Biophysics of the Cell PDF

Summary

This document is a set of lecture notes on the biophysics of the cell. It covers various topics including cell transport mechanisms, resting potentials, and active transport, offering an overview of the subject for students. It provides a summary of concepts, including diagrams and equations and lists references to other readings and resources.

Full Transcript

Foreword  In the course of three months - our staff will guide you through the secrets of Me- - dical Biophysics Both lectures, and practicals are obligatory for students.  You will attend Lectures and Practicals according to timetable (your questions e.g. how to g...

Foreword  In the course of three months - our staff will guide you through the secrets of Me- - dical Biophysics Both lectures, and practicals are obligatory for students.  You will attend Lectures and Practicals according to timetable (your questions e.g. how to get credit, substitution in the case of illness, etc. are discussed with teachers during Practical sessions ) For Instructions to organization of study and details ask following teachers: Prof. Jakuš - head, Dr. Simera-vicehead Content of study Covers following topics.: Biophysics of Cell, Transport membrane mechanisms, Resting and Action potentials , Muscle contraction, Synapse, Basics of respiration, Heart and circulatory sys- ems, Senses, Hearing, Vision. Changes in body due to action of mechanical an electromagnetic influences, Effects of Sound, Infrared and Ultravio- let radiations, Radioactivity, Diagnostic methods in human medicine: X-ray, Utrasound, Computer tomography, Magnetic tomography, etc. Therapy in human medicine, Biocybernetics, Modern Machines, Nanotechnology and many others. For more details look for my Lectures being available to see and download from our faculty homepage: www.jfmed.uniba.sk/index.php?id=3649 Study Literature - Source 1.Lectures – the content results from Professors experience, also from Textbook of Medical Biophysics (in Slovak ), also from Ganong´s Textbook of Physiology Content of some Lectures and Practicals ,Programme of Lectures, Requirements and condition how to obtain credits, points etc. are available on web.page: www.jfmed.uniba.sk/index.php?id=3649 2.Textbooks- Nave & Nave: Physics for Health Sciences,1985, Ronto,Tarjan et al.:An introduction to Biophysics with Medical Orientation, 1999, 3. Booklet- Kukurova et al.:Biophysical Elixir, 1991 4. Worksheet for Practicals Jakus,Poliacek, Simera :Practical Tasks in Medical Biophysics ,2013 , it contains theory and personal protocol to particular tasks. Medical Biophysics. Biophysics of a Cell. Transport membrane mechanisms. Resting membrane potential. LECTURE 1 Ján Jakuš (www.jfmed.uniba.sk/index.php?id=3649) Martin 2014 Medical Biophysics is an interdisciplinary subject of medical scien- ces,explaining basic problems of a human body at a level of atoms, molecules, cells, tissues, and organs answers the physical problems that appear in biology, chemistry, anatomy, physiology... explains effects of radiation, giving rules and recommendations for their use and safety explains and creates new methods and devices for diagnosis and treatment of human diseases Medical Biophysics - kind of Medicine Science, a part of Biophysics HUMAN CELL Definition: Cell is a basic anatomical and functional unit of the body with total number of 60.000 bilions and size from 4-120 µm (10-6 m). Number of cells composes tissues (206 bones ,600 muscles, thousands of nerves ), number of tissues builds organs (heart, lungs, kidney.. ) Typical signs of living cell: own meta- bolism, excitability, reproduction Composition: Cytoskeleton -surface membrane,cytoplasm, organelles (for details see our videos at Practical Sessions also look a book of Biology) SURFACE MEMBRANE  Surface Membrane of RBC Surface Membrane (SM) Intracellular SM- covers subcellular structures (e.g.Nucleus, Golgi complex, Mitochondria) Plasmatic SM - covers the surface of each cell Functions: semipermeability, division, protec- tion, integrative roles, transport of ions, source of enzymes, storage of electric charges, etc. Composition: SM is Phospholipid bilayer- 45% Hydrophilic heads (consisting of phosphates- soluble in water) Hydrophobic tails (consisiting of hydrocarbon fatty acids-insoluble in water- 45%). Proteins bilayer (peripheral, integral) - 50% , + Sugar + Cholesterol (5%) Heads are (+) electrically charged and directed towards the membrane exterior, tails are charged negatively (–), being oriented to membrane interior Transport Membrane Mechanisms are responsible for movement of water and solutes across the cell membrane are of vital importance for cell metabo- lism, for production of cell electricity i.e. (resting and action membrane potentials) Types: PASSIVE - it does not need deli- very of a free energy. (Simple and Facilita- ted Diffusion, Osmosis, Filtration). ACTIVE - free energy from ATP is needed and must be delivered (Na-Kpump, Ca-pump, H-pump, exo/ endo-cytosis, and phagocytosis) Simple Diffusion through cell membrane Simple Diffusion is a kind of passive membrane transport of H20, solutes, or gases (O2, CO2) from the space with a higher concentration towards the space with lower one (along the concentration gra- dient), untill the equilibrium is established. Total volume of solution does not change in both of spaces. Rate of diffusion:Fick Law: J = - d. conc.grad. [d- koeficient of diffusion] Generally: diffusion depends - linearly on a conc. gradient, solubility of a matter, and on ambient temperature Nonlinearly depends on a size of particles Types of diffusion: Simple, Facilitated, Throu- gh the protein channels Scheme of Facilitated Diffusion Facilitated Diffusion is a passive transport mechanism of bigger molecules (e.g.aminoacids),along a concentration gradient, when substance binds to a protein carrier the carrier is protein placed within the membrane and undergoes a process of conformation (is a change of its chemistry) after binding of molecule and conformation, the carrier shifts (turns around ) and finally releases substance on an opposite site of a cell membrane Diffusion through the protein (ion selective) channels is a passive transport of ions Na+, K+, Ca2+, Cl- ,or low molecular soluble sub- stances through the protein channels within the membrane, along the concen- tration gradient Protein channels are :1.“voltage“gated - they are open or closed (gating) due to a membrane electricity,or 2.„ligand“gated- when e.g. a hormone binds to a channel, thus opening it. „Voltage“ and „ligand“ gated protein (ion selective) channels Filtration is a passive transport of water and small particles from a space with higher hyd- rostatic pressure to a space with lower one the power that drives Filtration is Pressure gradient of a hydrostatic pressure (not a concentration gradient ! ) examples: filtration and resorption in capillary loop or in kidneys Osmosis is kind of passive transport through the semipermeable cell membrane, when only water moves from a space with lower concentration (lower osmotic pressure) to a space with higher concentration (higher osmotic pressure), till to equilibrium.Total volume of solution in both compartments will change. Simply –water wants to dilute more concentrated solution (Van Hoff´s Law) normal osmolarity 300 mOsm/l- isotonic solution with blood plasma (e.g. 0.9 % NaCl, or 5% of glucose) Below 0.9%- hypotonic solution Above 0.9% - hypertonic solution example: Osmotic fragility of RBC ( see practicals ) OSMOSIS – scheme Changes in size of RBC due to osmosis (HAEMOLYSIS) ACTIVE MEMBRANE TRANSPORTS  transport of molecules among cells against the concentration, or electric gradients, a delivery of free energy from ATP is crucial. Classification: Primary active transport through the selectíve ions channels. Pumps : Na +- K+ pump (in all cells), Ca 2+- pump (in muscle cells), H+- proton pump (in cells of stomach producing HCl) Secondary active transport when a substance (e.g. glucose) binds on ion (Na+), then this complex (Na+ glucose) is carried through the membrane actively (the glucose-Na+ contransport), exo-/endo, phagocytosis Na+-K+ pump (Na+- K+ ATPase) Na+- K+ pump – scheme Na+-K+ pump (Na+- K+- ATP-ase) - It is an enzyme, placed within the cell membrane (number =106 molecules within a membrane of one neuron ) - it carries 3 ions of Na+ from inside to outside, and at the same time, 2 K+ from outside to inside of the cell - It can exchange max. 200 Na + and 133 K+ / sec. (maximal capacity of pump) - It requires delivery of free energy (from ATP) - It is important for renewal of electric charges on body cells Exocytosis, Endocytosis (Phagocytosis) ACTIVE membrane transports.: Exocytosis and Endocytosis.  Exocytosis - “cell vomiting“ is a release of larger molecules by the protrusion of a cellular membrane, under delivery of energy and Ca2+ ions Endocytosis –“cell eating“ is an uptake of molecules by a cellular membrane, e.g. ingestion of bacteria by leukocytes (phagocytosis). It needs a delivery of energy, too. Resting membrane potential (RMP) It is an electric potential difference measured between (+) charged cell exterior and (–) charged cell interior. Its value is negative and equals to a Sum of Equilibrium Potentials of all 3 ions (K+, Na+, Cl-). is a result of membrane semipermeability i.e. different leakage of cell membrane for 3 main ions (K+, Na+, Cl-). permeability of cell membrane for ions at rest is: K+ : Na+ : Cl- = 1 : 0.04 : 0.45 K+ : Na+ : Cl- = 100 : 4 : 45 (%) Value of RMP for nerve cells is: -70 mV, sceletal muscle:– 90 mV, heart muscle:- 80mV, smooth muscle: -50 mV (non-stabile) Equilibrium Potential (EP) is a value of electrical voltage that just stops the passive diffusion of ions (K+ ,Na+ ,Cl -) along their concentration gradients Cell Inside (-) charged Cell Outside(+) cha. (because PROTEINS inside) (because Na + outside) Concentration and electrical gradients of K+, Na+, Cl- ions OUTSIDE INSIDE Nernst formula Each ion has its own Equilibrium Potential (mV) which can be counted: (Nernst counted it only for K+ ) Goldman´s Equation Sumation of all Equilibrium potentials (for K, Na, Cl ) results in a real value of Resting Membrane Potential ( e.g. V m = -70 mV for neuronal cells) Goldmann counted it for all 3 ions (their concentrations outside and inside) + the permeabilities of membrane for 3 ions. for comming and attention

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