High School Biology : Understanding Active Sites

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #142 : Dna, Rna, And Proteins

Which of the following inhibitors will block the active site of a protein?

Possible Answers:

Non-competitive inhibitor 

All of these will block the active site of a protein

Uncompetive inhibitor

Allosteric inhibitor

Competitive inhibitor

Correct answer:

Competitive inhibitor

Explanation:

Proteins can be inhibited in numerous ways by different types of inhibitors. Competitive inhibitors will compete with substrate for the active site to block the protein from performing its function. If there is enough substrate and very little competitive inhibitor, proteins will perform their functions almost as if there were no competitive inhibitors.

In contrast, allosteric inhibitors bind to regions of the protein away from the active site, but change the shape of the active site such that substrate cannot bind. Since there is no direct competition, increasing substrate concentration cannot overcome allosteric inhibition. Non-competitive inhibition is a type of allosteric inhibition. Uncompetitive inhibition occurs when the inhibitor will only bind to the enzyme-substrate complex, locking the substrate in place and preventing other substrates from binding.

Example Question #143 : Dna, Rna, And Proteins

The active site of a protein works in a way similar to __________.

Possible Answers:

a hole in a wall

a gate in a fence

a motor in a car

the shuffle button on an MP3 player

a lock and key

Correct answer:

a lock and key

Explanation:

The active site on a protein is the area where a substrate can attach. This relationship is most often described using a metaphor of a lock and a key because each protein has an active site specific to one substrate much like a lock can only be opened by one key.

Example Question #12 : Protein Structure

__________ modification of an enzyme permits an effector molecule to bind the enzyme at a site other than the active site. This can modulate the enzyme's activity to make it either more or less active.

Possible Answers:

Inhibitory 

Cofactor

Agonist

Antagonist

Allosteric

Correct answer:

Allosteric

Explanation:

The key here is to know that if something binds the enzyme at a location other than the active site, the type of modification is defined as allosteric. The other words more generally describe things that can bind to receptors, enzymes, etc., but the best and most specific answer is "allosteric."

Example Question #13 : Protein Structure

Which of the following best describes why an enzyme loses its catalytic capabilities when exposed to extremely high temperatures?

Possible Answers:

All of these statements describe mechanisms by which heat destroys the catalytic activity of an enzyme

The bonds maintaining the shape of the enzyme are broken, and the active site loses its conformation and can no longer bind its proper substrate

All substrates are degraded at high temperatures, and therefore there is no reaction to catalyze

Covalent modifications made to the enzyme are disrupted by high temperatures and the enzyme cannot bind its substrate

The activation energy of the reaction becomes so great that the enzyme cannot overcome the energy, and therefore cannot catalyze reactions

Correct answer:

The bonds maintaining the shape of the enzyme are broken, and the active site loses its conformation and can no longer bind its proper substrate

Explanation:

It is important to know that when exposed to high temperatures, all proteins become denatured, and lose their native shape/conformation.

This has nothing to do with the activation energy of the reaction (eliminating that answer). While some substrates may be degraded at high temperatures, the word "all" renders this answer incorrect, nor does this describe what happens to the enzyme. Covalent modificatinos can change enzymatic function, but do not have anything to do with higher temperature.

The correct answer is that the enzyme itself is denatured, thus changing the shape and the way the active site is shaped, resulting in an inability to efficiently bind its substrate. The structure of the enzyme is dictated by intermolecular forces, which are susceptible to interference from temperature changes (unlike covalent bonds).

Example Question #14 : Protein Structure

Which mode of enzyme inhibition involves an inhibitor molecule binding the active site of the enzyme?

Possible Answers:

Mixed inhibition

Irreversible inhibition

Uncompetitive inhibition

Competitive inhibition

Non-competitive inhibition

Correct answer:

Competitive inhibition

Explanation:

Competitive inhibition is the only type of inhibition in which the inhibitor molecule directly binds the active site of the enzyme, thereby 'competing' with the actual substrate for location on the enzyme. The other choices involve binding elsewhere on the enzyme (non-competitive) or binding the enzyme-substrate complex but not an isolated enzyme (mixed), but none of them describe binding the active site except for competitive. 

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