Structure of Antibody in detail

 Structure of antibody:-

Antibody Structure and Types

Antibodies, also called immunoglobulins (Ig), are glycoproteins produced by B-lymphocytes in response to antigens. They are essential components of the immune system, capable of recognizing and neutralizing foreign molecules such as bacteria, viruses, and toxins.

1. Structure of an Antibody

An antibody molecule is typically Y-shaped and consists of four polypeptide chains:

• Two Heavy Chains (H-chains): Longer chains that determine the antibody class.
• Two Light Chains (L-chains): Shorter chains that pair with heavy chains.

These chains are connected by disulfide bonds. Each chain has:

• Variable Region (V-region): Located at the tips of the Y; responsible for antigen binding.
• Constant Region (C-region): Determines antibody class and effector function.

Functional Domains:

• Fab (Fragment antigen-binding): Contains the variable region; binds antigen.
• Fc (Fragment crystallizable): Contains constant region; mediates immune effector functions like complement activation or binding to receptors on immune cells.

Diagram: Antibody

 

2. Types of Antibodies

Antibodies are classified into five main classes based on their heavy chain structure:

Antibody	Heavy Chain	Key Features	Functions
IgG	γ	Most abundant in serum; crosses placenta	Long-term immunity, opsonization, complement activation
IgA	α	Found in mucosal surfaces, saliva, tears, breast milk	Protects mucosal surfaces, prevents pathogen adherence
IgM	μ	Pentamer in serum; first antibody produced	Primary response, complement activation
IgE	ε	Low concentration; binds mast cells & basophils	Allergic reactions, defense against parasites
IgD	δ	Very low concentration; mostly on B-cell surface	B-cell activation and receptor function

 

3. Determination of Molecular Weight

The molecular weight of antibodies can be measured by:

• SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis): Separates heavy (~50 kDa) and light chains (~25 kDa).
• Gel Filtration / Size-Exclusion Chromatography: Determines the native molecular weight (~150 kDa for monomeric IgG).
• Ultracentrifugation: Measures sedimentation behavior to estimate molecular weight.

Summary:

• IgG: ~150 kDa
• IgA (monomeric): ~160 kDa; (dimeric in secretions): ~320 kDa
• IgM (pentamer): ~900 kDa
• IgE: ~190 kDa
• IgD: ~180 kDa

4. Key Points

• Antibodies recognize specific antigens via their variable regions.
• Different classes (IgG, IgA, IgM, IgE, IgD) have distinct biological roles.
• Molecular weight varies with chain composition and polymerization state.

Biotechnology MCQ Quiz

1. What is the primary function of antibodies?

Provide energy to cells Recognize and neutralize antigens Carry oxygen in blood Produce hormones

2. Which part of the antibody binds antigens?

Fab region Fc region Heavy chain constant region Light chain constant region

3. Which antibody class is most abundant in serum?

IgG IgA IgE IgM

4. Which antibody is responsible for allergic reactions?

IgG IgA IgE IgD

5. IgM exists in serum mainly as:

Pentamer Monomer Dimer Trimer

6. Which part of the antibody determines its class?

Heavy chain constant region Light chain variable region Fab region Light chain constant region

7. Which antibody is secreted in mucosal surfaces?

IgG IgA IgM IgE

8. Molecular weight of monomeric IgG is approximately:

150 kDa 50 kDa 25 kDa 900 kDa

9. Which antibody is found on the surface of immature B cells?

IgG IgA IgD IgE

10. Which technique can measure antibody molecular weight?

SDS-PAGE Gram staining PCR ELISA

What is sterilization and Types of sterilization

Sterilization in Plant Tissue Culture

Sterilization is a critical prerequisite in plant tissue culture to prevent microbial contamination that can ruin cultures. All culture materials—vessels, instruments, media, and explants—must be aseptic. The choice of sterilization technique depends on the type of material, heat sensitivity, and culture requirements.

1. Dry Heat Sterilization

Principle: Microorganisms are killed by oxidation of cellular components, including proteins and nucleic acids, at high temperatures.

Applications: Heat-tolerant materials like glassware, Teflon plasticware, and some metal instruments.

Procedure:

• Place items in a hot air oven at 160–180°C for 2–3 hours.
• Glass bead sterilizers (~300°C) are used for instruments like forceps and scalpels.

Advantages:

• No moisture required; useful for materials that cannot be autoclaved.

Limitations:

• Time-consuming; unsuitable for heat-sensitive materials.

2. Flame Sterilization

Principle: Direct heat destroys microbial contaminants by protein denaturation and oxidation.

Applications: Instruments such as forceps, scalpels, and needles, as well as the mouth of culture vessels before inoculation.

Procedure:

• Dip the instrument in 95% ethanol.
• Pass through a Bunsen burner flame until alcohol burns off.

Advantages:

• Rapid; can be repeated multiple times during culture work.

Limitations:

• Only suitable for metal instruments; care needed to avoid burns.

3. Autoclaving

Principle: Moist heat under pressure denatures microbial proteins and nucleic acids, killing all forms of microbial life, including spores.

Applications: Culture media, glassware, plasticware (heat-tolerant), and some instruments.

Procedure:

• Autoclave at 121°C, 15 psi, for 15–40 minutes (longer for large volumes).
• Ensure vessels are properly sealed and only opened after pressure reaches zero.

Advantages:

• Reliable sterilization of large volumes; widely used.

Limitations:

• Heat-sensitive materials cannot be autoclaved.

4. Filter Sterilization

Principle: Microbes are physically removed using membrane filters.

Applications: Heat-sensitive compounds, including growth regulators (GA3, zeatin, ABA), vitamins, urea, and enzymes.

Procedure:

• Pass solutions through a 0.45 μm or smaller membrane filter.
• The filter assembly is pre-sterilized by autoclaving.
• Add compounds to cooled autoclaved medium (~40°C) under laminar flow.

Advantages:

• Preserves activity of heat-labile substances; allows aseptic handling.

Limitations:

• Only applicable to liquids; small volumes; does not sterilize surfaces.

5. Wiping with 70% Ethanol

Principle: Ethanol denatures proteins and disrupts cell membranes, killing microbes.

Applications: Surfaces, laboratory platforms, laminar flow cabinet interiors, and operator hands.

Procedure:

• Wipe the surface thoroughly with 70% ethanol.
• Allow to air dry before starting work.

Advantages:

• Simple, rapid, and effective for routine disinfection.

Limitations:

• Limited to surface sterilization; does not penetrate porous materials.

6. Surface Sterilization of Explants

Principle: Chemicals inactivate microbes present on the surface of plant tissues, allowing clean culture initiation.

Applications: All plant tissues used as explant material.

Procedure:

• Treat explants with sterilants such as:
• Calcium hypochlorite (9–10%)
• Sodium hypochlorite (2%)
• Mercuric chloride (0.1–1%)
• Silver nitrate (1%)
• Hydrogen peroxide (10–12%)
• Bromine water (1–2%)
• Antibiotics (4–50 mg/L)
• Duration: 15–30 minutes, followed by thorough rinsing to remove residues.

Advantages:

• Essential for eliminating microbial contamination on explants.

Limitations:

• Chemical toxicity may damage tissues; concentration and duration must be carefully optimized.

Summary Table

Method	Principle	Applications	Advantages	Limitations
Dry Heat	Oxidation of microbial components	Glassware, Teflon, metal instruments	No moisture; simple	Time-consuming; heat-sensitive materials cannot be used
Flame Sterilization	Direct heat	Forceps, scalpels, needles, culture vessel mouths	Rapid; repeated use	Only for metal instruments; safety concerns
Autoclaving	Moist heat under pressure	Media, vessels, heat-tolerant instruments	Reliable; kills spores	Heat-sensitive items cannot be used
Filter Sterilization	Physical removal of microbes	Heat-sensitive solutions, growth regulators, enzymes	Preserves heat-labile compounds	Limited to liquids; small volumes
70% Ethanol Wiping	Protein denaturation, membrane disruption	Surfaces, laminar flow cabinet, operator hands	Quick, simple, effective	Only surface sterilization; no penetration
Surface Sterilization	Chemical inactivation of microbes	Plant explants	Eliminates surface contamination	May damage tissue; requires optimization

 

Definition of Biotechnology

Biotechnology is a rapidly evolving field that combines biology, microbiology, biochemistry, genetics, and engineering to develop useful products, processes, and technologies for human benefit. It involves the controlled and deliberate use of living organisms, cells, or their components to perform technically useful operations, either for production or as service applications.

Several definitions highlight its scope:

• According to the U.S. National Science Foundation, biotechnology is “the controlled use of biological agents, such as micro-organisms or cellular components, for beneficial use.”
• The European Federation of Biotechnology defines it as “the integrated use of biochemistry, microbiology, and engineering science to achieve technological application of the capabilities of micro-organisms, cultured tissues, cells, and their components.”
• J.D. Bu’lock (1987) describes it as “the controlled and deliberate application of simple biological agents—living or dead, cells or cell components—in technically useful operations.”
• The British Biotechnologists summarize it as “the application of biological organisms, systems, or processes for practical purposes.”
• Gibbs and Greenhalgh (1983) define it as “the use of living organisms in systems or processes for the manufacture of useful products, involving bacteria, fungi, algae, yeast, plant and animal cells, or their components.”

Key Points:

• Biotechnology is interdisciplinary, linking life sciences with technology and engineering.
• It has applications in medicine, agriculture, environment, and industry.
• Modern biotechnology includes techniques like genetic engineering, tissue culture, recombinant DNA technology, and bioinformatics.
• It enables the production of drugs, vaccines, biofuels, improved crops, and eco-friendly industrial products.
• Biotechnology is also vital for diagnostics, environmental protection, and sustainable development.

In short, biotechnology harnesses the power of living systems to solve real-world problems and improve human life, making it one of the most impactful scientific disciplines of the 21st century.

 

Applications of Plant Tissue Culture in Modern Agriculture

Plant tissue culture is a revolutionary technique in biotechnology that allows the rapid propagation and improvement of plants. Its applications are extensive and have transformed modern agriculture and crop improvement programs.

1.     Development of Disease-Free Plants – Tissue culture helps generate healthy plants from diseased or infected ones, ensuring higher yield and quality.

2.     Reduction of Reproductive Cycle Time – It accelerates breeding programs by shortening the time required for plants to reach maturity.

3.     Haploid Plant Production – Enables fixed enrichment of haploid plants, which are vital for developing pure lines and inbred crops.

4.     Somatic Hybridization – New plants can be created by hybridizing cells from different species or varieties, producing novel traits.

5.     Development of Disease-Resistant Strains – Tissue culture supports breeding of plants with resistance to pathogens.

6.     Transgenic Plant Cultivation – Integration of foreign genes into plants for improved traits like pest resistance.

7.     Mass Production of Economically Important Plants – Large-scale propagation is possible in a short time.

8.     Asexual Propagation – Eliminates the need for sexual reproduction, allowing new plants to grow from any part of the parent plant.

9.     Creation of Unusual Hybrids – Protoplast fusion enables the development of plants with unique genetic combinations and novel traits.

Fig: - Application of Plant Tissue Culture

Plant tissue culture, therefore, is essential for sustainable agriculture, genetic improvement, and meeting global food demands efficiently.