AP Biology : DNA, RNA, and Proteins

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understanding Post Transcription Modification

Which of the following choices is not a true characteristic of spliceosomes?

Possible Answers:

Most spliceosomes are found in the nucleus

They are composed of small nuclear RNA molecules (snRNAs)

Both prokaryotes and eukaryotes have spliceosomes

They splice introns from primary RNA transcripts

Correct answer:

Both prokaryotes and eukaryotes have spliceosomes

Explanation:

The spliceosome is a complex structure composed of small nuclear RNA molecules (snRNAs) and other proteins. They are often located in the nucleus. The spliceosome splices introns from the primary RNA transcript. This process occurs through splicing at 5’ and 3’ sites that are identified by particular nucleotide sequences. Prokaryotic cells do not contain spliceosomes. 

Example Question #9 : Understanding Post Transcription Modification

Which statement correctly describes the process of alternative splicing?

Possible Answers:

Alternative splicing can create a variety of proteins from the same primary transcript

There are different methods of alternative splicing (spliceosomes, self-splicing, etc.)

In alternative splicing, some primary RNA transcripts are spliced and others are not

There are different alternative splicing processes between prokaryotes and eukaryotes

Correct answer:

Alternative splicing can create a variety of proteins from the same primary transcript

Explanation:

Alternative splicing is the process where many different proteins can be formed from a primary transcript. This can be done in a number of ways, including using different splice sites, maintaining introns, and splicing out exons. Alternative splicing is an important process because it increases cellular efficiency; if many proteins can result from the same primary transcript, then the genome doesn’t need to code for as many unique transcripts.

Example Question #1 : Understanding Translation Processes

Which of the following processes converts mRNA codons into proteins?

Possible Answers:

Transcription

Glycolysis

Apoptosis

Replication

Translation

Correct answer:

Translation

Explanation:

Translation is the process of converting an mRNA codon sequence into protein via the ribosome, so that is the correct answer. Apoptosis is programmed cell death. Transcription is close, but it is the process of making RNA from DNA. Glycolysis is the process of creating two pyruvate molecules from glucose, and produces two ATP.

Example Question #2 : Understanding Translation Processes

Which of the following templates is used during translation?

Possible Answers:

tRNA

mRNA

DNA

microRNA

rRNA

Correct answer:

mRNA

Explanation:

mRNA is the template used during translation. The mRNA strand is read and "translated" into a polypeptide by tRNA.

DNA would be the template for transcription, not for translation.

Example Question #1 : Understanding Translation Processes

Which of the following statements regarding codons is true?

Possible Answers:

The AUG codon begins the process of translation for every transcript of mRNA

The length of each codon is dependent on the amino acid it codes for

None of the other choices are correct

There is one codon for each amino acid

Correct answer:

The AUG codon begins the process of translation for every transcript of mRNA

Explanation:

Every codon is composed of three RNA nucleobases, and codes for a specific amino acid; however, there can be multiple codons that code for one amino acid. The start codon, AUG, signals the beginning of translation and codes for methionine.

Example Question #1 : Understanding Translation Processes

Which of the following statements regarding translation is false?

Possible Answers:

Adjacent amino acids in a sequence are joined via peptide bonds

There is only one start codon (AUG) that signals the beginning of translation

tRNA works to bring amino acids corresponding to the codons in the mRNA sequence to the ribosome

There is only one stop codon (UAG) that signals the end of translation

Correct answer:

There is only one stop codon (UAG) that signals the end of translation

Explanation:

While there is only one start codon (AUG), but there are three different stop codons (UGA, UAG, and UAA) that can each signal for the end of translation, or termination. During the translation process, tRNA is used to bring amino acids (corresponding to the codons in the mRNA sequence) to the ribosome, which become attached via peptide bonds to form a polypeptide.

Example Question #1 : Translation

Which of the following statements concerning the genetic code is false?

Possible Answers:

More than one codon can code for the same amino acid

An amino acid can only be produced from one codon

tRNA will always carry one amino acid to the ribosome

A codon will always code for the same amino acid

Correct answer:

An amino acid can only be produced from one codon

Explanation:

The genetic code is degenerative, meaning that multiple codons can code for the same amino acid. It is also unambiguous: a particular codon will always code for one amino acid. That being said, it would be wrong to assume that an amino acid will only have one codon, as an amino acid can have multiple different codons that code for it.

Example Question #1 : Translation

Which of the following statements concerning translation is true?

Possible Answers:

The first amino acid, methionine, is positioned in the A site of the ribosome

The poly A tail serves as an attachment site for the ribosome

mRNA is read by the ribosome in 3'-to-5' direction

The growing amino acid chain is found in the P site of the ribosome

Correct answer:

The growing amino acid chain is found in the P site of the ribosome

Explanation:

In translation, the mRNA is positioned in the ribosome and read in the 5'-to-3' direction. Initiation of translation is triggered by a tRNA attached to a methionine entering the P site of the ribosome. The mRNA will then be read, and additional amino acids will be added to the chain, which grows in the P site. New tRNA enters the A site and old tRNA exits the E site, but the amino acid chain is always anchored to the tRNA in the P site.

Example Question #2 : Understanding Translation Processes

What happens when the ribosome encounters a stop codon?

Possible Answers:

An anticodon-codon pairing is made with a final tRNA that releases the completed polypeptide chain

A chaperone is recruited to help fold the polypeptide chain

A special terminal amino acid is placed on the polypeptide chain 

A release factor is recruited, which dissociates the translation complex and releases the completed polypeptide chain

Correct answer:

A release factor is recruited, which dissociates the translation complex and releases the completed polypeptide chain

Explanation:

Stop codons are a signal for the ribosome to recruit a release factor. Release factors are proteins that dissociate the translation complex and release the polypeptide chain.

There are no tRNAs that match stop codons and there is no "special" terminal amino acid. Chaperones are involved in folding proteins, but they are not involved in the termination of translation.

Example Question #1 : Translation

Where does translation occur?

Possible Answers:

The cytoplasm

The Golgi apparatus

The nucleus

The mitochondria

Correct answer:

The cytoplasm

Explanation:

Translation, the process of synthesizing a polypeptide from an mRNA template, primarily occurs in the cytoplasm. Another possible answer would be the rough endoplasmic reticulum. Both the rough endoplasmic reticulum and cytoplasm contain ribosomes, which are essential for translation.

The mitochondria are essential for cellular respiration, and are the site of the citric acid cycle and electron transport chain. The nucleus houses DNA and synthesizes ribosomes (in the nucleolus). The Golgi apparatus modifies and packages proteins in vesicles after translation is complete.

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