9.2 maintaining a balance the role of enzymes next for revision click here

9.2 Maintaining a Balance

The Role of Enzymes

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Where does it fit in the Syllabus?

1. Most organisms are active in a limited temperature range

Students learn to:

• identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates

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Where does it fit in the Syllabus?

Students learn to:

• identify the role of enzymes in metabolism

• describe the chemical composition of enzymes

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

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Identifying the role of enzymes on metabolism

Let’s see what you remember…

Question 1

Metabolism is a term used to describe….

a. All the chemical processes occurring in the body

b. Only the chemical processes associated with digestion

c. Only the chemical processes associated with respiration and circulation.

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Question 1


a. All the chemical processes occurring in the body

EXCELLENT!!!

DID YOU KNOW…

All the processes of chemical and physical change which goes on in the living organism are a part of metabolism. Building up of new tissue, replacing of old tissue, converting food to energy, disposing of waste materials, etc – all the activities that maintain our lives!

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Question 1


b. Only the chemical processes associated with digestion

NICE TRY!!!

DID Y

OU KNOW

… Metabolism is the process of chemical and physical change which goes on continually in the living organism for it’s maintenance. Whether it is producing new tissue, replacing of old tissue, converting food to energy or disposing waste material – metabolism consists of all the activities that help maintain our life!

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Question 1


c. Only the chemical processes associated with respiration and circulation.

Getting there!!!

NEXTDID

YOU K

NOW… Metabolism is the process of chemical and physical

change which goes on continually in the living organism for it’s maintenance. Whether it is producing new tissue, replacing of old tissue, converting food to energy or disposing waste material – metabolism consists of all the activities that help maintain our life!

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Question 2

There are two basic phases of metabolism – these are called Anabolism and Catabolism.

Which of the following answers best defines these phases?

b. Anabolism involves the synthesis of large molecules from smaller ones, while Catabolism is the breakdown of large molecules to smaller ones.

a. Catabolism involves the synthesis of large molecules from smaller ones, while Anabolism is the breakdown of large molecules to smaller ones.

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almost!!!


Question 2


a. Catabolism is the synthesis of large molecules from smaller ones, while Anabolism is the breakdown of large molecules to smaller ones.

This is often one of those concepts that is easy to be confused by, but a simple way to think of it is the ABCD of Metabolism – Anabolism Builds, Catabolism Destroys.

In the image on your left Anabolism is shown by the green arrows, whereas Catabolism is shown by the orange arrows

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Great work!!!


Question 2


b. Anabolism is the synthesis of large molecules from smaller ones, while Catabolism is the breakdown of large molecules to smaller ones.

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A simple way to remember this is the ABCD of Metabolism – Anabolism Builds, Catabolism Destroys.

In the image on your left, Anabolism is shown by the green arrows, whereas Catabolism is shown by the orange arrows

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Great work!

After answering these two questions, we now understand that metabolism is important for

life to function, & that the phases of metabolism include

• Anabolism (synthesizing large molecules or products from smaller molecules) &

• Catabolism (breaking down large molecules or products to smaller molecules).

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These reactions can sometimes occur without assistance, but the rate of metabolic reaction is rather low, because of the energy demand.

NEXTBACK Figure 1. Activation energy requirements without catalyst


However, metabolic reaction is increased with the presence of enzymes which are biological catalysts, which require lower energy. This means that it is involved, but not changed by a chemical reaction.

NEXTBACKFigure 2. Activation energy requirements without catalyst and with enzyme

catalyst

Question 3

So what is an enzyme’s composition?

Describe the chemical composition of enzymes

b. Enzymes are protein molecules that have different compositions depending on their function.

a. Enzymes are made up of amino acids

c. All of the above

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Question 3


a. Enzymes are made up of amino acids

Partly right!!!

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The major chemical composition of enzymes is proteins. These proteins are made up of amino acids which are joined by peptide bonds. The chemical composition of these amino acids can determine the function of the enzyme.Fig 3. Structure of α-

Amylase, an enzyme in Human Saliva

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Question 3



b. Enzymes are protein molecules that have different compositions depending on their function.

Partly right!!!

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Question 3


c. All of the above

That’s right!!!

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Enzymes, as we know, interact with other substances to undergo chemical reactions. We also know that their chemical composition determines what they react with. The chemicals that enzymes react with are called substrates.

So let’s see how enzymes and substrates interact…

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EnzymeDifferent Substrates

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Enzymes are designed to accommodate certain substrates to undergo a chemical reaction. This reaction occurs at a specific site on the enzyme called the active site

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Enzyme(with a red active site)

Substrates

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

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When the substrate/s meet at the active site of the enzyme and interact, this is called the enzyme-substrate complex. In the example below, this interaction leads to the two substrate components forming a combined product.

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Enzyme(with a red active site)

Two Substrates forming a larger compound


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Enzyme Enzyme

Substrate/sSubstrate/s

Question 4

What kind of reaction is occurring in each example?

b. Example A – Anabolism, Example B – Catabolism

a. Example A – Catabolism, Example B – Anabolism

A B

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Question 4


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Enzyme Enzyme

Substrate/sSubstrate/sA B

a. Example A – Catabolism, Example B – Anabolism


This model shows the enzyme breaking the large product into separate substrates = catabolism

This model shows the enzyme assisting the smaller substrate components form to a large product = anabolism

That’s right!!!

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Question 4


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Enzyme Enzyme

Substrate/sSubstrate/sA B

This model shows the enzyme breaking the large product into separate substrates = catabolism

This model shows the enzyme assisting the smaller substrate components form to a large product = anabolism

b. Example A – Anabolism, Example B – Catabolism


Almost there!

• To look at the overall reaction as an equation would look like this:

E + S ↔ ES↔ P + E where E = Enzyme

S = Substrate

ES = Enzyme–Substrate Complex

P = ProductNB. Notice how the Enzyme remains unchanged throughout the whole reaction

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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.

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Enzyme

AppropriateSubstrates

Enzyme

Inappropriate Substrates


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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


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Question 5


a. A basketball fitting into a basketball hoop


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…

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Question 5

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

b. A hand fitting into a glove


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.

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Question 5


c. A USB fitting in a USB port


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.

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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.

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Enzyme

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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


a. A tyre fitting on a car

Question 6


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…

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

Question 6


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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!

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c. An appliance fitting in an operating power socket

Question 6


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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

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Well done!!!You have completed this lesson on enzymes which will provide you with a basis to do your

research task where you will need to develop your own model to describe enzyme-substrate

interactions!

If you would like to go back to any questions, click on the images below…Question 1 Question 2

Question 3 Question 4


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Revision Page




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References

Images sourced from the following:

• (1-2)Nature Education, (2010). Figure 3: Enzymes and activation

energy, Protein Function, Nature Education. http://www.nature.com/scitable/topicpage/protein-function-14123348

• (3)Ramasubbu, N., Paloth, V., Luo, Y., Brayer, G.D., Levine, M.J.

(1996). Structure of human salivary alpha-amylase at 1.6 A resolution: implications for its role in the oral cavity, Acta Crystallographica, 52(3). 435 –446. DOI:10.1107/S0907444995014119

9.2 maintaining a balance the role of enzymes next for revision click here

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