AP Biology : Understanding Translation Processes

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #92 : Dna, Rna, And Proteins

The start codon (AUG) codes for which of the following amino acids?

Possible Answers:

Lysine

Alanine

Methionine

Histidine

Correct answer:

Methionine

Explanation:

The start codon (AUG) codes for the amino acid methionine. The start codon is the nucleotide triplet on the mRNA strand that signals the start of the codons to be translated. Each codon triplet binds to a complementary anticodon triplet on a tRNA molecule that carries a corresponding amino acid. 

Example Question #21 : Understanding Translation Processes

Which of the following choices is not a true characteristic of the initiation stage of translation?

Possible Answers:

The mRNA strand is scanned for a start codon

Ribosomal subunits are recruited

All of the binding sites in the recruited ribosome stand empty

A protein complex of initiation factors forms at the 5' end of the mRNA strand

Correct answer:

All of the binding sites in the recruited ribosome stand empty

Explanation:

In the initiation stage of translation, a 5’ cap forms at the 5’ end of the mRNA strand, which is composed of the small ribosomal subunit and initiation factors. Initiation factors are proteins that facilitate the start of translation during the initiation stage. Once this complex is assembled, it “scans” the mRNA strand for the start codon, AUG. The initiator tRNA molecule coding the anticodon UAC and carrying the corresponding amino acid methionine is recruited and binds to the start codon. This makes methionine the first amino acid in the polypeptide chain. The large ribosomal subunit then associates with the complex, placing the methionine tRNA in the P-site of the large subunit. There is an alternative model of initiation in which the mRNA scanning complex does not form at the 5’ end. This model is believed to occur under stress responses.

Example Question #22 : Understanding Translation Processes

Which of the following choices best describes how antibiotics inhibit translation?

Possible Answers:

Antibiotics inhibit DNA polymerase from synthesizing mRNA

They prevent the formation of the translation initiation complex 

They block the aminoacyl site of ribosomes

All of these methods

Correct answer:

All of these methods

Explanation:

Antibiotics are able to inhibit protein synthesis in prokaryotes in a number of ways. The specific method of inhibition depends on the antibiotic that is used. Examples of the antibiotics that target translation are rifamycin, linezolid, and tetracyclines. Rifamycin inhibits RNA polymerase and the resulting synthesis of mRNA. Linezolid blocks the formation of the translation initiation complex. Tetracyclines obstruct the aminoacyl “A” site of ribosomes. Inhibiting translation is an effective way to kill bacteria and treat bacterial infections. Antibiotics specifically target prokaryotic cells, ensuring no harm to the host eukaryotic cells. 

Example Question #23 : Understanding Translation Processes

What amino acid is always the first one to be added during translation?

Possible Answers:

Alanine

Tryptophan

Glycine

Methionine

Cysteine

Correct answer:

Methionine

Explanation:

There is only one codon that signals the start of translation: AUG. This codon codes for the amino acid methionine so this amino acid will also be at the N-terminus of all proteins, however it may be removed and/or modified later.

Example Question #25 : Translation

All of the following types of RNA are involved in translation in the creation of proteins except __________.

Possible Answers:

peptide RNA

transfer RNA

messenger RNA

ribosomal RNA

Correct answer:

peptide RNA

Explanation:

The three types of RNA involved in Translation are messenger RNA, transfer RNA, and ribosomal RNA.

Example Question #24 : Understanding Translation Processes

Why is it beneficial for there to be "redundancies" in the code for transcribing mRNA into proteins?

Possible Answers:

None of these

It allows the same three-nucleotide sequence to code for several different amino acids.

It allows DNA polymerase to correct mistakes in the genetic code.

It allows an mRNA molecule to function whether it contains thymine (T) or uracil (U).

It allows for silent mutations to occur that do not alter the sequence of amino acids.

Correct answer:

It allows for silent mutations to occur that do not alter the sequence of amino acids.

Explanation:

Many amino acids have multiple three-nucleotide sequences that correspond with them. If a sequence that codes for leucine (UUA) is mutated by only one letter (to UUG), then it will still form a functional protein, since the mutated sequence also codes for leucine. Redundancy allows occasional mutations to occur without corrupting the amino acid sequence.

DNA polymerase is not involved in the transcription of mRNA to amino acids.

A single three-nucleotide sequence can only code for a single amino acid, although many amino acids can be coded for by multiple nucleotide sequences (redundancy).

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