C1.1 Enzymes and Metabolism Flashcards
what are enzymes
bio catalysts made of proteins
why are enzymes used as a way to control chemical reactions?
some are only produced under particular conditions, at certain stages or with particular substrates
why are enzymes necessary
enable reactions to occur at high rates
how is control over metabolism exerted
through enzymes
what does anabolic refer to
larger molecules built up from smaller molecules through condensation reactions
examples of anabolism
synthesis of proteins from amino acids
synthesis of polysaccharides from simple sugar
photosynthesis
what is catabolism
the breakdown of larger molecules into smaller molecules, hydrolysis reactions
examples of catabolism
hydrolysis of macromolecules into monomers in digestion
oxidation of substrates in respiration
shape of enzymes
usually large, globular proteins, rounded
properties of the active site of enzymes
binding to the substrate molecule
holding on to it while chemical reaction takes place
lowering the energy of the transition state
what is the induced fit model
as the enzyme substrate complex forms, a slight change of shape is required in the enzyme and substrate.
this change raises the substrate to the transition state where it can react with
what is the lock and key model
the active site is of complementary shape to the substrate and fits it perfectly
most enzymes seem to follow the model
what are immobilised enzymes
enzymes that are embedded in membranes and are often more stable than free enzymes, providing a better environment for activity
what are immobilised enzymes usually used for
food processions, pharmaceuticals or wastewater treatment
advantages of immobilised enzymes
permits reuse of enzyme
product is enzyme free
enzyme may last longer
what is denaturation
occurs when the weak intramolecular interactions within the globular protein break. This changes shape of the active site
what happens to enzyme activity as temperature increases
increased kinetic energy leads to increases reactions and collisions
optimum temperature in enzymes?
after the optimum point, enzyme activity decreases due to denaturation
what happens when the pH value is not optimum for enzymes
a change in pH from the optimum value alters the bonding patterns, progressively changing the shape of the molecule, active site is inactive
effects are usually reversible
what happens when substrate molecules are in excess of enzymes
a plateau of reactions is reached since all possible enzymes are already being used
energy of the enzyme substrate complex
it exists at a local energy minimum and is quite stable
transition state
the point where there is a maximum value of energy. Immediately the product is formed and energy released is
activation energy
to bring about reaction, a small amount of energy is needed initially to break or weaken bonds in the substrate, forming the transition state. That is activation eergy
how do enzymes work, in terms of energy
by lowering the amount of energy required to activate the reacting molecules by providing a new alternative reaction pathway
extracellular enzymes
enzymes exported from cells, secreted by endocytosis to work externally
intracellular enzymes
remain within cells and work there
examples of intracellular enzyme catalysed reactions
glycolysis and the krebs cycle
example of active energy
chemical potential to heat transfers it to active energy
how much stored energy is available in a molecule
only part which is known as free energy and can be used for work
exergonic reactions
reactions that release free energy. the products have less stored energy than the reactants
oxidation of glucose is example
endergonic reactions
reactions in which energy is absorbed. Products have more stored energy than reactants
synthesis of proteins is example
how are endergonic and exergonic reactions made possible
they are made possible in metabolism by both being coupled to each other through ATP
what do molecules of ATP do in metabolism
they work as intermediates, linking energy absorbing and energy yielding reactions
what type of metabolic pathway is glycolysis
linear
what type of metabolic pathway is cyclical
krebs cycle
what are enzyme inhibitors
they lower the rate of enzyme action
competitive inhibitors
molecules that sufficiently resemble the substrate and compete for the active site
non competitive inhibitors
they are unlike the substrate molecule but still combine with the enzyme. they attach close to the active site, party blocking access or changing its shape
adding excess substrates do not overcome its effects
what are allosteric regulators
molecules that change the shape and activity of an enzyme by binding at an active site
what are allosteric activators
temporarily stabilises the enzyme shape as an active and effective catalyst
what are allosteric inhibitors
changes the shape to an inactive form
what are statins
example of competitive inhibitors. partially block access to active ste
taken to reduce excess blood cholesterol and reduce risk of CHD
End product inhibition
as the product molecule accumulates, the steps in the production process are switched off
end product inhibition that converts threonine to isoleucine
isoleucine acts as a non competitive inhibitor by binding to allosteric site of enzyme threonine deaminase
inhibition of the enzyme turns off production of isoleucine
when isoleucine concentration is low, metabolic pathway can proceed as inhibition is low
as concentration increases, inhibition takes place and pathway regulated
when isoleucine concentration falls and enzyme acts in converting threonine to isoleucine
mechanism based inhibition
when a molecule that has a similar substrate structure binds to the active site, molecule is then modified to produce a reactive group, which reacts irreversibly to form a stable inhibitor enzyme complex
penicillin as mechanism based inhibition
it inhibits transpeptidase, causing bacterial cell walls to be weak. This can cause lysis of bacteria through osmosis
penicillin resembles part of the peptide chain of the way and transpeptidase binds to it instead
