PHYSICAL PROPERTIES OF PROTOPLASM

PROTOPLASM:T HE word protoplasm, coming from the Greek, protos, first, and plasma, a thing formed, means literally "the first creation." It was used by Purkinje in 1840 for the formative material of the animal embryo and by von Mohl in 1846 for the contents of a plant cell.

.The modern view is to regard the cell as a system, a mixture of many different substances, often separated from each other by phase boundaries or membranes, whose mutual interaction results in the varied phenomena we associate with life. Noone of these substances can be considered as "living" except insofar as it is indispensable for the continuance of life. On this view salts are as fundamental a part of the make up of protoplasm as are proteins, for no cell can function in complete absence of salts. Properties of protoplasm is an incorrect although a convenient phrase.

Biophysical study of the cell (using the word cell rather than protoplasm) means applying the knowledge of physics to explain what we observe living things to do. Movement, transmission of nerve impulses, reception of stimuli by sense organs, energy transformations, absorption of material, reproduction, are all represented on this program. The great majority of investigations involve applying the principles of classical physics but because of the small size of cells the approach must be by the micro method and the problem is always more complicated than the physicist is accustomed to deal with. Conseqlllently the accuracy of quantitative work is not so great and often we must be satisfied with order of magnitude.

ViscosityThe term consistency is perhaps a better designation for the resistance of a cell interior to flow since it a cell the "lines of force" are such as would appear only if all three poles were unlike, an obviously impossible situation. How ever, the series of changes which we observe during cell division is entirely too complex to be considered here and we are very far from a rational interpretation of them. For many interesting observations on the behavior of specific structures in cells the reader is referred to the article by Chambers (1924)2 in the General Cytology and to other books on cytology (Wilson, 1925 ;10 Gray, 1931;3 Sharp, 19349).involves no implication as to whether the flow is truly viscous and proportional to the deforming force, or whether

plastic, occurring only after a critical deforming force is reached. Experiment has shown that the cell interior is in some cases a gel and in others quite liquid. It is also observed that a region near the surface of many cells is of greater consistency than the interior and is designated as the ectoplasm or cortical layer to distinguish it from the more liquid endoplasm. There are likewise special regions in the cell which may be jelled while others are not. Such gross differences as the above may be detected by the methods of micro dissection and microinjection of material (oil or water droplets) whose behavior as observed with the microscope give evidence of the nature of the region concerned. Thus Chambers (1917)14 has shown that the aster, whose appearance precedes the division of a cell into two, is a region in which jelled fibers grow out from a center and only the spaces between the fibers are liquid. The granules in the cell are pushed in lines between the fibers. In fixed and sectioned preparations of cells the granules appear to form rays and where two asters are present with a spindle between them the whole picture is like that of a field of force between unlike poles. Such an interpretation is tempting, but there is grave evidence against this view, most convincing the fact that when three asters appear in

Tension at the SurfaceFor tension studies, only cells can be used which lack rigid protecting membranes or a gelled surface layer or the determination must be made after the protecting coats are removed. Although the word "plasma membrane" is used for the external surface of a cell, which is responsible for its osmotic behavior, much evidence is accumulating to indicate that this surface layer is of molecular thickness. It is probably not correct to speak of the surface tension of a cell in the sense of an interfacial tension between two pure nonmiscable liquids but a definite tension can be measured, which represents the sum of surface and elastic forces best designated as "tension at the surface." Indeed, the whole question of a membrane becomes a matter of definition and all gradations of surface films exist from the monolayer through multilayers to molecular structures sufficiently thick to be unequivocally designated a membrane. \when it is recalled that even monolayers may exhibit the properties of two dimensional gases, liquids and solids with all degrees of two dimensional viscosity an No one would deny that a soap bubble in air can be said to possess surface tension but its value will depend on the bulk concentration of soap. An albumen bubble also possesses a surface tension which depends not only on the bulk concentration of albumen but also on the area of its surface, i.e., it possesses elastic properties, with increased tension for greater areas, and in addition shows hysteresis (Harvey and Danielle, 1936).29 The values for tension of albumen bubbles depend on whether the tension (calculated from the simple relation P=4T /r,d elasticity (Langmuir, 1936)38 the complex situation in regard to the cell becomes obvious. where P = pressure, T = tension, and r = radi us of the bubble) is determined as the bubble is expanded or as it is contracted.

Kinetic MethodJust before the completion of first cleavage of an Arbacia egg the two hlastomeres are connected by a small stalk. If one blastomere is punctured, the remaining one will discharge its contents through the stalk due to an excess internal pressure from the tension at the surface. From moving pictures, the rate of discharge can be determined by measuring the decrease in volume of the blastomere. It follows a law which would indicate elastic forces at the surface. Assuming Poisseuille's la\\! (and using a measured value for viscosity of the egg fluid at this stage of development), Satchel and Burton (1936)4;' calculated the excess internal pressure to be 62 dynes/cm2 and the tension 0.09 dynes/em, agreeing well with the Harvey (1931)26 and Cole (1932)15 figures for the same egg.

Building materialSuspension substance that makes up the physical basis of all living things.

1) Carries on the process of 2) Metabolism3) Reception of food and oxygen4) Processes food and oxygen5) Eliminates waste products6) MACROMOLECULES/organic compounds

i. Proteinsii. lipids

iii. carbohydratesiv. nucleic acids

(These are organic materials that are life supporting and are in the cells of the human body)….

i. Proteins 15% building block (amino acids) Order of these blocks determine the function of the protein molecule which in turn

gives the cell its characteristic builds new tissue repairs Source of heat and energy makes up antibodies hormones ENZYME CONTROL

controls speed of chemical reaction (release energy from fat)

ii. lipids 2% non water soluble stores energy component of cell membrane protects against cold/heat Assists in digestive process component of hormones

iii. carbohydrates 1% cell energy releases large amounts of energy when bonds are broken thru metabolism Three classifications of carbs monosaccharides-glucose disaccharides- sucrose polysaccharids- starch

iv. Nucleic acids 1% Blueprint DNA-nuclear command/control/reproduction info RNA- in nucleus and cytoplasm messengers or transfer agents

(A) Protoplasm behave both gel and sol…

Gel: Present in solution form. Sol: Present in semisolid materials, like jelly.

(B) COHESISENESS: Intra__moleculer forces between molecules of protoplasm.

( C) VESCOSITY: Brownian moment: Zigzag zigzag movement of molecules. Ameoboid Movement. : pseudopodia formation …Perform in Amoeba CYLOSIS OR SYTOPLASMIC STREAMING :

Movement of cytoplasm inside the cell as in Paramecium

(D) SURFACE TENSION : The surface molecules like lipids and proteins have less surface tension. The molecules inside the protoplasm have high surface tension.

REFERENCE BOOKS1. N. K. Adam, Physics and Chemistry of Surfaces (Oxford, 1930).2. R. Chambers, The Physical Structure of Protoplasm in General Cytology, edited by E. V. Cowdry (Chicago,1924).3. J. Gray, Textbook of Experimental Cytology (Cambridge,1931).4. W. D. Harkins, Surface Energy and Surface Tension in Colloid Chemistry, edited by ]. Alexander, Vol. I (New York, 1926).5. L. V. Heilbrunn, The Colloid Chemistry of Protoplasm (Berlin, 1928).6. R. Hoeber, Physikalische Chemie der Zelle and Gewebe.7. E. K. Rideal, Surface Chemistry (Cambridge, 1930).8. W. Seifritz, Protoplasm (New York, 1936).9. L. Sharp, Introduction to Cytology (New York, 1934).10. E. B. Wilson, The Cell in Development

Prepared by Amjad khan23/10/2014