Enzymes

Factors Affecting Enzyme Activity

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Temperature: 

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Explain the shape of the graph of temperature and enzyme activity. You must use as many key words as possible.

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As temperature increases more kinetic energy is supplied to the molecules involved and this thus leads to faster molecular movement of the enzyme and substrate molecules which means their more successful collisions occur per second (between substrate molecules and the active sites of enzymes) and thus more enzyme-substrate complexes are formed per second and intern more enzyme-product complexes forming, and thus reaction speed increasing. This trend continues up until a point, known as the maximum for a given reaction and is illustrated by the constant increase in enzyme activity illustrated by the graph. After this maximum point we see an acute drop in the rate of enzyme activity. This is as a result of the enzymes denaturing when the heat breaks the hydrogen bonds within the protein(s) and thus the shape is altered, at this point the shape of the active site is altered and thus no longer complementary meaning a successful reaction will not occur

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What is Q10? Explain its importance?

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Q10 is a temperature coefficient which is calculated by dividing the rate of a given reaction at (t+10) degrees celsius, by the rate of the reaction at T degrees celsius. It is important in calculating the amount by which the rate of the reaction increases as the temperature is increased by 10 degrees. This is valuable in lab testing to determine an exact temperature increase required and other such values for experimentation

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Explain the effect of temperature on enzyme structure making reference to specific bonds

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As the temperature increases the hydrogen bonds within the proteins are broken as they do not require huge amounts of energy to be broken. The peptide bonds between nucleotides in the polypeptide chain are not broken as they energy required to overcome these bonds is greater than the energy supplied by an excess of heat and thus the primary structure of the protein is not actually altered so the protein structures are not changed. Due to the hydrogen bonds being broken the protein is no longer in a tight complex structure and thus the hydrophobic/hydrophilic interactions are no longer acting either. The disulfide linkages between sulfur groups are broken too. As the protein loses shape the ionic interactions between strands and strand segments break and the active site shape further changes as the proteins tertiary structure changes.

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pH:

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Explain the shape of the graph of the ph and enzyme activity using as many key words as possible

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Enzymes work within a narrow pH range and will work most effectively at their optimum pH illustrated by a peak on the graph, typically around neutral (7), A pH which is too high or too low alters the rate of the reaction. When pH rises above 7 and becomes too high an enzyme will begin to denature meaning no/ far fewer enzyme-substrate complexes can be formed and intern fewer enzyme-product complexes are formed. There are hydrogen bonds within the tertiary structure of a protein and thus when more H+ ions which are essentially protons, they interfere with the hydrogen bonds and also migrate to the negatively charged regions where ionic interactions are occurring. When the ionic interactions of an active site are altered as H+ ions cluster to any negatively charged regions (R groups and areas of hydrogen bonds) the active site shape alters making it no longer complementary to the substrate molecule. The H+ ions essentially replace the Hydrogen bonds and in doing so alter active site shape.

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What is pH? How is it calculated?

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pH is an indication of whether a substance is acidic, alkaline or neutral. Acids will dissociate into a product plus hydrogen ions which are positively charged. pH is calculated using a scale ranging from 0-14 with 0-6 being acidic values, 7 being neutral and 8-14 meaning a solution is alkaline

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Explain why different enzymes have different optimum pHs?

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Different enzymes have different functions and act in different parts of the body and are thus in different environments with different pHs. Enzymes have thus had to adapt to the pH surrounding them and this has lead to varying optimum pHs. If we look the the example of the stomach, pepsin works in the stomach in which hydrochloric acid, with a very low pH, is required to kill bacteria. Due to this environment pepsin as an enzyme works best in the more acidic pHs of 1 or 2 whereas proteins which may work extracellularly will have more neutral pHs of closer to 7. Amylase enzymes which digest starch to maltose work optimally at 6.8 pH which is far nearer to neutral as they are active in the oral cavity.

Explain the effect of pH on enzyme tertiary structure. Mentioning specific bonds is key and how proton presence affects enzyme folding.

As mentioned in the first section of pH, protons and H+ ions cluster around the negatively charged areas of amino acids in the protein and any negative R groups which are exposed to form hydrogen bonds or ionic bonds. When this clustering occurs the protein shape alters as protons take the place of Hydrogen bonds. This enables the alpha helix to stretch out more and “uncondense.” pH changes to protein structure and active site change are temporary unless at extremely pHs in which case the bonds may not be able to reform even at neutral pH as the chain may be too spread out.

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Substrate Concentration:

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Describe and explain the graph using as many key terms as possible

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The graph shows that as the substrate concentration increases the rate of enzyme activity and thus the rate of the reaction increase too, up until a point of maximal rate at which a plateau is observed and the enzyme concentration becomes the limiting factor/reagent and thus the enzyme activity rate cannot further increase. The reason for activity increasing as further substrate is added is that more enzyme substrate complexes can form, simply because there are more molecules present which increases the chance and likelihood of successful collisions occurring. As a result of more enzyme substrate complexes forming, more enzyme product complexes form and thus more overall product is formed. At the maximum rate adding further substrate will not lead to an increased reaction rate as nearly all enzymes are occupied with substrates (all) and thus no successful collisions could occur

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Enzyme Concentration;

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Describe and explain the graph using as many key terms as possible

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As enzyme concentration increases more active sites on the enzyme become available and thus more successful collisions occur and so more enzyme substrate complexes can form which in turn means more enzyme product complexes can form and so more product is produced. As observed on the graph there is an increase in rate of reaction and enzyme activity as the enzyme concentration is increased, during this time the enzyme concentration is the limiting factor. The reaction rate reaches a plateau at which even if more enzymes were to be added the rate of the reaction would not increase any further, at this stage the substrate concentration is the limiting factor. The reason for the initial increase is that in the presence of more enzymes the chance for successful collisions of enzyme and substrate molecules is increased and thus reaction rate increases. At the plateau all substrate molecules are occupied by enzymes and are formed in an enzyme substrate complex and so no new products can be formed and so reaction rate levels.

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Enzyme Inhibitors:

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• ●  Enzyme inhibitors are substances which reduce overall enzyme activity by binding with

  the enzyme molecule in a way which influences how the substrate may bind to the

  enzyme

• ●  Some enzyme inhibitors will block the active site of an enzyme entirely while others will

  change the active site shape

• ●  They work as they inhibit the amount of enzyme product complexes formed, if the active

  site is blocked then now products will be formed and if the shape of an active site is

  altered, fewer if any product complexes will form

• ●  Inhibitors which form covalent bonds with enzymes, permanently preventing them from

  binding to any substrate molecules, are referred to as non-reversible inhibitors and the type of inhibition is non reversible inhibition

 

• ●  Some substances may temporarily bind with enzymes and this temporary binding can be reversed with environmental change within the enzyme, these are reversible inhibitors and cause reversible inhibition

• ●  The two types of reversible inhibitors are competitive inhibitors and noncompetitive inhibitors

  Competitive Enzyme Inhibitors:

• ❏  Competitive inhibitors are enzyme inhibitors with similar shape to that of the substrate molecule and thus compete with the substrate molecule to bnd to the enzyme's active site. Once successfully bound to an enzyme, it blocks the active site and prevents any further enzyme substrate complexes being formed

• ❏  The degree of inhibition is based on the relative concentration of the substrate and of the inhibitor molecules

• ❏  Increased inhibitor molecule numbers mean more successful inhibitor and enzyme collisions per unit time which means that there is a decreased number of free active sites on enzymes meaning fewer successful collisions between enzyme and substrate meaning fewer enzyme-substrate complexes are formed

• ❏  Increased substrate concentration will reduce inhibitor effect, there would be less successful enzyme-inhibitor collisions and thus the inhibition rate would lower and more enzyme product complexes would form

• ❏  Enzyme-inhibitor complexes are catalytically inactive

• ❏  Although named a complex, a inhibitor bound to an enzyme will not be chemically

  changed once bound as a substrate molecule would be

• ❏  Ifacompetitiveinhibitorbindsirreversiblytoanenzymes’activesiteitiscalledan

  inactivator

• ❏  It should be noted that an inhibitor may not be fullycomplementory to an active site, just

  complementary enough to bind with it in some way

Non-competitive Enzyme Inhibitors:

• ❏  Anoncompetitiveinhibitorbindstotheenzymeatapointotherthantheactivesite(as the competitive inhibitors do), this can be phrased as the inhibitor binding with an allosteric site on an enzyme. When this occurs the tertiary structure of a an enzyme is layered and this alteration leads to a change in the tertiary structure of the enzyme which means the active site is no longer able to bind to any substrate molecules, as the active site shape is now no longer complementary to the substrate molecules shapes

• ❏  ANon-competitiveenzymeinhibitorisnotaffectedbyanincreaseinsubstrate concentration, this is because if no substrate molecule is complementary to the active site shape, regardless of substrate quantity, no successful collisions and enzyme substrate complexes will be formed

• ❏  Once all enzyme allosteric sites are inhabited by the inhibitor th erection will stop

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• ❏  While some on-competitive inhibitors are reversibly bound, others will be irreversibly

  bound

  End-Product Inhibition:

• ❏  End product inhibition is inhibition in which an enzyme functions as normal and catalyses the production of product molecule(s), but this product molecule remains tightly bound to the enzyme in a way such that no further substrate can bind to the enzyme

• ❏  An example could be in negative feedback where end product inhibition is common

• ❏  Its role is to assure a cell does not produce an excess of product and only produces as

  much as a cell requires

• ❏  This links to enzymes being synthesised in an inactive form prior to their use, some

  amino acids are produced in a way with more amino acids than required at the active site, thus some of the enzymes amino acids must be removed prior to the enzyme functioning so the active site ca assume the correct shape. This is common of Digestive enzymes to assure that when a molecule is in the cell it does not digest any of the cells other molecules. Trypsin is produced in the small intestine in the form of trypsinogen

before us; equally pepsin is produced as pepsinogen before being converted to active pepsin

➔ Metabolic Process Control:

• ❏  Activity of enzymes is controlled by inhibitors and can be done using end product

  inhibition

• ❏  An Example would be beta Galactosidase which catalyses the reaction in which

  galactose is formed in conjunction with Glucose when Lactose and Water react

• ❏  Galactose here acts as a competitive inhibitor

  Inhibitors as Poisons:

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Certain inhibitors are poisons, cyanide is a non-reversible inhibitor of the enzyme cytochrome oxidase which catalyses a part of aerobic respiration

This sort of inhibition is fatal as the only way to reverse such an inhibition would be with new enzymes which would take time to be produced
Cyanide is a type of metabolic poison as it prevents a metabolic reaction from occurring properly, metabolic poisons can be used in research to better understand enzyme function in certain reactions

Medicinal Drug Inhibitors:

• ❏  Some inhibitors are positive in that they inhibit enzymes which would otherwise have negative consequences

• ❏  Bacteria for example, is inhibited by the inhibitor of penicillin in a non-reversible inhibition

• ❏  Aspirin, non-reversibly inhibits the COX enzyme which stimulates inflammation and pain,

  and thus aspirin inhibits inflammation and reduces pain