Cell membrane, Biology

Assignment Help:

CELL MEMBRANE

As discrete units of life  all living cells are separated from each other and from their external environment by an  extremely delicate (75 A to 100 a= 0.00075 to 0.001 thick ) covering  membrane invisible under  light  microscope. The covering is called cell membrane,  plasma membrane,  cytoplasmic  membrane or plasmalemma . Its  presence was presumably  visualized by Naegeli and Cramer(1855)  and confirmed by  E. Overton(1899) who believed   that it was a double layer of lipid molecules .Since  then, scientists have been making efforts to properly  elucidate the molecular structure of this  membrane. Gorter  and gremdel (1925) postulated  that it was a bimolecular lipid layer formed mainly  of  polar lipids  with  the double hydrophobic  tails of their  molecules in both  layers directed towards  the interior of the  membrane, and their  polar , hydrophilic heads, at the two surfaces of the membrane.

Danielli and  Davson (1935) ascertained that the plasma membrane contains a good amount  of globular proteins in addition  to the  lipids. They postulated  a lipid  protein bilaye r moderl  of  membrane  structure  with hydrated  globular protein molecules  adsorbed upon both exposed  surfaces of the original  biomolecular  lipid       layer, forming a protein lipid  sandwich  Later (1954)  Danielli  further proposed that there were places where lipid bilayer  is perforated  by pores lined by protein molecules, only polar solute molecules and  ions can  pass through  these  pores.

Using electron  microscopy  Robertson (1959) observed that the plasma membrane has a characteristic  trilaminar  appearance in  a dark light dark or  railway track  pattern . Each  dark line consists of a pleated sheet of protein on surface and sheet of polar heads of lipid molecules,  while the light  central line  consists of a bilayer  of nonpolar  fatty  acid of lipid molecules Robertson .called  the trilaminar  structure a unit  membrane which is continuous  with certain membranous  structures  present inside a cell.


Related Discussions:- Cell membrane

Dna structure, A)Which of the following statements about DNA structure is t...

A)Which of the following statements about DNA structure is true? 1.The nucleic acid strands in a DNA molecule are oriented ant parallel to each other, meaning they run in opposite

Define magnesium levels in erythrocytes and lymphocytes, Define Magnesium l...

Define Magnesium levels in erythrocytes and lymphocytes? Magnesium levels in erythrocytes and lymphocytes: These measures appear to provide a more accurate assessment of body M

Explain objective anti-arrhythmic pacemaker defibrillators, Explain Objecti...

Explain Objective Anti-arrhythmic pacemaker defibrillators? After reading this unit, you should be able to: 1 describes the classification of ant arrhythmic drugs; 2 understand

Kingdom fungi, what are the characteristis in species in the phyla division...

what are the characteristis in species in the phyla division

What are diastolic compressive forces, Q. What are Diastolic Compressive Fo...

Q. What are Diastolic Compressive Forces? Coronary perfusion pressure equal to pressure gradient between the coronary arteries and the pressure in LV in diastole. When coronary

Photosynthesis., C4 plants have higher net photosynthetic rate because ...

C4 plants have higher net photosynthetic rate because a.they have no photorespiration b.can photosynthesise in low in

Determine uses of soybean protein, Determine uses of Soybean protein? S...

Determine uses of Soybean protein? Soybean protein concentrates have been used as stabilized dispersions in milk- like beverages and simulated dairy products, such as sour crea

Define the appropriate controls and the possible results, After the virus c...

After the virus capsid containing vimentin gets into the nucleus it is broken down and the DNA is released. Whether capsid proteins are broken down into amino acids or remain intac

In which type of animals does the placenta exist, In which type of animals ...

In which type of animals does the placenta exist? What is its main function? True placenta is present in placental mammals. The placenta is produced from the chorion of the

Define iron factors affecting absorption of dietary iron, Define Iron Facto...

Define Iron Factors affecting absorption of dietary iron? We have read earlier that iron in foods occurs either as haem or non-haem iron. Haem iron comprises of iron in combina

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd