Cell Biology PDF

# Cell Biology ## Dr. Maggie Amer ## Cell Structure - **1-Cell Membrane:** This is a layer that surrounds the cell. It is composed of a phospholipid bilayer and various proteins. The cell membrane controls what goes in and out of the cell. - **Plasma Membrane:** A thin membrane that enclose...

# Cell Biology ## Dr. Maggie Amer ## Cell Structure - **1-Cell Membrane:** This is a layer that surrounds the cell. It is composed of a phospholipid bilayer and various proteins. The cell membrane controls what goes in and out of the cell. - **Plasma Membrane:** A thin membrane that encloses the cell and separates it from its surroundings. It regulates the passage of molecules into and out of the cell. - **Nuclear Envelope:** A double membrane that surrounds the nucleus. It regulates the passage of molecules between the nucleus and the cytoplasm. - **Nuclear Pore:** Small channels in the nuclear envelope that allow for the transport of molecules between the nucleus and the cytoplasm. - **Chromatin (DNA):** The genetic material of a cell, which is composed of DNA and protein. - **Nucleolus:** A dense region within the nucleus that is involved in the synthesis of ribosomes. - **Centriole:** A small, cylindrical structure that is involved in the organization of microtubules. - **Intermediate Filament:** A type of protein filament that provides structural support to the cell. - **Ribosome:** A small, granular structure that is involved in protein synthesis. - **Rough Endoplasmic Reticulum(RER):** A network of membranes that is studded with ribosomes. It is involved in the synthesis and processing of proteins. - **Lysosome:** A small, membrane-bound organelle that contains enzymes that break down cellular waste products. - **Flagellum:** A whip-like structure that helps the cell to move. - **Cytoplasm:** The jelly-like substance that fills the cell and surrounds the organelles. - **Microtubule:** A type of protein filament that provides structural support to the cell and is involved in cell movement. - **Smooth Endoplasmic Reticulum(SER):** A network of membranes that is not studded with ribosomes. It is involved in the synthesis of lipids and steroids. - **Free Ribosome:** A ribosome that is not attached to the ER. These ribosomes synthesize proteins that are used within the cell. - **Mitochondrion:** A bean-shaped organelle that is responsible for the production of ATP (energy). - **Vesicle:** A small, membrane-bound sac that transports substances throughout the cell. - **Golgi Complex:** A stack of flattened, membrane-bound sacs that are involved in the sorting and packaging of proteins and lipids. - **2- Nucleus:** The control center of the cell and is responsible for storing genetic information. It is surrounded by a double membrane called the nuclear envelope. - **3-Cytoplasm:** A gel-like substance that fills the cell and surrounds the organelles. ## Organelles - **Membranous:** - **Mitochondria:** These are the powerhouses of the cell, responsible for the production of ATP (energy). Mitochondria are bean-shaped organelles with a double membrane, the inner membrane folded into cristae. - **Shape:** Variable-Granular, Rod-like - **Structure:** A membranous vesicle surrounded by double walled membrane. - **Outer Membrane:** Smooth. - **Inner membrane:** Projects inwards cavity. It is found in the form of shelves called "cristae". - **Function:** ATP production. - **Note:** The number of mitochondria and cristae are directly proportional with cell activity. - **Endoplasmic Reticulum(ER):** A network of interconnected membranes that extend from the nuclear membrane through the cytoplasm. There are two types: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). - **Structure:** Series of intercommunicating membranes channels in the form of tubules or cisternae. - **Rough Endoplasmic Rerticulum(RER):** - **Function:** Synthesizes, stores, and delivers proteins. - **Smooth Endoplasmic Rerticulum(SER):** - **Function:** 1. **Lipid Synthesis:** Steroid hormones. 2. **Glycogenesis:** Deposited glycogen in liver and muscle. 3. **Calcium Storage:** For muscular contraction. 4. **Drug Detoxification.** - **Golgi Apparatus(GA):** A stack of flattened, membrane-bound sacs called cisternae. These are involved in the processing and packaging of proteins and lipids. - **Structure:** It is composed of different types of sacs. - **1- Sacculus (Flattened Vesicles):** Arranged in sacs called "Cisterna," one above the other with two faces: - **Cis (immature) Face:** Towards ER. - **Trans (mature) Face:** Towards the outside of the cell. - **2-Transfer Vesicle (micro vesicle):** These arise from the RER and carry synthesized proteins. They migrate to the cis face of the GA, where they discharge their contents. - **3-Secretory Vesicle (macrovesicle):** Arises from the sacculus of the trans face. These separate as secretory vesicles containing the enzymes or other proteins that were synthesized. - **Secretory Vesicle may:** - Migrate to the cell membrane and discharge enzymes outside. - Remain in the cytoplasm as a lysosome. - **Function:** 1. Secretory activity of the cell. 2. **Formation of Acrosome** in sperm. This helps facilitate the penetration of sperm into the ovum. 3. **Formation of Lysosome.** - **Lysosome (Ly):** Small, membrane-bound organelles that contain enzymes that can break down waste products, old organelles, and other cellular debris. - **Structure:** Membranous vesicles that contain hydrolytic enzymes, such as proteases, lipases, and nucleases. - **Function:** Digestion of cellular waste products. - **Synthesis:** They are synthesized by the RER and then move to the GA by transfer vesicles. - **Location:** They are present in all cell types. - **Appearance:** They do not appear under a light microscope but appear as rounded vesicles under an electron microscope. - **Types:** - **Primary Lysosome:** Newly synthesized lysosomes with hydrolytic enzymes. The primary lysosome may fuse with a phagosome or autophagosome. - **Secondary Lysosome:** They are formed by fusion of a primary lysosome with a phagosome or autophagosome. They are involved in the digestion of cellular debris and waste products. - **Function:** 1. **Heterophagy:** Digestion of foreign particles. 2. **Autophagy:** Digestion of some organelles (e.g., mitochondria) to get energy during starvation. 3. **Autolysis:** Digestion of the whole cell. This happens when the cell is damaged or is no longer needed. The lysosomal membrane ruptures, releasing the lysosome's enzymes, which digest the cell. - **Fate:** - **Phagosome (Phagocytic Vesicles):** A vesicle that engulfs foreign particles. - **Residual body:** A leftover body after digestion by lysosome. - **Secondary Lysosome (2ry LY):** A vesicle formed by the fusion of a primary lysosome and a phagosome or autophagosome. - **Exocytosis:** The process of releasing a substance from the cell. - **Autophagic Vacuole:** A vesicle that contains old cytoplasmic content such as mitochondria. - **Non-Membranous:** - **Ribosome (Rb):** Found attached to the RER (Rough Endoplasmic Reticulum) or free in the cytoplasm. These are responsible for the synthesis of proteins. They themselves consist of two subunits: a large subunit and a small subunit. The large subunit contains three rRNA molecules whereas the small subunit contains one rRNA molecule. - **Attached to the RER:** These ribosomes synthesize proteins that are either secreted outside the cell or become part of membranes. - **Free:** These synthesize proteins for use within the cell. Examples of these proteins include mitochondrial, matrix, and nuclear proteins. - **Centrioles:** Small cylindrical structures found near the nucleus that are essential for cell division. They form the spindle fibers that pull chromosomes to the poles during cell division. Two centrioles at right angles to one another come together to form a centrosome. Each centriole is made up of nine bundles of microtubules arranged in a cylinder like a cylinder. Each bundle is made up of 3 microtubules. So each centriole contains 9 x 3 = 27 microtubules. - **Cytoskeleton:** This is a network of protein fibers found in the cytoplasm that gives shape to the cell, helps move organelles, and aids in cell division. The cytoskeleton has three major components: 1. **Microfilaments:** These are made up of the protein actin. They are the thinnest filaments and are involved in cell movement, contraction, and cytokinesis. 2. **Intermediate Filaments:** These are made up of various proteins. They are of intermediate thickness and are involved in providing structural support to the cell. 3. **Microtubules:** These are made up of the protein tubulin. They are the thickest filaments and are involved in cell movement, organelle transport, and the formation of the spindle fibers during cell division. This information about different cell structures and their functions is presented in a more structured format. Please let me know if you need any further edits.