Current Affairs 11th Class

It is an another technique of separation. In which patricles of different charges and sizes are separated under the influence of electric field. e.g., nucleic acids, proteins, amino acids, nucleotides can be separated by this method. The technique was discovered by Russian physicist Alexender Reuss in 1807. In immunoelectrophoresis antibodies coupled with radioisotopes, specific enzymes or fluorescent dyes are used in detection of particular proteins. The technique is highly sensitive. It can separate molecules in picogram and nanogram quantities and distinguish proteins which differ from each other in only one amino acid.

The concentration of various ions in different parts is now studies by using a glass microelectrode. It has silver wire dipped in KCl solution. This technique is used for studying the movement of ions through ions channels. The ions channels are intrinsic membrane proteins. For studying this passive transport of ions through ion channels Neher and Sakman developed a Patch clamp technique for which they are awarded Nobel prize in 1991.

Microscopy (Gk. Micros = small ; skopein = to see) It is practice of using microscopes for the study of finer details of small objects including cells and tissues. Microscope are instruments consisting of lenses (made of glass / Lithium fluoride / electromagnetic lens) which magnify and resolve small objects not visible to unaided eye for the study of their details. The term microscope was coined by Faber in 1625. Magnification : Is the power of enlargement, which is the ratio of \[\text{Magnification}=\frac{\text{Size of the image with}\,\text{the instrument}}{\text{Size of the image with unaided eye}}\] Magnification of a microscope is roughly equal to the multiple of magnifying power of objective lens and ocular lens (eye piece) e.g., if the magnification power of an ocular lens is \[10\,X\] and of the objective is \[40\,X,\] then the total magnifying power of a microscope is \[10\times 40=400\,X\] (the magnification power of a microscope is represented by the symbol 'X'). Resolving power : It is the ability of a system to distinguish two close objects as two distinct objects. Its values is calculated by Abbe equation - \[{{L}_{m}}=\frac{0.61\lambda }{NA}\] Here, \[\lambda -\] is wavelength of used light, \[NA-\] Numerical Aperture, \[(NA=n\sin \theta )\] Numerical aperture is multiple of refractive index of medium (n) and \[\sin \theta \], which is sine of angle substended by optical axis and outer ray covered by objective. The value for best objective \[\sin e\,70{}^\circ =0.94.\] The resolving power of human eye is 100mm or microns (0.1 mm). This means that two points less than 100mm apart appear as one point to our eyes. Father of microscopy is Leeuwenhoek. He built first 270 X magnification microscope in 1672.

Some of the biological molecules undergo changes after their synthesis. We can cite here the case of RNA. The transcription of hnRNA from DNA ultimately leads to the formation of m-RNA. These changes can be studied through pulse-labelling technique.

They are unstable isotopes which function like normal elements but emit positive or negative particles, e.g., \[^{3}H\](Tritium), \[^{14}C\](Carbon), \[^{32}P\](Phosphorus), \[^{35}S\](Sulphur), \[^{42}K\](Potassium), \[^{131}I\](Iodine). Radioactivity is recorded in different parts by Geiger counter or scintillation counter or autoradiography to know regions of use and transport. The tracers have been used for knowing pathway of mineral transport (Stout and Hoagland, 1939), organic solute transport (Vernon and Aronoff, 1952), carbon assimilation (Calvin, 1955). Where radioactive elements are not available, heavy isotopes are used, e.g., \[^{15}N{{,}^{18}}O.\] Their fate is recorded by mass spectroscopy and density gradient centrifugation. Meselson and Stahl (1958) studied DNA replication and Ruben et al (1941) evolution of oxygen (photolysis of water) in photosynthesis by using heavy isotopes.

(1) Simple microscope : It is also known as magnifying glass and consists of a convergent lens. Leeuwenhoek (1683) designed a primitive microscope and discovered cells with it. It was the first tool ever used to observe biological objects. Its magnification power was 14 – 42 times only, so it is considered as simple microscope. (2) Compound microscope or Light microscope : The first compound microscope was assembled by Zacharias Janssen and J. Janssen, the Dutch spectacles makes in 1590. The compound microscope was prepared by Kepler and Galileo in 1611. However, it was not used for laboratory study. It is simplest, widely used microscope having three lens i.e., condensor, which collects the light rays and precisely focuses them on the objects; objective lens, which magnifies the image by three objective lenses, i.e., low power (10x), high power (45x) and oil immersion lenses. In a compound microscope an object can be magnified upto 1000 times and the magnification is independent of intensity of light, size of microscope and numerical aperture. The light microscope is also called bright field microscope because it forms the image when light is transmitted through the object. (3) Fluorescent microscope : It was developed by Coons (1945). It is observed that when ultraviolet light is irradiated on certain chemical substances, they absorb it and emit visible light. These chemical substances are called fluoro-chromes. The fluorescent substances e.g., quinine sulphate, rhodamine and auramine are used to stain the cellular objects and these objects are easily visible as fluorescent areas when illuminated with ultraviolet light. (4) Polarizing microscope : It was invented by Tolbart. In this microscope the plane polarised light is used as a source of illumination. Unlike the ordinary light, plane polarised light vibrates only in one direction and the cellular objects are easily visible as they appear bright against the dark ground. Polarizing microscope is helpful in studying the spindle fibres in the cells. (5) Ultraviolet microscope : It was invented by Caspersson. In this microscope the source of illumination is ultraviolet radiations having shorter wavelengths \[(1500\text{ }{AA}\text{ }\text{ }3500\text{ }{AA})\] as compared to ordinary visible light. In this microscope, the lenses are made of fluoride, lithium fluoride or quartz instead of glass. Ultraviolet microscope is helpful in quantitative determination of all those cell components which absorb ultraviolet rays. (6) Phase contrast microscope (i) Discovered by Dutch man Fredericke Zernicke (1935). (ii) Source of illumination is visible light. (iii) It is used to study living cells and tissues without staining and effect of chemical and physical agents on the living cells. (iv) It is also used to study spindle formation, pinocytosis, karyokinesis, cytokinesis etc. (v) It is draw back is low magnification power so subcellular organelles smaller than \[0.2\,\mu ,\] like ribosomes, lysosomes, ER, cannot be visualised. (7) Interference microscope (Morten et.al.) (i) It’s principle is similar to that of the phase contrast microscope and gives / studies quantitative data. (ii) Nomarski interference contrast microscope is useful to study mitosis /cell components in living state. (iii) more...

1 micron \[(\mu )={{10}^{-6}}\] or one millionth 1 micrometer \[(\mu m)={{10}^{-6}}m,\,\,{{10}^{-4}}cm,\,\,{{10}^{-3}}mm=1000nm\] 1 Nanometer\[(nm)={{10}^{-9}}m,\,\,{{10}^{-7}}cm,\,\,{{10}^{-6}}mm,\,\,{{10}^{-3}}\mu m=10\overset{{}^\circ }{\mathop{A}}\,\]  1 Angstrom \[(\overset{{}^\circ }{\mathop{A}}\,)={{10}^{-10}}m,{{10}^{-8}}cm,\,{{10}^{-7}}mm,\,\,{{10}^{-4}}\mu m.\] 1 Picometer \[(pm)={{10}^{-12}}m,\,{{10}^{-3}}nm\] 1 Femtometer \[(fm)={{10}^{-15}}m,\,{{10}^{-6}}nm\] 1 Attometer \[={{10}^{-18}}m,\,\,{{10}^{-9}}nm\] Common unit of measurement in Microscopy and cytology is nanometer while unit of measurement of cell is micron.