GRE Subject Test: Biology : Cell Biology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

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Example Question #1 : Gre Subject Test: Biology

Which of the following is an example of the secondary structure of a protein?

Possible Answers:

Peptide bonding between amino acids

Hydrogen bonding between R groups

Disulfide bonds between cysteine residues

Hydrophobic interactions

Hydrogen bonding between an amine and carbonyl group

Correct answer:

Hydrogen bonding between an amine and carbonyl group

Explanation:

By definition, the secondary structure of a protein is the hydrogen bonding between the amine and carbonyl groups in the amino acid chain. This usually occurs in the form of alpha-helices or beta-pleated sheets.

The linear sequence of the amino acids formed by peptide bonds is the primary protein structure. Interactions of R groups determines the tertiary structure. These interactions can be in the form of disulfide bonds, hydrogen bonding, or hydrophobic interactions.

Example Question #1 : Proteins

Hemoglobin is a protein that consists of four subunits: two copies of the  and two copies of the  subunit. How many individual polypeptide chains are present in a fully folded molecule of hemoglobin?

Possible Answers:

Two

Four

Three

One

Correct answer:

Four

Explanation:

This question is primarily asking the difference between quaternary protein structure and lower levels of folding. In quaternary protein structure two or more folded polypeptide chains interact with one another to form a functional protein. In the case of hemoglobin, we are told that there are four subunits, indicating that there are four polypeptide chains. It does not matter that there are two copies of each subunit; they are each their own polypeptide chain. Subunits are folded independently first, then joined into quaternary structure by non-covalent intermolecular forces.

Example Question #2 : Cell Biology

What level of protein structure is determined only by hydrogen bonds?

Possible Answers:

Quaternary structure

Tertiary structure

Primary structure

Secondary structure

Correct answer:

Secondary structure

Explanation:

Secondary protein structure is exclusively dependent on hydrogen bonding.

Primary protein structure is established by the sequence of amino acid residues, joined by covalent peptide bonds at the ribosome. Once the primary structure is established, secondary structure arises as a result of hydrogen bonding between the backbones of the amino acids (not the functional groups). Secondary structures take the forms of alpha-helices or beta-pleated sheets, both of which can exist within a single molecule. Tertiary structure forms from hydrogen bonding between functional groups, hydrophobic interactions, and disulfide linkages. Quaternary structure can involve hydrogen bonding and other intermolecular forces and is present only when multiple polypeptides come together to form a single protein complex.

Example Question #2 : Macromolecules

What is the name of the bond that links amino acids together in protein primary structure?

Possible Answers:

Glycosidic bond

Phosphodiester bond

Peptide bond

Hydrogen bond

Correct answer:

Peptide bond

Explanation:

Amino acids are covalently linked to one another by peptide bonds. The carboxylic acid portion of an amino acid connects to the amino terminus of the other amino acid, producing water as a byproduct. Peptide linkages are formed in the ribosome complex and result in the primary structure of the protein, Later, hydrogen bonding between amino acids plays a key role in secondary and tertiary protein structure.

Glycosidic bonds link adjacent monosaccharides in a carbohydrate polymer. Phosphodiester bonds are catalyzed by DNA ligase and are used to join nucleotides together to build nucleic acid chains.

Example Question #1 : Gre Subject Test: Biology

An amino acid monomer at neutral pH will be found in what form?

Possible Answers:

Zwitterion

Positively charged

Negatively charged

Uncharged

Correct answer:

Zwitterion

Explanation:

At neutral pH an amino acid monomer will be found in the zwitterionic form in which there is a positive charge on the amino group and a negative charge on the carboxyl group. At very low an/or very high pH (less than 2 or greater than 12) there can be an overall negative or positive charge found on the amino acid, depending on the R-group.

Example Question #2 : Understanding Protein Structure

Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein __________ structure.

Possible Answers:

quaternary

tertiary

None of these

secondary

primary

Correct answer:

tertiary

Explanation:

Ionic bonds, disulfide bridges, hydrogen bonds and hydrophobic interactions are all examples of protein tertiary structure when they occur within a single polypeptide chain. However, if these interactions were to occur between separate polypeptide chains then they would be defining the quaternary structure of the protein. The linear sequence of amino acids within a protein makes up the primary structure. Protein secondary structure is defined by the localized three-dimensional structure of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha helices and Beta pleated sheets are examples of secondary structures. 

Example Question #2 : Gre Subject Test: Biology

The linear sequence of amino acids in a protein determines its __________ structure.

Possible Answers:

primary

tertiary

quaternary

atomic

secondary

Correct answer:

primary

Explanation:

The linear sequence of amino acids within a protein makes up the primary structure.  Protein secondary structure is defined by the localized three-dimensional structure of of amino acids. These localized structures are normally constructed through hydrogen bonding networks. Alpha-helices and beta-pleated sheets are examples of secondary structures.  Protein tertiary structure is defined by the longer range interactions between amino acids within a single polypeptide chain. These interactions include ionic bonds, disulfide bridges, hydrogen bonds, and hydrophobic interactions. Protein quaternary structure is defined by the interactions between polypeptide chains. This often occurs in the formation of dimers and higher multimers.

Example Question #3 : Proteins

How do enzymes speed up reactions?

Possible Answers:

By providing additional energy to the system

By lowering the activation energy required to begin the reaction

By increasing the substrate concentration

By altering the net change in free energy of the reaction

Correct answer:

By lowering the activation energy required to begin the reaction

Explanation:

Enzymes speed up reactions by lowering the energy required to begin the reaction (the activation energy). They do not have any direct effect on the change in free energy, nor do they provide extra energy to the system. Enzymes also cannot alter the substrate concentration. Catalytic action will never be able to influence the equilibrium constant or equilibrium concentrations of a reaction.

Example Question #1 : Understanding Protein And Enzyme Function

Which of the following is not typical of an enzyme?

Possible Answers:

It increases the rate of a reaction

It increases the amount of products made

It lowers the activation energy of a reaction

It orients the substrates so they can react

Correct answer:

It increases the amount of products made

Explanation:

Enzymes are used to increase the rate of a reaction. This is accomplished by lowering the activation energy required for substrates to react, often by altering the transition state. Enzymes do not, however, increase the amount of products formed; they simply help the equilibrium be reached more quickly. In other words, enzymes change the rate of a reaction, but not the equilibrium.

Example Question #1 : Understanding Protein And Enzyme Function

Which of the following will not result from enzymatic activity in a cell?

Possible Answers:

Making a reaction more exothermic

Increasing the reverse rate of a reaction

Increasing the forward rate of a reaction

Decreasing the activation energy for a reaction

Correct answer:

Making a reaction more exothermic

Explanation:

Although it may seem counterintuitive, both the forward and reverse reaction rates are sped up by an enzyme. Without this happening, more product would be created by the enzyme than normal, and enzymes DO NOT increase the amount of products created in a system. Enzymes also do not affect the enthalpy of a reaction, so making a reaction more exothermic is not an acceptable answer.

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