GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Cellular Structures and Functions

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

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Example Question #1 : Cell Membrane And Cell Wall

Which type of membrane protein spans the entire width of the membrane?

Possible Answers:

Glycolipid

Glycoprotein

Carrier protein

Peripheral protein

Correct answer:

Carrier protein

Explanation:

Integral proteins are proteins that connect the inside of the cell to the outside by traversing the phospholipid bilayer. Carrier proteins, for example, allow substances to pass the membrane by letting them cross through channels.

Example Question #1 : Cellular Structures And Functions

Which of the following typically describes molecules that easily diffuse through the plasma membrane (lipid bilayer) of animal cells?

Possible Answers:

Polarity, size, and lipid solubility coefficient do not affect a molecule's ability to diffuse through a lipid bilayer

Nonpolar, large in size, and have a large lipid solubility coefficient

Polar, small in size and have a large lipid solubility coefficient

Nonpolar, small in size, and have a large lipid solubility coefficient 

Small in size, have a small lipid solubility coefficient, but polarity does not affect diffusion rates

Correct answer:

Nonpolar, small in size, and have a large lipid solubility coefficient 

Explanation:

The correct answer is nonpolar, small in size, and have a large lipid solubility coefficient. The center of the lipid bilayer is nonpolar and composed of fatty acid chains; therefore, nonpolar molecules diffuse through more easily. Diffusion does not use transport proteins to shuttle molecules through the lipid bilayer, so smaller molecules are able to diffuse more easily between the phospholipids that comprise the bilayer. Finally, a higher lipid solubility coefficient means that the molecule is more soluble in lipids and less soluble in aqueous solutions. A low lipid solubility means that the molecule is more aqueous-soluble than lipid-soluble.  

Example Question #1 : Cell Biology

Dense specialized plasma membrane microdomains that cluster cholesterol, sphingolipids, and protein receptors, and are also sites of receptor trafficking and assembly of signal molecules, are called __________.

Possible Answers:

micelles 

phosphoinositides

None of the other answers

lipid rafts

integrins

Correct answer:

lipid rafts

Explanation:

The correct answer is lipid rafts. Lipid rafts are more dense, less fluid domains of the plasma membrane. In addition to clustering cholesterol and sphingolipids, large transmembrane-domain proteins also localize here.

Integrins are transmembrane receptors, micelles are small lipid spheres, and phosphoinositides are a family of lipid molecules. 

 

Example Question #1 : Cell Biology

Many retroviruses, including (human immunodeficiency virus) HIV and other lentiviruses, generally bind what structure on the plasma membrane of vertebrate cells?

Possible Answers:

Phosphatidylcholine

Oligosaccharides

Glycoproteins

Cholesterol

Lipopolysaccharides

Correct answer:

Glycoproteins

Explanation:

The correct answer is glycoprotein. HIV and many lentiviruses, which are also retroviruses, bind the CD4 glycoprotein. Lipopolysaccharides are found in bacteria, not vertebrates. Oligosaccharides are sugar polymers and generally function in cell-cell signaling. Cholesterol and phosphatidylcholine are components of the plasma membrane, not necessarily extracellularly exposed. The latter two help define the shape and rigidity of the plasma membrane. 

Example Question #1 : Cell Biology

What is the name for dense microdomains of the plasma membrane that are enriched in cholesterol and sphingolipids and are centers for signal molecule assembly and receptor trafficking?

Possible Answers:

Lipid rafts

Phospholipid bilayer

Endosomes

Micelles

None of these

Correct answer:

Lipid rafts

Explanation:

The correct answer is lipid rafts. These are dense portions of the phospholipid bilayer that are slightly thicker due to the increased presence of cholesterols and sphingolipids and are hubs for many processes. Micelles are single layer phospholipids that form spheres. Endosomes are intracellular compartments that are often important for transport of materials to the plasma membrane. 

Example Question #6 : Cell Membrane And Cell Wall

Which polymer is the primary component of plant cell walls?

Possible Answers:

Phospholipids

Cellulose

Chitin

Peptidoglycan

Correct answer:

Cellulose

Explanation:

Cell walls can vary in composition based on what organism is being discussed. In the case of plant cells, cellulose is the primary component. Bacteria use peptidolgycan in their cell walls, and fungi use chitin.

Example Question #7 : Cell Membrane And Cell Wall

Which of the following encloses a plant cell in a rigid framework and cannot be digested by humans?

Possible Answers:

Cell membrane

Nuclear envelope

Cell wall

Cytoskeleton

Plasma membrane

Correct answer:

Cell wall

Explanation:

The cell wall is composed of cellulose and encloses a plant cell in a rigid framework. Plant cells have both cell membranes and cell walls. Plant cell walls cannot be digested by humans due to the beta glycosidic bond in its structure. The cell membrane forms the outer boundary of a cell and isolates cell contents from the environment. The cell membrane regulates movement of materials into and out of the cell. The cell membrane is also referred to as the plasma membrane. The nuclear envelope regulates movement into and out of the nucleus. The cytoskeleton gives shape and support to cells and is typically involved in cell movement.

Example Question #1 : Cell Membrane And Cell Wall

An unknown molecule is identified by a researcher. He notices that the structure is abundantly found in cell walls of bacteria. Upon further analysis, which of the following will be observed by the researcher?

Possible Answers:

Its synthesis occurs in the cytoplasm only

More than one of these are true

It has repeating units of glucose derivatives

It has a phosphate head group

Correct answer:

It has repeating units of glucose derivatives

Explanation:

The most abundant molecule in bacterial cell walls is peptidoglycan. Recall that peptidoglycan contains repeating NAG-NAM units, which are made from glucose. In addition, peptidoglycan also has peptides attached to these oligosaccharides. These units form bonds with each other to create a strong and a robust cell wall. Peptidoglycan is synthesized in cytoplasm and on cell membrane before finally being transported to the cell wall.

Recall that phosphate head groups are found on phospholipids, which make up cell membranes (not cell walls).

Example Question #9 : Cell Membrane And Cell Wall

Gram positive bacteria have __________ cell wall(s) and Gram negative bacteria have __________ cell wall(s).

Possible Answers:

one . . . one

one . . . two

two . . . two

two . . . one

Correct answer:

one . . . one

Explanation:

Gram stain is a laboratory technique used to distinguish bacteria. Gram positive and Gram negative bacteria are distinguished based on their cell walls. Gram positive bacteria have a single thick cell wall (outside its cell membrane). Upon Gram staining, these bacteria will hold the Gram stain because of their thick cell wall. The Gram negative bacteria also have only one cell wall; however, it is a lot thinner and is sandwiched between two cell membranes. The thin nature of the cell wall makes it easier for the Gram stain to leak out of the bacterial cell.

Example Question #1 : Cell Biology

Which of the following is true regarding cell walls?

I. They are only found in bacteria that can be Gram stained

II. Some organisms that have cell walls can undergo photosynthesis

III. They expand when a cell is placed in a hypoosmolar environment

Possible Answers:

I, II, and III

I and III

II and III

II only

Correct answer:

II only

Explanation:

Cell walls are robust structures found in most bacteria, fungi, and plants. Gram stain depends on the properties of the cell wall. Some bacteria don’t stain well with Gram stain (such as Mycobacterium that causes tuberculosis) because of unique cell walls (not lack thereof). Fungal and plant cell walls are also made up of polysaccharides. Fungal cell walls contain a special molecule called chitin whereas plant cell walls contain cellulose. Recall that plants obtain energy from sunlight via photosynthesis; therefore, photosynthetic organisms do contain cell walls.

One of the biggest function of a cell wall is to prevent cellular swelling. Recall that a cell placed in a hypoosmolar solution will swell due to the influx of water; however, this cellular swelling will not occur in a cell containing cell wall because the robust cell wall prevents contents of the cell from expanding, thereby preventing cellular lysis.

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