MPP Lecture 5 - Cellular Membranes PDF

1. Describe the relative composition and size of body fluid compartments. - Body is comprised of ~55-60% fluid, with the remaining mass being solid tissues such as vessels and organ tissue. - All cells are surrounded by extracellular fluid. - Cells within the circu...

1. Describe the relative composition and size of body fluid compartments. - Body is comprised of ~55-60% fluid, with the remaining mass being solid tissues such as vessels and organ tissue. - All cells are surrounded by extracellular fluid. - Cells within the circulation are surrounded by blood/plasma - Cells outside the circulation are surrounded by interstitial fluid - When talking about intracellular fluid, this is fluid inside all cells, regardless of location (interstitial vs blood/plasma) ECF: high in Na+, Cl-, Ca2+, HCO-3 ICF: high in K+, free protein 2. Explain the structure of the plasma membrane, including its lipid bilayer, cholesterol content, and associated proteins, emphasizing how these components contribute to membrane fluidity and cellular homeostasis. I. Overview of the Plasma Membrane Function: Acts as a barrier, gateway for cellular communication, and regulator of cellular homeostasis. Composition: three key lipids 1. Phospholipids 2. Cholesterol 3. glycolipids II. Lipid Bilayer Structure: ○ Composed mainly of phospholipids, a phosphorylated glycerol backbone (head region) and two fatty acids (tails) ○ Phospholipids: Have hydrophilic heads (water-attracting) and hydrophobic tails (water-repelling). ○ Arrangement: Hydrophobic tails face inward, hydrophilic heads face outward. Function: ○ Creates a semi-permeable barrier, allowing selective entry and exit of substances. ○ Fluidity is crucial for: Movement of molecules within the membrane. Proper functioning of membrane proteins. III. Cholesterol  Structure: ○ Interspersed within the phospholipid bilayer. Function: ○ Temperature Regulation: High temperatures: Prevents the membrane from becoming too fluid, maintaining stability. Low temperatures: Prevents the membrane from becoming too rigid, ensuring flexibility. ○ Role in Fluidity: Modulates the membrane's fluidity, ensuring it is balanced and functional across different environmental conditions. IV. Associated Proteins Types: ○ Integral Proteins: Embedded within the lipid bilayer; often span the membrane, ex: pores,channels,carriers ○ Peripheral Proteins: Loosely attached to the membrane surface or to integral proteins, associated with ICF or ECF surfaces Functions: ○ Transport ○ Signal Transduction ○ Cell Recognition ○ Structural Support V. Contribution to Cellular Homeostasis Cellular Homeostasis: ○ The membrane's selective permeability, controlled by its lipid and protein composition, allows: Regulation of internal environment. Control of ion concentrations. Proper nutrient intake and waste elimination.  3. Compare and contrast diffusion and osmosis, and describe their roles in cellular transport. DIFFUSION Net overall movement of particles from a region of higher concentration to a region of lower concentration. This is a passive process that uses kinetic energy from the random movement of particles. OSMOSIS Movement of water across a semi-permeable membrane in response to a solute concentration gradient—water will move toward higher solute concentration. Concentration differences of impermeable solutes between the ICF and ECF establish osmotic pressure differences, and it is this pressure difference that causes water to move. Osmosis will create a volume change; HOWEVER, the diffusion of solutes does not cause a volume change. 4. Analyze the mechanisms and transport kinetics of simple diffusion, facilitated diffusion, and active transport (primary and secondary) for solute and ion movement across the plasma membrane. Simple Diffusion: Passive, driven by concentration gradients, no saturation, rate influenced by permeability, temperature, and surface area. Facilitated Diffusion: solute moves across the membrane with assistance of integral proteins (channels, carriers) down a concentration gradient, without the expenditure of cellular energy (passive) Primary Active Transport: ATP-dependent, moves solutes against gradients, can reach saturation (Vmax), rate influenced by ATP levels and transporter functionality. Secondary Active Transport: Gradient-driven (indirectly ATP-dependent), moves solutes against gradients via co-transport, can reach saturation (Vmax), rate influenced by the electrochemical gradient and transporter availability. 5. Differentiate between the functions and energy requirements of integral membrane proteins (pores, channels, and carriers), including their roles in facilitated diffusion and active transport. I. Pores  Function: a. Structure: Pores form open, non-selective passages through the membrane, allowing the free diffusion of specific small molecules (usually water or ions). b. Example: Aquaporins are pores that facilitate the movement of water across the membrane. c. Role in Transport: Primarily involved in simple diffusion or osmosis, allowing substances to move along their concentration gradient. Energy Requirements: d. No Energy Required: Pores do not require energy (ATP) since they facilitate passive transport, allowing molecules to move down their concentration gradient. II. Channels Leak-Ion channels e. Function: Ion movement is passive and dependent on a concentration gradient. f. Structure: Always open, no gates, no conformational states, permeability is constant g. Example: Na+ and K+ leak channels are required to maintain the resting membrane potential. Energy Requirements: h. No Energy Required: Passive movement of ions means that no ATP is required. Movement of ions is dependent on the concentration gradient of a specific ion. Ions will only move from a region of high concentration to low concentration. Gated-Ion Channels Function: i. Structure: One gate with sensors that respond to specific stimuli: 1. voltage/electrical 2. chemical/ligand 3. mechanical/force/stretch  j. Example: Ion channels (e.g., sodium, potassium, calcium channels) are critical for maintaining ion gradients and electrical activity in cells. k. Role in Transport: Opening and closing gates is called “gating” and represents different conformational states. Energy Requirements: l. No Energy Required: Channels operate through facilitated diffusion, a passive process that does not require ATP. However, the movement is still driven by the concentration or electrochemical gradient. FINISH FLSSHCARDS FOR THESE BELOW III. Carriers (Transporters) Function: m. Structure: Have at least two gates. Carriers bind to specific molecules on one side of the membrane, undergo a conformational change, and release the molecule on the other side. This process is often slower than channel-mediated transport. n. Types: i. Facilitated Diffusion Carriers: Assist in the passive movement of molecules down their concentration gradient without the use of energy. ii. Active Transport Carriers: Move molecules against their concentration gradient, requiring energy (usually ATP). o. Role in Transport: i. Transport kinetics: speed limit for how much solute can be transported across the membrane by carrier-mediated transport. ii. Transport maximum (Tm): transport rate when saturation occurs. Energy Requirements: p. Facilitated Diffusion Carriers: i. No Energy Required: Like channels, these carriers operate passively, moving molecules down their concentration gradient. ii. Example: The glucose transporter (GLUT) facilitates glucose uptake into cells based on its concentration gradient. q. Active Transport Carriers: i. Energy Required: These carriers use ATP to actively transport molecules against their concentration gradient. ii. Primary Active Transport: Directly uses ATP to pump molecules across the membrane. Three “P pumps”: 1. –Na+ K+ ATPase 2. –Ca2+ ATPase 3. –H+ K+ ATPase (proton pump) iii. Secondary Active Transport: Uses the energy stored in an electrochemical gradient created by primary active transport to move other molecules (e.g., sodium-glucose cotransporter). 1. CO-TRANSPORTER (symports) a. Move two molecules in the same direction across the membrane. 2. COUNTER-TRANSPORTER (exchangers, antiporters) a. Move two molecules in opposite directions across the membrane.