2.5 Enzymes

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  • Created by: sofiedb
  • Created on: 20-02-18 17:20
Function of enzymes
control the metabolism of the cell (globular proteins catalysing biochemical reactions) - they lower the minimum energy/activation energy that reactants need to react, which increases the reaction rate
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Enzyme environment
watery environment: enzymes & substrate mix/collide - collisions allow substrate to bind to the active site on the enzyme so the reaction can occur
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General formula
Enzyme + substrate --> enzyme*substrate --> enzymes*product --> enzyme + product (E+S --> ES --> EP --> E+P)
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fastest enzyme
acetylcholinesterase - active in synapses of nerves & muscle fibres, hydrolyses the acetylcholine to choline & an acetate group (catalyses 3*10^7 molecules of acetylchol
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Active site
special area on the molecule where the actual catalytic reaction takes place - result of the polypeptide chain(s)
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Enzymes
large polypeptides with a tertiary or quaternary conformation - biological catalysts - globular proteins that can speed up a biochemical reaction
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Specificity of enzyme-substrate interaction
interaction between the substrate & active site of the enzyme is highly specific (1 type fits into the site) - enzyme-substrate specificity means that 1 enzyme can only catalyse 1 type of reaction
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Induced fit theory
when the substrate enters the active site, it triggers a change in the 3D shape of the enzyme, allowing a tighter fit (induced fit) - possible because of the flexibility of the protein molecules that make up the enzyme
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Bonds and induced fit
when the enzyme & substrate(s) fit together tightly, the enzyme induces the weakening of bonds within the molecules of the substrate(s) reducing activation energy needed for the reaction
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Completion of reaction
when the enzyme-catalysed reaction is completed, products are released from the enzyme
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induced fit theory vs. lock & key theory
induced fit theory offers an explanation for why some enzymes catalyse one type of reaction (involving different types of substrates) rather than 1 specific reaction/substrate
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Lock & key hypothesis
the enzyme functions as a lock while the substrate functions as a key, implying that each enzyme can catalyse only 1 specific reaction
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Activation energy
the minimum energy that reacting particles should possess in order for a reaction to occur
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Catalytic reaction
when an enzyme converts the substance into products (e.g. when amylase hydrolyses starch to produce di- and monosaccharides)
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What does catalysis involve?
molecular motion & the collision of substrates with the active site - motion of atoms & molecules in a liquid is random & depends on the temp.) - catalysis is only possible if the substrate & active site are correctly aligned to allow for binding
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Exothermic reaction
a reaction where product formation is associated with the release of energy (usually heat) - i.e. exergonic reaction
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Endothermic reaction
a reaction where product formation is associated with the absorption of energy (heat) - i.e. endergonic reaction
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Rate of activity of enzymes & temperature
low temp: enzymes are inactive due to low kinetic energy & hardly any collision with the substrate molecules, too high temp: enzymes denature causing a drop in enzyme activity - below optimum point, for every 10˚C increase in temp = 2x reaction rate
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Rate of activity & substrate concentration
increase in concentration: increase in rate of enzymatic conversion - if all active sites are occupied by a substrate then increasing concentration will have no further affect
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Vmax
at Vmax = max. rate possible, substrates have to wait for available active sites before they can bind
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Rate of activity & pH
enzymes work in different environments (pepsin in stomach: pH=2, trypsin in small intestine: pH=7.5)
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Effect of pH on activity
enzymes are made up of amino acids so they tend to donate/accept H+ ions when pH drops below/increases above the optimum point - affects the tertiary & quaternary structure causing a change in the conformation of the active site & a drop in activity)
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Denaturation
caused by extreme pH values, heat & presence of heavy metals - irreversible change to a protein causing it to lose its function - destroys the tertiary/quaternary conformation of a protein & when circumstances are extreme, the secondary structure)
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Minor temp. increase/change in pH
possible that denaturation is reversible & the protein can fold back into original/functional conformation
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beta sheets & alpha helices in denaturation
beta sheets & alpha helices lose their form & the protein reverts to the primary conformation (no longer a functional active site)
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Immobilisation of enzymes
attaching enzymes to a material to restrict movement (immobilisation) - permits a higher concentration of enzymes allowing a faster rate of reaction - allows immediate separation of enzymes from reaction mixture for recycling &reduces production cost
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Other benefits of immobilisation of enzymes
more stable & less likely to degrade due to fluctuations in pH & temperature
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Mobilised enzymes
if enzymes are not immobilised, they are often present in the final product which restricts the concentration that can be used for processing food for human consumption to avoid adverse effects
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Largest industrial sectors
detergent industry, food industry, pharmaceutical industry
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Advantages of production of lactose-free milk
no ill effects after consumption, quicker fermentation (e.g. in yoghurt production as bacteria ferment glucose & galactose is more readily available than lactose), sweeter tasting milk (glucose + galactose is sweeter than lactose)
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Method 1: production of lactose-free milk
lactose-free products produced by adding enzyme lactase (fungus) to milk which breaks down lactose into its constituent monomers (glucose & galactose) - method leaves the enzyme in the end product & the presence of lactase can cause problems
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Method 2: production of lactose-free milk
lactase can be immobilised in alginate beads while the milk is allowed to flow past - no lactase ends up in final dairy product (better for consumption)
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Catalase reaction
source: potato, ginger, garlic, animal liver // substrate: hydrogen peroxide // product: oxygen
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Factors affecting catalase
source of catalase, temp., concentration of substrate, concentration of enzyme, pH
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Measuring rate of reaction for catalase
nr. of oxygen bubbles produced, distance moved by meniscus in a connected glass tube, oxygen produced (gas syringe), time taken for a filter paper disc (soaked int eh enzyme) to rise to the surface of the hydrogen peroxide solution
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Lipase reaction
substrate: lipids // product: fatty acids
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Factors affecting lipase
temp., concentration of substrate, concentration of enzyme, type of milk
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Measuring rate of reaction for lipase
drop in pH is observed after a specific time interval (pH meter or change in universal indicator paper)
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Pepsin reaction
substrate: protein (e.g. egg white) // product: amino acids & short peptides
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Factors affecting pepsin
temp., concentration of substrate/enzyme, pH
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Measuring rate of reaction for pepsin
decrease in mass of boiled egg white soaked in an enzyme
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Amylase reaction
substrate: starch // product: maltose
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Factors affecting amylase
temp., concentration of substrate/enzyme, pH
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Measuring rate of reaction for amylase
time taken for blue colour of starch-iodine complex to disappear, measuring the decrease in blue colour after a specific time interval using a colorimeter
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Other cards in this set

Card 2

Front

Enzyme environment

Back

watery environment: enzymes & substrate mix/collide - collisions allow substrate to bind to the active site on the enzyme so the reaction can occur

Card 3

Front

General formula

Back

Preview of the front of card 3

Card 4

Front

fastest enzyme

Back

Preview of the front of card 4

Card 5

Front

Active site

Back

Preview of the front of card 5
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