Membrane Dynamics and Transport Systems

Membrane Dynamics

CLOs (Course Learning Outcomes)

• Understand communication mechanisms, integration, and homeostasis involved in various bodily functions.
• Regulation of blood pressure, breathing, urine concentration, energy balance, and body movements.
• Describe coordinated responses of physiological systems in maintaining homeostasis and regulating change and growth.
• Propose and execute lab experiments in physiology, analyzing and interpreting results effectively.
• Recognize and explain the principle of homeostasis and the use of feedback loops in controlling human physiological systems.
• Understand basic physiological principles of cells and tissues, and body systems

Objectives

• Understand different types of transport systems.
• Identify different types of passive and active transport systems, including their characteristics.
• Differentiate between endocytosis and exocytosis.
• Differentiate between ligand and voltage-gated channels.
• Differentiate between uniport, symport, and antiport.
• Differentiate between hypotonic, isotonic, and hypertonic solutions.

Transport Systems

• Cells use three main transport systems: passive transport, active transport, and endocytosis/exocytosis.

Passive Transport

• Passive transport requires no energy because the solute moves down its concentration gradient, from high to low concentration.
• The two types of passive transport are diffusion and osmosis.

Active Transport

• Active transport requires energy because the solute moves against its concentration gradient, from low to high concentration.
• The two types of active transport are primary transport and secondary transport.

Endocytosis/Exocytosis

• Endocytosis/exocytosis transports large molecules.

Diffusion

• Solute moves from an area of high concentration into an area of low concentration.
• Diffusion stops once equilibrium is reached.
• There are three types of diffusion: Lipid/Simple, Channel, and Facilitated.
• Lipid/Simple diffusion involves lipid-soluble substances.
• Channel diffusion uses membrane proteins.
• Facilitated diffusion uses membrane proteins.

Channel Diffusion

• Uses carrier proteins which are hollow in the middle
• Primary function is transporting ions and water in and out of cells.
• Two types: non-gated/leaky channels and gated channels.
• Non-gated/leaky channels are for water transport.
• Gated channels have doors that open during transportation and are used for ion transport.

Gated Channels

• Ligand-gated channels have a receptor that requires a ligand to bind for the gate to open.
• Once the gate is open, ions are transported.
• For voltage-gated channels, the membrane potential must reach a specific value to open the gate.
• The specific voltage value differs for all channels.
• Once the voltage value is reached, the door opens and ions can be transported.

Lipid & Facilitated Diffusion

Lipid Diffusion

• Substances that are lipid soluble can cross the plasma membrane without assistance.
• Examples of substances that can pass through lipid diffusion include O2, CO2, and urea

Facilitated Diffusion

• Facilitated Diffusion uses membrane proteins that have the ability to change shape to transport molecules.
• These proteins change shape during the transport process, moving substances in and out of cells.
• Facilitated diffusion is used for large molecules like glucose and amino acids.
• Facilitated diffusion enables the transport of several different substances.

Question 1

• A diabetic drug binds to channels on beta cells, opening them and allowing ion transport.
• The type of channel the drug binds to is a ligand channel.

Osmosis

• Water moves from low to high solute concentrations.
• Solute concentration changes due to water movement.
• Concentration increases in areas from which water leaves.
• Concentration decreases in areas where water enters.
• Osmosis stops once equilibrium is reached due to no more driving force.

Tonicity

• Tonicity refers to the concentrations of solutions based on the amount of solute present.
• There are three classifications of solutions based on tonicity: hypotonic, isotonic, and hypertonic.

Hypotonic solution

• Contains a low amount of solute.

Isotonic solution

• Has an equal amount of solute.

Hypertonic solution

• Contains a high amount of solute.

Effect of Osmosis on Animal Cells

• Red blood cells (RBCs) were added to three solutions with unknown tonicities to demonstrate osmotic effects.
• In a hypertonic solution, there is more solute outside the cell, causing water to leave the cell.
• In an isotonic solution, the amounts of solute inside and outside the cell are equal, so there is no net water movement.
• In a hypotonic solution, there is more solute inside the cell, causing water to enter the cell.
• In an isotonic solution, the size of RBCs stays the same due to equal solute concentration and balance in water movement.
• In a hypertonic solution, RBCs decrease in size because water moves out of the cell due to higher external solute concentration.
• In a hypotonic solution, RBCs increase in size because water moves into the cell due to higher internal solute concentration.

Primary Active Transport

• Uses a direct form of energy (ATP) to transport solute and goes from low to high solute concentration.

Sodium-Potassium Pump

• All cells have a sodium-potassium pump.
• The sodium-potassium pump is a primary active transport system.
• Sodium and potassium are transported by the sodium-potassium pump.
• Sodium (Na+) levels are high outside the cell.
• Potassium (K+) levels are low outside the cell.
• Potassium (K+) levels are high inside the cell.
• Sodium (Na+) levels are low inside the cell.
• The pump transports 3 Na+ out and 2 K+ in.

Secondary Active Transport

• Uses an indirect form of energy (not ATP).
• The first molecule moves down its concentration gradient.
• Energy is collected to transport the second molecule against its concentration gradient.

Uniport, Symport, Antiport

• These terms can describe passive or active transport.
• Uniport involves one type of solute transported in one direction.
• Symport involves two types of solute transported in the same direction.
• Antiport involves two types of solute transported in opposite directions.

Endocytosis/Exocytosis

• Transportation occurs via vesicle formation.
• Endocytosis involves vesicles transporting material into the cell.
• Exocytosis involves vesicles transporting material out of the cell

Question 2

• A pump in a distal tubule cell transports sodium and chloride into the cell using ATP.
• This pump would be classified as primary active transport.

Question 3

• A pump that transports sodium and chloride into a distal tubule cell using ATP is classified as symport.

Total Body Water

• Splits into two main compartments: Intracellular Fluid, which is the Fluid inside the cell Concentration of potassium is high in intracellular fluid Extracellular Fluid, which is Fluid outside the cell Concentration of sodium is high in extracellular fluid Split into 2 compartments: Interstitial Fluid: fluid between cells Plasma: fluid within blood vessels