SAT II Biology M : Enzymes

Study concepts, example questions & explanations for SAT II Biology M

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Example Questions

Example Question #22 : Molecular Biology

Which is an example of a biological catalyst that is not a protein?

Possible Answers:

Ribozymes

Spliceosomes

Transferases

Hydrolases

Lyases

Correct answer:

Ribozymes

Explanation:

This question ultimately hinges on knowing the difference between ribozymes and spliceosomes because transferase, hydrolase, and lyase should all be recognized as proteins that function as enzymes. Transferase catalyzes reactions that facilitate the transfer of functional groups. Hydrolase works to catalyze hydrolysis reactions. Lyase works to catalyze reactions that break down double bonds. Spliceosomes are a unit of proteins and RNA that work to catalyze reactions that splice out introns in RNA to form mature mRNA ready for translation. Ribozymes are important because they also splice RNA into mRNA, but they do not have a protein component to them. The discovery of Ribozymes was a breakthrough in that it was the first evidence that not all enzymes are proteins.

Example Question #52 : Sat Subject Test In Biology

What is the role of DNA helicase in DNA replication and DNA transcription?

Possible Answers:

None of these

DNA helicase relieves the torsional strain and "supercoiling" that DNA undergoes during replication/transcription, and in doing so helps maintain the DNA double helix.

DNA helicase replaces the RNA primers with DNA nucleotides in DNA replication. Helicase has no use in DNA transcription.

DNA helicase disrupts the hydrogen bonding between the two strands of DNA and exposes the insides of the DNA helix, allowing for other enzymes to replicate or transcribe the single-stranded DNA.

DNA helicase binds Okazaki fragments to one another on the lagging strand, and helps create a unified strand of DNA. It has no use in DNA transcription.

Correct answer:

DNA helicase disrupts the hydrogen bonding between the two strands of DNA and exposes the insides of the DNA helix, allowing for other enzymes to replicate or transcribe the single-stranded DNA.

Explanation:

DNA helicase is an enzyme that is able to slip between the two strands of DNA and disrupt the hydrogen bonds that keep the DNA in the double helix structure. This disruption opens up the DNA helix, and exposes sections of DNA that can then be transcribed or replicated. As helicase moves down the double helix, the DNA reforms into a double helix since the enzyme is no longer blocking the hydrogen bonds.

Example Question #1 : Enzymes

Which of these is a key characteristic of all enzymes?

Possible Answers:

An enzyme reduces the amount of activation energy needed in a system for a certain chemical reaction to occur.

An enzyme catalyzes a reaction, allowing it to happen faster than it would without the enzyme.

An enzyme is not depleted in a reaction.

An enzyme is a protein product, usually created from 2 or more polypeptide chains. The structure of the enzyme determines the function of the enzyme.

All of these

Correct answer:

All of these

Explanation:

These are all definitive traits of an enzyme. Enzymes are proteins which are extremely helpful in speeding up certain reactions without being depleted by the reactions themselves (as such, they are catalysts for these reactions). Enzymes reduce the amount of energy needed for a reaction to occur, generally because they facilitate reactions by recognizing reactants and bringing them into contact with each other. This occurs when the reactants bind to certain parts of the enzyme (active sites), which causes the enzyme to change shape and bring the reactants into contact with each other (and then the reactants can bind to form the product). 

Example Question #31 : Molecular Biology

Which of the following enzymes is directly associated with polypeptide formation, and has the function of binding amino acids to each other at the ribosome?

Possible Answers:

Ligase

Peptidyl transferase

tRNA synthetase

Topoisomerase

ATP synthase

Correct answer:

Peptidyl transferase

Explanation:

Peptidyl transferase is the enzyme that works in conjunction with tRNA molecules to extend a growing polypeptide chain at the ribosome during translation. Ligase is not used at all in translation, nor is topoisomerase or ATP synthase. tRNA synthetase is used to bind the correct amino acids to corresponding tRNA molecules, but it is not used to extend the polypeptide at the ribosome.

Example Question #32 : Molecular Biology

Which of the following enzymes performs the critical function of removing RNA primers from DNA in DNA replication, and replacing the RNA with DNA?

Possible Answers:

DNA polymerase III

DNA polymerase I

DNA polymerase II

DNA primase

Ligase

Correct answer:

DNA polymerase I

Explanation:

While all the answer choices are important in DNA replication, only DNA Polymerase I performs this particular function. Ligase helps bind the newly replaced DNA nucleotides to the rest of the DNA strand. DNA polymerase III is the main synthesizing enzyme of DNA replication, and creates the majority of the DNA strand. DNA polymerase II is less well known than I and III, but it is believed to perform as a repair enzyme which removes incorrectly paired segments of DNA (which can then be filled back in by DNA polymerase I).

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