1.4 biological reactions are regulated by enzymes Flashcards
(182 cards)
1
Q
what kind of proteins are enzymes?
A
large globular proteins
2
Q
what stage of structure do enzymes have?
A
they have a specific tertiary structure
3
Q
what are enzymes’ roles?
A
they catalyse metabolic reactions in living organisms
4
Q
what would happen to reactions in the absence of catalysis?
A
most reactions in biological systems would take place far too slowly to provide products at an adequate pace for metabolising organisms
5
Q
enzymes are able to increase the rate of reaction by a factor of up to __ over uncatalysed reactions?
A
10^20
6
Q
are enzymes proteins of high or low molecular weight?
A
high molecular weight
7
Q
what are enzymes sensitive to?
A
- temperature changes (being denatured at high temperatures)
- pH
8
Q
what do enzymes possess which chemical reactions take place in?
A
active site
9
Q
what do endotherms do?
A
regulate their body temperatures so enzymes can function at near-optimum temperatures inside the organism
10
Q
what are examples of endotherms?
A
birds and mammals
11
Q
what are extracellular enzymes and where are they released from?
A
- enzymes that are secreted by cells for use outside of the cell
- they function outside of cells
12
Q
where are intracellular enzymes found?
A
in the cytoplasm or attached to cell membranes
(they work inside cells)
13
Q
where do the actions of intracellular enzymes take place?
A
they act inside the cells
14
Q
what is an example of a protective enzyme?
A
lysozyme
15
Q
are enzymes large or small molecules?
A
large
(100s of amino acids, most of which are involved in maintaining the specific shape of the enzyme but very few (often fewer than 10) form the actual active site)
16
Q
what is the basis of the lock and key model?
A
- substrate molecules bind with enzyme molecules at the active site as a consequence of their complementary shapes
- only one substrate can fit into the enzyme’s active site
- both structures have a unique shape
17
Q
what happens in an enzyme-catalysed reaction?
A
enzyme + substrate —> enzyme-substrate complex —> enzyme-product complex —-> enzyme + product
18
Q
in reality, what actually happens instead of the lock and key model?
A
induced fit
19
Q
what is induced fit in enzymes?
A
- substrate binds to the enzyme’s active site
- the shape of the active site changes and moves the substrate closer to the enzyme
- amino acids are moulded into a precise form
- enzyme wraps around substrate to distort it
- this lowers the activation energy (as puts a strain on the substrate)
E+S —> ES —> P+E
20
Q
what does the induced fit model take into account?
A
that proteins (enzymes) have some three-dimensional flexability
21
Q
according to the induced fit model, when can reactions only take place?
A
after induced fit has occured
22
Q
do enzymes lower or increase the activation energy needed to drive a reaction?
A
they lower the activation energy
23
Q
what is the active site dependent on?
A
- the sequence of amino acids in the polypeptide
- if the sequence of amino acids changes then the active site will change shape and the substrate will not bind tot he active site because they are no longer compulsory
(the active site has a specific shape)
24
Q
when a substrate and an enzyme collide successfully, how does the substrate bind to the active site?
A
by interactions with R groups/polar atoms of the amino acids that make up the active site
25
the ability of the R groups and the substrate to form bonds is affected by what?
- temperature
-pH
26
how does the substrate bonding to the active site increase the chance of the bonds breaking?
- bonds in the substrate are distorted, which puts strain on the bonds that are going to be broken and icnrease the change that they will break
27
what is activation energy?
the minimum amount of energy needed for the reaction to take place
28
when an enzyme-substrate reaction forms, the activation energy needed for the reaction to take place is ___?
reduced
(the reaction takes place faster)
29
does the enzyme change during the reaction?
no, it is unchanged
30
are enzymes specific to a particular substrate?
yes
31
what are the 2 hypotheses of how enzymes work?
1. lock and key hypothesis
2. induced fit hypothesis
32
what is the lock and key hypothesis?
- the substrate must be complementary to the active site of the enzyme so that it can bind to it
- the active site is a fixed shape so a substrate has to collide in the correct orientation with the active site in order that bonds can form and produce an enzyme-substrate complex
- while the substrate binds to the enzyme chemical changes can take place and the substrate molecules are either digested (broken down) or combined to form new products
- the enzyme is not affected by the reaction and can be reused
33
what is the induced fit hypothesis?
- as the substrate molecule enters the active site forces of attraction between the substrate and the R groups/polar atoms of the amino acids in the active site are formed
- this causes the shape of the active site to change and stronger bonds are then formed with the substrate. this weakens/strains the bonds in the substrate, which lowers the activation energy of the reaction.
- when the products are released from the substrate, the active site returns to its original shape
-(the enzyme is not affected and can be reused)
34
why can changes in the pH of a solution change the bonding between amino acids?
- hydrogen and ionic bonds in the tertiary structure are altered
- interaction of polar and charged R-groups changes
- active site changes shape
- enzyme is denatured
35
what does the change in charge on some side groups change the ability of?
it changes the ability of the enzyme’s active site to form bonds with a substrate
if bonds are not formed then the enzyme may not be able to lower the activation energy and the enzyme is inactivated/denatures
36
what can small changes in pH cause to enzyme structure?
large changes?
small changes - small reversible changes in enzyme structure (+ reduce its activity) - inactivation
large changes - can permanently change the structure of the protein - denaturation
37
what does any change to the charges due to a change in pH do to enzymes?
- it would reduce the ability of the substrate to bind to the side groups of the amino acids lining the active site
38
what happens to particles as temperature increases?
particles gain kinetic energy
39
what happens to enzymes up to the optimum temperature?
- bonds remain intact and can form enzyme-substrate complexes as there is no change to the active site
40
what happens to the number of successful collisions as temperature increases? what does this mean for the rate of reaction?
the enzymes and substrates have more kinetic energy so there are more successful collisions
and therefore more enzyme-substrate complexes are formed and the rate of reaction increases
41
what happens to enzymes above the optimum temperature?
- the increased heat gives more energy to particles
- bonds in the enzyme begin to vibrate and eventually break (weak hydrogen bonds are broken first)
- eventually there is a loss of secondary and tertiary structure, the 3D shape of the active site changes and the active site can no longer form bonds with the substrate
- the enzyme is now fully denatures
42
what is the relationship between the substrate molecules and the active site?
- the substrate shape is complementary to the shape of the active site
43
why can a change in pH inactivate an enzyme? [3]
- opposite charges attract/same charges repel
- if charges change then different bond may form
- shape of active site changes/active site unable to form bonds with substrate/cannot form enzyme-substrate complex
44
what is a similarity and difference between the lock and key hypothesis and the induced fit hypothesis?
similarity:
- substrate bonds to the enzyme/ forms an enzyme-substrate complex
differences:
- lock and key model- active site is fixed
- induced fit - active site can change shape to improve the bonding to the substrate
45
what are catalysts?
a substance that speeds up chemical reactions without being permanently altered at the end of it/remains unchanged
46
what is a metabolic pathway?
sequences of chemical reactions each controlled by a specific enzyme
(the initial substrate is converted by a series of intermediate compounds into the final product all by different enzymes)
47
what is an example of an extracellular enzyme?
lipase in digestion
48
what is an example of an intracellular enzyme?
respiratory enzymes
49
what are some factors that affect the rate of enzyme-catalysed reactions?
- temperature
- pH
- substrate concentration
- enzyme concentration
- inhibitors
- activators
50
what happens to enzymes as temperatures increase?
- increased temp
- increases speed of molecular movement/motion
- increases chances of molecular collisions
- more enzyme-substrate complexes
- at 0-42.C rate of reaction is proportional to temp
- enzymes have optimum temp for their action (usually 37.C in humans)
- about ~42.C, enzyme is denatured due to heavy vibrations that break bonds between secondary and tertiary structures
- shape is changes - active site can’t be used anymore
51
what is generally the optimum temperature for enzymes?
between 37-40.C
52
what happens to enzymes as the temp increases beyond the optimum?
bonds that stabilise the enzyme’s teritary structure (hydrogen bonds, ionic, disulphide) and secondary structure (hydrogen bonds) are broken
the active site is altered and the substrate can no longer bind to the enzyme - DENATURED
53
when above the optimum temperature, why do the bonds within the secondary and tertiary structures get broken?
due to heavy vibrations
54
what happens to enzymes as temperature decreases?
- temp decreases
- enzymes become less and less active, due to reductions in speed of molecular movement - low kinetic energy
- below freezing point - INACTIVATED
- regain their function when returning to normal temperature (as the shape was unchanged)
55
what is the word to describe enzyme ms at too high temperatures?
too low?
too high - denatured
too low - inactivated
56
thermophilic definition
heat-loving
57
psychrophiles definition
cold-loving
58
hyperthermophilic definition
organisms that are not able to grow below +70.C
59
the reaction rate ____ for every 10.C rise in temperature (in the range 4-40.C)
doubles
60
what can we use to give a quantitative reading of colour?
a colourimeter
(it measures the absorbance of light when it passes through a cuvette of coloured liquid)
61
what is the acidity of a solution measured by?
what is it expressed in terms of?
the concentration of hydrogen ions (H+)
expressed in terms of pH
62
what is the pH of pure water?
what is the pH of acids?
what is the pH of alkalis?
pure water - pH 7
acids - pH 0-6
alkalis - pH 8-14
63
what kind of pH levels will denature enzymes?
extreme pH levels
e.g very alkali or very acidic
- the structure of the enzyme is changed
64
what happens to enzymes at pH values slightly different from the enzyme’s optimum value?
small changes in the charges of the enzyme and its substrate molecules will occur
- this change in ionisation will affect the binding of the substrate with the active site
65
does each enzyme have its own optimum pH?
yes
- where the rate of reaction is maximum
66
what shape of graph does the effect of pH on the rate of enzyme controlled reactions display?
bell-shaped curves
67
what type of bonds can changes in pH affect?
changes in pH can affect the ionic and hydrogen bonds responsible for the specific tertiary shape of enzymes
68
what is the relationship between the rate of reaction and enzyme concentration?
directly proportional
(as enzyme concentration increases, the rate of reaction increases)
69
what does the relationship between the rate of reaction and enzyme concentration assume?
it assumes substrate concentration is constant
70
what is the relationship between the rate of reaction and the substrate concentration?
- the rate of reaction increases as the substrate concentration increases
- however it reaches a maximum when there is no further increase in the reaction rate despite an increase in substrate concentration as all the active sites of the enzymes are occupied
71
how is the rate of change measured on a graph?
- draw a tangent at the point and find the gradient
72
what is the word used to describe temperature-rate of reaction graphs?
asymmetrical
73
why might scientists use a buffer when (e.g perfecting a process which uses an enzyme to produce a valuable medicine)?
to control the pH
- it keeps it closer to optimum pH
74
what are some examples of reactions that occur in metabolic pathways?
- anabolic reactions, building up molecules e.g protein synthesis
- catabolic reactions, breaking molecules down e.g digestion
75
why are enzymes called ‘biological’ catalysts?
biological - bc made/produced by living cells
catalysts - bc speed up a chemical reaction but remain unchanged
76
what are the properties enzymes and chemical catalysts share?
- they speed up reactions
- they are not used up
- they are not changed
- they have a high turn-over number i.e they catalyse many reactions per second
77
do enzymes only catalyse reactions that are energetically favourable and would happen anyway?
yes
but without enzymes, reactions in cells would be too slow to be compatible with life
78
are enzymes soluble?
yes
- bc they have hydrophilic R groups on the outside of the molecule
(bc globular proteins are soluble in water)
79
what determines the bonds the amino acids make with each other?
the elements in the R group
80
extracellular enzymes info
- some enzymes are secreted from cells by exocytosis and catalyse extracellular reactions
81
what does ‘enzyme specificity’ mean?
that an enzyme is specific for its substrate
82
what information does the induced fit model give us about enzymes?
they are flexible (not rigid)
83
do you say an enzyme works by the lock and key theory?
it’s better to say that ‘it’s mechanism can be explained by’
84
how do enzymes work?
by lowering the activation energy
85
does the line go through the origin on a time-mass of product graph?
yes bc at zero time, no reaction has happened
86
is inactivation reversible?
yes
87
why are enzymes denatured at very high and very low pH?
- the charged on the amino acid side-chains of the enzyme’s active site are affected by hydrogen or hydroxyl ions
- at low pH, excess H+ ions are attracted to negative charges and neutralise them
- at high pH, excess OH- ions neutralise the positive charges
- this disrupts the ionic and hydrogen bonds maintaining the shape of the active site
- the shape changes, denaturing the enzyme
- no enzyme-substrate complexes form and enzyme activity is lost
88
is there high enzyme concentration in the body?
no because once a product leaves the active site, the enzyme molecule can be reused, so only a low enzyme concentration is needed to catalyse a large number of reactions
89
what is the turn-over number?
the number of substrate molecules that one enzyme molecule can turn into products in a given time
90
what is a competitive inhibitor?
- inhibitor has a similar structure to the substrate
- blocks active site
- but cannot react with the enzyme
- e.g arabinose competes with glucose for the active sitrs on glucose oxidase enzyme
91
what is an example of a competitive inhibitor?
arabinose competes with glucose for the active sitrs on glucose oxidase enzyme
92
when the substrate concentration is low, what happens to the rate of reaction with competative inhibitors? why?
- it is reduced
- bc the inhibitor competes successfully for the active site; fewer substrate molecules are converted into product and thr rate ot reaction is reduced
93
when the substrate concentration is high, what happens to the rate of reaction with competitive inhibitors?why?
- the maximum reaction rate is still achieved
- bc the effect of the competitive inhibitor is overcome when thr high concentration of substrate molecules compete successfully for thr active sites of thr enzymes
(the inhibitor is out-competed)
94
what are non-competitive inhibitors?
- inhibitor has no real structural similarity to the substrate
- binds to site other than active site
- binding changes the shape of the active site
95
how does non-competitive inhibitors work?
- the inhibitor attaches to the enzyme at a position away from the active site (allosteric site)
- the substrate molecule can still bind to the active site (they don’t compete with the substrate)
- substrate cannot be converted into product; thr inhibitor molecule changes the shape of thr active site preventing induced fit
- they affect bonds within the enzyme molecule and alter its overall shape, including that of thr active site
binds to the allosteric site and alters the shape of the active site
96
when the substrate concentration is low, what happens to the rate of reaction with non-competitive inhibitors? why?
- substrate molecules are converted into products when no inhibitor is attachrd to thr enzyme
- substrate molecules are not converted into products when an inhibito molecule is bound to the enzyme
- the substrate binds to the enzyme when a non-competitive inhibitor is present but cannot be converted to product
- the rate of reaction is reduced
97
when the substrate concentration is low, what happens to the rate of reaction with non-competitive inhibitors? why?
- at high substrate concrntration all enzyme active sites are occupied
- substrate molecules bound to enzymes with attached inhibitors are NOT converted into product - maximum reaction rates are never achieved
- the effect of the inhibitor is not overcome by increasing the substrate concentration
- all the enzyme molecules with bound non-competitive enzyme do NOT convert substrate to product; the effect is equivalent to lowering enzyme conc
98
with non-competitive inhibitors, can thr maximum reaction rate be achieved?
no
- the effect of the inhibitor cannot be overcome by increasing the substrate concentration
99
with competitive inhibitors, can the maximum reaction rate be achieved?
yes
- the effect of the inhibitor is overcome by very high substrate concentrations
100
what are the two types of inhibitors?
- competitive inhibitors
- non competitive inhibitors
101
why is it wastful for a sequence of chemical reactions to continue if the end product is being producrd at a rate surplus to requirements?
when the end product of the pathway begins to accumulate, it may act as an inhibitor of the first enzyme in the metabolic pathway
102
what are enzymes classified according to?
the type of chemical reaction that they catayse
103
what type of enzymes are hydrolases?
enzymes that catalyse hydrolysis reactions
e.g maltose - catalyses the hydrolysis of maltose into two glucose molecules
104
what type of enzymes are oxidoreductases?
enzymes that catalyse reactions involving oxidation and reduction
(they play an important role in thr biochemistry of respiration)
105
what is enzyme inhibition?
the decrease in rate of an enzyme-controlled action by another molecule e.g an inhibitor
an inhibitor combines with an enzyme and prevents it forming an enzyme-substrate complex
106
what is the relationship between the concentration of competitive inhibitors and thr rate of reaction?
as thr conc of competitive inhibitors increases, the rate of reaction decreases
(inversely proportional)
107
is the competitive inhibitor permanently bound to the active site?
generally no
so when it leaves, another molecule can take its place
(howveer in some cases it may be permanent)
108
do non-competitive inhibitors bind reversibly or irreversibly?
some bind reversibly while others irreversibly
109
what are immobilised enzymes?
enzyme molecules bound to an inert material, over which the substrate molecules move
110
how does immobilised enzymes work?
- they are fixed, bound or trapped on an intert matrix such as sodium alginate beads or cellulose microfibrils
- these can be packed into glass columns
- substrate is added to the top of the column and as it flows down, its molecules bind to the enzyme molecules’ active sites
- once set up, the column can be used repeatedly
- the enzyme is fixed and does not contaminate the products
- the products are therefore easy to purify
111
what is an example of how immobilised enzymes are used widely in industrial processes?
e.g fermentation
they are used widely in industrial processes as they can readily be recovered for reuse
112
will smaller beads or larger beads in immobilised enzymes produce a higher rate of reaction?
smaller beads
- if a given volume of material is used to make larger beads, there will be a smaller total surface area than if thr same volume has been used to make small beads. so if small beads are made, the substratr molecules will have easier access to enzyme molecules so will producr a higher rate of reaction
113
how does the rate of reaction of immobilised enzymes change with tempetature?
- immobilising enzymes with a polymer matrix makes them more stable because it creates a microenvironment allowing reactions to occur at higher temperatures (or more extreme pHs than normal)
- trapping an enzyme molecule prevents the shape change that would denature its active site, so the enzyme can be used in a wider range of physical conditions than if it were free in solution
- MAINTAINS SHAPE OF ACTIVE SITE
114
why do enzymes immobilised in beads have a lower rate of reaction than those immobilised on a membrane (if all other factors are constant)?
- some of the active sites are inside the beads and the substrate takes time to diffuse to them
- enzymes on a membrane are readily available for binding, so theu give a higher rate of reaction
115
what are some advantages of immobilised enzymes?
- enzyme can tolerate higher temperatures/greater range of pHs
- products are not contaminated with the enzyme
- enzymes are easily recovered for reuse
- several enzymes with different pH or temperature optima can be used in one process
- enzymes can be easily added or removed (giving more control over reaction)
116
what are 3 uses of immobilised enzymes?
1. manufacture of lactose-free milk
2. biosensors
3. high-fructose corn syrup (HFCS) manufacture
117
how is lactose-free milk made with immobilised enzymes?
- the milk is passed down a column containing immobilised lactase
- the lactose binds to its active sites and is hydrolysed into its components, glucose and galactose
118
how is high-fructose corn syrup (HFCS) manufactured with immobilised enzymes?
- HFCS is manufactured in a multi-step process from starch
- it uses several immobilised enzymes requiring different physical conditions
119
what do biosensors do?
- turn a chemical signal into an electrical signal
- they rapidly and accurately detect, identify and measure even very low concentrationd of important molecules
120
how do biosensors work?
they work on the principle that enzymes are specific and are ablr to select one type of molecule from a micture, even at very low concentrations
121
how is using a biosensor in the detection of blood glucose done with immobilised enzymes?
the enzyme glucose oxidase, immobilised on a selectively permeable membrane placed in a blood sample binds glucose. this produces a small electric current, detected by thr electrode and read on a screen
(enzymes can also be immobilised on to test strips, where different strips may detect a variety of molecules. testing strips with glucose oxidase immobilised on to them are used for detecting glucose in urine)
122
what are the 2 ways to investigate reactions involving enzymes?
measure:
1. the disappearance of substrate
2. the appearance of product
123
during enzyme investigation, what are the independent variables you can change?
- pH
- temperature
- concentration of substrate
- concentration of enzyme
124
during enzyme investigation, what are the dependent variables you can measure?
- time
- volume
- mass
- absorbance/transmission
(you can then use these measurements to calculatr the rate at which substrate disappears or product is made)
125
how do you calculate rate when you have time as the dependent variable?
rate = 1 / time
126
how do you calculate rate when you have quantity as the dependent variable?
rate = quantity / time
127
from a graph, what are the 3 different rates that can be calculated when investigating enzymes?
1. rate between two times
2. initial rate - i.e at the instant that substrate and enzymes are mixed (draw a tangent going through (0,0))
3. rate at a particular time (tangent)
128
does the initial rate always have the highest concentration of substrate?
yes
(so there is the highest frequency of successful collisions and the highest rate)
129
when investigating the effect of pH on an enzyme what do you need to use? why?
a buffer
bc enzymes are affected by pH
it is a solution of chemicals that can maintain a constant pH
130
what does immobilised enzymes mean?
it stabilises the enzyme molecules and means they have a wider range of optimum pH and temperature
(less affected by pH and temperature changes)
131
how does immobilised enzymes help in industry?
1. immobilised enzymes can be recovered and reused:
- reduces costs
- also means that only small amounts of an enzyme are needed
- the product is not contaminated by the enzyme
- several enzymes can be used at once acting on a specific substrate
2. lower/higher tempetatures can be used and still have higher yields than using the free enzyme
132
what is an industrial example of the use of immobilised enzymes?
immobilised lactase, which is used to produce lactose free milk
- the enzyme is immobilised in alginate gel beads
- milk is passed over the beads and the enzymes digest the lactose into glucose and galactose
- the milk is not contaminated by the enzyme and the beads can be used many times
133
how does immobilised enzymes have a wider range of optimum pH and temprtature?
it reduces the ability of the polypeptide chain to move and changes to temperature and pH have less of an effect on the 3D shape of the enzyme
134
why can immobilised enzymes be used as biosensors or analytical reagents?
bc enzymes are specific to a particular substrate
135
how does the biosensor (glucose oxidase electrode) work? (used to test blood sugar in diabetics)
- the enzyme glucose oxidase is immobilised in a gel
- a small sample of blood is passed over the enzyme
- when glucose in the blood comes into contact with the enzyme, a reaction occurs, which releases energy (chemical)
- the energy released is converted into electrical impulses
- the more energy released, the higher the concentration of glucose in the blood
- a digital display of accurate concentration is availablr by referring to reference data stored in the processing unit
136
what type of structure does a protein have? (primary, secondary, teritary or quaternary)
tertiary
137
what is end-product inhibition?
the product of one reaction acts as the substrate for the next, and the end product acts as a competitive inhibitor for an enzyme earlier in the pathway
138
what are the 2 main ways that immobilised enzymes are fixed to an inert matrix?
1. entrapment - held inside a gel e.g silica gel
2. micro-encapsulation - trapped inside a micro-capsule e.g alginate beads
139
what are the 2 main types of reactions that make up metabolism?
1. anabolic reactions / anabolism
2. catabolic reactions / catabolism
140
what is anabolism?
building up reactions
e.g protein synthesis where amino acids are built up into more complex polypeptides
a set of metabolic pathways that SYNTHESISE complex molecules from smaller, simpler molecules
141
what is catabolism?
breaking down reactions
e.g digestion of proteins, where complex polypeptides are broken down into simple amino acids
a set of metabolic pathways that BREAKDOWN complex molecules into smaller, simpler molecules
142
what bonds hold together the active site?
peptide, hydrogen, ionic and disulphide bonds
143
what does ‘immobilised’ mean?
held in place / stuck onto something to stop them moving
e.g alginate gel beads or reagent sticks
144
how are alginate gel beads made?
- mix enzyme with alginate (a type of gel)
- then drop into calcium chloride solution
- produces small beads
145
what are a problem with using alginate beads for immobilised enzymes?
- enzymes can’t come into contact with enzymes inside (only around outside)
146
what does it mean if you’re lactose intolerant?
you cannot produce the enzyme lactase
- so can’t convert lactose + water -> glucose + galactose
147
how can you test blood/urine for glucose?
with reagent sticks
148
what is a problem with using reagent sticks to test blood for glucose?
blood is red so you can’t compare to the colour chart
149
how is enzyme activity measured?
the substrate converted by a known amount of enzyme in a given molecule time
150
succinate dehydrogenase is an enzyme found in mitochondria and is involved in respiration. thr enzyme catalyses the conversion of succinate into fumarate. why is this the ONLY reaction succinate dehydrogenase can catalyse?
- the ACTIVE SITE has a SPECIFIC SHAPE
- succinate has a COMPLEMENTARY shape
- therefore binds/fits into the active site
151
malonate is a competitive inhibitor of succinate dehydrogenease. explain how malonate inhibits succinate dehydrogenase?
- malonate has similar shape/structure to substrate
- malonate has a complementary shape/structure to the active site
- malonate binds to the active site
- prevents succinate binding/fewer enzyme-substrate complexes are formed
152
why does the initial rate of reaction have a greater rate than further along in the reaction?
- maximum/higher concentration of substrate
- all active sites occupied
153
describe and explain the effect of temperature on the rate of activity of an enzyme (from a graph)?
- increase from__.C to ___.C
- fall from __.C to __.C
- increase in kinetic energy
- molecules move faster (not more)
- more successfull collisions/more enzyme-substrate complexes formed
- up to optimum
- above optimum increased vibrations
- hydrogen bonds break
- loss/change of SHAPE of active site
- denature
154
why is a higher yield of (e.g juice) obtained when using free enzymes between temperatures 20.C and 40.C (at beginning) than when usign immobilised enzymes? (immibilised enzymes had higher yield at higher temps)
- free enzymes can move
- increased chance of successful collisions/more enzyme substrate complaxes formed
155
suggest a reason for the differences seen in the results for the enzymes bound to the gel membrabe surface with those immobilised inside the beads
(enzymes bound to gel membrane surface had higher yield than enzymes immobilised inside beads)
- increased juice extracted with membrane bound enzymes because membrane bound enzymes are more accessible to substrate
- enzymes immobilised inside bead - substrate has to diffuse/pass into bead
156
why might end product inhibition be useful to a cell?
- prevents (build up/overproduction) of end product
OR
-pathway stops when (sufficient/enough) product is made
OR
- regulating the production of product
157
what bonds holds together the secondary structure of proteins?
hydrogen bonds
158
which bonds are the weakest/which bonds will break first when enzymes are exposed to high temperatures?
hydrogen bonds, then ionic bonds, then disulphide bridges
159
what bonds in the tertiary structure would be present in enzymes found in bacteria that live in hot volcanic springs?
many disulphide bonds as it is likely to be able to withstand quite high temperatures
160
explain how the induced fit mechanism differs from the lock and key model? [2]
- lock and key ACTIVE SITE shape already fixed
- (3D) active site changes shape when substrate binds
161
define metabolism
the sum of all the enzyme controlled chemical reactions taking place in a cell
162
what is an enzyme?
- a biological catalyst used to speed up the rate of chemical reactions
- they are not used up or permanently altered
163
what is the active site of an enzyme?
- a region on an enzyme that is complementary to the shape of a specific substrate
- the substrate binds and the reaction takes place
164
how does substrate concentration affect the rate of an enzyme-controlled reaction?
- if enzyme conc is fixed, the rate of reaction increases proportionally to the substrate conc
- once all active sites become full, the rate of reaction becomes constant (graph plateaus - enzyme conc is limiting factor)
165
how does enzyme concentration affect the rate of an enzyme-controlled reaction?
- if substrate conc is fixed, the rate of reaction increases proportionally to the enzyme conc
- when all of the substrate occupy active sites, the rate of reaction remains constant (graph plateaus - substrate conc is limiting factor)
166
what are some methods of immobilising enzymes?
- cross linking
- gel capsule / alginate beads / gel beads
- gel membrane
167
does the enzyme denature or does the active site denature?
the enzyme denatures
168
suggest why reducing the flow rate of material through a column with immobilised enzymes would result in an increased volume of product being collected?
- increases (contact) time between enzymes and substrate
- more time for enzyme to digest substrate
- more successful collisions/more enzyme substrate complexes formed
169
explain why the immobilised enzymes work at its maximum rate over a wider range of temperatures than the free enzymes?
- (stability/protection) from (increased/higher) temperature / more energy required to overcome weak bonds / reference to bonds forming stability
- shape of active site is maintained at higher temperatures
170
what provides a 3D active site?
the tertiary structure
171
how do buffers control pH?
by neutralizing small amounts of added acid or base
(by absorbing excess H+ or OH-)
172
why are enzymes spherical/globular in shape?
because the hydrophobic parts of the protein fold inwards while the hydrophilic parts become arranged around the surface
- it means enzymes are water soluble (+ easy transport out of cells)
173
what two features do globular proteins have that make them good enzymes?
- the tertiary structure of globular proteins means that enzymes have 3D shaped active sites
- spherical for easier transport
- soluble enabling them to catalyse more reactions
174
some amino acids that are not part of an enzyme’s active site are changed. explain whether or not this affects the functioning of the enzyme?
it does affect the functioning of the enzyme as the primary structure is changed. this changes the shape of the enzyme but also the shape of the active site
175
what are some examples of extracellular enzyme?
- the pancreatic enzyme trypsin
- digestive enzymes e.g lipase
176
what are some examples of intracellular enzymes?
- DNA helicase
- lysozomes
- catalase - which breaks down hydrogen peroxide into water and oxygen
177
describe one use of immobilised enzymes in medicine?
detection of blood sugar/ testing blood sugar (in diabetics)
(NOT diabetics/biosensor)
178
how does trapping an enzyme to an inert matrix explain why it can withstand higher temperatures?
the shape of the enzyme / 3D structure is maintained
- or it is stabilised - molecular movement is ‘reduced’
179
what are immobilised enzymes? describe the advantage of their use and how they are used in biosensors. [10]
- enzyme molecules that are fixed/bound/trapped
- to an inert matrix/alginate bead
- they are more stable at higher temperatures (∴ reaction rates may be faster by using higher temps)
- they can tolerate wider range of pH
- they are more easily recovered for re-use/separated from product
- several enzymes with different pH or temp. optima may be used at one time
- reactions can be more easily controlled by adding or removing enzymes
- they are specific so can select one type of molecule in a mixture
- so can be used for rapid detection of biologically important molecules
- they can also accurately measure the quantities present/are sensitive
- used in medical diagnosis/ e.g diabetes
- and environmental monitoring
- description of mechanism, some use a transducer to generate an electrical impulse that can be measured with a meter
- e.g blood sugar meter as used by diabetics
180
explain what is meant by the term biosensor? [2]
- measures metabolite/named substance
- by converting chemical electrical signal/energy into an electrical signal/energy
181
the enzyme, polyphenol oxidase, catalyses the production of dark brown coloured pigments from naturally occurring phenolic compounds (e.g catechol). this causes fruit to turn brown when exposed to the air.
banana puree is often given to young babies to eat, but it turns brown after preparation. explain how the method of the addition of lemon juice (citric acid) prevents this from happening [2]
any 2 from:
- enzyme (not at/below) optimum pH
- enzymes (inactivated/denatured) / change to shape of active site
- less/no enzyme-substrate complexes formed
182
the enzyme, polyphenol oxidase, catalyses the production of dark brown coloured pigments from naturally occurring phenolic compounds (e.g catechol). this causes fruit to turn brown when exposed to the air.
banana puree is often given to young babies to eat, but it turns brown after preparation. explain how the method of vaccum packing it (air free) prevents this from happening [2]
- no oxygen present
- oxygen needed for (oxidase/enzyme) activity / oxidation of it cannot take place
