2.1.4 Enzymes Flashcards
Enzyme definition
Biological catalysts
Globular proteins
Interact with substrate molecules and cause them to react at faster rates
Role of enzymes in reactions
Anabolic reactions are required for growth and catalysed by enzymes
Catabolic reactions release energy and catalysed by enzymes
Digestion is catalysed by enzymes
Example of an intracellular enzyme
Catalase breaks H2O2 to oxygen and water quickly as its a toxic product of many metabolic pathways and breaking it down prevents accumulation
Example of an extracellular enzyme
Amylase breaks down starch polymers into maltose
Needs to be broken down into smaller molecules to be able to enter cells
Produced by salivary glands and pancreas
Lock and key hypothesis
Active site of the enzyme is complementary to the shape of a specific substrate molecule
Enzyme-substrate complex is formed when substrate is bound to the active site
Substrate reacts and products are formed and released, leaving the enzyme unchanged
R groups within active site will interact with substrate, temporary bonds will form and put strain on bonds within substrate which helps the reaction
Induced fit hypothesis
Initial interaction between enzyme and substrate is weak but the interactions induce changes in enzymes tertiary structure that strengthen binding, puts strain on substrate molecule, weakens bonds in substrate which lowers activation energy for reaction
Effect of temperature on enzyme activity
Increase in temperature leads to more frequent successful collisions between enzyme and substrate (due to increase in kinetic energy)
However, at higher temperatures, bonds holding protein together vibrate more which strains bonds and eventually breaks them
Results in change in tertiary structure of enzyme, its denatured
Therefore active site changes shape and is no longer complementary to substrate
What’s temperature coefficient (Q10) and equation
Measure of how much rate of reaction increase with 10ºC rise in temperature
(Usually doubles)
R2÷R1
Effect of pH on enzyme activity
Active site will only be right shape at a specific H+ conc (optimum pH)
At other conc, shape of active site changes but minimal change is reversible
When pH changes more significantly, structure is irreversibly altered and enzyme is denatured
Due to H+ interactions with polar and charged R groups changing
More H+ the less R groups can interact with eachother, bonds break and shape change
Less H+ shape of enzyme changes
Effect of substrate concentration on enzyme activity
Number of substrate molecules in a particular volume increases
Leads to higher collision rate with active sites of enzymes, rate of reaction increases
Effect of enzyme concentration on enzyme activity
Increased number of active sites available in particular volume
Formation of enzyme-substrate complexes is at a faster rate
Rate of reaction only increases up to Vmax, at which point all active sites are occupied and ESC can’t be formed until products are formed, becomes a limiting factor
Experiment to investigate effect of temperature on catalase
Boiling tubes with same volume and conc of H2O2
Add equal volume of buffer solution to keep pH constant
Delivery tube to inverted measuring cylinder in trough filled with water
Put each boiling tube in different temperature water bath along with a boiling tube of catalase
Leave for 5 mins then add same volume and conc of catalase to each boiling tube
Record amount of oxygen produced in 60 seconds for each temp 3 times
Create a mean
How to carry out an experiment to measure rate of an enzyme-controlled reaction (starch)
Boiling tube of starch solution and amylase
Every minute, use a dropping pipette and place a drop into a well on a spotting tile
Add a drop of iodine in potassium iodide to each well after the solution
Time when solution doesn’t turn blue-black is when all starch has broken down
How to carry out serial dilutions
Create a starting solution
Add 1ml of it to a test tube and add 9ml of DW
Mix and add 1ml of that solution to another test tube and add 9ml of DW
Repeat
This creates a dilution of 1/10 then 1/100 then 1/1000 then 1/10000
What’s a cofactor
Inorganic, non-protein component to help enzymes carry out their function
What’s a coenzyme
Organic, non-protein component to help an enzyme carry out its function
Examples of cofactors
Iron, calcium, chloride, and zinc ions
Amylase contains chloride ion necessary for formation of correctly shaped active site
Examples of coenzymes
Most derived from vitamins
B5 is used to make coenzyme A, essential in breakdown of fatty acids and carbohydrates in respiration
What are prosthetic groups in enzyme controlled reactions
Tightly bind to enzymes and form permanent feature of it to allow it to carry out its function
Zinc ions form part of structure of carbonic anhydrase, necessary for metabolism of carbon dioxide
How do competitive inhibitors work
Molecule or part of molecules has a similar shape to substrate of an enzyme and therefore fits in the active site
This blocks the substrate from binding, prevents enzymes catalysing reactions
Substrate and inhibitor are competing, degree of inhibition depends on conc of substrate, enzyme and inhibitor
Mostly reversible bindings
Effect of competitive inhibiton on rate of reaction
Decreases rate but doesn’t alter Vmax of enzyme
What is non-competitive inhibition
Inhibitor binds to enzyme at allosteric site
Binding causes tertiary structure of enzyme to change, active site changes shape
Active site no longer has complementary shape to substrate, can’t bind, is inhibited
Doesn’t compete
Irreversible or reversible
Effect of non-competitive inhibiton on rate of reaction
Increasing conc of enzyme or substance doesn’t over come effect of inhibitor
Vmax changes
What’s end-product inhibition
Product of reaction acts as an inhibitor to enzyme that produced it
Ensures excess products aren’t made and resources aren’t wasted
