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In What cell organelle does photosynthesis occur?

Where does photosynthesis occur? The organelle where the photosynthesis occurs is the chloroplast. This poster will give you a complete concept about the exact locations of different cells and reactions of photosynthesis.
In what cell organelle does photosynthesis occur?
See more on photosynthesis: An overview of photosynthesis
                                               3 major classes of photosynthetic pigments
                                               What are photosystems? PSI &PSII
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cDNA library: Definition and Steps in the construction of cDNA library notes

cDNA library
In the last post, we discussed about the steps in recombinant DNA technology or gene cloning. In that post, we discussed genomic library as one of the source for getting our desired gene for cloning. In this post we will be discussing the second source of getting the gene of interest that is cDNA library.
cDNA library: Definition
cDNA library represents the collection of clones containing cDNA of an individual organism under study
It represents the collection of  mRNA complement of a single type of cell.
cDNA library: Definition and Steps in the construction of cDNA library

What is the advantage of cDNA library over genomic library?
Majority of the cases, we need to express a eukaryotic gene in a prokaryotic system like bacteria.  The default choice of gene expression is E.coli. Eukaryotic gene is made of both introns and exons. For a gene to synthesize protein, prokaryotic system should have splicing mechanism or pre-mRNA processing mechanism where introns are removed and exons are joined together. As prokaryote like E.coli lack this mechanism, it is very difficult to express a eukaryotic gene in prokaryotic host like E.coli. This problem is solved by using cDNA for gene cloning. cDNA id synthesized form processed mRNA after splicing, therefore introns are absent. Thus cDNA can be used directly for gene expression in E.coli.
Construction of cDNA library
The procedure is same for all other organism
Step 1: Isolation of mRNA from the cells and synthesis of cDNA from this eukaryotic functional mRNA
cDNA synthesis from processed or mature mRNA is achieved using the enzyme reverse transcriptase; an RNA dependent DNA polymerase.
Step2: Cloning of synthesized cDNAs in suitable vector like plasmid or λ phage
The cDAN synthesized are joined with suitable adaptors using T4 ligase and 5’ P group is removed using alkaline phosphatase. The most common vectors for cDNA cloning include plasmid and λ phages
Step 4: Introduction to a suitable host like bacterium.
Introduce this rDNA molecule with cDNA fragments into a host, most often E.coli bacterium. Plasmid will multiply inside forming numerous copies. We need to identify the host cells with these fragments from the rest of cells without rDNA molecule.
Step 5: Screening and Maintenance of set of clones containing cDNA
Screening of colonies with rDNA is similar to genomic library. The most common screening procedure includes DNA hybridization or immunological assays. The clones with cDNA (rDNA) are selected. Maintenance of such clones or colonies containing cDNAs is the cDNA library
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If a bacterium divides every 20 minutes-Formula

1. If a bacterial cell doubles every 20 minutes. How many bacteria will be formed in 2 hours?
If a bacterium divides every 20 minutes-Formula Equation

a) 4
b) 8
c) 16
d) 64

2. If you start out with a population density of 300 CFU/ml of a bacterium that divides every 30 minutes, what will the population density be at the end of three hours, assuming the cells are in the log phase of growth?
a) 26 CFU/ml
b) 3006 CFU/ml
c) 19200 CFU/ml
d) 9000 CFU/ml

3. A bacterial cell divides once in every minute and takes one hour to fill a cup. How much time will it take to fill half the cup?
a) 30 min
b) 29 min
c) 59 min
d) 60 min

Q1. Answer:
First find out the number of generation, let it be =n (no. of generation)
n=total time of division / time taken for one division
i.e. 2 hours=120 min/20 min=6
You can answer any question like this using the given formula
f=ix2n where    f=final number of bacteria
                        i=initial number of bacteria

Q2.  Answer: 19200 CFU/ml
F=300x2=19200 CFU/ml
Q3 Answer: 59 min as the growth is exponential.
Suppose 10000 bacteria is required to fill the cup and it takes 1 hour (60 min) to form 10000 bacteria. Then half the cup is 5000 bacteria and that is just before the final division, which is it takes 59 min to fill half the cup and 60 min to fill the cup as the growth is exponential.

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10 Quick facts on Microscope

1. The first microscope was invented by Zacharias Janssen and Hans Janssen

2. Electron Microscope was made by Knoll and Ruska

3. Class room microscope was invented by Kepler and Galileo

4. As compared to light microscope, the resolving power of electron microscope is 1000 times

5. Scanning electron microscope is important for its image which are three dimensional

6. High magnification of electron microscope is due to

7. Phase contrast microscope  is best for studying the process of mitosis

8. Resolving power of light microscope is 0.2 micrometer 

9. The simple microscope has the resolution of 0.1mm 

10. A compound microscope has 3 lenses 
Learn more:
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Worksheet on Bacteriophage

Bacteriophages are  viruses that attacks bacteria. This is a simplified worksheet that helps you to understand the structure of a bacteriophage. The same is given as interactive online quiz also. Enjoy learning bio... 
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ICAR Notification ARS 2016 and NET 2017

The Agricultural Scientists Recruitment Board (ASRB) will hold a combined ARS- 2016 (Preliminary) and NET (I)-2017 Examination during 16.05.2017 to 21.05.2017 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. (official notification)
The ARS-2016 (Mains) Examination will be conducted on 08.07.2017. Candidates are advised to read the notification carefully before filling the Online Application Form.

For ARS-2016: A candidate must hold a Master’s Degree or equivalent in the concerned discipline with specialization as defined in Appendix-VI, completed on or before 08.07.2017.
Age limit: 
For ARS-2016 A candidate must have attained the age of 21 years but not have attained the age of 32 years as on 01.01.2017. 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)-2017 :A candidate must have attained the age of 21 years as on 01.01.2017. There is no upper age limit for the National Eligibility Test.
Number of attempts:
How to apply: A candidate seeking admission to the examination must apply online in the prescribed Application Form available on the website:
Useful Links:
Previous Question Papers Free (ICAR ARS NET Preparation Resources)
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What are Photosystem? Definition and Summary of PS I and PS II

What are Photosystems antenna molecule complex?
The light harvesting complexes (LHC) formed by photosynthetic pigments are located on the thylakoid membrane of the chloroplast in two pigment systems called as Photosystem I and Photosystem II.

Definition: Each photosystem consists of collection of chlorophyll-a molecules, accessory pigments and associated proteins present on the surface of the thylakoid membrane of the chloroplast.
Each photosystems consists of two closely linked components namely reaction centre and antenna molecules.
Photosystems antenna molecule complex
Reaction centre molecules are the primary pigment which is chl-a molecules in green plants. Accessory pigments that surround the reaction centre forms the antenna complex. Accessory pigments include chl-b, carotenes and xanthophylls.

The antenna molecules made up of accessory pigments of photosystems absorb photons (light energy) get excited and transfer the excitation energy to the adjacent accessory pigment and finally reaching the reaction centre by resonance transfer.

Photosystem I (PS I): Reaction centre chl molecule has light absorption peak at 700 nm (P700). PS I occurs mostly on the inter-granal lamellae of the chloroplast. PSI uses light energy to convert NADP+ to NADPH + H+

Photosystem II (PS II): Reaction centre chl molecule has light absorption peak at 680 nm (P680). PS II occurs mostly on the granal lamellae of the chloroplast. PS II uses light energy for photolysis of H2O molecules, or oxidizing H2O molecules producing electrons, protons (H+) and O2.
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3 Major Classes of Photosynthetic Pigments

3 Major classes of photosynthetic pigments in plants
The primary site of photosynthesis is leaf. We have already discussed the exact site of lightdependent and light independent reaction of photosynthesis within the chloroplast in our last post
 An anabolic process by which chloroplast of green plants and other phototrophs synthesize carbohydrates (glucose) and evolve molecular O2 as by-product, using CO2, H2O and sunlight.
  It involves conversion of light energy into chemical energy
 Approx. 0.2 % of light falling on earth is used for photosynthesis
 90% of photosynthesis is in oceans, carried out by fresh water and marine algae
3 Major classes of photosynthetic pigments in plants

3 Major Classes of Photosynthetic pigments in Plants
  • Photosynthetic pigments are located in the thylakoid membranes of the chloroplast. These pigments are capable of converting the energy of sunlight to chemical energy. The pigments absorbs light rays from the visible region of the electromagnetic spectrum
  • The two major groups of pigments are a) Principal Pigments b) Accessory pigments
  • The principal pigment in all photosynthetic plants is chlorophyll-a.
  • Accessory pigments include chlorophyll-b, c, d, carotenoids and phycobilins.
  • In green plants, chlorophyll-a is the primary pigment and chlorophyll-b and carotenoids are the accessory pigments.
1. Chlorophylls:
  • Chlorophylls are magnesium porphyrin derivatives.
  • Chl-a is the primary pigment in photosynthesis and it forms the reaction centre of the photosystems (light harvesting complex, LHC).
  • Chl-b, c, d, e and bacteriochlorophyll are the other type of chlorophyll molecules.
  • Chl absorbs maximum at red and blue region and reflects green light.
  • A chlorophyll molecule consists of a hydrophobic pyrole head and hydrophilic phytol tail with a central Mg atom. The head is formed of 4 pyrole molecules linked together by methane (CH3) group to from a ring called porphyrin ring. The side group of chl-a is methyl group (-CH3) and chl-b is an aldehyde group (-CHO).
  • Chl-a is bluish green and chl b is yellow green.
2. Carotenoids:
  • Carotenoids are fat soluble, accessory pigments with yellow, orange or red colour found in all photosynthetic plants. These pigments absorb blue-violet region of the visible spectrum.
  • Carotenoids are of two groups, carotenes which are red or orange coloured (C40H56) and xanthophylls which are brown or yellow coloured (C40H56O2). The carotenes include α, β, carotene, lycopene, phytoene etc.
  • Xanthophylls include lutein, violaxanthin, zeaxanthin etc.
  • The functions of carotenoids are
  • Absorb more solar energy and transfer it to reaction centre and protects chlorophyll molecules from photo-oxidation
3. Phycobilins:
  • Water-soluble, red or blue accessory pigments present on cyanobacteria and red algae. The structure is similar to chlorophyll molecule but the central Mg is absent.
  • The two types of phycobilins are phycoerythrins which are red coloured and phycocyanins, which are blue coloured.
  • Thus the question how the light energy is converted to chemical energy in photosynthesis? The answer is these pigments can trap the energy of sunlight and the excited electron while moving through different electron acceptors releases some energy which is utilized for the phosphorylation of ADP to ATP. 
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