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Endoplasmic Reticulum Roles
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- Structure: The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets, representing a crucial component among various cell organelles.
- It looks like long tubules or round or oblong bags (vesicles).
- The ER membrane is similar in structure to the plasma membrane.
- Types: There are two types of ER– rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
- Functions:
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- The SER helps in the manufacture of fat molecules, or lipids.
- Act as Channel: The function of the ER is to serve as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus.
- Protein Synthesis: The ribosomes are the sites of protein manufacture.
- The manufactured proteins are then sent to various places in the cell depending on need, using the ER.
- In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying many poisons and drugs.
- Framework: The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.
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Golgi Apparatus
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- It is a system of membrane-bound vesicles (flattened sacs) arranged approximately parallel to each other in stacks called cisterns.
- These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.
- Function:
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- Its functions include the storage, modification and packaging of products in vesicles.
- In some cases, complex sugars may be made from simple sugars in the Golgi apparatus.
- The Golgi apparatus is also involved in the formation of lysosomes.
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Lysosomes:
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- Lysosomes are membrane-bound sacs filled with digestive enzymes. These enzymes are made by RER.
- Lysosomes are a kind of waste disposal system of the cell.
- Lysosomes are also known as the ‘suicide bags’ of a cell.
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Mitochondria
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- Powerhouse: Mitochondria are known as the powerhouses of the cell.
- The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.
- ATP is known as the energy currency of the cell.
- The body uses energy stored in ATP for making new chemical compounds and for mechanical work.
- Mitochondria have their own DNA and ribosomes. Therefore, mitochondria are able to make some of their own proteins.
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Plastids
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- Plastids are present only in plant cells.
- There are two types of plastids – chromoplasts (coloured plastids) and leucoplasts (white or colorless plastids).
- Plastids too have their own DNA and ribosomes.
- Chromoplasts containing the pigment chlorophyll are known as chloroplasts.
- Chloroplasts are important for photosynthesis in plants.
- Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.
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Vacuoles
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- Vacuoles are storage sacs for solid or liquid contents.
- Vacuoles are small sized in animal cells while plant cells have very large vacuoles.
- The central vacuole of some plant cells may occupy 50-90% of the cell volume.
- In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.
- In some unicellular organisms, specialized vacuoles also play important roles in expelling excess water and some wastes from the cell.
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