GRE Subject Test: Biology : GRE Subject Test: Biology

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

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Example Questions

Example Question #3 : Lab Techniques

When using a light microscope, the light waves that pass through or bounce off of a specimen are focused and magnified by which of the following?

Possible Answers:

Lens

Iris

Diaphgram

Occulars

Fine focus

Correct answer:

Lens

Explanation:

Light microscopes use lenses that range from 4x to 100x, are made of glass, and focus and magnify light rays.

The diaphragm regulates the amount of light that passes through an object being magnified. The iris controls the diameter of the beam of light entering the lens. The fine focus is used to move the objectives (lenses) to view objects clearly. The occulars are the lenses that one would look into to view the object. 

Example Question #1 : Lab Techniques

Which of the following is used to focus the electrons when using an electron microscope?

Possible Answers:

Magnetic field

Laser

Phase plate

Reticle

Lens

Correct answer:

Magnetic field

Explanation:

Electron microscopes use beams of electrons instead of light. The electrons are focused by magnetic fields rather than by lenses.

A phase plate is used with a light microscope to view details of objects characterized by differences in refractive index and, as such, have a difference in brightness or color. Tissues deep within the body can be imaged using the technique of multiphoton microscopy, in which photons are directed into tissues by an infrared laser. The reticle is a tiny grid pattern inserted into the eyepiece lens. It is used to make measurements of objects seen through the lens. 

Example Question #1 : Microscopy

Which of the following is not a type of the electron microscope?

Possible Answers:

Scanning transmission electron microscope 

Scanning electron microscope 

Reflection electron microscope 

Transmission electron microscope

Retraction electron microscope 

Correct answer:

Retraction electron microscope 

Explanation:

The incorrect answer is retraction electron microscope. Transmission electron microscope is the simplest type by using a high voltage electron beam to formulate an image. Scanning electron microscopes produces an image through a scanning electron beam. Reflection electron microscopes use an electron beam that scatters when it hits a specimen, the image is then compiled from the scattered electron pattern. Scanning transmission electron microscopes uses a thin ray of electrons that scatters through the specimen to resolve the image. 

Example Question #2 : Lab Techniques

When performing a western blot, what is the purpose of adding a secondary antibody?

Possible Answers:

Allow for detection of the protein sample

Block any interfering noise coming from the membrane

Separate the sample from other proteins

Ensure that the primary antibody binds properly to the sample

Correct answer:

Allow for detection of the protein sample

Explanation:

Typically, the secondary antibody is designed to have either a fluorescent or colorimetric tag to allow for detection. The primary antibody binds to the protein of interest, but (usually) does not have its own tag. The protein samples have already been properly separated during electrophoresis. Noise is blocked via various methods, but not by the secondary antibody. The secondary antibody does not influence the binding of the primary antibody. 

Example Question #1 : Electrophoresis And Blots

A student researcher overexpresses an exogenous protein in cell culture and wants to determine if that protein, is in fact, overexpressed. What technique would best demonstrate that this protein is expressed in these cells?

Possible Answers:

Northern blot

Southern blot

Electrophoretic mobility shift assay (EMSA)

Western blot 

None of the other answers

Correct answer:

Western blot 

Explanation:

The correct answer is Western blot. Western blots utilize antibodies to detect specific proteins in a cell lysate. Northern blots detect specific RNA within a sample, whereas Southern blots detect specfic DNA sequences within a sample. An EMSA detects whether or not a protein is active, and therefore can bind a specific sequence of DNA.  

Example Question #1 : Understanding Western Blots

After proteins are run on an SDS-PAGE gel, a transfer is executed. What is the purpose of the transfer in Western blot protocol?

Possible Answers:

Denature the proteins in the sample 

Move proteins from the SDS-PAGE gel to a nitrocellulose membrane

None of the other anwers

Probe the gel with an antibody to detect a protein of interest

Visualize the proteins run on the gel 

Correct answer:

Move proteins from the SDS-PAGE gel to a nitrocellulose membrane

Explanation:

After proteins are run on an SDS-PAGE gel and separated by size, they are transferred to a nitrocellulose membrane. This exposes the proteins so that an antibody can recognize and bind to the protein of interest. Once the antibody is bound, a fluorescent secondary conjugated antibody will facilitate the visualization of the protein of interest. 

Example Question #1 : Lab Techniques

Which of the following is not a similarity between enzyme-linked immunosorbent assays (ELISAs) and western blots, two common protein detection methods?

Possible Answers:

Requirement that the protein is denatured prior to detection

Information from the assays can be made quantitative with the right controls

Detection of protein using antibodies specifically generated against antigens

Tissue sample must be homogenized and the protein extracted to utilize the assay

Requirement of antibodies conjugated to a marker for detection

Correct answer:

Requirement that the protein is denatured prior to detection

Explanation:

The major difference between ELISA and western blot is the fact that ELISA detects naive protein in its original conformation, while western requires denaturation of the protein by SDS-PAGE prior to detection. This makes western blotting more stringent and better for quantification, although both assays can quantitatively assess protein levels if done properly. 

Example Question #411 : Gre Subject Test: Biology

A researcher is working with a protein that contains four subunits of differing molecular weights. If the researcher performs SDS-PAGE, how many distinct bands should he see on the gel?

Possible Answers:

Three

Four

One

Two

Correct answer:

Four

Explanation:

SDS-PAGE requires that proteins are denatured before they are run through the gel, typically by the addition of detergents and then heating the sample. Since the protein has four subunits that are all different molecular weights, we would see four distinct bands that represent the four subunits. If the subunits had the same molecular weight, we would only see one band.

Example Question #1 : Electrophoresis And Blots

Which of the following is a primary factor that dictates how far a protein will migrate during SDS-PAGE?

Possible Answers:

Size

Number of subunits

Degree of secondary structure

Degree of tertiary structure

Correct answer:

Size

Explanation:

The primary factor dictating how far a protein will migrate during SDS-PAGE is the size of the protein. One of the key features of SDS-PAGE is that the protein sample is denatured and covered in a detergent prior to being run through the gel. This essentially eliminates any complications from the degree of folding or the number of subunits. In fact, subunits will migrate according to their own molecular weights.

Example Question #411 : Gre Subject Test: Biology

Which of the following is true about SDS-PAGE?

Possible Answers:

The main ingredient in the gel is agarose

It requires a protein-denaturing gel


It is used to anaylze DNA fragments

Staining with ethidium bromide allows visualization of results

It separates proteins by charge

Correct answer:

It requires a protein-denaturing gel

Explanation:

SDS-PAGE requires a denaturing protein gel that separates proteins based on size. The primary ingredients are polyacrylamide and sodium dodecyl sulfate—SDS-PAGE refers to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In order to visualize the results, proteins separated via SDS-PAGE are transferred to a nitrocellulose membrane, where they are probed with antibodies for a specific protein of interest. 

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