The Cell: Modifications and Membrane PDF

THE CELL: MODIFICATIONS JAIRA ANGELINE T. BALISI Department of Environmental Science College of Science Tarlac State University WHY DO CELL NEED TO MODIFY ITS PARTS? ▪ To survive and have a comprehensive systematic physiology, organisms have developed some modifications in their struc...

THE CELL: MODIFICATIONS JAIRA ANGELINE T. BALISI Department of Environmental Science College of Science Tarlac State University WHY DO CELL NEED TO MODIFY ITS PARTS? ▪ To survive and have a comprehensive systematic physiology, organisms have developed some modifications in their structure. ▪ These modifications facilitate the acquisition of their needs and their adaptation to a changing environment: carry out specialized functions ▪ E.G., Mangroves as pneumatophores = plants that has specialized above ground roots Specialized Plant Cells Root cells are specialized in plant - cells that absorb dissolved minerals and water from the ground. Root cells grow in long lengths called root hairs to increase the surface area of the root system. This also helps anchor the plant. Xylem cells (Roots/Stem) - transport water from the roots in the upward direction. Phloem cells (Root/Stem)- transport nutrients in both directions to reach all parts of the plant. Guard Cells (epidermis) - open and close to allow the transfer of gases with the atmosphere as well as the transpiration of water Specialized Animal Cells ▪ Red Blood Cells - found in animals that transport oxygen throughout the body. Since transport is their primary function, they do not need a nucleus. ▪ Muscle cells - are long, fibrous cells that can contract. They allow animals to move and allow their organs to function in circulation as well as digestion. ▪ Epithelial cells - are the cells that line the outside, as well as the inside, of your body. They are the cells that make up your skin. Skin epithelium is located just below the surface of your skin. The epithelial cells are responsible for making new cells. Apical Modifications ▪ Cilia - membrane-covered extensions of the entire apical surface. They beat in waves, often moving a surface coat of mucus and trapped materials. ▪ Stereocilia - form single "finger-like“ projections that may be branched and have more of the characteristics of the cellular membrane proper. ▪ Flagella - also concerned with movement. ▪ Microvilli - plasma membrane- covered extensions of the cell surface. Their cores are composed of parallel actin microfilaments; these are anchored in a dense mat of filaments in the apical cytoplasm called the terminal web. ▪ Extracellular matrix - intricate network composed of an array of multidomain macromolecules organized in a cell/tissue-specific manner. Basal Modification ▪ Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. Lateral Modification ▪ Tight junctions – found between cells as connected areas of the plasma membrane that stitch cells together. ▪ Adherens junctions - join the actin filaments of neighboring cells together. ▪ Gap junctions - clusters of intercellular channels that allow direct diffusion of ions and small molecules between adjacent cells THE PLASMA MEMBRANE JAIRA ANGELINE T. BALISI Department of Environmental Science College of Science Tarlac State University What is the organelle that allows only essential substances to pass through? A. Vesicles B. Cell Wall C. Proteins D. Cell Membrane RECALL: ▪ Cell membrane has two functions, what are those? (1) to be a barrier keeping the constituents of the cell in and unwanted substances out and (2) to be a gate allowing transport into the cell of essential nutrients and movement from the cell of waste products  ▪ Hydrophilic heads (facing inside and outside = water-loving) THE PHOSPHOLIPID ▪ Hydrophobic Tail (inside of the heads/facing each other = repel water) BILAYER ▪ Water is very small that it can squeeze between the phospholipids and can enter the cell. How cell membrane allows substances to pass through? INTEGRAL AND PASSIVE AND ENODCYTOSIS EXTERNAL ACTIVE AND PROTEINS TRANSPORT EXOCYTOSIS STRUCTURES (EMBEDDED) IN THE CELL/PLASMA MEMBRANE: INTEGRAL PROTEINS CHANNEL MARKERS RECEPTORS NOTE: All are made integral protein, and they assist in the entry/exit of (polar) materials in the cell (let it be actively or passively).  1. CHANNELS (Transport Protein) ▪ these are special tube-like structures that allows large molecules to enter the cell. ▪ Some channels are always open, some are open and shut, some are 1 way, and some are 2 way. ▪ What are the three types of channels within the plasma membrane? ▪ Mostly, gate opens in response to a specific stimulus: voltage across the membrane (voltage-gated channels), mechanical stress (mechanically gated channels), or the binding of a ligand (ligand-gated channels).  ▪ All your cells have a protein nametag that says that they are belong to your body. If the cell doesn’t have your nametag, the 2. MARKERS white blood cells (your army soldiers) won’t recognize and will destroy it. ▪ E.g., Sodium Potassium ATPase and Pma1  3. RECEPTORS ▪ these are the special sensing structures. ▪ They are like the cells eye, ears, and mouths. ▪ They communicate to the inside what’s going on the outside. ▪ They are kind of like blobs with antennas. ▪ E.g., The ion channel linked receptor; The enzyme-linked receptor; and The G protein- coupled receptor Special Receptor Protein: Peripheral Membrane Protein ▪ Peripheral proteins are only located in the inner or outer surface of the phospholipid bilayer like floating iceberg = can be an Extrinsic Protein ▪ They are like blobs with antennas made up of carbohydrates. ▪ They can bind to the corresponding ligands to initiate signaling pathways because they have a special sensing structure. ACTIVE V. PASSIVE TRANSPORT Active transport involves the movement of molecules from lower concentration to higher concentration with the use of energy through "pumping" the molecules uphill in concentration. Passive transport involves the movement of molecules from higher concentration to lower concentration and no amount of energy is required.  PASSIVE TRANSPORT (High to Low; No Energy) Diffusion: Concentration gradient is the term for the difference between the concentrations of molecules in the two areas. Facilitated diffusion: It involves the diffusion of solutes through transport proteins but is still passive transport because the movement of the solutes is down the concentration gradient. Osmosis: Diffusion of water molecules through a selectively permeable membrane from higher water concentration to lower water concentration.  ACTIVE TRANSPORT (Low to High; W/ Energy) ▪ NEED OF TRANSPORT PROTEIN - protein pumps; transport the small molecules or small ions across a cell membrane ▪ The larger molecules (E.g., starch) can also be transported actively through the membrane with the help of vesicle transport processes called endocytosis and exocytosis. ENDOCYTOSIS VS. EXOCYTOSIS ▪ EXOCYTOSIS - vesicle attaches to the cell membrane from the inside and then opens to form a pocket, expelling its contents to the outside. ▪ ENDOCYTOSIS – phagocytosis; cell membrane envelope something on the outside and surround it, taking it into the cell. ENZYMES ▪ are proteins that help speed up metabolism or chemical reactions ▪ Membrane-embedded transporters move ions and larger solutes across membranes, receptors mediate communication between the cell and its environment and membrane-embedded enzymes catalyze chemical reactions. Affecting the enzyme activity ▪ Temperature: Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working. ▪ pH: Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Best pH – optimum values ▪ Substrate: Enzymes will work best if there is plenty of substrate. As the concentration of the substrate increases, so does the rate of enzyme activity. However, the rate of enzyme activity does not increase forever.  OXIDATION REDUCTION REACTION ▪ type of chemical reaction that involves a transfer of electrons between two species.