Variation

The cell membrane has different lipid and protein compositions in distinct types of cells and may have therefore specific names for certain cell types:

• Sarcolemma in myocytes

• Oolemma in oocytes

• Axolemma in neuronal processes - axons

• Historically, the plasma membrane was also referred to as the plasmalemma

Permeability

The permeability of a membrane is the rate of passive diffusion of molecules through the membrane. These molecules are known as permeant molecules. Permeability depends mainly on the electric charge and polarity of the molecule and to a lesser extent the molar mass of the molecule. Due to the cell membrane's hydrophobic nature, small electrically neutral molecules pass through the membrane easier than charged, large ones. The inability of charged molecules to pass through the cell membrane results in pH partition of substances throughout the fluid compartments of the body.

Problems:

1. Calculate the time of sedentary life and the frequency of hoppings from one membrane layer to another one of the lipids of sarcoplasmic reticulum membrane if the coefficient of lateral diffusion is D=45 µm²/sec and the area of one phospholipid molecule is А=1,9 nm² .

2. Calculate the root mean square displacement of protein molecules in 2 sec if the coefficient of lateral diffusion for them is approximately 10-12 mm₂/sec.

3. How will the electrical (specific) capacity of membrane change at its transition from liquid-crystal state to the gel if it is known that in liquid-crystal state the thickness of hydrophobic layer is 3,9 nm and in the state of gel it is 4,7 nm. Permittivity of lipids  2.

4. Calculate the permittivity of membrane lipids if the thickness of membrane is d=10 nm, specific capacitance is С=1,7 mF/m².

5. At the phasic transition of membrane phospholipids from liquid-crystal state to the gel the thickness of bilayer changes. How will the capacitance of membrane change? How will the electrical field strength change in membrane?

Joint work of the student with a teacher - 5 minutes

After performance of the practical part of work a teacher checks the correctness and sequence of problems solving by students. Then a teacher conducts the interrogation of students with the analysis of the theme. Finds out types and functions of biological membranes.

Control of the final level of knowledge - 15 minutes

A teacher checks the results of solved problems. Students pass the tests for the control of knowledge. The teacher evaluates the work of students according to the competencies above.

Literature

Basic:

1. Remizov А.N., Maxina А.G., Potapenko А.Y. Medical and biological physics: textbook – 9^th edition,

reimpression – Moscow: Дрофа, 2010. – 558 pages.: illustrated.

2. Remizov А.N., Maxina А.G., Potapenko А.Y. Collection of problems in medical and biological

physics: study guide – 4^th edition, reimpression – Moscow: Дрофа, 2010. – 189 pages.

3. Antonov V.F. Physics and biophysics: textbook – Moscow: ГОЭТАР-Медиа, 2008. – 480 pages.

4. Antonov V.F., Chernysh А.М., Kozlova Y.K., Korzhuyev А.V. Practicum: study guide. – 3^rd edition,

revised and enlarged – Moscow: ГОЭТАР-Медиа, 2008. – 336 pages.

5. Samoilov V.О. Medical biophysics. St. Petersburg: СпецЛит, 2007. – 496 pages.

6. Timanyuk V.A., Zhivotova Y.N. Biophysics. Moscow, 2004 – 703 pages.