The central dogma of life

The Central Dogma outlines the flow of genetic information from DNA to RNA to proteins. It governs the processes of transcription and translation, crucial for gene expression.

DNA Structure and Replication

• DNA Strands: DNA is double-stranded, and its strands are anti-parallel. One runs from 5′ to 3′, while the complementary strand runs from 3′ to 5′.
• Replication Steps:
  • Helicase: Unzips DNA strands.
  • Primase: Adds RNA primers to the 5′ end.
  • Replication: DNA is replicated bidirectionally.

Transcription

• Initiation: RNA polymerase, guided by a promoter sequence, begins transcription in the nucleus.
• Elongation: RNA polymerase adds RNA nucleotides to the growing strand, using one DNA strand (template strand).
• Termination: Post-transcriptional modifications, including removing non-coding introns, result in mature mRNA.

Translation

• Process: Occurs in ribosomes, converting mRNA into amino acids.
• tRNA: Carries amino acids, reading mRNA codons, and forming peptide bonds.

Post-Translational Modifications

• Processes: Include forming disulfide bonds, proper folding, adding biochemical groups, proteolytic cleavages, and assembling into multimeric proteins.

Revision

• Gene Expression: Converts genetic information into functional molecules.
• Genetic Code: Specifies the relationship between DNA/RNA sequences and amino acids.
• Directionality: Crucial in DNA and RNA synthesis (5′ to 3′).
• Point Mutations: Impact protein structure and function.
• Free Radicals: Increase electron energy, causing DNA mutations.
• UV Radiation: Affects DNA and protein amino acids.
• Replication Origin: Multiple origins in eukaryotes for efficient replication.
• Sliding Clamp: Keeps DNA polymerase stable during replication.
• Primers: Essential for DNA polymerase to start synthesis.
• Helicase and Topoisomerase: Responsible for opening and relieving twisting forces in DNA replication.

Questions-Answers

1. Central Dogma Definition:
   • Q: What does the Central Dogma of Life describe?
   • A: The Central Dogma describes how genetic information in DNA is used to create mRNA and then proteins.
2. Transcription vs. Replication:
   • Q: How does transcription differ from replication in DNA?
   • A: Transcription uses RNA polymerase to create an RNA strand complementary to a DNA template strand, while replication duplicates DNA.
3. Promoter in Transcription:
   • Q: What is the role of a promoter in transcription?
   • A: A promoter sequence guides RNA polymerase to the starting point of transcription on the DNA.
4. Post-Transcriptional Modifications:
   • Q: What are post-transcriptional modifications, and why are they necessary?
   • A: Post-transcriptional modifications include removing non-coding introns and joining coding exons to form mature mRNA. These modifications are necessary for functional protein synthesis.
5. Translation and tRNA:
   • Q: Where does translation occur, and what is its purpose?
   • A: Translation occurs in ribosomes, converting mRNA into amino acids to synthesize proteins.
   • Q: How does transfer RNA (tRNA) contribute to translation?
   • A: tRNA carries specific amino acids and reads mRNA codons to ensure the correct amino acid is added during translation.
6. Start and Stop Codons in Translation:
   • Q: Explain the importance of the start and stop codons in translation.
   • A: The start codon signals the beginning of protein synthesis, while stop codons signal the end, ensuring the correct length of the protein.
7. Directionality in DNA Strands:
   • Q: Why is the directionality of DNA strands crucial in transcription and replication?
   • A: Directionality (5′ to 3′) dictates the order of nucleotides in the growing strand and is essential for the accuracy of DNA and RNA synthesis.
8. Significance of Point Mutations:
   • Q: What is the significance of point mutations in DNA?
   • A: Point mutations can be silent, missense, nonsense, or frameshift mutations, potentially impacting protein structure and function.
9. Impact of R-Group Changes:
   • Q: Why is a change in the R-group of an amino acid likely to have the most significant impact on enzyme function?
   • A: R-group changes can alter the charge or shape of the protein’s active site, affecting its function.
10. Central Dogma’s Significance:

• Q: What’s the central dogma’s significance in molecular biology?
• A: The central dogma describes how genetic information flows from DNA to RNA to proteins, forming the foundation of molecular biology.

11. Coupling in Prokaryotic Cells:

• Q: Why is coupling in prokaryotic cells advantageous during transcription and translation?
• A: Coupling allows simultaneous transcription and translation, increasing efficiency.

12. DNA Supercoiling:

• Q: How does DNA supercoiling affect DNA structure?
• A: Supercoiling condenses DNA and helps it fit into the cell’s limited space.

13. Role of Free Radicals:

• Q: What is the role of free radicals in causing DNA mutations?
• A: Free radicals increase electron energy and can lead to collisions with DNA, potentially causing mutations.

14. UV Radiation’s Effect on Central Dogma:

• Q: In terms of the central dogma, what does UV radiation primarily affect?
• A: UV radiation can lead to DNA mutations and changes in protein amino acids, impacting the translation step of the central dogma.

15. Multiple Origins of Replication in Eukaryotes:

• Q: Why do eukaryotic chromosomes have multiple origins of replication?
• A: Multiple origins enable more efficient replication for larger chromosomes.

16. Role of Sliding Clamp in DNA Replication:

• Q: How does the sliding clamp contribute to DNA replication?
• A: The sliding clamp keeps DNA polymerase stably attached to the DNA strand, facilitating replication.

17. Essential Role of Primers in DNA Replication:

• Q: Why is the use of primers essential in DNA replication?
• A: Primers provide the 3′ OH required for DNA polymerase to start synthesizing new DNA strands.

18. Helicase’s Function in DNA Replication:

• Q: What is the role of helicase in DNA replication?
• A: Helicase unwinds the DNA double helix by breaking hydrogen bonds between base pairs.

19. Topoisomerase in DNA Replication:

• Q: What is the main function of topoisomerase during DNA replication?
• A: Topoisomerase breaks and rejoins the DNA double helix to relieve twisting forces generated during the replication process.