Q1. Explain the flow of genetic material as it is presented by the “central dogma.”

Background

Topic: Central Dogma of Molecular Biology

This question tests your understanding of how genetic information is transferred from DNA to RNA to protein in cells.

Key Terms:

• DNA (Deoxyribonucleic Acid)

• RNA (Ribonucleic Acid)

• Transcription

• Translation

• Protein Synthesis

Step-by-Step Guidance

1. Start by defining the central dogma: it describes the flow of genetic information within a biological system.

2. Explain that the process begins with DNA, which stores genetic information in the nucleus (or nucleoid in prokaryotes).

3. Describe transcription: the process by which a segment of DNA is copied into messenger RNA (mRNA).

4. Outline translation: the process where the mRNA is used as a template to assemble amino acids into a polypeptide (protein) at the ribosome.

Try explaining the central dogma in your own words before checking the answer!

Q2. Describe the structural features of RNA and state how RNA differs from DNA. (a) Describe the structural features of DNA and RNA nucleotides.

Background

Topic: Nucleic Acid Structure

This question tests your knowledge of the molecular structure of nucleic acids and the differences between DNA and RNA.

Key Terms:

• Nucleotide

• Ribose vs. Deoxyribose

• Uracil vs. Thymine

• Single-stranded vs. Double-stranded

Step-by-Step Guidance

1. List the three components of a nucleotide: a phosphate group, a five-carbon sugar, and a nitrogenous base.

2. Compare the sugars: RNA contains ribose, while DNA contains deoxyribose (which lacks an oxygen atom at the 2' position).

3. Identify the nitrogenous bases: DNA uses adenine, guanine, cytosine, and thymine; RNA uses adenine, guanine, cytosine, and uracil (instead of thymine).

4. Discuss the structural differences: DNA is typically double-stranded and forms a double helix, while RNA is usually single-stranded.

Try drawing or listing the differences before checking the answer!

Q3. Recall the role of each of the following enzymes in DNA replication: gyrase, helicase, DNA polymerase I and DNA polymerase III, primase, and ligase.

Background

Topic: DNA Replication Enzymes

This question tests your understanding of the specific functions of enzymes involved in prokaryotic DNA replication.

Key Terms:

• Gyrase (Topoisomerase II)

• Helicase

• DNA Polymerase I

• DNA Polymerase III

• Primase

• Ligase

Step-by-Step Guidance

1. Start by listing each enzyme and its general function in the replication process.

2. Explain how helicase unwinds the DNA double helix at the replication fork.

3. Describe the role of gyrase in relieving supercoiling ahead of the replication fork.

4. Discuss how primase synthesizes short RNA primers needed for DNA polymerases to begin synthesis.

5. Differentiate between DNA polymerase III (main enzyme for DNA synthesis) and DNA polymerase I (removes RNA primers and fills in gaps).

6. Explain how ligase seals nicks in the sugar-phosphate backbone, joining Okazaki fragments on the lagging strand.

Try matching each enzyme to its function before checking the answer!

Q4. Describe how the directionality of DNA impacts replication and compare and contrast DNA replication on the leading and lagging strands. (a) Include the following terms in your discussion: anti-parallel, semi-conservative replication, origin of replication, Okazaki fragments, replication fork, lagging strand, and leading strand.

Background

Topic: DNA Replication Mechanisms

This question tests your understanding of the structural and functional aspects of DNA replication, including strand directionality and replication features.

Key Terms:

• Anti-parallel

• Semi-conservative replication

• Origin of replication

• Okazaki fragments

• Replication fork

• Lagging strand

• Leading strand

Step-by-Step Guidance

1. Begin by explaining that DNA strands are anti-parallel, meaning they run in opposite 5' to 3' directions.

2. Describe how replication starts at the origin of replication and proceeds in both directions, forming replication forks.

3. Discuss semi-conservative replication: each new DNA molecule consists of one old and one new strand.

4. Compare the leading strand (synthesized continuously in the 5' to 3' direction) and the lagging strand (synthesized discontinuously as Okazaki fragments).

5. Explain how the lagging strand requires multiple primers and the joining of Okazaki fragments by ligase.

Try outlining the differences between the strands before checking the answer!

Q5. Describe the process of transcription and translation in prokaryotes. Include the role of each of the following: RNA polymerase, ribosomal RNA, messenger RNA, and transfer RNA. (a) Distinguish between codons and anticodons.

Background

Topic: Gene Expression in Prokaryotes

This question tests your understanding of how genetic information is expressed as proteins in prokaryotic cells.

Key Terms:

• Transcription

• Translation

• RNA polymerase

• mRNA (messenger RNA)

• rRNA (ribosomal RNA)

• tRNA (transfer RNA)

• Codon

• Anticodon

Step-by-Step Guidance

1. Describe transcription: RNA polymerase binds to DNA and synthesizes a complementary mRNA strand.

2. Explain how mRNA carries the genetic code from DNA to the ribosome.

3. Discuss translation: ribosomes (composed of rRNA and proteins) read the mRNA sequence and assemble amino acids into a polypeptide.

4. Describe the role of tRNA: each tRNA has an anticodon that pairs with a codon on the mRNA and carries the corresponding amino acid.

5. Distinguish between codons (three-nucleotide sequences on mRNA) and anticodons (complementary sequences on tRNA).

Try summarizing the steps of gene expression before checking the answer!