Chapter 3: Enzymes Flashcards
what are enzymes
- enzymes are globular proteins/fibrous CHONs that catalyse metabolic reactions inside and outside the cell
- they remain unchanged after catalysis
what are metabolic reactions + types
- biochemical processes
- two types: anabolism and catabolism
what is the active site of the enzyme
where the substrate can sit in
what is the function of catalytic residues (part of enzymes)
takes part in breaking the bonds of the substrate to catalyse the reaction
what is the function of R groups in enzymes
- holds the substrate in the active site
- forms temporary bonds with substrate
how is the substrate held in the enzyme active site
substrate is held by temporary bonds with the r groups of amino acids residues in enzyme active site
what are the two types of enzyme residues
- contact residues
- catalytic residues
what are contact residues
- contact residues fit with the substrate
- these residues determine enzyme specificity
what are catalytic residues
catalytic residues act on those bonds in the substrate that are broken by enzyme action
what is a substrate
chemical/reactant on which an enzyme works
which enzymes have more specific functions
- sucrase
- maltase
- amylase
- urease
- catalase
which enzymes have more general functions
- lipase
- protease
what is specificity of enzymes
- 1 type of enzyme only binds to one type of substrate molecule
- this is because the enzyme active site shape is complementary to the substrate shape
- only substrates with a complementary shape to the enzyme active site can sit into the enzyme active site
what are the two ways a substrate fits/sits into an enzyme
- lock and key hypothesis
- induced fit hypothesis
what is lock and key hypothesis
- complementary shape fitting
- both enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock
what are anabolic reactions
Anabolic reactions involve the building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product
what are catabolic reactions
Catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules
what is induced fit hypothesis
- enzyme would mould around the substrate
- the enzyme function is more general here (e.g. lipase, protease)
what is the quantity of enzymes produced
- enzymes remain unchanged after the reaction
- enzymes can be reused
- therefore only a small quantity is produced
- they have a high turnover rate (means they can catalyse many reactions per unit time)
what is an enzyme substrate complex
a temporary complex formed when an enzyme binds to its substrate molecule
what is the product
end material of a chemical/enzymatic reaction
what are intracellular enzymes
- act inside cells
- responsible for catalysing reactions that occur in metabolic pathways
what are examples of intracellular enzymes
- anaerobic respiratory enzymes (cytoplasm)
- aerobic respiratory enzymes (mitochondria)
- photosynthetic enzymes (chloroplasts)
- hydrolytic enzymes (lysosome)
what are extracellular enzymes
- an enzyme that is secreted (the release of useful substances out) by a cell
- functions outside of that cell
what are examples of extracellular enzymes
- amylase secreted into saliva for hydrolysis of starch -> maltose
- thrombin (protease) secreted into blood plasma for fibrinogen -> fibrin
- acrosomal enzymes in the sperm acrosome
how do enzymes speed up reactions and increase effective collisions
- reduces activation energy by providing an alternative pathway
- holds substrates in best position to occur
how does the activation energy change upon the addition of an enzyme into a reaction
decreases
what is the formula for rate of product formation
(final product conc. - initial product conc.)/(final time - initial time)
what is enzyme activity
rate of enzyme catalysed reaction
how is enzyme activity measured
by measuring the rate of substrate disappearance and the rate of product formation
what are the factors affecting enzyme activity
- pH
- temperature
- enzyme and substrate concentration
- inhibitor concentration
what is the formula for effect of temperature on reaction rate
- Q10 =2
- everytime the temperature increases by 10C, the rate will double until after optimum temperature
how does temperature affect rate when it is significantly below the optimum temperature
- enzyme inactive
- rate of reaction low
how does temperature affect rate when the temperature is increasing until optimum temperature
- increase kinetic energy/molecular motion of enzyme and substrate
- increase frequency of effective collisions
- more enzyme-substrate complex formed
- rate increases (Q10=2)
how does temperature affect rate when it is optimum temperature
maximum capacity
how does temperature affect rate above optimum temperature
- kinetic energy continues to increase and atoms in molecules vibrate vigorously until hydrogen bonds are broken and the enzyme is denatured
- the secondary and tertiary structure is disrupted and the active site shape changes
- the substrate can no longer fit active site and the enzyme substrate complex is not formed
- the rate decreases
what is the limiting factor of the reaction before the graph plateaus
enzyme
what is the limiting factor of the reaction after the graph plateaus
substrate
what is the formula for rate of reaction
change in product formation/change in time
what does it mean when enzymes are saturated
when all active sites on enzymes are occupied
what is the limiting factor
limits the max rate of reaction
what does increasing the limiting factor do
increase the rate of reaction
what happens to the velocity of the reaction when the substrate concentration increases at low substrate concentration
the velocity increases
what happens to the velocity of the reaction when it is at high substrate concentration/reaches maximum rate
Vmax
what is the michealis-menten constant (Km)
the michealis-menten constant is the substrate concentration that produces 1/2 Vmax (the substrate concentration when velocity = vmax/2)
what does the michealis-menten constant indicate about an enzyme
the affinity of an enzyme for its substrate
how does Km (michealismenten constant) affect the affinity of an enzyme for its substrate (how does it indicate the affinity)
- the lower the Km, the higher the affinity of binding between the enzyme and its substrate
- the higher the Km, the lower the affinity of binding between the enzyme and its substrate
what are inhibitors
inhibitors are small molecules that prevent the normal action of enzymes
what are the three concepts of inhibitors
- binding location
- reversible and irreversible binding
- competitive or noncompetitive inhibitor
what are the inhibitors binding location
inhibitors either bind to the active site of the enzyme or the allosteric site
how does inhibitors binding location work
when the inhibitor sits in the allosteric site, the enzyme changes its structure so the substrate can no longer sit in the active site
what are reversible inhibitors
- can bind and leave the enzyme
- usually forms weak bonds with the enzyme
what are irreversible inhibitors
- do not leave enzyme after binding
- usually forms strong bonds with enzyme
- enzyme is permanently inactivated
what are competitive inhibitors
- an inhibitor whereby its ability to inhibit the enzyme depends on substrate concentration
- the inhibitor occupies the active site and blocks out substrates
what are non-competitive inhibitors
- an inhibitor that can inhibit the enzyme regardless of substrate concentration
- the inhibitor binds to the allosteric site and changes the shape of the enzyme so no substrate can sit in
is binding at the active site reversible or irreversible
irreversible
is binding at the allosteric site reversible or irreversible
can be both
which inhibitor (competitive or noncompetitive) reaches Vmax/plateaus faster
noncompetitve
what is a metabolic pathway
a series of reactions
what is end product inhibition
- when enough product is formed, the metabolic pathway can be switched off by end product inhibition
- usually its a competitive/non competitive inhibitor
what are immobilized enzymes
enzymes that have been fixed to a solid surface or trapped inside beads of agar gel
how are immobilized enzymes made
- physical absorption e.g. resin
- physical entrapment e.g. alginate/microcapsule
- chemical bonding e.g. glutaraldehyde
what are the advantages of enzyme immobilisation
- enzyme is easily recovered and reused again
- the product will not be contaminated by enzymes
- enhance enzyme stability to temperature and pH changes (held in shape and protected by pH and temperature changes)
- allow several enzymes to participate in the process simultaneously
how are immobilized enzymes used in industry
- lactase - to make lactose free milk
- amylase - to make high fructose syrup for corn-starch
- semisynthetic penicillin
