Enzymes Flashcards
intracellular enzymes
enzymes that are produced and found inside the cell
extracellular enzymes
Extracellular enzymes are produced inside the cell but are secreted by cell via exocytosis and catalyse reactions outside cells (eg. digestive enzymes in the gut)
what is the structure of enzymes?
globular proteins making them soluble in water. The tertiary structure of the active site is complementary to the structure of substrate making the enzymes specific.
how do enzymes increase the rate of reaction?
- enzymes lowers the activation energy barrier meaning more substrate molecules have enough energy to cross the activation barrier and react
example of intracellular enzymes
catalase which hydrolysis toxic hydrogen peroxide into water and oxygen
examples of extracellular reactions
- amylase which hydrolyses carbohydrates
- trypsin which hydrolyes proteins
what is meant by turnover number of an enzyme?
the number of reactions than an enzyme molecule can catalyse per second
why are enzymes called biological catalyst?
‘Biological’ because they function in living systems
‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed
Induced fit model
- when the substrate molecule approaches the active site of the enzyme it starts to form temporary bonds with the amino acid in the active site, so the tertiary structure of the enzymes adjusts so that the active site moulds itself tightly around the substrate.
Lock and key theory
-the substrate has a complentary shape to the active site on the enzyme
-binds forming a enzyme-substrate complex
-releasing the enzyme-product complex
Catabolic reactions
The breakdown of complex molecules into simpler products. Happens when a single substrate is broken down into two or more molecules
Examples of a catabolic reaction
Cellular respiration and hydrolysis reaction
Anabolic reactions
Building of more complex from simpler ones. Drawing 2 or more substrates into the active sites, forming bonds between them and releasing a single product
Example of anabolic reactions
Protein synthesis and photosynthesis
the effect of temperature on enzyme activity?
as we increase the temperature the rate of reaction increases as the enzyme and substrate gain more kinetic energy so vibrate more which increases the number successful collisions between the enzyme and substarte molecule increases therefore more enzyme-substrate complexes are formed. past the optimum temperature the increase vibrations break the hydrogen and ionic bonds holding the tertiary structure of the active site causing it to change. Eventually it will be no longer complementary to the substrate molecule so the enzyme has denatured and fewer enzyme-substate complexes are formed
why is the rate of reaction slow when temperature is low?
Molecules move relatively slowly as they have less kinetic energy
Less kinetic energy results in a lower frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to less frequent enzyme-substrate complex formation
formula for temperature coefficient
temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
temperature coefficient when 10degrees is added
For most enzyme-catalysed reactions the rate of the reaction double.s for every 10 °C increase in temperature
The temperature coefficient (Q) for a reaction that follows this pattern is: Q₁₀ = 2
effect of PH on enzyme activity
-at a low PH the hydrogen ions attract te negative R groups in the hydrogen and ionic bonds causing them to break . This changes the tertiary struvture of the enzyme therefore the active site to is no longer complemenatry meaning less enzyme-substrate complexes are formed.
-at high PH. The OH- groups also cause bonds to break=same explnation but attracts positive parts instead
example of optimum PH’s of enzymes
- pepsin is found in the stomach, an acidic environment at pH 2,
- trypsin 8
effect of substrate concentration on the rate of reaction
– At low concentrations of substrate molecules there is a low frequency of collisions between the substrate molecule and the active site so less enzyme-substrate complexes are formed so the rate of reaction is low. At high substrate concentrations the frequency of collisions increases. the substrate concentration is the limiting factor. Eventually the graph levels off as the active site becomes saturated therefore there a no free active sites for the substrate molecule to collide with.
effect of enzyme concertation on the rate of reaction
As the enzyme
concentration increases there are more successful collisions between the active site and the substrate; there are more
enzyme-substrate
complexes formed; sidiconds all the substrate it used up; and the substrate concentration becomes the limiting factor;
what are cofactors?
-ionorganic permenantly bound to an enzyme .
-produce specific shape of the enzyme active site but do not take part in the reaction
what are coenzymes?
small organic non-protein molecules that bind temporarily to the active site of enzyme molecules. they chemically changed in a reaction. also derived from vitamins e.g (NAD)
-as volume/concentartion increases rate of raction increases
what are prosthetic groups?
- a non-protrein molecule that is permanently attached to an enzyme molecule. e.g the enzyme carbonic anhydrase contains a zinc ion present. and amylase contains chloride ions
the effect of competitive inhibitors on the rate of reaction
- competitive inhibitors are similar shape to the substrate molecule
-Substrate competes with inhibitor;
Both the substrate and the inhibitor have a complimentary, specific shape to the active site; there will be fewer enzyme-substrate complexes; more substrate reduces the chance of the inhibitor getting into the active site.
examples of competive inhibitors
- penicillin which used to treat bacteria infections and binds irreversibly
- methotrexate which is used to treat certain cancers binds reversibly.
effect of non-competitive inhibitors
they bind to a different part of the enzyme (allosteric site) which causes the tertiary structure of the enzyme to change so the shape of the enzyme changes and is no longer complementary to the substrate molecule, so an enzyme-substrate can no be formed reducing the rate of reaction. Increasing the substrate molecule cannot reduce the effect of non competitive inhibitors.
what is end-product inhibition
a way of regulating a enzyme catalysed reaction when a product molecule remains tightly bound to the enzyme so the enzyme cannot form more of the product than the cell needs.
how are metabolic sequences controlled?
the product of the last enzyme catalysed reaction attaches to a the allosteric site of the first enzyme in the pathway changing the tertiary structure of the enzyme. preventing the pathway from running acting as a non-competitive enzyme.
Inactive precursor
- no biological activity until it’s metabolised by an enzyme into its active form
