How a Molecule's Biological Function is Related to Shape

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  • 0:02 Function & Shape
  • 0:28 Enzymes
  • 1:19 Hormones
  • 2:28 Antibodies
  • 3:43 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson goes over numerous instances of how a molecule's biological function is related to its shape. You'll learn how all of this works with familiar real-world examples.

Function & Shape

Function is clearly related to shape. It would be hard to drive a car with square wheels. It's difficult to imagine a dog running at full speed on its hind legs for long. The mechanics and biomechanics of it all simply don't work. This macroscopic view of function and its relation to shape is no different on the smaller side of biology. Let's find out why with several examples in this lesson.

Enzymes

Let's start with a good example of this by turning to enzymes, which are molecules that help speed up biochemical reactions. A real-world example of an enzyme is something like lactase, an enzyme that helps us digest milk. All enzymes retain a specific shape that helps them complete their function.

You can think of an enzyme as a paperclip. The paperclip is clearly folded in such a way as to perform its job of holding pieces of paper together. If an enzyme is unable to maintain its shape, which could occur due to unfavorable environmental conditions involving heat or acid, then it unravels and can no longer do its job. We can think of this as unraveling a paperclip; if we unravel a paperclip, then how in the world is it going to perform its job of holding paper together? It can't, and so it won't, precisely because it has lost its proper shape.

Hormones

Another great example of the intersection of biological function and a molecule's shape is hormonal action. Hormones are biochemicals that help our body's various cells, tissues, and organs communicate with one another. For example, the hormone epinephrine is produced by the adrenal glands. The hormone can travel to the heart, latch on to beta-1 receptors, and cause the heart to beat faster as a result. In order for a hormone to deliver its message for the intended target, it must bind to the target's receptor; but it can't do that unless it has the proper shape.

You can think of the hormone as a key, and the receptor as a lock. You know that you can't open your front door unless the key's shape matches the lock's inner mechanism in a complementary fashion. If it doesn't, you can't open the door. Hormones work in a similar way. If a hormone has a shape that properly fits a receptor, then it can induce a biochemical response within the target. This means epinephrine can tell the heart to beat faster because it fits the beta-1 receptors. Another hormone, such as ghrelin, does not have the right shape, doesn't fit the receptor, and so does no such thing.

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