AP Biology : Translation

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #3 : Understanding Ribosomes, T Rna, And Anti Codons

What is the purpose of tRNA?

Possible Answers:

To form part of the ribosome

To bring information from within the nucleus to the cytoplasm

To aid in the transcription of genes

To bring amino acids to ribosomes

Correct answer:

To bring amino acids to ribosomes

Explanation:

tRNA is a special type of RNA that has the function of forming bonds with amino acids and bringing them to ribosomes to complete translation. tRNA carries anticodons, allowing it to bind to mRNA in the active site of a ribosome. It can then transfer its amino acid residue to the ribosome, where it is incorporated into the growing polypeptide chain. The tRNA molecule is the released from the ribosome and recycled.

rRNA forms part of the ribosome structure and mRNA brings information from the nucleus to the cytoplasm. Transcription is the process of making an RNA transcript from a DNA template, and is performed by an RNA polymerase.

Example Question #3 : Understanding Ribosomes, T Rna, And Anti Codons

How does a ribosome detect that the correct amino acid is being added during translation?

Possible Answers:

Translation factors

Appropriate base pairing between mRNA and rRNA 

It doesn’t; correct sequences are checked later by chaperones during protein folding

Appropriate base pairing between the mRNA and tRNA

Correct answer:

Appropriate base pairing between the mRNA and tRNA

Explanation:

Amino acid sequence is determined by the sequence of codons on mRNA. tRNA is responsible for bringing new amino acids to the ribosome. Interactions between the codons on mRNA and the anticodons on tRNA are what allow the formation of the appropriate peptide bonds.

Chaperones are later used to facilitate the development of protein structure, but are not involved in checking protein sequence.

Example Question #31 : Translation

If the enzyme, aminoacyl-tRNA synthetase malfunctions, which of the following processes will be impeded?

Possible Answers:

DNA replication

Translation

Transcription

None of the other answers

Post-transcriptional RNA processing

Correct answer:

Translation

Explanation:

Aminoacyl-tRNA synthetase is responsible for "charging" tRNA with amino acids. During translation, tRNA molecules that are bound to specific amino acids are fed into the ribosome in a specific order that is complementary to the mRNA strand. Once a tRNA is used up, it loses its amino acid. As a result, it must interact with aminoacyl-tRNA synthetase before it can be used again in translation.

A malfunction in aminoacyl-tRNA synthetase would result in a shortage of charged tRNA molecules and a decrease in translation processing.

Example Question #2 : Understanding Ribosomes, T Rna, And Anti Codons

Which of the following correctly pairs each kind of RNA with its function?

Possible Answers:

mRNA carries genetic information from DNA

tRNA carries proteins to ribosomes

rRNA associates with proteins to form the ribosome

mRNA carries genetic information from DNA

tRNA carries amino acids to ribosomes

rRNA associates with proteins to form the ribosome 

mRNA carries amino acids to ribosomes

tRNA carries genetic information from DNA

rRNA associates with proteins to form the ribosome

mRNA carries amino acids to ribosomes

tRNA associates with proteins to form the ribosome

rRNA carries genetic information from DNA

mRNA carries proteins to ribosomes

tRNA carries amino acids to ribosomes

rRNA associates with proteins to form the ribosome 

Correct answer:

mRNA carries genetic information from DNA

tRNA carries amino acids to ribosomes

rRNA associates with proteins to form the ribosome 

Explanation:

The three types of RNA discussed are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). mRNA forms during transcription when RNA polymerase synthesizes RNA from the DNA template. Post-transcriptional modification is required for the mRNA to mature and exit the nucleus. Once in the cytoplasm, the mRNA will bind to a ribosome composed of rRNA and proteins. The ribosome will then recruit tRNA molecules to the complex in order to synthesize the protein product. Each amino acid binds to a specific kind of tRNA. tRNA brings the amino acids to the growing end of the newly forming polypeptide at the ribosome by binding to the codon of the mRNA.

Example Question #1 : Understanding Ribosomes, T Rna, And Anti Codons

Which of the following choices is the enzyme that adds amino acids to tRNA molecules?

Possible Answers:

Aminoacyl-tRNA synthetase

RNA polymerase

Primase

Synthase

Correct answer:

Aminoacyl-tRNA synthetase

Explanation:

The enzyme aminoacyl-tRNA synthetase joins tRNA molecules with a corresponding amino acid. First, an amino acid is bound to aminoacyl-tRNA synthetase using ATP. Then, the tRNA molecule containing the corresponding anticodon binds to the enzyme. The correct tRNA molecule is identified by aminoacyl-tRNA synthetase by its anticodon sequence and other areas of its structure. Last, the tRNA molecule covalently bonds to the amino acid and is released from aminoacyl-tRNA synthetase.

Example Question #1 : Understanding Ribosomes, T Rna, And Anti Codons

How are ribosomal units typically organized during translation?

Possible Answers:

Two small subunits

A large subunit and a small subunit

Two subunits of equal size

A single large complex

Correct answer:

A large subunit and a small subunit

Explanation:

Ribosomes are non-membranous organelles that direct protein synthesis by reading mRNA and joining amino acids into strands of polypeptides. Ribosomes exist in both free and membrane-bound states. They are synthesized in both the nucleolus and cytoplasm. The components that make up these non-membranous organelles are rRNA molecules and a variety of proteins. Ribosomes have a large and a small subunit, together called the translational apparatus. The small ribosomal subunit reads the mRNA strand and the large ribosomal subunit joins amino acids into polypeptides. 

Example Question #11 : Understanding Ribosomes, T Rna, And Anti Codons

Which of the following choices will most likely be found in the aminoacyl site of the large ribosomal unit?

Possible Answers:

Initiation factors

The growing polypeptide chain

The tRNA molecule with the next amino acid to be added to the polypeptide chain

The amino-acid free tRNA

Correct answer:

The tRNA molecule with the next amino acid to be added to the polypeptide chain

Explanation:

The large ribosomal subunit has three sites that interact with tRNA molecules—the peptidyl “P” site, the aminoacyl “A” site, and the exit “E” site. The P-site holds the tRNA corresponding to the most recently added amino acid, which is attached to the growing polypeptide chain by a peptide bond. The A-site holds the tRNA with the next amino acid to be added to the chain. Finally, the E-site holds the free tRNA without an amino acid that was previously in the P-site.

Example Question #12 : Understanding Ribosomes, T Rna, And Anti Codons

If the codon in the mRNA strand is 5' CAG, what is the anticodon strand sequence?

Possible Answers:

5' GUC

3' GUC

3' GTC

3' CUG

5' GTC

Correct answer:

3' GUC

Explanation:

The mRNA strand is synthesized 5' to 3' and contains the codons. tRNA contains the anticodons needed for the corresponding amino acid, and is paired to the codon 3' to 5'.

Example Question #12 : Understanding Ribosomes, T Rna, And Anti Codons

The mRNA codon for methionine is 5' AUG 3'. What is the corresponding anticodon found on the methionine tRNA?

Possible Answers:

3' AUG 5'

3' UAC 5'

5' UAG 3'

5' ATG 3'

3' TAC 5'

Correct answer:

3' UAC 5'

Explanation:

The anticodon of any codon will be the RNA nucleotides that complement the codon sequence. In RNA, adenine (A) complements uracil (U) while cytosine (C) complements guanine (G). Hence, for the codon 5' AUG 3', the complements will be 3' UAC 5'. Note that many of the incorrect answers contain thymine (T), a nucleotide not found in RNA.

Example Question #13 : Understanding Ribosomes, T Rna, And Anti Codons

Which of the following amino acids is responsible for the initiation of the translation of a polypeptide?

Possible Answers:

Alanine

Leucine

Asparagine

Methionine

Valine

Correct answer:

Methionine

Explanation:

The start codon for any strand of RNA begins with the codon that codes for the amino acid methionine. This is the first amino acid in a polypeptide chain. The abbreviation for methionine is: Met.

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