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MITOSIS AND MEIOSIS

Cell Division

ROLES

Mitosis and Meiosis are processes of cell division where the former give rise to two new cells while the latter give rise to four new cells. The basic purpose of mitosis is to repair damaged tissues and give way for the healing of wounds, while meiosis plays an important role in the propagation of species. MITOSIS - has four different phases: Prophase, Metaphase, Anaphase, and Telophase. Each event in the cycle of mitosis has a specific function to take part in cell reproduction. STAGES OF MITOSIS Prior to cell division, a cell is in its normal stage. No signs of changes and development can be seen. The cell is under Interphase stage. When the cell is ready to reproduce, it now begins to makes various changes. MITOSIS PMAT Prophase-  Mitosis starts with prophase and the following are the different events happening at this stage: At first, human cell which contains 46 number of chromosomes is diploid (2n).  At the start of prophase, chromosomes become thick and condense. Two chromatids then stick together by cohesin of the centromere producing sister chromatids.  Nuclear membrane becomes thin. The spindle begins to form.  The pair of centrioles start to move in the opposite poles of the cell.  The microtubules begin to polymerize from the duplicated centrosomes rapidly form and disassemble as they grow out of the centrosomes Metaphase -  The following are the observable events in metaphase: Chromosomes are most compacted during this stage.  Chromatids line up at the middle of the equator of the cell while remaining attached in the spindle fiber.  Metaphase is especially useful in cytogenetics because chromosomes can easily be seen at this stage.  A complex checkpoint mechanism determines whether the spindle is properly assembled. Only cells with correctly assembled spindles enter anaphase. Anaphase -  Changes from metaphase into anaphase is marked by separation of sister chromatids. A major reason for chromatid separation is the decreasing speed of the cohesin molecules joining the sister chromatids by the protease separate in spindle.  Two types of movements occur during anaphase:  During the first part of anaphase, the kinetochore microtubules shorten, then chromosomes move toward the spindle poles.  During the second part of anaphase, the spindle poles separate as the non-kinetochore microtubules move in opposite poles of the cell. This movement is due to catalyzed motor proteins that bind microtubules with opposite polarity and then move toward the end of two directions, along with this, the nuclear membrane ruptured. Telophase -  The nuclear membrane reforms, and the chromosomes begin to decondense into their interphaseform.  A cleavage furrow begins to form in the cell membrane which is an indication that one cell will soon give rise to another one.

 Telophase is followed by cytokinesis or the division of the cytoplasm into two daughter cells. The daughter cells resulted from this process have identical genetic compositions, 46 chromosomes in human only, i.e. diploid (2n) in form. MEIOSIS Meiosis is a kind of cell division happening during the formation of gametes in human. There are two rounds of cell division happening in meiosis and the resulting daughter cell is haploid (2n). PMAT I and II Meiosis I- Interphase I

- Before meiosis begins, the cell goes through the three stages of interphase: G1, S, and G2. The DNA in

the cell is replicated during the S, or Synthesis, stage Meiosis I - Prophase I

- Meiosis is divided into two phases, beginning with Meiosis I. The first stage of Meiosis I is Prophase I.

During the beginning of this stage, the chromosomes condense.

- During the middle of prophase I, homologous chromosome undergo synapsis, or pairing up. This is

followed by an exchange of DNA between non-sister chromatids. This exchange is called recombination, or crossing over

- At the end of prophase I, the nuclear membrane breaks down, the centrosomes have migrated to the

opposite ends of the cell, and the spindle fibers/apparatus is being formed. Meiosis I - Metaphase I

- During this stage the spindle fibers, or microtubules, attach to the centromere of each chromosomes.

The chromosomes are then aligned at the equator, or metaphase plate, of the cell. Meiosis I - Anaphase I

- Next is anaphase I. Here the homologous chromosome are pulled apart to opposite ends of the cell. It

is important to note that the sister chromatids remain attached at the centromere of each chromosome. Meiosis I - Telophase I

- In telophase I, the microtubules break down, nuclear membrane reforms, and the chromosomes

return to uncondensed state. The cell then divides into two haploid daughter cells by cytokinesis. Meiosis II - Prophase II

- Meiosis II follows Meiosis I. The process is similar to mitosis, but the results are genetically different.

The first stage of Meiosis II is prophase II. The chromosomes again condense, while the nuclear membrane breaks down and spindle apparatus begins to form in each of the daughter cells. Meiosis II - Metaphase II

- Next comes metaphase II. During this stage the spindle fibers attach to the kinetchores of each sister

chromatid, and the chromosomes align at the equator of the cell. The alignment of the sister chromatids is completely random.

Meiosis II - Anaphase II

- This is followed by anaphase II, where the cells elongated and the sister chromatids are finally

separated and pulled to opposite ends of the cells. The sister chromatids are now considered chromosomes. Meiosis II - Telophase II

- During telophase II, the chromosomes uncoil, new nuclear membrane forms, the spindle fibers are

broken down, and the cells are split once again during cytokinesis, forming four new haploid cells called gametes. If a male gamete and a female gamete combine, they form a new diploid zygote which can go on to become an embryo NOTES

- Each two daughter cells produced in Meiosis I are both haploid (n), since Meiosis I is immediately

followed by Meiosis II, the two haploid cells in Meiosis I separate again, this time containing just haploid (n) number of chromosome, that is 23 chromosomes in human, and then resulting to four (4) new haploid egg cells or sperm cells.

- All the four sperm cells produced from Meiosis I and II are all functional and fertile.

- Only one egg cell becomes fertile among the four, the remaining 3 will be just a polar body and

therefore, not fertile. GAMETOGENESIS SPERMATOGENESIS

- Spermatogenesis is the process wherein the haploid spermatozoa is produced in the seminiferous

tubules of male testis in the process of mitotic cell division. At first spermatocyte divides in Meiosis I resulted in two new cells. Secondly, spermatocyte divide into two equal haploid cells during Meiosis II giving it 4 new cells OOGENESIS

- Oogenesis is developed in the female reproductive system. Immature egg cells are being replenished

with Follicle Stimulating Hormones (FSH) until such time of maturity. After many years of development, ovulation occurs. Soon the eggs undergo cell division. Each ovum contains the diploid number of chromosomes. A second round of meiotic cell division will happen, this time each ovum will contain a haploid number of chromosomes, resulting into 4 new egg cells. One of the four egg cells will grow into a mature cell which is eventually fertilized by a sperm cell. The remaining three will just be a polar body and infertile

DISORDERS AND DISEASES THAT RESULT FROM THE MALFUNCTION OF

THE CELL DURING THE CELL CYCLE

CANCER - A disease resulting from uncontrolled growth and division of abnormal cells. Symptoms : Symptoms are highly variable and may include, persistent lump, weight loss and other unexplained changes in the body. Causes : Caused by gene mutations that may result from exposure to chemicals, carcinogens, radiation, and other causes. Treatment : Treatment may include surgery, chemo or targeted therapy, radiotherapy and palliative care.

CILIOPATHY - Ciliopathies comprise a group of disorders associated with genetic mutations encoding defective

proteins, which result in either abnormal formation or function of cellular cilia. Types : Bardet-Biedl syndrome, polycystic kidney disease, or retinitis pigmentosa Means : Characterized typically by obesity, retinal dysfunction and degeneration, learning disabilities, the presence of extra fingers or toes, abnormalities of the kidney, liver, and heart, short stature, and subnormal development of the genital organ. (PKD) is an inherited disorder in which clusters of cysts develop primarily within your kidneys, causing your kidneys to enlarge and lose function over time. Also, it can cause cysts to develop in your liver and elsewhere in your body. The disease can cause serious complications, including high blood pressure and kidney failure. Treatment : Causal therapies are not available, the diseases cannot be cured but only alleviated by symptomatic therapy. The therapies are also different for the various ciliopathies. PARKINSON’S - A chronic and progressive movement disorder that initially causes tremor in one hand, stiffness or slowing of movement. Warning: Urgent medical attention is usually recommended by healthcare providers Life: May be dangerous or life threatening Treatment: Treatments can help manage condition, no known cure Testing: Often requires lab test or imaging Duration: Can last several years or be lifelong Population: Common for ages 60 and older ALZHEIMER’S - Alzheimer's disease is a progressive neurologic disorder that causes the brain to shrink (atrophy) and brain cells to die. Alzheimer's disease is the most common cause of dementia — a continuous decline in thinking, behavioral and social skills that affects a person's ability to function independently. Symptoms : Memory loss is the key symptom of Alzheimer's disease. Early signs include difficulty remembering recent events or conversations. As the disease progresses, memory impairments worsen and other symptoms develop.

Causes : The causes include a combination of age-related changes in the brain, along with genetic, environmental, and lifestyle factors. Treatment : There is no treatment that cures Alzheimer's disease or alters the disease process in the brain. HUNTINGTON’S - Huntington's disease (HD) is an inherited neurological illness causing involuntary movements, severe emotional disturbance and cognitive decline. Symptoms : movement, cognitive, and psychiatric disorders, with symptoms widely varying between individuals Causes : Caused by gene mutations that may result from exposure to chemicals, carcinogens, radiation, and other causes. Treatment :Huntington’s disease is not curable, but treatments include medications, therapies, and lifestyle changes to help the patient cope with the condition. CYSTIC FIBROSIS - Cystic fibrosis (CF) is an inherited disorder that causes severe damage to the lungs, digestive system and other organs in the body. Symptoms : Salty tasting skin, wheezing, shortness of breath, sinusitis, inability to exercise, male infertility, lung infections Causes : Caused by mutation (change) in the cystic fibrosis transmembrane conductance (CFTR) gene. Treatment : Cystic fibrosis cannot be cured. Several treatment options are available to help manage symptoms and reduce complications. Though incurable, medications can help in managing symptoms SICKLE CELL - An inherited blood disorder where red blood cells (RBCs) become sickle/crescent shaped. It causes frequent infections, swelling in the hands and legs, pain, severe tiredness, and delayed growth or puberty. Symptoms : Pain, anemia, swelling of hands and feet, infections, delayed puberty, vision problem Causes : Result of a point mutation, a change in just one nucleotide in the gene for hemoglobin. Treatment : Treatments might include medications and blood transfusions. For some children and teenagers, a stem cell transplant might cure the disease. TAY-SACHS - A metabolic genetic disorder which shows a progressive deterioration of mental and physical abilities due to nerve damage in brain and spinal cord. It results in lose of muscle control and eventually leads to blindness, paralysis and death. Symptoms : Increasing muscle weakness leading to paralysis, decreasing cognitive and motor skills, loss of hearing and difficulty swallowing. Causes : It is caused by a defect (mutation) in a gene that leads to nerve damage. Treatment : There is no cure for Tay-Sachs disease. Palliative care helps manage symptoms and complications.

PHENYLKETONURI - A genetic condition that causes increased levels of phenylalanine (an amino acid) in the body. Symptoms : The symptoms include intellectual disability and other serious health issues. Causes : It is an inherited metabolic disorder leading to an increased level of phenylalanine in the blood Treatment : It usually lasts for whole life, but symptoms can be controlled through diet recommended by the doctor. COLOR BLINDNESS - Is an inability to see the difference between certain colors. Though many people commonly use the term "color blind" for this condition, true color blindness — in which everything is seen in shades of black and white — is rare. Symptoms : May not distinguish different shades of red and green, different shades of blue and yellow or any colors Causes : Certain eye diseases and some medications also can cause color blindness. Treatment : Presently, there is no treatment for color blindness. But the condition can be corrected as certain treatments help in perceiving better colors. Contact lenses or glasses can be used in some situations ANEUPLOIDY - Aneuploidy is a genetic disorder where the total number of chromosomes doesn’t equal 46. If there’s an extra chromosome copy (trisomy) you’ll have 47. If you’re missing a chromosome copy (monosomy), you’ll have 45. Symptoms : The most common symptom of aneuploidy is a miscarriage, which is when a pregnancy ends early Causes : Aneuploidy is the result of a genetic error that most often happens before the fertilization of sperm and egg cells. Treatment : You can’t prevent aneuploidy from occurring. But you can reduce the risk of having a baby with birth defects by: Eating a well-balanced diet, getting genetic screenings done before you plan on becoming pregnant, not smoking or drinking alcohol, taking prenatal vitamins. Types: Down Syndrome, Trisomy 18 (Edward’s Syndrome), Trisomy 13 KLINEFELTER - A genetic condition in which a male has an extra X-chromosome. Symptoms : Symptoms include muscle atrophy, unusual body structure and hair. Causes : This is not an inherited condition and happens as a random error called chromosomal nondisjunction that occurs during cell division. Treatment : Mild cases may not require treatment. For most others, it is best to start hormonal therapy at the onset of puberty. TURNER SYNDROME – A condition affecting female, due to partially or completely missing sex chromosome. Most of them can lead normal life with regular medical care.

Symptoms : There is a partial or complete absence of an x chromosome that affects the overall development and learning ability of the child. Causes : The exact cause is unknown. Turner syndrome is a condition resulting from a sex chromosomal defect in female infants. Treatment : Hormone therapy is the primary treatment. Other treatments are recommended based on the types and severity of symptoms. TRIPLE X SYNDROME - A genetic disorder characterized by the presence of an additional X chromosome in female children. They are often taller than average girls. Symptoms : Girls with this condition are taller than the average height. Causes : The disease is usually caused by some random genetic error. Treatment : There is no cure. Treatment may help manage symptoms. TRISOMY - Trisomy is a genetic condition where there is an extra copy of a chromosome. Symptoms : Very small and frail, overlapping fingers, heart defects, low set ears, intellectual issues and brain problems Causes : is a genetic condition caused by an alteration in the number of chromosomes where the affected person has three copies of one of the chromosomes instead of two Treatment : There is no cure for trisomy DOWN SYNDROME - A genetic disorder associated with physical growth delays, characteristic facial features and mild to moderate developmental and intellectual disability. It is caused by the presence of full or partial extra copy of chromosome 21. Symptoms : Symptoms are intellectual disability and characteristic facial profile. Causes : A chromosomal disorder in the individual with an extra chromosome. Treatment : A variety of therapies can be used in early intervention programs and throughout a person's life to promote the greatest possible development, independence, and productivity. CELL MEMBRANE - The Cell membrane surrounds every living cell. It separates one cell from the neighboring cells and give protection to it. The cell membrane also permits the entry and exit of nutrients and waste materials in the cell. A three layer is made up of fat protein-fat layer. Fats provide flexibility while protein provides. LIPIDS CELL MEMBRANE Glycolipids - found on the surface of all plasma membranes containing sugar molecules which have important roles in interactions of the cell with its surroundings. Phospholipids - are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue. Sterols - They occur naturally in plants, animals, and fungi, and can be also produced by some bacteria. They control membrane fluidity and permeability.

CARBOHYDRATES - Carbohydrates in the cell membrane do not exist as pure sugars but occur in the conjugated form wherein the carbohydrate moiety is covalently attached to either lipids or proteins and termed glycolipids and glycoproteins, respectively. PROTEINS CELL MEMBRANE INTEGRAL MEMBRANE PROTEINS - permanently embedded within the plasma membrane. Its function is to channel molecules across the membrane. Other integral proteins act as cell receptors PERIPHERAL MEMBRANE PROTEINS - They are involved in cell signaling. Often associated with ion channels and transmembrane receptors. Most peripheral membrane proteins are hydrophilic. LIPID - anchored are proteins located on the surface of the cell membrane that are covalently attached to lipids embedded within the cell membrane which serves to anchor the protein to the cell membrane.