SAT II Biology M : Enzymes

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

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Enzymes

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

Possible Answers:

Lyases

Hydrolases

Spliceosomes

Ribozymes

Transferases

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 #2 : Enzymes

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

Possible Answers:

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.

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

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.

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

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

All of these

An enzyme is not depleted in a reaction.

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 #3 : Enzymes

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

Topoisomerase

ATP synthase

tRNA synthetase

Peptidyl transferase

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 #4 : Enzymes

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 primase

Ligase

DNA polymerase I

DNA polymerase III

DNA polymerase II

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).

Learning Tools by Varsity Tutors

Incompatible Browser

Please upgrade or download one of the following browsers to use Instant Tutoring: