Cell Division - Mitosis and Meiosis PDF

Duration: 130 min Middle School Grades: 6 - 8 CCSS, NGSS Cell Division Click to open in Lifeliqe Review and Recall: Cytoplasm Review and Recall:  THE CELL CYCLE AND DIVISION The production of new cells to bring abo...

Duration: 130 min Middle School Grades: 6 - 8 CCSS, NGSS Cell Division Click to open in Lifeliqe Review and Recall: Cytoplasm Review and Recall:  THE CELL CYCLE AND DIVISION The production of new cells to bring about growth, the replacement of damaged cells in the wounded body parts, and the production of new generations of individuals among some group of organisms take place through one of the wonderful processes taking place in the body of living things called cell division. As we all grow, why do cells divide instead of just getting bigger? X  Cells gain nutrients from their surroundings and excrete their waste to their surroundings by the process of diffusion. The rate of diffusion decreases with increase in cell size making the cell less efficient. Therefore, instead of increasing in size, with growth, the cells reproduce to grow larger in number and maintain their efficiency.  CELL DIVISION Two kinds of cell division: Mitosis – takes place in our body cells or somatic cells Meiosis – takes place in the ovaries (female) testes (male). Responsible for the formation of gametes or sex cells (sperm and egg cell). The process of cell division is repeated over and over in a process called cell cycle.  INTERPHASE Interphase is described as the resting stage, resting because the cell is not dividing but very active in performing metabolic activities. The metabolic activities are geared towards protein synthesis that brings about the growth of the cell and DNA replication. 90% of the entire cell cycle is devoted to the interphase.  INTERPHASE What are the three sub phases/stages of interphase? G1 (Gap 1) phase S (synthesis) phase G2 (Gap 2) phase  THE CHROMOSOME The presence of two complete sets of chromosomes in an organism's cells, with each parent contributing a chromosome to each pair. Haploid refers to the presence of a single set of chromosomes in an organism's cells. Haploid (N) Diploid 2(N) How many chromosomes and chromatids? How many chromosomes and chromatids? STAGE 1: G1 (GAP 1) PHASE This is the longest phase among cells The cell at this stage is still young and undergoes rapid growth until it attains its normal size. Organelles are formed Proteins are produced such as the enzymes needed in S phase.  STAGE 2: S (SYNTHESIS) PHASE The DNA, the main composition of the chromosomes inside the nucleus of the cell, doubles at this stage through a process called replication. STAGE 3: G2 (GAP 2) PHASE Preparation for cell division Assembly of proteins such as microtubules that cause the chromosomes to move during cell division.  STAGE 1: PROPHASE The nuclear membrane and nucleolus begin to dissolve Chromatins undergo changes until they become double stranded and are called chromatids. The double-stranded chromosomes are connected together at one point by a centromere. Spindle fibers later become well developed.  STAGE 2: METAPHASE The double-stranded chromosomes called chromatids align themselves at the equator of the cell. Each chromatid is attached to the spindle by a structure in the centromere called kinetochore.  STAGE 3: ANAPHASE Forces originating from the poles pull the chromatids to move and consequently, the centromere splits separating the chromatids into new, single-stranded chromosomes. The chromosomes then migrate toward their respective poles.  STAGE 4: TELOPHASE The chromosomes now have reached the opposite poles and the spindle disappears. At the poles, the chromosomes uncoil and the nucleolus and the nuclear membrane begin to reform. Simultaneously, the cytoplasm divides and a plasma membrane partitions the cell into two.  CYTOKINESIS Cleavage furrow forms The formation of the new plasma membrane completely divides the cell into two identical daughter cells. At this point, each chromosome in the resulting daughter cell is composed of only one chromatid. FOR EASY RECALL, USE THE ACRONYM PMAT P – prophase M – metaphase (middle) A – anaphase (away) T – telophase 2n indicates that there are two sets of these chromosomes, one from each parent. So, in humans, 2n = 46, meaning 46 chromosomes total in a diploid cell (23 pairs). n stands for the number of unique chromosomes in a set (the haploid number). For humans, n = 23, which represents 23 unique chromosomes. Review and Recall: Humans have 23 pairs of chromosome. Provide the number of chromosomes and chromatids inside the table. Phases of Mitosis No of chromosomes Number of chromatids PROPHASE 46 92 METAPHASE 46 92 ANAPHASE 92 92 TELOPHASE 92 92 END OF MITOSIS 46 46 (SEPARATED CELLS)  Let’s Try: Dogs have 78 TOTAL NUMBER (DIPLOID) of chromosomes. Provide the number of chromosomes and chromatids in each stage of mitosis. Phases of Mitosis No of chromosomes Number of chromatids INTERPHASE 78 78 PROPHASE 78 156 METAPHASE 78 156 ANAPHASE 156 156 TELOPHASE 156 156 END OF MITOSIS 78 78 (SEPARATED CELLS) MEIOSIS  PROPHASE I each chromosome is composed of two sister chromatids containing identical genetic information crossing over – happens randomly MEIOSIS  METAPHASE I the centrioles are now at opposite poles of the cell with meiotic spindle the chromosome pairs line up next to each other along the center (equator) of the cell. The meiotic spindle fibers attach to the kinetochore of the chromosome Independent assortment MEIOSIS  ANAPHASE I Each of the homologous chromosomes get pulled towards opposite poles of the cell The sister chromatids of each chromosome remain attached to one another and don’t come apart. MEIOSIS  TELOPHASE I The chromosomes arrive at opposite poles of the cell. Cleavage furrow appears and the cytoplasm starts to divide A nuclear membrane forms around each set of chromosomes to create two new nuclei.  MEIOSIS II Cells move from meiosis 1 to meiosis 2 without copying their DNA. “mitosis for haploid cells” Just have one chromosome but still consist of two sister chromatids The sister chromatids separate, making haploid cells with non-duplicated chromosomes.  PROPHASE II Now, there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids) In each daughter cells the chromosomes condense again into visible X-shaped structures. Nuclear membrane around the nucleus dissolves The centrioles duplicate Spindle forms again  METAPHASE II The chromosomes line up end-to-end along the equator of the cell. The centrioles are now at opposites poles in each of the daughter cells. Meiotic spindle fibers at each pole of the cell attach to each of the sister chromatids  ANAPHASE II The chromosomes are pulled to opposite poles The separated chromosomes are now individual.  TELOPHASE II The chromosomes complete their move to the opposite poles of the cell A membrane forms around each set of chromosomes to create four new cell nuclei Nuclear membrane forms around each set of chromosomes. There are four granddaughter cells, each with half a set of chromosomes (haploid) MALES – four cells are all sperm cells FEMALES – one of the cells is an egg cell while other three are polar bodies. Meiosis leads to the formation of haploid cells. However, these cells are still incapable of fertilization until they further mature as gametes in a process called gametogenesis. Gametogenesis in males is called spermatogenesis and oogenesis in females.  MALES – four cells are all sperm cells FEMALES – one of the cells is an egg cell while other three are polar bodies. These haploid cells will become diploid during the process of fertilization, when sperm cells unite with the egg cells making into another organism. This process also shows how the organisms, like us humans are made.  GENETIC DISORDERS ASSOCIATED WITH MEIOSIS TURNER SYNDROME (45,XO) seen in female individuals small and underdeveloped ovaries, uterus, and oviducts lose the ability of normal ovarian function do not experience puberty at a normal age DOWN SYNDROME (TRISOMY 21) 3 chromosome in the 21 st chromosome most cases are not due to inheritance, but on random mistakes short stature short neck short arms and legs KLINEFELTER SYNDROME (47, XXY) underdeveloped prostate gland and testes lack of facial and body hair breast enlargement small penis TRISOMY X (47, XXX) the abnormal presence of an extra X chromosome mild symptoms or none at all no unusual physical features behavioral and emotional difficulties Cancer is a large group of diseases that can start in almost any organ or tissue of the body when abnormal cells grow uncontrollably, go beyond their usual boundaries to invade adjoining parts of the body and/or spread to other organs. The latter process is called metastasizing and is a major cause of death from cancer. A neoplasm and malignant tumor are other common names for cancer. Cancer is the second leading cause of death globally, accounting for an estimated 9.6 million deaths, or 1 in 6 deaths, in 2018. Lung, prostate, colorectal, stomach and liver cancer are the most common types of cancer in men, while breast, colorectal, lung, cervical and thyroid cancer are the most common among women.