BIOL2050W2 L2: Molecular Genetics on 03/03/2025 (Mon)

Introduction

• Overview of routine molecular experimental techniques used to address specific research questions.

• Importance of understanding DNA properties:

  • DNA’s preference for double-stranded structure and hybridization to complementary base pairs.

  • Negative charge of the sugar-phosphate backbone of DNA, which can be exploited in experiments.

MicroRNA in Plants

• MicroRNA: Small 21-nucleotide RNA sequences that regulate gene expression by binding to complementary genes.

  • Functions include degrading transcripts and preventing translation, adding another layer of regulation.

• Discussion of research conducted by PhD supervisor Andy, focusing on microRNA production in plants (2009-2012).

• Upcoming relevance for students in plant molecular biology module (Bio 3.1).

Nucleic Acid Hybridization

• Concept of nucleic acid hybridization: DNA and RNA prefer to be double-stranded.

• Major techniques:

  • Southern Blotting: For DNA detection, developed by Edward Southern.

  • Northern Blotting: For RNA detection.

  • Other techniques include Western (protein) and Eastern blotting (post-translational modifications).

Southern Blotting Techniques

• Purpose of Southern blotting:

  • Identification of gene sources, length of transcripts, and status of DNA (e.g., methylation).

  • Analysis of gene family members, such as ligases and double-stranded RNA binding proteins (DRB).

• Process of Southern Blotting:

  1. Digest DNA with restriction endonucleases.

  2. Separate DNA fragments using agarose gel electrophoresis.

  3. Denature DNA to make it single-stranded.

  4. Transfer DNA to a solid membrane.

  5. Label DNA with a nucleic acid probe.

  6. Detect hybridized DNA with radioactive probe.

Restriction Endonucleases

• Explanation of restriction endonucleases used in DNA digestion:

  • Enzymes from bacteria that cut DNA at specific sequences (e.g., EcoRI, BamHI, SalI).

  • Affects DNA mobility in gels based on cut frequency.

Application in Research

• Example of Andy's research to identify double-stranded RNA binding protein family members in Arabidopsis:

  • Use of EcoRI to cut DNA around the DRB domain.

  • Analysis of hybridization patterns indicating multiple family members (DRB1 through DRB5).

  • Functionality associated with microRNA production.

Northern Blotting Techniques

• Purpose of Northern blotting:

  • Assess RNA expression levels and patterns in various tissues.

  • Confirm gene expression in knockout mutants.

• Process of Northern Blotting:

  1. Size separation of RNA without the need for digestion.

  2. Transfer RNA onto a membrane using capillary action.

  3. Synthesize a specific nucleic acid probe for the target gene.

  4. Detect and quantify hybridized RNA using a probe.

Results from Andy’s Research

• RNA from various tissues showed expression of DRB1 across seedlings, roots, leaves, stems, and flowers.

• Comparison of wild-type versus DRB1 knockout demonstrated significant impacts on plant health and development due to absence of DRB1.

MicroRNA Processing and Function

• Role of DRB1 in processing microRNA:

  • Interaction with Dicer-like 1 for mature microRNA production.

  • Impact of microRNA on gene regulation and plant development.

• Consequences of knocking out the DRB1 gene leading to phenotype disruptions.

In Situ Hybridization Techniques

• Overview of in situ hybridization as a contemporary method to avoid radioactivity:

  • Steps include fixing samples, denaturing nucleic acid, and using fluorescent probes.

  • Visualization with fluorescence microscopy.

• Applications for studying gene expression patterns in various tissues, including comparisons between microRNAs and mRNA.

Conclusion

• Emphasis on the connection between theoretical genetic concepts and practical molecular biology techniques.

• Importance of understanding these techniques for future research and applications in biotechnology.