Enzymes Flashcards
Where do reactions in the body occur?
Sequences called metabolic pathways
What happens in catabolic reactions with an example?
Building up molecules
E.g. protein synthesis
What happens in anabolic reactions with an example?
Breaking down molecules
E.g. digestion
What do metabolic pathways consist of?
A sequence of enzyme controlled reactions in which a product of one reaction becomes the reaction of the next
What type of proteins are enzymes?
Globular proteins
Why are enzymes called biological catalysts?
Biological because they’re made by living cells
Catalysts because they speed up reactions but remain unchanged at the end
What does metabolism refer to?
All the reactions in the body
What 4 things do enzymes share with chemical catalysts?
Speed up reactions
Not used up
Not changed
Have high turn over number (catalyse many reactions per second)
How are enzymes structured?
Tertiary structure proteins with specific 3d globular shape
Why are enzymes water soluble?
Protein chain folds so hydrophilic R groups are on the outside of the molecule
What three sites of a cell can enzymes act at?
Extracellular
Intracellular
Membrane bound, intracellular
What happens with extracellular with an example?
Some enzymes are secreted by exocystosis and catalyse extracellular reactions.
E.g amylase is secreted by saprotrophic fungi to digest food prior to absorption.
What happens with intracellular with an example?
Act in solution inside cells
E.g enzymes in solution in chloroplast stroma catalyse glucose synthesis
What happens with intracellular membrane-bound with an example?
Intra may be attached to membranes
E.g. Mitochondria cristae and chloroplast grana- transfer electrons and hydrogen ions in ATP formation
What is an active site?
Site on the enzyme with a particular 3d structure that permits bonding with a substrate
What happens when an enzyme and substrate successfully collide?
Temporary bonds are made at active site, forming a substrate-enzyme complex
When the reaction is complete, products are released, leaving the enzyme unchanged and the active site ready to receive another substrate molecule
What is the lock and key theory?
Active site has unique shape that means only a fully complimentary substrate shape will bind and form e-s complex.
What is the induced fit theory?
Active site is not fully complimentary to the substrate. As substrate binds, active site slightly changes shape to accomodate.
Example for induced fit:-
Lysozyme (antibac in saliva, mucus, tears)
Active site is a grove, sugars on bac cell wall fit into it. Grove closes over sugars and lysozyme changes shape around them and hydrolyses bonds holding them together.
Cell wall is weakened, bacteria absorb water by osmosis and burst.
What is activation energy?
The minimum energy required for molecules to react, breaking existing bonds and forming new ones
What happens when kinetic energy is increased?
The chance of successful collisions increases
What effect do temperatures above 40oc have on proteins in most organisms?
They irreversibly denature
What effect do enzymes have?
Alter molecule shape, allowing reactions to occur at lower temperatures, lowering the activation energy
How do you calculate production rate?
Increase in mass/ volume
Divided by increase in time
How do you calculate percentage change in product production?
(Actual increase in mass/initial mass) x 100
How do you calculate change in rate of reaction on a straight line ?
Change in y/ change in x
How do you calculate change in reaction rate on a curved line?
Put a ruler on the graph touching a specific point, make tangent, calculate tangent gradient then change in y/change in x
What are the 4 factors affecting enzyme activity?
Temperature
pH
Substrate conc
Enzyme conc
What is the effect of increased temp on enzyme action up to its optimum?
As temp increase, substrate and enzyme molecules gain kinetic energy and move around more. Increased chance of successful collisions so more s-e complexes formed = higher rate of reaction
How does a too high temp denature enzymes?
So much energy gained that vibration causes breaking of hydrogen holding tertiary structure, changing active site so substrates don’t fit = no complexes
What do enzyme inhibitors do?
Combine with enzyme and prevents enzyme-substrate complex formation, reducing reaction rate
How do competitive inhibitors work?
Molecules which have similar shape to substrate compete to bond to active site, when successful they block the active site, forming an enzyme-inhibitor complex. NOT PERMANENTLY BOUND.
Example of competitive inhibitor:-
Malonate, competes with substrate involved in respiration
How do non-competitive inhibitors work?
Don’t have a similar shape to substrate, bind to another site on enzyme called allosteric site, causes active site shape to change. Enzyme substrate complexes can’t be formed as binding isn’t possible.
Example of non-competitive inhibitor:-
Potassium cyanide, inhibitor of an enzyme involved in respiration, preventing ATP production
What are immobilised enzymes?
Enzymes are immobilised when they have been fixed to, or entrapped in, an inert material ,over which the substrate molecules move.
Examples of how enzymes can be immobilised:-
Can be fixed to, or trapped in, alginate beads or polymer membrane ( or sometimes a matrix of cellulose microfibrils)
Why don’t immobilised enzymes contaminate product?
They’re fixed
Why are immobilised enzymes used widely in industrial processed e.g fermentation?
They can easily be recovered and reused
Why can immobilised enzymes work at at a wider range of physical conditions?
A micro environment is created for them, increasing their stability and making them less susceptible to changes in pH, temperature or organic solvents which may otherwise denature their active site.
Why do beas immobilised have a lower reaction rate than membrane immobilised?
The substrate takes time to to diffuse into the bead to access the enzyme.
What are the five advs of immobilised enzymes?
- increasd stability and function over wider temp and pH range.
- products not contaminated with enzyme.
- enzymes easily recovered for reuse.
- a sequence of columns can be used so enzymes with diff optimums can be used in one process.
- enzymes can be easily added/removed, giving increased control over reaction.
How are enzymes more efficient than inorganic catalysts for industry?
Higher turn over number.
Very specific.
Work at lower temps = more economical.
How are immobilised enzymes used for lactose free milk?
Milk containg lactose is passed down a column containing immobilised lactase. Lactose binds to lactase active sites and hydrolyses into glucose + galactose and lactose free milk flows on through.
How are immobilised enzymes used for high fructose corn syrup manufacture?
HFCS is manufactured from starch in multi-step process.
Uses several immobilised enzymes which require different physical conditions. They include:-
-amylase
-glucoamylase
-glucose isomerase
What is a biosensor?
A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which measures the concentration of a chemical.
How are immobilised enzymes used in biosensors?
Turn chemical signals into electrical ones.
Work on principal that enzymes are specfic and can select one molecule in a mixture, even at low concs.
How are biosensors used to detect glucose in blood?
Glucose oxidase enzyme, immobilised on a selectively permeable membrane is placed in a blood sample. It binds to glucose and produces a small electric current, detected by an electrode and displayed on a screen.
How else can enzymes be used for molecule detection?
Immobilised on test strips.
Glucose oxidase test strips are used for detecting glucose in urine.
