Biophysics

1. Biophysics Instructor: Dr. Amjad Ali Office: 2nd floor Email: amjad_uni@yahoo.com

2. Course Plan/Exams • Assignments/Presntation: 10 marks • Sessionals: 20+20=40 marks • Terminal: 50 marks

3. Course Contents • Introduction to biophysics • Basic concepts Osmosis, osmotic pressure, surface tension, diffusion, viscosity, thermal conduction, forces and energy • Molecular structure of biological systems at a glance • Energetics and Dynamics of Biological Systems Description of ATP, cell as an accumulator of electrochemical energy, energy consumption, respiration, mechanism of molecular energy transfer, thermodynamics and thermal molecular movement, mechanism of body temperature regulation, photosynthesis as a process of energy transfer and transformation, dynamics of blood flow, control of movement

4. Course Contents • Biological Membranes Membrane chemistry and structure, membrane physics, surface and interfacial tensions, diffusion and mobility of ions, electrostatic and mechanical properties of membranes • Mechanical Properties of Biological Materials fluid flow, blood circulation, muscle contraction, swimming, flying etc • Electric fields in cells and organisms Nerve Signals, nerve impulses, nervous system • Physical factors of the environment Temperature, pressure, mechanical oscillations (vibrations, sound, hearing and hearing aids, effect of ultrasound), electromagnetic fields in the environment, ionizing radiations

5. ebooks • Textbook: Biophysics by P. S. Mishra, 2010 • Reference books: • Molecular And Cellular Biophysics by Meyer B. Jackson, Cambridge University Press, 2006 • Biophysics by Roland Glaser, Springer, 2001 • An Introduction to Med. Biophysics by Parveen Parkash

6. What is “Biophysics” Biophysics is a specialized sub area of biology It is the science of physical principles of life itself and of biological systems. Biophysics is an interdisciplinary science that explains the laws and principles of physics which govern various biological processes. Biophysics spans all levels of biological organization from molecular scale to whole organism

7. What is biophysics? Let’s see what a book published in 1983 says…

9. Biological Functions • Biological activities happening in different organs of living body like kidney, liver, heart, lungs as well as those in intra-cellular and extra-cellular biological fluid are governed by fundamental laws of physics namely • Diffusion • Osmosis • Viscosity • Surface Tension

10. Osmosis • The spontaneous passage of solvent from a solution of lower concentration towards a solution of higher concentration when the two are separated by a semi permeable membrane is called osmosis • Osmosis is a special case of diffusion. It involves the diffusion of water through the semi permeable membrane to equalise the concentration of solutions on its two sides

11. Turgid plant wilting The cells have taken up water by osmosis; the cells are turgid and the tissue is firm These cells are short of water; the tissue is limp and the plant is wilting

12. Growth in a shoot tip cell division continues these cells will divide vacuoles forming cells absorb water by osmosis and expand

13. Effect of different solutions on blood cells

14. Osmosis • Osmosis releases energy, and can be made to do work, as when a growing tree root splits a stone. • Diffusion and Osmosis are both types ofPASSIVE TRANSPORT- that is, no energy is required for the molecules to move into or out of the cell. • Osmosis takes place due to difference in chemical potentials of water on two sides of membranes which leads to pressure gradient • Solute decreases chemical potential of water. Water tends to flow from where its chemical potential is higher to where it is lower • Reduced chemical potential causes reduced vapor pressure, lower freezing point and higher boiling point of the solution as compared with pure water

15. Osmotic Pressure • Osmosis may be opposed by increasing the pressure in the region of high solute concentration (hypertonic solution) with respect to that in the low solute concentration region (hypotonic solution). • The hydrostatic pressure which just stops osmosis is the osmotic pressure • The force per unit area, or pressure, required to prevent the passage of water through a selectively-permeable membrane and into a solution of greater concentration is equivalent to the osmotic pressure of the solution, or turgor. • Osmotic pressure is a colligative property, meaning that the property depends on the concentration of the solute but not on its identity.

16. Viscosity Viscosity is an internal property of a fluid that offers resistance to flow. • For example, pushing a spoon with a small force moves it easily through a bowl of water, but the same force moves mashed potatoes very slowly.

17. Some Examples • oil (most kinds): 920 kg/m3 • shampoo: 1000 kg/m3 • water: 1000 kg/m3 • glass marble: 2800 kg/m3 • steel ball bearing: 7800 kg/m3 http://www.spacegrant.hawaii.edu/class_acts/ViscosityTe.html

18. How to Measure it? • The measurement involves determining the velocity of the falling sphere. This is accomplished by dropping each sphere through a measured distance of fluid and measuring how long it takes to traverse the distance. Thus, you know distance and time, so you also know velocity, which is distance/time. • The formula is simply amounts to multiplying some numbers and then dividing by some others: • delta p = difference in density between the sphere and the liquid • g = acceleration of gravity • a = radius of sphere • v = velocity = d/t = (distance sphere falls)/(time of it takes to fall)

19. Surface Tension • Surface tension is measured as the energy required to increase the surface area of a liquid by a unit of area. The surface tension of a liquid results from an imbalance of intermolecular attractive forces, the cohesive forces between molecules: • A molecule in the bulk liquid experiences cohesive forces with other molecules in all directions. • A molecule at the surface of a liquid experiences only net inward cohesive forces. • A microscopic view of water illustrates the difference between molecules at the surface of a liquid and water molecules within a liquid

20. The unbalanced attraction of molecules at the surface of a liquid tends to pull the molecules back into the bulk liquid leaving the minimum number of molecules on the surface. It required energy to increase the surface area of a liquid because a larger surface area contains more molecules in the unbalanced situation. The molecules at the surface of this sample of liquid water are not surrounded by other water molecules. The molecules inside the sample are surrounded by other molecules.

21. Cohesive And Adhesive Forces • When a liquid comes into contact with a surface (such as the walls of a graduated cylinder or a tabletop), both cohesive and adhesive forces will act on it. • These forces govern the shape which the liquid takes on. • Due to the effects of adhesive forces, liquid on a surface can spread out to form a thin, relatively uniform film over the surface, a process known as wetting (wetting agents). Alternatively, in the presence of strong cohesive forces, the liquid can divide into a number of small, roughly spherical beads which stand on the surface, maintaining minimal contact with the surface. 

22. Cohesive Forces Cohesive forces are the inter-molecular forces (such as those from hydrogen bonding and Van der Waals forces) which cause a tendency in liquids to resist separation. These attractive forces exist between molecules of the same substance. For instance, rain falls in droplets, rather than a fine mist, because water has strong cohesion which pulls its molecules tightly together, forming droplets. This force tends to unite molecules of a liquid, gathering them into relatively large clusters due to the molecules' dislike for its surrounding. Adhesive Forces Adhesive forces are the attractive forces between unlike molecules. They are caused by forces acting between two substances, such as mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges). In the case of a liquid wetting agent, adhesion causes the liquid to cling to the surface on which it rests. When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the glasses surface. This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.

23. Effects of Cohesive and Adhesive Forces • When liquid is placed on a smooth surface, the relative strengths of the cohesive and adhesive forces acting on that liquid determine the shape it will take (and whether or not it will wet the surface). • If the adhesive forces between a liquid and a surface are stronger, they will pull the liquid down, causing it to wet the surface. However, if they cohesive forces among the liquid itself are stronger, they will resist such adhesion and cause the liquid to retain a spherical shape and bead the surface.

24. Meniscus is the curvature of a liquid's surface within a container such as a graduated cylinder. When liquid water is confined in a tube, its surface (meniscus) has a concave shape because water wets the surface and creeps up the side. Mercury does not wet glass - the cohesive forces within the drops are stronger than the adhesive forces between the drops and glass. When liquid mercury is confined in a tube, its surface (meniscus) has a convex shape because the cohesive forces in liquid mercury tend to draw it into a drop. Reading about http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolecular_Forces/Cohesive_And_Adhesive_Forces