Fundamentals of Molecular Biology. Part 1: Molecular Cell Biology - A. N. Ogoogurtsov 2011

Molecular Biology. Subject Matter and Core Sections of the Course
Diversity and Universality of Cells

Like ourselves, the individual Cells that make up our body can grow, reproduce, receive signals, respond to stimuli, and carry out an unimaginable variety of Chemical Reactions. These properties define a living Organism (or simply an organism, as we will refer to it hereafter).

Humans, like other Multicellular Organisms, consist of millions and billions of cells, yet There are also organisms consisting of a single Cell, which nevertheless exhibit all the properties characteristic of any other living being without exception. Therefore, it is no exaggeration to state that The Cell is the fundamental unit of life—the "building block" from which the entire diversity of life's "architecture" is constructed.

The beginning of the 21st century coincided with a "boom" in our understanding of the cell, its Organization, and the mechanisms of the processes taking place within it. The Amount of Information regarding cellular components, the structures they form and are built from, and the mechanisms of cellular integration, mutual influence, and interaction is growing exponentially.

Right now, at the dawn of the third millennium, humanity has achieved such a level of knowledge in physics, chemistry, and applied mathematics (computers), and has developed such micro- and nanoscale research techniques for complex biological objects, that it has become possible not only to track intracellular processes at the molecular

level, but also to control the biochemical "production" inside the cell, programming the work of cellular "biological factories" to obtain, on an industrial scale, the products necessary for humanity that cells are capable of synthesizing.

This is why knowledge of the mechanisms of intracellular processes forms The basis of modern biotechnology.

It is worth noting right away that the more we learn about biological processes, the more questions and areas of study arise, and the more tasks and problems await their researchers. For example, how information is transmitted within and between cells, and what the mechanism is by which a cell "decides" how precisely to respond to a particular external (or internal) event.

Molecular cell biology is a complex, integrative science that brings together biochemistry, biophysics, molecular biology, all types of Microscopy, genetics, physiology, computer visualization and modeling, and developmental biology.

Each of these fields is an independent science with its own Methods of theoretical and experimental research, while molecular cell biology integrates their findings, viewing The phenomenon of life itself as its object of study.

Cells possess a tremendous variety of SHAPES AND SIZES. Figure 1 shows micrographs of some cells.

Figure 1 (a) - a human egg cell, approximately 0.2 mm in diameter, surrounded by spermatozoa, from which division and differentiation give rise to the thirty trillion (30x10¹² = 2⁴⁵) cells of The Human Body.

Figure 1 (b) - Lactococcus lactis cells, eubacteria used in The production of cheese varieties such as Roquefort, Brie, and Camembert.

Figure 1 (c) - a colony of Methanosarcina archaebacteria, which obtain energy for survival by converting carbon dioxide and hydrogen into methane.

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Figure 1 - Micrographs of various cells

Figure 1(d) — Blood Cells: smooth, rounded, large, beret-like erythrocytes that transport oxygen; white, fluffy spheres representing leukocytes, which are part of The Immune System; and small, ellipsoidal platelets responsible for blood clotting upon injury.

Figure 1(e) — fossilized dinosaur eggs.

Figure 1(e) - colonies of the unicellular alga Volvox aureus; large spheres consist of individual cells visible in the figure as bright dots, and the large bright patches inside the spheres are daughter cell colonies.

Figure 1 (g) - a single cell—a cerebellar neuron—capable of forming over a hundred thousand contacts with other cells through an extensive dendritic network. The cell is visualized by introducing special fluorescent Proteins into it. The cell body itself is the gray sphere in the lower left corner of the figure.

Figure 1 (h) — a section of the intestinal wall, where cells form Epithelial Tissues. Each of the three finger-like structures shown in the figure consists of a stack of cells. Nutrients are transported from digested food through the intestinal epithelium into the bloodstream, which distributes them throughout the body. New cells are constantly generated at the base of these structures, while old cells are shed from the tips of these "pillars."

Figure 1 (i) - plant cells rigidly fixed in place by a cellulosic plant Skeleton. The space between cells is organized into capillaries for The transport of Water and nutrients.

Cell diversity is immense. Some cells are highly motile and easily change shape, such as amoebas and rotifers. Others are stable and stationary.

Oxygen is lethal to some cells, yet absolutely essential to others.

Most cells in a multicellular organism are interconnected and interdependent. Although some unicellular organisms can live in isolation, others form colonies or live in Symbiosis with Other types of organisms, such as Bacteria that help plants assimilate atmospheric nitrogen or bacteria residing in the human gut that aid in food Digestion.

However, despite all these and other differences, All cells share a similar Structure and carry out many complex processes in virtually the same way.

First of all, depending on whether they possess a Nucleus or not, all cells are divided into prokaryotic (anuclear, or more precisely, pre-nuclear) and eukaryotic.

Prokaryotic Cells consist of a region enclosed by a cell membrane without a distinct nucleus (Figure 2(a)).

Figure 2 - Transmission Cytology/cytology/93.html">ELECTRON MICROGRAPHS OF two cell types: a - Introduction/4.html">Prokaryotic Cell of Escherichia coli, b - Eukaryotic Cell of a WHITE BLOOD CELL

Bacteria are the most numerous organisms. The dry weight of a single Escherichia coli cell, for instance, is 25x10^-14 g (a quarter of a picogram), yet the total weight of all bacteria in the human body ranges from 1 to 1.5 kg. Estimates suggest there are 5x10³⁰ bacteria on Earth, weighing a staggering 10¹² kg (one billion metric tons). Prokaryotic cells have been discovered at a depth of 10 km in the ocean and at an altitude of 12 km in the atmosphere.

The amount of carbon contained in bacteria is comparable to the total carbon content of all plants on Earth.

Eukaryotic cells feature a well-defined structure comprising a Cell Nucleus and Cytoplasm, which consists of the Cytosol and cytoplasmic Organelles. Eukaryotes include all members of the PLANT AND ANIMAL kingdoms, Fungi (which exist in both multicellular forms, such as Molds, and unicellular forms, such as Yeasts), and Protozoans (from proto, primitive, and zoan, animals), which are exclusively unicellular.

It is currently believed that all cells descended from a common ancestor, given that their fundamental structures, key molecules, and primary metabolic processes are nearly identical. Detailed DNA analysis of various prokaryotic organisms has revealed two distinct types: true bacteria (or eubacteria) and archaebacteria. Assuming that organisms with more similar genes diverged more recently in their evolutionary history than those with significant genetic differences, researchers reconstructed the evolutionary Phylogenetic Tree shown in Figure 3.

Figure 3 - Evolutionary tree of species: - common ancestor, - ancestor of archaebacteria and eukaryotes

According to this evolutionary tree, archaebacteria and eukaryotes branched off from true bacteria before diverging from one another.

Many archaebacteria inhabit unusual, often extreme environments, offering a glimpse into the primordial conditions under which life first originated.

For example, halophiles ("salt-lovers") require high salt concentrations in their environment, while thermoacidophiles ("heat- and acid-lovers") thrive in hot (80°C) sulfur springs where the pH is typically below 2.

Other archaebacteria inhabit oxygen-free environments, synthesizing methane by combining water and CO₂.