AP Biology : Understanding Ribosomes, tRNA, and Anti-codons

Study concepts, example questions & explanations for AP Biology

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Example Questions

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

The amino acid leucine has several possible codons, due to the degeneracy of the genetic code. This means that there is more than one possible __________ for leucine.

Possible Answers:

rRNA

ribosome

mRNA

DNA

tRNA

Correct answer:

tRNA

Explanation:

Each tRNA contains the anticodon for a specific mRNA codon and carries the amino acid corresponding to that codon to ribosomes during translation. mRNA is produced by transcription from DNA, and ribosomes translate it into proteins. Multiple codons can code for a single amino acid, and so there can be several tRNA anticodons that could be used for a single amino acid.

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

Which of the following nucleic acids brings an amino acid through the cytosol to a ribosome during translation?

Possible Answers:

None of these choices are correct

tRNA

rRNA

mRNA

Correct answer:

tRNA

Explanation:

mRNA, tRNA, and rRNA all play a key role in the synthesis of proteins. tRNA (transfer RNA) is responsible for gathering amino acids in the cytosol and bringing them to the ribosomes when translation is taking place. mRNA (messenger RNA) is the template for translation. rRNA (ribosomal RNA) is a structural element of the ribosomes.

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

A codon in an mRNA sequence reads 5'-AAC-3'. What is its corresponding tRNA anticodon?

Possible Answers:

3'-AAC-5'

3'-UUG-5'

3'-TTG-5'

3'-CAA-5'

3'-GUU-5'

Correct answer:

3'-UUG-5'

Explanation:

An anticodon is the three-base sequence, paired with a specific amino acid, that a tRNA molecule brings to the corresponding codon of the mRNA during translation. The anticodon sequence is complementary to the mRNA, using base pairs in the anti-parallel direction. tRNA is read 3'-to-5', so the sequence would be 3'-UUG-5'. Keep in mind that adenine binds to uracil in RNA.

Codon:      5'-AAC-3'

Anticodon: 3'-UUG-5'

Example Question #4 : Understanding Ribosomes, T Rna, And Anti Codons

Where are anticodons found in cells?

Possible Answers:

mRNA

tRNA

rRNA

DNA

Correct answer:

tRNA

Explanation:

Anticodons are found on molecules of tRNA. Their function is to base pair with the codon on a strand of mRNA during translation. This action ensures that the correct amino acid will be added to the growing polypeptide chain. A tRNA molecule will enter the ribosome bound to an amino acid. The anticodon sequence will bind to the codon of the mRNA, allowing the tRNA to release the attached amino acid. This amino acid is then added to the peptide chain by the ribosome.

Example Question #5 : Understanding Ribosomes, T Rna, And Anti Codons

What is the purpose of tRNA?

Possible Answers:

To bring information from within the nucleus to the cytoplasm

To aid in the transcription of genes

To form part of the ribosome

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 #6 : Understanding Ribosomes, T Rna, And Anti Codons

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

Possible Answers:

Appropriate base pairing between mRNA and rRNA 

Appropriate base pairing between the mRNA and tRNA

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

Translation factors

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

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

Possible Answers:

Post-transcriptional RNA processing

None of the other answers

Transcription

Translation

DNA replication

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 #8 : Understanding Ribosomes, T Rna, And Anti Codons

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

Possible Answers:

mRNA carries amino acids to ribosomes

tRNA carries genetic information from DNA

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 associates with proteins to form the ribosome

rRNA carries genetic information from DNA

mRNA carries genetic information from DNA

tRNA carries proteins to ribosomes

rRNA associates with proteins to form the ribosome

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 #9 : 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

Primase

Synthase

RNA polymerase

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 subunits of equal size

A large subunit and a small subunit

Two small subunits

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. 

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