GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Protein Functions

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

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Example Questions

Example Question #1 : Help With Protein Functions

The 5' cap on eukaryotic mRNA molecules is recognized by which of the following proteins?

Possible Answers:

eIF4e

PABP

RNA polymerase

40s ribosomal subunit

Correct answer:

eIF4e

Explanation:

The 5' cap is recognized by the important translation factor eIF4e. Once bound, eIF4e helps transport the mRNA molecule to the ribosome and facilitates bonding to the ribosomal machinery.

The 3' poly-A tail is recognized by PABP. RNA polymerase is involved in transcription, not translation. The 40s ribosomal subunit is recruited by the initiation complex (including eIF4e, PABP, and various other translation factors).

Example Question #2 : Help With Protein Functions

When conducting a stain of chromosomes, certain regions along the chromosome will stain more darkly than the rest. This is due to the fact that these regions are more tightly condensed. What is the functional outcome of having one region more condensed (heterochromatin) than the rest (euchromatin)?

Possible Answers:

Heterochromatin unpacking requires many ATP and is energetically expensive. 

Heterochromatin is transcribed at a high frequency because there are a high number of genes in a small area. 

Heterochromatin is not transcribed/is transcribed at a lower rate because euchromatin saturates all available polymerase. 

Heterochromatin is typically not transcribed/transcribed at a lower rate because the tight packing limits accessibility to polymerases.

Heterochromatin does not contain any genes and is a structural component of the chromosome. 

Correct answer:

Heterochromatin is typically not transcribed/transcribed at a lower rate because the tight packing limits accessibility to polymerases.

Explanation:

Heterochromatin often contains simple, repetitive sequences, and although it cannot be said that it is completely void of coding sequences, it is not typically transcribed. The tight wrapping prevents polymerase from accessing the strand, and euchromatin typically contains the regions that get transcribed. Thus, heterochromatin is though to contain repressed or inactive genes. 

Example Question #3 : Help With Protein Functions

Small GTPases are important molecular switches and signaling pathways. What proteins are responsible for promoting the activation of these small GTPases?

Possible Answers:

Kinases 

Phosphatases

Nicotinamide adenine dinucleotide

Guanine nucleotide exchange factors 

Guanine triphosphate

Correct answer:

Guanine nucleotide exchange factors 

Explanation:

The correct answer is guanine nucleotide exchange factors. In order to activate small GTPases and subsequently stimulate downstream pathways, guanine nucleotide exchange factors bind inactive GTPases and cause the release of guanine diphosphate (GDP). This allows guanine triphosphate (GTP) to bind and active the GTPase. 

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

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