SAT II Biology E : Molecular Biology

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

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Example Questions

Example Question #1 : Enzymes

The reactants in an enzyme-catalyzed reaction are known as __________.

Possible Answers:

active sites

substrates

products

pHs

Correct answer:

substrates

Explanation:

A reactant is a substance that undergoes change during a reaction. During an enzyme reaction specifically, the reactant is called the substrate, as a substrate is the substance in which an enzyme acts on and changes. 

Example Question #5 : Enzymes

What can affect the productivity of an enzyme?

Possible Answers:

None of these

pH

Both pH and temperature

Temperature

Correct answer:

Both pH and temperature

Explanation:

Both pH and temperature can affect how productive an enzyme is. If an enzyme is functioning in an environment that is not at its optimal pH or optimal temperature, the enzyme's activity will decrease. 

Example Question #6 : Enzymes

Why are enzymes necessary for most cellular reactions?

Possible Answers:

Enzymes increase the temperature of the reaction.

They help reactions occur at a rate compatible with that necessary for sustenance of life.

Enzymes make it so reactions that are nonspontaneous occur spontaneously.

Enzymes supply the water necessary for biochemical reactions.

Correct answer:

They help reactions occur at a rate compatible with that necessary for sustenance of life.

Explanation:

An enzymes function is to speed up chemical reactions by lowering the activation energy. If our bodies did not have enzymes, the reactions would take place, but too slowly for our cells to adequately function.

Example Question #1 : Enzymes

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

Possible Answers:

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

None of these

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

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.

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 #2 : Enzymes

Which of these is a key characteristic of all enzymes?

Possible Answers:

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

All of these

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 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 #21 : Dna, Rna, And Proteins

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:

Peptidyl transferase

Ligase

ATP synthase

tRNA synthetase

Topoisomerase

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 #1 : 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:

Ligase

DNA polymerase I

DNA polymerase II

DNA polymerase III

DNA primase

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).

Example Question #7 : Enzymes

Many enzymes have sites on them where the binding of specific molecules will increase or decrease the activity of the enzyme. What is the name of this type of site?

Possible Answers:

Active site

Allosteric site

Catalytic site

Cofactor site

Binding site

Correct answer:

Allosteric site

Explanation:

The correct answer is "allosteric site." A molecule that binds to an enzyme's allosteric site induces a conformational change in the enzyme, decreasing or increasing the affinity of the enzyme’s binding sites to the substrate. The binding site binds and orients the substrate. The catalytic site lowers the activation energy of the reaction. The binding site and the catalytic site together make up the active site. Cofactors are parts of certain enzymes and are required for those enzymes to function.

Example Question #8 : Enzymes

If enzymes stop working, they have __________.

Possible Answers:

turned into a substrate 

reached their optimal temperature

reached their optimal pH

denatured

Correct answer:

denatured

Explanation:

Denature means to destroy the properties of a protein or other biological macromolecule. If an enzyme (which is a protein) stops working, it has denatured.

Example Question #1 : Dna Structure And Function

If a structural gene in an organism's genome is comprised of 29% guanine nucleotides, what percentage of the gene is comprised of cytosine nucleotides?

Possible Answers:

19%

42%

It cannot be determined from the given information.

29%

21%

Correct answer:

29%

Explanation:

This question is designed to catch a) students who are not reading the question carefully, and b) students unsure of which nucleotides pair with which.

The correct answer is 29%, because cytosine pairs with guanine in a 1:1 ratio. If you answered 21%, then you likely thought the question was more complex than it was.

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