Citric acid production and applications of submerged fermentation

Submerged fermentation is a type of fermentation in which the microorganisms are suspended in a liquid medium. The liquid medium also contains various other nutrients and growth factors in the necessary proportions in a dissolved or a particulate solids form.

The main application of submerged fermentation technique is in the extraction of metabolites (secondary metabolites) which are needed to be in liquid form for use.


  • The primary application of submerged fermentation is in the extraction process of metabolites (mostly secondary metabolites) that find applications in their liquid form.
  • Citric acid is one of the most important metabolites as the production volume of it is high, for the production of antibiotics like penicillin.
  • Submerged liquid fermentations are traditionally used for the production of microbially derived enzymes like cellulolytic enzymes.


  • Citric acid is widely distributed in plant and animal tissues.
  • It is an intermediate of the Krebb’s cycle, by which carbohydrate gets converted to CO2, in nature.
  • Citric acid can be produced on the industrial scale by employing submerged state fermentation as the fermentation method.

Type of bioreactor used for submerged fermentation: 

  1. Stirred tank bioreactor
  2. Airlift fermenter.

Selection of strain and storage:

  • Various criteria should be checked for the selection of production strains such as:

-High citric acid yield.

-Stability of the strain.

-Adequate amount of sporulation, etc.

Microorganisms used for the production of citric acid:

-Species of Penicillium and Aspergillus.

Aspergillus niger is used as the principal fungus for citric acid production as it can produce large quantities of citric acid while growing on a carbohydrate medium. 

  • Maintenance of the culture of the selected strain is the next important step in citric acid production and is done so by the storage of spores.

Steps used to carry out fermentation to ensure abundant production:

-High sugar concentration.

-Limited nitrogen/phosphorus concentration.

-Very low concentration of heavy metals like iron and manganese.

Submerged fermentation process:

-The strain used for the submerged fermentation of citric acid is Aspergillus japonicus.

-The organism shows sub-surface growth.

-Citric acid is produced within the culture solution.

-Using submerged fermentation for the production of citric acid is economical as compared to other fermentation methods.

Uses of citric acid:

  • It Is extensively used in the production of carbonated drinks.
  • It is used in plasticizers.
  • It is used as a chelating and sequestering agent.
  • Used in the pharmaceutical and food industries as an acidulant.


The advantages of submerged fermentation include:

  • The duration of the process is short, therefore saves time.
  • The overall cost of the process is low and the yield of products is high, making it a very economical process.
  • The process of purification and processing of the products is far simpler compared to other processes.
  • The cost of handling is low and the handling of the fermenter is easy therefore it reduces the labour involved.


  • The overall volumetric productivity of this process is low.
  • The effluent that is generated during the process is high in quantity.
  • The equipment that is used is expensive and complex.
  • The products that are obtained by using this process may be of low concentration.

Article by– Shaily Sharma (MSIWM041)



Fluorescence microscopy is an essential tool in molecular and cellular biology. It is a technique that allows one to study and visualize the cellular structures and dynamics of tissues and organelles, and macromolecular assemblies inside the cell. It was devised in the early twentieth century by various scientists like Köhler, Lehmann, Reichert and others.

The wide utilization of fluorescent proteins since their discovery have revolutionized the applications and use of the microscope in biological studies.

A fluorescence microscope uses the property of fluorescence to generate an image. It uses a high-intensity light source that excites the fluorescent molecule that may be inherently present in the sample to be studied or may be artificially labelled with a fluorescent molecule. The fluorescent molecule is called the fluorophore which is usually present in the fluorescent dye. 

Therefore, one could say that any microscope that works on the same basis to study the properties of organic or inorganic substances is a fluorescent microscope.See the source image

A fluorescence microscope is a type of optical microscope that uses fluorescence (ability of a substance to emit light on excitation) and phosphorescence (ability of a substance to continue emitting light even after the removal or withdrawal of the excitation factor). It may use these properties instead of or in addition to the properties of scattering, absorption, reflection and attenuation. 

The setup for the microscope may be simple as in an epifluorescence microscope or it may have a complicated design like that of a confocal microscope. A confocal microscope uses optical sectioning to provide a better resolution of the fluorescence image.


Fluorescent substances are the substances that absorb light of a particular energy and wavelength and then emit light of a longer wavelength and lesser energy.  

This phenomenon of fluorescent substances can be applied to the working of the fluorescent microscope. Fluorescent dyes (also called fluorochromes or fluorophores) are molecules that have the ability to absorb excitation light at a given wavelength, and then emit light of a comparatively longer wavelength after a delayed time interval.

In practical use, the sample is stained with a fluorescent dye and then illuminated with a blue light. The blue light (short wavelength) is absorbed by the fluorophores of the fluorescent dye, and the green light (which has longer wavelength) is emitted. This change is called the Stokes shift.

The light source that is used in fluorescent microscopy is a high intensity mercury arc lamp. The lamp emits white light when then passes through a device called an ‘exciter filter’. (as shown in the figure) This device filters the emission light to reveal the location of the fluorophores. It allows only the blue component of white light (white light comprises of coloured light of all wavelengths) to pass through and prevents the passage of light of other colors.

.See the source image

The dichroic mirror is used to reflect the blue light and allows the green light to pass. The angle of the mirror is fixed in such a way that the blue light is reflected towards the specimen placed below. It allows the passage of green light.

Finally, when the light reaches the ‘barrier filter’, it blocks out or removes all the remnants of the residual blue light from the specimen which may not have been ideally reflected by the dichroic mirror.

Thus, enabling the observer to perceive the glowing green portions of the specimen against the jet-black background of the dark field condenser that is used. The portions of the specimen that have not been stained remain invisible to the eye and this is how fluorescence microscopy provides a sharp image for the observation of the fine and intricate components of the sample to be studied.


The essential components of the fluorescence microscope are:

  • Fluorescent dyes (fluorophore): Chemical compounds that have the ability to re-emit light upon excitation. Examples include; nucleic acid stain like DAPI and Hoechst, phalloidin etc.Image result for fluorescence microscope structure
  • Light source: This is provided by a bright mercury vapor arc lamp, xenon lamp or LEDs with a dichroic excitation filter, lasers etc.
  • Heat filter: The lamp produces infrared rays which generate considerable heat. No other major uses of the heat filter exist.)
  • Exciter filter: The light undergoes cooling and passes through the exciter filter which allows the passage of the shorter waves which play a role in excitation of the fluorochrome dye coated sample on the slide and does not allow the other wavelengths to pass through.
  • Dichroic mirror: An accurate colour filter/mirror which selectively allows the passage of light of a particular wavelength and reflects the others. 
  • Condenser: A dark field condenser is usually used because it provides a dark background and it is easy to detect even mild fluorescence exhibited by the sample
  • Barrier filter: It removes all the remnants of the exiting light and is situated in the body tube of the microscope between the objectives and the eye piece. 

See the source image


  • Identify structures in fixed and live biological samples in microbiological studies.
  • Used in food chemistry for the assessment of the structural organization and spatial distribution of the components of food.
  • Used for the study of mineral like coal and graphene oxide in minerology.
  • Used in the textile industry for analysis of fibre dimensions. 

Article By- Shaily Sharma (MSIWM041)


Fluorescence Microscopy (

Immunofluorescence staining – PubMed (

Fluorescence Microscopy – Explanation & Labelled Images (



Que 1. Vaccine is prepared by

     a. weakened microorganism              b. toxins

        c. Surface protein                           d. all of the above

Que 2. The term vaccine and vaccination are coined by-

         a. Edward jenner                             b. Louis Pasture

         c. Robert Koch                                    d. Alexander Fleming

Que 3. Vaccine stimulates-

          a. T-cells                                               b. B-cells

          c. None of the above                      d. Both A and B

Que 4. Edward Jenner uses _______ to confer immunity against smallpox

          a. Polio virus                                     b. Cowpox virus

         c. HIV virus                                          d. Influenza virus

Que 5. _____ vaccine containing live organism which is weakened in the lab so that it cannot cause disease and activate the immune system against the antigen.

         a. Live attenuated                   b. Killed or Inactivated

         c. Subunit                                d. DNA

Que 6. Microorganism causing diseases are killed by the means of chemicals, heat or radiation. These are more stable and safer than live vaccines reason is that the dead microorganism cannot mutate back to cause diseases. Such type of vaccine is known as

         a. Live attenuated vaccine                  b. Killed or Inactivated vaccine

        c. Subunit vaccine                               d. DNA vaccine

Que 7. In ________ vaccine only the part which server as antigen and stimulate the immune system is used to prepare vaccine.

         a. Live attenuated                   b. Killed or Inactivated

         c. Subunit                                d. DNA

Que 8. The _____ vaccine is the DNA sequence used as vaccine.

         a. Live attenuated                   b. Killed or Inactivated

         c. Subunit                                d. DNA

Que 9. Examples of live attenuated vaccine-

        a. Mumps vaccine                   b. Measles vaccine

        c. Chickenpox                         d. All of the above

Que 10. Examples of DNA vaccine

        a. West nile virus                     b. Herpes virus

        c. Both A and B                      d. None of the above


1. (D), 2. (A), 3. (D), 4. (B), 5. (A), 6. (B), 7. (C), 8. (D), 9. (D), 10. (C)

For detail study click on the link Vaccine



Inflammation is part of the complex biological reaction of the tissues of the body to harmful stimuli, such as bacteria, damaged cells or irritants, and is a defensive reaction involving immune cells, blood vessels and molecular mediators. 

Inflammation has the purpose of removing the initial cause of cell injury, clearing necrotic cells and damaged tissues from the initial insult and inflammatory process, and initiating tissue repair.

Inflammation is a generalized response, and thus, opposed to adaptive immunity, which is unique to each pathogen, it is regarded as a mechanism of innate immunity. Too little inflammation could cause the harmful stimulus (e.g. bacteria) to slowly kill tissue and threaten the organism’s survival.

There are two main types of inflammation:

  1. Acute inflammation: It typically occurs for a short time (though sometimes severe). In two weeks or less, it generally resolves itself. Symptoms soon emerge of an injury or illness after acute inflammation is seen in the body.
  1. Chronic inflammation: It is a slower form of inflammation and usually less severe. Usually, it lasts longer than 6 weeks. Even when there is no prominent disease, injury or illness, it can happen, and it doesn’t necessarily stop when the disease or injury is cured. Autoimmune conditions and even prolonged stress have been associated with chronic inflammation.

Inflammation symptoms

The five major signs that indicate the presence of inflammation are:

  • heat
  • pain
  • redness
  • swelling
  • loss of function

Symptoms widely depend on the stage and condition that causes the inflammation in the body. Other symptoms that are observed in chronic inflammation include:

  • body pain
  • constant fatigue and insomnia
  • depression, anxiety, and other mood disorders
  • gastrointestinal issues, like constipation, diarrhea, and acid reflux
  • weight gain
  • frequent infections

Causes that lead to inflammation in the body

There are different factors which cause inflammation in the body. 

This include:

  • Acute and chronic disorders 
  • Some drugs 
  • The body cannot quickly remove exposure to irritants or foreign materials. 

A chronic inflammatory response may also arise from repeated episodes of acute inflammation. 

In persons with autoimmune conditions, there are also certain forms of foods that can induce or exacerbate inflammation. 

These foods include:

  • sugar
  • refined carbohydrates
  • alcohol
  • processed meats
  • trans fats

Treatment of Inflammation

There are a number of tests that can be carried out which show the presence of inflammation in the body. It can be as easy to combat inflammation as improving one’s diet.Inflammation is greatly subsided by eliminating sugar, trans fats, and processed foods. Some common anti-inflammatory foods are:

  • berries and cherries
  • fatty fish
  • broccoli
  • avocados
  • green tea
  • Tomatoes

Other remedies that can be practiced are:

  • Consistently take required vitamins. 
  • To decrease swelling and pain,  hot or cold treatment for physical wounds can be used.
  • Exercise more often.
  • Manage and lower the levels of stress. 
  • Stop smoking. 
  • Treat any preexisting conditions and control them.

Other treatment options:

NSAIDs and aspirin

In treating short-term pain and inflammation, non-steroidal anti-inflammatory drugs (NSAIDs) are typically the first line of protection. It is an over the counter drug.

NSAIDs that are popular include: 

  • Aspirin
  • ibuprofen (Advil, Motrin, Midol) 
  • naproxen (Aleve)


Corticosteroids are a form of steroid widely used to treat allergic reactions as well as swelling and inflammation. 

Typically, corticosteroids come as either a nasal spray or an oral pill. 

Article By- Ria Fazulbhoy (MSIWM031)

Research methodology

By- Ezhuthachan Mithu Mohanan, ( MSIWM043 )

Research methodology: The method of conducting research, by formulating problems, finding objectives, presenting result is all the crucial steps in any research. Sources of data and population consideration, ethical values, sample determination, methods executing plays a vital role before undertaking the research proposal.


  • Obtaining novel opinions and developing skills
  • Characterizing particular character, group or condition.
  • Finding interlinked connections
  • To test hypothesis.

In biological research following types can be included:


Identifying Research problem

  The initial step of any researcher is to identify the general are of interest. There are main two steps in formulating any research 

  • Understanding the problem
  • Reshape according to analytical view.

Having guidance and restoring problems already existing and engaging oneself in discussion makes it easy for identifying the research problem.

Literature review

 This is basically done to get a familiarity with the problem. Literature can be conceptual, empirical, etc. There are many source of literature; it could be abstracts, journals, bibliographies, conferences, academic journals, government reports, books. This helps in formulating problems. After the review one should focus on writing a synopsis.

Formulation of hypothesis:

Hypothesis is a tentative explanation made based on the available limited evidences. Formulating hypothesis enables to find the objective as well as result interpretation. Various approaches for formulating hypotheses:

  • Discussion with guide, and coworkers
  • Assessments of records and available data
  • Evaluating previous studies done
  • Personal investigation

Research design:

After the research problem is designed then the next step is to design the research. It involves choosing various components for  research Study.

Determining sample:

Selection of sample is utmost necessary for the development of any protocol or formulation. There are mainly two types of samples, which includes Nonprobability and probability.

  • Nonprobability sampling:  subjective methods of sampling
  • Probability sampling: It is simple random sampling, systematic sampling, cluster sampling

 Data Collection:

The process of gathering information enabling answer stated questions, testing hypothesis and evaluating outcomes. To maintain integrity of research accurate data collection is necessary.

Proper data collected must include:

  • Ability to answer research questions
  • Ability to repeat and validate the study
  • Less wastage of resources
  • No compromises for the fulfillment of requirement
  • No harm to human or subject studies

To maintain integrity there are two elements which is helpful

Quality assuranceQuality control
Before data collectionDuring or after data collection
Standardization of protocolCareful documentation of protocol.

Data analysis:

Process of applying statistical and logical techniques systematically, to describe, illustrate and evaluate data is known as data analysis.

Proper data analysis must include:

  • Skills to analyze data
  • Appropriate subgroup analysis
  • Acceptable discipline norms
  • Statistical significance
  • Clearly defined objective
  • Accurate results
  • Presenting data
  • Reliability and validity
  • Appropriate category considerations

 Testing hypothesis:

Process to evaluate the strength of evidence and providing framework for determination.

The two main steps in testing hypothesis is framing null hypothesis and alternative hypothesis

Null hypothesis: No statistical significance exists in the given set of observation. This is assumed to be true.

Alternative hypothesis: It is opposite to null hypothesis

 Interpretation: After analytical and experimental study, the drawn inferences is known as interpretation. The major aspects of interpretation is 

  • Establish continuity
  • And establish explanation concepts.
  • Preparation of report:

There should always be the necessary documentation of each and every result. The research reports contains following  elements

  • Description and methodology
  • Obtained results
  • The recommendations made

There are two types of Research reports 

  • Technical reports: which aim to specific group of people, including scientist, researchers, guides, belonging to the area
  • Popular reports: which can be understood my lay man or common people, in more easy and feasible way, with less technical words.
  • Presentation of results: It can be done in various ways including writing research papers, presenting in conferences, writing drafts, discussing, Seminar presentation or oral presentation.

Corona Virus


Que 1: Latin word “corona” means

        a. Crown                  b. Lethal

        c. Spherical             d. Contagious

Que 2: Coronavirus belongs to _______ subfamily-

        a. Avulavirinae            b. Comovirinae

        c. Orthocoronavirinae       d. Parvovirinae

Que 3: SARS cov was transmitted from-

        a. Civet cats             b. Camels

        c. Dogs                      d. Bats

Que 4: MERS cov was transmitted from-

         a. Civet cats          b. Camels

         c. Dogs                   d. Bats

Que 5: Arrange in sequence

                a. A- Nucleocapsid  protein and Rna

                    B- Lipid bilayer membrane

                    C- Spike glycoprotein 

                b. A- Lipid bilayer membrane

                    B- Spike glycoprotein 

                    C- Nucleocapsid  protein and Rna

                c. A- Nucleocapsid  protein and Rna

                    B- Spike glycoprotein 

                    C- Lipid bilayer membrane

                d. None of the above


1. (a)  2. (c)  3. (a)  4. (b)  5. (c)

For detail study click on the link Corona Virus

Agglutination Reactions

Agglutination is defined as the antigen-antibody reaction in which antibodies cross-link particulate antigens resulting in the visible clumping of particles. Antibodies that show such reactions are called agglutinins.

Agglutination reactions work on the principle of cross-linking of the polyvalent antigens. Following are the advantages of agglutination reactions: 

  1. easy to perform 
  2. require no expensive equipment, and 
  3. detects antibody concentrations as low as nanograms per milliliter. 

Types of agglutination reactions: 

  1. Hemagglutination:
    type of agglutination reaction is routinely performed to type red blood cells (RBCs), wherein RBCs are mixed with antisera to the A or B blood-group antigens on a slide. The presence of antigen on the cell surface is proved by forming a visible clump on the slide. This RBC typing forms the basis for matching blood types for transfusions.
  2. Bacterial Agglutination:

This type of agglutination reaction is performed to diagnose infection and provide a way to type bacteria. Any bacterial infection elicits the production of serum antibodies within the host. 

These serum antibodies are specific for surface antigens on the bacterial cells, which bacterial agglutination reactions can detect.

Bacteria is added to the previously serial diluted array of tubes containing serum from a patient thought to be infected with a given bacterium. The last tube, which shows visible agglutination, reflects the serum antibody titre of the patient. Thus, the agglutinin titre is the reciprocal of the greatest serum dilution that elicits a positive agglutination reaction.

  1. Active agglutination 

In this type of agglutination, epitopes of interest are naturally found on a test particle, such as antigens found on RBCs, bacterial and fungal cells.


Examples –

  1. Blood grouping and cross-matching
  2. Widal test for diagnosis of typhoid fever 
  3. Brucella agglutination test for Brucellosis 
  4. Weil Felix test for Rickettsiosis
  5. Passive agglutination: 

Passive agglutination is useful when the epitope of interest does not occur naturally on the cells or particles to be agglutinated. The epitopes or soluble antigens are chemically fixed to carrier particles such as – latex, polystyrene, bentonite.

 Passive agglutination is also useful when pathogen culture is not feasible, e.g., viral diseases. 

Synthetic beads offer better consistency, uniformity, and stability. In addition, those agglutination reactions which employ synthetic beads are rapidly read within 3 to 5 minutes of mixing the beads with the test sample.  




  1. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition 
  2. Kuby Immunology – 5thEdition 


Synonym: Localized Anaphylaxis 


Atopy is defined as the tendency of an individual to produce IgE antibodies in response to various environmental antigens and thus develop strong immediate hypersensitivity (allergic) responses. Individuals with allergies to environmental antigens (e.g., pollen, house dust) are atopic. 

Localized anaphylaxis involves reactions limited to a specific target tissue or organ and often involves epithelial surfaces at the site of allergen entry. Atopy is thus defined as the tendency to manifest localized anaphylactic reactions, and this tendency is inherited. 

Atopic allergies include a wide range of IgE-mediated disorders, including allergic rhinitis (hay fever), asthma, atopic dermatitis (eczema), and food allergies

Allergic Rhinitis:

This is commonly known as “hay fever” and results from the reaction of airborne allergens with the sensitized mast cells in the conjunctivae and nasal mucosa, which induces the release of pharmacologically active mediators from mast cells. The mediators thus cause localized vasodilation and increased capillary permeability. The symptoms of allergic rhinitis usually include watery exudation of the conjunctivae, upper respiratory tract and nasal mucosa, and sneezing and coughing.


Asthma, a common manifestation of localized anaphylaxis, is triggered by degranulation of mast cells with the release of mediators, but instead of occurring in the nasal mucosa, the reaction develops in the lower respiratory tract. This results in the contraction of the bronchial smooth muscles and thus eventually leads to broncho-constriction. 

Food Allergies:

A variety of foods can induce localized anaphylaxis in allergic individuals. In addition, localized smooth-muscle contraction and vasodilation can be induced by allergen cross-linking of IgE on mast cells along the upper or lower gastrointestinal tract resulting in symptoms such as vomiting or diarrhea. 

Atopic Dermatitis:

Atopic dermatitis (allergic eczema) is an inflammatory disease of the skin frequently associated with a family history of atopy. This disease is observed most commonly among young children, often developing during infancy. Serum IgE levels are often elevated, and the allergic individual develops erythematous skin eruptions filled with pus. 



  1. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition 
  2. Kuby Immunology – 5thEdition.

Antigen presenting cells


The population of specialized cells: 

  1. to capture microbial and other antigens,
  2. display MHC complexes in association with these peptide fragments of protein antigens on its surface to lymphocytes, and
  3. provide signals that stimulate the proliferation and differentiation of the lymphocytes (co-stimulatory signal) are known as the antigen-presenting cells (APCs). 

APCs are conventionally referred to as those cells which display antigens on their surface to the T lymphocytes. A dendritic cell is the major type of APC which is involved in initiating the T cell responses. 

Macrophages and B cells also present antigens to the T lymphocytes but in different types of immune responses. The follicular dendritic cell, a specialized cell type, displays antigens to B lymphocytes during particular phases of humoral immune responses. APCs thus link responses of the innate immune system to responses of the adaptive immune system, and therefore they may be considered components of both systems. 

Types of APCs: 

  1. Dendritic Cells

Dendritic cells form one of the most important APCs for activating naive T cells. These cells constitutively express a high level of class II MHC molecules and deliver a co-stimulatory activity and thus play major roles in innate responses to infections and link innate and adaptive immune responses.

  1. Antigen-Presenting Cells for Effector T -Lymphocytes

In addition to dendritic cells; macrophages and B lymphocytes perform important antigen-presenting functions in CD4+ helper T cell-mediated immune responses. 

  1. Macrophages present antigen to helper T lymphocytes at the sites of infection, which leads to helper T cell activation and production of molecules that further activate the macrophages. These macrophages must be activated by phagocytosis of particulate antigens before expressing class II MHC molecules or the co-stimulatory B7 membrane molecule.
  1. B cells present antigens to helper T cells in lymph nodes and spleen, a key step in the cooperation of helper T cells with B cells in humoral immune responses to protein antigens. These B cells constitutively express class II MHC molecules but must be activated before expressing the co-stimulatory B7 molecule. 

Note: Cytotoxic T lymphocytes (CTLs) are effector CD8+ T cells that can recognize antigens on any nucleated cell and become activated to kill the cell. Thus, all nucleated cells are potentially APCs for CTLs. 

  1. Follicular Dendritic Cells: 

Follicular dendritic cells (FDCs) are cells with membranous projections found intermingled in specialized collections of activated B cells, called germinal centers, in the lymphoid follicles of the lymph nodes, spleen, and mucosal lymphoid tissues. 



  1. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition 
  2. Kuby Immunology – 5thEdition.


Synonym: Programmed cell death

Pronunciation: ah-poh-toh’-sis: Greek, (1) apo- away from and (2) ptosis, a falling or dropping 

Apoptosis’ has been derived from a Greek word that describes the falling of the leaves from a tree or petals from a flower. This term was coined to differentiate this form of programmed cell death from the accidental cell deaths caused by inflammation or injury (necrosis). 


Programmed cell death is an active process, first described in 1972 and usually proceeds by a distinct series of cellular changes known as apoptosis. 

Apoptosis is thus the genetically programmed death of cells that is both a natural development process and the body’s means of destroying abnormal or infected cells. 

Events of apoptosis:

During apoptosis, firstly, as a result of cleavage between nucleosomes, chromosomal DNA fragmentation occurs. 

Following chromatin condensation, the cell shrinks in and breaks up into membrane-enclosed fragments known as apoptotic bodies. 

These apoptotic cells and cell fragments are efficiently recognized and phagocytosed by macrophages and the neighbouring cells, and thus, eventually, these cells, which die by apoptosis, are rapidly removed from tissues. 


This removal of the apoptotic cells from the tissues is mediated by the expression of certain signals on the cell surface. These signals are generally known as the “eat me” and include phosphatidylserine, which is restricted normally towards the inner leaflet of the plasma membrane. However, during apoptosis, phosphatidylserine becomes expressed on the cell surface, where it is recognized by receptors expressed by phagocytic cells. 

Genes involved in apoptosis:

Programmed cell death was innovatively studied during the development of C. elegans, which eventually provided the critical initial insights that led to understanding the molecular mechanism of apoptosis. These pioneering studies conducted in the laboratory of Robert Horvitz helped initially identify three genes that played key roles in regulating and executing apoptosis. 

Mutagenesis of C. elegans in the year 1986 helped identify the genes involved in the developmental cell death (ced-3and ced-4). If either ced-3 or ced-4 was inactivated by mutation, the normally programmed cell deaths did not occur. 

A third gene known as the ced-9 functioned as a negative regulator of apoptosis. Whenever this gene ced-9 was inactivated by mutation, the cells failed to survive and instead underwent apoptosis, leading to death. Conversely, if this gene was expressed at an abnormally high level, the normally programmed cell deaths failed to occur.



  1. The Cell: A Molecular Approach by Geoffrey M. Cooper – 8thEdition 
  2. Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition