--> Cell division in prokaryotic organisms is simpler than in eukaryotes. This is because prokaryotes have much less complex DNA, and they don't have to worry about ensuring that each of the new cells receives an approximately equal number of organelles. All cells reproduce by dividing the middle until the cell membrane pinches closed and two new daughter cells are formed. In prokaryotes,once the DNA of the cell is replicated, each copy moves toward an opposite side of the cell by attaching to the cell membrane. The cell then elongates until it is approximately double its original size. At the end, the cell membrane on either side pinches inward and forms two new cells.
WHY CAN'T PROKARYOTIC CELLS PERFORM MITOSIS?
--> Prokaryotic cells cannot go through mitosis. This is because mitosis is a division of nucleus into nuclei containing the same number of chromosomes. However, prokaryotic cells do not have nucleus, thus making it impossible.
WHAT HAPPENS TO THE NUMBER OF CHROMOSOMES WHEN FERTILIZATION HAPPENS?
--> A sperm has 23 chromosomes, and an egg also has 23 of them. When they fertilize, there will be 46 chromosomes. An offspring that is going to be made will have 46 chromosomes at the end. But its sex will only have 23 of them. That is how a human is like. This offspring will have 46 chromosomes but they are all mixed of 23 chromosomes from the sperm, and the other 23 from the egg. Also when meiosis occurs, all the chromosomes perform cross over, so it all depends on which sperm and egg fertilizes. This is why there is no identical people in the world because the possibility is almost 0%. It is almost impossible to happen to make two identical people.
SUMMARY:
There are two ways of reproduction for living things. Asexual reproduction, offsprings are identical to the original cell or organism. It only requires one parent, and sexual reproduction, it requires two parents and offsprings get genes from both of the parents. Cell division is the reproduction of cells. Roles of Asexual reproduction are reproduction of an entire single-celled organism, growth of a multicellular organism, growth from a fertilized egg into an adult, and repair and replacement of cells in an adult. For sexual reproduction is that sperm and egg production.
Binary fission is a type of cell division which occurs in prokaryotic cells. Two identical cells arise from one cell. Cell cycle consists of two stages. Interphase, duplication of cell contents, which includes G1, S, and G2, and mitotic phase, the division of duplicated contents, which includes mitosis and cytokinesis.
There are two types of reproduction of eukaryotic cells. Mitosis and Meiosis. Mitosis progresses through a series of stages. Interphase, prophase, prometaphase, metaphase, anaphase, telophase. Cytokinesis often overlaps telophase. During interphase, cytoplasmic contents are duplicated and two centrosomes form in the cytoplasm, and in the nucleus, chromosomes duplicate during the S phase. During prophase, in the cytoplasm, microtubules begin to emerge from centrosomes, forming the spindle. In the nucleus, chromosomes coil and become compact, and nucleoli disappears. During metaphase, spindle is fully formed, and chromosomes align at the cell equator, kinetochores of sister chromatids are facing the opposite poles of the spindle. During anaphase, sister chromatids separate at the centromeres, daughter chromosomes are moved to opposite pole of the cell, and the cell elongates due to lengthening of nonkinetochore microtubules. During telophase, the cell continues to elongate, the nuclear envelope forms around chromosomes each pole, establishing daughter nuclei, the spindle disappears, and chromatin uncoils. In cytokinesis, cytoplasm is divided into separate cells. Cleavage furrows is formed for animal cells for division, and cell plate is formed for plant cells.
Cancer cells escape controls on the cell cycle. They divide quickly. often in the absence of growth factors. They spread to other tissues through the circulatory system. Tumors get formed. There are three classifications of cancer by origin, carcinomas, sacromas, leukemias, and lymphomas.
Meiosis is a reproduction of sex cells. It also consists a series of stages but they perform twice. During prophase I, contents in nucleus duplicate. During metaphase I, tetrads align at the cell equator. During Anaphase I, homologous pairs separate and move toward the end of the cell. During telophase I, duplicated chromosomes have reached the poles and a nuclear envelope forms around them. Next stage is meiosis II, which follows meiosis I without chromosomes duplication. During metaphase II, duplicated chromosomes align at the cell. During anaphase II, sister chromatids separate and chromosomes move toward opposite poles. During telophase II, chromosomes have reeached the poles of the cell, and a nuclear envelope forms around each set of chromosomes.
KEY TERMS:
-chromatin: DNA+ proteins
-centromere: a join of sister chromatids. Made of protein
-cell cycle: an ordered sequence of events for cell division
-mitosis: division of the nucleus
-cytokinesis: division of cytoplasm
-mitotic spindle: composed of microtubules, produced by centrosomes to divide the chromosomes
-centrosomes: structures in the cytoplasm that organize microtubule arrangement, only in animal cells
-growth factor: proteins that stimulate division
-cell cycle control system: a set of molecules, including growth factors, that triggers and coorinates events of the cell cycle
-carcinomas: a type of cancer that arise in external or internal body coverings
-sarcomas: a type of cancer that arise in supportive and connective tissue
-leukemias/lymphomas: a type of cancer that arise from blood-forming tissues
This diagram shows movement of chromosomes during mitosis. The first step is prophase, when the chromosomes are form and nuclear envelope begins to dissolve. The second step is metaphase, when chromosomes line up in the middle of the cell. Spindles get attached to the centromere. During anaphase, the chromosomes are pulled apart from each other toward the end of the cell. During the last step, telophase, cleavage furrows are formed, and at the same time nuclear envelope begin to reform. The result of this step is two identical daughter cells.
This video shows more details about mitosis.
5 FACTS:
1) Mitosis is a reproduction of cells, and meiosis is a reproduction of sex cells.
2) Cytokinesis is division of cytoplasm.
3) Cells control how many cells they will reproduce, but cancer cells do not.
4) Animal cells form cleavage furrow, and plant cells form cell plate.
5) There are 46 chromosomes in human cells. After duplication it will go up to 92, and after division of sex cells, each will have 23.
0 件のコメント:
コメントを投稿