Chapter 7: Life at the Edge: Protecting the Cell

# Chapter 7: Life at the Edge: Protecting the Cell Since Forever ## Prepared by: MR. KEVIN FRANCIS E. MAGAOAY Faculty, SHS Biology Department ## Learning Objectives: - Describe the structural components of the plasma membrane and relate the structure to its function - Describe each transport me...

# Chapter 7: Life at the Edge: Protecting the Cell Since Forever ## Prepared by: MR. KEVIN FRANCIS E. MAGAOAY Faculty, SHS Biology Department ## Learning Objectives: - Describe the structural components of the plasma membrane and relate the structure to its function - Describe each transport mechanism - Enumerate important materials that enter and exit the cell and identify the transport mechanism used to move them - Define tonicity and its effects on the cell ## Overview: - Review of the structure and components of the plasma membrane - Transport mechanism ## Meet the Plasma Membrane The image is of the plasma membrane labeled showing its main components: - Protein Channel - Globular Protein - Glycoprotein - Cholesterol - Glycolipid - Integral Protein - Surface Protein - Peripheral Protein - Filaments of the cytoskeleton - Alpha-Helix protein - Hydrophobic tails - Extracellular fluid - Carbohydrate - Hydrophilic heads - Phospholipid bilayer - Phospholipid molecule ## Plasma Membrane The plasma membrane: - Follows a FLUID MOSAIC MODEL - Selectively permeable - A film only 8nm thin - It would take around 8000 plasma membranes to equal the thickness of a sheet of paper ## Discovery of the Plasma Membrane - The existence of the plasma membrane was discovered in the 1890s and its chemical components were discovered in 1915. - In 1935, Hugh Davson and James Danielli theorized that the structure of the plasma membrane resembles a sandwich. - In 1972, Garth L. Nicolson proposed the Fluid Mosaic Model. ## Components of the Plasma Membrane | Component | Function | |---|---| | Phospholipid | Main fabric of the membrane | | Cholesterol | Cell insulation | | Protein | Transport of substances through the membrane and cell recognition | | Carbohydrates | Cell recognition | ## Phospholipid - Composed of 3 carbon glycerol backbone with two fatty acid molecules attached to carbon 1 and 2, and a phosphate containing group attached to the third carbon. - Amphipathic, has hydrophilic and hydrophobic regions. ## Membrane Proteins ### Integral Proteins - Penetrate the hydrophobic core of the plasma membrane. - Many are transmembrane that completely span the plasma membrane. ### Peripheral Proteins - Not embedded in the membrane at all. - Found on the periphery or on the sides of the membrane. ## Membrane Carbohydrates ### Glycolipids - Sugar chains covalently bonded to lipids ### Glycoproteins - Sugar chains covalently bonded to proteins ## Functions of Membrane Proteins and Carbohydrates ### Transport - A protein that spans the membrane may provide a hydrophilic channel across the membrane. ### Enzymatic Activity - A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. ### Signal Transduction - A protein built into the membrane may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. ### Cell to Cell Recognition - Some glycoproteins serve as identification tags that are specifically recognized by membrane proteins of other cells. ### Intercellular Joining - Membrane proteins of adjacent cells may hook together in various kinds of junctions such as gap junctions and tight junctions. ### Attachment to the cytoskeleton/ECM - Microfilaments or other elements of the cytoskeleton may have noncovalent bind to membrane proteins, a function that helps maintain cell shape. ## Classification of Transport Proteins - **Uniporter:** Transports substances in a unidirectional manner depending on the concentration gradient. - **Symporter:** Transports different types of molecules in the cell membrane at the same time. - **Antiporter:** Transport different types of molecules in the cell membrane in the opposite direction at the same time. ## Cell Transport Mechanism - Refers to the various ways by which different substances can be allowed to enter the cell. - If the exchange of substances occurs in the direction of the concentration gradient, there is no need for energy output from external factors. - If the exchange of substances occurs against the direction of the gradient, inputs of extra metabolic energy are required. ## Cell Transport Mechanism (Diagram) The image is of a diagram showing the cell transport mechanism, it's branches and main points: - **Passive Transport**: - Diffusion - Osmosis - Facilitated Diffusion - **Active Transport**: - Primary Active Transport - Secondary Active Transport - Bulk or Vesicular Transport - Endocytosis and Exocytosis - Phagocytosis and Pinocytosis - Receptor-mediated endocytosis ## Key Terms ### Solute - Refers to the substance that needs to be dissolved, catalyzed or broken down in order to be utilized by the cell. ### Solvent - Refers to the substance that will dissolve the solute such as water which is the versatile solvent. ### Concentration Gradient - Refers to how solute particles will move through a gas or solution from an area with a higher number of particles to one with a lower number of particles while being separated by a membrane. ## Passive Transport - Movement of a substance across a membrane with no energy investment. ## Diffusion - Happens when particles move from an area of high concentration to an area of low concentration. ## Factors that Affect Diffusion - Extent of the concentration gradient - Mass of the molecules diffusing - Temperature - Solvent density - Solubility ## Osmosis - The diffusion of free water across a selectively permeable membrane. - The diffusion of solvent from an area of lower solute concentration to an area of higher solute concentration. ## Osmosis in Action ### Tonicity - The ability of the surrounding solution to cause a cell to lose or gain water. ## Osmosis in Action (Diagram) The image is a diagram showing the osmosis in action with 3 different solutions: - **Hypertonic**: the solution has higher solute concentration than the cells - **Isotonic**: the solution has the same solute concentration as the cells - **Hypotonic**: the solution has lower solute concentration than the cells ## Facilitated Transport The image shows an illustration of facilitated transport, where a protein channel and carrier proteins help in the transport of molecules across the cell membrane. ## Active Transport - Uses energy to move solutes against their gradients - To pump a solute across a membrane against its gradient requires work, the cell must expand energy - Uses carrier protein ## Primary Active Transport - Binding of three Na ions to their active sites on the pump which are bound to ATP. - ATP is hydrolyzed leading to phosphorylation of the cytoplasmic side of the pump. - Phosphorylation is caused by the transfer of the terminal group of ATP to the transport protein making ATP become ADP. ## Secondary Active Transport - Once the Na ions are liberated, the pump binds two molecules of K to their respective binding sites causing dephosphorylation of the pump. - Two K ions are transported into the cell. ## Endocytosis/Exocytosis The image is of a diagram showing the process of endocytosis and exocytosis. Endocytosis is the process by which cells take in substances from the outside environment, while exocytosis is the process by which cells release substances into the outside environment. ## Phagocytosis The image is of a diagram showing the process of phagocytosis, where the membrane of a cell engulfs a solid particle and encloses it within a vesicle. ## Pinocytosis The image is of a diagram showing the process of pinocytosis, where the membrane of a cell engulfs a droplet of fluid and encloses it within a vesicle. ## Receptor-Mediated Endocytosis The image is of a diagram showing the process of receptor-mediated endocytosis, where specific molecules bind to receptors on the cell membrane, triggering the formation of a vesicle that encloses the molecules.