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

National approach to deal with the prevention of obesity, Define National A...

Define National Approach to deal with the Prevention of Obesity? A number of countries have adopted a national approach to deal with the prevention of obesity and other non-com

Define Stolon - Types of hyphae, Define Stolon - Types of Hyphae? Mic...

Define Stolon - Types of Hyphae? Microscopically, hyphae are aseptate and coenocytic. There are 3 kinds of hyphae: (a) Stolon - These grow horizontally on substratum surfa

Importance of meiosis, Meiosis becomes significant for the following reason...

Meiosis becomes significant for the following reasons. Constant Number of Chromosomes: It brings about a reduction in the chromosome number from a diploid (2n) condition to

Male gamete and the female gamete in a flowering plant, What is (a) the mal...

What is (a) the male gamete, and (b) the female gamete in a flowering plant?   (a) The male gamete in a flowering plant is the pollen grain (strictly, the gamete is the male

Study of phylems, iwant to know all about phylem protozoa?

iwant to know all about phylem protozoa?

Airway management - respiratory failure, Airway Management To improve...

Airway Management To improved ventilation, suctioning, IPPB, Ultrasonic mist therapy and postural drainage with clapping and vibrating are all employed to halt the progress o

Explain about the obliques muscles, Explain about the Obliques muscles ...

Explain about the Obliques muscles The superior and inferior oblique muscles form an angle of about 51 0 with the optical axis. The oblique muscles produce cyclorotation becau

Clinical trials for changing nutrient requirements with age, Define Clinica...

Define Clinical Trials for Changing nutrient requirements with age? Several clinical trials provide evidence of changing nutrient requirements with age. The metabolic demand fo

Explain why the plasmid is described as a vector, Humans produce insulin fr...

Humans produce insulin from certain cells in the pancreas.The insulin gene is isolated from a human pancreas cell and then inserted into a plasmid.The DNA responsible for the synth

Blood transfusion , Blood transfusion  The blood of Raja cannot be t...

Blood transfusion  The blood of Raja cannot be transfused to Rama because the blood group of Raja is ‘B' and blood group of Rama is ‘A'. If Raja's blood with group ‘B' is

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