enzymes Flashcards
what is metabolism?
the combination of anabolic and catabolic reactions that are catalysed by enzymes
what is a metabolic pathway?
a series of enzyme controlled reactions.
product of one is the reactant in the next
what are anabolic reactions?
build up molecules
e.g. protein synthesis
what are catabolic reactions?
break down molecules
e.g. digestion
definition of enzyme
a biological catalyst, globular protein, that alters the rate of a chemical reaction without being used up.
remains unchanged
why are enzymes called a biological catalyst?
they are made up of living cells
they lower activation energy
properties of enzymes
they:
speed up reactions
aren’t catalysed
aren’t used up
have a high turn-over number
are soluble
structure of enzymes
protein tertiary structure
active site with specific 3D shape
where are the sites of enzyme action
extracellular
intracellular (in solution or membrane bound)
extracellular enzyme action
outside cells
enzymes secreted by exocytosis
e.g. amylase produced in salivary glands
intracellular enzyme action in solution
inside cells
e.g. enzymes in glycolysis, cytoplasm respiration
intracellular enzyme action membrane bound
attached to membranes
e.g. mitochondria cristae, chloroplast grana
role of the active site
enzymes act on its substrate, making temporary bonds at the active site
form enzyme substrate complexes
what is an enzyme substrate complex
temporary molecule formed when the substrate binds to the enzyme
what is the lock and key model
substrate and active site have a complementary shape
only substrates that exactly fit the enzyme can be catalysed
enzymes are specific to 1 substrate
enzyme specificity
enzymes are specific to 1 substrate
what is the induced fit model
substrate binds to enzymes active site
shape of active site changes slightly
esc formed
product released
lysozyme and the induced fit model
- antibacterial enzyme in mucus, saliva, tears
- folds around sugars in cell wall of bacteria
disrupts structure
breaks bonds
bacterial cell wall absorbs water = bursts
what is activation energy
the minimum energy put into a chemical system for a reaction to occur
molecules need enough KE to collide and react
what is catalysis?
the lowering of activation energy
what is the collision theory?
for a reaction to occur, particles involved must collide with enough energy so bonds are broken
higher temp = higher KE = more successful collisions = more ESCs formed
how do different factors change enzyme action?
environmental conditions alter the 3D structure of enzymes
bonds in tertiary structure break = changes shape of active site = reduces ability to form ESCs = lowers reaction rate
what is denaturation?
the permanent change of an enzymes structure
due to high temps or extreme pHs
affect of low temperature on enzymes
particles have low KE
few successful collisions
less ESCs formed per unit time
fewer product formed
affect of extremally high temperature on enzymes
KE increases
vibrations in enzyme molecules weaken bonds holding the 3D tertiary structure of active site together
active site loses shape
substrate no longer complementary
no more ESCs
enzyme denatured
affect of extreme pH on enzymes
small changes from optimum = reversible changes in enzymes = reduces efficiency
large change from optimum = disrupts ionic / hydrogen bonds in enzyme = permanent changes to shape of active site = prevents ESC formation = enzyme denatures
affect of enzyme concentration on enzymes
excess substrate, increase in enzyme conc = increased reaction rate (plenty of active sites)
not in excess = substrate limiting = no effect of adding more enzymes
affect of substrate concentration on enzymes
increased substrate conc = increase collisions = higher reaction rate
eventually further substrate increase = no effect, enzymes all have full active sites (enzyme conc limiting)
what are pH buffers?
counteract changes in pH
neutralise acid or alkaline
what is a cofactor
a non-protein substrate that binds to an enzyme allowing a reaction to occur
what is an inhibitor?
a molecule/ion that binds to an enzyme, reducing the rate of reaction by interfering with the shape of the active site
reversible or irreversible
what is a competitive inhibitor?
complementary in shape to active site of enzyme
prevents ESC formation by blocking the active site
don’t bind permanently
- increases substrate conc reduces the effect
what is an non-competitive inhibitor?
bind to enzyme away from active site, at allosteric site.
alter shape of active site
no ESCs form
always produces a lower rate of reaction
what are calibration curves?
used to predict the concentration of unknown solutions based on comparing concentrations of known solutions
what are immobilised enzymes?
enzymes fixed, bound or trapped in an inert matrix
e.g. cellulose microfibrils, sodium alginate beads
advantages of immobilised enzymes
- increased stability = dentatutre at higher temps, used over wider range of pH
- products uncontaminated with enzyme
- enzymes easily added and removed = control over reaction
- enzymes easily recovered for reuse
uses of immobilised enzymes
- lactose free milk
- high fructose corn syrup
- biosensors
how are immobilised enzymes used in making lactose free milk?
milk passed down column containing immobilised enzymes
lactose binds to active site on lactase
what are biosensors?
convert chemical into electrical energy
used in blood glucose detection
why is it more efficient to use enzyme immobilised onto a membrane than in beads?
it takes longer for substrate to diffuse into the beads to reach the centre where the active site is
why does reducing flow rate increase the volume of product in immobilised enzymes?
- increases contact time between enzyme and substrate
- more time for enzyme to function
- more successful collisions
- more ESCs form
