GRE Subject Test: Biology : Macromolecules

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

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Example Questions

Example Question #1 : Understanding Protein And Enzyme Function

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

Possible Answers:

Replisome

TATA box

Chromosome

Spliceosome

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 #12 : Proteins

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 cooled the solution, thus reducing the reaction rate

The enzyme has been noncompetitively inhibited

The unknown compound is a competitive inhibitor

Cannot be determined from the given information

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

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 #1 : 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 blocks  gates in striated muscle cells

It degrades myelin sheaths in the motor cortex

It inhibits  channels in the cerebellum

It attacks neural synapses in the brain stem

It inhibits acetylcholine transmission in the spinal cord

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 #2 : 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, IV

I, II, and III

I, III, and IV

I and II

I, II, III, and 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 #11 : Macromolecules

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, III, and IV

II and IV

III only

II and III

I, II, III, and IV

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 #16 : Proteins

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, III, and IV

I, II, and III

I, and II

I, II, and IV

I, and IV

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 #1 : 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 increase the reaction rate.

Enzymes lower the activation energy of a reaction.

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

Biological catalysts do not have to be proteins.

Enzymes do not alter the equilibrium of the reaction. 

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. 

Example Question #11 : Understanding Protein And Enzyme Function

The activity of certain enzymes can be modulated via effector binding to __________ sites; regulation at these sites often results in a conformational changes that alters the activity level of the enzyme either positively or negatively without the effector binding to the active site.

Possible Answers:

active

competitive 

inhibitory

kinase

allosteric

Correct answer:

allosteric

Explanation:

The definition of allosteric enzyme regulation is that a cofactor or molecule binds and interacts with a site on the enzyme other than the active site. This often changes something about the shape of the enzyme which changes something about its interaction with its substrate, thus modulating how active the enzyme is.

Example Question #12 : Understanding Protein And Enzyme Function

I. Cytochrome c oxidase, an important enzyme in the electron transport chain, uses copper ions as cofactors.

II. Cofactors are always metal ions, such as iron and copper.

III. An enzyme will have a binding site specific for one type of cofactor.

IV. Some cofactors can be formed from vitamins C, B12, and K, and these cofactors then serve to facilitate electron transport in many biological processes. 

Possible Answers:

I, III, and IV

I, II, and III

I only

II and III

I and IV

Correct answer:

I and IV

Explanation:

Cofactors are not always metal ions, nor are enzymes limited to interactions with a single cofactor. Cofactors can be metal ions, but they can also be organic molecules, and an enzyme may be able to bind and be altered by many of them. The other two statements are true. 

Example Question #12 : Macromolecules

When presented with its ligand, glutamate, a metabotropic glutamate receptor (mGluR) can do any of the following except __________.

Possible Answers:

open to permit passage of sodium ions through the channel pore

modulate transcription factor activation

activate the pathway that results in PKC activation

change conformation to go from inactive to active

trigger an increase in intracellular calcium ion concentration

Correct answer:

open to permit passage of sodium ions through the channel pore

Explanation:

The key here is knowing that metabotropic receptors are NOT ion channels. They exert their effects through downstream signaling cascades. Ions cannot travel through a metabotropic receptor.

All other answers are potential outcomes of activating an mGluR.

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