Enzymes Flashcards
Enzyme
Biological catalyst that are globular proteins ( tertiary structure)
‘biological’ Because they are made of living cells/ produced bi cells
Speed up chemical reactions without changing themselves
metabolism
Refers to all the reactions of the body
Reactions occur in sequences called metabolic pathways
Anabolic reactions
Building up muscle eg. Protein synthesis
Catabolic reactions
Breaking molecules down eg. Digestion
properties of enzymes
- Speed up reactions
- Not used up
- Not changed
- High turnover number eg. catalyses many reactions per second
- Specific (One enzyme per type of reaction)
Site of enzyme action
extra. intra
Extracellular - enzymes outside the cell
Intracellular - enzymes that act inside the cell
active site
enzme ac
Enzyme acts on its substrate which makes temporary bonds at the active site forming enzyme - substrate complex
when a reaction is complete, products are released, leaving enzyme unchanged and active site is ready to receive another substrate molecule
lock and key model
Substrate is imagined fitting into the active site as a key fits into a lock
Shape of lock and key are specific to each other
induced fit model
Enzyme active site forms a complementary shape to the substrate after binding
activation energy
Minimum energy required to start a chemical reaction
How enzymes work
Work by modifying substrate so the reaction requires a lower activation energy when substrate enters active sites
Shape of molecule alters, allowing reactions to occur at lower temperatures
Rate of production
Percentage increase in Mass
RoP- increase in mass/time
PinM- actual increase/ initial x100
As temp increase up to OPT TEMP
Enzymes and substrate gain kinetic energy
Greater chance of collisions between enzyme active site and substrate (successful collisions’)
therefore more enzyme-substrate meaning complexes formed meaning greater rate
Above optimum temp
becomes denatured
Enzyme gains too much kinetic energy
H bonds holding active site together break causing active sites to change shape
therefore substrate cannot enter active sites so no enzyme-substrate complexes are formed
Eventually reaction stops
at low temp
Enzyme is inactivated as molecules have very low kinetic energy
Shape is unchanged and the enzyme will Work again if temperature is raised
Effect of pH on rate of reaction
Enzymes wwork with a narrow pH range
Small pH changes cause small reversable changes
Large pH changes causes enzymes to denature
the changes on amino acid side chains of Enzymes active site is affected by hydrogen and hydroxide ions
a buffer will maintain pH, prevent changes, would alter rate or denature above a certain poin
At low pH
excess H+ ions are attracted to negative charges and neutralies them
at high pH
excess OH- ions neutralise the positive charge
Disrupts the ionic and hydrogen bonds maintaining shape of the active site- denatured
No enzyme - substrate complexes form and enzyme activities lost
substrate conc
Rate of reaction increases as concentration of substrate increases- more enzyme - substrate complexes formed
Beyond a certain point the rates no longer increases as conc of enzyme becomes a limiting factor
enzyme conc
Rate of reaction increases as enzyme conc increases as there are more active sites for substrate to bind to
Increase in concentration beyond a certain point has no effect on the rate so substrate concentration becomes a limiting factor
enzyme inhibition
- Decrease in enzyme controlled action rate by another substance
- Inhibitor combines with an enzyme and prevents it from forming an enzyme - substrate complex
Competitive inhibition
- Have molecular shape complimentary to active sites and similar to substrate
- Compete for active site meaning blocked entry for substrates
- Rate in which product is formed decreases
- higher conc of competitive inhibitor lowers rate
- increasing substrate conc increases rate
EG. malonic acid competes with succinate for active site of Succinate dehydrogenase
non competive inhibitor
- Doesn’t bind to active sites, binds to enzyme at ‘allosteric site’ doesn’t compete with substrate
- Binding to non-competitive inhibitor changes shape of active site preventing binding of substrate
- Enzyme substrate complexes not formed
- Increasing substrate conc has no effect on rate
EG. Cyanide attaches to enzyme cytochrome oxidase to inhibit respiration
immobilised enzymes
Enzymes are immobilised when they are fixed, bound or trapped on an inert matrix eh. Alginate beads/ microfibrils
gel membrane- membrane bound enzmes are more accessible to substrate
