The cell cycle, immune system, cell envelope

The existence of the cell period from the date of its formation by dividing mother cell to its own division or death is called the term "cell cycle".Different cells of different duration.For example, basal and hematopoietic cells of the small intestine and epidermis are capable of entering the cell cycle every 12-16 hours in adult organisms, they multiply quickly enough.The short life cycles of cells last about 30 minutes, they occur during rapid crushing of eggs from amphibians, echinoderms and other animals.A large number of species in cell culture experimental conditions, cell cycle has a short duration of about 20 minutes.At a predominant amount of actively dividing cells duration period between mitoses is from 10 to 24 hours.

The phases and periods of the cell cycle. cell cycle of animals and plants consists of two periods: interphase (the period of the synthesis of proteins and DNA), and mitosis (cell division period).Interphase comprises several periods:

1. G1-phase - is the period of growth, during which the synthesis of proteins, RNA and other components of the cell.

2. S-phase - in this interval there is a process of synthesis of interphase daughter DNA molecules of the cell nucleus and the doubling of intracellular organelles (centrioles);

3. G2-phase - a period during which there is preparation for mitosis.

Cells that are not divided, G1-phase may be absent, in this period, they are in a resting phase (G0).

process of cell division (mitosis) has two stages:

1. Nuclear fission cells - mitosis.

2. The division of the cell cytoplasm - cytokinesis.

regulation of cell activity. Changing periods of the cell cycle occurs in the interaction of proteins - cyclins and cyclin-dependent kinases.Cells in the G0 phase capable of entering into a loop under the influence of various growth factors.Epidermal, and platelet factor nerve growth factor, are in constant interaction with receptors driven intracellular signaling system that leads to the transcription of protein coding genes.Thus kinases may be active only in the interaction with specific cyclins, the contents of which are constantly changing throughout the cycle.

disruption of the normal regulation of the cell cycle leading to the formation of solid tumors.For the formation of malignant tumors is responsible p53 protein: it stimulates the synthesis of p21 protein, which in turn inhibits cyclin CDK complex, which inevitably leads to cell cycle arrest in the G1 phase and the G2.The cell with the damaged DNA can not enter into the phase S. During the occurrence of mutations leading to the loss or alteration of the protein p53 gene, does not occur and cell cycle blockade enter mitosis, producing mutant cells, some of which are killed, and the other part leading to the formation of malignanttumors.

cellular immunity. reaction of the immune system of the body to any stimulus, called the immune response in which antibodies are not involved and complex set of proteins present in the blood (the complement system), called the term "cell-mediated immunity."It is directed mainly against microorganisms surviving in phagocytes and against microorganisms that infect other cells.It is especially effective against viruses, fungi, protozoa, bacteria and tumor cells.The system of cellular immunity is very important in tissue rejection.

sheath cells. rigid cell wall, placed on the outside of the cytoplasmic membrane that performs safety, structural and transport functions - is the cell membrane.Yet it is called a cell wall, it is present in most of the bacteria, fungi, archaea and plants.As for the animals, and many simple, they do not have a cell wall.