Membrana Plasmática PDF

## Membrana Plasmática **Function:** - The membrane surrounds the cell, defines its limits, and maintains the essential differences between the cytosol and the extracellular environment. **Structure of Phospholipids:** - **Head:** - Choline - Phosphate - Glycerol - **Tails:** - Sat...

## Membrana Plasmática **Function:** - The membrane surrounds the cell, defines its limits, and maintains the essential differences between the cytosol and the extracellular environment. **Structure of Phospholipids:** - **Head:** - Choline - Phosphate - Glycerol - **Tails:** - Saturated fatty acid - Unsaturated fatty acid (*cis-double bonds*) **Lipid Bilayer:** - It is a structure that can only be seen under an electron microscope. - The most abundant lipids in the membrane are phospholipids. - Phospholipids have a polar head group (with phosphate) and two hydrophobic hydrocarbon tails. - In animals, the tails are made of fatty acids, and they are typically 12-24 carbons long. **Cholesterol** - Along with phospholipids, cholesterol exists in the lipid bilayer. - It functions in the maintenance of the membrane's mechanical stability. - Cholesterol **decreases** fluidity. **Movements in the Membrane:** - Lipids can rotate on their axis. - Lipids can diffuse laterally. - Lipids can flex. - Flip-flop movement is rare and occurs mainly during apoptosis. **Membrane Proteins:** - There are different types: - **Integral proteins:** Pass through the lipid bilayer. These are called transmembrane proteins. - **Peripheral proteins:** Bound to the membrane's lipid surface. - **Lipid-anchored proteins:** Covalently linked to lipid groups. - Proteins can act as: - **Anchors:** Help the proteins pass through the membrane. - **Channels:** Allow the diffusion of water molecules. - **Transporters:** Facilitate the passage of a substance across the membrane. - **Receptors:** Bind to specific molecules. **Transport Across the Membrane** **Proteins of Transport:** - Cells usually have specialized proteins that facilitate the movement of small water-soluble molecules. - There are two main types of transport: - **Transporters:** bind to the molecule and change conformation. - **Channels:** form a pore through which substances can pass. **Characteristics of the Chemical Composition of Cells:** - The speed at which a molecule crosses a lipid bilayer depends on its size and solubility. **Diffusion of Water Molecules:** - Water molecules rapidly diffuse across the plasma membrane through **aquaporins**. - **Osmosis:** Movement of water from a less concentrated solution to a more concentrated solution. **Osmosis in Different Conditions:** - **Isotonic:** No net movement of water. - **Hypotonic:** Water diffuses into the cell causing it to swell. - **Hypertonic:** Water diffuses out of the cell causing it to shrink. **Active Transport:** - Requires energy. - There are three types: - **Uniporters:** Transport one molecule across the membrane in one direction. - **Symporters:** Transport two molecules across the membrane in the same direction. - **Antiporters:** Transport two molecules across the membrane in opposite directions. **Sodium-Potassium Pump:** - This is a type of active transport protein. - Uses ATP energy to move sodium ions out of the cell and potassium ions into the cell. - The pump helps maintain the concentration gradient of these ions. **Mitochondria and Chloroplast:** **Mitochondria:** - Occupies 20% of the cytoplasm, responsible for cellular respiration. - It oxidizes pyruvate in the presence of oxygen. - Produces ATP. **Anerobic Respiration** - Occurs in the absence of oxygen, produces a lower amount of ATP. **Structure of Mitochondria:** - **Outer membrane:** Smooth. - **Inner membrane:** Folded into cristae. - **Matrix:** The space between the inner and outer membranes. - **Intermembrane space:** The space between the two membranes. **Origin of Mitochondria:** - They originated from aerobic bacteria. - They have their own DNA. - They replicate independently of the nucleus. **Mitochondrial DNA:** - Circular. - Inherited through the maternal lineage. **Role of the Inner Mitochondrial Membrane on ATP Production:** - It is a barrier that prevents the free diffusion of most substances across the membrane. - It has high concentrations of proteins involved in ATP synthesis. - It is the site of the electron transport chain and ATP synthase. **Components of the Cell** **Four main families of molecules:** - **Sugars:** They provide energy and building blocks for other molecules. - **Fatty acids:** They are the building blocks of fats, oils, and phospholipids. - **Amino acids:** They are the building blocks of proteins. - **Nucleotides:** They form DNA and RNA, and they serve as energy carriers. **Glycerol and Phosphate:** - Are components of phospholipids. **Fatty Acids:** - Can be saturated or unsaturated. - **Unsaturation** refers to the presence of double bonds. **Proteins:** - Formed by the assembly of amino acids. - Stabilized by peptide bonds. **Nucleotides:** - Composed of a sugar, a phosphate group, and a nitrogenous base. **The Importance of the Membrane:** - The **plasma membrane** regulates what enters and leaves the cell. - It is a barrier that protects the cell from its surroundings. - It allows the cell to communicate with its environment. **Specializations of the Membrane:** - **Microvilli:** Finger-like projections of the plasma membrane. Increase the surface area of the cell, which increases absorption. - **Stereocilia:** Long, non-motile projections of the plasma membrane. They are found in the epididymis and inner ear, and they are involved in absorption and sensory transduction.