Module 2: Enzymes Flashcards
What is an enzyme?
Tertiray globular protein that is a biological catalyst, which can speed up reactions by lowering activiation energy
How do enzymes show specificity?
Have a specific shape so the substrate has a specific shape for the enzyme active site
Define catabolism
Break down complex molecules into smaller ones, releasing energy in metabolic pathways
Define anabolism
Build up molecules from simple ones - components synthesised and assembled into cells to form tissues, organs and whole organisms
Define metabolism
Almost all reactions in living organisms are catalysed by enzymes
Define intracellular enzymes. Give an example
Catalyse reactions in a metabolic pathway within cells e.g. catalase to break down hydrogen peroxide into oxygen and water to prevent accumulation and therefore poisoning of the body.
Define extracellular enzymes. Give examples
Secreted from cells and used outside of cells e.g. trypsin (protease) catalyses the break down of proteins into small peptide chains, which can then be broken down into amino acids by other proteases. Prouced by the pancreas and released into the small intestines. The amino acids released are absorbed by the intestine lining.
Starch broken down partially into maltose by amylase - produced by salivary glands and pancreas - mouth and small intestines. Maltase breaks the maltose down into glucose in the small intestines.
Why is the active site of an enzyme so important? What would happen is it changed shape?
Provides a complementary shape for the substrate molecule. Without the specific shape reactions would not take place, because the substrate would not fit into the active site, and so an ESC would not form, and no product would form
Define activation energy
The energy needed for a reaction to start
What do enzymes do to the activation energy? Why?
Lower activation energy providing an alternative route in order to increase the rate of reaction
What is the lock and key mechanism?
The enzyme active site is complementary to the shape of the substrate, and the substrate fits into the active site perfectly, like a key has a specific shape to a lock - specificity. Temporary bonds form between the R-groups of the active site and the substrate
This forms and enzyme substrate complex where the substrate reacts and forms products in an enzyme product complex
What is the induced-fit hypothesis?
The active site changes shape slightly when the substrate reacts with the enzyme. Means the binding is more effective. R-groups of amino acids give a precise conformation. Strain put on the substrate due to binding, weakening bonds in the substrate, lowering the activation energy
What interaction occurs between the substrate and enzyme to help the reaction along?
R-groups of enzyme active site and substrate interact to form temporary bonds, which puts strain on the bonds within the substrate, helping the reaction along.
What is the effect of temperature on an enzyme?
Slow reaction at low temps = molecules have low KE, so fewer collisions between enzyme and substrate
Higher temps = more collisions occur and with more KE to break bonds in the substrate. Optimum temp occurs here and product is formed quickly and efficiently
Highest temps = molecules vibrate too much breaking the H bonds within the enzyme - denaturation - changes specific 3D shape of active site so no longer complementary with substrate - tertiary structure altered
What is the effect of pH on enzyme activity?
Change from optimum reduces rate of reaction
H ions interact with R groups of amino acids
Breaks H and ionic bonds at active site
pH very different from the optimum will denature enzyme changing the specific 3D shape of the enzyme active site - no longer complementary
How can the pH of a reaction be maintained?
Use of a buffer
How does subsrate concentration affect enzyme activity?
As substrate conc. increases initial rate of reaction increases - more substrate available to bind with active site
At high substrate conc. all enzyme active sites are occupied - more substrate added has no effect - enzyme working at Vmax - plateau in graph occurs
How does enzyme conc. affect enzyme acivity?
Same as with substrate concentration - active sites available initially so increased rate of reaction - more product produced - directly proportional
All active sites full so Vmax reached and reaction graph plateaus as rate can no longer increase
Adding more substrate would increase rate of reaction again
What is the temperature coefficient (Q10)?
Measure of how much the rate of reaction increases with a 10 degree increase in temperature
What is the typical Q10 for enzyme controlled reactions?
2 - means rate doubles with every 10 degree increase
Define cofactor
Non-protein molecule that is either part of the enzyme structure or forms a temporary association with it. Help ensure the reaction occurs at the same rate.
Define prosthetic group
Non-protein groups or cofactors that are permanently bound to the enzyme
Give an example of a prosthetic group
Zinc ions (Zn2+) form part of the structure of carbonic anhydrase - necessary for the metabolism of carbon dioxide
Define coenzymes
Organic non-protein molecules that bind temporarily to the active site
What happens to coenzymes during a reaction?
Chemically changed and need to be recycled to their original shape
Give an example of coenzymes
Water soluble vitaminse.g. B3 used to synthesis NAD so H atoms can be transferred between molecules in respiration to form NADH
Give an example of a cofactor
Chlorine (Cl-) helps form the correctly shaped active site in amylase for the breakdown of starch
Describe competitive inhibition
The inhibitor has a similar shape to the substrate molecule and competes for the active site
Inhibitor binds to an enzyme active site before a substrate molecule can
This blocks the substrate from the active site
The substrate is unable to bind with the active site so no ESC, and no product can form
This reduces the rate of reaction
How can the effects of competitive inhibtion be reversed?
Increasing substrate concentration
Describe non-competitive inhibition
Inhibitor binds to another site in the enzyme called the allosteric site
This distorts the shape of the active site so substrate is unable to bind to the active site
The inhibitor may bind permanently or temporarily- determines whether reversible or not
No ESC formed, so no product - decrease rate of reaction
Give an example of a competitive inhibitor
Statins work against enzymes in the synthesis of cholesterol. This can reduce blood cholesterol conc. decreasing the risk of heart disease
Give ans example of a non-competitive inhibitor
Organophosphates used in insecticides and herbicides inhibit acetyl cholinerterase - used for nerve impulses. Can lead to muscle cramps, paralysis and even death if ingested
Define inactive precursor enzymes
Enzymes produced in an inactive form as they may cause damage in the place produced, and are only activated under certain conditions
What has to happen to precursor enzymes?
A change in tertiary structure particularly the active site. Adding a cofactor allows this
What is a precursor protein called before activation by a cofactor?
Apoenzyme
What is a precursor enzyme activated by a cofactor called?
Holoenzyme
What are proenzymes or zymogens?
Chacnegs in tertiray structure from another enzyme e.g. protease can change the conditions e.g. pH or temp. activating a precursor enzyme
Describe end-product inhibition
As an enzyme converts substrate to product the rate of reaction is lowed down or inhibited
The end product binds to an allosteric site
Prevents further substrate binding
As product levels fall the enzyme can become active again
This can prevent too much product forming at once and only on demand - negative feedback
