Principles of biotechnology
Biotechnology is the integration of natural science and engineering to achieve the technological use of organisms, cells, or their molecules to produce goods and services. Modern biotechnology rests on two core principles:
Genetic engineering
- Altering the chemistry of genetic material (DNA and RNA)
- Introducing these molecules into host organisms
- Changing the phenotype of the host
- Also called recombinant DNA (rDNA) technology
Bioprocess engineering
- Maintaining aseptic (sterile) conditions in chemical engineering processes
- Using microbes or eukaryotic cells in controlled bioreactors
- Producing large quantities of desired molecules (antibiotics, vaccines, enzymes)
- Encompasses upstream processing, fermentation, and downstream processing
Restriction endonucleases
Restriction enzymes are called molecular scissorsbecause they cut DNA at specific sites. Werner Arber, Daniel Nathans, and Hamilton Smith shared the 1978 Nobel Prize in Physiology or Medicine for their discovery. A bacterium produces restriction enzymes to protect itself against foreign DNA (e.g., bacteriophage DNA). The bacterium's own DNA is protected by methylation at the same recognition sites.
Nomenclature
EcoRI
E = Escherichia (genus, first letter)
co = coli (species, first 2 letters)
R = RY13 (strain name)
I = first enzyme isolated from this strain (Roman numeral)
Types of restriction enzymes
| Type | Cut site relative to recognition | Use in biotech? |
|---|---|---|
| Type I | Cuts at a random site away from recognition sequence | No |
| Type II | Cuts within or very close to recognition sequence | Yes (most important for rDNA technology) |
| Type III | Cuts 24 to 26 bp away from recognition site | No |
Palindromic sequences
Type II restriction enzymes recognise short, specific double-stranded DNA sequences called palindromic sequences. A palindromic sequence in DNA reads the same on both strands in the 5' to 3' direction:
Example: EcoRI recognition site
5' — G A A T T C — 3'
3' — C T T A A G — 5'
Reading top strand 5' to 3': G-A-A-T-T-C
Reading bottom strand 5' to 3': G-A-A-T-T-C (same!)
Sticky ends vs blunt ends
Sticky (cohesive) ends
The enzyme cuts asymmetrically, leaving short single-stranded overhangs. These can base-pair with complementary overhangs from other fragments cut by the same enzyme, facilitating ligation.
EcoRI: 5'-G AATTC-3' gives
5'-G and AATTC-3' overhangs
Blunt ends
The enzyme cuts both strands at the same position, leaving no overhangs. Blunt-end ligation is less efficient than sticky-end ligation.
SmaI: 5'-CCC GGG-3' gives
5'-CCC and GGG-3' — no overhangs
Try this
- Use the restriction enzyme visualiser below to compare EcoRI, HindIII, SmaI, and BamHI — see exactly where each cuts and what end type is produced.
Restriction enzyme visualizer
Select an enzyme to see its recognition sequence, palindrome structure, and cut pattern.
EcoRI
Isolated from: E. coli RY13 (name derived from first letter of genus + two letters of species + isolation order)
5'
G
A
A
T
T
C
3'
3'
G
A
A
T
T
C
5'
5'
···G | AATTC···
3'
3'
···CTTAA | G···
5'
5'···G
3'···CTTAA
AATTC···3'
G···5'
Quick comparison
| Enzyme | Recognition | End type | Overhang |
|---|---|---|---|
| EcoRI | GAATTC | sticky | 4 nt |
| HindIII | AAGCTT | sticky | 4 nt |
| SmaI | CCCGGG | blunt | None |
| BamHI | GGATCC | sticky | 4 nt |
Cloning vectors and pBR322
A cloning vector is a DNA molecule that can carry a foreign DNA fragment into a host cell and allow it to replicate there.
Essential features of a cloning vector
Origin of replication (ori)
A specific DNA sequence where replication starts. Controls copy number. Without ori, the vector cannot replicate autonomously in the host.
Selectable marker gene
A gene (usually antibiotic resistance) that allows identification of transformed cells. Untransformed cells do not grow on selective medium. Examples: ampR, tetR, neomycin resistance.
Cloning site(s)
Restriction enzyme recognition sequences where foreign DNA can be inserted. Ideally unique (appearing once in the vector), so the vector is linearised at exactly one position when cut.
pBR322: the classic plasmid vector
pBR322 (p = plasmid, B and R = Bolivar and Rodriguez, 322 = plasmid number) was one of the first widely used cloning vectors. It has: size 4,361 bp, ampR gene (ampicillin resistance), tetR gene (tetracycline resistance), an origin of replication (ColE1 type), and multiple restriction sites within tetR (BamHI, SalI) and within ampR (PvuI, PstI).
Insertional inactivation
When you insert a foreign DNA fragment into the BamHI site within tetR, the tetR gene is disrupted. Recombinant bacteria become ampR but tetS. To identify recombinants:
- Plate bacteria on ampicillin medium — only transformed cells survive.
- Replica-plate surviving colonies onto tetracycline medium.
- Colonies that grow on ampicillin but NOT on tetracycline = recombinants (tetR disrupted by insert).
- Colonies that grow on BOTH = non-recombinant (no insert, tetR intact).
Other cloning vectors
| Vector | Insert size | Use |
|---|---|---|
| Plasmids | Up to ~10 kb | Small gene cloning, expression in bacteria |
| Bacteriophage lambda | ~20 kb | Cloning larger fragments in E. coli |
| Cosmids | ~45 kb | Genomic libraries |
| BAC (Bacterial Artificial Chromosome) | 100 to 300 kb | Genome sequencing projects |
| YAC (Yeast Artificial Chromosome) | 200 to 2000 kb | Very large fragment cloning; Human Genome Project |
| Ti plasmid | Variable | Transforming plant cells; T-DNA integrates into plant genome |
Competent cells and transformation
Transformation is the process by which a host cell takes up recombinant DNA from outside. Cells must first be made competent (permeable) before they can take up DNA.
Chemical transformation (CaCl2 method)
- Grow bacteria to log phase (actively dividing).
- Chill cells in ice-cold CaCl₂ solution — increases membrane permeability.
- Mix with recombinant plasmid DNA on ice.
- Heat shock at 42°C for 60 to 90 seconds — causes sudden DNA uptake.
- Immediately chill on ice, then allow cells to recover in nutrient medium before plating on selective medium.
Biolistics (gene gun)
Used mainly for plant cells, which have a rigid cell wall. DNA is coated onto gold or tungsten microparticles (1 to 3 µm diameter). These are accelerated by a high-pressure helium burst and fired directly through the cell wall. The DNA integrates into the genome.
Microinjection
Recombinant DNA is directly injected into the nucleus of animal cells using a fine glass microneedle. This method is precise but labour-intensive and is used especially for making transgenic animals.
Disarmed Ti plasmid (Agrobacterium method)
Agrobacterium tumefaciens naturally transfers T-DNA from its Ti plasmid into the plant cell nucleus, where it integrates into the plant genome. Scientists have "disarmed" the Ti plasmid by removing tumour-causing genes while retaining the T-DNA transfer machinery. A gene of interest inserted into T-DNA is thus delivered efficiently into plant cells.
NEET-style problem · Competent cells and transformation
Question
A researcher wants to introduce a recombinant plasmid carrying an insect-resistance gene into wheat cells. Which method of transformation is most appropriate and why?
Solution
Wheat cells have a rigid cell wall that cannot be breached by chemical transformation (CaCl₂ method). The best choice is biolistics (gene gun), which physically propels DNA-coated gold microparticles through the cell wall directly into the cytoplasm and nucleus. The Agrobacterium Ti plasmid method is an alternative but works better for dicot plants; wheat is a monocot, though improvements in Agrobacterium-mediated transformation of wheat have been made. For high-throughput transformation of cereals, biolistics remains the primary method.
Polymerase Chain Reaction (PCR)
PCR was developed by Kary Mullis in 1983 (Nobel Prize in Chemistry, 1993). PCR allows amplification of a specific DNA segment in vitro. Starting from a tiny amount of template DNA, PCR can generate billions of copies.
Three steps per cycle
1. Denaturation
Hydrogen bonds break; dsDNA separates into two ssDNA templates.
2. Annealing
Short primers (usually 18 to 24 nt) bind to complementary sequences flanking the target region.
3. Extension
Taq polymerase synthesises new DNA strand 5' to 3' from each primer. Duration: approximately 1 min per kb target length.
Amplification mathematics
Copies after n cycles = 2^n
After 10 cycles: 2^10 = 1,024 copies
After 20 cycles: 2^20 = 1,048,576 copies
After 30 cycles: 2^30 = 1.07 × 10^9 copies (about 10^9 fold amplification)
Why Taq polymerase?
Early PCR used E. coli DNA polymerase, which was destroyed at 94°C — a new batch had to be added each cycle. Thermus aquaticus (a bacterium from Yellowstone hot springs) has a thermostable polymerase (Taq) that survives 94°C, enabling fully automated PCR in thermocycler machines.
Try this
- Use the PCR simulator below to step through denaturation, annealing, and extension, and watch the copy count increase exponentially.
PCR step simulator
Walk through each PCR step and watch the copy count double every cycle.
Denaturation
94 – 98°C
1
of 30 (standard)
2^1
2
Denaturation
94 – 98°CHigh heat breaks the hydrogen bonds between complementary base pairs. The double-stranded DNA melts into two single-stranded templates. Each strand will serve as a template in the next step.
Key conceptWhy high temperature? Hydrogen bonds are weak individually but collectively strong — you need 94+ °C to separate an entire chromosome region reliably.
Annealing
50 – 65°CExtension
72°C
Adjust cycle count manually
PCR ingredients checklist
| Component | Role |
|---|---|
| Template DNA | Source of the target sequence to amplify |
| Forward primer | Binds 3' end of top strand; defines left boundary |
| Reverse primer | Binds 3' end of bottom strand; defines right boundary |
| Taq polymerase | Thermostable enzyme; synthesises new strand 5' to 3' |
| dNTPs | Building blocks (dATP, dTTP, dGTP, dCTP) for new strands |
| MgCl₂ buffer | Cofactor for Taq; optimal ionic environment |
NEET-style problem · PCR
Question
A forensic scientist finds a tiny blood stain at a crime scene. The DNA quantity is far too small for conventional analysis. Describe the PCR-based approach and state the expected copy number after 25 cycles.
Solution
The forensic scientist would use PCR to amplify specific STR (short tandem repeat) loci used in forensic DNA profiling. Steps: (1) Extract DNA from the stain. (2) Set up PCR with locus-specific primers, Taq polymerase, dNTPs, and MgCl₂ buffer in a thermocycler. (3) Run 25 cycles of denaturation (94°C), annealing (~55°C), and extension (72°C). After 25 cycles: 2^25 = 33,554,432 copies (about 33 million) — enough for capillary electrophoresis-based profiling.
Gel electrophoresis and Southern blotting
After restriction digestion or PCR, DNA fragments must be separated and visualised. Gel electrophoresis separates fragments by size.
Principle
DNA is negatively charged due to phosphate groups. In an electric field it migrates toward the positive electrode (anode) through the agarose gel matrix. Agarose acts as a molecular sieve: small fragments move faster and travel farther; large fragments move slower and stay closer to the loading well.
Important NEET point: EtBr staining
Ethidium bromide (EtBr) is a fluorescent intercalating dye. It inserts between the stacked base pairs of double-stranded DNA. When exposed to UV light, the EtBr-DNA complex emits orange-red fluorescence, revealing DNA bands. EtBr is a mutagen (carcinogen) and must be handled carefully.
Southern blotting
Developed by E.M. Southern in 1975. Used to detect a specific DNA sequence in a complex mixture.
- Run restriction-digested genomic DNA on an agarose gel.
- Denature DNA in the gel (alkali treatment makes DNA single-stranded in situ).
- Transfer (blot) the single-stranded DNA from the gel to a nitrocellulose or nylon membrane by capillary action or electroblotting.
- Hybridise with a labelled probe — a short single-stranded DNA sequence complementary to the gene of interest, labelled with radioactivity or a fluorescent tag.
- Wash off unbound probe.
- Detect by autoradiography or fluorescence imaging. A band indicates the gene is present.
Northern blotting applies the same principle to RNA. Western blotting applies it to proteins (antibodies as probes instead of nucleic acid probes).
Recombinant DNA technology: step-by-step
Isolation of gene of interest
Use restriction enzymes to cut the gene from donor DNA, or use PCR to amplify it, or synthesise it chemically (for short genes). For eukaryotic genes: isolate mRNA, use reverse transcriptase to make cDNA (lacks introns, can be expressed in prokaryote hosts).
Selection of suitable vector
Choose a vector appropriate for the host: plasmid for bacteria; Ti plasmid or biolistics for plants; viral vectors for animals. The vector must have ori, selectable marker, and a restriction site compatible with the gene insert.
Restriction digestion of gene and vector
Cut the vector and gene insert with the same restriction enzyme (or compatible enzymes). This creates complementary sticky ends on the insert and the linearised vector.
Ligation
DNA ligase (usually T4 DNA ligase) joins the phosphodiester bonds between the vector and insert at the sticky ends. The result is a recombinant plasmid carrying the gene of interest.
Transformation into host
Introduce the recombinant plasmid into competent host cells: bacteria (CaCl₂ + heat shock); plants (biolistics or Agrobacterium); animals (microinjection or viral vectors).
Selection and screening of recombinants
Plate transformed cells on selective medium. Use insertional inactivation, colony PCR, or restriction digest of extracted plasmid to confirm the insert is present.
Expression of the protein
Grow confirmed recombinants under conditions that drive expression of the gene. For industrial production, scale up in bioreactors. Purify the protein downstream.
NEET-style problem · rDNA technology
Question
A gene coding for human insulin has been cloned into pBR322 at the BamHI site within tetR. Bacteria are plated on ampicillin, then replica-plated on tetracycline. A colony grows on ampicillin but NOT on tetracycline. What does this tell you?
Solution
A colony that is ampicillin-resistant but tetracycline-sensitive (amp^R, tet^S) has taken up a plasmid in which the tetR gene has been disrupted by an insert. Since the insert was placed at the BamHI site inside tetR, this disruption indicates that the insulin gene (or some foreign DNA) has been successfully inserted into pBR322. This colony is a recombinant. Non-recombinants would grow on both plates (both genes intact); untransformed bacteria would grow on neither.
Bioprocess engineering and bioreactors
Once recombinant organisms are created and verified, industrial production requires scaling up from flask cultures to large bioreactors capable of producing kilograms of product.
Sparged stirred-tank bioreactor
The most common design for microbial biotechnology. Key components:
- Stirrer/impeller: mixes contents uniformly, preventing nutrient depletion in localised zones.
- Sparger: introduces sterile air or oxygen as fine bubbles from the bottom of the tank (essential for aerobic metabolism).
- Baffles: prevent vortex formation that would reduce mixing efficiency.
- pH control system: acid or base addition maintains optimal pH.
- Temperature control: jacket or coils with coolant or hot water.
- Foam control: antifoam agent or mechanical foam breaker prevents excessive foaming.
- Sampling port: allows periodic withdrawal of culture for testing without contaminating the batch.
Upstream vs downstream processing
Upstream processing
All steps BEFORE fermentation:
- Preparation and sterilisation of growth medium
- Sterilisation of equipment and bioreactor (autoclaving)
- Preparation of a pure seed culture (inoculum)
- Inoculation of the bioreactor with the production organism
Downstream processing
All steps AFTER fermentation:
- Separation of biomass (centrifugation, filtration)
- Cell disruption if product is intracellular
- Product extraction and initial purification
- Chromatography for high-purity fractionation
- Formulation, quality control, packaging
NEET tip: Downstream processing (also called bioseparation) is typically the most expensive part of the overall bioprocess, accounting for 60 to 90% of total production cost.
Worked problems
NEET-style problem · Restriction enzymes
Question
A plasmid (4 kb) is cut with EcoRI and gives two fragments of 1 kb and 3 kb. The same plasmid cut with BamHI gives one linear fragment of 4 kb. When both enzymes are used together, three fragments are obtained: 0.8 kb, 1.2 kb, and 2 kb. How many EcoRI and BamHI sites are present in the plasmid?
Solution
EcoRI sites: Two fragments from a circular plasmid cut with one enzyme means there are 2 EcoRI sites (each cut on a circle adds one fragment).
BamHI sites: One linear fragment from a circular plasmid means there is 1 BamHI site (one cut linearises the circle).
Double digest confirmation: 2 EcoRI + 1 BamHI = 3 total cuts on a circular molecule gives 3 fragments. The 3 fragments (0.8 + 1.2 + 2 = 4 kb) sum correctly.
NEET-style problem · PCR amplification
Question
A PCR amplification starts with 50 template DNA molecules. After 20 cycles, how many copies of the target region are theoretically present?
Solution
Each cycle doubles every DNA molecule. After 20 cycles, each starting molecule gives 2^20 copies. With 50 starting molecules: 50 × 2^20 = 50 × 1,048,576 = 52,428,800 copies (approximately 5.2 × 10^7). For NEET calculations, assume 100% efficiency and use 2^n per starting template.
Quick-recall cheat sheet
| Concept | Key fact |
|---|---|
| Restriction enzymes discovered by | Werner Arber, Daniel Nathans, Hamilton Smith (Nobel 1978) |
| EcoRI recognition site | 5'-GAATTC-3' — palindromic; cuts between G and A; sticky ends (4 nt, 5' overhang) |
| SmaI recognition site | 5'-CCCGGG-3'; cuts between CCC and GGG; blunt ends |
| Type II restriction enzymes | Only type used in rDNA technology; cuts within or adjacent to recognition site |
| PCR inventor | Kary Mullis, 1983 (Nobel 1993) |
| Taq polymerase source | Thermus aquaticus (hot spring bacterium); thermostable |
| PCR step temperatures | Denaturation 94 to 98°C; Annealing 50 to 65°C; Extension 72°C |
| PCR copies after 30 cycles | 2^30 = approximately 10^9 (from 1 starting copy) |
| Gel electrophoresis — DNA direction | Negative → positive (anode); smaller fragments travel farther |
| EtBr | Intercalates DNA; fluoresces orange-red under UV |
| Southern blotting | DNA from gel transferred to nitrocellulose membrane; hybridised with labelled probe |
| pBR322 — selectable markers | ampR (ampicillin) and tetR (tetracycline) |
| Insertional inactivation | Insert into tetR: amp^R, tet^S = recombinant |
| Competent cells (CaCl₂) | Ice-cold CaCl₂ + heat shock at 42°C for DNA uptake |
| Biolistics | Gold/tungsten microparticles coated with DNA; gene gun; used for plant cells |
| Ti plasmid host | Agrobacterium tumefaciens; T-DNA integrates into plant genome |
| Bioreactor sparger | Introduces air/O₂ as fine bubbles; critical for aerobic fermentation |
| Downstream processing | Separation + purification of product after fermentation; most expensive step |
Test yourself
Biotechnology quiz
12 NEET-style questions on restriction enzymes, PCR, gel electrophoresis, and vectors.
EcoRI recognises the sequence 5'-GAATTC-3'. This sequence is called a:
Frequently asked questions
How often does Biotechnology: Principles and Processes appear in NEET?
Biotechnology: Principles and Processes contributes 3 to 5 questions per NEET paper. High-yield topics include: restriction enzymes (types, palindromic sequences, sticky vs blunt ends, naming convention), PCR (steps — denaturation, annealing, extension; Taq polymerase), gel electrophoresis (principle, EtBr staining, UV visualization), cloning vectors (pBR322 features, insertional inactivation), and competent cell transformation methods.
What are restriction enzymes and what is a palindromic sequence?
Restriction endonucleases are enzymes that cut double-stranded DNA at specific recognition sequences (restriction sites). They were called "molecular scissors" by Werner Arber. A palindromic sequence in molecular biology is a sequence where the base sequence on one strand reads the same as the complementary strand read in the opposite direction (5' to 3'). Example: EcoRI recognises 5'-GAATTC-3' and cuts between G and A on each strand, producing sticky (cohesive) ends with 4-nucleotide overhangs (5'-AATT-3'). Sticky ends allow compatible fragments to join. SmaI (5'-CCCGGG-3') cuts in the centre producing blunt ends.
What are the steps of PCR and which enzyme is used?
PCR (Polymerase Chain Reaction) amplifies a specific DNA segment in vitro using three repeating steps: (1) Denaturation: heat at 94-98°C to separate double-stranded DNA into two single strands. (2) Annealing: cool to 50-65°C so specific primers bind (anneal) to their complementary template sequences. Two primers define the region to be amplified. (3) Extension (Elongation): heat to 72°C where Taq polymerase (a thermostable DNA polymerase from Thermus aquaticus bacterium) synthesises new DNA from the primer in 5' to 3' direction. Each complete cycle doubles the target DNA. After n cycles, 2^n copies are produced. After 30 cycles: 2^30 ≈ 10^9 fold amplification.
What is insertional inactivation and why is it used in pBR322?
pBR322 is a plasmid cloning vector that has two antibiotic resistance genes: ampR (ampicillin resistance) and tetR (tetracycline resistance), plus multiple restriction sites within tetR. When a foreign DNA fragment is inserted into a restriction site within tetR, it disrupts the tetR gene (making the bacterium tetracycline-sensitive). But the ampR gene remains intact. So: cells with recombinant plasmid = ampR (survive ampicillin) but tetS (killed by tetracycline). Cells with non-recombinant plasmid = ampR AND tetR. By first plating on ampicillin (selects for transformed cells) then replica plating on tetracycline (recombinants cannot grow), you can identify which colonies carry the insert. This is insertional inactivation used for selection of recombinants.
What is the difference between upstream and downstream processing in bioprocess engineering?
In bioprocess engineering (production of biologicals using microbes or cells in bioreactors): Upstream processing includes all steps BEFORE the fermentation/production step: preparation of nutrient medium, sterilisation (autoclaving, filtration), preparation of seed culture, inoculation of the bioreactor. Downstream processing includes all steps AFTER fermentation to obtain the final purified product: separation of biomass (centrifugation, filtration), product extraction, purification (chromatography, precipitation, ultrafiltration), formulation, quality control, and packaging. Downstream processing is often the most expensive part of bioprocess manufacturing.
How does gel electrophoresis separate DNA fragments?
Gel electrophoresis separates DNA fragments by size. DNA is negatively charged (due to phosphate groups), so it migrates toward the positive electrode (anode) when an electric field is applied. Agarose gel acts as a molecular sieve: smaller DNA fragments pass through the pores more easily and travel faster (further from the well). Larger fragments move slower (stay closer to well). After electrophoresis, the gel is stained with ethidium bromide (EtBr), a fluorescent dye that intercalates between DNA bases. When viewed under UV light, EtBr-DNA complexes fluoresce orange-red, revealing bands at specific positions. A DNA ladder (size marker with fragments of known sizes) is run alongside to determine the sizes of unknown fragments.
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