Cell Cycle and Cell Division PDF

Insert Topic Title Activity CELL CYCLE Types AND CELL Seatwork DIVISION Others  Learning Objectives Identify disorders and diseases that result from the malfu...

Insert Topic Title Activity CELL CYCLE Types AND CELL Seatwork DIVISION Others  Learning Objectives Identify disorders and diseases that result from the malfunctioning of the cell during the cell cycle identify and describe the stages of mitosis and meiosis Identify disorders and diseases that result from abnormal number of chromosomes Explain the stages of the cell cycle Discuss the three checkpoints essential in the cell cycle  THE CELL CYCLE Those actively dividing cells illustrate the cell cycle , which describes the events that occur in one complete round of cell division. Biologists divide the cell cycle into stages.  THE CELL CYCLE Interphase – cell prepare for cell division; performs its regular functions such as protein synthesis, DNA replication, and others. Next is mitosis , during which the contents of the nucleus divide. In cytokinesis , the cell splits into two daughter cells.  INTERPHASE During G phase, the cell grows, carries out its basic functions, and produce the new organelles and other components it will require if it divides.  INTERPHASE Most often, cells stop in G1 before DNA replication and enter the G0 stage (resting stage), where cells may stay at this stage for days to years before proceeding to cell division. Muscle cells, nerve cells  INTERPHASE During S phase, enzymes replicate the cell genetic material and repair damage DNA. In G2 phase, the cell continues to grow but also prepares to divide, producing the proteins that will help coordinate mitosis; chromosomes start to condense and become visible.  CELL CYCLE CHECKPOINTS Cells are equipped with checks and balance that ensure their integrity. The cell can be delayed or halted at three checkpoints. These checkpoints monitor or check the progression of the cell cycle before the next stage of the cell cycle commence.  G1/S CHECKPOINT Checks for the size of the cell, nutrients level available. Cell do not reach their adequate size or those that have DNA damage are arrested, unless they are corrected. Normal cells are allowed to proceed to the next cell cycle phase.  G2/M CHECKPOINT It checks the integrity of the DNA and any replication damage. In this stage DNA or replication damage is corrected or repaired. Cells that are irreparable DNA damage goes to apoptosis.  M CHECKPOINT Checkpoint during mitosis, particularly during metaphase stage. Wrong alignment and attachment are irreversible, so mitosis is halted unless strayed chromosomes are captured by spindle.  REGULATING THE CELL CYCLE How do cells know when to divide? “Maturation promoting factor” (MPF) is composed of proteins called cyclin and kinase. Aside from cyclin family, scientists have discovered other proteins that help regulate the cell cycle as follows:  REGULATING THE CELL CYCLE a. Internal regulators – make sure that mitosis does not occur unless the chromosomes have replicated; prevent the cells from entering anaphase if the spindle are not properly attached to chromosomes. b. External regulators – example are chemical balance and sufficient nutrients of the cell; most important external regulator is the growth factor that stimulate the growth and division of the cells.  MITOSIS Mitosis is a period of continuous activity which is necessary for the survival of eukaryotic organisms. Somatic cellular divisions in an organism’s body involved mitosis. Mitosis is also a means of asexual reproduction in some organisms.  PROPHASE DNA coils very tightly, shortening and thickening the chromosomes. Two centrosomes migrate toward opposite ends of the cell, and the spindle begins to form. Nuclear envelope breaks into small pieces. centrosomes  METAPHASE The spindle aligns the chromosomes down the center, or equator, of the cell. This alignment ensures that each cell will receive one copy of each chromosome.  ANAPHASE The centromeres split and the spindle fibers pull the sister chromatids toward opposite poles of the cell. Some microtubules in the spindle lengthen in a way that moves the poles farther apart, stretching the dividing cell.  TELOPHASE The spindle disassembles, and the chromosomes begin to unwind. A nuclear envelope and nucleolus form at each end of the stretched out cell. As telophase ends, the division of the genetic material is complete, and creates two daughter cells.  CYTOKINESIS In cytokinesis, the cytoplasm and the two nuclei are distributed into the two forming daughter cells, which then physically separate. The process also separates the organelles and other macromolecules.  CYTOKINESIS In an animal cell, the first sign of cytokinesis is the cleavage furrow, a slight indentation around the middle of the dividing cell.  CYTOKINESIS In a plant cell, the first sign of cell wall construction is the cell plate, a structure that appears at the midline of the dividing plant cell.  MEIOSIS A cell division that takes place in sexually mature organisms. Meiosis includes two divisions(meiosis I and meiosis II), creating four haploid cells from one specialized diploid cells. Meiosis shuffles genetic information. MEIOSIS I  PROPHASE I The nuclear membrane and the nucleolus starts to disappear. The homologous chromosomes condense and become visible. Allele-shuffling mechanism called crossing over occurs. A spindle begins to form from microtubules. This crossing over results in genetic recombination.  METAPHASE I The homologous chromosomes (tetrads) align along the equator of the cell. Spindle fibers increase in number and attached to the kinetochore of each chromatid to facilitate movement.  ANAPHASE I Each of the homologous pair of chromosomes (dyads) get pulled towards opposite poles of the cell as the spindle fibers retract. The sister chromatids still remain attached at their centromere and move together toward the poles.  TELOPHASE I & CYTOKINESIS During telophase I, the nuclear envelope reforms and spindle fibers disappear. In cytokinesis I, the cytoplasm and cell divides resulting in two cells that are technically haploid – there is one chromosome and two chromatids for each chromosome.  INTERKINESIS I This is a short pause between meiosis I and meiosis II. This is similar to interphase wherein the chromosomes unfold into very thin threads and the cell produces proteins, BUT there is no replication of chromosomes. MEIOSIS II  PROPHASE II Chromatin begins condensing into chromosomes. Spindles begin to form from microtubules; the nuclear envelope breaks up.  METAPHASE II Chromosomes line up in single file along the equator of the cell. This is in contrast to metaphase I. Each chromosomes is composed of sister chromatids that are joined by centromere.  ANAPHASE II Sister chromatids are pulled to opposite poles of the equator. Spindle fibers not attached to chromatids will elongate the cell to prepare it for division. The sister chromatids are now called sister chromosomes.  TELOPHASE II & CYTOKINESIS During telophase II, the nuclear envelope reforms and spindle fibers disappear. In cytokinesis II, cytoplasm and cell divides producing 2 non-identical haploid daughter cells. The overall results: one diploid cell has divided into four haploid cells.  GAMETOGENESIS Spermatogenesis Oogenesis The process where diploid cells undergo cell division and differentiation through meiosis to mature haploid gametes or sex cells is called gametogenesis.  COMPARISON BETWEEN MITOSIS AND MEIOSIS MITOSIS MEIOSIS Produces genetically identical cells Produces genetically unique cells Results in diploid chromosome Results in haploid chromosome number number Results in diploid cells Results in haploid cells Produces two new cells Produces four new cells Takes place throughout the organism’s Takes place only during the life reproductive years of an organism Involved in asexual reproduction Involved in sexual reproduction  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS What happens when the body loses control over cell division? Sometimes, a tumor – an abnormal mass of tissue – forms. Biologist classify tumors into two groups. Brain Tumor  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS Benign tumor are usually slow-growing and harmless, unless they become large enough to disrupt nearby tissue or organs. Warts and moles are example of benign tumors of the skin.  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS In contrast, a malignant tumor invades adjacent tissue. Because it lacks a surrounding capsule, a malignant tumor is likely metastasize, meaning that its cells can break away from the original mass and travel in the bloodstream or lymphatic system to colonize other areas of the body.  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS Cancer – a disease characterized by the uncontrolled division of cells. It happens when the regulators of the cell cycle break down.  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS “p53 gene” – tumor-suppressor gene; one of the culprit of cancer. In normal cells, the job of it is to monitor the integrity of the DNA and to check that it is undamaged. If irreparable, p53 directs the cell to kill itself. P53 can be damaged by cancer cells.  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS Down syndrome (Trisomy 21) – may affect both males and females; has an extra full or partial chromosome at chromosome 21. Effect: problems in brain and physical development such as flattened face along the nose bridge area, short neck, small ears, stunted height, small hands and feet, a tongue that tends to stick out of the mouth, and almond eyes. DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS Turner syndrome – only affect females and is rare; a person lacks one chromosome; has an X0 chromosome. Effect: experiences developmental problems such as short, underdeveloped, and sterile females. Puberty does not occur in these females, and their secondary characteristics do not develop. DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS  DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS Klinefelter syndrome – found only in males having an extra X chromosomes; also called as XXY syndrome. Effect: person have underdeveloped, sterile males, with some breast development; slow learners, but are not mentally retarded; puberty may be late or not complete at all; testicles and the penis are smaller than average. DISEASES ASSOCIATED WITH THE CELL CYCLE AND ABNORMAL CHROMOSOME NUMBERS