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

What are the three main types of rna, What are the three main types of RNA?...

What are the three main types of RNA? What is meant by heterogeneous RNA? Messenger RNA, or mRNA, transfer RNA, or tRNA, and ribosomal RNA, or rRNA, are the three main kinds of

Explain the role of lipoprotein, Explain the Role of Lipoprotein ? As d...

Explain the Role of Lipoprotein ? As discussed in the previous section, serum concentrations of Lp(a) are elevated in South Asians irrespective of their migrant status. Several

Explain the primary root growth, Explain the Primary Root Growth? Prim...

Explain the Primary Root Growth? Primary Growth in Roots :  Roots grow down and through the soil by adding new cells at the tip of the root (called the root tip). There is a

Indications for surgery of mitral regurgitation, Q. Indications for Surgery...

Q. Indications for Surgery of mitral regurgitation? Surgery is indicated in all symptomatic patients (class II and above) with severe mitral regurgitation and normal or decreas

Which are vessels that drain filtered blood from the kidneys, Q. Which are ...

Q. Which are the vessels that drain filtered blood from the kidneys? The renal veins carry the blood that has been reabsorbed in the nephron tubules and the venous vessels that

Explain the use of bacterial vaginosis in pregnancy, Use of Bacterial vagin...

Use of Bacterial vaginosis In pregnancy  Bacterial vaginosis has been associated with premature labor and complications of delivery, and symptomatic bacterial vaginosis in preg

What is peristomium. describe, What is peristomium. Describe? The segme...

What is peristomium. Describe? The segment behind the prostomium in annelids which contains the oral opening. This segment like the prostomium isn't a true segment and has no s

Ethylene - apical dominance, Ethylene - Apical Dominance Ethylene also...

Ethylene - Apical Dominance Ethylene also plays a role in the inhibition of lateral bud growth. It is present in those tissues like shoot apex where auxins are also present. I

Solubility, Solubility You are aware that gases are soluble in liquid...

Solubility You are aware that gases are soluble in liquid. Solubility of a gas in a liquid depends on the partial pressure, temperature and presence of other solutes. Table

Define carbohydrate requirement to avoid underweight problem, Define Carboh...

Define Carbohydrate requirement to avoid underweight problem? Liberal amounts of easy to digest carbohydrates should be included in the diet. The intake of dietary fibre should

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