Enzymes- Topic 2

Question 1

what are enzymes?

Answer 1

-biological catalysts that speed up the rate of reaction without being used in the reaction itself
-globular proteins that have a specific shape (tertiary)

Question 2

why are enzymes specific?

Answer 2

-so that they are specific in the reactions that they catalyze meaning one enzyme will only react with molecules of one substrate

Question 3

where is the site of reaction in enzymes?

Answer 3

-the active site it has a highly specific shape and other molecules of different substrates wont fit into the active site

Question 4

how do enzymes work?

Answer 4

-a substrate is converted into a product, the substrate first binds to the active site to form an enzyme substrate complex then the substrate is converted into a product while attached to the enzyme and finally the product is released

Question 5

what is the lock and key hypothesis?

Answer 5

-the active site is complementary to the shape of the substrate so only one active site on each molecule and one substrate that will fit together
-the substrate fits into the enzyme like a key in a lock this specificity leads to the lock and key hypothesis

Question 6

what are the forces that hold the enzyme and substrates in place?

Answer 6

-the forces that hold the enzyme and its substrate are weak temporary bonds e.g. usually hydrogen bonds

Question 7

what is the induced fit model and how does it relate to enzyme activity?

Answer 7

-it has been discovered that competitors for an active site which are molecules of a similar shape to the substrate could fit, this could mean that the substrate and active site are a little flexible
-when the enzyme and substrate form a complex, structural changes occur so that the active site fits precisely around the substrate

Question 8

what is the transition state in relation to the induced fit model?

Answer 8

-when a substrate molecule binds the active site changes shape and fits itself around the molecule which distorts it into forming the transition state

Question 9

according tot he induced fit model what happens the enzyme after its finished the reaction?

Answer 9

-once the reaction has occurred and products are formed they move away from the active site as they can no linger fit
-the flexible enzyme returns to its original shape ready to bind to the next molecule of substrate

Question 10

what is activation energy?

Answer 10

-the energy required to start a reaction is called the activation energy
-before a substrate can change into a product the substrate must overcome an energy barrier called the activation energy (Ea)

Question 11

the larger the activation energy…

Answer 11

-the slower the reaction will be because only a few substrate molecules will by chance have sufficient energy to overcome the activation energy barrier

Question 12

what is the equation for the transition state?

Answer 12

-substrate A + enzyme-> enzyme substrate complex -> product + enzyme

Question 13

what do enzymes do to activation energy? how do they do this?

Answer 13

-lower it so that most molecules can easily get over the activation energy barrier and quickly turn it into products
-enzymes lower the activation energy by stabilizing the transition state and they do this by changing the conditions within the active site if the enzyme

Question 14

what is a cofactor ?

Answer 14

-a non- protein chemical compound that is bound to a protein and is required for the protein’s biological activity

Question 15

what are coenzymes ?

Answer 15

-an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction

Question 16

what is a holoenzyme ?

Answer 16

-the complete active enzyme with its cofactor

Question 17

what is a apoenzyme?

Answer 17

-the enzyme without its cofactor

Question 18

what are the 6 factors that affect the rate of enzyme reactions ?

Answer 18

-temperature
-pH
-substrate concentration
-enzyme concentration
-competitive inhibitors
-non competitive inhibitors

Question 19

what is a denatured enzyme?

Answer 19

-an enzyme that has lost its 3D or tertiary structure so it is no longer able to function

Question 20

why does temperature effect the rate of enzyme reactions?

Answer 20

-all enzymes have an optimum temp at which the work the fastest- mammalians is 40 degrees
-an increase in temp provides more kinetic energy to the substrate molecules and the number of collisions between enzyme and substrate will increase so the rare of reaction will increase
-above the optimum temp the enzymes are denatured, the bond holding the structure together are broken and the active site looses its shape and will no longer work

Question 21

why does pH effect the rate of reactions in enzymes?

Answer 21

-they have an optimum pH at which they work the fastest for most enzymes its 7 or 8 some like protease that in the stomach can work at pH 1
-if the pH changes much from the optimum the chemical nature of the amino acids can change which can disrupt the bonds and so the tertiary structure may break down and they enzyme can become denatured

Question 22

why does the substrate concentration effect the rate of enzyme reactions ?

Answer 22

-it effects the rate of reaction until a certain point
-at low substrate concentrations there are lots of free active sites and so the rate of reaction is slow
-when more substrates are added more enzyme substrate complexes can be formed as there are more active sites filled and the rate of reaction will increases
-eventually increasing the amount of substrates will have no effect on the rate of reaction as the active sites are saturated so no more enzyme substrate complexes can be formed
-on a graph it produces a straight horizontal line after the peak

Question 23

why does enzyme concentration effect the rate of enzyme reactions?

Answer 23

-at low concentrations there is lots of competition for the active sites and the rate of reaction is low
-as the enzyme concentration increase there are more active sites available and so the rate of reaction increases
-eventually increasing the amount of enzymes will have no effect because the concentration of substrates will become the limiting factor
-on a graph the rate of reaction will increase linearly until a peak which then levels off

Question 24

what are inhibitors ?

Answer 24

-they inhibit the activity of enzymes which reduces the rate of reaction sometimes this is necessary to ensure that a reaction does not proceed too fast but other times it isn’t wanted
-there are two types competitive and non competitive
-they can be found naturally but also used artificially in drugs and pesticides

Question 25

what are competitive inhibitors and what are their job?

Answer 25

-they have a similar structure to the normal substrate and fit into the active site of an enzyme, it prevents the substrate from entering
-it competes with the substrate for the active site so the rate of reaction is slower
-if there is a high concentration of these inhibitors then they will take up all the active sites and stop the reactions

Question 26

what are non competitive inhibitors and what are their job?

Answer 26

-different in structure compared to the substrate and so does not fit into the active site and instead binds to another part of the enzyme which changes the enzymes shape including the active site so it can no longer bind to the substrate
-non competitive enzymes reduce the amount of active enzymes so they decrease the rate of reaction

Question 27

what are another name for competitive inhibitors and why is this?

Answer 27

-sometimes these inhibitors can bind fairly weakly to the enzyme and so can be washed out easily and so also can be called reversible inhibitors
-other bind very tightly and so cannot be washed out so are celled irreversible inhibitors

Question 28

what is one example of a non competitive inhibitor ?

Answer 28

-the poison cyanide

Question 29

what is the job of immobilized enzymes?

Answer 29

-to maximize efficiency of enzymes
-immobilized enzymes are trapped within or attached to appropriate inorganic or organic materials

Question 30

what are the 4 ways in which enzymes can be immobilized?

Answer 30

-absorption
-entrapment
-encapsulation
-cross linkage

Question 31

what happens during absorption to immobilize enzymes?

Answer 31

-the enzymes are attached by weak forces to an inert substance such as glass or a matrix

Question 32

what happens during entrapment to immobilize enzymes?

Answer 32

-the enzymes are trapped within polymers such as alginate beads or microspheres

Question 33

what happens during encapsulation to immobilize enzymes?

Answer 33

-the enzymes are trapped inside a selectively permeable membrane such as nylon

Question 34

what happens during cross linkage to immobilize enzymes?

Answer 34

-the enzymes are covalently bonded to a matrix, such as cellulose, as a consequence of chemical reactions (or even to each other using linkage chemicals)

Question 35

what are some of the advantages of enzyme immobilization?

Answer 35

-enzymes are thermostable and they remain stable and are more effective over a wider range of temperature
-more resistant to changes on pH
-enzymes can be retained and reused
-commercial processes can be continuous which is faster can causes less waste
-the end product is not contaminated by the enzymes

Question 36

what are some of the uses of enzymes as analytical and diagnostic reagents?

Answer 36

-they are used in analytical and diagnostic reagents because of their high specificity and sensitivity
-Clinistix strip contains 2 enzymes which helps to identify the amount of glucose in certain substances e.g. urine

Question 37

how do Clinistix strips work in testing for glucose?

Answer 37

-when dipped into the first sample the first enzyme, glucose oxidase, converts any glucose molecules by a reaction with atmospheric oxygen into gluconic acid and hydrogen peroxide
-the second enzyme peroxidase allows the hydrogen peroxide to react with an indicator to give a purple color
-the more glucose that is present in the urine, the more intense the purple color

Question 38

what are some of the disadvantages of immobilized enzymes?

Answer 38

-can be costly to set up
-depending in the way that thew enzyme is attached the active site may be blocked and so the enzyme may not work
-it also may alter the stability of the enzyme