MLSC 3063 Notes - Nucleic Acid Characterization

Principles of Molecular and Immunologic Studies

Course and Module Details

  • Course Code: MLSC 3063
  • Instructor: Professor Labiner
  • Module: Module 2
  • Lecture: 3A - Nucleic Acid Characterization

Objectives of Nucleic Acid Characterization (Parts A & B)

  • Students will be able to:
    • Describe restriction endonucleases and their applications in producing a DNA restriction map.
    • Diagram the Southern blot procedure.
    • Explain depurination and denaturation of resolved DNA.
    • Describe the procedure involved in blotting (transfer) DNA from gel to membrane.
    • Discuss the purpose and structure of probes utilized in blotting procedures.
    • Outline how a nucleic acid probe identifies a sequence.
    • List conditions that favor probe hybridization.
    • Recount conditions that hinder nucleic acid annealing by homology.
    • Calculate the melting temperature of a given double-stranded DNA (dsDNA) sequence.
    • Compare radioisotopic and non-isotopic labeling choices for nucleic acids.
    • Detect nucleic acid sequences using ethidium bromide or SYBR green staining.
    • Explain the utility of Northern and Western blots.
    • Describe the methodology of microarrays, including design and application.

Restriction Endonucleases

  • **Definition: **

    • Restriction Endonucleases are specialized proteins found exclusively in microorganisms. They recognize specific nucleotide sequences typically 4 to 6 nucleotides long, enabling them to cut the DNA phosphate backbone at or near the recognition site without causing damage to the bases.

  • Characteristics:

    • Recognize symmetrical double-stranded DNA (dsDNA).
    • Utilized for the digestion of DNA, producing restriction fragments ranging from 100 to 1000 base pairs (bp).
    • Serve as crucial molecules for hybridization procedures such as the Southern blot or for the direct identification of mutations.

  • Discovery and Function:

    • Discovered in E. coli strains to restrict viral infection by certain bacteriophages (viruses targeting bacteria).
    • They serve as a bacterial mechanism to resist viral attacks and eliminate viral sequences.

  • Nomenclature:

    • Named based on the bacteria from which they are isolated (e.g., EcoRI from Escherichia coli species, strain R, first identified).

  • Specific Example - EcoRI:

    • EcoRI recognizes the sequence 5'-G-A-A-T-T-C-3'.
    • It cuts one strand of dsDNA at one GA point and the second strand at a complementary AG point.
    • The resulting fragments have single-stranded 'sticky ends' that facilitate recombination with other DNA pieces, stabilized by the enzyme DNA ligase.

  • Other Examples of Restriction Endonucleases and Recognition Sequences:

    • EcoRI from E. coli, sequence: 5'-G-AATTC-3' (3'-C-TTAAG-5')
    • EcoRV from E. coli, sequence: 5'-G-ATATC-3'
    • HindIII from Haemophilus influenzae, sequence: 5'-A-AGCTT-3'

Restriction Enzyme Mapping

  • Mapping Example:
    • Overview of restriction enzyme mapping is illustrated with enzymes BamH1 and Xhol, which can produce restriction fragments of varying length based on their recognition sites within a plasmid.
    • Example sizes of fragments include:
    • 4.3 kb, 3.7 kb, 4.0 kb
    • 2.8 kb, 2.3 kb
    • 1.7 kb, 1.9 kb, 1.2 kb, etc.

Southern Blot Overview

  • Introduction:

    • Developed by Sir Edwin Southern in 1975.
    • Involves digestion of nucleic acids by restriction endonucleases and subsequent separation by gel electrophoresis.
    • This can involve DNA (Southern) or RNA fragments (Northern).

  • Procedure Details:

    • The nucleic acids are separated based on size through gel electrophoresis.
    • The resolved RNA or denatured DNA fragments are then transferred onto a semi-solid membrane (like nitrocellulose or nylon) and immobilized.
    • The membrane-bound nucleic acids are hybridized to a specifically labeled probe for detection.

  • Probes:

    • Probes are typically homologous single-stranded nucleic acids labeled for detection and visualization.
    • For genomic (wild-type) DNA extraction, over 10 micrograms of DNA is required for the Southern blot method since it does not amplify DNA. Amplified DNA only requires 1-5 micrograms and must be cut into fragments of 100-1000 bp.

  • Denaturation:

    • Denaturation is achieved by using NaOH or heat, generating single-stranded DNA (ssDNA) from larger fragment sizes.
    • The transfer to solid supports such as nitrocellulose or nylon filters occurs following denaturation.

  • Detection Steps:

    • A single-strand probe is then added to the membrane to detect the sequence of interest through hybridization.

Electrophoresis & Blotting Procedure

  • Equipment and Materials:

    • Use agarose gel for electrophoresis, comparing to size markers to separate known sizes of DNA fragments.
    • The separated DNA is then transferred onto nitrocellulose paper for further analysis.
    • Capillary transfer can be facilitated under specific conditions using horizontal stacks of absorbent material and reservoir setups.

  • After Transfer:

    • Post-transfer, the nitrocellulose paper contains tightly bound DNA, ready for hybridization and detection.

Conclusion of Lecture Notes

  • All procedures (from restriction enzyme digestion to Southern blotting) are fundamental techniques in molecular biology and provide essential insights into nucleic acid characterization and analysis.
  • Understanding these techniques promotes advanced comprehension of genetic identification, mapping, and diagnostic applications in molecular studies.