Fill in the gaps with the following words. spontaneously / boundaries / tends / aqueous / distributed / constituents / residues

spontaneously / boundaries / tends / aqueous / distributed / constituents / residues

1. Unequal crossing over between homologous chromosomes ______________ to promote the duplication of material rather than its reduction

2. Fungi are virtually the only organisms capable of breaking down lignin, one of the major ______________ of wood.

3. Water in an animal’s body is ______________ between the intracellular and extracellular compartments.

4. As in mitosis, however, the ______________ between phases are somewhat artificial, and the phases, in fact, grade into one another.

5. Calmodulin is a protein containing 148 amino acid ______________ that mediates Ca⁺⁺ function.

6. The mixture of these substances and water is called an ______________ solution.

7. The covalent bonds within a water molecule sometimes break ______________.

Translate into Russian

1. What is measured is the average frequency with which the mutational event takes place per cell division. What is estimated is the frequency of mutation in an infinite number of cell divisions.

2. Thus far we have considered only one pair of homologous chromosomes and the alleles they carry.

3. What is commonly found, however, is partial linkage or restricted recombination.

4. Which of these classes a given mutant will occupy depends upon conditions.

5. That the large DNA molecule is genetic material is demonstrated by the fact that at least some genetic markers pass with it from cycle to cycle.

6. Just how this recombination takes place is yet to be discovered.

7. To what extent the mechanism of recombination of linked genes is the same in all systems is a problem which has not yet been fully clarified.

8. That these patterns can be critical for the survival of all but the most robust of algae is illustrated by the findings of Fogg.

9. What is so remarkable about proteins is that they are not only the main building material of the cell, but are also the regulators of all the activities carried out by the living machine.

10. It is interesting to note that although insulin is one of the smallest proteins we know, it is not the simplest in structure since it is composed of two polypeptides.

11. The general procedure we have just outlined was employed by Summer, who in 1926 was the first to crystallize an enzyme, urease.

12. What this alternate swelling and contraction of mitochondria has to do with the functioning of this organelle is not certain.

13. What happens to the messenger RNA and to the transfer RNA is not known for certain.

14. That this electron transport fragment can also act as an anion transport machine is possibility.

15. What we envisage is a process whereby a certain cellular organelle develops by selecting the proper macromolecule from its environment.

16. What we have said about animal viruses holds reasonably well for bacterial viruses.

UNIT 21 Mechanical Properties of Biological Membranes

The mechanical properties of the biological membrane are very important for understanding a number of cell physiological functions such as cell movement, cell division, vesiculation, and membrane fusion. In the same way, the mechanical properties of tissues, as well as the streaming properties of the blood are controlled by the viscoelastic properties of cell membranes.

It must be stressed that physical parameters, for example viscosity, elasticity, strain etc. are defined for homogeneous phases and materials. Hence, they are not proper parameters of highly organized supramolecular structures like biological membranes. In some cases it may be convenient to use these parameters, but then they must be considered as effective parameters, which we explained in the introduction to Section 2, and which we have already used in many other cases.

The effective membrane viscosity, for example, is a parameter which was measured using specific effects, as for example the rotation or translocation of a spin-marker in the membrane. This is possible using special fluorescence methods or electron spin resonance techniques (ESR). Considering the membrane as a homogeneous phase, and the marker molecule as a macroscopic body with a particular shape, one can calculate the viscosity, applying usual phenomenological equations for movement. Knowing the method of measurement, as well as the applied equations, this measurement can be reproduced any time, and the measured parameter is exactly denned. The problem which arises from using an equation, which is not adequate for the movement of a molecule in a heterogeneous phase, is not relevant because it is included in the definition. On the other hand, however, it means that by measuring these effective viscosities by different methods, one gets different parameters but not a viscosity according to the original physical definition. This is the difference between molecular, and the usual macroscopic kinds of measurement, where viscosity is independent of the measurement method.

Applying different markers, the parameters measured in this way depend on the kind of marker molecule (protein, lipid), and on the regions of the molecule where the marker was bound; for example, different locations in the fatty acid of a lipid. These differences indicate the inhomogeneity in the plane of the membrane, as well as the anisotropy of the mechanical properties of the biological membrane in general.

Define the following words using a dictionary

Vesiculation, fusion, viscosity, elasticity, strain, inhomogeneity

Complete the sentences

1. The mechanical properties of the biological membrane…
2. In the same way, the mechanical properties of tissues,…
3. It must be stressed that physical parameters,…
4. In some cases it may be convenient…
5. Considering the membrane as a homogeneous phase, and the marker molecule as a macroscopic body with a particular shape,…
6. The problem which arises from using an equation,…
7. Applying different markers, the parameters measured in this way…