SAT II Biology E : Molecular Biology

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

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Example Questions

Example Question #6 : Dna, Rna, And Proteins

At what point does transcription occur in relation to gene expression?

Possible Answers:

It is the last step in this process

Transcription is a process that only occurs in eukaryotes

It is the first step

Transcription is unrelated to gene expression

It is the step following translation

Correct answer:

It is the first step

Explanation:

Transcription is the first process of gene expression and happens before translation.

Example Question #7 : Dna, Rna, And Proteins

What happens when one of the three codons of UAG, UAA, or UGA reach the A site on a ribosome that is helping facilitate translation?

Possible Answers:

Initiation 

Elongation

Processing

Termination

Propagation 

Correct answer:

Termination

Explanation:

UAG, UAA, and UGA are stop codons so when they enter the A site of a ribosome they will initiate the termination of translation.

Example Question #8 : Dna, Rna, And Proteins

In eukaryotes, translation of mRNA into a polypeptide is performed by what type of ribosome if the polypeptide is to be secreted from the cell?

Possible Answers:

A ribosome bound to the rough endoplasmic reticulum

A ribosome in the fluid of the nucleus

Cytosolic ribosome

A ribosome bound to the smooth endoplasmic reticulum

A ribosome bound to the plasma membrane

Correct answer:

A ribosome bound to the rough endoplasmic reticulum

Explanation:

The correct answer is a ribosome bound to the rough endoplasmic reticulum. The rough endoplasmic reticulum is covered with bound ribosomes, giving it its “rough” appearance. Proteins that are to be secreted from the cell are translated by ribosomes in the rough ER before moving through the Golgi apparatus and eventually ending up in a vesicle to be secreted from the cell. There are no ribosomes found in the nucleus, bound to smooth ER, or bound to the plasma membrane.

Example Question #9 : Dna, Rna, And Proteins

Which of the following mutations is a single nucleotide base pair change that results in a codon for a different amino acid?

Possible Answers:

Nonsense mutation

Deletion

Insertion

Silent mutation

Missense mutation

Correct answer:

Missense mutation

Explanation:

A missense mutation is a type of point mutation (single base pair change) that alters the codon to the creation of a different protein.   

A silent mutation is also a point mutation with a change in one base pair, but with the resulting strand still coding for the same protein (hence the term "silent"). 

A nonsense mutation changes a codon from coding for an amino acid to coding for termination of the protein. The protein may or may not still be functional depending on how much of it is terminated when the mutation occurs.

An insertion is a mutation in which one or more base pairs is added to the coding sequence. Unless the insertion is in a multiple of three (preserving the frame because a codon is made up of three base pairs), it results in a "frame shift" that alters the reading frame of the codons to the right, causing it to code for a different set of proteins.

A deletion is another type of frame shift mutation, in which a base pair (or more) is deleted from the coding sequence, altering the reading frame to code for different proteins in many cases. As with insertions, if the deletion is in a multiple of 3, the frame is preserved as each codon consists of 3 base pairs.

Example Question #10 : Dna, Rna, And Proteins

Disulfide bonds can add stability to the structure of a protein. The formation of disulfide bonds occurs in the formation of what level of protein structure?

Possible Answers:

Quaternary

Secondary

Primary

Tertiary

During translation

Correct answer:

Tertiary

Explanation:

The correct answer is "tertiary." Translation is a process performed by ribosomes to link amino acids together in a chain, and the order of the amino acids is based on a code from mRNA. The order of the amino acids in the chain is the primary structure. The secondary structure is the folding in that chain, mainly based on hydrogen bonds between parts of the chain and the surrounding water molecules. The tertiary structure is the actual three-dimensional structure of the protein. Disulfide bonds are covalent bonds between cysteine residues and are stronger than hydrogen bonds and give a stable, three-dimensional structure to what was originally just a chain of amino acids.

Example Question #21 : Molecular Biology

Which of the following most accurately describes the primary structure of a protein?

Possible Answers:

The non-covalent interactions between multiple protein subunits which come together to form a larger protein

The alpha helicies of the protein

The hydrogen bonds between amino acids in the protein

The linear amino acid sequence of the protein

The final three-dimensional structure of the protein

Correct answer:

The linear amino acid sequence of the protein

Explanation:

The primary structure of a protein is simply the linear amino acid sequence from which the protein is made. "Secondary structure" refers to the folding and coiling of this single strand as it interacts with itself, forming hydrogen bonds between amino acids of that strand. Alpha helices and beta-pleated sheets are two different types of secondary structures that can be formed by hydrogen-bonding between amino acids of a protein sequence that has folded over onto itself. "Tertiary structure" refers to the final three-dimensional structure of a single protein subunit. "Quaternary structure" refers to the non-covalent interactions between multiple protein subunits which come together to form a larger protein.

Example Question #22 : Molecular Biology

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

Possible Answers:

Ribozymes

Lyases

Transferases

Hydrolases

Spliceosomes

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 #1 : Enzymes

Which of the following statements about enzymes is true?

Possible Answers:

Enzymes are lipids.

Enzymes work best only at certain temperatures.

Enzymes will work at any pH value.

Enzymes are useful for slowing down reactions in living things.

Correct answer:

Enzymes work best only at certain temperatures.

Explanation:

Enzymes have an "optimal temperature," or best temperature that they work at. If that temperature is below or above its optimal temperature, the enzyme will decrease in activity; if the temperature change is great enough, the enzyme could even denature (no longer work).

Example Question #2 : Enzymes

Cellular respiration involves a series of chemical reactions. Which of the following is a primary way that enzymes affect these reactions?

Possible Answers:

They take the place of oxygen as a reactant

They change the location of the reactions in the cell

They decrease the pH of the products

They increase the rate of reactions

Correct answer:

They increase the rate of reactions

Explanation:

The questions is asking how enzymes affect reactions. The function of an enzyme is to speed up chemical reactions, which will increase the overall rate of the reaction, thus "increasing the rate of the reaction" is the correct answer. 

Example Question #3 : Enzymes

The role of an enzyme in a chemical reaction is to change which of the following?

Possible Answers:

The temperature at which the reaction occurs

The activation energy of the reaction

The type of reaction

The pH at which the reaction occurs

Correct answer:

The activation energy of the reaction

Explanation:

The function of an enzyme is to speed up chemical reactions. They do this by lowering the activation energy, which is the minimum energy that must be available for a chemical reaction to occur. If the energy required is lowered, the reaction can go faster. Thus the correct answer is an enzyme changes "the activation energy of the reaction."

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