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Cell Division Cell Division: • The process by which a cell divides into two new daughter cells is called cell division. • Before cell division occurs, the cell replicates or copies its entire DNA. This replication of DNA solves the problem of information overload because each daughter cell gets one complete copy of genetic information. Name we use to describe the new cells that are created. Two types of reproduction: • Asexual Reproduction – The production of genetically identical offspring from a single parent. – Enables populations to replicate very quickly. – Bacteria and many single-celled organisms. Two types of reproduction: • Sexual Reproduction – Offspring produced by sexual reproduction inherit some of their genetic information from each parent. – Involves the fusion of two separate parent cells. – Most plants and animals. The process of cell division: • What do you think would happen if a cell were simply to split in two, without any advance preparation? The process of cell division: • Even small cells like the bacterium E. coli have tremendous amounts of genetic information in the form of DNA. – The total length of this bacterium’s DNA molecule is roughly 1000x longer that the cell itself. – Genetic information is bundled into packages of DNA known as chromosomes. Prokaryotic Chromosomes • Prokaryotes lack a nuclei and many of the organelles found in eukaryotes. Their DNA molecules are found in the cytoplasm along with most of the other contents of the cell. • What do prokaryotic chromosomes look like? Eukaryotic Chromosomes • Eukaryotic cells generally have much more DNA than prokaryotes and, therefore, contain multiple chromosomes. – Fruit flies have 8 chromosomes per cell – Human cells have 46 chromosomes per cell – A carrot has 18 chromosomes per cell. Eukaryotic Chromosomes • Chromatin = chromosomes which are tightly coiled around histones (proteins). Eukaryotic Chromosomes • Chromosomes make it possible to separate DNA precisely during cell division. The Cell Cycle: • Cells go through a series of events known as the cell cycle as they grow and divide. • During the cell cycle a cell: – Grows – Prepares for division – Divides to form two daughter cells. Prokaryotic Cell Cycle: • The prokaryotic cell cycle is a regular pattern of growth, DNA replication, and cell division that can take place very rapidly under ideal conditions. • Form of asexual reproduction known as binary fission. Eukaryotic Cell Cycle: • Consists of four phases: G1, S, G2, and M. • The length of each phase and the length of the entire cell cycle vary depending on the type of cell. G1 Phase: Cell Growth • Cells do most of their growth • Cells increase in size and synthesize new proteins and organelles. • “G” stands for “gap” – However; both G1 and G2 are actually periods of intense growth and activity. S Phase: DNA Replication • “S” stands for “synthesis” • New DNA is synthesized when the chromosomes are replicated. • At the end of the S phase the cell contains twice as much DNA as it did at the beginning. G2 Phase: Preparing for division • Many of the organelles and molecules required for cell division are produced. • When the events of this phase are completed the cell is ready to enter the M phase. M-Phase: Preparing for division • Produces two daughter cells. • “M” stands for “mitosis” **Both “G” phases and “S” phase are part of Interphase. Two types of Cell Division 1) Mitosis: – Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase. Depending on the type of cell, mitosis may last anywhere from a few minutes to several days. • Centromere – the area where the duplicated DNA strands are held together. • Chromatid – each DNA strand in the duplicated chromosome. • Centrioles – organelles which will aid in the division of the cell. Cytokinesis: • Completes the process of cell division – splits one cell into two. • In Animals: – The cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. • In Plants: – A cell plate forms halfway between the divided nuclei, and gradually develops into two cell membranes. The cell wall then forms between the two new membranes.