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Antigen Presenting Cells (APC)-Definition,Mechanism of action and Examples

Definition of APC: Any cell that can process and present antigenic peptides in association with class II MHC molecules and deliver a co-stimulatory signal necessary for T cell activation.
These cells possess class II MHC molecules on the surface.
APCs include macrophages (monocytes as blood macrophages and histiocytes as tissue macrophages), B cells and dendritic cells.
Mechanism of APC
B cell as Antigen presenting cell
Step 1: B cell activation=Antigen binding to Naïve B cell receptor followed by Antigen degradation inside B cell
Step 2: B cell acts as antigen presenting cells (APCs). Degrades antigenic peptides are displayed on MHC Class II recetor.
-T cell receptor (TCR) of Th cell binds to MHC class II bound antigenic peptide
-TCR activates B cells by secreting chemokines such as interleukins
Step 3: Clonal selection and Differentiation: That activated B cell  divide continuously forming clone of B cells with that specificity
Late these B cells differentiate into Plasma cells and memory B cells
Step 4: Plasma cells produce antibodies and are released into the blood stream that binds to the antigen and neutralize it. Thus preventing further infection
-Memory B cells produced are responsible for immunologic memory. (when the same antigen attacks the body for the second time, memory B cells recognizes it quickly and trigger an enhanced immune response, thus preventing further infection).

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B cells as Antigen Presenting Cells or APCs-Mechanism

Definition of APC: Any cell that can process and present antigenic peptides in association with class II MHC molecules and deliver a co-stimulatory signal necessary for T cell activation. This interaction enhances immune response.
B cell as Antigen presenting cell 
B cells as Antigen Presenting Cells or APCs


Step 1: B cell activation=Antigen binding to Naïve B cell receptor followed by Antigen degradation inside B cell
Step 2: B cell acts as antigen presenting cells (APCs). Degrades antigenic peptides are displayed on MHC Class II recetor.
-T cell receptor (TCR) of Th cell binds to MHC class II bound antigenic peptide
-TCR activates B cells by secreting chemokines such as interleukins
Step 3: Clonal selection and Differentiation: That activated B cell  divide continuously forming clone of B cells with that specificity
Late these B cells differentiate into Plasma cells and memory B cells
Watch this video for better concept clarity
Step 4: Plasma cells produce antibodies and are released into the blood stream that binds to the antigen and neutralize it. Thus preventing further infection
-Memory B cells produced are responsible for immunologic memory. (when the same antigen attacks the body for the second time, memory B cells recognizes it quickly and trigger an enhanced immune response, thus preventing further infection).

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CSIR UGC NET JRF Life Sciences Notification 2018 June

CSIR will hold   the Joint CSIR-UGC Test on 17th June, 2017 for determining the eligibility of the Indian National  candidates for the award of Junior Research Fellowships (JRF) and for determining eligibility for appointment of  Lecturers (NET) in certain subject areas falling under the faculty of Science & Technology. The award of Junior Research  Fellowship (JRF) to the successful eligible candidates will depend on their finding admission/placement in a university/  national laboratory/ institution of higher learning and research, as applicable.
CSIR UGC NET JRF June2018 Notification
Exam DateCSIR-UGC JRF NET :17th June, 2018.

Age Limit & Relaxation:
  • For Junior Research Fellowships  (JRF):Maximum 28 years as on 01-07-2017 (upper age limit may be relaxed up to 5 years in case of candidates belonging to SC/ST/OBC, Physically handicapped/Visually handicapped and female applicants).
  • For LS (NET): No upper age limit.
Important Dates:
CSIR Important Dates
    Educational Qualification:
    • BS-4 years program/BE/BTech/BPharma/MBBS/Integrated BS-MS/MSc or equivalent degree with at least 55% marks for general and OBC (50% for SC/ST candidates, physically and Visually Handicapped candidates).
    • Candidates enrolled for M.Sc or having completed 10+2+3 years of the above qualifying examination are also eligible to apply in the above subject under the Result Awaited (RA) category on the condition that they complete the qualifying degree with requisite percentage of marks within the validity period of two years to
      avail the fellowship from the effective date of award.
      Such candidates will have to submit the attestation format (Given at the reverse of the application form) duly certified by the Head of the Department/Institute from where the candidate is appearing or has appeared.
    • BSc (Hons) or equivalent degree holders or students enrolled in Integrated MS-PhD program with at least 55% marks for general and OBC candidates; 50% marks for SC/ST candidates, physically and visually handicapped candidates are also eligible to apply.Candidates with bachelor’s degree, whether Science, engineering or any other discipline, will be eligible for fellowship only after getting registered/enrolled for PhD/Integrated PhD program within the validity period of two years.
    • The eligibility for lectureship of NET qualified candidates will be subject to fulfilling the criteria laid down by UGC. PhD degree holders who have passed Master’s degree prior to 19th September 1991, with at least 50% marks are eligible to apply for Lectureship only.
    Syllabus
    The question paper shall be divided into three parts, (A, B & C) as per syllabus & Scheme of Exam.
    Part 'A' shall be common to all subjects including Engineering Sciences. This part shall contain questions pertaining to General Aptitude with emphasis on logical reasoning, graphical analysis, analytical and numerical ability, quantitative comparison, series formation, puzzles etc.
    Part 'B' shall contain subject-related conventional Multiple Choice questions (MCQs), generally covering the topics given in the syllabus.
    Part 'C' shall contain higher value questions that may test the candidate's knowledge of scientific concepts and/or application of the scientific concepts. The questions shall be of analytical nature where a candidate is expected to apply the scientific knowledge to arrive at the solution to the given scientific problem.
    Negative marking for wrong answers, wherever required, shall be applicable as per subject wise scheme of Exam.
    Examination fee:
    Examination Centres: Bangalore, Bhavnagar, Bhopal, Bhubaneshwar, Chandigarh, Chennai, Cochin, Delhi, Guntur, Guwahati, Hyderabad, Imphal, Jammu, Jamshedpur, Karaikudi, Kolkata, Lucknow, Nagpur, Pilani, Pune, Raipur, Roorkee, Srinagar, Thiruvananthapuram, Udaipur and Varanasi.



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    How do some cells become brain cells and others become skin cells, when the DNA in all cells is exactly the same?

    How is cell specialization achieved?
    The genetic makeup or DNA of all cells in an adult body is the same. How do some cells become brain cells and others become skin cells, when the DNA in all cells is exactly the same? How this happens?
    The reason is differential expression of genes in cells.
    Watch this video for more or see the post
                During the process of cell specialization, in each cell types; only specific genes are “turned on” and transcribed to RNA and translated to proteins. Rest of the genes remain inactive. That is, genes active in the neurons may not be active in skin cells.
    For instance, genes for actin and myosin filaments are present in all animal cells, but these genes are primarily active in muscle cells. Cell specialization involves the preferential or selective activation of specific genes leading to the synthesis of some specific proteins like antibodies in plasma cells or Hb in erythrocytes.

    House keeping genes vs Luxury genes
    Remember, there are some genes that are expressed in all types of cells or genes essential for survival  of all cell types like genes making membranes or genes of major metabolic pathways like glycolysis.. These genes are called ‘house keeping’ genes.

    But genes that are expressed in only certain types of cells or expressed differentially are called ‘luxury genes’ or smart genes’. Eg: IgG genes in plasma cells; opsin genes for vision (in eyes). This differential expression leads to cell specialization.

    After fertilization, the first cell the zygote has nucleus of both the gametes where the cytoplasm is entirely provided by egg. Thus the zygote has only maternal effect genes contributed by egg cytoplasm only. This is conducive for the zygote development. On first division, zygotic gene are expressed that will trigger further development and differentiation.

    In short: Zygote-> determination ->differentiation (to specialized cells and tissues).
    How do some cells become brain cells and others become skin cells, when the DNA in all cells is exactly the same?
    Characteristics of Cell Differentiation:
    • Cell differentiation is a stable phenomenon. Take the example of neurons, once differentiated persist throughout lifetime.
    • Differentiation is induced by specific stimuli.
    • But once differentiated or established, these cells are stimulus independent.
    • Differentiation is accomplished by morphological difference of that fated or determined cell. Look at the figure different shapes or morphology of various types of cells in our body.
    • Ultimately differentiation is controlled by genetic factors.

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    20 Functions of Cell membrane or Plasma membrane

    Definition of Cell membrane: A thin semi permeable membrane that serves as a boundary between the interior of a cell and its extracellular environment and is present in both animal and plant cells.
    -Also present in both eukaryotic and prokaryotic cell

    Synonym: plasma membrane, plasma lemma, bio membrane
    In plant cells, a thick cellulosic cell wall is also present which surrounds the plasma membrane.

    Composition: Cell membrane is made up of lipid, protein and small amount of carbohydrate.
    20 Functions of Cell membrane
    See more:
    Functions of Plasma membrane
    1. Protection: It protects the cell from its surroundings or extracellular environment. Plant cell possess wall over the plasma membrane for extra protection and support.
    2. Holding cell contents: Plasma membranes hold the semi fluid protoplasmic contents of the cell intact; thus keeping the individuality of the cell.
    3. Selective Permeability: Cell membrane allows only selected or specific substances to enter into the cell and are impermeable to others.
    • Gases like O2 and CO2 can diffuse rapidly in solution through membranes.
    • Small compounds like H2O and methane can easily pass through where as sugars, amino acids and charged ions are transported with the help of transport proteins.
    • The size of the molecules which can pass through the plasma membrane is 1-15 A0. This property is responsible for keeping a cell ‘as a cell’, an individual unit.  
    4. Shape: It maintains form and shape of the cell. It serves as site of anchorage or attachment of the cytoskeleton; thus providing shape to the cell (especially in animal cells without cell wall).
    5. Organelles: Cell membrane delimits or covers all sub-cellular structures or organelles like nucleus, mitochondria, plastids, Golgi apparatus, endoplasmic reticulum, microbodies etc. thus protecting them form the surroundings and also helps in maintaining a constant internal environment.
    6. Compartmentalization: Cell membrane separate the cells from their external environment and cell organelle from cytosol. It help the cells and their organelles to have their own microenvironments, structural and functional individuality.
    7. Cell Recognition: With the help of glycolipids and glycoproteins on its surface, cell membranes are able to differentiate similar cells from dissimilar ones, foreign substances and cells own materials. Cell recognition is useful for tissue formation and defence against microbes.
    8. Antigens: Cell membranes possess antigens which determine blood grouping, immune response, acceptance or rejection of a transplant (graft rejection by MHC’s on plasma membrane). 
    9. Microvilli: They are microscopic finger like projections of plasma membrane present on some cells like intestinal epithelial cells, which are involved in a wide variety of functions, including increasing surface area for absorption, secretion, cellular adhesion etc.
    10. Sheaths of cilia and flagella: Cilia and flagella are projections from the cell; made up of microtubules which are covered by an extension of the plasma membrane.
    11. Cytoplasmic bridges in plasmodesmata and gap junctions: Plasmodesmata in plant cells and gap junctions in animal cells; meant for intercellular transport and communication,  form cytoplasmic bridges between adjacent cells through plasma membrane.
    12. Endocytosis and Exocytosis: Bulk intake of materials or endocytosis occurs through development of membrane vesicles or invagination and engulfing by plasma membrane.
    Exocytosis: It is reverse of endocytosis that provides for releasing waste products and secretory materials ot of the cells with the help of plasma membrane.
    13. Impulse transmission in neurons: The transmission of a nerve impulse along a neuron from one end to the other occurs as a result of electrical changes across the plasma membrane of the neuron
    14. Cell metabolism: Cell membranes control cell metabolism through selective permeability and retentivity of substances in a cell.
    15. Electron transport chain in bacteria: In bacteria; Electron transport chain is located in cell membrane.
    16. Osmosis through cell membrane: It is movement of solvent molecules (generally water) from the region of less concentrated solution to the region of high concentrated solution through a semi permeable membrane. Here the semi permeable membrane that helps in osmosis is the cell membrane. Eg: Root cells take up water from the soil by osmosis
    17. Carrier proteins for active transport: They occur in the cell membranes and control active transport of substances. Example, GLUT1 is a named carrier protein found in almost all animal cell membranes that transports glucose across the bilayer or plasma membrane.
    18. Plasma Membrane enzymes: Many enzymes are present on the plasma membrane with wide variety of catalytic activity. Example: Red blood cell plasma membranes contain a number of enzymes such as ATPases, anion transport protein, glyceraldehyde 3-phosphate dehydrogenase, protein kinases, adenylate cyclase, acetylcholinesterase.
    19. Cell Membrane Receptors: Receptor on the plasma membrane performs signal transduction, converting an extracellular signal into an intra-cellular signal. Membrane possess receptors for hormones, neurotransmitters, antibodies and several other biochemicals.
    20. Plasma membrane assisted Cell movements: Undulation and pseudopodia are cell membrane phenomenon involved in cell movement. Amoeba, macrophages and WBCs move with the helps of temporary organelles like pseudopodia. Pseudopods are temporary cytoplasmic projections of the cell membrane in certain unicellular protists such as Amoeba. Some mammalian cells such as fibroblasts can move over a solid surface by wave like undulations of the plasma membrane.
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    ICAR NET ARS Practice Test Agronomy Quiz

    The word agronomy has been derived from two  greek words, agros- field and nomos- to manage. Literally agronomy means the art of managing field. Agronomy is that branch of agricultural science , which deals with the management of field to provide favorable environment to the crop for higher productivity in terms of quantity and quality both. 
    ICAR NET ARS Practice Test
    1. International Institute of Tropical Agriculture is situated at
    India
    Japan
    Nigeria
    none of these
    2. ICARISAT is located at
    India
    Indonesia
    Mexico
    China
    3. Food and Agriculture Organization (FAO) has its headquarters in
    Rome
    Tokyo
    Geneva
    Paris
    4. Green revolution has been most successful in
    wheat and potato
    wheat and rice
    tea and coffee
    rice and barley
    5. World environmental day celebrated in
    5th june
    15th june
    15th July
    5th July
    6. AGMARK indicates
    quality and puirty
    quality
    quantity
    purity
    7. India is divided into following agroclimatic zone?
    15
    18
    21
    22
    8. CIMAP, Lucknow is mainly working on
    cereal crops
    sugar crops
    fruits and vegetables
    medicinal and aromatic crops
    9. The tree acceptable for paper industries is
    Khejri
    Juliffora
    Eucalyptus
    Rohida
    10. Highest total fertilizer consumption is in the state?
    Uttar Pradesh
    Punjab
    Haryana
    Tamil nadu
    Score =
    Correct answers:
    Learn more: MCQ on Agronomy
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    ARS 2017 and NET 2018 Notification Important Dates Previous Question Paper

    The Agricultural Scientists Recruitment Board (ASRB) will hold a combined ARS 2017 (Preliminary) and NET (I)-2018 Examination during 06.04.2018 to 13.04.2018 in Online mode at 23 Centres across India in a staggered slot-wise examination format as per the Rules and Scheme of Examination indicated in this notification. The ARS-2017 (Mains) Examination will be conducted on 24.06.2018. Candidates are advised to read the notification carefully before filling the Online Application Form.
    The ARS (Preliminary) Examination is a qualifying examination and its marks will not be carried forward for determining final merit of the candidates. All those candidates desirous of appearing for ARS Examination are required to take both the Preliminary and Mains Examination and viva-voce. Only those candidates who qualify the ARS 2017 (Preliminary) Examination as per standards given in Appendix-VII will be eligible to appear in the ARS-2017 (Mains) Examination, further restricted to 15 candidates for one vacancy. 
    Candidates declared successful in ARS-2017 (Mains) Examination and viva-voce will be recommended for appointment as Scientists in Agricultural Research Service (ARS) of Indian Council of Agricultural Research (ICAR) in the Pay Band-III of 15,600-39,100 plus Research Grade Pay of  6,000/-. 
    Age limit:
    For ARS-2017 : A candidate must have attained the age of 21 years but not have attained the age of 32 years as on 01.01.2018. Age relaxation is admissible to the various categories as per Rule 2 of the Rules of the Examination as given in APPENDIX –IV. 
     For NET (I)-2018:  A candidate must have attained the age of 21 years as on 01.01.2018. There is no upper age limit for the National Eligibility Test. 

    Number of Attempts:
    For ARS - 2017 (a) The number of attempts for appearing in the Agricultural Research Service Examination will be limited to SIX for Unreserved category candidates (whether M.Sc./Ph.D.) including the in-service candidates of I.C.A.R. However, this restriction will not apply to SC and ST candidates who are otherwise eligible. The number of attempts for Other Backward Classes category and Divyang (belonging to General/OBC category) candidates will be NINE. 

    For NET (I) - 2018 There is no restriction on number of attempts for appearing in the National Eligibility Test.  
    How to apply:- A candidate seeking admission to the Examination must apply online in the prescribed Application Form available on the website: http://www.asrb.org.in. Important Instructions to the candidates for filling online application are given in Annexure-I. A candidate must read the provisions, contained in this Notification for Combined ARS-2017 and NET (I)-2018 Examination carefully and abide by the same. 
    A candidate must fulfil all the conditions of eligibility regarding age limits, educational qualifications, etc. prescribed for admission to the examination. The online Application process will be opened from 1000 Hrs on 06.02.2018 till 1700 Hrs on 02.03.2018 after which the link will automatically get disabled. 
    The candidates are not required to attach copy of any of the documents /certificates in support of their candidature at the time of submission of online application. The candidates in their own interest must satisfy themselves about their eligibility for the examination. In the event of any ineligibility being detected by the Board at any stage, including after declaration of result, their candidature shall be cancelled and they shall be liable for legal action. Due care should be taken by the candidates to fill up their application form. No request for change in any field i.e., Centre of Examination, Discipline, Name, Father’s Name, Date of Birth, Gender, E-mail Id, Mobile No., Phone No., Category, Medium of Examination etc. will be considered under any circumstances except bonafide spelling mistakes etc. Candidates are, therefore, advised to be very careful while filling up their application forms. 
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    ds or ssDNA has more absorbance? Double stranded and Single stranded DNA UV absorbance and Hyperchromic effect

    ds or ss DNA has more absorbance?
    • The absorbance of isolated nucleotides is > ss RNA or ss DNA>ds DNA.
    • The increase in absorbance of ss DNA over ds DNA is termed as hyperchromic effect. In other words, dsDNA is hypochromic with respect to ss DNA. Hyperchromic effect is due to the presence of exposed nitrogenous bases in ss DNA.  See the graph below to get a clear picture.
    Hyperchromic and hypochromic effect dsDNA vs ssDNA absorbance graph

    Definition: Hyperchromic Shift or Effect 

    • The phenomenon of increased UV absorbance by denatured DNA is known as the hyperchromic shift. 
    • The purine and pyrimidine bases in DNA strongly absorb ultraviolet light. Double-stranded DNA absorbs less strongly than denatured DNA due to the stacking interactions between the bases. On denaturation, the bases are exposed thereby showing increased absorbance.
    • This is the order of UV absorbance from high to low free nucleotides->ssDNA->dsDNA
    • The phenomenon of decreased UV absorbance by ds native DNA compared to ss denatured DNA is known as hypochromic effect
                     *ss=single stranded, ds=double stranded
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