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

Investigations process of acute pericarditis, Q. Investigations process of ...

Q. Investigations process of acute pericarditis? 1) Blood Examination Erythrocyte sedementaion rate (ESR) may be elevated in tuberculous; collagen and purulent pericarditis.

What is the functional unity of the kidneys, Q. What is the functional unit...

Q. What is the functional unity of the kidneys? The functional (filtering) unity of the kidneys is the nephron a nephron is made of efferent arteriole, afferent arteriole, glom

Contamination due to pathogens - water pollution, Contamination due to Path...

Contamination due to Pathogens - Water Pollution Sewage is a source of pathogenic viruses, bacteria, worms and other parasites. The extent of contamination by these pathogens

What are food hydrocolloids, What are food hydrocolloids? Food hydroco...

What are food hydrocolloids? Food hydrocolloids are hydrophilic polymers of vegetable, animal, microbial or synthetic origin that generally contain many hydroxyl groups and ma

Urine sugar testing, Testing for urine sugars is not recommended for either...

Testing for urine sugars is not recommended for either diagnosis or monitoring of patients with diabetes. This is because a urine sugar is not a reliable test. When no facilities a

#title.circulatory system, #question.what is the mechanism of circulatory s...

#question.what is the mechanism of circulatory system .

Discuss about troponin receptor site, Skeletal muscle A. The myosin hea...

Skeletal muscle A. The myosin head is activated (energized) by the conversion of GTP (that is bound to myosin) to GDP and Pi (that are bound to myosin). B. Detachment of the

Explain process to control of breathing, Explain process to Control of Brea...

Explain process to Control of Breathing? The rate of breathing is controlled by the medulla, the segment of brain stem just above the spinal cord. If the brain stem is cut just

Techniques of open mitral valvotomy , Open Mitral Valvotomy :  Techniqu...

Open Mitral Valvotomy :  Technique: A median stemotomy is done; peri cardium opened and stay sutures taken. After heparinisation ascending aorta is cannulated and then SVC

Explain about the freeze drying Method, Explain about the freeze drying Met...

Explain about the freeze drying Method? The Techniques of freeze-drying have been developed over the past half-century for the purpose of preserving certain biological material

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