Biotechnology Principles and Processes: A Comprehensive Study Guide

Definition and Scope of Biotechnology

  • Biotechnology involves techniques that utilize live organisms or enzymes from organisms to generate products and processes that are beneficial to humanity.

  • Primitive forms of biotechnology include microbe-mediated processes used in the production of items such as curd, bread, and vine.

  • Modern biotechnology encompasses a wide range of advanced processes and techniques, including:

    • In vitro fertilisation (IVF) resulting in "test-tube" babies.
    • The synthesis and functional use of a gene.
    • The development of DNA vaccines.
    • The correction of defective genes.

  • The European Federation of Biotechnology ($EFB$) provides a comprehensive definition: "The integration of natural science and organisms, cells, parts thereof, and molecular analogues for products and services."

Principles of Biotechnology

  • The foundation of modern biotechnology rests on two core engineering principles:

  1. Genetic Engineering: This involves the introduction of foreign genetic material into host organisms to alter the phenotype of that host.

  2. Bioprocess Engineering: This focuses on maintaining a sterile environment within chemical engineering processes. This sterility ensures that only the desired microbe or eukaryotic cell is grown in large quantities for the industrial manufacture of biotechnological products like antibiotics, vaccines, or enzymes.

Conceptual Basis of Genetic Engineering

  • Traditional hybridization in plant and animal breeding often leads to the inclusion and multiplication of undesirable genes alongside desired ones.

  • Genetic engineering overcomes this by specifically selecting genes of desirable qualities from one organism and transferring them to a host organism, resulting in an organism with targeted traits.

  • Key techniques in genetic engineering include:

    • Creation of recombinant DNA ($rDNA$).
    • Use of gene cloning.
    • Gene transfer mechanisms.

  • Replication and Cloning:

    • Chromosomes contain a specific DNA sequence termed the origin of replication ($ori$), which is the starting point for DNA replication.
    • For an alien piece of DNA to multiply within a host, it must be integrated into a chromosome containing an $ori$.
    • When alien DNA is linked to an $ori$, it can replicate and multiply within the host. This process is known as Cloning, which refers to making multiple identical copies of a template DNA.

Recombinant DNA Technology Origins

  • The first recombinant DNA was created by Stanley Cohen and Herbert Boyer in 19721972.

  • They isolated an antibiotic-resistant gene from the bacterium Salmonella typhIMURIUMSalmonella\,typhIMURIUM and introduced it into Escherichia coliEscherichia\,coli.

  • Procedural Details:

    • The antibiotic-resistant gene was cut from the SalmonellaSalmonella DNA using restriction endonuclease enzymes.
    • Plasmids (autonomously replicating circular extra-chromosomal DNA) were used as vectors to transfer the alien DNA into E. coliE.\,coli.
    • The antibiotic-resistant gene was linked to the plasmid vector using the enzyme DNA ligase.
    • Once inside the host, DNA polymerase utilized the host's machinery to multiply copies of the antibiotic-resistant gene through Gene Cloning.

Three Basic Steps in rDNA Technology

  1. Identification of DNA containing the desired genes.
  2. Introduction of the identified DNA into the host organism.
  3. Maintenance of the introduced DNA in the host and its successful transfer to the progeny.

Tools of Recombinant DNA Technology

  • The primary tools required for $rDNA$ technology include:
    1. Restriction enzymes
    2. Polymerase enzymes
    3. Ligase enzymes
    4. Cloning vectors
    5. Competent host (for transformation with recombinant DNA)

Restriction Enzymes (Molecular Scissors)

  • These enzymes are produced by specific bacteria as a defense mechanism against bacteriophages (bacterial viruses). They prevent viral replication by cutting the phage DNA into fragments.

  • Restriction enzymes cleave DNA at specific base pair sequences called recognition sequences.

  • The first discovered restriction endonuclease was Hind IIHind\,II.

  • Nomenclature of Restriction Enzymes (Example: Eco RIEco\,RI):

    • First Letter ($E$): Represents the genus of the prokaryotic cell (EscherichiaEscherichia).
    • Next Two Letters ($co$): Represent the species name (colicoli).
    • Third Letter ($R$): Indicates the specific strain of bacteria (RY 13RY\,13).
    • Roman Numeral ($I$): Indicates the order in which the enzyme was discovered from that strain.

  • Classification of Nucleases:

    • Exonucleases: Remove nucleotides from the physical ends of the DNA strand.
    • Endonucleases: Make cuts at specific internal positions within the DNA.

  • Recognition and Action:

    • Each restriction endonuclease recognizes a specific palindromic nucleotide sequence (a sequence that reads the same forward and backward when the orientation of reading, such as 5′5' to 3′3', is kept identical).
    • Example Palindrome (Eco RIEco\,RI site):
      • 5′−G A A T T C−3′5' - G\,A\,A\,T\,T\,C - 3'
      • 3′−C T T A A G−5′3' - C\,T\,T\,A\,A\,G - 5'
    • The enzyme cuts at a point slightly away from the center of the palindrome but between the same two bases on both strands (e.g., between $G$ and $A$).
    • This staggered cut leaves single-stranded protruding portions called Sticky ends. These ends facilitate the binding of DNA ligase by forming hydrogen bonds with complementary cut DNA fragments.

Separation and Isolation of DNA Fragments

  • Cutting DNA with restriction endonucleases produces various fragments which are separated using Gel Electrophoresis.

  • Gel Electrophoresis Process:

    • DNA fragments are negatively charged and move toward the positive electrode (anode) under an electric field.
    • The most common matrix used is Agarose Gel, a natural polymer derived from sea-weeds.
    • The gel acts as a sieve; smaller fragments move faster and further through the pores than larger fragments.

  • Visualization and Extraction:

    • DNA is invisible to the naked eye and must be stained with Ethidium bromide.
    • Separated DNA bands appear as bright orange under UV radiation.
    • The process of cutting the separated DNA bands out of the agarose gel and extracting them from the gel piece is called Elution.

Cloning Vectors (Vehicles for Cloning)

  • A vector acts as a vehicle to transport foreign DNA into a host cell. Common vectors include Plasmids and Bacteriophages.

  • Salient Features of a Vector:

  1. Origin of Replication ($ori$): A specific sequence where replication initiates. It controls the copy number of the linked DNA.

  2. Selectable Marker: Genes that allow for the identification and elimination of non-transformants while permitting the growth of transformants (cells that have taken up the vector). Common markers include resistance genes for antibiotics such as ampicillin, chloramphenicol, tetracycline, or kanamycin.

  3. Cloning Sites (Recognition Sites): Locations where the alien DNA is inserted. Ligation is typically performed at a restriction site within one of the antibiotic resistance genes.

    • Example: In vector pBR 322pBR\,322, a foreign DNA can be ligated at the Bam H1Bam\,H1 site of the tetracycline resistance gene. This causes the recombinant plasmid to lose its tetracycline resistance (tetRtet^R) but retain its ampicillin resistance (ampRamp^R).
    • Selection Procedure: Transformants are grown on ampicillin medium. Those that survive are then replica-plated onto tetracycline medium. Recombinants will grow on ampicillin but die on tetracycline, while non-recombinants will grow on both.

Insertional Inactivation

  • This is an alternative selection method based on color production using a chromogenic substrate.

  • A plasmid may carry a gene for the enzyme β\beta-galactosidase.

  • If the gene is functional, the enzyme reacts with a chromogenic substrate to produce a blue color.

  • When a foreign gene is inserted into the code for β\beta-galactosidase, the gene becomes inactivated (insertional inactivation). Consequently, the bacterial colonies do not produce color and appear white, identifying them as recombinant colonies.

Vectors for Plants and Animals

  • Plants: AgrobacteRIUM tUMefaciensAgrobacteRIUM\,tUMefaciens, a dicot pathogen, uses a "T-DNA" fragment from its tumor-inducing (TiTi) plasmid to transform plant cells into tumors. Scientists have disarmed this plasmid, removing its pathogenicity while keeping its ability to deliver desired genes.

  • Animals: Retroviruses naturally transform animal cells into cancerous ones. These have been disarmed and repurposed to carry desirable genes into animal hosts.

Competent Host and DNA Introduction

  • Since DNA is hydrophilic, it cannot pass through cell membranes easily. The host must be made "competent."

  • Methods of Introduction:

    1. Chemical/Heat Shock: Treating cells with divalent cations (e.g., calcium) increases pore efficiency. The $rDNA$ is incubated with cells on ice, subjected to a heat shock at 42∘C42^\circ C, and returned to ice.
    2. Microinjection: Recombinant DNA is injected directly into the nucleus of an immobilized host cell using a micro-needle (used for transgenic animals).
    3. Gene Gun (Biolistics): High-velocity micro-particles of gold or tungsten coated with DNA are bombarded onto plant cells.

Processes of Recombinant DNA Technology

  • The technology follows a specific sequence:

  1. Isolation of Genetic Material:

    • Cells are broken using enzymes: lysozyme for bacteria, cellulase for plants, or chitinase for fungi.
    • RNA is removed by ribonuclease; proteins are removed by protease.
    • Purified DNA is precipitated by adding chilled ethanol, appearing as fine threads.
    • Spooling is used to wind these DNA threads onto a reel.

  2. Cutting DNA at Specific Locations:

    • Purified DNA and vector DNA are incubated with specific restriction endonucleases.
    • Agarose gel electrophoresis checks the progress of the digestion.
    • The cut gene of interest and cut vector are joined using DNA ligase to form Recombinant DNA.

  3. Amplification using PCR (Polymerase Chain Reaction):

    • Denaturation: Double-stranded DNA is heated to separate into single strands.
    • Annealing: Two sets of primers (single-strand DNA sequences 2020-3030 bases long) bind to complementary sequences.
    • Extension: Taq polymeraseTaq\,polymerase (a thermostable enzyme from the bacterium ThermUS AQUatICUSThermUS\,AQUatICUS) extends the primers using supplied nucleotides.
    • The cycle can be repeated to amplify the segment approximately one billion times.

  4. Insertion and Expression:

    • The $rDNA$ is introduced into the host (Transformation).
    • The cells are cultured under optimal conditions to express the foreign gene and produce the desired protein.

Bioreactors and Downstream Processing

  • Bioreactors: Large vessels (100100 to 10001000 litres) where raw materials are biologically converted into products using microbial, plant, or human cells.

    • They provide optimal temperature, pHpH, substrate, salts, vitamins, and oxygen.
    • Stirred-tank reactor: Usually cylindrical with a curved base. It includes an agitator system, oxygen delivery, foam control, temperature and pHpH control, and sampling ports.

  • Downstream Processing: Standard procedures to separate and purify the desired product from the culture. This includes formulation with suitable preservatives before the product is ready for use.