GRE Subject Test: Biology : Macromolecules

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

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Example Questions

Example Question #21 : Macromolecules

Once a G-protein coupled receptor (GPCR) has bound to its ligand, which of the following steps allows the  subunit to dissociate from the receptor and trigger downstream cascades?

Possible Answers:

Degradation of the GPCR's C-terminal tail that is bound to the  unit

None of these

Exchanging the G-protein's association with a magnesium ion for a calcium ion

Exchanging the G-protein's bound ADP for an ATP

Exchanging the G-protein's bound GDP for a GTP

Correct answer:

Exchanging the G-protein's bound GDP for a GTP

Explanation:

The G-proteins associated with the intracellular terminal of a GPCR dissociate when the change in conformation of the G-protein allows for a GTP to replace a GDP bound to the G-protein. ATP and ions are not at play here, nor is there degradation of the receptor's intracellular tail. It is the binding of GTP alone that triggers the cascading results of the protein's activation.

Example Question #22 : Macromolecules

Toll-like receptors (TLRs) are known for their role in innate immunity in humans and in many other organisms. How do these receptors induce downstream signaling to induce an innate immune response? 

Possible Answers:

Recognition of pathogen-associated molecular patterns (PAMPs)  

Recognition of coagulation factors (platelet clotting factors)

Recruitment of macrophages

Recognition and dimerization of integrins

Recruitment of natural killer cells

Correct answer:

Recognition of pathogen-associated molecular patterns (PAMPs)  

Explanation:

TLRs are transmembrane receptors that have an extracellular leucine-rich region that recognize PAMPs. Recognition of a pathogen factor causes the intracellular toll-interleukin-1 domain to bind adaptor proteins to induce expression of genes responsible for initiating an innate immune response. 

Example Question #23 : Macromolecules

Paracrine signaling refers to which type of cell signaling?

Possible Answers:

Cell signaling across a synapse

Same cell signaling

Long range cell signaling

Intracellular signaling

Close range cell signaling 

Correct answer:

Close range cell signaling 

Explanation:

Paracrine signaling refers to close range cell to cell signaling. This is different from endocrine signaling in which signaling molecules (hormones) are released into the blood stream in order to communicate with distant cells.

Autocrine signaling is a type of signaling in where the signaling molecule and the receptor for that messenger are found on the same cell. Cell signaling across a synapse is called synaptic signaling. 

Example Question #24 : Macromolecules

Which of the following requires a carrier protein in order to be transported through the bloodstream?

Possible Answers:

Glycine

Sucrose

ATP

Steroid

Correct answer:

Steroid

Explanation:

Blood is an aqueous solution and will easily dissolve polar, hydrophilic molecules. Nonpolar molecules, however, do not easily exist in this solution and require a bound polar group, such as a carrier protein, to exist in equilibrium.

Proteins, carbohydrates, and nucleic acids all contain polar groups, allowing them to dissolve in the blood. Lipids, however, are nonpolar and require transport proteins. Steroids are a class of lipids and will require protein assistance for transport in the blood.

Sucrose is a carbohydrate, glycine is a polar amino acid, and ATP is a polar nucleic acid derivative.

Example Question #25 : Macromolecules

Which of the following molecules is amphipathic?

Possible Answers:

Glutamate

Maltose

Triglyceride

Phospholipid

Correct answer:

Phospholipid

Explanation:

Amphipathic molecules contain both polar and nonpolar regions, making them an extremely diverse class with an array of functions. For example, bile is an amphipathic molecule whose nonpolar region interacts with fats and whose polar region interacts with the aqueous environment of the small intestine.

Most lipids are entirely nonpolar and hydrophobic. Phospholipids, however, are formed from a glycerol molecule bound to two hydrophobic fatty acid tails and a hydrophilic phosphate head. This structure allows phospholipids amphipathic properties. Most notably, phospholipids are able to interact with the aqueous environments in the cell cytosol and extracellular environment, while maintaining the hydrophobic region of the cell membrane that acts as a semipermeable barrier.

Triglycerides are considered nonpolar. Glutamate is an acidic amino acid with highly polar properties. Maltose is a six-carbon sugar (carbohydrate) and is highly polar.

Example Question #26 : Macromolecules

Which of the following lipid classifications has the primary purpose of storing energy for the body?

Possible Answers:

Glycolipids

Glycerolipids

Glycerophospholipids

Sterols

Correct answer:

Glycerolipids

Explanation:

Lipids have a variety of functions in the human body, one of which is the storage of energy for later use. This function is accomplished by triglycerides (also called triacylglycerols), which belong to the class of glycerolipids.

Example Question #27 : Macromolecules

Fatty acids can vary in length. Which of the following fatty acids chains cannot not be synthesized in the human body?

Possible Answers:

A twenty-four-carbon fatty acid chain

A nineteen-carbon fatty acid chain

A fourteen-carbon fatty acid chain

An eighteen-carbon fatty acid chain

A twelve-carbon fatty acid chain

Correct answer:

A nineteen-carbon fatty acid chain

Explanation:

Fatty acids synthesized in the human body always have an even number of carbon atoms usually between 12 and 28. Odd-numbered fatty acid chains will occasionally be found in plants and marine animals.

Example Question #28 : Cell Biology

A phospholipid contains which of the following components?

I. Fatty acids

II. Phosphate

III. Sulfate

IV. Glycerol

Possible Answers:

I, II, and IV

II and IV

I, III, and IV

I and II

I and IV

Correct answer:

I, II, and IV

Explanation:

A phospholipid is made up of two fatty acids and a phosphate group with an R-group attached to a glycerol backbone. The phosphate group allows for one end of the molecule to be polar while the fatty acids allow for the other part to be nonpolar. Phospholipids are a major component of the bilayered cellular membrane 

Example Question #28 : Macromolecules

What factor determines whether humans are capable of digesting a polysaccharide?

Possible Answers:

The linkage between monomers

The branching pattern of the polysaccharide

The number of carbons in the carbohydrate

The number of monomers in the polysaccharide

Correct answer:

The linkage between monomers

Explanation:

Carbohydrate monomers (monosaccharides) can be joined together with either alpha or beta linkages. Humans have the enzymes necessary in order to break down alpha linkages, but not beta linkages. Cellulose is a polysaccharide in which the monomers joined together by beta linkages, so humans cannot digest cellulose. Some bacterial species are capable of cleaving these linkages and have developed symbiotic or mutualistic relationships with animals. These bacterial species inhabit the mammalian digestive tract, cleaving beta linkages and gaining protection from the outside environment.

The size and branching pattern of a carbohydrate do not affect its ability to be digested.

Example Question #2 : Understanding Carbohydrates

Which polysaccharide is the primary form of energy storage in plants?

Possible Answers:

Peptidoglycan

Glycogen

Cellulose

Starch

Correct answer:

Starch

Explanation:

The two most common polysaccharides found in plant cells are starch and cellulose. Starch is the primary source of energy storage, while cellulose is used to construct the plant's cell walls.

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