Skip to main content

π“†ž Western Blotting Notes


Western Blotting (Immunoblotting)

❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ 

Introduction


Western blotting, also known as immunoblotting, is a widely used analytical technique for the detection, identification, and quantification of specific proteins in a complex biological sample. The technique combines protein separation by gel electrophoresis with specific antigen–antibody interaction.
The method was developed by Towbin et al. (1979) (Burnette 1981---its group work) and is called “Western” in analogy to Southern blotting (DNA) and Northern blotting (RNA).



Principle


The principle of Western blotting involves:

Separation of proteins based on molecular weight using SDS-PAGE
Transfer (blotting) of separated proteins onto a membrane
Specific detection of the target protein using primary and secondary antibodies
Visualization using enzymatic or fluorescent detection systems
πŸ‘‰ Antigen–antibody specificity is the core principle of Western blotting.


Steps Involved in Western Blotting

1. Sample Preparation

Protein samples are extracted from cells or tissues
Lysis buffers (RIPA, Tris buffer) are used
Protease inhibitors prevent protein degradation
Proteins are denatured using:
SDS
Ξ²-mercaptoethanol or DTT
Heat (95°C)


2. Protein Separation – SDS-PAGE


Proteins are separated based on molecular weight
SDS gives proteins a uniform negative charge
Smaller proteins migrate faster through the gel
Molecular weight markers (protein ladder) are run simultaneously


3. Transfer of Proteins (Blotting)


Proteins are transferred from gel to membrane.

Membranes used:
Nitrocellulose
PVDF (Polyvinylidene difluoride)


Transfer Methods 
Method,Description
Wet transfer
High efficiency, commonly used
Semi-dry transfer
Faster, less buffer
Dry transfer
Rapid, modern method


4. Blocking


Membrane is incubated with blocking agents to prevent non-specific binding

Common blocking agents:
BSA
Non-fat dry milk
Casein


5. Antibody Incubation


Primary Antibody
Binds specifically to the target protein
Can be monoclonal or polyclonal
Secondary Antibody
Binds to primary antibody

Conjugated with:
Horseradish peroxidase (HRP)
Alkaline phosphatase (AP)
Fluorescent dyes


6. Detection


Detection is done by adding substrate that reacts with enzyme on secondary antibody.
Detection Methods
Method,  Description


Colorimetric
Visible color formation
Chemiluminescent
Light emission (most sensitive)
Fluorescent
Multiplex detection


7. Visualization and Analysis


Bands appear corresponding to the target protein
Band intensity reflects protein quantity
Molecular weight is determined using protein ladder.


Applications of Western Blotting

Detection of specific proteins in complex samples
Diagnosis of diseases (e.g., HIV confirmatory test)
Detection of post-translational modifications
Protein expression studies
Validation of gene expression data
Study of signaling pathways
Quality control in recombinant protein production

Advantages


High specificity and sensitivity
Can detect low abundance proteins
Confirms protein size and identity
Widely accepted diagnostic tool


Limitations
Time-consuming and labor-intensive
Requires high-quality antibodies
Semi-quantitative
Prone to non-specific binding
Expensive reagents

Post-translational modifications

Precautions
Avoid protein degradation
Proper blocking is essential
Antibody dilution must be optimized
Avoid air bubbles during transfer
Wash steps should be adequate


Conclusion


Western blotting is a powerful, reliable, and specific technique for protein analysis. Due to its accuracy and versatility, it remains a gold standard method in molecular biology, biomedical research, and clinical diagnostics.







1. Western blotting is mainly used for detection of
A. DNA
B. RNA
C. Protein
D. Lipids
✅ Answer: C
2. Western blotting is also known as
A. Southern blot
B. Northern blot
C. Immunoblot
D. Dot blot
✅ Answer: C
3. The principle of Western blotting is based on
A. DNA–DNA hybridization
B. RNA–RNA hybridization
C. Antigen–antibody interaction
D. Enzyme–substrate binding
✅ Answer: C
4. Which electrophoresis technique is used in Western blotting?
A. Agarose gel electrophoresis
B. Native PAGE
C. SDS-PAGE
D. Isoelectric focusing
✅ Answer: C
5. SDS in SDS-PAGE provides proteins with
A. Positive charge
B. Negative charge
C. Neutral charge
D. Variable charge
✅ Answer: B
6. Protein separation in SDS-PAGE is based on
A. Charge
B. Shape
C. Size (molecular weight)
D. Solubility
✅ Answer: C
7. Which membrane is commonly used in Western blotting?
A. Cellulose acetate
B. Nylon
C. Nitrocellulose
D. Agarose
✅ Answer: C
8. Another membrane used in Western blotting is
A. PET
B. PVDF
C. Teflon
D. Polystyrene
✅ Answer: B
9. Purpose of blotting in Western blotting is
A. Protein amplification
B. Protein transfer to membrane
C. Protein digestion
D. Protein staining
✅ Answer: B
10. Blocking step prevents
A. Protein denaturation
B. Non-specific antibody binding
C. Protein transfer
D. Enzyme inactivation
✅ Answer: B
11. Common blocking agent used is
A. Agarose
B. BSA
C. Ethanol
D. Acetone
✅ Answer: B
12. Primary antibody binds to
A. Secondary antibody
B. Enzyme
C. Target protein
D. Substrate
✅ Answer: C
13. Secondary antibody binds to
A. Antigen
B. Primary antibody
C. Membrane
D. Substrate
✅ Answer: B
14. Enzyme commonly attached to secondary antibody
A. DNA polymerase
B. Restriction enzyme
C. Horseradish peroxidase
D. RNA polymerase
✅ Answer: C
15. Chemiluminescent detection uses
A. Fluorescent dye
B. Radioisotopes
C. Light emission
D. Color precipitation
✅ Answer: C
16. Which is the most sensitive detection method?
A. Colorimetric
B. Radioactive
C. Chemiluminescent
D. Coomassie staining
✅ Answer: C
17. Protein ladder is used to determine
A. Protein concentration
B. Protein purity
C. Molecular weight
D. Protein activity
✅ Answer: C
18. Wet transfer method is
A. Less efficient
B. Highly efficient
C. Very slow
D. Obsolete
✅ Answer: B
19. Semi-dry transfer uses
A. Large buffer volume
B. No electricity
C. Less buffer
D. High temperature
✅ Answer: C
20. Which disease diagnosis uses Western blot as confirmatory test?
A. Tuberculosis
B. Malaria
C. HIV
D. Dengue
✅ Answer: C
21. Which reducing agent is used in sample preparation?
A. EDTA
B. DTT
C. NaCl
D. Urea
✅ Answer: B
22. Ξ²-mercaptoethanol is used to
A. Break peptide bonds
B. Reduce disulfide bonds
C. Add charge
D. Stain proteins
✅ Answer: B
23. PVDF membrane must be activated using
A. Water
B. Acetone
C. Methanol
D. Ethanol
✅ Answer: C
24. Which buffer is commonly used for protein transfer?
A. TAE buffer
B. TBE buffer
C. Tris-Glycine buffer
D. PBS
✅ Answer: C
25. Which step follows blocking?
A. Detection
B. Sample loading
C. Primary antibody incubation
D. Transfer
✅ Answer: C
26. Western blotting is a
A. Quantitative technique
B. Semi-quantitative technique
C. Non-analytical method
D. Staining method
✅ Answer: B
27. Which blotting technique detects RNA?
A. Southern
B. Western
C. Northern
D. Eastern
✅ Answer: C
28. Eastern blotting is used for
A. DNA
B. RNA
C. Proteins
D. Post-translational modifications
✅ Answer: D
29. Which antibody is enzyme-labeled?
A. Primary
B. Secondary
C. Both
D. None
✅ Answer: B
30. Colorimetric detection produces
A. Light
B. Fluorescence
C. Colored precipitate
D. Heat
✅ Answer: C
31. Purpose of washing steps is to
A. Fix proteins
B. Remove unbound antibodies
C. Stain proteins
D. Denature proteins
✅ Answer: B
32. SDS is a
A. Reducing agent
B. Detergent
C. Buffer
D. Enzyme
✅ Answer: B
33. Which technique confirms protein size and identity?
A. ELISA
B. Western blot
C. PCR
D. Northern blot
✅ Answer: B
34. Protein degradation is prevented by
A. SDS
B. Protease inhibitors
C. BSA
D. Methanol
✅ Answer: B
35. Which antibody has higher specificity?
A. Polyclonal
B. Monoclonal
C. Both same
D. None
✅ Answer: B
36. Over-blocking can cause
A. High background
B. Signal loss
C. Protein degradation
D. Gel breakage
✅ Answer: B
37. Which detection method allows multiplexing?
A. Colorimetric
B. Chemiluminescent
C. Fluorescent
D. Radioactive
✅ Answer: C
38. Western blotting cannot detect
A. Protein expression
B. Molecular weight
C. DNA mutation
D. Protein modification
✅ Answer: C
39. Loading control protein commonly used
A. Actin
B. DNA polymerase
C. Restriction enzyme
D. RNA polymerase
✅ Answer: A
40. Which step is most critical for specificity?
A. Gel preparation
B. Blocking
C. Antibody incubation
D. Sample heating
✅ Answer: C
41. Which blotting uses radioactive probes?
A. Western
B. Southern
C. Northern
D. Both B and C
✅ Answer: D
42. Nitrocellulose membrane has
A. High mechanical strength
B. Low protein binding
C. High protein binding
D. No protein binding
✅ Answer: C
43. Signal intensity depends on
A. Gel thickness
B. Protein amount
C. Buffer volume
D. Transfer time only
✅ Answer: B
44. Which step confirms successful transfer?
A. Blocking
B. Antibody binding
C. Ponceau S staining
D. Detection
✅ Answer: C
45. Western blotting is used in
A. Proteomics
B. Clinical diagnostics
C. Molecular biology research
D. All of the above
✅ Answer: D
46. Which buffer is used for washing membrane?
A. TE buffer
B. TBS-T
C. TAE
D. SSC
✅ Answer: B
47. Primary antibody is usually
A. Enzyme-linked
B. Fluorescent
C. Unlabeled
D. Radioactive
✅ Answer: C
48. Which technique preceded Western blotting?
A. ELISA
B. Southern blot
C. Northern blot
D. PCR
✅ Answer: B
49. Protein bands appear as
A. Spots
B. Smears
C. Distinct bands
D. Wells
✅ Answer: C
50. Western blotting combines electrophoresis with
A. Hybridization
B. Immunodetection
C. Sequencing
D. Amplification
✅ Answer: B

Labels:

Comments

Post a Comment

Popular Posts

Biological Databases – Types of Data and DatabasesNucleotide Sequence Databases (EMBL, GenBank, DDBJ)

Biological Databases – Types of Data and Databases Nucleotide Sequence Databases (EMBL, GenBank, DDBJ) 1. Introduction Biological databases are systematic, computerized collections of biological information that allow efficient storage, retrieval, updating, and analysis of large volumes of biological data. With the advent of genome sequencing, molecular biology, and bioinformatics, biological databases have become essential tools in biological research. These databases support studies in genomics, proteomics, evolutionary biology, taxonomy, medicine, agriculture, and biotechnology. 2. Types of Data Stored in Biological Databases Biological databases store diverse types of biological information, including: 1. Sequence Data DNA sequences RNA sequences Protein sequences 2. Structural Data Three-dimensional structures of proteins Nucleic acid structures 3. Functional Data Gene functions Enzyme activity Regulatory elements 4. Genomic Annotation Data Gene location Exons, introns Promoters a...
Post a Comment
Read more

••CLASSIFICATION OF ALGAE - FRITSCH

      MODULE -1       PHYCOLOGY  CLASSIFICATION OF ALGAE - FRITSCH  ❖F.E. Fritsch (1935, 1945) in his book“The Structure and  Reproduction of the Algae”proposed a system of classification of  algae. He treated algae giving rank of division and divided it into 11  classes. His classification of algae is mainly based upon characters of  pigments, flagella and reserve food material.     Classification of Fritsch was based on the following criteria o Pigmentation. o Types of flagella  o Assimilatory products  o Thallus structure  o Method of reproduction          Fritsch divided algae into the following 11 classes  1. Chlorophyceae  2. Xanthophyceae  3. Chrysophyceae  4. Bacillariophyceae  5. Cryptophyceae  6. Dinophyceae  7. Chloromonadineae  8. Euglenineae    9. Phaeophyceae  10. Rhodophyceae  11. Myxophyce...
Post a Comment
Read more

RFLP (Restriction Fragment Length Polymorphism)

RFLP (Restriction Fragment Length Polymorphism ) Introduction RFLP is one of the earliest DNA-based molecular marker techniques. It detects variation in DNA sequences between individuals, caused by mutations, insertions, deletions, or restriction enzyme recognition site changes. First developed in late 1970s–1980s. Used extensively in genetic mapping, DNA fingerprinting, and gene detection. It is co-dominant, locus-specific, and highly reproducible. Principle RFLP is based on the fact that DNA from different individuals may differ in the presence or absence of restriction enzyme recognition sites, leading to different fragment sizes after digestion. Key idea: DNA → Restriction enzyme digestion → Fragments → Gel separation → Detection using labeled probe → Polymorphism analysis Materials Required Genomic DNA from the organism Restriction enzymes (e.g., EcoRI, HindIII) Agarose or polyacrylamide gel Nylon or nitrocellulose membrane Radioactive or non-radioactive DNA probe Autoradiography ...
Post a Comment
Read more

Protein Sequence DatabasesPIR, SWISS-PROT and TREMBEL

Protein Sequence Databases PIR, SWISS-PROT and TREMBEL 1. Introduction Protein sequence databases are biological databases that store information about amino acid sequences of proteins, along with their functional, structural, and biochemical characteristics. Since proteins are the functional molecules of the cell, protein databases are essential for understanding gene expression, metabolism, enzymatic activity, signaling pathways, and evolution. Protein sequence databases mainly contain data derived from translated nucleotide sequences and experimental protein studies. 2. Types of Protein Sequence Databases Protein sequence databases are broadly classified into: A. Primary Protein Databases Contain original protein sequence data Minimal or no manual annotation B. Secondary Protein Databases Derived from primary databases Provide curated functional and structural information C. Composite Protein Databases Combine protein data from multiple sources Reduce redundancy 3. Protein Informati...
Post a Comment
Read more

༺☆ DOT BLOT (DOT BLOTTING)

DOT BLOT (DOT BLOTTING) *ੈ✩‧₊˚༺☆༻*ੈ✩‧₊˚*ੈ✩‧₊˚༺☆༻*ੈ✩‧₊˚ Introduction Dot blot is a simple and rapid molecular biology technique used to detect specific DNA, RNA, or proteins immobilized directly onto a solid membrane without electrophoretic separation. It is a modification of Southern, Northern, and Western blotting, but unlike them, dot blot does not involve gel electrophoresis. The technique is mainly used for screening large numbers of samples, qualitative or semi-quantitative analysis, and diagnostic purposes. Principle of Dot Blot The principle of dot blotting is based on specific binding between a target molecule and a labeled probe or antibody. The sample containing DNA/RNA/protein is directly applied as a dot on a nitrocellulose or nylon membrane. The molecules bind to the membrane by hydrophobic and electrostatic interactions. The membrane is then incubated with a specific probe (for nucleic acids) or antibody (for proteins). Detection is achieved using radioactive, enzymatic, ...
Post a Comment
Read more

❃LC-MS (LIQUID CHROMATOGRAPHY – MASS SPECTROMETRY)

LC-MS (LIQUID CHROMATOGRAPHY – MASS SPECTROMETRY)  ┏━━━━━ •❃°•°❀°•°❃•━━━━•━━━┓ 1. INTRODUCTION LC-MS is a hyphenated analytical technique combining Liquid Chromatography (LC) and Mass Spectrometry (MS). It is used for separation, identification, and quantification of compounds in complex mixtures. LC separates analytes based on polarity, size, or charge, while MS detects molecules based on mass-to-charge ratio (m/z). Developed in the 1970s–1980s, LC-MS is now widely used in pharmaceutical, clinical, environmental, and food analysis. Importance : Detects trace levels of compounds (ng–pg range) Analyzes non-volatile, thermally labile compounds that cannot be analyzed by GC-MS Provides structural information through mass fragmentation Example: Detection of drugs in plasma, protein identification in proteomics, pesticide residue analysis in food. 2. COMPONENTS OF LC-MS The LC-MS system has three main parts: A. Liquid Chromatograph (LC) Function: Separates components of a mixture befor...
Post a Comment
Read more

Exploitation of Somaclonal and Gametoclonal Variations for Plant Improvement

Exploitation of Somaclonal and Gametoclonal Variations for Plant Improvement  1. Introduction Plant tissue culture often induces genetic and epigenetic variations among regenerated plants. These variations, when stable and heritable, can be exploited as a source of novel traits for crop improvement. Somaclonal variation: Variation arising in plants regenerated from somatic cells cultured in vitro. Gametoclonal variation: Variation arising in plants regenerated from gametic cells (anther, pollen, ovule culture). Both provide additional genetic variability beyond conventional breeding. 2. Somaclonal Variation 2.1 Definition Somaclonal variation refers to genetic variation observed among plants regenerated from somatic tissue cultures, such as callus, suspension cultures, or explants. Term coined by Larkin and Scowcroft (1981). 2.2 Sources of Somaclonal Variation Chromosomal changes Aneuploidy Polyploidy Chromosome rearrangements Gene mutations Point mutations Insertions and deletions...
Post a Comment
Read more

❥ Southern Blotting Notes

Southern Blotting  ❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥  Introduction Southern blotting is a molecular biology technique used for the detection of specific DNA sequences in a complex mixture of DNA. It was developed by Edwin M. Southern in 1975. The method involves restriction digestion of DNA, separation by gel electrophoresis, transfer (blotting) onto a membrane, and hybridization with a labeled DNA probe. Principle of Southern Blotting The technique is based on the principle of complementary base pairing. A single-stranded labeled DNA probe hybridizes specifically with its complementary DNA sequence immobilized on a membrane. Detection of the label confirms the presence and size of the target DNA fragment. Steps Involved in Southern Blotting. 1. Isolation of DNA Genomic DNA is extracted from cells or tissues. DNA must be pure and intact to ensure accurate results. 2. Restriction Enzyme  Digestion DNA is digested using specific restriction endonucleases. Produces DNA f...
1 comment
Read more

❃HPLC – High Performance Liquid Chromatography

HPLC – High Performance Liquid Chromatography ┏━━━━━ •❃°•°❀°•°❃•━━━━•━━━┓  1. Introduction High Performance Liquid Chromatography (HPLC) is an advanced analytical technique used for the separation, identification, and quantification of components present in a mixture. It is based on the differential distribution of analytes between a stationary phase and a liquid mobile phase under high pressure. HPLC is widely used in biochemistry, biotechnology, pharmaceuticals, food analysis, environmental studies, and clinical diagnostics. 2. Principle of HPLC The principle of HPLC is based on partition, adsorption, ion-exchange, or size-exclusion mechanisms, depending on the type of column used. A liquid mobile phase is pumped at high pressure through a column packed with fine stationary phase particles Sample components interact differently with the stationary phase Components with stronger interaction elute slower Components with weaker interaction elute faster Separated components are detec...
Post a Comment
Read more

❥NORTHERN BLOTTING

NORTHERN BLOTTING – 30 MARK DETAILED NOTES  π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž❥ π“†ž ❥ π“†ž❥ π“†ž❥  Northern blotting is a molecular biology technique used to detect specific RNA molecules in a complex mixture. It provides information about gene expression, RNA size, and transcript abundance by hybridizing RNA with a labeled complementary DNA or RNA probe. πŸ“Œ Named by analogy to Southern blotting (DNA detection). 2. Principle The principle of Northern blotting is based on: Separation of RNA molecules by size using denaturing agarose gel electrophoresis Transfer (blotting) of separated RNA onto a nylon or nitrocellulose membrane Hybridization of membrane-bound RNA with a labeled complementary probe Detection of RNA–probe hybrids by autoradiography or chemiluminescence ✔ Only RNA sequences complementary to the probe will be detected. 3. Types of RNA Analyzed mRNA (most common) rRNA tRNA miRNA and siRNA (with modified protocols) 4. Requirements / Materials Total RNA or poly(A)+ RNA Denaturing agarose ...
Post a Comment
Read more