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Cell Theory and Modern Cell Theory

Robert Hooke was the first to describe cell and he published his observation in his book Micrographia (1670). He sliced a piece of cork and placed under his microscope. He observed honey comb like structural units and called it as the “cell”.
Robert Hooke
Leeuwenhoek (1674) was the first one to observe live cells under microscope. He observed many things including bacteria under his primitive microscope and drew beautiful sketches of his observations.
If you want to see this classical book, follow this link
Cell theory was actually a generalization of observations made by many scientists around the world.
Cell theory was proposed by Theodor Schwann, Matthias Schleiden and Rudolf Virchow
cell theory
The three tenets are
1. All living organisms are composed of one or more cells (Schwann and Schleiden, 1838-39).

2. The cell is the basic structural and functional unit of life (Schwann and Schleiden, 1838-39).
Schleiden proposed that new cells arise from within the old cells, specifically from the nucleus. This was corrected by Rudolf Virchow who proposed “Theory of cell lineage” stating that “omnis cellulae e cellula” (all cells arise from pre-existing cells).

3. All cells arise from pre existing cells by cell division (Rudolf Virchow, 1858).

Modern cell theory
Some more points are added with the advancement of our knowledge in cytology and molecular biology.
• The cell contains hereditary information DNA which is passed on from cell to cell during cell division
• All cells are basically the same in chemical composition and metabolic activities
• All basic chemical and physiological functions are carried out inside the cells (digestion, movement etc)
• A cells activity depends on the activities of sub cellular structures within the cell (organelles, plasma membrane etc)

Learn more:
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What are Place cells and Grid Cells in Brain? Nobel Prize in Physiology and Medicine 2014 explained

How Place cells and grid Cells functions in brain's spatial representation system?
Awarded to: Dr John O’Keefe, Dr May-Britt Moser & Dr Edvard I Moser
Nobel prize 2014 winners in Physiology and Medicine
Discovery: How nerve cells in the rat brain works in finding out and recollecting a place (sense of place) or How it works in navigation ability?
What is the ‘sense of place’?
It gives a perception of the position of the body in the environment and in relation to surrounding objects. It is how we find places?
Let me explain with an example, in day to day life, we used to move around to find places that we need to go. Suppose I want to go to a nearby Zoo and this is my first time visit. Once I reached there, my brain relates the place with some surrounding objects. Within 2 to 3 visits to the same Zoo, I could locate it without any further help. Now I have the “sense of that place”. Now my brain has perception of position of that Zoo actually in relation to some surrounding objects. Suppose that entire area has been reconstructed. Now I may not be able to locate the Zoo all on a sudden as the surrounding objects that my brain used for positioning or relocating has changed.
How do we navigate to a place?
It is linked with a sense of distance and direction that is based on the integration of motion and knowledge of previous positions. Our brain creates a mental map in connection with an environment or place.
This sense of place and ability to navigate are one of the most complex processes in brain.
Dr John O’Keefe Experiment (Finding the Place cells)
Dr John O’Keefe
Experimental Organism: rats
He discovered place cells. He allowed the rats to move freely in a bounded area. Certain nerve cells were active when the rat reached a particular place in the environment. He called this cell as “place cells” and the environment as “place field” (Fig. 1). Different place cells were activated at different places. Place cells are located in a part of the brain called hippocampus.
He also showed that place cells has memory functions also. Different place cells become active at different places and the combination of activity in many place cells creates an internal neural map representing a particular environment. Thus place cells together form a spatial reference map system or sense of place for the brain in connection with a particular environment or place. Place cells provide a cellular substrate for memory processes, where a memory of an environment or place is stored as specific combinations of place cells.
Dr May-Britt Moser & Dr Edvard I Moser (Finding the Grid cells)
Dr May-Britt Moser & Dr Edvard I Moser
When the rat passed certain locations, certain nerve cells in the entorhinal cortex were activated. They called these cells as grid cells because of its unusual firing pattern. A single grid cell fires or gets activated when the rat reaches particular locations in an environment. These locations are arranged in a hexagonal pattern (Fig 2). They concluded that grid cells are involved in measuring movement distances and thus provided a metric to the spatial maps in hippocampus.
Brains navigational system involves other type of nerve cells like head direction cells and border cells. Head direction cells act like a compass and are active when the head of an animal points in a certain direction. Border cells are active in reference to walls that the animal encounters when moving in a closed environment.
Place cells and Grid cells in Brain
Grid cells, head direction cells, border cells together with place cells form a complex network within the hippocampus. This network constitutes a comprehensive positioning system, an inner GPS in the brain (Fig. 3). Similar grid and place cell systems are found in many mammalian species including humans.
Applications: A better understanding of neural mechanisms underlying spatial memory is important in understanding and treating memory disorders including dementia and Alzheimer’s. O’ Keefe and co-workers showed in mouse model of Alzheimer’s disease that the degradation of place fields correlated with the deterioration of the animal’s spatial memory. The discovery of place cells and grid cells is undoubtedly a major leap in our understanding of how specialized nerve cells work together to execute higher cognitive function like ‘sense of place’ and navigational ability. Hopefully this understanding may help us to treat brain disorders in a better manner in near future.
Image credit: Original Paper- Download (PDF)
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Types of DNA binding domains with examples

DNA binding proteins interact with DNA by means of various structural motifs, and can stimulate or repress transcription of messenger RNA, depending on the properties and location of the DNA sequence to which they bind.

DNA binding proteins are classified into four types:- homeodomain proteins, zinc finger proteins, leucine zipper proteins, and helix loop helix proteins.
I) Homeodomain protein :
  • This protein consists of three linked alpha helices (helices 1, 2and 3). Helices 2 and 3 are arranged in a conspicuous helix turn helix motif.
  • A 60 amino acid long region (homeodomain) within helix 3 binds specifically to DNA segments that contain the sequence 5’ATTA3’
Examples of homeodomain proteins are:
a) Octanucleotide binding protein 1 (OCT –1), which regulates the histone gene H2B, the thymine kinase gene, and SnRNP genes
b) Octanucleotide binding protein 2 (OCT-2) , which regulates various immunoglobulin genes.
pituitary specific factor 1(Pit 1), which regulates the growth hormone gene, the thyroid stimulated hormone gene, and the prolactin gene.

II) Zinc finger protein
a) it has one alpha helix
b) It contains one zinc atom bound to four cysteine amino acids
c) It contains a hormone binding region
d) A 70 amino acid long region near the zinc atom binds specifically to DNA segments.
Zinc finger
Examples of  Zinc finger proteins are:
a) Transcription factor IIIA(TFIIIA), which engages RNA polymerase II to the gene promoter
b) Sp1(First described for its action on the SV40 promoter), which engages RNA polymerase II to the gene promoter by binding to the GC box
c) Glucocorticoid receptor, estrogen receptor, progesterone receptor, thyroid hormone receptor (erbA), retinoid acid receptor, and the vitamin D3 receptor.

III) Leucine Zipper Protein
  • It consists of of an alpha helix that contains a region in which every seventh amino acid is leucine, which has the effect of lining up all the leucine residues on one side of the alpha helix.
  • The leucine residues allow for dimerization of the two lecine zipper proteins and formation of Y shaped dimer.
  • Dimerization may occur between two of the same proteins(homodimers, eg., Jun-Jun) or two different proteins(heterodimers, eg., Fos-Jun).
  • It contains a 20 amino acid long region that binds specifically to DNA segments.
 Leucine zipper
Example of Leucine Zipper proteins are:
a)CCAAT/ enhancer binding protein (C/EBP), which regulates the albumin gene and the alpha 1 anti trypsin gene.
b) Cyclic AMP response element binding protein (CREB), which regulates the somatostatin gene and the proenkephalin gene.
c)Finkel osteogeneic sarcoma virus (Fos) protein, a product of of the c fos protooncogene, which regulates various genes involved in the cell cycle and cell transformation.
d)Jun Protein, a product of the c-jun proto-oncogene, which regulates various genes involved in the cell cycle and cell transformation.

IV) Helix loop helix protein (HLH)
  • It consists of a short alpha helix connected by a loop to a loner alpha helix.
  • The loop allow for dimerization of two HLH proteins and formation of Y shaped dimer.
  • Dimerization may occur between two of the same proteins (homo dimers) or two different proteins (heterodimers)
helix loop helix
Example of Helix loop helix proteins are:
a) MyoD protein, which regulates various gees involved in muscle development.
b) Myc protein, a product of the c myc protooncogene, which regulates various genes involved in the cell cycle.
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Genetics Practice Problems and Answers

1. The ability to taste a chemical called PTC is inherited as an autosomal dominant allele. What is the probability that children descendant from parents both heterozygous for this trait can taste PTC
a) 0
Answer. If you let T represent allele for the ability to taste PTC, then the cross would be Tt xTt. The Punnet square that follows show that ¾ of the offspring have ability to taste PTC (1/4 TT +1/2 Tt)

Ans: 3/4

2. Which of the following is true of gametes produced by an individual with genotype Dd?
 a)1/2D and 1/2D
b) 1/2D and 1/2d
c) 1/2Dd and 1/2dD
d)All Dd
Ans: d)All Dd

3. Three genes A,B,C  are located on a chromosome. The cross over percentage between A and B is 10% while that between A and C is 8% while that between B and C exhibits a cross over percentage of 18%. What will be the correct order of these genes in the chromosome.
a) XYZ
d)none of these
Ans: b)YXZ

4. What is the cross over percentage between two genes which are 10 map units apart?
a) 5%
b) 10%
c) 20%
d) 100%
Ans: The actual distance between two genes is represented as map unit. One map unit is equivalent to the percentage (%) of crossing over between the two genes.
Ans: b) 10%

5. For the cross AABBCCDd X AAbbCcDd, what is the probability that an offspring will be?
a) 1/16 b) 1/8  c) ¼ d) 3/8
It is not practical to make Punnett square for genotypes involving more than two genes. In this problem, you asked about the frequency of one specific offspring, AABbCcDd. To solve this problem, look at each gene separately.
·         Looking at the first gene, the parents are AA X AA and all offspring will be AA (frequency of 1)
·         For the second gene, BB X bb, all offspring will be Bb (frequency of 1)
·         For the third gene, the parents are CC x Cc, which products ½ CC and ½ Cc.
·         For the fourth gene, Dd x Dd, produces ¼ DD, ½ Dd and ½ dd
To find the probability of AA is 1, of Bb is 1, of Cc is ½, and of Dd is ½.
Then find the product of these frequencies.
·         For AABbCcDd the product is 1 X 1 X ½ X ½ =1/4
      Answer c) ¼ 

6. If you roll a pair of dice, what is the probability that they will both turn up a three?
The chance that one dice will turn up a three is 1 in 6, or 1/6.
For both dice to turn up a three, the probability is determined by multiplying the probability of each event happening independently, or 1/6 x 1/6 =1/36
Answer: d)1/36
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ICAR ARS NET Model Questions on Agricultural statistics

1. Unit less measure of dispersion is
a) Range
b) Standard deviation
c) Mean deviation
d) CV

2. Which measure of central tendency requires data arrangement in ascending or descending order for its estimation?
a)Arithmetic mean
d)Harmonic mean

3. The most frequent occurred value of data or whose frequency is maximum is known as
a)Arithmetic mean
d)Harmonic mean
Measures of Central Tendency (Mean, Median, and Mode)
Points to remember: Measure of Central Tendency
4. In a symmetrical distribution of data which pair is correct?
a) Mean = Median=Mode
b) Mean > Median >Mode
c) Mean < Median<Mode
d) Mean = Median>Mode

5. To calculate the average speed, which item of central tendency is most suited?
b) Mode
c) Weighted HM
d) Weighed AM

6. Mean deviation is the least when calculated about (minimal property)
c)arithmetic mean
d)geometric mean

7. The hypothesis of committing type I error is known as
a) test of significance
b) level of significance
c) composite hypothesis
d) none of the above

8. For comparison of two means from independent samples which test is applicable
a) F test
b) t test
c) z test
d) chi square test

9. The coefficient of variation can be calculated by using the formula
a) Standard deviation / geometric mean x 100
b) Arithmetic mean /Standard deviation x 100
c) Square root of Standard deviation/ arithmetic mean x 100
d) Standard deviation / arithmetic mean x 100

10. Arithmetic mean and variance are always equal in
a) Binomial
b) Poisson distribution
c) Normal distribution
d) None of the above

Learn more:
1. d) CV
2. b)Median
3. c)Mode
4. a) Mean = Median=Mode
5. c) Weighted HM
6. a)median
7. b) level of significance
8. b) t test
9. d) Standard deviation / arithmetic mean x 100
10. b) Poisson distribution
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ICAR ARS NET II Notification 2014

The Agricultural Scientists Recruitment Board (ASRB ) will hold a combined ARS-2014(Preliminary) Examination and NET-2014(II) during 22.9.2014 to 28.9.2014 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

Candidates are advised to read the notification carefully before filling the Online Application Form. 

Important Dates
  • ARS-2014(Preliminary) Examination and NET-2014(II) during 22.9.2014 to 28.9.2014 in Online mode.
  • The ARS-2014 (Main) Examination will be conducted on 28.12.2014.
  • The last date for filling up of online application form is 1700 hrs on 08.09.2014

Books to Refer for  ICAR ARS NET
Age limit
  •  For ARS-2014: A candidate must have attained the age of 21 years but not have attained the age of 32 years as on 01.08.2014. Age relaxation is admissible to the various categories as per rules. For details please refer to the Rule 2 of the Rules of the Examination .
  •  For NET-2014 (II): A candidate must have attained the age of 21 years as on 01.08.2014. There is no upper age limit for the National Eligibility Test. 
Application fee for ars net exam

Transaction charges for Debit Card/Credit Card/NEFT/Challan payment, as the case may be, have to be borne by the candidate. 

The fee must be paid online through the website:
i. Payment can be made through Debit Card/Credit Card from any Bank.
ii. Payment using the online Challan generated (in case of payment to be made using  Challan) can be made in any of the branches of the Syndicate Bank (list of the branches of Syndicate Bank can be obtained from the Branch locator link on : In such cases, the paid copy of the ASRB portion of the Online generated challan for application fee must be uploaded in the
relevant place of the application form without which the application will summarily be rejected. 
How to apply:
  • A candidate seeking admission to the Examination must apply online in the prescribed 
  • Application Form available on the website: .  A candidate must read the provisions contained in this Notification for Combined ARS-2014 and NET –2014 (II) 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 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.
  • No request for change in any field i.e., Name, Father’s Name, Date of Birth, Gender, E-mail Id, Mobile No., Phone No., Category. etc. will be considered under any circumstances. Candidates are therefore advised to be very careful while filling up their application forms. 
Candidates are required to keep ready the following relevant details /information /documents:
a) Combined Notification for ARS Examination-2014 and NET-2014 (II).
b) Name ( as recorded in Secondary level Examination certificate)
c) Father’s name ( as recorded in the Secondary level Examination certificate)
d) Complete Address for Correspondence
e) Complete Permanent Address
f) Matriculation or equivalent Certificate
g) Master’s Degree Certificate/Provisional Degree Certificate/Transcript/ 
Marksheets; if available.
h) Doctorate Degree Certificate/Provisional Degree Certificate/Transcript/
i) Center opted for Combined ARS-2014 (Preliminary) Examination and
NET-2014 (II) (Please check the Examination Centers in this notification in
Appendix – I). 
j) Center opted for ARS-2014 (Main) Examination (Please check theExamination Centers in this notification in Appendix - II). 
k) Scanned copy of recent passport size photograph taken against white
background only of a maximum size of 150 kB in .jpg format only with theface covering at least 2/3
rd of the total space and taken without spectacles.
l) Scanned copy of signatures taken in Black/Blue ink on a white paper only in .jpg format only.
m) Debit Card/Credit Card details for online payment of fee.
n) Valid and active e-mail id.
Plan of NET 2014
  • Online Test Multiple Choice Questions (MCQ)  Demo Test *
  • Total Number of Questions: 150
  • Total Marks: 150
  • Duration of Test: 2 (Two) hours
Previous Question Papers Free (ICAR NET Preparation Resources)
First and foremost thing is to begin the preparation now onwards
"Wishing the very Best "
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Immunology Practice Test on Antibodies or Immunoglobulins

Immunoglobulins or specific antibodies or gamma globulins are blood proteins, which are found to be defensive only against the specific microorganisms, or their toxins that evoked that particular antibody. Immunoglobulins are glycoproteins, made up of 4 polypeptide chains (linked by disulphide bonds). There are two long chains, called heavy or H chains, and two short chains, called light or L chains. The four polypeptide chains are held together to form Y shaped molecule. The top two tips of this  shaped molecule bind to the specific antigens in a lock and key fashion, forming an antigen antibody complex.
1. Newborns
receive maternal B cells
respond to antigens as well as adults
have virtually a fully complement of maternal IgG antibodies
receive IgM antibodies from the mother through placental transfer
2. IgE
is bound together by J chain
is present in high concentration in serum
differs from IgG antibody because of its different H chains
bind to mast cells through its Fab region
3. IgA
is present in milk and saliva
is involved in hay fever
crosses the placenta
activates complement by the classical pathway
4. Human IgM
crosses the placenta
protects mucosal surfaces
is largely restricted to the circulation
is the antibody produced by high affinity plasma cells
5. Cells destined to become IgA producing plasma cells do not...
produce J chain
produce secretory component
migrate from mucosal areas on stimulation with antigen
home to any mucosal area
6. Immunoglobulin light chains
are joined chains by peptide bonds.
are present in the Fab fragment of IgG
all have the same amino acid composition.
are not found in every major immunoglobulin class
7. Ig heavy chains are
expressed by T cells
not important to binding of antigen
not glycosylated
encoded by a constant exon, variable exon, diversity exon and joining exon
8. The Fab portion of Ig
contains the J chain
binds to an Fc receptor
contains the idiotype of the Ig
mediates biological effector functions of Ab molecules
9. The Fc region of antibody
contains both heavy and light chains
is required for antigen binding
generally confers biological activity on the various molecules
is not a requirement for placetal transmission
10. Tears contain
all of the above
Score =
Correct answers:
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Books to refer for GATE Biotechnology Exam Syllabus wise

Engineering Mathematics
  • Linear Algebra: Matrices and determinants, Systems of linear equations, Eigen values and Eigen vectors.
  • Calculus: Limit, continuity and differentiability, Partial derivatives, Maxima and minima, Sequences and series, Test for convergence, Fourier Series.
  • Differential Equations: Linear and nonlinear first order ODEs, higher order ODEs with constant coefficients, Cauchy’s and Euler’s equations, Laplace transforms, PDE- Laplace, heat and wave equations.
  • Probability and Statistics: Mean, median, mode and standard deviation, Random variables, Poisson, normal and binomial distributions, Correlation and regression analysis.
  • Numerical Methods: Solution of linear and nonlinear algebraic equations, Integration of trapezoidal and Simpson’s rule, Single and multistep methods for differential equations.

a) Microbiology: Prokaryotic and eukaryotic cell structure; Microbial nutrition, growth and control; Microbial metabolism (aerobic and anaerobic respiration, photosynthesis); Nitrogen fixation; Chemical basis of mutations and mutagens; Microbial genetics (plasmids, transformation, transduction, conjugation); Microbial diversity and characteristic features; Viruses.
Books to refer: 
b)Biochemistry: Biomolecules and their conformation; Weak inter-molecular interactions in bio macromolecules; Chemical and functional nature of enzymes; Kinetics of single substrate and bi-substrate enzyme catalyzed reactions; Bioenergetics; Metabolism (Glycolysis, TCA and Oxidative phosphorylation); Membrane transport and pumps; Cell cycle and cell growth control; Cell signaling and signal transduction.
Books to refer: 
c) Molecular Biology and Genetics: Molecular structure of genes and chromosomes; DNA replication and control; Transcription and its control; Translational processes; Regulatory controls in prokaryotes and eukaryotes; Mendelian inheritance; Gene interaction; Complementation; Linkage, recombination and chromosome mapping; Extrachromosomal inheritance; Chromosomal variation; Population genetics; Transposable elements, Molecular basis of genetic diseases and applications.Complementation; Linkage, recombination and chromosome mapping; Extrachromosomal inheritance; Chromosomal variation; Population genetics; Transposable elements, Molecular basis of genetic diseases and applications.
Books to refer: 
d) Process Biotechnology: Bioprocess technology for the production of cell biomass and primary/secondary metabolites, such as baker’s yeast, ethanol, citric acid, amino acids, exo-polysacharides, antibiotics and pigments etc.; Microbial production, purification and bioprocess application(s) of industrial enzymes; Production and purification of recombinant proteins on a large scale; Chromatographic and membrane based bioseparation methods; Immobilization of enzymes and cells and their application for bioconversion processes. Aerobic and anaerobic biological processes for stabilization of solid / liquid wastes; Bioremediation.
Books to refer: 

e) Bioprocess Engineering: Kinetics of microbial growth, substrate utilization and product formation; Simple structured models; Sterilization of air and media; Batch, fed-batch and continuous processes; Aeration and agitation; Mass transfer in bioreactors; Rheology of fermentation fluids; Scale-up concepts; Design of fermentation media; Various types of microbial and enzyme reactors; Instrumentation in bioreactors.
f) Plant and Animal Biotechnology: Special features and organization of plant cells; Totipotency; Regeneration of plants; Plant products of industrial importance; Biochemistry of major metabolic pathways and products; Autotrophic and heterotrophic growth; Plant growth regulators and elicitors; Cell suspension culture development: methodology, kinetics of growth and production formation, nutrient optimization; Production of secondary metabolites by plant suspension cultures; Hairy root cultures and their cultivation. Techniques in raising transgencies.
g) Characteristics of animal cells: Metabolism, regulation and nutritional requirements for mass cultivation of animal cell cultures; Kinetics of cell growth and product formation and effect of shear force; Product and substrate transport; Micro & macro-carrier culture; Hybridoma technology; Live stock improvement; Cloning in animals; Genetic engineering in animal cell culture; Animal cell preservation.
Books to refer: 

h)Immunology: The origin of immunology; Inherent immunity; Humoral and cell mediated immunity; Primary and secondary lymphoid organ; Antigen; B and T cells and Macrophages; Major histocompatibility complex (MHC); Antigen processing and presentation; Synthesis of antibody and secretion; Molecular basis of antibody diversity; Polyclonal and monoclonal antibody; Complement; Antigen-antibody reaction; Regulation of immune response; Immune tolerance; Hyper sensitivity; Autoimmunity; Graft versus host reaction.
Books to refer: 
i) Recombinant DNA Technology: Restriction and modification enzymes; Vectors: plasmid, bacteriophage and other viral vectors, cosmids, Ti plasmid, yeast artificial chromosome; cDNA and genomic DNA library; Gene isolation; Gene cloning; Expression of cloned gene; Transposons and gene targeting; DNA labeling; DNA sequencing; Polymerase chain reactions; DNA fingerprinting; Southern and northern blotting; In-situ hybridization; RAPD; RFLP; Site-directed mutagenesis; Gene transfer technologies; Gene therapy.
Books to refer: 
j)Bioinformatics: Major bioinformatics resources (NCBI, EBI, ExPASy); Sequence and structure databases; Sequence analysis (biomolecular sequence file formats, scoring matrices, sequence alignment, phylogeny); Genomics and Proteomics (Large scale genome sequencing strategies; Comparative genomics; Understanding DNA microarrays and protein arrays); Molecular modeling and simulations (basic concepts including concept of force fields).
Books to refer:
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