Types of cells
There are two types of cells, prokaryotic cells (Upper picture) and eukaryotic cells (Lower picture). Eukaryotic cells being plant, animal, fungi, and protist cells and prokaryotic cells being bacteria. Eukaryotic cells have a nucleus that contains DNA, organelles, and are usually larger than prokaryotic cells. Prokaryotic cells do not have organelles or a nucleus, their DNA is contained within the cytoplasm of the cell. Eukaryotic cells are much larger than prokaryotic cells, in some cases ten times the size.
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Organelles: the processes of the cell
Organelles inside eukaryotic cell include the nucleus, mitochondria, lysosomes, ribosomes, endoplasmic reticulum, and Golgi apparatus. Each of these organelles serve a specific purpose in the cell. The nucleus is center of the cell and houses the DNA. The DNA is instructions for all activities throughout the cell. Mitochondria are organelles that take food and turn it into Adenosine Triphosphate (ATP), the best form of energy cells can use. Lysosomes use enzymes to digest worn out organelles, molecules, food particles, and remove waste from the cell. Ribosomes use transcribed mRNA sent from the DNA inside the nucleus to create protein distributed throughout the cell. The endoplasmic reticulum has two parts, the Rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER). The RER is studded with ribosomes that begin to make proteins, when the protein is being made it is pushed to the middle of the of the RER to the lumen and then the protein is folded and moved to the golgi apparatus. The SER has little or no ribosomes and makes lipids. The golgi apparatus has two sides, the closest to the nucleus is called the cis and the furthest the trans. Proteins are pushed to the lumen and modified, sorted and shipped to their proper destination. All of these organelles have specific objective to ensure a cells is functioning effectively. If any one of these organelles failed to carry out its tasks the cell would not function properly.
Division: How we make more cells
Eukaryotic cells usually divide rapidly when food is accessible. The dividing of cells is called mitosis. Interphase is the phase of the cell that is nondividing and is categorized further into three sub phase: G1,S, and G2. Most of cell's life is spent in G1. In order for cells to move on from G1 to the next phase they must pass a test called checkpoint. Checkpoints are processes in the cell that make sure the cell is functioning properly and ready to move on to divide. If a cell is unable to pass the test, the cell will repair itself by signaling a repair gene such as p53, which signals proteins to repair the cell. If the cell cannot be repaired the cell will be signaled to eliminate itself, called apoptosis. In S phase the cell copies its DNA by DNA replication and then has to go through another checkpoint before leaving S phase to move to G2. G2 is another checkpoint before the cell can enter mitosis.
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All about mitosis
In mitosis there are 4 phases, prophase, metaphase, anaphase, and telophase. Condensation occurs during prophase, which is the coiling up of the chromosomes. The nuclear membrane breaks down, the mitotic spindle attaches to the chromosomes and the nucleoli becomes invisible. The chromosomes line up in the middle of the mitotic spindle in metaphase and go through another checkpoint. During anaphase the chromosomes are called chromatid and are carefully separated from each other and then called chromosomes again. Telophase is the last phase, in this phase the chromosomes uncoil, the nuclear membrane reforms, the mitotic spindle breaks down and the nucleoli reforms. The final phase in cell division is called cytokinesis, which is the separation of the cytoplasm. After cytokinesis is complete, two daughter cells are formed.