causes the rate of reaction to increase
What happens once the products forms in the active site?
product has a different shape so no longer fits in the active sire and is released.
BUT the enzyme remains unchanged and can be reused.
What is the activation energy?
This is the energy required for a reaction to proceed
What do enzymes do to the activation energy?
They lower the activation energy which speeds up the rate of reaction. They do this by holding the substrate molecule in such a way that the reaction proceeds more easily.
What are the two ways of following an enzyme reaction?
- measuring product formation
- measuring substrate conversion
Measuring product formation
2H₂O₂ <—-> O₂ + 2H₂O
oxygen formation per unit time can be measured using a gas syringe
measuring substrate conversion
Starch <—–> maltose (enzyme: maltase)
Add iodine solution and follow the loss of the blue black colour using a colorimeter
What is the effect of enzyme conc. on enzyme activity (with a fixed concentration of substrate)?
- As the enzyme concentration increases the RoR
increases - until a certain point where increasing the enzyme concentration has no further effect on the rate.
Explain why the enzyme conc increasing increases the RoR?
- as the enzyme conc. increases the number of active sites increases.
- more substrate molecules can bind to the active site to form ESC
- so more products form which increases the RoR
- until a certain point when all the substrate molecules are occupying active sites and the maximum rate is reached
What is the effect of enzyme conc. on enzyme activity (with excess substrate)?
As the enzyme conc. increases the RoR increases
- the RoR is directly proportional to the enzyme concentration.
(3: substrate conc, in excess)
Explain why the Enzyme conc. increasing increases the RoR (with excess substrate)?
- as the enzyme conc. increases the number of active sites increases
- more substrate molecules can bund to the active site to form the ESC
- so more products form which increases the RoR
What is the effect of substrate conc. on enzyme activity
As the substrate conc. increases the RoR increases
-until a certain point when increasing the substrate concentration has no further affect on the rate
Explain why increasing the substrate complex increases the RoR
- as the conc. of substrate molecules increases, collisions between substrates and active sites occur more often
- more ESC form
- So more products form which increases the RoR
- until a point is reached when all the active sites are occupied with substrate
- Further increases in substrate conc. Has no effect on increasing the rate
- the enzymes are working at their fastest rate - V max
What is the effect of temperature on enzyme activity?
- As the temperature increases, the RoR increases slowly then more quickly
- Above the optimum temperature increasing the temperature cause the RoR to decrease
What is the meaning of the optimum temperature?
The temperature where the rate of reaction is fastest
What happens at low temps with enzymes?
Enzymes and substrates move slowly so collisions between the substrate and active site don’t occur often so the rate is slow
What happens as the temp increases to the enzymes?
It increases the kinetic energy of the substrates and enzymes increases
What happens to the collisions when the temp increases?
The frequency of collisions between substrate and active site increase so more ESC form so more product form so rate increases.
What happens when enzymes are above the optimum temperature?
- The enzyme molecules vibrate until the bonds maintaining the tertiary structure break.
- The enzyme become denatured and the shape of the active site changes
- The active site and substrate are no longer complementary in shape
- Less ESC, EPC, and product formed and rate decreases
Important about enzymes!
They do not all have an optimum temp of 37 degrees.
what is the effect of pH on enzyme activity?
- Reducing or increasing the pH away from the optimum decreases the RoR
Explain why reducing and increasing the pH from the optimum decreases the RoR
- pH is a measure of the H+ concentration which affects the tertiary structure of the enzyme
- H+ interfere with hydrogen bonds, ionic bonds and the R groups of some AA and cause H and ionic bonds to break
- This can change the shape of the active site so the substrate is no longer complementary and ESC can’t form so the rate decreases.
What are inhibitors?
They reduce the rate or stop enzyme catalysed reactions
What type of inhibitors are there?
- reversible
- irreversible
What type of reversible inhibitors are there?
- competitive
- non competitive
What type of irreversible inhibitors are there?
- competitive
- non competitive
what are competitive inhibitors ?
- Have a similar shape to the substrate and compete with the substrate for the active site
- they can occupy the active sire and prevent the formation of ESC so reduce the RoR
What does increasing the concentration of the substrate do to the effects of the competitive inhibitor?
It reduces the effects as it’s more likely that a substrate molecule can bind to the active site than a competitive inhibitor
What is a non competitive inhibitor
- Non competitive inhibitors bind to the enzyme away from the active site - allosteric site
- they do not compete with the substrate for the place in the active site
What does the non-competitive inhibitor do?
- disrupts the tertiary structure of the enzyme
- changes the shape of the active site so the substrate is no longer complementary and can’t bind
What does increasing the substrate concentration do to the non competitive inhibitor?
it will not reduce the effect of the inhibitor
Why must enzyme action be controlled?
To prevent the build up of excessive products which may be wasteful or toxic to the cell
How and what are control of metabolic sequences?
- involves a series of enzyme-controlled reactions E.g. respiration and photosynthesis
- in these processes the product of one reaction becomes the substrate for the next reaction
What is the end product inhibitor?
The end product binds to an enzyme in the pathway away from the active site which changes the shape of the active site so the initial substrate can no longer bind
What causes inborn errors of metabolism?
- If the DNA that codes for the enzyme is mutated then the enzyme may not function.
- These diseases are caused by the lack of a functioning enzyme in a metabolic sequences
what is the site that non-competitive inhibitors bind to called?
Allosteric site
