Hydrophobic Interactions
Acid tails align to form a hydrophobic region.
Interaction with nonpolar molecules like glucose and sucrose due to carbon-oxygen bonds, despite being large molecules.
Passive Diffusion
Small molecules like nitrogen gas can pass through membranes unhindered.
After achieving equilibrium across membranes, molecules will continue to move due to diffusion.
Role of Glycoproteins
Serve in mechanical protection and cell recognition.
Formed by sugars linked to lipids/proteins (glycosylation).
Polar Molecules
Small polar molecules (e.g., water) can cross membranes depending on concentration differences.
Despite cells being 70% water, extracellular environments often have much higher water concentrations.
Water Movement
Water tends to move into cells due to concentration gradients.
Concentration differences dictate the movement of water into cells despite large intracellular concentrations.
Large Molecules
Uncharged large molecules like glucose struggle to move across cell membranes without assistance.
Special protein channels aid in transporting substances like glucose across membranes.
Ions and Membrane Permeability
Fully charged ions cannot pass through biological membranes easily.
Ionic forms of salts prevent crossing under normal conditions without damaging the membrane.
Forces Influencing Transport
Chemical Gradient: Concentration differences drive movement across membranes.
Electrical Gradient: Charges influence ion movement, preventing certain ions from moving in unfavorable directions.
The combined influence is known as the Electrochemical Gradient.
Diffusion Driven Transport
Passive and assisted diffusion is used to move substances along concentration gradients.
Active Transport
Movement against gradients requires energy, typically derived from ATP.
Types include uniporters, antiporters, and symporters for different transport strategies.
Functionality
The pump maintains osmotic balance by transporting 3 sodium ions out and 2 potassium ions into the cell.
Requires ATP for energy as both ions are moved against their gradients.
Results of Pumping Process
Creates a more negative intracellular environment.
Results in a higher concentration of sodium outside the cell and potassium inside.
Role in Cellular Function
Allow potassium to leak out once a concentration threshold is met, balancing concentrations and maintaining membrane potential.
Membrane Potential
Defined as the electrical difference across the membrane, measured in millivolts.
Resting Membrane Potential: Achieved when the chemical force of potassium moving out equals the electrical force keeping it in.
Mechanism
Action potentials are electrical signals generated by the influx of sodium, followed by depolarization in response to stimuli.
They result in a wave of signal propagation through nerve fibers.
Sodium Channels
Voltage-gated channels facilitate rapid influx of sodium ions during depolarization, propelling the action potential down the axon.
Role of Glial Cells
Myelinated nerve fibers have glial cells wrapped around them, providing insulation and speeding up signal propagation.
Nodes of Ranvier
Gaps between myelinated segments where sodium channels are concentrated to boost the action potential quickly.
Conversion of Signals
At synapses, electrical signals convert to chemical signals to cross the gap between neurons, then back to electrical signals in the receiving cell.