2.1.4 Enzymes Flashcards
1
Q
why are enzymes called biological catalysts
A
because they speed up metabolic reactions in living organisms
2
Q
what type of proteins are enzymes
A
globular proteins with a tertiary structure
3
Q
what is enzyme’s activity affected by
A
- pH
- temperature
- concentration of enzymes + susbtrate
4
Q
what can enzymes affect by regulating metabolic reactions at a cellular and whole organism level
A
- structure
- function
5
Q
what does it mean if an enzyme catalyses intracellular reactions
A
- they act within cells
6
Q
give an example of an intracellular enzyme
A
- catalase works insides cells to catalyse the breakdown of hydrogen peroxide to harmless O2 and H2O
- hydrogen peroxide is a toxic and if accumulated it can kill cells
7
Q
what does it mean if an enzyme catalyses extracellular reactions
A
- they work outside the cells
- they’re often secreted from the cells where they’re made and act on their substrates extracellularly
8
Q
give examples of extracellular enzymes
A
- digestive enzymes: they digest large molecules and the products of digestion are absorbed into bloodstream
- amylase is found in saliva secreted by salivary glands and catalyses the hydrolysis of starch into maltose in the mouth
- trypsin catalyses the hydrolysis of peptide bonds to turn polypeptides into smaller ones (and eventually amino acids)
9
Q
describe the structure of enzymes
A
- globular proteins which has an active site with a specific shape where a complimentary substrate binds to
10
Q
what determines an enzymes active site shape
A
the enzyme’s tertiary structure
11
Q
what does the lock and key hypothesis propose
A
- when substrate binds to active site an enzyme-substrate complex is formed
- substrate reacts and products are formed in an enzyme-product complex
- products are released + enzyme is unchanged and can take part in subsequent reactions
12
Q
what does the induced fit hypothesis propose
A
- when the substrate fits in the active site, the active site changes shape slightly to mould itself around the substrate
- when an enzyme-substrate complex is formed, it weakens the bonds holding it together
- this lowers activation energy needed to break the bonds for the reaction to proceed
13
Q
how do enzymes lower the activation energy of a reaction
A
- chemical reactions need energy to activate
- chemicals can be heated to inc kinetic energy and collisions therefore
> however in living cells temp can’t be raised by a lot as proteins would denature - as enzymes have complimentary active site to substrate they can speed up reaction by helping molecules to collide successfully and reduce activation energy
14
Q
what is effect of increasing temp on enzyme’s rate of reaction
A
- as temp increases there’s higher frequency of successful collisions when substrate enters active site
- more enzyme-substrate complex are formed
- so more enzyme-product complex are formed
- more product released from active site
- faster rate of reaction
15
Q
what is effect on rate of reaction at optimum temp
A
- maximum number of successful collisions
- maximum ESC
- maximum EPC
- maximum product released
- maximum rate of reaction
16
Q
what happens to rate of reactions as the temp goes above optimum temp
A
- enzymes denature as it loses tertiary structure due to high heat causing molecules to vibrate and move around more
> this strains the bonds and eventually breaks them (weak hydrogen bonds + ionic interactions break) - active site no longer specific + complimentary to substrate
- less ESC
- less EPC
- less product released
17
Q
what is optimum temperature
A
- the temperature at which the enzyme works best
> it’s at which the enzyme has its maximum rate of reaction
18
Q
what is the temperature coefficient, Q10
A
- Q10 = RT / RT - 10
- its a measure of the rate of change as a result of increasing the temp by 10C
> so if the Q10 is 2, it means for every 10C rise in temp the rate of reaction is doubled
19
Q
what is pH
A
- a measure of the H+ ion concentration
- the higher the H+ concentration, the lower the pH (acidic)
20
Q
what impact does pH have on enzymes
A
- the H+ ions can disrupt the bonding in enzymes
- as they interact with charged R-groups present on amino acids so the R-groups can’t interact with each other + leads to bond breaking
> hydrogen bonds + ionic interactions between amino acid R-groups hold proteins in their 3D shape
> ionic interactions and hydrogen bonds will be affected the most - this then changes shape of the active site + so rate of reaction is decreased
21
Q
what happens to the rate of reaction as pH is altered slightly above/below optimum
A
- ionic bonding is disrupted as less or more H+ ions are present so tertiary protein structure is changed
- active site changing shape slightly means substrate doesn’t fit properly so less ESC + less EPC + less products
- mild pH change effects are reversible
22
Q
what happens to the rate of reaction as there is an excess/deficiency of H+ ions
A
- severe disruption of ionic bonds of enzymes
> enzyme denatures as active site is lost so the substrate can no longer bind - no ESC + EPC + so no products formed
23
Q
what is the effect of substrate concentration on rate of enzyme-catalysed reactions
A
- as substrate conc increases so does the rate of reaction
- there is a higher ratio of substrate to enzyme molecules so there will be more frequent collisions with the active site leading to successful collisions as more ESC are formed
24
Q
what does it mean if the rate of reaction of an increasing substrate conc reaches V-max
A
- all active sited are occupied
- reaction can’t continue as enzymes are the limiting factor
> adding more substrate means they can’t successfully collide + fit into active site
25
what is the effect of enzyme concentration on rate of enzyme-catalysed reactions
- as enzyme conc increases so does the rate of reaction
- more active sites available so more successful collisions between enzyme and substrate forming more ESC
- if the enzyme conc increases further there will be no increase in rate of reaction because substrate will be limiting factor as there aren't enough to occupy the extra active sites
- unless the substrate concentration is not increased, the rate of reaction stays the same
26
how would you maintain and monitor the temperature in a PAG
- maintain = thermostatically electric water bath
- monitor = thermometer
27
how would you maintain and monitor the pH in a PAG
- maintain = pH buffers
- monitor = pH probe
28
what is an independent variable
- the variable that you change
> e.g. conc of a solution or temp etc
29
what is a dependent variable
- the variable you measure to see how the independent variable has affected it
30
define cofactors
- cofactors are small non-protein molecules that help enzymes to carry out their function
> some enzymes can only work if a cofactor is attached to it
31
what are inorganic cofactors
- they help by binding the enzyme and substrate together
- don't directly participate in the reaction so aren't used up / changed
32
where are inorganic cofactors obtained from
- obtained via diet as minerals, including iron, calcium, chloride and zinc ions
33
what is an example of an inorganic cofactor
- the enzyme amylase has the cofactor chloride ions that help form the shape of the active site
34
what are coenzymes
- organic cofactors that participate in the reaction + and are changed
- often act as carriers by making chemical groups between diff enzymes
- coenzymes need to be recycles to their original state, sometimes by a diff enzyme
35
where are coenzymes derived from
- derived from vitamins (organic molecules found in the diet)
36
what is an example of a coenzyme
- coenzyme NAD is derived from vitamin B3
37
what are prosthetic groups
- they're cofactors that are tightly bound, by covalent bonds, to the enzyme and form a permanent feature of the protein
38
what is an example of a prosthetic group
- zinc ions form important part of structure of carbonic anhydrase
> enzyme necessary for metabolism of CO2
39
how are cofactors bound to enzymes
- some are loosely or temporarily bound to enzyme protein in order to activate them
- others like prosthetic groups are permanently bound to them
40
what are inhibitors
- molecules that prevent the enzyme from carrying out their normal function of catalysis
> they bind to enzyme and can influence how a substrate binds to enzyme or effects enzyme's turnover number
> some block or change shape of active site
41
what are competitive inhibitors
- molecule with a similar shape to substrate + so competes with substrate to bind with the active site, blocking the substrate from entering it
> prevent enzyme from catalysing the reaction
42
what does the degree of inhibition depend on in competitive inhibition
- conc of substrate and inhibitor molecules + enzymes
- if there's higher conc of competitive inhibitors they will collide more often with active site and reduce free enzyme active sites for substrate molecules to bind with
- inc substrate con 'dilutes' / weakens effect of inhibitors as more substrate are likely to collide + bind withe active site
43
what effect does competitive inhibitors have on rate of reaction
- reduces rate of formation of ESC + EPC and therefore product form formation
> lower rate of reaction
- however V-max not change because if substrate conc increased enough, that there is more substrate than inhibitor, the original Vmax can still be achieved
44
are enzyme inhibition by competitive inhibitors reversible or not
- most competitive inhibitors only bind temporarily so effect is reversible
- increasing substrate conc can reduce effect of reversible competitive inhibition
- however some such as aspirin are irreversible
45
what is an inactivator
- if competitive inhibitor binds irreversibly to the enzyme's active sit it's called an inactivator
46
what are non competitive inhibitors
- inhibitors that bind to the enzyme at the allosteric site (location other than the active site)
> causes tertiary structure to change + so active site changes shape
- active site no longer complimentary to substrate so can't bind
> no ESC + EPC + products formed
47
what is the effect of non competitive inhibitors on rate of reaction
- inc substrate con has no effect as active sites are altered
- inc inhibitors will decrease rate of reaction further as more active sites become unavailable
48
what is end product inhibition
- term used for enzyme inhibition that occurs when the products of a reaction acts as an inhibitor to the enzyme that produce it
> serves as negative feedback
- works by product tightly binding to enzyme so it can't form more of the product than the cell needs
49
what can enzyme inhibitors be used for
- used by organisms to control metabolic reactions
> allows products to be produced in specific amounts
50
can irreversible inhibitors be removed
- no, they remain attached to the enzyme
