M2 (Biological Molecules) Ch4: Enzymes Flashcards
Enzymes
Enzymes are biological catalysts - they are gllobular proteins that interact with substrate molecules causing them to react faster
Metabolism
Metabolism is the sum of all the different reactions and reaction pathways happening in a cell or organism
Anabolic
Anabolic - reactions used for building up (growth)
Catabolic
Catabolic - reactions used for breaking down substrates
Vmax
Vmax - enzymes only increasing a reaction to a point - maximum initial velocity of the enzyme-catalysed reaction
Activation energy
Activation energy is the energy needed for most reactions to start because molecules need to collide in the right orientation, of which high temperatures and pressure (energy) increases frequency of sucessful collisions
Lock and key hypothesis
Lock and key hypothesis:
substrate binds to active site, enzyme substrate complex forms, substrates then react and products are formed in an enzyme product complex
Induced fit hypothesis for enzymes
-As substrate forms bonds with amino acids in the active site of the enzyme, tertiary structure of enzyme changes so that the active site moulds itself tightly around the substrate
-Bonds formed between substrate and enzyme help catalyse the reaction
Intracellular enezymes
Intracellular enzymes are found within cells
Extracellular enzymes
Extracellular enzymes works outside of the cell
Examples of extracellular enzymes
Extracellular enzymes:
-Catalase (hydrogen peroxide > water + oxygen)
-Amylase (starch > maltose)
-Trypsin (proteins > peptides)
How does the structure of amino acids determine enzyme activity?
How structure of amino acids determine enzyme activity:
-Specific 3D shape/Tertiary structure > formation of active site > binds to substrate > catalyses the reaction
Trypsin
Trypsin is a protease enzyme, and is produced in pancreas and then released into the small intestine
Amylase
Amylase is produced by salivary gland and pancreas, and breaks down starch polymers into maltose (a disaccharide)
Maltase
Maltase is an enzyme present in the small intestine, and break downs maltose into glucose (a monosoaccharide) which is small enough to be absorbed by cells lining the digestive enzyme to be absorbed into the bloodstream
Digestion of starch
Digestion of starch
1). Amylase beaks down starch polymers into maltose (disaccharide)
2) Maltase breaks down maltose into glucose (monosaccharide) so that it’s small enough to be absorbed into bloodstream
Factors that affect enzyme activity
The factors that affect enzyme activity are pH, temperature, enzyme concentration and
substrate concentration
How does temperature affect enzyme activity?
Temperature increases the kinetic energy of particles meaning they collide more often, which increases the rate of the reaction
What must happen in order for enzymes to catalyse reactions?
Enzymes must come into contact with the substrate, and the enzyme has to be complementary to the substrate
What is meant by ‘temperature coefficient Q10’?
Temperature coefficient Q10 is a measure of how much the rate of a reaction increases with a 10 degree rise in temperature
How do high temperatures affect the rate of enzyme activity? (below or at the optimum)
High temperatures -> increased kinetic energy of molecules -> increased chance of collisions between enzyme and substrate -> rate of reaction faster -> increasing by 10 (Q10) doubles rate of reaction
How does pH affect the rate of enzyme activity? (below or at the optimum)
Changing the pH changes number of hydroxide and hydrogen ions present
-These interact with the charges on the enzyme’s amino acids, affecting hydrogen and ionic bonding, so resulting in changes to the tertiary structure
Optimum pH
Optimum pH is the point at which enzymes work the best. This is because if the pH is too acidic or alkaline, the active site can be altered.
What is renaturation?
Renaturation is when the optimum pH of enzymes are restored meaning the enzyme returns to it’s original shape
How does substrate and enzyme concentration affect enzyme activity?
As concentration of substrate/enzyme increases, there is a higher collision rate with active sites of the enzymes, meaning there are more enzyme-substrate complexes, rate of reaction increases
What are Enzyme Inhibitors ?
Enzyme inhibitors are molecules that prevent enzymes from carrying out their function. They can be competitive or non-competitive.
Competitive Inhibitors
Competitive inhibitors blocks substrates from entering active site to stop the enzyme from catalysing the reaction, as it binds to the active site due to having a similar shape to the substrate. The inhibitor and substrate are in competition with eachother to reach the active site. Effects are usually reversible but can be non-reversible eg penicillin and aspirin
How can the effect of competitive inhibitors be reduced?
Reduce the effect of competitive inhibitors by increasing the concentration of the substrate - meaning vmax can still be reached
Non-competitive inhibitors
Non-competitive inhibitors binds to the allosteric site (away from the active site) which causes tertiary structure of enzyme to change, meaning the shape changes, therefore reducing the rate of reaction as substrate can no longer bind to active site. Effects can be reversible or non-reversible
Effect of increasing substrate conc on non-competitive inhibitors
Increasing substrate concentration does not overcome the effect the non-competitive inhibitor
End product inhibition
In end product inhibition, the final product in the metabolic pathway inhibits an early-stage enzyme to reduce the rate of the metabolic pathway. It stops excess product being made and resources being wasted.
Cofactors
Cofactors are non-protein helper components that help enzymes carry out their function. They may transfer atoms or groups from one reaction to another in a multi-stop pathway or form part of the active site
Coenzymes
Cofactors that are organic molecules are called coenzymes. They are derives from vitamins found in diet
Inorganic cofactors
Inorganic cofactors are obtains from diet as minerals ie iron, calcium, chloride, zinc ions
Prosthetic groups
Prosthetic groups are cofactors that are permanetly attached to enzymes in order for them to carry out their function eg haem for haemoglobin, and zinc for carbonic anhydrase
Precursor activation
Precursor activation is when enzymes are produced in an inactive form called inactive precursor enzymes. A cofactor is added to them to change their shape/tertiary structure so active site changes and they can be activated.
Precursor protein before adding cofactor
Precursor proteins before adding a cofactor is called an apoenzyme
Precursor protein after adding cofactor
Precursor proteins after adding a cofactor is called a holoenzyme
What are precursor enzymes called?
Precursor enzymes are called zymogens or proenzymes
Why is the rate of amylase action found by measuring substrate dissapearance?
-Starch is the substrate
-Starch concentration can be measured via iodine test
Why is the rate of catalase action found by measuring product build-up?
-Oxygen gas is a product of catalase action
-Oxygen can be collected eg via gas syringe
Enzymes used in secretion that acts in the small intestine
Amylase and trypsin are secretion enzymes used in the small intestine
Example of a multi-step metabolic process controlled by a series of enzymes inside animal cells
Respiration is a multi-step metabolic process controlled by a series of enzymes inside animal cells
Role of the digestive enzymes in the small intestine
The digestive enzymes in the small intestine catalyse hydrolysis reactions, characterised by the breaking of bonds by addition of a molecule of water
How do competitive inhibitors treat people suffering with bacterial infections
Competitive inhibitors eg penicillin, inhibits the bacteria by binding to the active site to prevent the entrance of the substrate
Intracellular enzymes
Intracellular enzymes control metabolism inside cells
Which reactions do digestive enzymes in the small intestine catalyse?
Digestive enzymes in the small intestine catalyses hydrolysis reactions
Breakdown of hydrogen peroxide
Catalase breakdowns hydrogen peroxide into water and oxygen
Effect of increasing/ pH and/or temperature above the optimum on enzymes
Changes the enzyme’s structure as it can affect chemical bonds within the active site -> denatured
Zymogens
Zymogens:
-Inactive precursor enzymes
-Needs to be cleaved to be activated (activation of the enzyme is irreversible)
-Inactive precursors are a way of regulating enzyme activity
-Eg chymotrypsin which is a precursor to trypsin
Inactive precursors function
Inactive precursors are a way to regulate enzyme activity
End of a protein
Ends of a protein does not have a peptide bond
-Has an amino group on one end a carboxyl group on the other
Protein structure
Proteins - polymers made up of amino acid monomers - connected by peptide bonds - end of proteins are amine group on one end and a carboxyl group on the other
Why is insulin given via injection into the blood rather than by pill for people with type 1 diabetes?
-Insulin in pill form -> will break down by protease enzymes in the stomach or the small intestine
-If some insulin managed to escape digestion it would likely be denatured by the low pH of the stomach
-If survived both things -> would not be small enough to be abosbred in the small intestine in the bloodstream and therefore would not reach the body tissues
Intracellular enzymes
Intracellular enzymes:
-Enzymes that are present inside the cell membrane
-Intracellular enzymes may reside in the cytoplasmic fluid or they may be bound to cellular organelles.
Extracellular enzymes
Extracellular enzymes:
-Extracellular enzymes are those which are present outside the cell - reactions do not occur inside the cell eg on leaves
Catalase
Catalase:
Catalase is an enzyme found in the cells of most organisms that breaks hydrogen peroxide down into water and oxygen. Hydrogen peroxide and catalase are combined and the volume of oxygen generated is measured in a set time.
