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Cells and their Structures
The cytoplasm is a fluid that contains all of the cell’s organelles and is structured by a network of fine tubes and fibers called microtubules and microfilaments, collectively known as the cytoskeleton.
Cell membrane- The cell membrane is what holds the entire cell and its contents in place and keeps the good things in and the bad things out. It’s semi-permeable membrane allows certain substances to penetrate it while keeping foreign, potentially dangerous substances out. It is a bilayer composed of proteins and phospholipids. They have heads that are hydrophilic and tails that are hydrophobic.
The endoplasmic reticulum is a network of membranes that create channels. One function of the ER is to move materials throughout the cytoplasm and to the plasma membrane. It is also necessary for the synthesis of materials and their packaging and distribution to sites as needed.
Cell walls are made of cellulose and are found only in plant cells. It is a shielding barrier that supports and helps the plant cell keep its shape, allowing plants to grow to huge lengths. It also contains small holes called plasmodesmata that allow nutrients, waste, and ions to pass through,
The nucleus is the control center of the cell that contains genetic material. It regulates reproduction and helps carry out the cell’s functions. The nucleus is surrounded by a nuclear envelope and there are pores that allow RNA and proteins to pass through. The nucleus also contains chromatin and the nucleolus.
Mitochondria are known as the powerhouses of the cell. Each cell is surrounded by a double membrane and has a membrane with many folds fitted into its internal structure. The folds are covered with enzymes necessary for the chemical reactions that release energy. The internal membranes, called cristae, increase the surface area, allowing for more biochemical activity. They are active in cellular respiration.
Membrane proteins are usually located in close proximity to the cell membrane, oftentimes lodged inside of it. They play an essential role in active transport. There are two types of proteins: peripheral proteins and integral proteins. \Some of these are important conduits for ions, molecules, and other substances.
Ribosomes are small, circular organelles that are numerous in a cell. They are engaged in the synthesis of proteins that will be exported from the cell to be used by different organs of the body.
Chloroplasts produce food for the cell and are only found in plant cells and a few protists. They participate in photosynthesis and contain the green pigment chlorophyll which uses sunlight to make sugars. Inside the chloroplasts are several flat membranous sacs called thylakoids which contain the chlorophyll. Within these sacs, photosynthesis takes place.
Microtubules are thick, sturdy spirals composed of small subunits called tubulin. They play a role in cell division, connecting to chromosomes and helping them split and move to the new daughter cell. Microtubules also combine to form cilia or flagella, which help push the cell along.
Centrioles play a crucial part in meiosis or mitosis. They are found near the nucleus and are made of microtubules. They are often found in pairs, traveling towards the poles of the nucleus when it is time for the cell to divide.
Microfilaments are long, skinny proteins that work with microtubules to create the structure that allows the cell to keep its shape and move. With the microtubules, they combine to form the cytoskeleton of the cell.
The Golgi complex gathers simple molecules and merges them to make more complex molecules. It takes these large molecules and receives vesicles and fluids’ from the ER. The vesicles are then rewrapped and transported to the cell membrane or either stored for later use.
Vacuoles are storage compartments found both in animal and plant cells. They may store food, nutrients, and waste products. Plants may use vacuoles to store water and they also help support the plant.
Peroxisomes contain oxidizing enzymes. These enzymes make certain toxic substances harmless by adding oxygen to them. They are very similar to lysosomes. They digest fatty acids and amino acids, aid in the breakdown of alcohol, and play a role in cholesterol synthesis.
Chromosomes hold the information essential to the cell’s growth and reproduction. They are composed of segments of DNA called genes. Until it is time for the cell to reproduce, they usually remain uncoiled as loose strands called chromatin.
Lysosomes contain enzymes created by the cell and digest food or foreign materials. They are specialized vesicles that break down complex molecules. The enzyme proteins are first made in the ER and are then packaged in a vesicle and transported to the Golgi apparatus.
