1. Membrane potential

Plasma membrane

separates inside of cell from outside fluid
allows for internal electrolytes to be different from outside

Inside plasma membrane

Cytosol

Outside plasma membrane

Extracellular fluid

What components have higher concentration inside the cell 

K+, proteins 

What components have higher concentration outside the cell 

Na+, Cl-, Ca2+

Permeability

the ease with which a substance can cross a cell membrane

Do all cells have the same permeability

No, different cells have variation of selective permeability

Passive transport is

the movement of substances across a membrane without the use of energy, relying on concentration gradients.

Active transport

the movement of substances across a membrane against their concentration gradient, requiring energy input.

Diffusion

passive transport of ions and molecules down their concentration gradient

Carrier mediated transport

involves the active or passive movement of substances across a membrane via specific carrier proteins,

Diffusion of uncharged molecules 

Diffuse down or along the chemical concentration gradient of the molecule 

Diffusion of charged molecules and ions

Diffuse based on BOTH chemical concentration gradient and electrical concentration gradient

Electrochemical gradient

Sum of forces of all chemical and electrical gradients acting across cell membranes 

Diffusion of O2 in body

moves from lungs into blood, into interstitial spaces, then into cells

Diffusion of CO2 in body 

moves from cells, to interstitial spaces, into blood, and out through lungs 

Diffusion of H2O in body

moves across epithelium of digestive tracts into body tissues

Lipid bilayer permeability

Permeable to small nonpolar molecules like oxygen and carbon dioxide (HYDROPHOBIC)

Large molecules and hydrophilic molecules

are largely impermeable to the lipid bilayer, requiring specific transport mechanisms to cross membranes.

Osmosis 

is the diffusion of water across a selectively permeable membrane, driven by concentration gradients.

Osmotic pressure

force of water movement into that solution resulting from its solute concentration

Tonicity

effects of osmotic solutions on cells.

Isotonic

no net osmosis, no net gain or loss of water

Hypotonic extracellular solution 

less solutes, more water than intracellular solution – water will flow _into_ cell

Hypertonic extracellular solution 

more solutes, less water than intracellular solution – water will flow _out___ of cell

Factors influencing diffusion

Distance
Size
Temp
Gradient
Charge

How does distance influence diffusion

concentration gradients effective only over short distances – few cells are more than 125 μm from a blood vessel

How does size of molecule affect diffusion 

smaller diffuse faster 

How does temp affect diffusion 

Higher temp is faster diffusion

How does gradient affect rate of diffusion

A greater concentration gradient increases the rate of diffusion,

What would happen if a cell suddenly became very permeable to K+ ions?

K+ would move out of cell because normally K has higher intracellular concentration

Carrier mediated transport- specificity 

proteins are generally specific to certain molecules or ions, allowing them to bind and facilitate transport across the membrane.

Carrier mediated transport- saturation limits

rate of transport subject to number of transport proteins available

Carrier mediated transport- regulation

various control factors exist that affect activity of carrier proteins

Cotransport

both molecules are transported in the same direction at the same time

Counter transport (antiport) 

both molecules go in opposite directions across the membrane 

Facilitated diffusion

molecules passively move down gradient using transport protein, can reach saturation

Why is facilitated diffusion different from passive diffusion in terms of saturation

facilitated transport proteins that can become saturated, limiting the rate of transport when all binding sites are occupied.

Examples of active transport

Ion pumps
Secondary active transport

Secondary active transport 

Using a carrier protein, one substance moves down its gradient, and this energy is used to move another substance against its gradient 

Which of the following are anions?
A. Sodium ions and potassium ions
B. Chloride ions
C. Calcium ions
D. All of the above are anions
E. None of the above are anions

B. Chloride ions

Transmembrane potential

difference in electrical potential between inside and outside of cell

Resting membrane potential

At rest cells have more negative charge inside due to high levels of potassium ions and negatively charged proteins, compared to the outside.

Sodium-potassium exchange pumps

are integral membrane proteins that maintain the cell's resting membrane potential by actively transporting sodium out and potassium into the cell.

Resting potential of nerve cells 

-70 mV

Resting potential of muscle cells

-85mV

Ion flow

a form of electrical current that occurs due to the movement of ions across the cell membrane, driven by electro-chemical gradients

Gated channels

open in response to various stimuli

Chemically gated channels 

open or close when bound to specific chemicals 

voltage gated channels

open or close in response to trans-membrane potential

Ex of chemically gated channel

Acetylcholine gated sodium ion channel

Acetylcholine gated sodium ion channel

Found in neuromuscular junctions, where acetylcholine binds, allowing sodium ions to enter the cell, leading to depolarization.

Ex of voltage gated channels 

Found in excitable membranes, where at rest the channels are closed and open in response to changes in membrane potential, allowing sodium or potassium ions to flow through.

Depolarization

trans-membrane potential becomes less negative

Hyperpolarization

Transmembrane potential becomes more negative

Repolarization

trans-membrane potential returns to resting potential after depolarization process