NUCLEIC ACID ISOLATION PPT (1)

Nucleic Acid Isolation Notes

Purpose of Nucleic Acid Extraction

  • Genetic Studies: Understanding genetic material and hereditary traits.
  • Cancer Research: Analyzing genetic changes associated with cancer.
  • Detection of Microorganisms: Identifying bacteria, viruses, or fungi present in samples.
  • Human Identity Testing: Establishing identity through DNA fingerprinting.

Common Sources for Nucleic Acid Isolation

  • Body Fluids: Whole blood, sperm, urine, saliva.
  • Biological Samples: Hair, bones, nails, tissues, buccal swabs.
  • Cultured Microorganisms: Bacteria, yeast cultures.
  • Plant or Animal Tissues: Various specific tissues for genetic study.

Key Differences Between DNA and RNA Isolation

  • DNA: Stable, long and thin strands; sensitive to pipetting and vortexing.
  • RNA: Unstable, often requires testing for RNA viruses.

Basic Steps in DNA Isolation

  1. Cell Lysis: Break the cell membrane to release nucleic acids.
  2. Removal of Membrane Lipids: Separate lipids from nucleic acids.
  3. Removal of Proteins: Use enzyme/proteinase to eliminate proteins from the mixture.
  4. Precipitation with Alcohol: Isolate the nucleic acids using alcohol.

Specimen Collection Guidelines

  • Bacteria: Collect during mid to late-log growth phase.
  • Fungi: Harvest during luxuriant growth of mold or yeast phase.
  • Blood: Freshly collected or from luminol-stained material.
  • Tissue Samples: Use fresh or preserved samples.
  • Human Cells: Obtain from swabs, sediments, etc.
  • Plant Material: Collect roots or meristem samples,

Yield of DNA from Different Specimen Sources

  • Blood: 50-200 µg (from 1 mL), buffy coat yields 100-500 µg.
  • Bone Marrow: 30-70 µg (1 mL).
  • Cultured Cells: 1-10 µg (10^6 cells).
  • Tissues: 2-250 µg (1 mg).
  • Note: Yields will vary with conditions and specimen type.

Specimen Preparation for RNA Isolation

  • Keep samples frozen in liquid nitrogen or buffer to inactivate RNases.
  • Isolate RNA from bacteria and fungi through chemical lysis or grinding in liquid nitrogen.

Yield of RNA from Various Specimen Sources

  • Blood: 1-10 µg (1 mL).
  • Buffy Coat: 5-10 µg (1 mL).
  • Cultured Cells: 50-150 µg.
  • Fixed Tissues: Typically lower yield due to processing.

Disruption Techniques for Nucleic Acid Isolation

  1. Mechanical Disruption: Physical disruption of cell walls or membranes.
  2. Enzymatic Disruption: Use proteins (e.g., Proteinase K) to digest proteins.
  3. Chemical Disruption: Solubilize cell membranes using detergents like SDS or CTAB.

Isolation Methods

  • Liquid Phase: Organic (phenol-chloroform) or inorganic methods for larger volumes.
  • Solid Phase: Uses column filters or magnetic beads, preferred due to ease and automation.

Methods for DNA Isolation

  1. Organic Isolation: Separates nucleic acid based on solubility; uses phenol and chloroform.
  2. Inorganic Isolation: Uses low pH and high salt to selectively precipitate proteins.
  3. Solid Phase Isolation: Rapid extraction using silica-based products to isolate DNA efficiently.

Sample Assessment: Quantification of Nucleic Acids

  • Electrophoresis: Visualizes nucleic acids; uses agarose or polyacrylamide gels with fluorescent dyes.
  • Spectrophotometry: Measures absorbance at 260 nm, with results indicating concentration and purity of DNA/RNA.
      - High-quality DNA: Ratio of 1.8 to 2.0.
      - Contamination indicators:

Spectrophotometer Use for DNA Quantification

  1. Preparation: Run the spectrophotometer and prepare cuvettes (control and test).
  2. Downtime: Use distilled water as control and mix with purified DNA sample.
  3. Calibration: Set to DNA settings, read absorbance, and calculate concentration and purity.

Common Contaminants and Absorbance Peaks

  • Organic compounds: 230 nm
  • Phenols: 270 nm
  • Proteins: 280 nm
  • Particulate matter: >330 nm

Conclusion

  • Proper techniques and practices are essential for successful nucleic acid isolation for research and diagnostic purposes. Knowledge of sources, methods, and assessments assures high-quality results in genetic studies.