cell division

• Mitosis is the process by which cells divide to produce two genetically identical daughter cells.
• Cell continuity means that all cells develop from pre existing cells.
• Cells divide for reproduction in single celled organisms, growth in multicellular organisms, and repair.
• Chromosomes are made of DNA and protein, contain all of our genetic information, occur in pairs in all body cells, and are found in the nucleus of all cells.
• Every species has a characteristic number of chromosomes.
• When the cell is not dividing, the chromosomes are long, thin threads called chromatin.
• At cell division, the chromatin contracts to form clearly distinguishable chromosomes.
• Genes are sections of DNA that cause the production of a protein, only 3% of the DNA in a human chromosome is in the form of DNA, and the other 97% is called “non coding” DNA and its function is yet unknown.
• All the genes in an organism make up its genome.
• A haploid cell has one set of chromosomes, denoted with the letter n, and the number of chromosomes is given as n=2 or n=3 etc.
• In many organisms, the sex cells or gametes are the only cells that are haploid.
• Human gametes are n = 23, the egg and sperm contain 23 chromosomes.
• A diploid cell has two sets of chromosomes, denoted by 2n, for example, 2n = 6.
• Human body cells ( somatic cells) are 2n = 46, they contain 46 chromosomes or 23 pairs.
• The function of Meiosis is to allow for sexual reproduction, as each gamete produced by meiosis only contains half the number of chromosomes so that when they recombine at fertilization the full number is restored.
• Meiosis is a form of nuclear division in which the 4 daughter nuclei contain half the chromosome number of the parent nucleus.
• Gametes are haploid cells capable of fusion.
• Examples of carcinogens include Cigarette smoke and UV radiation.
• During sexual reproduction, which egg and sperm fuse together is random, so there are (2^23)^2 or approximately 70 million million different combinations possible.
• Radiotherapy involves the use of targeted radiation to kill the cancer cells.
• In humans, the sperm and egg cells are gametes.
• There are 23 chromosomes in a human haploid cell, meaning there are 2^23 possible combinations or approximately 8.4 million in each gamete.
• When a diploid cell divides by meiosis, it produces four daughter cells that are haploid.
• Carcinogens are cancer causing agents.
• Chemotherapy involves the use of chemicals to kill the cancer cells.
• Meiosis also allows for variation, as each daughter cell formed by meiosis does not contain identical genes to the parent, leading to variation among a species.
• Gametes form from a diploid cell with 46 chromosomes and each gamete contains 23 chromosomes.
• Cancer treatments include Surgery, Chemotherapy, and Radiotherapy.
• Surgery involves the removal of the tumour surgically.
• The chromosomes are in pairs in a diploid cell, these pairs are called homologous pairs, a homologous pair consists of two chromosomes that each have genes for the same feature at the same position.
• Humans have 22 homologous chromosomes (autosomes) and a pair of sex chromosomes X or Y.
• The cell cycle describes the life cycle of the cell, it includes the changes that take place in a cell during the period between one cell division and the next.
• The period when the cell is not dividing is called interphase, a cell spends up to 90% of its life in interphase.
• The other period (10%) is when the cell is dividing, either by mitosis or meiosis.
• Interphase is the phase in the cell cycle when the cell is not dividing, during interphase the chromosomes are visible as chromatin.
• The cell is very active in interphase, it produces new organelles e.g mitochondria and chloroplasts, and the chromosomes contract and become visible as individual strands.
• Cytokinesis is when the cytoplasm is split in two to form two cells and it is the final stage and often overlaps with telophase.
• In plant cells, vesicles containing cell wall material combine together along the middle of the cell and form a cell plate, the cell plate forms a new cell wall that fuses with the existing membrane, and the two cells are separated.
• Each chromosome makes an identical copy of itself when the chromosomes make a copy of themselves they are attached to each other at a point called the centromere.
• Cancer is a group of disorders in which certain cells lose their ability to control both the rate of mitosis and the number of times mitosis takes place.