Unit 1.4 Enzymes Flashcards
Tell me all about enzymes
- Proteins that have a specific structure (active site) complimentary to their substrate
- They catalyse metabolic reactions without being used up or changed during the reaction
- They are tertiary proteins
- They have specific 3D/globular shape due to sequence of their amino acids (active site)
- Always has ase at end
What the 2 types of enzyme location
- Intracellular enzymes
- Extracellular enzymes
Tell me about intracellular enzymes
Enzymes that act in solution inside cells
e.g.
- Hydrolases inside lysosomes which hydrolyse (break down) substances taken into the cell by phagocytosis
- ATPases in mitochondria involved in aerobic respiration
Tell me about extracellular enzymes
Enzymes that act outside cells
e.g.
- Digestive enzymes released from cells by exocytosis into the alimentary canal such as amylase
- Saprotrophic fungi secrete enzymes on to their food
- Intracellular membrane bound = enzymes that are attached to the cell membrane
Tell me how enzymes work
- Enzymes reduce the level of activation energy needed
- Makes reactions happen at lower temperatures
- No enzymes = reactions in cells too slow to be compatible with life
Graph example:
If u were to draw the difference with/without enzymes - Activation energy would be lower (at the top)
- And so it would finish before the reaction without the enzyme, so u draw it earlier
What are the 2 models of enzyme action
- Lock and key model/hypothesis
- Induced fit model/hypothesis
Tell me about the “lock and key” model/hypothesis
Active site of enzyme and substrate molecule must have a complementary shape if they are to fit together
Visuals:
1. Show enzyme, it’s active site and the substrate
2. Enzyme and substrate connect is called enzyme substrate complex
3. The substrate within enzyme seems to have cut in half is called enzyme products complex
4. Enzyme is unchanged still, and so the products are removed off of enzyme, as halfs ig
However, research been done, above not given full story. Evidence that enzymes actually changed shape slightly to complete the fit during the reaction
Tell me about the “induced fit” model/hypothesis
e.g. lysozyme, an anti-bacterial enzyme, in human saliva, mucus and tears
As substrate binds, active site of lysozyme enzyme changes shape slightly so it fits more closely around the substrate, sugars on bacterial cell wall, (held by oppositely charged groups on substrate and around active site). The change in shape puts a strain on the substrate molecules, destabilising it, so the reaction can occur more easily
Visuals:
1. Enzyme with different active site and the substrate with also different shape
2. As it connects, the enzyme changes it’s shape to allow it to fit
3. Then the same as the other model, cuts in half within
4. Products are in half n shi
The sugars on the bacterial cell wall fit into the active site. The bonds holding them together are hydrolysed. The cell wall is weakened; the bacteria absorb water by osmosis and burst
With an enzyme used in a reaction, why is the rate of product gradually slower until it stops?
- First off, rate of chemical reaction depends on frequency of successful collisions between substrate + active
- So at the beginning, it’s a rapid initial rate of reaction
- due to number of bindings of substrates and enzymes being pretty high
- However over time, there’s less number of substrate molecules than product
- Chances of collision between substrate and active site decreases, slower reaction
- Then it’s just a matter of time until all substrate molecules converted
- Reaction stops
How about for how a reactions rate becomes constant (e.g. in graph, straight line)
- Can be cuz of concentration of the enzyme
- Like all the enzymes are occupied and so substrate molecules gon have to wait
What are the 3 factors affecting enzyme activity
- Temperature
- pH
- Concentration
How does temperature affect enzyme activity?
- At low temperatures = slow reaction, less kinetic energy, fewer successful collisions, fewer enzyme substrate complexes formed
- At optimum temperature = at its fastest rate pretty much
- At higher temperatures = enzyme denature, bonds holding 3D shape vibrate and break, active site loses specific shape
How does pH affect enzyme activity?
- Extra H+ or OH- (acidic or alkaline) can modify the chemical structure of amino acids forming the enzyme
- Causes chemical bonds holding 3D structure to break
- Resulting in loss of structure of active site
How does concentration affect enzyme activity?
- I mean if there’s less enzymes than the substrate molecules, technically can effect rate I suppose?
- Same with the other way round too btw
How to keep pH constant during an experiment?
Use a buffer, it’ll absorb excess ions
What are inhibitors?
A substance that slows down/stops enzyme actions
Can be reversible
What are the 2 inhibitors?
- Competitive inhibitors
- Non-competitive inhibitors
Tell me about competitive inhibitors
- Similar shape to substrate molecules
- Allows then to bind to active site
- Blocks active site to stop substrates from entering
- N° of ESC’s (enzyme substrate complexes) reduced, rate = slow
Be rational on what happens if u increase/decrease n° of substrate
Also inhibitor leaves site after a short time
In addition, some are irreversible, permanently bound, therefore more substrate does nothing to rate
Visuals:
1. Pacman and his substrate
2. Inhibitor connects to substrate (house and shaded ig)
3. Pacman binds but inhibitor blocks active site
Tell me about non-competitive inhibitors
- Binds to enzyme, away from the active site
- Therefore tertiary structure of enzyme changed/distorted
- Substrate molecules and active site no longer complementary
- ESC’s cannot form
- Enzyme = non-functional
They don’t compete with substrate, increasing substrate conc. = no effect
In addition, as many non-competitive inhibitors are irreversible, enzymes in effect just denature
Visuals:
1. Pacman and his substrate
2. What is Pacman got on his mouth
3. Ye now it don’t fit
Tell me all about immobilised enzymes
An enzyme that has been fixed to an inert/substance/support/matrix, over which the substrate molecules move
- Enzymes are expensive, so they make immobilised enzymes to reuse it and save money
- Typically for industrial processes
To make an immobilised enzyme:
- Cross linked/covalently bonded to another substance e.g. collagen/cellulose microfibrils
- Absorption/carrier bound - hydrophobic/ionic bond to a solid/support
- Entrapment/Inclusion - enzyme suspended in a matrix
As enzyme is fixed, doesn’t get mixed up with product, cheaper to separate. Readily recovered for reuse
How can toxin a-amanitin lead to the death of an organism?
- Inhibits mRNA production so prevents transcription/translation
- Prevents protein synthesis so may affect vital processes e.g. respiration or could prevent haemoglobin being made
What are biosensors?
Measures the concentration of a named substance by converting chemical energy into electrical energy
