Category: Cell

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Centrioles are barrel/cylindrical-shaped cell organelles found in the cytoplasm of many eukaryotic cells. They are found in paired and mainly composed of tubulin proteins. They are present mostly in the centrosome. Centrioles play important role in microtubules dynamics and the separation of chromosomes during cell division. During cell division, each centriole goes to the opposite pole of the cell.

Centrioles are found mostly in animal cells and a few plant cells such as Charophytes, Mosses, and Ginkgo. But centrioles are absent in conifers, angiosperms, and fungi.

Normally, each centriole is made up of nine microtubule triplets. Sometimes in the microtubule is arranged in doublets (flies) and single (nematodes). The microtubule is mainly composed of a globular protein called tubulin. The size of the centriole is about 250 nm in diameter and 500 nm in length.

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The 0.5% sodium chloride (NaCl) solution is a hypotonic solution for RBC. The isotonic solution for RBCs is 0.9% NaCl solution. Any solution that is below the concentration of 0.9% NaCl is referred to as the hypotonic solution for RBCs. And any solution that is above the concentration of 0.9% NaCl solution is referred to as the hypertonic solution for RBCs.

The solute concentration of RBCs is similar to the solute concentration of 0.9% NaCl (isotonic solution). When the concentration of NaCl decreased below 0.9% (i.e. 0.5%), the concentration of solute present in that solution is less than the solute concentration of RBCs. Thus, the NaCl solution is referred to as the hypotonic solution.

When RBCs are put in the hypotonic solution, the water molecule (solvent) enters the RBCs. As a result, the RBCs become swell and rupture.

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A high white blood cell (WBC) number in the blood indicates Leukaemia. Leukaemia is also known as the cancer of the blood cells, particularly the white blood cells. Leukaemia is derived from the term Leucocytes (White blood cells). In leukemia, uncontrol and abnormal growth of white blood cells take place in the bone marrow. Bone marrow is the site of hematopoiesis or the formation of blood cells.

The hematopoietic stem cells undergo proliferation and maturation to form a different types of blood cells. The hematopoietic stem cells either develop into myeloid/myelogenous cells or lymphoid/lymphogenous cells. The myeloid cells are the progenitor cells for red blood cells, white blood cells such as basophils, eosinophils, and neutrophils and platelets. The lymphoid cells are the progenitor cells for lymphocytes and NK cells. Leukemia cells are normally undeveloped or immature white blood cells.

According to the speed of disease progression, Leukaemia is of two types: Acute leukaemia (disease progresses quickly) and Chronic leukemia (disease progresses slowly). According to cell types, Leukaemia is of two types: Myelogenous leukaemia (Leukaemia of myeloid cells) and Lymphocytic leukaemia (Leukaemia of lymphoid cells).

The symptoms of leukaemia are pale skin, swollen lymph nodes, weight loss, fever,  red spots in the skin, enlargement of the spleen and liver.

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Myosins (500,000 Da) are a family of motor proteins present in the muscles cell. They help in muscle contraction. Among different classes of myosin proteins, Myosin II is the major class of myosin that is present in muscle cells.

Structurally, the myosin protein has three domains. They are the head domain, the neck domain, and the tail domain. The myosin II consists of six polypeptide chains. They are two heavy chains (200,000 Da) and four light chains (15,000-20,000 Da). The N terminal domain of the heavy chain is globular in structure. It forms the head domain. The C terminal domain of the heavy chain forms a coiled structure that holds the two heavy chains together.

The head domain of each myosin consists of an ATPase enzyme. The ATPase activity of the head breaks down the ATP into ADP and pi. The hydrolysis of ATP helps in the movement of the myosin head during muscle contraction.

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The stem cells found in the umbilical cord are “Cord blood stem cells”. Stem cells show three basic characteristics. They are (i) Stem cells divided to produce daughter cells (ability to renew themselves), (ii) stem cells differentiate to form specialized cell types (tissues from all three germ layers: ectoderm, endoderm, and mesoderm), and (iii) stem cells have the ability to renew the tissue (blood cells, gut epithelium, and skin cells) they populate.

There are three types of stem cells: Embryonic stem cells: Are present in the inner cell mass of the blastocyst, three to five days after an egg cell is fertilized by a sperm. They are pluripotent in nature and can give rise to every cell type. Tissue-specific stem cells or adult stem cells: These types of stem cells are differentiated to generate different cell types for the organ in which they present. Induced pluripotent stem cells: Engineered stem cells generated in the lab.

Umbilical cord stem cells are found in Wharton’s jelly, umbilical cord, amnion/placenta, and umbilical cord vein. The umbilical cord stem cells are multipotent stem cells capable of differentiating to form different types of cells.  There are three main types of stem cells present in the umbilical cord blood stem cells. They are (i) hematopoietic stem cells, (ii) mesenchymal stem cells, and (iii) a very small population of embryonic-like stem cells.

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British scientist Robert Hooke (1635-1703) coined the term “cell” in the year 1665. He introduced the term “cell” to name the microscopic honeycomb-like cavities in the cork. Under the microscope, he observed tiny honeycomb-like structures in the dead cork and plant tissue. The honeycomb-like structures are plant cell walls made up of cellulose.

Robert Hooke published his findings in the book “ Micrographia “. The book was published by the Royal Society, London, the United Kingdom in 1665. The term ‘cell” was introduced in this book. The microscope used by Robert Hooke to study the cell was manufactured by Christopher Cock White of London.

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During cell division, tubulin proteins present in the spindle fibers regulate the movement of chromosomes towards the poles. Prometaphase is a transition phase between the prophase and the metaphase in mitosis. During the prometaphase, microtubules from the centriole attach to the kinetochores of the condensed sister chromatid.

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The plasma membrane is a thin membrane that surrounds and protects a living cell. It is present in every living cells (bacteria, plants, and animals). The membrane separates the inner content of the cell (cytoplasm, organelles, nucleus) from the outer environment. Bacterial and plant cells possess a cell wall outer to the plasma membrane. The plasma membrane is semipermeable and only allows selective molecules to pass through it. The plasma membrane keeps a fixed environment inside the cell for cellular metabolism.

The plasma membrane consists of two layers of lipid and proteins scattered on it. The lipids are of three types: glycolipids, phospholipids, and sterols.

Glycolipids are carbohydrates containing lipids. The carbohydrate molecule is attached to the lipid by a glycosidic bond. Glycolipids are present in both eukaryotic cells. The glycolipids play a crucial role in cellular recognition during the immune response, A, B, O blood grouping, and cell-cell interaction. The enzyme glycosyltransferases add the carbohydrate molecule to the lipid molecule in the Golgi apparatus.

Each phospholipid molecule has a hydrophilic head (interact with water environment) and two hydrophobic tails. The head contains a phosphate group, and the tails contain fatty acids. The head and tails are joined together by a glycerol molecule. Phospholipids are synthesis in the membrane of the endoplasmic reticulum.

Sterols (C17H28O.) are a group of lipids synthesized by plants, animals, fungi, and some bacteria. Cholesterol is a sterol lipid present in the plasma membrane animal cells. Cholesterol is the precursor molecule for steroid hormone and fat-soluble vitamins. Phytosterol is present in the plasma membrane of plants, and ergosterol is present in the plasma membrane of microorganisms.

Proline is an amino acid. It is not a constituent molecule of the plasma membrane.

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The cancer-causing agents are called carcinogens. The carcinogen may be any substance, molecules, radiation, gas, or pollution that promotes the formation or development of cancer. Many radioactive substances emitted radiation like gamma rays and alpha particles cause DNA damage and are potential carcinogens. Non-radioactive carcinogens include tobacco smoke, asbestos dust, and synthetic chemicals like pesticides.

Carcinogens mostly altered cell metabolism or induced mutation in DNA. If a mutation takes place in a gene involved in cell cycle checkpoints, then the cell undergoes uncontrolled cell division and leads to tumor formation. During normal conditions, DNA damages are identified by regulatory proteins and triggered signal that leads to programmed cell death. But if any regulatory protein of the programmed cell death pathway is mutated, then the cell escapes apoptosis and becomes a cancer cell.

Examples: Nicotine, hydrogen cyanide (HCN), formaldehyde (HCHO), and benzene in tobacco cause cancer in the mouth, lung, and throat: ultraviolet rays cause skin cancer; N-nitroso chemicals in processed meat cause colorectal cancer; and pesticides such as organochlorine and creosote cause sarcoma and leukemia.

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Mitosis is a process where a single cell divides into two genetically identical daughter cells in which the total number of chromosomes is maintained. Thus, the mitotic division is also known as equational division. Mitosis occurs only in eukaryotic cells such as animal cells, plant cells, Amoeba, algae, etc. On the other hand, prokaryotic cells such as bacteria, which lack a nucleus, divide by a process called binary fission.

Mitosis occurs both in the haploid and diploid individuals as well as both in haploid and diploid cells. When a diploid cell (2n) undergoes mitosis, the cell is divided to produces two genetically identical diploid daughter cells (2n). Similarly, a haploid cell (n) undergoes mitosis, the cell is divided to produces two genetically identical haploid daughter cells (n).

In the bees, ants, and wasps (Hymenoptera), males are haploid, possessing a single set of chromosomes that comes from their mother. The cell in these haploid (n) organisms undergoes mitotic division to produce two identical haploid cells (n). Similarly, in diploid (2n) organisms, the diploid cell undergoes mitotic division to produced two identical diploid (2n) cells.