Physical properties of protoplasm............

1. PHYSICAL PROPERTIES OF PROTOPLASM
PROTOPLASM:
THE word protoplasm, coming fromthe Greek, protos, first, and plasma, a thing
formed, means literally "the first creation." Itwas used by Purkinjein 1840 for the
formativematerial 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 fromeach other by phaseboundaries or membranes,
whosemutual interaction results in the varied phenomena we associatewith life.
Noone of these substances can be considered as "living" except insofar as it is
indispensablefor the continuance of life. On this view salts are as fundamental a
part of the make up of protoplasmas are proteins, for no cell can function in
complete absenceof salts. Properties of protoplasmis an incorrect although a
convenient phrase.
Biophysicalstudy of the cell (using the word cell rather than protoplasm) means
applying the knowledgeof physics to explain what we observeliving things to do.
Movement, transmission of nerveimpulses, reception of stimuli by senseorgans,
energy transformations, absorption of material, reproduction, are all represented
on this program. Thegreat majority of investigations involve applying the
principles of classical physics butbecauseof the small sizeof cells the approach
must be by the micro method and the problem is always morecomplicated than
the physicistis accustomed to deal with. Conseqlllently the accuracy of
quantitative work is not so great and often we must be satisfied with order of
magnitude.

2.  Viscosity
The term consistency is perhaps a better designation for the resistanceof a cell
interior to flow since it a cell the "lines of force" aresuch as would appear only if
all three poles were unlike, an obviously impossiblesituation. How ever, the
series of changes which we observeduring 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)2in 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 proportionalto 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 surfaceof many
cells is of greater consistency than the interior and is designated as the ectoplasm
or cortical layer to distinguish it fromthe 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) whosebehavior
as observed with the microscope giveevidence of the nature of the region
concerned. Thus Chambers (1917)14has 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
 Tensionat the Surface
For tension studies, only cells can be used which lack rigid protecting membranes
or a gelled surfacelayer or the determination mustbe made after the protecting
coats are removed. Although the word "plasma membrane" is used for the
external surfaceof a cell, which is responsiblefor its osmotic behavior, much
evidence is accumulating to indicate that this surfacelayer is of molecular

3. thickness. Itis probably not correct to speak of the surfacetension of a cell in the
senseof an interfacial tension between two pure nonmiscableliquids but a
definite tension can be measured, which represents the sum of surfaceand elastic
forces best designated as "tension at the surface." Indeed, thewhole question of
a membrane becomes a matter of definition and all gradations of surfacefilms
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 surfacetension 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)38the
complex situation in regard to the cell becomes obvious. whereP = pressure, T=
tension, and r = radius of the bubble) is determined as the bubble is expanded or
as it is contracted.
Kinetic Method
Just beforethe completion of firstcleavage of an Arbacia egg the two
hlastomeres are connected by a small stalk. If one blastomereis punctured, the
remaining one will dischargeits contents through the stalk due to an excess
internal pressurefromthe tension at the surface. Frommoving pictures, the rate
of dischargecan 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 pressureto be 62 dynes/cm2 and the tension 0.09 dynes/em,
agreeing well with the Harvey (1931)26 and Cole(1932)15figures for thesame
egg.

4.  Building material
Suspension substancethatmakes up the physicalbasis of all living things.
1) Carries on the process of
2) Metabolism
3) Reception of food and oxygen
4) Processes food and oxygen
5) Eliminates wasteproducts
6) MACROMOLECULES/organic compounds
i. Proteins
ii. lipids
iii. carbohydrates
iv. 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
 Sourceof 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

5.  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) Protoplasmbehave both gel and sol…
 Gel: Presentin solution form.
 Sol: Presentin 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 …Performin Amoeba
 CYLOSIS ORSYTOPLASMICSTREAMING :
Movement of cytoplasminside the cell as in Paramecium

6.  (D) SURFACE TENSION :
 The surface molecules like lipids and proteins have less surface
tension.
 The molecules inside the protoplasm have high surface tension.
REFERENCE BOOKS
1. 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 khan
23/10/2014