GRE Subject Test: Biology : Understanding Protein and Enzyme Function

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

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Example Questions

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Example Question #1 : Understanding Protein And Enzyme Function

How do enzymes speed up reactions?

Possible Answers:

By providing additional energy to the system

By altering the net change in free energy of the reaction

By increasing the substrate concentration

By lowering the activation energy required to begin 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 #2 : 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 orients the substrates so they can react

It increases the amount of products made

It lowers the activation energy of a reaction

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 #3 : Understanding Protein And Enzyme Function

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

Possible Answers:

Increasing the forward rate of a reaction

Making a reaction more exothermic

Decreasing the activation energy for a reaction

Increasing the reverse rate of 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.

Example Question #4 : Understanding Protein And Enzyme Function

What is the group of proteins needed for cell synthesis in bacteria called?

Possible Answers:

Replisome

Chromosome

Spliceosome

TATA box

Cytostome

Correct answer:

Replisome

Explanation:

The replisome is coded for by essential genes passed between bacteria. Without these proteins, a bacterial cell cannot form more cells. "-some" stands for a collection of proteins that function together, and "repli-" for replication. The TATA box is a DNA sequence involved in the indication of the start of a gene, chromosomes are collected strands of genetic material, the spliceosome removes introns from pre-mRNA, but this, along with all post translational modification, only occurs in eukaryotes. The cytosome is the part of the cell that is specialized for phagocytosis.

Example Question #1 : Understanding Protein And Enzyme Function

After an unknown compound is added to an enzyme-mediated reaction mixture, the enzyme rate is reduced but  remains constant. Which of the following best explains this situation?

Possible Answers:

The unknown compound is a competitive inhibitor

The pH of the solution was changed by the unknown compound and deactivated the enzyme

The enzyme has been noncompetitively inhibited

Cannot be determined from the given information

The unknown compound cooled the solution, thus reducing the reaction rate

Correct answer:

The enzyme has been noncompetitively inhibited

Explanation:

The Michaelis-Menten constant  is temperature and pH dependent. It is the substrate concentration at which the rate is half of . Noncompetitive inhibitors alter the shape of an enzyme, slowing down the reaction rate without affecting . Competitive inhibitor bind to enzyme active sites, increasing the .

Example Question #6 : Understanding Protein And Enzyme Function

The Gila monster, H. suspectum, produces a neurotoxic venom containing helothermine, which causes lethargy and partial paralysis of the limbs. Considering that this toxin partially inhibits voluntary muscle contraction, which of the following is the most likely mechanism?

Possible Answers:

It inhibits acetylcholine transmission in the spinal cord

It attacks neural synapses in the brain stem

It degrades myelin sheaths in the motor cortex

It blocks  gates in striated muscle cells

It inhibits  channels in the cerebellum

Correct answer:

It inhibits  channels in the cerebellum

Explanation:

Helothermine is a peptide toxin that inhibits calcium channels in the cerebellar granule cells. The cerebellum is the part of the brain that controls voluntary muscle movements such as those in the limbs, and the toxin must be inhibiting very specifically to cause those two symptoms and not total paralysis or other problems.

Example Question #7 : Understanding Protein And Enzyme Function

Proteins have many functions. Which of the following can be functions of proteins?

I. Enzymes

II. Transcriptional regulators

III. Structural proteins

IV. Hormones 

Possible Answers:

I, III, and IV

I, II, and III

I, II, III, and IV

I and II

I, III, IV

Correct answer:

I, II, III, and IV

Explanation:

Proteins serve all of these functions and many more. Most enzymes are proteins, which help to catalyze spontaneous reactions. Ribozymes can also serve this function but are instead made out of RNA. Proteins can act as transcriptional regulators which can turn on or off gene transcription. Structural proteins, such as actin, can help to maintain the shape of a cell. Other small proteins, such as insulin, can act as hormones which can diffuse throughout the body relaying important messages. 

 

Example Question #2 : Understanding Protein And Enzyme Function

Enzymes come in many shapes and sizes and serve various functions. Which of the following are characteristics of enzymes?

I. Allow non-spontaneous reactions to occur

II. Bring substrates together in the proper orientation for catalysis

III. Reduce the activation energy of the reaction

IV. Reduce the free energy change of reaction

Possible Answers:

II and IV

I, II, III, and IV

II, III, and IV

II and III

III only

Correct answer:

II and III

Explanation:

Enzymes are capable of many things but they are not able to help facilitate non-spontaneous reactions. An enzyme can however help spontaneous reactions occur much faster. Enzymes help catalyze reactions by orienting substrates in the necessary positions for reaction. Without enzymes, substrates would have to bump into each other with the exact necessary orientation and energy, which is very rare. Enzymes are capable of lowering the activation energy of a reaction but have no effect on the overall free energy change of a reaction; recall the distinction between kinetics and thermodynamics.

Example Question #9 : Understanding Protein And Enzyme Function

Which of the following are true about enzyme inhibition?

I. Enzymes can be inhibited by end-products of that enzymatic pathway

II. Competitive inhibitors can lower an enzymes 

III. Non-competitive inhibitors inhibit enzyme action by binding to a site other than the active site

IV. Non-competitive inhibitors can lower an enzymes 

Possible Answers:

I, and II

I, and IV

I, II, and IV

I, III, and IV

I, II, and III

Correct answer:

I, III, and IV

Explanation:

Enzymes can be inhibited by end products of an enzymatic pathway. This is illustrated in the case of ATP acting as an inhibitor of enzymes found within the pathway for ATP production. This prevents the overabundance of a certain end-product. Competitive inhibitors do not lower an enzymes . Maximal velocity can still be achieved in the presence of a competitive inhibitor, but it requires a higher concentration of substrate to do so. Non-competitive inhibitors can lower an enzymes . This is because non-competitive inhibitors bind to sites other than the active site, known as allosteric binding sites.

Example Question #10 : Understanding Protein And Enzyme Function

Which of the following statements about the general roles and properties of biological enzymes is not true?

Possible Answers:

Enzymes are consumed and depleted over the course of a reaction.

Biological catalysts do not have to be proteins.

Enzymes lower the activation energy of a reaction.

Enzymes do not alter the equilibrium of the reaction. 

Enzymes increase the reaction rate.

Correct answer:

Enzymes are consumed and depleted over the course of a reaction.

Explanation:

Enzymes are not consumed or used up during a reaction, rather they simply increase the rate of reaction by making it "easier" for the reaction to occur, i.e. lowering the activation energy. Equilibrium is not altered by the presence of an enzyme. There are examples of catalytic RNA molecules (ribosomes) and therefore biological catalysts are not always proteins. 

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