Probably no more frequently studied in the school curriculum of biology concepts than a cell.With her friends in the 5th grade at the natural history, then 6 considering the variety and how proliferating cells, ways of dividing it.In the 7th and 8th grades, she studied in terms of plant, animal and human origin.Grade 9 includes consideration of internal processes taking place in it, that is, the molecular structure.In 10 and 11 it is cell theory, the discovery and evolution.
program is built so because these small structures, "the building blocks of life," are the most important elements of any organism.All vital functions, processes, growth and development, the establishment - everything connected with life, carried out by them and in them.Therefore, in this article we look at the highlights of reproduction, cell development and the history of their discovery.
Opening cells
These structural particles are extremely small in size.Therefore, for their discovery it took a long time and the creation of a specific technology.For the first time the cellular structure of living plant tissue saw Robert Hooke.That was in 1665.In order to consider them, he invented the world's first microscope.This product bears little resemblance to modern magnifying devices.Rather, it was like a few arranged between a loop, giving the increase.
Using this device, the scientist considered the cut balsa wood.What he saw was the beginning of the development of a number of related sciences and biology in general.A plurality of closely contiguous cells of approximately equal size and shape.Hooke called them cella, which means "cell".
subsequently made a number of discoveries that have allowed knowledge to grow, accumulate and lead to more science involved in their learning.
- 1675 - scientist Malpighi studied a variety of cell shape and came to the conclusion that it is more often rounded or oval bubbles filled life juice.
- 1682 - N. Grew confirmed the findings of Malpighi, and also studied the structure of the cell membrane.
- 1674 - Antoni van Leeuwenhoek opened bacterial cells and blood and sperm structure.
- 1802-1809 biennium.- Sh-Brissot Mirbeau and JB Lamarck tissues and suggest the existence of similarity between animal and plant cells.
- 1825 - reveals the core of the Purkinje cells in the genital birds.
- 1831-1833 biennium.- Robert Brown reveals the presence of the nucleus in plant cells and introduces the concept of the significance of the internal composition of the cell wall and not, as previously thought.
- 1839 - Theodor Schwann concludes that all living organisms are composed of cells, as well as the similarities between a past (future cell theory).
- 1874-1875 biennium.- Chistyakov Strasburger and open methods of reproduction of cells - mitosis, meiosis.
All further discoveries in the structure of cells, their functions, and the role of diversity in the life of organisms were made quickly enough due to the intensive development of a special magnifying and lighting equipment.
cell reproduction
Each cell in a lifetime does a cell cycle - the time of her life from the moment of birth to death (or division).Moreover, it does not matter, it is an animal or plant.The life cycle is the same for all of them, and often, at the end of its cells multiply by dividing.
Of course, not all organisms, this process is identical.For eukaryotic and prokaryotic it is fundamentally different, there are also some differences in the breeding of plant and animal cells.
As proliferating cells?There are several basic ways.
- mitosis.
- meiosis.
- amitosis.
Each of them represents a number of processes, phases.And all of these processes are specific to multicellular organisms, both plant and animal origin.In unicellular reproduction occurs by simply dividing in two.That is how cell proliferation is not the same.There is even such a thing as cell suicide.This self-destruction of cells in place of the processes of fission.
As proliferating cells, such as bacteria, blue-green algae, some of the simplest?Asexually, the easiest way: the contents of their cells doubled in the cell wall is formed from lateral or longitudinal constriction and one cell is divided into two completely new, identical maternal organism.
This process is called direct cell division.Multiply them and single-celled bacteria, but it has no relation to the mitotic or meiotic processes to.They occur only in the body of multicellular organisms.
Mitosis
In multicellular beings contains billions of cells.And each of them seeks to complete its life cycle, it is leaving offspring, and died.Cells reproduce by division, but this process, not all of them equal.
somatic structures (these include all cells of the body except sex) their way to breeding or choose mitosis amitosis.This is very interesting, capacious and complex process in which one parent diploid cell (ie, a double set of chromosomes) formed two identical to her daughter with the same diploid structure.
whole process includes two main points:
- karyokinesis - nuclear fission and its entire contents.
- Cytokinesis - the division of the protoplasm (cytoplasm and all cellular organelles).
these processes advance simultaneously, leading to the formation of high-grade motherboard reduced size copies.
Mitosis consists of four phases (prophase, metaphase, anaphase, telophase) and the state before division - interphase.Consider every detail.
Interphase
growth and reproduction of cells is carried out throughout the life of the organism.However, not all cells have the same period of existence.Some of them die within two to three days (blood cells), some are still operating lifetime (nervous).
But in the life of every cell most of the time saved is a condition called interphase.This preparation for the division of mature cell formed which takes up 90% of the entire process.
biological significance of this step in the accumulation of nutrients, RNA and protein synthesis of DNA molecules.After all, after dividing into each daughter cell must get exactly the number of organelles, substances and genetic material, as it was in the mother.For this to happen the doubling of all available structures including DNA strands.
Overall, the interphase takes place in three stages:
- presynthetic;
- synthetic;
- postsynthetic.
Result: accumulation of nutrients, energy and DNA molecules for further fission processes.Therefore, this stage - is just the beginning of how the proliferating cells in the future.
Prophase
At this stage, the following key processes:
- dissolved nuclear membrane;
- disappear (dissolve) the nucleoli;
- chromosomes become visible under the microscope due to twisting (helix) structure;
- centrioles to the poles of the cells differ, pulling and forming division spindle.
At this stage, breeding animal cells does not differ from that of all others.
Metaphase
This phase is rather short, about 10 minutes.Its basis is that the chromatids line up along the equator of the cell.Thread spindle one end cling centriole at the poles of the cell, and the other for the centromere of each chromatid.Between genetic structure is almost not related so easily ready for disconnection.
Anaphase
The shortest stage of the entire mitotic cycle.The duration of about 3 minutes.During this period, each chromatid goes to his pole cells and currently completes the missing half, turning in the normal structure of chromosomes.
However, this education requires a special enzyme - telomerase.It passed its accumulation in the interphase.
Telophase
Each cell pole appears complete its genetic material which is worn in the nuclear envelope, forming the core.There are nucleoli.The whole process takes about 30 minutes.That is quite a long time.This is because the formation of nucleolar and nuclear membrane requires high energy costs and the availability of building materials - nutrients (proteins, carbohydrates, enzymes, fats, amino acids).
Cytokinesis
This process completes the entire mitotic cycle.The protoplasm is divided with organelles strictly in half, and each individual subsidiary receives exactly the same as her sister.Then cells were formed across the constriction protein (actin nature) which compresses structure across and divides it into two equal, but smaller in size compared to the parent cells.
At this stage, there are some differences from animal cells, both plant cell proliferates.The fact that the vegetable protein structures smaller and actin do not.Therefore, the middle is not formed hauling and partition on both sides that lay cellulose.This imparts rigidity plant cell forms a skeleton of the cell wall.
growth and multiplication of cells on the path followed by the usual life cycle: specialization, formation of tissues and then organs active work and division, or death.
sex cells and their reproduction
the question of how a cell reproduces, the answer can be given to the refinement of what it was.After all, we reviewed the processes of mitosis characteristic only of physical structures.Whereas germ cells multiply in a somewhat different way, or rather, meiosis.
This process is the basis for such vital functions in animals as gametogenesis, ie sexual reproduction.The development of germ cells occurs in several stages.Therefore, meiosis - even more complex and capacious division than mitosis.
for plant cell meiosis - sporogenesis basis, that is, the formation of sex cells.The main biological role of meiosis for all organisms is that as a result he produced four haploid (with a half or a single set of chromosomes) germ cells.What for?To at fertilization (merger of male and female sex cells) is restored in the new diploid zygote (embryo future).This gives the genetic diversity of organisms, resulting in a combination of genes, the emergence and consolidation of new features.
structure during meiosis
are two main divisions in meiosis: reducing and equational.Each of them includes all the same phase as that of mitosis: prophase, metaphase, anaphase and telophase.Consider a little more each of them.
reduction division
essence: one diploid cells form two haploid, with a half set of chromosomes.Phases:
- prophase I;
- metaphase I;
- anaphase I;
- telophase I.
on each of the phases are repeated all the same transformation that at appropriate stages in mitosis.However, one difference is still there: in the interphase the doubling of the DNA occurs, it is only divided in half, and all.Therefore, in each daughter cell gets only half of the genetic information.This initial propagation of animal cells and plant relating to sex.
equational division
second meiotic division, resulting in the formation of even two cells from each of the previous one.Now there are four identical haploid analogue, which become germ cells of animals or plants.Stage equational division: prophase II, metaphase II, anaphase II, telophase II.
Thus, the question of how a cell reproduces, is rather complicated and succinct answer.After these processes, as well as all others that take place in living beings, are very thin and composed of a plurality of stages.
