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Let us understand the position of cell organelles in an animal cell in order to
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understand the function of each organelles in a three-dimensional manner. Let's begin with the cell membrane, the outermost boundary in an animal cell. The
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cell membrane is a thin flexible phospholipid bilayer barrier that surrounds the cell and protects it from the environment. As you see here the
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barrier prevents or regulates movement of water and other polar molecules. So
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these are specialized protein channels on cell membrane for exchange of molecules. Next is the cytoplasm. It is a jelly like substance that fills the cell
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and contains all of the cell organelles, composed of water, salts and various
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organic molecules. First let us move to the center of the cell where nucleus is
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located. The nucleus is a double membrane bound organelle. It is a controlling
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center of the cell that contains the cells DNA, the genetic material that
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contains the instructions for building proteins that regulates all cell activities. The nucleus is surrounded by a nuclear envelope as you see here which
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is a double membrane that protects the DNA. Then within the nucleus there is a clearly distinct
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dense spherical structure which is called as nucleolus. So this is the nucleolus. It is made
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up of DNA, RNA and proteins. The DNA in the nucleolus consists of ribosomal DNA often called
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as rDNA genes which encode the ribosomal RNA that is used to build ribosomes or
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nucleolus is involved in ribosome subunit synthesis or it is a ribosome
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production factory. Now as you see the outer nuclear membrane is in continuous
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connection with rough endoplasmic reticulum. Endoplasmic reticulum is a network of tubes that produce, modifies and transports proteins and other
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molecules throughout the cell. It's often the largest organelle that runs throughout the cell in majority of the cells The rough endoplasmic reticulum has ribosomes that is studded on its surface involved in the synthesis of secretory and membrane proteins It is also the
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site of protein folding especially the formation of thysulfide bonds, processing like initial glycosylation and also involved in quality control
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That means misfolded proteins are degraded in ER called as ER associated degradation
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Apart from rough endoplasmic reticulum, there is smooth endoplasmic reticulum where ribosomes
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are absent therefore the surface is smooth. SER is involved in lipid metabolism. It synthesizes
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membrane lipids including phospholipids and cholesterol and also steroid hormones such as
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estrogen and testosterone. SCR is abundant in liver where it is involved in detoxification of
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drugs makes them more soluble and easier to excrete from the body. In muscle cells, ER is called as
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sarcoplasmic reticulum where it stores calcium in its lumen. Now let us back to the organization
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the nuclear membrane is in continuous connection with RER or rough endoplasmic reticulum
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The RNA that moves out from the nuclear membrane that is translated either by ribosomes that is
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present in the cytoplasm or by ribosomes that is studded on the RER or rough endoplasmic reticulum
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so proteins in endoplasmic reticulum is modified processed by RER then that is transferred to
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Golgi apparatus so as you see this RER is also located near the Golgi apparatus the proteins
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received from the RER is modified sorted and packaged at Golgi for delivering to targeted
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destinations. It is called as the sorting center of the cell. As you see here it is made up of
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flattened sacks that is stacked or pouches called cisternae. It has three functionally distinct
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regions The receiving site that is close to RAR which is called as the cis region or reception site of proteins from RAR Then the medial region or the middle region it is called as medial cisternae that is involved in modification addressing or tagging and finally
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the trans scolge or where modified proteins are pinched off as vesicles. The proteins from the RER
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endoscholgy where it is addressed. For example, a protein that is to be targeted to lysosome
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is tagged with manose 6-phosphate. Similarly, a different tag for mitochondrial proteins like that
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Untagged proteins are normally secreted out of the cell by exocytosis. From golgy apparatus
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proteins are packed in vesicles and are transported to different destinations within the cell where
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these vesicles fuse with that organelle releasing the proteins to the inside of that organelle
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The next organelle that is in connection with RER called G is lysosome. Lysosomes are single
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membrane bond sacs of digestive enzymes that break down old and damaged cell parts called
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is autophagy and also involved in extracellular digestion of bacteria or other pathogens that is
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taken inside and this digestive enzyme inside this lysosome break down these pathogenic
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organisms and releases the material. So from nuclear membrane there is a continuous membranous
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connection to RER then to Colg apparatus then digestive enzymes are often fused with lysosomes
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so there is a continuous connection and this forms the endomembrane system of the cell
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The next organelle is the mitochondrion. Mitochondrion are the powerhouses of the
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cell due to its ability to produce energy as ATP by electron transport and oxidative phosphorylation
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This energy fuels all cellular activities. It is also involved in beta oxidation
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then you can see centrioles these are paired barrel shaped organelles that is located in
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the cytoplasm of animal cells they are near to the nuclear envelope centrioles play a role in
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organizing microtubules that serve as the cell skeletal system they are involved in positioning or the locations of nucleus and other organelles within the cell and also involved in production of spindle fibers during cell
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division. In the background you can see a meshwork that is going on and that meshwork
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is called as the cytoskeleton. The cytoskeleton is a complex dynamic network of interlinking
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protein filaments present in the cytoplasm of old cells. The cytoskeleton is responsible for
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contraction, cell motility, movement of organelles and vesicles through the cytoplasm, cytokinesis
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establishment of intracellular organization of the cytoplasm, establishment of cellular polarity and many other function that is essential for cellular homeostasis and survival. It provides
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the structure and shape to the cell. There is one more organelle just like lysosome but with a
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specific function called peroxisomes. They are small membrane-bound organelles which contain oxidative enzymes such as catalase, uric acid oxidase etc. It is involved in the breakdown
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of harmful hydrogen peroxide that is produced in the cell into water and oxygen
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Peroxisomes are also involved in the breakdown of fatty acid molecules called beta oxidation
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In multicellular organisms or animal cells, cilia is present on the surface of the cell
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but functions to move a cell or groups of cells or to help transport fluid or materials past them
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It has different functions within a multicellular organism. For example, the respiratory tract in humans is lined with cilia that keep inhaled dust, smoke
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and potentially harmful microorganisms from entering the lungs. Hope now you know
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the arrangement of different cell organelles within the cell and their function. Take care, stay blessed. Thank you so much for your support
