BIO105 DNA, Gene Regulation, and Translation

DNA, Gene Regulation, and Translation Practice Questions

1. Gene Control

• Question: What part of a gene controls when and where it is turned on?
• Answer: B) Promoter
• Explanation: The promoter region of a gene is responsible for initiating transcription. It is the site where RNA polymerase binds to start the process of transcribing DNA into RNA. The promoter determines when and in which cells a gene is expressed.

2. Transcription Enzyme

• Question: What enzyme reads DNA and builds RNA during transcription?
• Answer: D) RNA polymerase
• Explanation: RNA polymerase is the enzyme that synthesizes RNA from a DNA template during transcription. It reads the DNA sequence and adds complementary RNA nucleotides to the growing RNA molecule.

3. tRNA Function During Translation

• Question: During translation, what carries the correct amino acid to the ribosome?
• Answer: B) tRNA
• Explanation: Transfer RNA (tRNA) molecules are responsible for bringing the correct amino acids to the ribosome during translation. Each tRNA has an anticodon that is complementary to a specific codon on the mRNA, ensuring the correct amino acid is added to the growing polypeptide chain.

4. Ribosome Site Order During Protein Synthesis

• Question: What is the correct order of ribosome sites during protein synthesis?
• Answer: C) A → P → E
• Explanation: The ribosome has three main sites: the A (aminoacyl) site, the P (peptidyl) site, and the E (exit) site. During translation, tRNA molecules enter at the A site, move to the P site where the peptide bond is formed, and then exit at the E site.

5. Translation Termination

• Question: Which of the following would stop translation?
• Answer: A) A stop codon enters the A site
• Explanation: Translation is terminated when a stop codon (UAA, UAG, or UGA) enters the A site of the ribosome. Stop codons do not have corresponding tRNAs, and instead, release factors bind to the ribosome and trigger the release of the polypeptide chain.

6. Mutation and Uncontrolled Cell Division

• Question: Which mutation most likely causes uncontrolled cell division?
• Answer: B) Promoter for a skin gene fusing with the PDGF transcription unit
• Explanation: If the promoter for a skin gene fuses with the PDGF (platelet-derived growth factor) transcription unit, it can cause the PDGF gene to be expressed in skin cells at inappropriate times or levels. PDGF is a growth factor that stimulates cell division, so its misregulation can lead to uncontrolled cell proliferation and potentially cancer.

7. Gene Expression

• Question: Which of the following is true about gene expression?
• Answer: C) Transcription factors help turn specific genes on or off
• Explanation: Transcription factors are proteins that bind to DNA and regulate gene expression. They can either activate (turn on) or repress (turn off) the transcription of specific genes by influencing the binding of RNA polymerase to the promoter.

8. Cancer Example: PDGF Production

• Question: In the cancer example from class, why was PDGF produced in the wrong place?
• Answer: C) The skin gene promoter was fused to the PDGF gene, causing skin cells to produce PDGF
• Explanation: As explained previously, the fusion of a skin gene promoter to the PDGF gene leads to ectopic expression of PDGF in skin cells, contributing to uncontrolled cell growth.

9. Codon Nucleotide Count

• Question: How many nucleotides are in a single codon?
• Answer: C) 3
• Explanation: A codon is a sequence of three nucleotides that codes for a specific amino acid or a stop signal during translation. This triplet code is fundamental to the genetic code.

10. Transcription Factor Role

• Question: What is the role of a transcription factor?
• Answer: C) Binds to the promoter and regulates gene expression
• Explanation: Transcription factors bind to specific DNA sequences in the promoter region of genes and regulate gene expression by either enhancing or inhibiting the binding of RNA polymerase and the initiation of transcription.

11. Non-Nucleotide Structure

• Question: Which of the following is NOT made of nucleotides?
• Answer: C) Protein
• Explanation: Proteins are made of amino acids, not nucleotides. DNA and RNA are nucleic acids composed of nucleotide monomers. Promoters are regions of DNA, thus made of nucleotides.

12. Mutation Impact on Amino Acid Sequence

• Question: A mutation in which region of the gene would most directly affect the amino acid sequence?
• Answer: C) Coding region of the transcription unit
• Explanation: Mutations in the coding region of a gene directly alter the mRNA sequence, which in turn affects the amino acid sequence of the protein. Mutations in the promoter or introns have regulatory effects but do not directly change the amino acid sequence.

13. Instructions from DNA to Ribosome

• Question: Which molecule brings instructions from DNA to the ribosome?
• Answer: B) mRNA
• Explanation: Messenger RNA (mRNA) carries the genetic information from DNA in the nucleus to the ribosome in the cytoplasm, where the information is translated into a protein.

14. Ribosome P Site Activity

• Question: What happens at the P site of the ribosome?
• Answer: B) Growing protein chain is held
• Explanation: The P site (peptidyl-tRNA site) of the ribosome is where the tRNA holding the growing polypeptide chain is located. During translation, the peptide bond is formed between the amino acid attached to the tRNA in the A site and the growing polypeptide chain held by the tRNA in the P site.

15. Genetic Code Description

• Question: The genetic code is described as:
• Answer: B) Three-nucleotide sequences called codons that code for amino acids
• Explanation: The genetic code is a set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences). Each codon, consisting of three nucleotides, specifies a particular amino acid or a stop signal.