GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Enzyme Types

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

Example Question #51 : Biochemistry

Which of the following types of enzymes is responsible for joining molecules by forming new chemical bonds?

Possible Answers:

Transferases

Ligases

Lyases

Isomerases

Correct answer:

Ligases

Explanation:

Ligases are enzymes that catalyze the formation of new bonds between molecules. A classic example is DNA ligase, an enzyme that synthesizes phosphodiester bonds in the DNA backbone.

Transferases move small molecules from one molecule to another, sometimes altering the functional groups of a compound. Isomerases convert molecules from one isomer to another. Lyases are enzymes that break bonds through a means other than hydrolysis (typically by formation of a double bond). 

Example Question #52 : Biochemistry

Chymostrypsin cleaves a polypeptide into two smaller subunits by using water in order to make the new amino and carboxyl termini. Based on this mechanism, what type of enzyme is chymostrypsin?

Possible Answers:

Oxidoreductase

Lyase

Hydrolase

Ligase

Correct answer:

Hydrolase

Explanation:

Since chymotrypsin uses a water molecule in order to cleave the polymer, it is considered a hydrolase enzyme.

Example Question #53 : Biochemistry

During glycolysis, glucose-6-phospate is rearranged in order to form fructose-6 phosphate. The enzyme that accomplishes this does not change the intermediate's chemical formula in any way, but simply alters the shape of the molecule.

Based on this action, what type of enzyme is involved in this step in glycolysis?

Possible Answers:

Hydrolase

Isomerase

Lyase

Oxidoreductase

Correct answer:

Isomerase

Explanation:

Since the enzyme has changed the shape of the molecule without altering its chemical formula, the enzyme has simply made a new isomer of the molecule. This action is accomplished by isomerase enzymes.

Example Question #1 : Help With Enzyme Types

Which of the following is not a class of enzymes that alter epigenetic states?

Possible Answers:

None of these

DNA methyltransferases

Histone methyltransferases

Pioneer transcription factors

Histone acetyltransferases 

Correct answer:

None of these

Explanation:

All answer choices fit the description. Epigenetics (above the gene) are heritable modifications of chromatin and DNA that affect gene expression. Pioneer transcription factors are able to bind DNA in heterochromatin and recruit enzymes that promote euchromatin formation which allows other transcription factors to bind and effect gene expression. Histone methyltransferases and acetyltransferases methylate and acetylate histones, respectively, to alter gene expression. DNA methyltransferases are also enzymes that confer epigenetic changes to DNA by methylation, which usually represses gene expression. 

Example Question #2 : Help With Enzyme Types

Which of the following are not enzymes that act on DNA?

Possible Answers:

Acetylases

Ligases 

Methylases 

Topoisomerases 

Polymerases 

Correct answer:

Acetylases

Explanation:

The correct answer is acetylases. DNA can be directly methylated by methylases, mended during DNA repair by ligases, uncoiled by topoisomerases, and replicated by polymerases. However, DNA cannot be acetylated. Epigenetic associated-acetylation occurs only on histones to determine the chromatin state of a specific region. 

Example Question #3 : Help With Enzyme Types

What is the name of the class of enzymes that permit a phospholipid in the cellular membrane to move from facing the exoplasm (outside of the cell) to the cytosol (cellular interior)?

Possible Answers:

Phospholipases

Flippases

Floppases

Kinases

Migratases

Correct answer:

Flippases

Explanation:

Flippases use ATP to permit membrane lipids to reorient themselves in the cellular membrane, specifically in the direction from extracellular to intracellular facing. Floppases catalyze the reverse movement: intracellular to extracellular. Migratases are not a class of enzyme. Phospholipases and kinases catalyze other types of reactions and certainly can act on lipids, but not this particular lipid movement. 

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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