Question

Plasma membranes are underrated. Describe how aspects of the plasma membrane structure (physical components and their arrangement) enables FOUR aspects of neuronal activity. Use the terms 'semi-permeable' and 'fluid mosaic' in your response.

Short and simple answers welcome.

Answer 1

Plasma membrane is an absolute requirement for all living organims as it is responsible for the relationship of a cell with the outside world .The detailed structure of the membrane was studied only after the invention of electron microscope in the 1950s .Meanwhile chemical studies on the plasma membrane enabled the scientist to deduce the possible structure of plasma membrane .The chemical studies done specially on the red blood cells ,enabled the scientist to deduce the possible structure of plasm membrane .On the basis of this structure ,the cell membrane is composed of lipids that are arranged in a bilayer .These lipids are arranged within the membranes with the polar heads towards the outer sides and the hydrophobic (non polar ) tails towards the inner side .The polar heads interact with water and are hydrophillic .This ensures that the nonpolar tail of the saturated hydrocarbons or hydrophobic tail is protected from the aqueous environment .Later, revealed the cell membrane also possess proteins and carbohydrate .In human being the membrane of the RBC has approximately 52% protein and 40 % lipid .Depending on the ease of extraction ,membrane protein can be classified as integral or peripheral .The peripheral protein lie on the surface and the integral protein are partially or totally buried in the membrane .The integral protein which run through lipid bilayer are known as tunnel protein .Thus the membrane can be described as protein iceberg floating in phospholipids.An improved model was proposed by Singer and Nicolson which was widely accepted as Fluid Mosaic Model.According to this the quasi fluid nature of lipid enables lateral movement of proteins within the overall bilayer .The cell employs a number of transport mechanism

A) Endocytosis:-It invloves intake of materials in the form of carrier vesicles formed by invgination of small regions of plasma membrane.It is of two type :-

a)Pinocytosis-It is also celled cell drinking process as fluid materials having high molecular weight such as protein ,amino acids ,fats etc in the form of globules of fluid enter the cytoplasmaby invagination of plasma membrane.Globules of fluid materials are aclled pinosomes.

b) Phagocytosis:-It is a bulk intake of large solid particles by the cell using the plasma membrane .It is also called cell eating proces.It occurs in all protozoans and in special cells of metazoans .It is pinched off from the plasma membrane inside the cytoplasm in the form of food vacuole or phagocytic vesicle .

B)Exocytosis:-It is a process of exudating the secretory products or undigested waste products to the outside of the cell cytoplasm through plasma membrane .This process is also celld cell vomiting or ephagy .

The passage of substance across the plasma membrane occurs by various mathods such as active and passive transport.

C)Passive transport:- Many molecules can move across the membrane without any requirement of energy and this is called passive transport .Neutral molecules may move across the membrane by the process of simple diffuion along the concentration gradient i.e from higher concentration to lower concentration .Water may also move across the plasma membrane from higher to lower concentration by diffusion through membrane called osmosis.As the polar molecule cannot pass through the nonpolar lipid bilayer ,they require a carrier protein of the membrane to facilitate their transport across the membrane.

D)Active transport:-It is an uphill movement of materials across the membrane where the solute particles move against the concentration gradient i.e, from lower to higher concentration.Such a transport requires energy which is obtained from ATP .Thus it is energy dependent process.

Thus the aspect of plasma membrane enables four aspect of neuronal activity .