Скажите, о чем, судя по заголовку, может идти речь в данном тексте? Читая текст, найдите подтверждение вашему предположению.

Определите, какой характер носит текст; представляет ли он собой описание, объяснение, повествование, рассуждение.

3) Найдите в тексте следующие слова и словосочетания, дайте их русские эквиваленты и запомните их:

within a relatively narrow range, activity of hydrogen ions, at the required level, systems obeying the equation, to prevent dissociation, enzyme, to proceed, medium, to affect the properties, solvent, solute particles, the primary source of energy, solar radiation, to store, the bonds of various compounds, to maintain, to derive from, in particular, to couple, the most common mediator, markedly, to alter, to inhibit.

4) Найдите в 1 абзаце предложение с Absolute Participle Construction и переведите его.

5) Скажите, в связи с чем употреблены следующие словосочетания:

1) osmotic pressure and ionic strength

2) energy requirements.

6) Объясните значения слов exergonicиendergonic.

7) Ответьте на вопрос: “What does the rate of biochemical reactions depend on?”

TEXT 3. THE CELL

The cell is the principal unit of living objects. The term living objects includes generally all objects that are capable of metabolism and reproduction. (Thus, viruses cannot be classified as living objects as they alone, without participation of living cells, are not capable of reproduction).

To support these two basic functions, certain structures designated as cell organelles were formed in the cell during evolution. They maintain a coordinated and regulated performance of the partial mechanisms (reaction processes) required for the perpetuation of basic life functions.

The following cell organelles are essential for the existence of living objects: nuclei, mitochondria, endoplasmic reticulum, ribosomes, lysosomes, and microbodies. Cell membranes, involved not only in the separation of the living system (cell) from the environment but also forming defined spaces inside the cell (functional compartments), are the main supporting structure of all these organelles and participate in the formation and function of most of them. They often represent up to 80% of the cell mass. The structureless, colloid system filling the cell space is designated as cytosol.

Occasionally, the cell possesses morphologically distinct granules which mostly contain products of cell activity, either as reserve compounds (glycogen, lipid drops) or as products to be transported out of the cell (proenzymes).

Independently living cells (unicellular organisms) usually contain all the above structures and, in addition, they possess a cell wall and possibly some contractile structures (cilia and flagella).

A differentiation of functions based on differentiation of structures is found in multicellular organisms. Thus, in differentiated cells of higher organisms a different quantitative ratio of the cell organelles (occasionally with differences in their fine structure, e.g., in the number of cristae in mitochondria of liver cells and cardiac muscle cells), as well as a different distribution inside the cell (e.g., accumulation of mitochondria in the cell, where endergonic processes take place) are observed.

The outer part of the plasma membrane binds complex chemical structures (proteins, glycoproteins), also designated as glycocalyx. They serve to discriminate between the species’ own cells and those of other species. If these structures enter parenterally higher organisms they behave as antigens and induce the formation of different specific antibodies in specially differentiated cells.

Cells, even in an organ, usually are not in the closest possible contact; this is due to negative charges of surface-localized cell structures that arc mutually repelled. This results in narrow spaces between cells, the sum of which in the whole organ or organism is designated as extracellular space (ECS). Similarly, the sum of all compartments inside the cell (e.g. the space of the nucleus, mitochondria, etc.) is called intracellular space (ICS).

From the functional point of view, no living object (not even cells and their organelles) is unlimited with respect to the length of its existence.

Starting at its origin from another cell, every all undergoes the so-called life cycle, at the end of which either it divides to give rise to a new individual or it dies. The duration of this cycle is species-specific and ranges, according to the present knowledge, from hours to tens of years. During the life cycle of the cell, different phases, lasting for different time intervals according to the cell type and characterized by a limited course of very specific metabolic processes, exist. These phases are designated as G₁, S, G₂ etc. Cells that do not divide any longer and die after a certain time (e.g., cells of the gray matter) are permanently in the G_i phase. The so-called differentiated cells belong to this group.

Covering of a portion of DNA molecules in the nucleus by histones was previously considered as the molecular basis of differentiation. This view became untenable after it has been shown that histones play a determining role in the formation of the supercoil in which they become a permanent part of deoxyribonucleoprotein filaments and arc metabolically restored only during DNA replication.

According to present views, the process of cell differentiation is a permanent, largely irreversible, functional blocking of genes. This process is assumed to be directed by products of activity of "architectural genes" and "temporal genes".

Notes on the text:

perpetuation – сохранение

unicellular – одноклеточный

contractile – сжимающийся, сокращающийся

cilia – реснички

flagella – жгутики

differentiated – видоизмененный

cardiac muscle – сердечная мышца

with respect to – относительно

untenable – несостоятельный

Задания к тексту:

1. Прочтите текст. Выразите свое согласие или несогласие с данными ниже утверждениями, основываясь на информации, полученной из текста. Используйте выражения that’s right, that’s wrong.

1. The cell is the principal unit of unanimate objects.

2. Cell organelles maintain a coordinated and regulated performance of the partial mechanisms.

3. Cell membranes are the main supporting structure of all the organelles.

4. Cell membranes participate in the formation of the unanimate objects.

5. A differentiation of functions based on differentiation of structures is found in multicellular organisms.

6. Cells usually are in the closest possible contact.

7. Negative changes of surface–localized cell structures are naturally attracted.

8. The sum of all compartments inside the cell is called intracellular space.

9. Every living object is unlimited with respect to the length of its existence.

10. The process of cell differentiation is not a permanent, functional blocking of genes.