2.1.4 Enzymes Flashcards
enzyme definition
globular protein with specific tertiary structures
enzyme features
globular (roughly spherical, soluble, unique shape)
biological catalyst (increased rate of reaction while staying chemically unchanged)
specific (has unique shape due to order of amino acids, allows active site to be complementary to shape of substrate)
extracellular definition
found outside of cells
intracellular definition
found inside of cells
metabolite definition
substance formed in or necessary for metabolism
anabolic definition
synthesis of larger molecules from smaller molecules
catabolic definition
breaking down of larger molecules into smaller molecules
turnover number in enzymes
number of substrate molecules converted per second by a single enzyme (when the enzyme is the rate-limiting factor)
turnover number formula
turnover number = max rate of reaction/given enzyme concentration
kcat = Vmax/[ET]
temperature coefficient (Q10)
measure of rate of change in rate of reaction when temperature increases by 10°C
Q10 = 2 means every 10°C, rate of reaction doubles
factors affecting enzyme activity
temperature
pH
substrate conc.
enzyme inhibitors (competitive and non-competitive)
how temperature affects enzyme activity
temperature increases
KE in substrates and enzymes increase
more successful collisions occur
more ESCs can form so faster rate of reaction
temperature in denaturing of enzymes
temperature increases over optimum too much KE bonds vibrate too much and bonds break disrupts tertiary structure of protein active site is altered and no longer complementary to the substrate’s shape protein denatured irreversible so reaction stops
optimum temperature/pH definition
temperature/pH at which enzyme has highest rate of activity
how enzymes adapt to extremely cold environments
more flexible structures (especially at active site)
less stable than enzymes working at higher temperatures
slight temperature changes will denature them
how enzymes adapt to extremely hot environments
more stable than other enzymes
due to more bonds (specifically disulphide bridges and hydrogen bonds) in tertiary structure
so more resistant to change in temperature
how pH affects enzyme activity
pH not at optimum
affects distribution of charge on enzyme molecule
disrupts hydrogen and ionic bonds
enzyme loses tertiary structure
changes shape of active site of enzyme
substrate no longer attracted to active site (due to altered charge)
substrate can’t bind to active site as no longer complementary
no ESCs formed = no reaction = no product
enzyme denatured at extreme pHs relative to optimum
how substrate concentration affects enzyme activity
increased concentration
higher likelihood of successful collisions
more ESCs can form
faster rate of reaction
how competitive inhibitors affect enzyme activity
similar shape to enzyme’s substrate
shape is complementary to active site so can bind and block active site, forming enzyme-inhibitor-complex
prevents ESCs forming, slows rate of reaction, less products formed
reversible as competitive inhibitors bind to active site temporarily
Vmax eventually reached at higher substrate concentration
how non-competitive inhibitors affect enzyme activity
ligand binds to allosteric site of enzyme
alters tertiary structure of enzyme, changes shape of of active site
substrate no longer fits into active site, no ESCs can form so rate of reaction decreases
irreversible as non-competitor inhibitors binds permanently to enzyme
Vmax never reached
effect of increasing enzyme conc. on enzyme activity for fixed substrate conc.
no enzyme = no ESCs formed = no reaction
more enzymes = more active sites = more ESCs = more product formed and higher rate of reaction
rate will continue to rise as long as substrate is in excess
all substrate molecules will be occupying all active sites and max rate will be reached
increasing enzyme conc has no effect on rate of reaction (substrate conc is limiting factor)
rate of reaction decreases since as substrate is used up
end-product inhibition
term used for enzyme inhibitors that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
potassium cyanide
non-competitive inhibitor of enzyme cytochrome oxidase, needed for respiration
decreases use of oxygen so ATP can’t be made
organism has to respire anaerobically
lactic acid build up in blood
small amounts for adults = loss of consciousness in 10s, coma in 45 mins, death in 2 hours
inhibitors as drugs examples
viral infections treated by protease inhibitors
antibiotics treat bacterial infections
ethanol for treatment when ingesting antifreeze
how viral infections are treated
protease inhibitors inhibit protease enzymes required to build their viral coat
competitive inhibitors
how bacterial infections are treated
antibiotic penicillin
inhibits enzyme that builds cell wall
prevents bacteria from reproducing
some bacteria are resistant as they have enzymes that break down penicillin
how to treat ingestion of antifreeze
ethylene glycol (in antifreeze) broken down in liver by alcohol dehydrogenase into oxalic acid (highly toxic, leads to death) treated by huge dose of ethanol acts as inhibitor of alcohol dehydrogenase, slows production of oxalic acid so ethylene glycol can be removed
cofactor definition
substances that must be present to ensure that enzyme-controlled reactions take place at the right rate
cofactors
coenzymes
prosthetic groups
inorganic ion cofactors
coenzymes definition and features
small, organic non-protein molecules that binds to the active site at the same time or just before the substrate does
take part in reaction
converted back to original state (usually by different enzyme)
coenzymes examples
many B group vitamins are examples of coenzymes
pyruvate dehydrogenase from vitamin B3
prosthetic group definition and features
permanent parts of some enzymes
vital to 3D shape, function and charges of enzyme
prosthetic group example
carbonic anhydrase has Zn2+ prosthetic group, allows red blood cells to combine carbon dioxide with water to form carbonic acid so CO2 can be transported around the blood
inorganic ion cofactor definition
increase rate of reaction, combine with enzymes or substrates which helps ESC to form more easily by altering charge or shape of the ESC
inorganic ion cofactor example
amylase breaks down starch into maltose
only functions properly in the presence of Cl-
induced fit hypothesis method
enzymes have active sites complementary to substrate molecule
substrate molecules form into the enzymes active site
active site changes shape slightly to mould itself around substrate
ESC formed, IM forces bind substrate molecule to active site
bonds in tertiary structure of substrate destabilise
substrate molecule converted to product molecules
still on active site, forms enzyme-product complex
product molecules slight different shape to substrate, detach from active site
enzyme free to catalyse another reaction with another substrate molecule of same type
