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

Define about the deficiency of cyanocobalamin, Define about the Deficiency ...

Define about the Deficiency of cyanocobalamin? Malabsorption of vitamin B 12 can occur at several points during digestion. By far, the most important condition resulting in v

Butter, Ask question #Minimum 100 words role of micro organisms in preparat...

Ask question #Minimum 100 words role of micro organisms in preparation of butter accepted#

Explain cardiac examination auscultation and its techniques, Explain cardia...

Explain cardiac examination auscultation and its techniques? Auscultation of the heart sound and associatcd sound is very important to diagnose the cardiovascular diseases. It

Define carbohydrate requirement for cancer patients, Define Carbohydrate re...

Define Carbohydrate requirement for cancer patients? Adequate amount (60% of total energy) of carbohydrates should be provided. If a very high calorie diet is being given, emph

Explain bidirectional superior vena cavo, Explain Bidirectional Superior ve...

Explain Bidirectional Superior vena cavo pulmonary shunt bidirectional glenn "This is a palliative produce where blood from superior vena cava is diverted to the pulmonary arter

Cell theory, Cell theory is one of the four (or five) unifying concepts in...

Cell theory is one of the four (or five) unifying concepts in the biology. The cell theory states that all the living things are composed of at least one cell and that cell is the

Describe mitochondria and explain why it would happen, Describe what would ...

Describe what would happen if people lost all of their mitochondria and explain why it would happen.

Lead, Le a d It is common cause of poisoning in cattle. Lead poisonin...

Le a d It is common cause of poisoning in cattle. Lead poisoning in other species is limited by reduced accessibility, more selective eating habits, or lower susceptibility.

What is pleiotropy, What is pleiotropy? Pleiotropy (or pliotropy) is th...

What is pleiotropy? Pleiotropy (or pliotropy) is the occurrence in which a single gene conditions several dissimilar phenotypical traits. Some phenotypical traits might be s

What are the main prophylactic measures against malaria, Q. What are the ma...

Q. What are the main prophylactic measures against malaria? The major preventive measures against malaria are the elimination of the treatment of infected people, vector mosqui

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