9.2 Maintaining a Balance The Role of Enzymes. DO NOW Explain using a drawing or equation, how enzymes interact with appropriate substrates. (3 marks)

9.2 Maintaining a Balance

The Role of Enzymes

DO NOW

Explain using a drawing or equation, how enzymes interact with appropriate substrates. (3 marks)

Describe an enzyme’s specificity on substrates using a simple model. This model below demonstrates how enzymes are substrate specific. This particular model is a ‘lock and key model’. The appropriate substrate (the ‘key’) is the proper fit for the enzyme (the ‘lock’). Inappropriate substrates may not interact with the enzyme.

Enzyme

AppropriateSubstrates

Enzyme

Inappropriate Substrates

Question 5

Which example provides the best comparison to the ‘lock and key’ model?

b. A hand fitting into a glove

a. A basketball fitting into a basketball hoop

c. A USB fitting in a USB port

Describe an enzyme’s specificity on substrates using a simple model. 

Question 5

Which example provides the best comparison to the ‘lock and key’ model?

a. A basketball fitting into a basketball hoop

Describe an enzyme’s specificity on substrates using a simple model. 

This example has many limitations, namely that the basketball itself (as a substrate or product) does not necessarily bind to an active site on the basketball ring. Also, the basketball is not metabolized in any fashion by the ring. The basketball ring does not change amidst the reaction, which is a common trait between it and the enzyme.

NOT QUITE THERE…

Question 5

Which example provides the nearest comparison to the ‘lock and key’ model?

b. A hand fitting into a glove

Describe an enzyme’s specificity on substrates using a simple model. 

Not quite…This example has many limitations, namely that the glove itself might need to expand or shrink to accommodate the hand. There is an active site on the inside lining of the glove, so it does have a common element with an enzyme, but perhaps not one in which there is a reaction that occurs without the glove being affected.

Question 5

Which example provides the best comparison to the ‘lock and key’ model?

c. A USB fitting in a USB port

Describe an enzyme’s specificity on substrates using a simple model. 

WELL DONE!!!This example demonstrates a reasonable comparison to the ‘lock and key’ model. They are both specific ( a USB port can’t interact with a CD or pencil for instance), so there is a highly specific active site, and the substrate (the USB) could undergo a reaction (if only by its data) from it’s interaction with the port.

Describe an enzyme’s specificity on substrates using a simple model. Another model used to demonstrate enzyme – substrate interactions is the ‘induced fit’ model.

In this model, the enzyme’s active site alters to accommodate the specific substrate/s for which it reacts.

Enzyme

Describe an enzyme’s specificity on substrates using a simple model. 

Question 6

Which example provides the best comparison to the ‘induced fit’ model?

b. A softball fitting in a catcher’s mitt or hand

a. A tyre fitting on a car

c. An appliance fitting in an operating power socket

Describe an enzyme’s specificity on substrates using a simple model. 

a. A tyre fitting on a car

Question 6

Which example provides the best comparison to the ‘induced fit’ model?

This example is actually more suited to perhaps a lock and key approach. What it has in common is an active site, but the enzyme (in this instance a car) doesn’t reshape itself to accommodate the tyre.

On the right track…

Describe an enzyme’s specificity on substrates using a simple model. 

b. A softball fitting in a catcher’s mitt or hand

Question 6

Which example provides the best comparison to the ‘induced fit’ model?

This example is a good model of the ‘induced fit‘ enzyme–substrate interaction. The ball, being the substrate is easily accommodated by the mitt (or enzyme) which then changes it’s active site to better accommodate the substrate.

Excellent!

Describe an enzyme’s specificity on substrates using a simple model. 

c. An appliance fitting in an operating power socket

Question 6

Which example provides the best comparison to the ‘induced fit’ model?

Not exactly…This example actually is much more of a ‘lock and key’ model. If we were to talk about the bread in this image as a substrate however, we would notice that the bread rack (a possible enzyme active site) may press firm against the bread, and is an induced fit, but the appliance and the socket don’t share the same comparison

Now it’s your turn…

• YOUR TASK: In groups you will need to develop an everyday example of a lock and key model & an induced fit model.

• Remember to include the following components:

Enzyme Substrate E-S Complex Active Site Reaction/Product E-S Interaction

Now we understand enzyme interaction, let’s move on…

1. Most organisms are active in a limited temperature range

• 1b) identify the pH as a way of describing the acidity of a substance

• 1A) identify data sources, to test the effect of:– increased temperature– change in pH– change in substrate concentrations on the

activity of enzyme(s) 

Competitive Inhibition

• Sometimes, another substrate can impede the function of the appropriate substrate, because it is a close but incomplete fit to the active site. This prevents the proper substrate from reacting & inhibits enzyme function.

Enzyme

AppropriateSubstrates

Competitive Inhibitor

• pH is a scale measure of the concentration of hydrogen ions in a

solution.

• This is most often associated with;

Acids (pH 0-6), Bases/Alkalines (pH8-14)

and Neutral Solutions (pH 7).

pH

• Each enzyme functions best within a certain pH range. For example, the enzyme pepsin, which works in your stomach, functions best in a strongly acidic environment. Lipase, an enzyme found in your small intestine, works best in a basic environment.

The role of pH on enzyme function

• When the pH changes, the active site progressively distorts and affects enzyme function. What happens to catalysis when an enzyme is subjected to a pH far from its optimum range?

The role of pH on enzyme function

Enzyme

AppropriateSubstrates

• Chemical reactions speed up as temperature is increased, so, in general, catalysis will increase at higher temperatures. However, each enzyme has a temperature optimum, and beyond this point the enzyme's functional shape is lost.

The role of temperature on enzyme function

• When an enzyme’s functional shape is lost, and it no longer has the ability to interact with its substrate or be reversed, this is called denaturalisation. The animation below shows a denatured enzyme.

The role of temperature on enzyme function

Enzyme

AppropriateSubstrates

• When there is significantly more substrate than enzyme, it takes much longer for enzymes to interact with each substrate

The role of substrate concentration on enzyme function

• When enzyme activity plateaus, it is called the saturation point.

• How would this be different if there was much more enzyme to substrate?

The role of substrate concentration on enzyme function

Reflection

• Explain (in under 8 lines) at least 3 ways in which enzyme substrate interaction can be impeded or stopped altogether.