Q1. The Central Dogma: Fill in the blanks

Background

Topic: Central Dogma of Molecular Biology

This question tests your understanding of how genetic information flows from DNA to RNA to protein, a fundamental concept in biology.

Key Terms:

• DNA bases: The nucleotide sequence in DNA (A, T, C, G).

• RNA bases: The nucleotide sequence in RNA (A, U, C, G).

• Amino acids: Building blocks of proteins.

• Transcription: The process of copying DNA into RNA.

• Translation: The process of converting RNA into a protein sequence.

Step-by-Step Guidance

1. Recall that genetic information is stored in DNA as a sequence of nucleotide bases.

2. During transcription, this information is copied into RNA, which also consists of nucleotide bases.

3. During translation, the sequence of RNA bases is read in sets of three (codons) to specify amino acids, which are then linked to form a protein.

4. Review the answer choices and match each step of the central dogma to the correct sequence: DNA bases → RNA bases → amino acids.

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Q2. mRNA Codons and Translation

Background

Topic: Codons and the Genetic Code

This question tests your understanding of how mRNA is read by ribosomes in three-nucleotide units (codons) and how each codon specifies an amino acid or a stop signal.

Key Terms:

• Codon: A sequence of three RNA nucleotides that codes for an amino acid.

• Ribosome: The molecular machine that reads mRNA and synthesizes proteins.

• Polypeptide: A chain of amino acids.

Step-by-Step Guidance

1. Understand that mRNA is read in sets of three nucleotides (codons).

2. Each codon corresponds to a specific amino acid or a stop signal.

3. Use a codon table to determine which amino acid is specified by a given mRNA codon.

4. Remember that translation occurs in the ribosome, where tRNA brings the correct amino acid for each codon.

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Q3. Directionality of Nucleic Acid Synthesis

Background

Topic: DNA and RNA Synthesis

This question tests your understanding of the chemical directionality of nucleic acid synthesis, specifically which part of the sugar molecule new nucleotides are added to.

Key Terms:

• 3' OH: The hydroxyl group on the 3' carbon of the sugar in a nucleotide.

• 5' and 3' ends: Refers to the directionality of nucleic acid strands.

Step-by-Step Guidance

1. Recall that nucleic acids (DNA and RNA) have directionality, with a 5' end and a 3' end.

2. New nucleotides are always added to the 3' OH group of the sugar, extending the chain in the 5' to 3' direction.

3. Review the structure of a nucleotide and identify the 3' OH group.

4. Consider why this directionality is important for replication and transcription.

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Q4. DNA Strand Polarity and Replication

Background

Topic: DNA Replication and Strand Polarity

This question tests your understanding of the antiparallel nature of DNA strands and how new DNA is synthesized during replication.

Key Terms:

• Leading strand: Synthesized continuously in the 5' to 3' direction.

• Lagging strand: Synthesized discontinuously in fragments (Okazaki fragments).

• Origin of replication: The site where DNA replication begins.

Step-by-Step Guidance

1. Identify the directionality of each DNA strand at the replication fork.

2. Recall that DNA polymerase synthesizes new DNA in the 5' to 3' direction.

3. Determine which strands are synthesized continuously (leading) and which are synthesized discontinuously (lagging).

4. Use the diagram to locate the origins and the direction of synthesis for each strand.

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Q5. Template and Coding Strands in Transcription

Background

Topic: Transcription and DNA Strand Roles

This question tests your understanding of which DNA strand serves as the template for mRNA synthesis and the relationship between the coding and template strands.

Key Terms:

• Template strand: The DNA strand used by RNA polymerase to synthesize mRNA.

• Coding strand: The DNA strand with the same sequence as the mRNA (except T instead of U).

• Sense strand: Another name for the coding strand.

Step-by-Step Guidance

1. Identify the two DNA strands: one is the template, and one is the coding strand.

2. The template strand is read by RNA polymerase in the 3' to 5' direction to synthesize mRNA in the 5' to 3' direction.

3. The coding strand has the same sequence as the mRNA, except T is replaced by U.

4. Use the diagram to determine which strand is the template based on directionality and sequence.

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