The human body is composed of trillions of cells, which constantly grow, divide and die. For the most part, cells are healthy and perform vital functions, but sometimes they do not form or behave properly. Cancer begins when an abnormal cell grows and does not stop dividing. Cancer cells also do not cancer biology benign tumors the laws cancer biology benign tumors contact inhibition, which means that cancerous cells propagate when they touch another cell normal cells stop dividing when this happens.
This proliferation of cancerous cells enables the disease to quickly form tumors and spread throughout the body. Keywords cancer, cell cycle, type of tumors, genetics of cancer Rezumat Scopul acestui articol este de a explica ce modificări funcţionale apar atunci când celulele normale se transformă în celule canceroase. Organismul uman este alcătuit din trilioane de celule care cresc, se divid şi mor. Majoritatea celulelor sunt sănătoase şi îndeplinesc funcţii vitale, dar uneori celulele nu se comportă corespunzător.
Cancerul debutează atunci când celulele cresc anormal şi nu se mai opresc din multiplicare. Celulele canceroase nu se supun regulii inhibiţiei de contact, ceea ce înseamnă că ele se vor multiplica chiar dacă vor fi în contact cu alte celule celulele normale se opresc din diviziune atunci când sunt în contact cu o altă celulă.
Această proliferare a celulelor canceroase permite formarea tumorilor şi răspândirea lor în organism. Cuvinte cheie cancer ciclu celular tipuri de tumori genetică oncologică Introduction Why does a normal cell suddenly become a foreign for the body, breaking the rules, dividing recklessly, invading other tissues, usurping resources, and in some cases eventually killing the body in which it lives?
To understand how and why cells rebel, we need to understand the normal functions of cell growth and reproduction. Cancer biology benign tumors in cell biology, biochemistry and molecular biology has provided astonishingly detailed information about the molecules and processes that allow cells to divide, grow, differentiate and perform their essential functions.
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This basic knowledge of cell biology has also led to practical discoveries about the mechanisms of cancer. Specific molecules that control the progression of a cell through the cell cycle regulate cell growth. An understanding of normal cell cycle processes and how those processes go awry provides key information about the mechanisms that trigger cancer.
The loss of control of the cell cycle is one of the critical steps in the development of cancer. Although cancer comprises at least different diseases, all cancer cells share one important characteristic: they are abnormal cells in which the processes regulating normal cell division are disrupted.
That is, cancer develops from changes that cause normal cells to acquire abnormal functions. These changes are often the result of inherited mutations or are induced by environmental factors such as UV light, X-rays, chemicals, tobacco products and viruses.
All evidence suggests that most cancers are not the result of one single event or factor. Rather, around four to seven events are usually required for a normal cell to evolve through a series of premalignant stages into an invasive cancer. Often many years elapse between the initial event and the development of cancer. The development of molecular biological techniques may help in the diagnosis of potential cancers in the early stages, long before tumors are visible.
What is cancer? Cancer results from a series of molecular events that fundamentally alter the normal properties of cells.
In cancer cells, the normal control cancer biology benign tumors that prevent cell overgrowth and the invasion of other tissues are disabled. These altered cells divide and grow in the presence of signals that normally inhibit cell growth, therefore they no longer require special signals to induce cell growth and division. As these cells grow, they develop new characteristics, including changes in cell structure, decreased cell adhesion and production cancer biology benign tumors new enzymes.
These heritable changes allow cancer biology benign tumors cell and its progeny to divide and grow, even in the presence of normal cells that typically inhibit the growth of nearby cells.
Modificările funcţionale ale celulelor canceroase în raport cu celulele normale
Such changes allow the cancer cells to spread and invade other tissues. The abnormalities in cancer cells usually result from mutations in protein-encoding genes that regulate cell division. Over time, more genes become mutated. This is often because the genes that make the proteins that normally repair DNA damage are themselves not functioning normally because they are also mutated.
Consequently, mutations begin to increase in the cell, causing further abnormalities in that cell and the daughter cells. Some of these mutated cells die, but other alterations may give the abnormal cell a selective advantage that allows it to multiply much more rapidly than the normal cells.
This enhanced growth describes most cancer cells, which have gained functions repressed in the normal, healthy cells. As long as these cells remain in their original location, they are considered benign; if they become invasive, they are considered malignant.
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Cancer cells in malignant tumors can anthelmintic science definition metastasize, sending cancer cells to cancer biology benign tumors sites in the body where new tumors may form. Genetics of cancer Alterations in the same gene are often associated with different forms of cancer. These malfunctioning genes can be broadly classified into three groups: The first group, called proto-oncogenes, produces protein products that normally enhance cell division or inhibit normal cell death.
The mutated forms of these genes are called oncogenes. The second group, called tumor suppressors, makes proteins that normally prevent cell division or cause cell death. The third group contains DNA repair genes, which help prevent mutations that lead to cancer. Controlled cell growth is maintained by regulation of proto-oncogenes, which accelerate growth, and tumor suppressor genes, which slow cell growth. Mutations that produce oncogenes accelerate growth, while those that affect tumor suppressors prevent the normal inhibition of growth.
In either case, uncontrolled cell growth occurs.
Tipuri[ modificare modificare sursă ] Un neoplasm poate fi benign, potențial malign sau malign cancer.
In normal cells, proto-oncogenes code for the proteins that send a signal to the nucleus to stimulate cell division. These signaling proteins act in a series of steps called signal transduction cascade or pathway. This cascade includes a membrane receptor for the signal molecule, intermediary proteins that carry the signal through the cytoplasm and transcription factors in the nucleus that activate the genes for cell division.
In each step of cancer biology benign tumors pathway, one factor or protein activates papilloma virus esame citologico next; however, some factors can activate more than one protein in the cell.
Oncogenes are altered versions of the proto-oncogenes that code for these signaling molecules.
The oncogenes activate the signaling cascade continuously, resulting in an increased production of factors that stimulate growth 1,2. Cell cycle An initial appearance of malignant transformation is represented by the disturbance of cell divizions.
Normal cells grow and divide in accordance with the cell cycle. Mutations in proto-oncogenes or in tumor suppressor genes allow a cancerous cancer biology benign tumors to grow and divide without the normal controls imposed by the cell cycle. The major events in the cell cycle are described in Figure 1.
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Figure 1. Cell cycle The cell cycle is an ordered process of events that occurs in four stages. During the two gap phases, G1 and G2, the cell is actively metabolizing, but not dividing. In S synthesis phase, the chromosomes duplicate as a result of DNA replication. During the M mitosis phase, the chromosomes separate in the nucleus and the cancer biology benign tumors of the cytoplasm cytokinesis occurs. There are checkpoints in the cycle at the end of G1 and G2 that can prevent the cell form entering the S or M phases of the cycle.
Cells that are not in the process of diving are in the G0 stage, which includes most adult cells.
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Several proteins control the timing of the events in the cell cycle, which is tightly regulated to ensure that cells divide only when necessary. The loss of this regulation is the hallmark of cancer 3. Major cancerul de colon switches of the cell cycle are cyclin-dependent kinases. Each cyclin-dependent kinase forms a complex with a particular cyclin, a protein that binds and activates the cyclin-dependent kinase.
The kinase part of cancer biology benign tumors complex is an enzyme that adds a phosphate to various proteins required for progression of a cell through the cycle. These added phosphates alter the structure of the protein and can activate or inactivate the protein, depending on its function.
Cancer cells do not stop dividing, so what stops a normal cell from dividing?
In terms of cell division, normal cells differ from cancer cells in at least four ways: Normal cells require external growth cancer biology benign tumors to divide.
When synthesis of these growth factors is inhibited by normal cell regulation, the cells stop dividing. Cancer cells have lost the need for positive growth factors, so they divide whether or not these factors are present.
Consequently, they do not behave as part of the tissue — they have become independent cells. Normal cells show contact inhibition; that is, they respond to contact with other cells by ceasing cell division.
Therefore, cells can divide to fill in a gap, but they stop dividing as soon as there are enough cells to fill the cancer biology benign tumors. This characteristic is lost in cancer cells, which continue to grow after they touch other cells, causing a large mass of cells to form. Normal cells age and die, and are replaced in a controlled and orderly manner by new cells. Apoptosis is the normal, programmed death of cells.
Normal cells can divide only about fifty times before they die. This is related to their ability to replicate DNA only a limited number of times. Each time the chromosome replicates, the ends telomeres shorten. In growing cells, the enzyme telomerase replaces these lost ends. Adult cells lack telomerase, limiting cancer biology benign tumors number of times the cell can divide.
However, telomerase is activated in cancer cells, allowing an unlimited number of cell divisions. Normal cells cease to divide and die when there is DNA damage or when cell cancer biology benign tumors is abnormal.
Cancer cells continue to divide, even when there is a large amount of damage to DNA or when the cells are abnormal. These progeny cancer cells contain the abnormal DNA; so, as the cancer cells continue to divide, they accumulate even more damaged DNA. There is also strong evidence that the excessive addition of methyl groups to genes involved in the cell cycle, DNA repair and apoptosis is characteristic for some cancers 4,5. There may be multiple mechanisms leading to the development of cancer.
This further complicates the difficult task of anemie cancer biology benign tumors mois grossesse what causes cancer. Tumor biology cancer cells behave cancer biology benign tumors independent cells, growing without control to form tumors.
Tumors grow in a series of steps. The first step is hyperplasia, meaning that there are too many cells resulting from uncontrolled cell division. These cells appear normal, but changes have occurred that result in some loss of control of growth.
The second step is dysplasia, resulting from further growth, accompanied by abnormal changes to the cells. The third step requires additional changes, which result in cells that are even more abnormal and can now spread over a wider area of tissue. These cells begin to cancer biology benign tumors their original function; such cells are called anaplastic. At cancer biology benign tumors stage, because the tumor is still contained within its original location called in situ and is not invasive, it is not considered malignant — it is potentially malignant.
The last step occurs when the cells in the tumor metastasize, which means that they can invade surrounding tissue, including the bloodstream, and spread to other locations. This is the most serious type of tumor, but cancer biology benign tumors all tumors progress to this point.
Noninvasive tumors are said to be benign. The type of tumor that forms depends on the type of cell that was initially altered. There are five types of tumors: Carcinomas result from cancer biology benign tumors epithelial cells, which cover the surface of our skin and internal organs.
Most cancers are carcinomas. Sarcomas result from changes in muscle, bone, fat or connective tissue. Leukemia results from malignant white blood cells. Lymphoma is a cancer of the lymphatic system cells that derive from bone marrow.