Enzymes Flashcards
What are enzymes?
Globular proteins with complex tertiary structures (some are quaternary)
What are intracellular enzymes and example?
Enzymes that act inside the cell
CATALASE
- catalase converts hydrogen peroxide into water/oxygen preventing damage to cells , as H2O2 is product of metabolic reactions
What are extracellular enzymes?
Enzymes that catalyse reactions outside cells
AMYLASE - hydrolyses starch into simple sugars
- secreted by salivary glands/pancreas
TRYPSIN - secreted by pancreas/enter SI
- breaks proteins into amino acids/peptides
What makes the enzyme have a specific active site?
Active site shape determined by complex tertiary structure of the protein
- Proteins are formed from chains of amino acids held together by peptide bonds
- The order of amino acids determines the shape of an enzyme
- If the order is altered, the resulting three-dimensional shape changes
What is the locks and key theory?
That enzymes have a complementary active site to the substrate
- they are rigid structure that lock into each other very precisely
What is the induced fit theory?
The enzyme’s active site can change shape slightly as substrate enters enzyme - conformational changes
How do enzymes lower activation energy? What is activation energy?
Provide alternative energy pathway with lower activation energy
- otherwise extreme high temps/pressure would be needed
ACTIVATION ENERGY: amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed
How do enzymes speed up chemical reactions ?
Reduce the stability of the bonds in reactants
- destabilisation of bonds makes substrate more REACTIVE
How does pH effect enzyme activity?
Below /above optimum pH , solutions with excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause HYDROGEN AND IONIC bonds to break , which hold the tertiary structure
- breaking of bonds alters shape of active site, so ESC forms less easily —> denatured enzyme
How does temperature affect enzyme activity?
LOWER TEMPS :
- molecules have less KE
- less frequent successful collisions between substrate/active site , so less frequent ESC formation
- substrate/enzymes also collide with less energy - less likely for bonds to form/break
HIGHER TEMPS:
- Molecules have more KE, so more frequent successful collisions
- more frequent ESC formation
- substrate/enzyme collide with more energy - more likely for bonds to form/break (reaction occurs)
What happens when temp is too high ?
increased kinetic energy of enzyme = a strain on enzyme
- causing the weaker hydrogen and ionic bonds ,that hold the precise shape of enzyme, to break
- changes tertiary structure of enzyme
- active site damaged/not complementary to substrate anymore
Temp coefficient Equn / what is it?
The temperature coefficient is the ratio between the rates of that reaction at two different temperatures
- rate of the reaction doubles for every 10 °C increase in temperature
Q10 = 2
Equn: Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
How does enzyme conc affect enzyme activity?
Higher the enzyme conc , greater no. Active sites available
- more ESC formation
If substrate conc is constant - rate of reaction increase LINEARLY
If substrate conc is limited , increasing enzyme conc has no effect/ rate will plateau
How does substrate conc affect enzyme activity/rate of reaction?
greater the substrate concentration, the higher the rate of reaction
- more likely for ESC formation
Substrate increased until all active cites become saturated
- so increasing substrate conc will no longer have any effect - plateaus
What are the reversible inhibitors? What effect will be cause by increasing conc of this inhibitor ?
Competitive- similar shape to enzyme’s substrate , so blocks active site
Non competitive - bind to enzyme at an alternative site , so changes shape of active site
Increasing conc of inhibitor - reduces rate of reaction and will stop reaction completely eventually
What is the effect of increasing subtrate conc when inhibitors are present ?
COMPETITIVE: increasing substrate conc, increase rate of reaction
- more successful collisions / more ESC formed
NON COMPETITIVE: increasing substrate conc cannot increase rate of reaction
- as shape. Of active site is already changed/ESC still cannot for
What is end product inhibition ? how does this control metabolic pathways ?
Reversible, non competitive inhibitors can act as regulators in metabolic pathways
Enzymes are inhibited by the product of the reaction they catalyse
- end product of reactions binds to alternative site on original enzyme - change shape of active site/ prevent formation of ESC
- end product can detach from enzyme, so active site reforms/ can be used again
What are non reversible inhibitors ?
Some inhibitors can form covalent bonds with enzymes, inhibiting them permanently
- Complete inactivation
How stop enzyme being completely deactivated ?
Produce more of enzyme being inhibited
Non reversible inhibitors as metabolic poison eg?
CYANIDE: inhibits cytochrome oxidase , which is a mitochondrial enzyme for aerobic respiration
- fatal ,as it stops metabolic reactions
Non reversible inhibitors as medicine eg.?
PENICILLIN : Inhibits transpeptidase(enzyme that hepatitis form cross links in bacterial cell walls)
- leads to destruction of bacteria
ASPIRIN : non reversible inhibition of COX (enzyme that helps produce prostaglandins for stimulating inflammation/pain )
- leads to reduction of inflammation/pain
What are cofactors? And the 3 types?
A non protein compound required for enzyme activity to occur
3 types of:
Coenzymes
Activators
Prosthetic groups
How do ions act as cofactors ?
Inorganic ions help stabilise structure of enzyme/ may take part in reaction at active site
E.g chloride ions act as a cofactor for AMYLASE
How do coenzymes work/function?
Organic cofactors involved in carrying electrons/chemical groups between enzymes , helping catalysis (accept and donate H+ ions)
- some permanently bind to enzyme they assist
- some bind temporarily
What vitamin group is used in production of coenzymes?
B ( produces FAD)
How do prosthetic groups act as cofactors and example of this ?
- permanent part of enzyme structure
- essential for enzyme functioning properly , as they help form 3D form of enzyme
Zn 2+ are preothetic group for carbonic anhydrase
Cl- ae cofactors for enzyme amylase
PRACTICAL : measuring catalase activity
Set up apparatus :
Conical flask containing catalase source and hydrogen peroxide
Delivery tube from conical flask to measuring
cylinder containing water,in a box of water
- measure amount of oxygen produced every 30 seconds for 3 minutes
Measure effect of substrate concentration - vary conc of hydrogen peroxide (serial dilution)
temperature by putting hydrogen peroxide in different water baths , alongside catalase source
PRACTICAL: amylase activity using iodine
- Amylase / starch equiibrilated to same temps
- combined
- test for Starch at reg intervals*, by adding to iodine in potassium iodide solution , until goes BLUE BLACK colour
- test on white spotting tile
CAN BE ALTERED TO INVESTIGATE PH, TEMP/ ENZYME/SUBSTRATE CONC - use serial dilutions
What are pH buffers?
Maintain specific pH
