Enzyme Theory - Class notes 3

Question 1

what are enzymes?

Answer 1

enzymes are organic catalysts.
enzymes are proteins - globular
enzyme names typically end with the suffix -ase
enzyme names typically have a prefix that indicates its general activity.
>maltase - acts on maltose
>amylase - acts on amylose and amylopectin
>oxido-reductase - takes part in oxidation/reduction reactions
> protease - acts proteins
>lipase - acts on lipids
enzyme reaction are affected by changes in temperature, pH and substrate concentration
enzymes are very specific, i.e., they only act on a specific substrate

Question 2

what is metabolism?

Answer 2

metabolism refers to the chemical reactions that occur owithin an organism. Someone with a high metabolism, therefore, has a generally high rate of chemical reactions taking place within their cells and systems

Question 3

what are the components of metabolism?

Answer 3

catabolism + anabolism = metabolism

Question 4

what is catabolism?

Answer 4

catabolism refers to reactions that break more complex molecules into simpler ones, e.g., digestion of starch, proteins and lipids.

Question 5

what is anabolism?

Answer 5

anabolism refers to reactions that convert simpler molecules into more complex ones, e.g., amino acids into proteins, glucose into starch or glycogen, etc.

Question 6

how do enzymes relate to meabolism?

Answer 6

enzymes govern nearly all chemical reactions, thus enzymes directly directly affect our metabolic rates.

Question 7

what is activation energy?

Answer 7

activation energy is the energy required to initiate a chemical reaction.

Question 8

how are enzymes involved in activation energy?

Answer 8

enzymes reduce the activation energy required, hence reactions proceed more rapidly.

Question 9

know activation energy graph

Answer 9

(see diagram)

Question 10

know lock and key hypothesis for enzyme activity

Answer 10

(see diagram)

Question 11

what are the steps in the induced fit hypothesis?

Answer 11

(see diagram)

1) active site has a more open shape than lock and key
2a) when subrate makes contact with the active site, the enzyme undergoes a conformational change (i.e., it changes shape) that allows the active site to fit ‘snugly’ around the substrate.
2b) as the enzyme changes shape, strain is placed upon chemical bonds within the substrate (for catabolic reactions). this strain reduces the amount of energy required to break that bond - in other words, the activation energy is lowered.

Question 12

Know the diagram for induced fit - anaboli reaction.

Answer 12

(see diagram)

Question 13

what happens in anabolic reactions involving enzymes?

Answer 13

for anabolic reactions, the enzyme lowers the activation energy for bond formation by aligning the two substrate molecules.

Question 14

what is the turnover? give an example

Answer 14

turnover number relates to the amount of substrate catalysed by an enzyme (under optimum conditions) per unit time (when substrate in is excess).

example:
catalase has a very high turnover number = 5600000 hydrogen peroxide molecules per minute (that’s one molecule of catalase)

Question 15

what factors affect the rate of reactions involving enzymes?

Answer 15

enzyme concentration
substrate concentration
pH
Temperature

Question 16

Know the graph of the effect of changing substrate concentration on rates of reactions.

Answer 16

(see diagram)

Question 17

What is happening in region A of the graph of the effect of changing substrate concentration on rates of reactions.

Answer 17

(see diagram)
rate of reaction increases as substrate concentration increases. This increase is proportional (at low concentrations).As there is more substrate, there is more enzyme/substrate complexes formed - hence more product results per unit time.

Question 18

what is happening in region B of the graph of the effect of changing substrate concentration on rates of reactions?

Answer 18

the rate of reaction increases but at a decreasing rate. this is due to a number of active sites being occupied by substrate molecules.

Question 19

what is happening in region C of the graph of the effect of changing substrate concentration on rates of reactions?

Answer 19

the reaction levels off at a constant rate - even though substrate concentration is still increasing. This is due to a saturation of enzyme active sites. in other words, at high levels of substrate concentration all active sites are occupied at any given time. the substrate has to effectively ‘queue’ for the next avaliable active site. in other words, we have reached the turnover number for this enzyme now that we have excess substrate.

Question 20

What is enzyme inhibition?

Answer 20

in order to control ratesof biochemical reactions, the enzyme activity must be regulated in some way. One way that enzymes are regulated is via inhibitors. in a sense, inibitors act like ‘dimmer switches’ re. enzyme activity. i.e., if you increase the amount of inhibitors, fewer enzymes are active and hence the reaction slows down. conversely, if you decrease the amount of inhibitors, more enzymes are active and the reaction increases.

Question 21

what are the two types of enzyme inhibition?

Answer 21

Competitive and non-competitive inhibition

Question 22

what does competitive inhibition relate two?

Answer 22

it relates to a substrate competing with an inhibitor for an enzyme’s active site.

(SEE AND KNOW DIAGRAM)

Question 23

what does non-competitive inhibition relate two?

Answer 23

non- competitive inhibition involves inhibitors that bind to the enzyme somewhere other than the active site, e.g., an inhibitor binding site. Thus, there is no direct competition between the substrate and inhibitor.

Question 24

What do some non-competitive inhibitorsdo?

Answer 24

some non-competitive inhibitorsactually result in a change in the shape of the active site, therefore preventing an induced fit by the enzyme. This change in shape is called ALLOSTERIC inhibition.

(SEE AND KNOW DIAGRAM)

Question 25

know the enzymeinhibtior graph

Answer 25

seediagram

Question 26

know the competitive inhibition at high substrate concentrations diagram

Answer 26

seediagram

Question 27

know the non-competitive inhibition at high substrate concentrations diagram

Answer 27

see diagram

Question 28

what happens on curve 2 with a competitive inhibitor?

Answer 28

as the substrate concentration increases, the rate of reaction increases but at a slower rate when compared to the same reaction whereno inhibitor is present (seecurve 1). at high substrate concentrations, the rate of reaction approaches the optimal rate seen in curve 1.

keeping in mind that inhibitor concentration remains constant, as substrate concentration increases, the ratio of substrate to inhibitor increases, i.e., more substrate than inhibitor.Thus at highersubstrate concentrations, there is a greater probability of the substrate binding to the active site (over the inhibitor)

Question 29

what happens on curve 3 with a non-competitive curve?

Answer 29

initially as the substrate concentration increases, the rate of reaction increases. However, the rate of reaction levels off at fairly low concentrations of substrate. the optimal rate of reaction (where the curve levels off) is significantly lower than the optimal rate seen incurve 1.

as the non-competitive inhibitor is binding at a different site, there is no direct competition between the inhibitor and the substrate. the inhibitor can bind to the enzyme at the same time as the substrate, but binding of the inhibitor affects the binding of the substrate (i.e., no induced fit occurs). hence, the ratio of substrate to inhibitor is a lesser factor re. the rate of reaction. in other words, all of the inhibitor can be active all of the time. also, keep in mind that the inhibitor may stay in the inhibitor site for an extended period of time. non-competitive inhibitors essentially lower the enzyme concentration of the system.

Question 30

Know the diagram of end product inhibition

Answer 30

see diagram.
End product, in excess, will inhibit its own production (in order to reduce excess) by acting as an inhibitor on one of the enzymes.