Biotechnology: Principles and Processes

Principles of Biotechnology

This chapter Biotechnology: Principles and Processes, focuses on the fundamental principles and detailed processes involved in biotechnology, with a specific emphasis on recombinant DNA technology and its tools.

Introduction to Biotechnology

• Definition:
  • Biotechnology refers to the use of living organisms, cells, or their enzymes to develop products and processes beneficial to humans.
• Definition by EFB (European Federation of Biotechnology):
  • Biotechnology is defined as the integration of natural sciences with organisms, cells, their components, and molecular analogues to generate products and services.
• Scope:
  • Biotechnology includes both traditional applications and modern molecular approaches.

• Traditional Examples:
  • Preparation of curd
  • Bread making
  • Wine production

• Modern Biotechnology:
  • Modern biotechnology involves deliberate modification of genetic material to develop organisms with improved or novel characteristics.
• Examples:
  • In vitro fertilisation (test-tube babies)
  • Gene synthesis
  • DNA vaccines
  • Gene therapy

• Note –
  • The development of recombinant DNA technology made it possible to create organisms with new, non-naturally occurring capabilities.
  • This approach is commonly termed genetic engineering.

Paul Berg is regarded as the father of genetic engineering and received the Nobel Prize in 1980 for his pioneering work in recombinant DNA technology.

Principles of Biotechnology

Two Core/fundamental Techniques:

1. Genetic Engineering

• Genetic engineering involves deliberate modification of genetic material (DNA or RNA).
• It includes:
  1. Isolation of specific genes
  2. Formation of recombinant DNA
  3. Gene cloning
  4. Gene transfer into host organisms

• Purpose
  • To introduce one or a set of desirable genes into a host organism without transferring unwanted genes.
• Result
  • Alteration of phenotype of the host organism.

2. Bioprocess Engineering

• Bioprocess engineering focuses on maintaining sterile, contamination-free conditions for the large-scale growth of desired microorganisms or eukaryotic cells.

• Purpose: To produce biotechnological products such as:
  • Antibiotics
  • Vaccines
  • Enzymes
  • Industrial metabolites
• This requires controlled environmental parameters and aseptic conditions to ensure growth of only the intended organism.

Recombinant DNA Technology

• Definition
  • Recombinant DNA (rDNA) technology involves joining DNA from different sources and introducing it into a host organism to produce new genetic combinations.

Basic Steps & Concepts in Genetically Modifying an Organism

Three essential steps are involved in the formation of a genetically modified organism (GMO):

1. Identification of DNA with Desirable Genes

• The first step involves locating and isolating the gene responsible for the desired trait.

Limitations of Traditional Methods

• Sexual reproduction introduces genetic variation.
• Hybridization may transfer undesirable genes along with desired ones.
• Asexual reproduction preserves traits but does not introduce specific new traits selectively.

Advantage of Genetic Engineering

• Genetic engineering allows precise isolation and transfer of only the required/desirable gene.

Terminology

• The desirable gene may be referred to as:
  • Gene of interest
  • Target gene
  • Foreign gene
  • Alien gene
  • Source DNA
  • Inserted gene
• All terms indicate the specific gene selected for transfer.

2. Introduction of Identified DNA into the Host

• The isolated (desired) gene is linked to a vector, commonly a plasmid.
• A vector is used to deliver alien DNA into the host organism.

Vector

• A plasmid is an autonomously replicating, circular, extra-chromosomal DNA molecule of bacterial cell.

Restriction Enzymes

• DNA is cut at specific recognition sequences using restriction endonucleases (molecular scissors).

DNA Ligase

• The enzyme DNA ligase joins the cut DNA fragment with vector DNA by forming phosphodiester bonds.

• The newly formed circular DNA molecule is called recombinant DNA.
• This recombinant plasmid is then introduced into a suitable host organism (e.g., E. coli).

3. Maintenance of Introduced DNA in the Host and Transfer to Progeny

• A foreign DNA fragment cannot replicate independently unless it is associated with a replication origin.

Origin of Replication (Ori)

• Ori is a specific DNA sequence that initiates replication.
• When foreign DNA is linked to a vector containing an ori sequence, it gains the ability to replicate within the host cell.

• Integration or stable maintenance within the host ensures:
  • Replication of the inserted gene
  • Transmission to daughter cells
  • Production of multiple identical copies
• This process of generating identical copies of a DNA sequence is called cloning.

Recombinant DNA Technology

• Involves joining and inserting foreign DNA into a host organism to produce new genetic combinations.

Tools of Recombinant DNA Technology

To perform genetic engineering or recombinant DNA technology, three major biological tools are required:

1. Enzymes (restriction enzymes, polymerase enzymes, ligases)
2. Cloning vectors (DNA carrying vehicle)
3. Competent Host Organisms (bacterial, plant, or animal cell).

These tools collectively enable cutting, joining, transfer and multiplication of desired DNA fragments.

1. Restriction Enzymes (R.E)(molecular scissors)

• Definition:
  • Restriction enzymes are specific nucleases that cleave (cut) DNA at specific nucleotide sequences known as recognition sites.

Discovery and Significance

• First identified in bacteria by Werner Arber in 1963.
• Later, Arber along with Hamilton Smith and Daniel Nathans received the Nobel Prize for discovery of restriction endonucleases.
• Discovery of these enzymes laid the foundation of recombinant DNA technology.

• Werner Arber observation: restriction-modification (R-M) system
  • Bacteria defend against foreign DNA using two enzyme types.
  • One enzyme (methylase) adds methyl groups to host’s own DNA to protect it, while the other (restriction endonuclease) cuts unmethylated, foreign (viral) DNA at specific sites to degrade it.
  • By differentiating between self (methylated) and non-self (unmethylated) DNA, bacteria maintain their genomic integrity while destroying viral DNA.

First Restriction Endonuclease

• Hind II was the first restriction endonuclease to be isolated (in 1968).
  • Source: Haemophilus influenzae Rd
  • Property: Recognised a specific six base-pair sequence
  • Cut DNA at a precise location within that sequence
• This demonstrated that DNA can be cut at specific, predictable sites.

Today, over 900 restriction enzymes are known.

Nature and Classification of Nucleases

• Restriction enzymes belong to a broader class called nucleases.
• Types of Nucleases:
  1. Exonucleases: Remove nucleotides sequentially from the ends of DNA.
  2. Endonucleases: Cleave DNA at specific internal positions.
• Restriction endonucleases are used in recombinant DNA technology because they cut within DNA at defined (specific) sequences.

Naming of Restriction Enzymes

The naming system reflects the bacterial source:

Example: EcoRI (pronounced “Eco R one”)

• E → Genus (Escherichia)
• co → Species (coli)
• R → Strain (RY13)
• I → Roman number 1, Indicates order of isolation from that strain

• All letters derived from genus and species are written in italics in scientific notation.

Recognition Sequence and Palindromes

• Each restriction enzyme recognises a specific DNA sequence known as the recognition site.
• These sequences are typically palindromic.

Definition of Palindromic Sequence

• A palindromic sequence reads the same in the 5′ → 3′ direction on both strands when orientation is kept constant.

Example (EcoRI recognition site):

5′ — GAATTC — 3′
3′ — CTTAAG — 5′

• This palindromic sequence is recognized only by EcoRI and is also called the recognition sequence for the enzyme.
• Such sequences allow symmetrical cutting of DNA.

Mechanism of Action

• Restriction enzymes:
  • Bind to recognition sequence
  • Cleave both DNA strands
  • Cut slightly away from the centre of palindrome
• This produces either:
  1. Sticky (cohesive) ends or
  2. Blunt ends

Sticky Ends

• Staggered (non-linear) cuts made by restriction enzymes in DNA produce short, single-stranded overhangs known as sticky ends (or cohesive ends).
• Example: EcoRI produces sticky ends.
• Properties:
  • Overhangs are complementary
  • Can form hydrogen bonds with matching (complementary) sequences (easy annealing)
  • Facilitate joining of foreign DNA and vector DNA
  • Increase efficiency of ligation (Joining)

Annealing = recombine (DNA) in the double-stranded form.

Blunt Ends

• Produced when cuts are straight (linear) across both strands.
• Example: Hind II produces blunt ends.

Sticky ends are preferred in recombinant DNA formation due to ease of joining.

Final Result of Restriction and Ligation

When both vector DNA and foreign DNA are cut with the same restriction enzyme:

• Complementary sticky ends are produced
• DNA fragments anneal through hydrogen bonding between sticky ends.
• DNA ligase seals the sugar-phosphate backbone.

• This creates recombinant DNA — a new combination of genetic material formed in vitro.

Separation and Isolation of DNA Fragments

Gel Electrophoresis

• Purpose:
  • To separate DNA fragments based on size.
• Principle:
  • DNA carries negative charges due to phosphate groups.
  • Under an electric field:
    • DNA migrates toward the anode (positive electrode)
    • Migration occurs through agarose gel matrix
  • Matrix:
    • Agarose is a polysaccharide extracted from seaweeds.
    • It forms a porous gel acting as a molecular sieve.
• Separation Mechanism:
  • Smaller DNA fragments being lighter, move faster
  • Larger fragments being heavier, move slower
  • Separation occurs due to size-dependent mobility

• Visualization of DNA
  • DNA fragments are not visible directly.
  • They are visualised by:
    • Staining with ethidium bromide (EtBr)
    • Exposure to ultraviolet (UV) radiation
  • Result:
    • DNA bands appear as bright orange fluorescent bands under UV light.

• Elution – After DNA fragments separation:
  • Desired DNA band is cut from gel
  • DNA is extracted and purified
• This step is called elution.
• Purified DNA fragments are then used for recombinant DNA construction.

Summary of Tools Workflow

1. Cutting DNA: DNA is cut at specific sites using restriction enzymes.
2. Separating DNA: DNA fragments are separated by agarose gel electrophoresis.
3. Visualizing DNA: Desired fragments are visualised using EtBr staining under UV light.
4. Extracting DNA: Required DNA fragment is extracted from the gel by elution.
5. Ligation: DNA ligase joins foreign DNA with vector DNA.
6. Transformation: Recombinant DNA is introduced into a competent host cell.

2. Cloning Vectors

• Definition:
  • Cloning vectors are DNA molecules that carry foreign DNA into a host cell and ensure its replication inside the host.
• They are also referred to as carrier DNA or vehicle DNA.
• When a vector replicates inside the host, the attached foreign DNA is also replicated. This enables cloning, i.e., production of multiple identical copies of the inserted gene.

Types of Cloning Vectors

• Vectors commonly used in genetic engineering include:
  • Plasmids
  • Bacteriophages
  • Cosmids
  • Yeast Artificial Chromosomes (YACs)
  • Bacterial Artificial Chromosomes (BACs)
  • Transposons
• However, plasmids and bacteriophages are most widely used in basic recombinant DNA work.

1. Plasmids
   • Circular, extra-chromosomal DNA molecules
   • Present naturally in bacteria
   • Replicate independently
   • May exist in 1–100 copies per bacterial cell
2. Bacteriophages
   • Viruses that infect bacteria
   • Can carry larger DNA inserts
   • Replicate efficiently inside bacterial cells

Essential Features of a Cloning Vector

To function efficiently, a cloning vector must possess the following features:

1. Origin of Replication (ori)

• Definition
  • A specific DNA sequence from which replication initiates.
• Function
  • Enables replication of vector DNA inside the host cell
  • Any foreign DNA linked to ori also replicates
  • Determines copy number of the recombinant DNA
• Control of Copy Number – The nature of ori regulates how many copies of DNA are produced:
  • High-copy origin → large number of DNA copies
  • Low-copy origin → limited number of copies
  • Importance: This is important when large amounts (multiple copies) of target DNA are required.

2. Selectable Marker

• Definition
  • A gene present in the vector that allows identification and selection of transformants (cells that have taken up the vector) from non-transformants.
• Function of Selectable Marker:
  • Eliminates non-transformants
  • Allows only transformed cells to grow under selective conditions

Transformation: The process of introducing foreign DNA into a host cell.

Common Selectable Markers

1. Antibiotic Resistance Genes

• Common markers include genes for resistance to antibiotics like ampicillin, chloramphenicol, tetracycline, or kanamycin.

2. Color-Producing Genes (Chromogenic Markers)

• Some vectors contain genes that produce coloured products in the presence of specific substrates.
• These are used for visual differentiation of recombinants.
• Thus used as markers.

3. Cloning Sites (Restriction Sites)

• Definition
  • Specific recognition sequences for restriction enzymes present in the vector.
• Requirement
  • A vector must contain at least one unique restriction site to allow insertion of foreign DNA.
• Single Site Preference
  • it is highly preferable for a restriction enzyme to have only one unique recognition site within a vector (plasmid).
  • Reason:
    • Multiple restriction sites can cause unwanted cuts in the vector DNA.
    • Unwanted cuts make the cloning process less efficient.
    • It increases the risk of insertion of foreign DNA at the wrong location.
• Multiple Cloning Site (MCS)
  • Many modern vectors contain a short DNA segment with several unique restriction sites ( for various RE) clustered together.
  • This region is called a polylinker or MCS.
• Example: pBR322 Plasmid

pBR322 was one of the first artificial cloning vectors, constructed in 1977 by Bolivar and Rodriguez.

Key features:

• Origin of replication (ori)
• Two antibiotic resistance genes:
  • ampR (ampicillin resistance)
  • tetR (tetracycline resistance)
• Several unique restriction sites

Some restriction sites lie within antibiotic resistance genes, enabling insertional inactivation.

Insertional Inactivation

• Definition
  • Insertion of foreign DNA into a functional gene (e.g. Antibiotic resistance gene) of the vector, leading to disruption of that gene.
  • This property is used to distinguish recombinant plasmids from non-recombinant plasmids.
• Two main methods are used:

A. Antibiotic Resistance–Based Selection

• Recombinant plasmids lose resistance to one antibiotic due to the insertion of foreign DNA.
• Selection is done by growing cells on media with different antibiotics.
• Transformants grow on ampicillin media but not on tetracycline media.
• Non-recombinants grow on both.

B. Chromogenic (color producing) Substrate–Based Selection

• Principle:
  • Foreign DNA is inserted into the gene encoding β-galactosidase, which normally produces blue colour in the presence of a chromogenic substrate.

Mechanism

1. Insertional Inactivation: Foreign DNA insertion disrupts the β-galactosidase coding region.
2. Loss of Enzyme Activity: The enzyme becomes non-functional.
3. Color Reaction in Presence of Substrate:
   • Non-recombinant colonies: Functional β-galactosidase present → colonies appear blue.
   • Recombinant colonies: Enzyme inactive due to insertion → colonies remain white.

Identification

• Recombinant colonies can be identified visually (white colonies) without using multiple antibiotic plates.

4. Vectors for Cloning Genes in Plants and Animals

Learning from Nature

• Certain bacteria and viruses naturally transfer DNA into eukaryotic cells in order to infect them.
• After modification of their virulent (disease-causing) genes, these organisms can be used as vectors to deliver desirable genes into eukaryotic cells without causing infection.

Example 1: Agrobacterium tumefaciens

1. Natural Role:
   • Infects dicot plants
   • Transfers a DNA segment called T-DNA into plant cells
   • Causes tumour formation (crown gall disease)
2. Modified Ti Plasmid (Disarmed Vector):
   • Disease-causing genes removed
   • DNA transfer mechanism retained
   • Used to introduce desired genes into plants

Example 2: Retroviruses

1. Natural Role:
   • Naturally integrate their genetic material into animal cells
2. Modified Retroviral Vectors:
   • Disease-causing components removed
   • Used as vectors for gene transfer in animal cells

Conclusion

• Scientists develop modified (disarmed), non-virulent vectors from natural pathogens to deliver genes of interest into plant cells.
• They retain the natural DNA delivery mechanism but remove disease-causing genes.
• Thus, these modified systems function as safe and efficient vehicles for gene transfer without causing disease.

3. Competent Host for Transformation with Recombinant DNA

• Definition
  • A competent host is a cell that has been treated to allow uptake of recombinant DNA.
  • Host systems commonly used:
    • Escherichia coli
    • Yeast
    • Plant cells
    • Animal cells

Why DNA Cannot Enter Cells Easily

• Principle
  • DNA is negatively charged and hydrophilic.
  • The cell membrane is selectively permeable and hydrophobic in nature.
  • Therefore, naked DNA cannot pass through the membrane efficiently.
  • To enable DNA entry, cells must be made competent (capable).

Methods for Making Bacterial Cells Competent

1. Divalent Cation Treatment

• Principle
  • Divalent cations (e.g., Ca²⁺) neutralize negative charges on DNA and cell membrane.
• Mechanism
  • Bacterial cells are treated with calcium chloride.
  • Ca²⁺ ions increase membrane permeability.
  • DNA binds to the cell surface.
• Result
  • Increased efficiency of DNA uptake through cell wall pores.

2. Heat Shock Method

• Principle
  • Sudden temperature change induces transient membrane permeability.
• Procedure
  • Cells incubated with recombinant DNA on ice.
  • Brief heat shock at 42°C.
  • Rapid return to ice.
• Effect
  • Heat shock creates temporary pores in the membrane.
  • Recombinant DNA enters the bacterial cell.
  • This process is called transformation in bacteria.

Gene Transfer in Eukaryotic Cells

• In eukaryotic systems, the term transformation is replaced by transfection.
• Several vectorless gene transfer methods are used.

1. Microinjection

• Principle
  • Direct physical delivery of DNA into nucleus.
• Mechanism
  • Recombinant DNA injected using fine glass micropipette.
  • DNA delivered directly into nucleus of animal cell.
• Advantage
  • Highly precise but technically demanding.

2. Biolistics (Gene Gun Method)

• Principle
  • Physical bombardment of cells with DNA-coated particles.
• Mechanism
  • Microscopic gold or tungsten particles coated with DNA.
  • Particles accelerated at high velocity.
  • DNA enters plant cells.
• Application
  • Widely used in transformation of crop plants such as rice, wheat and maize.

3. Electroporation (not mentioned in NCERT)

• Principle
  • Application of electrical pulse creates temporary membrane pores.
• Mechanism
  • Electric field disrupts membrane integrity briefly.
  • DNA enters through transient pores.
• Application
  • Used in bacterial and eukaryotic cells.

4. Chemical-Mediated Gene Transfer (not mentioned in NCERT)

• Certain chemicals enhance DNA uptake.
• Example: Polyethylene glycol (PEG) increases permeability and promotes DNA entry.

5. Disarmed Pathogen Vectors

• Use modified pathogens to transfer recombinant DNA into host cells.
• Example:
  1. Agrobacterium tumefaciens (Ti plasmid) for plants
  2. Disarmed retroviruses for animal cells
• These modified vectors retain delivery ability but lack disease-causing genes.

Processes of Recombinant DNA Technology

Recombinant DNA technology follows a sequential order of steps:

1. Isolation of genetic material (DNA)
2. Cutting of DNA at specific sites
3. Amplification of gene of interest (if required)
4. Ligation into vector
5. Introduction into host
6. Selection and multiplication
7. Production and downstream processing

1. Isolation of the Genetic Material (DNA)

• Principle
  • DNA must be obtained in pure form, free from proteins and RNA.

Step 1: Cell Disruption

• Cells are broken open to release DNA.
• Enzymes used:
  • Lysozyme – breaks bacterial cell wall
  • Cellulase – digests plant cell wall
  • Chitinase – digests fungal cell wall

Step 2: Removal of Contaminants

DNA in cells is associated with proteins (e.g., histones) and RNA.

• RNA removed using ribonuclease
• Proteins removed using protease

Step 3: DNA Purification

• Chilled ethanol is added.
• DNA precipitates as visible white threads and can be spooled out.
• Result
  • Purified DNA is finally extracted, making it suitable for further restriction digestion.

2. Cutting of DNA at Specific Locations

• Principle
  • Restriction endonucleases cut DNA at specific recognition sequences.
• Procedure
  1. Enzyme Incubation: Purified DNA is incubated with an appropriate restriction enzyme under optimal conditions.
  2. Common Enzyme Use: Both source DNA and vector DNA are cut with the same restriction enzyme.
• Monitoring of Digestion
  • Agarose Gel Electrophoresis is used to confirm DNA digestion.
• Principle of Gel Electrophoresis
  • DNA is negatively charged.
  • Under an electric field, DNA moves toward the positive electrode (anode).
  • Smaller DNA fragments migrate faster than larger fragments.

Preparing Recombinant DNA

• Restriction Cutting: Source DNA and vector DNA are cut using a specific restriction enzyme.
• Mixing: The gene of interest from source DNA is mixed with the cut vector DNA.
• Ligation: DNA ligase joins the DNA fragments, forming recombinant DNA.

3. Amplification of Gene of Interest using PCR

• Definition
  • Polymerase Chain Reaction (PCR) is an in vitro (in lab) technique used to synthesise millions to billions of copies of a specific DNA segment.
  • Conceptually, PCR is controlled DNA replication performed outside the cell.
• Historical Note
  • PCR was developed by Kary Mullis in 1985.

Principle

• PCR amplifies a selected DNA region using:
  1. Template DNA (containing gene of interest)
  2. Two sequence-specific primers
  3. Thermostable DNA polymerase
  4. Deoxynucleotide triphosphates (dNTPs)
• Repeated cycles of heating and cooling result in exponential amplification of the target DNA.

Essential Components

1. Template DNA: Contains the gene of interest.
2. Primers:
   • Short single-stranded oligonucleotides
   • Complementary to sequences flanking the target region
   • Provide free 3′-OH group for DNA polymerase action
3. DNA Polymerase:
   • Taq DNA polymerase is commonly used
   • Isolated from Thermus aquaticus
   • Remains active at high temperatures
4. dNTPs: Building blocks for new DNA synthesis.
5. Buffer System: Maintains optimal pH and ionic strength.

Steps in a Single PCR Cycle

Each cycle consists of three stages:

1. Denaturation
   • Temperature: 90–98°C (commonly ~94°C)
     • Double-stranded DNA is heated
     • Hydrogen bonds break
     • DNA separates into two single strands
     • Single strands act as templates
2. Annealing
   • Temperature: 40–60°C (commonly ~52–55°C)
     • Primers bind to complementary sequences
     • Each primer attaches to the 3′ end of target sequence
     • Determines specificity of amplification
3. Extension (Elongation)
   • Temperature: 72°C (optimum for Taq polymerase)
     • Taq polymerase extends primers
     • Adds complementary nucleotides
     • Synthesises new DNA strands
     • DNA between the two primers is copied

Amplification Pattern

• After one cycle → DNA quantity doubles.
• After ~30 cycles → approximately one billion copies are produced.

This exponential amplification makes PCR highly powerful.

Why Thermostable Polymerase is Essential

• During denaturation, high temperature would inactivate normal DNA polymerase.
• Taq polymerase:
  • Withstands repeated heating cycles
  • Remains functional throughout reaction
  • Enables automated thermal cycling

Applications of PCR

• Detection of pathogens
• Diagnosis of genetic mutations
• DNA fingerprinting
• Prenatal diagnosis
• Forensic analysis
• Gene cloning
• Gene therapy research

Further Use: The amplified DNA can be inserted into a suitable vector for cloning and further studies.

4. Insertion of Recombinant DNA into the Host Cell/Organism

• Purpose:
  • To introduce ligated recombinant DNA into a suitable recipient (host) cell for replication and expression.
• Principle:
  • Host cells must be made competent to take up foreign DNA.
  • After uptake, recombinant DNA replicates inside the host.
  • Transformed cells are identified using selectable markers.
• Making Cells Competent:
  • Recipient cells are treated (chemically or physically) to enable uptake of recombinant DNA.

Mechanism of Selection Using Antibiotic Resistance

Example: Ampicillin Resistance (ampR)

• Step 1: Recombinant plasmid containing ampicillin resistance gene is introduced into E. coli.
• Step 2: Cells are plated on agar medium containing ampicillin.

• Outcome
  • Transformed cells (with plasmid) survive.
  • Non-transformed cells die.
• Reason
  • The ampicillin resistance gene produces an enzyme that neutralises the antibiotic, allowing survival.

Selectable Marker

• Definition
  • A gene that enables identification and selection of transformed cells.
• Functions
  • Confers survival advantage
  • Eliminates non-transformants
  • Ensures only recombinant-bearing cells grow
• Example
  • Ampicillin resistance gene (ampR).

Conceptual Summary

• PCR → Amplifies gene of interest.
• Ligation → Inserts gene into vector.
• Transformation → Introduces recombinant DNA into host.
• Selectable marker → Identifies successful transformants.

Together, these coordinated steps enable cloning and expression of desired genes.

5. Obtaining the Foreign Gene Product

• Purpose:
  • To produce a desirable protein using recombinant DNA technology.
  • Most recombinant DNA applications focus on large-scale production of specific proteins.
• Concept:
  • After successful cloning of a gene of interest:
    • The gene must be expressed under suitable conditions.
    • The host system must provide an optimal environment for protein production.
  • When a protein-coding gene is expressed in a different host organism, the product is called a recombinant protein.

Cloning and Expression of Gene

• Principle
  • The foreign gene is inserted into a suitable cloning vector and introduced into a host cell.
• Process
  • Recombinant vector enters host cell.
  • Vector replicates inside host.
  • Gene of interest is transcribed and translated.
  • Desired protein is synthesised.
• Hosts Used
  • Bacteria (e.g., E. coli)
  • Yeast
  • Plant cells
  • Animal cells
• Outcome
  • Host cells act as biofactories for protein production.

Culture and Extraction of Recombinant Protein

After transformation:

• Cells containing recombinant DNA are grown under controlled laboratory conditions.
• Protein accumulates inside cells or may be secreted into the medium.
• The product is then:
  • Extracted
  • Purified
  • Processed for further use

Large-Scale Production of Recombinant Protein

For commercial quantities, laboratory-scale cultures are insufficient.

Two major systems are used:

A. Continuous Culture System

• Principle
  • Maintains cells in the log (exponential) growth phase.
• Mechanism
  • Fresh nutrient medium is continuously supplied.
  • Used medium is removed simultaneously.
• Result
  • Cells remain metabolically active.
  • Biomass increases significantly.
  • Higher yield of desired protein is obtained.
• This ensures sustained production.

B. Bioreactors

• Definition
  • Bioreactors are large vessels in which biological conversion of raw materials into specific products occurs using microbial, plant, animal, or human cells.
• Capacity
  • Usually range from 100 to 1000 litres or more.
• Purpose
  • Provide optimal growth conditions for maximum product formation (temperature, pH, oxygen).

Types of Bioreactors

Most commonly used: Stirred-tank bioreactors

• Two types:
  1. Simple stirred-tank bioreactor
  2. Sparged stirred-tank bioreactor (air bubbled through medium)

Structure and Working of Stirred-Tank Bioreactor

• Design
  • Cylindrical vessel
  • Curved base for effective mixing
• Principle
  • Continuous stirring ensures uniform distribution of nutrients and oxygen.
  • Air may be bubbled to enhance oxygen supply.
• Key Components
  • Agitator system – Ensures proper mixing
  • Oxygen delivery system – Supplies oxygen for aerobic respiration
  • Foam control system – Prevents excessive foam formation
  • Temperature control system – Maintains optimum temperature
  • pH control system – Maintains suitable pH
  • Sampling ports – Allow periodic withdrawal of culture samples

These systems together maintain ideal conditions for maximum recombinant protein production.

6. Downstream Processing

• Definition
  • Downstream processing refers to all post-biosynthesis steps required to make the product suitable for commercial use.
  • It begins after completion of the production phase.
• Purpose
  • After producing the desired product, it must undergo further processing to ensure purity, stability, and safety.

Steps in Downstream Processing

1. Separation and Purification

• Principle
  • The desired product must be isolated from:
    • Host cells
    • Culture medium
    • By-products
  • A series of purification steps are carried out to ensure high purity and quality.

2. Product Formulation

• The purified product is stabilised by:
  • Addition of preservatives
  • Suitable formulation for storage and transport

3. Clinical Trials (For Therapeutic Products)

• For drugs and vaccines, the product must undergo:
  • Safety testing
  • Efficacy evaluation

4. Quality Control

• Strict quality checks ensure:
  • Product consistency
  • Safety
  • Compliance with regulatory standards
• Note: Downstream processing protocols vary depending on the nature of the product.

Conceptual Flow Summary

Gene cloning → Gene expression → Protein production → Large-scale culturing → Bioreactor amplification → Purification → Formulation → Quality control

This integrated sequence ensures that recombinant products are safe, pure, and ready for use.

Chapter Summary

Core Concept

• Biotechnology involves the use of living organisms, cells, or their enzymes to develop commercially valuable products and processes.
• Modern biotechnology became possible with the development of recombinant DNA technology, also known as genetic engineering.

Foundational Principles

Modern biotechnology is based on two major techniques:

1. Genetic Engineering
   • Deliberate alteration of genetic material (DNA) to introduce desirable traits.
2. Bioprocess Engineering
   • Maintenance of controlled and sterile conditions for large-scale production of biological products.

Recombinant DNA Technology – Central Process

• Recombinant DNA technology enables the creation of new genetic combinations by joining DNA from different sources.
• It involves the following core tools:

1. Restriction endonucleases – Cut DNA at specific recognition sequences.
2. DNA ligase – Joins DNA fragments.
3. Cloning vectors – Carry foreign DNA into host cells.
4. Competent host cells – Allow uptake and replication of recombinant DNA.

Sequential Workflow of rDNA Technology

1. Isolation of Genetic Material
   • DNA is purified and freed from proteins and RNA.
2. Cutting of DNA
   • Restriction enzymes generate specific DNA fragments.
3. Amplification (if required)
   • PCR is used to amplify the gene of interest.
4. Ligation
   • Foreign DNA is inserted into a vector to form recombinant DNA.
5. Introduction into Host
   • Recombinant DNA is transferred into competent cells.
6. Selection of Transformants
   • Selectable markers help identify successful transformants.
7. Expression of Foreign Gene
   • Host cells synthesise the desired recombinant protein.
8. Large-Scale Production
   • Continuous culture systems and bioreactors are used to increase yield.
9. Downstream Processing
   • Product is purified, formulated, tested, and prepared for market release.

Industrial Production

Large-scale production requires:

• Continuous culture systems to maintain cells in active growth phase
• Stirred-tank bioreactors for optimal mixing, oxygen supply, temperature and pH control
• Strict quality control and downstream processing before marketing

Final Conceptual Understanding

Biotechnology integrates molecular biology tools with industrial processes to:

• Modify genetic material
• Clone and express specific genes
• Produce large quantities of useful proteins
• Deliver safe, purified products for medical, agricultural and industrial applications

Recombinant DNA technology is the core mechanism that makes modern biotechnology possible.