Cell Cycle: Mitosis & Meiosis PDF

The Cell Cycle: Mitosis and Meiosis  The Cell Lesso Cycle n1  A newborn baby has about 26,000,000, 000 cells.  The average adult male has around 36 trillion cells in their body, while average adult females have 28 trillion, researchers have found. Cell cycle is a se...

The Cell Cycle: Mitosis and Meiosis  The Cell Lesso Cycle n1  A newborn baby has about 26,000,000, 000 cells.  The average adult male has around 36 trillion cells in their body, while average adult females have 28 trillion, researchers have found. Cell cycle is a series of events that takes place in a cell as it grows and divides.  The main stages in cell cycle are: interphase (which can be further divided into gap 1, synthesis, and gap 2) cell division (karyokinesis and  Karyokinesis division of cell nucleus. Cytokinesis the division of the cytoplasm of the cell. This phase begins early during the telophase up to after the nuclei have formed in the daughter cells.  A cell spends most of its time in what is called interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division. The cell then leaves interphase, undergoes mitosis, and completes its division. The resulting cells, known as  Interphase (I) the growth period in the cell cycle and it is divided into three parts namely: a. Gap 1 () b. Synthesis (S) c. Gap 2 (. It is considered as the longest phase in the cell cycle  a. Gap 1 () the first part of the cell cycle the phase where normal metabolic functions is carried out inside the cell. It is also during this phase that the cell will increase its size so as to its number of organelles. However, cell cannot grow bigger than their normal size even with plenty of nutrients because cells have a required size limit. b. Synthesis (S) The second part of cell cycle. During this phase, the cell makes a copy of the genetic material in the form of nuclear DNA. The cell makes a copy of chromosomes that contains the exact copies of the parent’s genetic material during cell division. In addition to DNA replication, this is also the c. Gap 2 ( - It is in this stage that the cell will continue to carry out their normal functions and also undergo further growth. This stage ensures proper transitioning to the next page by having a critical checkpoint.  What is a Checkpoint? Who does the Checkpoints?  Checkpoint is a control point in the cell cycle where stop and go-ahead signals can regulate the cycle  Three important checkpoints  1. Phase Checks if the cell is growing enough Checks if the DNA inside has no damage or in perfect shape (cause if it has a damage and it would proceed to S phase it would replicate a the same damaged DNA) - Checks if the cell has enough resources for its survival.  2. Phase - Checks if the DNA is replicated - Checks if it is growing enough - Checks if it has enough resources to continue  3. M phase It happens in Mitosis specifically in metaphase To make sure that chromosomes that are made of DNA are lined up in the middle correctly and they are all attached to the spindle correctly cause if they are not,the chromosomes will not be separated correctly.  Cell Cycle Control System - cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle.  Cyclin the proteins in cells that are responsible for regulating the cell cycle Regulatory Proteins proteins that help regulate cells aside from the cyclin family.  The cell cycle is regulated by both internal and external regulators a. Internal regulators proteins found inside the cell that regulate the processes that happen inside the cell.  b. External regulators are proteins that respond to events outside the cell Lesso Mitosis n2  Mitosis the division of nucleus into two genetically identical nuclei containing the same full set of DNA ( Karyokinesis). It occurs in body cells or somatic cell except the egg cell and the sperm cell. This stage prepares the cell for cytokinesis.  It is divided into: Prophase Metaphase Anaphase Telophase  Mitosis or cell division is important as it is the first step in growth and differentiation. New individuals develop only when the number of cell increases. When a cell is not dividing, it is said to be at the interphase stage. Prior to mitosis, the DNA replicates, and this is referred to as S, or the synthesis stage. The period before and immediately after S phase are referred to as or presynthetic and or postsynthetic stages.  The major event in cell division is the splitting of the nucleus (karyokinesis) followed by cytoplasmic division (cytokinesis). ASTERS PROPHASE  In early Prophase Centrioles move to each pole of the cell. Chromosomes appear as long, thin threads. The nucleolus becomes less distinct. The nuclear membrane is still visible. Asters are formed.  In middle Prophase SPINDLE FIBERS The centrioles begin to organize spindle fibers. Sister chromatids are formed with a centromere as their point of attachment. In late Prophase Centrioles are nearly at the opposite sides of the nucleus. The nuclear membrane slowly disintegrates. Spindle fibers attach to the centromere of each chromosome. Chromosomes move toward the equator. The nucleolus is no longer METAPHA SE  The nuclear membrane has completely disappeared. The centromere of each double-stranded chromosome is attached to a spindle fibril at the equator. Centrioles are already at opposite ends of the poles. The chromosomes line up at the center of the cell forming metaphase plate. ANAPHASE  In early Anaphase Sister chromatids separate and begin moving toward opposite poles of the cell. Sister chromatids start to move toward the poles, seemingly being  In late Anaphase The two sets of new, single-stranded chromosomes start to migrate near their respective poles. Cytokinesis begins A slight cleavage furrow in the cell membrane begins to form in the region of the equator TELOPHASE 1. New nuclear membrane starts to form in each new cell. 2. Chromosomes become longer, thinner, and less distinct. 3. The nucleolus reappears. 4. Centrioles are replicated. 5. Cytokinesis is nearly complete. 6. Spindle fibers and asters disappear. (In plant cells, the primary wall or division plate forms a boundary between the two daughter cells.) 7. The cleavage furrow deepens and the cells finally divide into two parts. Lesso Meiosis n3  Meiosis a type of cell division used by multicellular organism in the formation of reproductive cells (gametes) such as sperm cells, egg cells, or spores. Meiosis is similar to mitosis in several ways. One meiotic process is also divided into the same four basic steps: prophase, metaphase, anaphase, telophase. Like mitosis, karyokinesis is followed by  The term “Ploidy” tells us the number of sets of chromosomes that are found within the nucleus. And the two most prominent are Haploid and Diploid. Haploid- containing one set of chromosomes Diploid- containing two sets of chromosomes, one from each parent.  Division of Meiosis Meiosis I- It is also known as Reductional Division because the ploidy is reduced from diploid to haploid. Meiosis II is known as Equitional Division because it is an analogous to mitosis, in which the sister chromatids are segregated, creating four haploid daughter cells. Meiosis I  Prophase I Chromosomes start to coil and shorten The nuclear envelope disintegrates Homologous chromosomes pair by a process called synapsis Exchange of genetic material (crossing-over) may occur between homologous chromosomes when the chromatids are broken.  Metaphase I The paired homologous chromosomes align at the metaphase plate. The chromosomes in pair are attached to spindle fibers  Anaphase I Homologous chromosomes separate. The chromosomes move toward opposite poles of the cell by the spindle fiber.  Telophase I Chromosomes reach opposite poles In most organisms, the nuclear membrane forms. This is followed by cytokinesis,  MEIOSIS II  Prophase II The nuclear membrane disintegrates New spindle fibers are formed around the chromosomes  Metaphase II The chromosomes align at the plate and are attached to their centromereto the spindle fibers  Anaphase II Each chromosomes is divided into two sister chromatids The chromatids (now called chromosomes) move to opposite poles.  Telophase II Nuclear membrane is formed around each set of chromosomes Spindle fibers disintegrate. The cell undergoes cytokinesis.  Meiosis is the main event involved in the process of gamete formation called gametogenesis. Gamete formation in males is called spermatogenesis while gamete formation in female is