GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Translation and Proteins

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

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Example Questions

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Example Question #1 : Help With Ribosome And T Rna Structure

To which of the following structures in a typical molecule of tRNA is an amino acid attached?

Possible Answers:

Anticodon loop

Variable loop

D loop

CCA tail

Correct answer:

CCA tail

Explanation:

Amino acids are attached to the CCA tail of a tRNA. These are found at the 3' end of tRNA molecules and are important for recognition by aminoacyl tRNA synthetases (enzymes that actually attach the amino acids to the tRNA). The anticodon loop, as the name suggests, contains the anticodon, which will be important during translation for recognizing mRNA sequences. The D-loop and the variable loop are other portions of the tRNA that are important for maintaining structure and recognition.

Example Question #2 : Help With Ribosome And T Rna Structure

Chloramphenicol prevents protein translation by which of the following mechanisms?

Possible Answers:

It blocks the peptidyl transferase reaction on ribosomes

It blocks the translocation reaction on ribosomes

It blocks the binding of aminoacyl tRNA to the A site of the ribosome

It blocks initiation of RNA chains by binding to RNA polymerase

Correct answer:

It blocks the peptidyl transferase reaction on ribosomes

Explanation:

Tetracycline blocks the binding of aminoacyl tRNA to the A site of the ribosome.

Cyclohexamide blocks the translocation reaction on ribosomes.

Rifamycin blocks the initiation of RNA chains by binding to RNA polymerase.

Chloramphenicol blocks the pepidyl transferase reaction on the ribosome.

Example Question #3 : Help With Ribosome And T Rna Structure

During translation, which site in the ribosome allows for tRNA moelcules to enter the complex? 

Possible Answers:

P site

E site

R site

A site

Correct answer:

A site

Explanation:

The ribosomal complex has three sites where tRNA moelcules can be oriented during the process of translation: the A site, the P site, and the E site. During polypeptide elongation, a tRNA with an attached amino acid will enter at the A site. It will then move to the P site, now holding the growing polypeptide chain. All tRNAs no longer holding an amino acid will exit the ribosome at the E site.

Example Question #4 : Help With Ribosome And T Rna Structure

On which of the following molecules could you find an anticodon?

Possible Answers:

rRNA

miRNA

mRNA

tRNA

Correct answer:

tRNA

Explanation:

In order to make sure that the proper amino acid is added to the growing polypeptide chain, an anticodon found on the tRNA carrying the amino acid must be a match for the codon found on the mRNA.

Example Question #5 : Help With Ribosome And T Rna Structure

Which of the following most accurately describes the chronological order of ribosome biogenesis in eukaryotes?

Possible Answers:

Ribosomal proteins are translated in the cytoplasm. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA is transported to the cytoplasm where the rRNA and ribosomal proteins form the 60S and 40S ribosomal subunits. 

Ribosomal proteins are translated in the cytoplasm and transported to the nucleolus. At the same time, rRNA genes are being rapidly transcribed in the cytoplasm. rRNA and ribosomal proteins form the 60S and 40S subunits in the cytoplasm. 

Ribosomal proteins are translated in the nucleous and transported to the cytoplasm. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA and ribosomal proteins form the 60S and 40S subunits in the cytoplasm, where they join to form a functional ribosome. 

Ribosomal proteins are translated in the cytoplasm and transported to the nucleolus. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA and ribosomal proteins form the 50S and 30S subunits in the nucleolus and are then transported to the cytoplasm for functional ribosome assembly. 

Ribosomal proteins are translated in the cytoplasm and transported to the nucleolus. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA and ribosomal proteins form the 60S and 40S subunits in the nucleolus and are then transported to the cytoplasm for functional ribosome assembly. 

Correct answer:

Ribosomal proteins are translated in the cytoplasm and transported to the nucleolus. At the same time, rRNA genes are being rapidly transcribed in the nucleolus. rRNA and ribosomal proteins form the 60S and 40S subunits in the nucleolus and are then transported to the cytoplasm for functional ribosome assembly. 

Explanation:

Ribosomal proteins are translated in the cytoplasm and rRNA genes are transcribed in the nucleolus. Following protein translation, these proteins enter the nucleus through nuclear pores and localize to the nucleolus. Here, transcribed rRNA associates with the ribosomal proteins to form the 60S and 40S eukaryotic ribosomal subunits. Prokaryotes have 50S and 30S subunits. The ribosomal subunits then translocate to the cytoplasm where they join together to form fully functional ribosomes. 

Example Question #1 : Translation And Proteins

How many ribosomal binding sites are there and what are their functions? 

Possible Answers:

There are three sites. A site binds aminoacyl-tRNA, P site binds peptidyl-tRNA, E site binds free tRNA before ribosomal exit

There are two sites. A site binds free tRNA before ribosomal exit, P site binds aminoacyl-tRNA

There are three sites. A site binds peptidyl-tRNA, P site binds aminoacyl-tRNA, E site binds free tRNA before ribosomal exit

There are three sites. A site binds free tRNA before ribosomal exit, P site binds aminoacyl-tRNA, E site binds peptidyl-tRNA 

There are two sites. A site binds free tRNA before ribosomal exit, P site binds peptidyl-tRNA 

Correct answer:

There are three sites. A site binds aminoacyl-tRNA, P site binds peptidyl-tRNA, E site binds free tRNA before ribosomal exit

Explanation:

The correct answer is there are three sites. A site binds aminoacyl-tRNA, P site binds peptidyl-tRNA, E site binds free tRNA before ribosomal exit. 

Example Question #1 : Help With Translation Processes

Which of the following is not a type of modification that can occur after translation?

Possible Answers:

Phosphorylation

Proteasomal degradation

Trimming

5' capping

Correct answer:

5' capping

Explanation:

Post-translational modifications that may occur after a protein is translated include numerous processes to alter the structure or function of the protein. Trimming modification involves removal of the N- or C - terminal propeptides from zymogens to generate mature proteins. Covalent alterations, including phosphorylation, glycosylation and hydroxylation, are frequently used to modify the structure or energy state of a protein. Proteasomal degradation requires the attachment of ubiquitin to defective proteins to tag them for degradation and digestion. Amino acids from degraded proteins can often be recycled to generate new molecules.

5' capping occurs in the nucleus after transcription and is required for transport of RNA out of the nucleus prior to translation.

Example Question #1 : Translation And Proteins

Which of the following is not a phase in translation?

Possible Answers:

Modification

Termination

Initiation

Elongation

Correct answer:

Modification

Explanation:

There are four phases in translation: activation, initiation, elongation, and termination. Activation is the process that joins the correct amino acid to the correct tRNA. When the tRNA has an amino acid bound to it, it is "charged." Initiation occurs when the small ribosomal subunit binds the 5' end of mRNA, with the help of initiation factors and other proteins. The structure then recruits a methionine tRNA to the start codon to begin the elongation process. Elongation occurs as charged tRNA molecules transfer their amino acids to the growing polypeptide. Termination results when a stop codon is recognized by release factors and the completed protein is released from the ribosome.

Modification of the transcript occurs after translation has been completed.

Example Question #3 : Help With Translation Processes

Which of the following ensures that viral gene translation occurs even when host translation is inhibited?

Possible Answers:

3' poly-A tail 

Promoter 

5' untranslated region (UTR) 

Internal Ribosomal Entry Sites (IRES)

5' guanine cap 

Correct answer:

Internal Ribosomal Entry Sites (IRES)

Explanation:

Viruses utilize IRES to allow translation to occur in a 5' cap-independent manner. Translational machinery (ribosomes) are located to the IRES so that translation can occur. 5' guanine cap and 3' poly-A tails are mRNA modifications that are normally necessary to initiate translation, but are cap-dependent. The promoter regulates genes expression on the level of transcription, whereas the 5' UTR regulates translation. 

Example Question #4 : Help With Translation Processes

Which amino acid is the "start" amino acid in a peptide chain? 

Possible Answers:

Methionine 

Arginine

Lysine

Threonine

Tyrosine 

Correct answer:

Methionine 

Explanation:

The correct answer is methionine. The ATG codon triplet in a mRNA strand codes for the start of the peptide, and this first amino acid that is coded by ATG is methionine. 

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