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How an Animal Cell Works
All animals -- no matter what their size-- are made up of tiny cells. Each one of these cells can grow, reproduce, respond to changes in the environment, move, and metabolize food for fuel. So how does an animal cell work? Tiny structures inside the cell called organelles work together to carry out all the cell's life functions. Learning the basic parts of the cell and their functions will help you understand how an animal cell works.
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Three Basic Parts of the Cell
The animal cell is made up of three basic parts: the cell membrane, the nucleus and protoplasm. Consider the cell membrane as the gatekeeper. It surrounds the cell contents and separates the cell from other cells and from the external environment. Nothing gets in or out without permission from the nucleus. The nucleus is the cell's brain and is in charge of growth, metabolism, and reproduction. It houses the chromosomes which contain the genetic instructions for making all the cell's proteins.
Protoplasm is made up of mostly water and inorganic ions (sodium, potassium, calcium, magnesium, for example) and proteins, lipids and carbohydrates and is the primary component of the cell. The protoplasm part that surrounds the nucleus and is involved in cell reproduction is called the nucleoplasm. The protoplasm outside of the nucleus is called the cytoplasm.
The fluid part of cytoplasm is called cytosol. Floating around in the cytosol are the animal cell's organelles, tiny metabolic units that perform a specific job to maintain the life of the cell.
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Basic Function of Animal Cell Organelles
Cytoskeleton - Protein structures that give the cell its shape
Centrosomes - These organelles contain short cylinders called centrioles that lie adjacent to the nucleus and play a part in reproduction
Mitochondria - These provide most of the cell's adenosine triphosphate or ATP, the enzyme that fuels most cell activities
Ribosomes - These structures are made in the nucleolus (a structure positioned inside the nucleus) and help synthesize proteins
Endoplasmic Reticulum - This organelle is a network of membrane enclosed tiny tubules with rough and smooth parts. The "rough" part of this organelle is covered with ribosomes and makes certain proteins. The "smooth" part stores calcium and contains enzymes that make lipids.
Golgi Apparatus - These organelles are like the UPS service, packaging, sorting and processing of proteins made by the rough ER to be secreted out of the cell or used to replace worn out cell parts.
Lysosomes - These structures are surrounded by a membrane and contain destroying enzymes to breakdown foreign or damaged materials in the cell.
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How the Animal Cell Parts Work Together
Making & Transporting Protein
Animal cells need proteins for the growth of new tissue and repair of damaged tissue. How does this work? Suppose an animal cell needs to make AB protein to rebuild a muscle cell. The chromosomes contain the genetic information or recipe to make the AB protein. The DNA (deoxyriibonucleic acid) code is not allowed to leave the nucleus so it is copied or transcribed onto a temporary carrier called messenger RNA.
Messenger RNA exits the nucleus into the cytosol. In the cytosol, messenger RNA along with another helper, transfer RNA guide the AB protein recipe to the ribosomes docked onto the endoplasmic reticulum. It is the ribosome's job to translate the AB protein recipe from DNA language to protein language. The ribosomes follow the recipe instructions using amino acids (the basic units that make up proteins) to build the AB protein.
After the AB protein is built, it is sent down through the endoplasmic reticulum for further processing (adding a carbon sugar, for instance). Then AB protein is directed to the Golgi apparatus for final packaging. The finished AB protein leaves the Golgi apparatus in a bubble like sac that is exported to its destination in the cell. An animal cell may make a protein to be exported to another cell. Sometimes the cell may make a mistake and the improperly made protein will exit the Golgi apparatus to merge with a lysosome to be destroyed. If the animal cell needs to repair its cell membrane, it retrieves the lipid recipe from the nucleus and manufactures it in the smooth endoplasmic reticulum.
Making proteins to rebuild, repair, or export the cell requires energy. Mitochondria make ATP to provide energy for these metabolic processes.
If an animal cell's nucleus, cell membrane or organelles fail to function properly, it can cause disease making it difficult for the organism to carry out life's basic functions.