GRE Subject Test: Biology : Lab Techniques

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

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Example Questions

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Example Question #1 : Lab Techniques

To what power would a microscope magnify an object if the 10x low-power objective were in place and the microscope has a standard eyepiece?

Possible Answers:

10000x

1x

10x

100x

1000x

Correct answer:

100x

Explanation:

The occular, or eye piece, has a magnification power of 10x. If the 10x low-power objective were in place, the magnification would be multiplicative.

Example Question #2 : Lab Techniques

Which term is used to describe the smallest structure that can be seen by a light microscope?

Possible Answers:

Optotype

Index of refraction

Optical transmission

Visual acuity

Resolving power

Correct answer:

Resolving power

Explanation:

Optical transmission is the amount of light that passes through a laboratory specimen. It can be used to measure the concentration of components in the specimen. Optotype is the variable-sized type used in testing visual acuity. Visual acuity is a measure of the resolving power of the eye; the smallest type that can be seen at a distance. The index of refraction is defined as the speed of light in a vacuum divided by the speed of light in a medium. 

The resolving power of a light microscope is the smallest structure that can be seen, approximately 1 micrometer (a millionth of a meter) by the microscope.

Example Question #3 : Microscopy

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:

Occulars

Iris

Lens

Diaphgram

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 #3 : Lab Techniques

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

Possible Answers:

Phase plate

Magnetic field

Reticle

Lens

Laser

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 #4 : Lab Techniques

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

Possible Answers:

Reflection electron microscope 

Transmission electron microscope

Scanning electron microscope 

Retraction electron microscope 

Scanning transmission 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 #413 : Gre Subject Test: Biology

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

Possible Answers:

Separate the sample from other proteins

Allow for detection of the protein sample

Ensure that the primary antibody binds properly to the sample

Block any interfering noise coming from the membrane

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 #5 : Lab Techniques

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

None of the other answers

Electrophoretic mobility shift assay (EMSA)

Western blot 

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 

None of the other anwers

Visualize the proteins run on the gel 

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

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

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:

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

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

Requirement that the protein is denatured prior to 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 #1 : Understanding Page And Sds Page

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:

Four

One

Two

Three

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.

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