Substrate Concentration: Definition & Effect on Enzyme Activity

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  • 0:01 What Are Substrates?
  • 1:15 Substrate Concentration
  • 2:17 Role in Enzyme Activity
  • 4:37 Lesson Summary
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Lesson Transcript
Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

This lesson will discuss what a substrate is and how it relates to enzymes. It will also explain what substrate concentration means and take a look at how substrate concentration affects enzyme activity.

What Are Substrates?

How do you make scrambled eggs? First, you need an egg, and then you have to crack the egg, mix it up, and stir it while cooking. What happened to the shell? Well, it's either thrown away or put into the compost pile. You can even add different ingredients like ham or cheese.

Why talk about scrambling eggs if we're talking about substrates? You can think of the substrate as the egg. A substrate is a substance that is used to make a final product. It is changed and reformed during the process. Sometimes chemical groups are added or taken away.

In the cell, enzymes bind and change substrates into their final product. When the enzyme is bound to the substrate, it is known as an enzyme-substrate complex. In this example, you would behave as an enzyme. You take the substrate (the egg) and change it into the final product (scrambled eggs). You take away chemical groups (the shell) and can add others (ham and cheese).

The removed chemical groups are recycled by the cell and used for other reactions. You are unchanged during the process. Enzymes are also unchanged while creating products.

Products themselves are often substrates for other cellular reactions, just as you can scramble eggs to make many other dishes, including casseroles, quiches, or egg and cheese biscuits.

Substrate Concentration

So how many scrambled eggs can you make? Well, that depends on the number of eggs you have. The amount of eggs is your concentration. Substrate concentration is the amount of substrate present that can be turned into product. The unit of measurement usually assigned to eggs is dozen. Substrate concentration can be measured in various ways. Since the substrates inside the cell are suspended in cellular fluid, substrate concentration is most commonly measured in molar concentration, or molarity (M), which is moles per liter.

A mole is 6.022x10^23 units of a substance. So if you had 6.022x10^23 eggs, you would have 1 mole of eggs (that's a lot of eggs!). Now if you put all these eggs (let's say we used a shrink ray to shrink the eggs to atomic size) into 1 liter of water, the molarity of your substrate would be 1 M (1 mole eggs/1 liter water). Concentrations are often denoted with brackets.

Substrate Concentration's Role in Enzyme Activity

If you're the enzyme, how does the concentration of the substrate (in this case the egg) affect your activity? Let's say you're a cook at a big breakfast restaurant and need to cook some scrambled eggs. If there are only five eggs, you have to hunt in the fridge for the eggs; once you find them, then you can cook them. If the other cooks (other enzymes) find them first, you'll have to wait or hunt for more eggs. If substrate concentration is low, enzymes have a lower chance of encountering the substrate, so its activity, or rate of reaction, is low.

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