Exam 3 - Cell Membrane And Transport Flashcards
Passive movement across cell membrane
- Will move passively if lipid soluble
- If not…need to move via channel or carrier proteins (selective)
Simple Diffusion
- Movement driven by a gradient
- carrier proteins can move in both directions
Facilitated
- Driven by a gradient but helped by movement of another molecule
- carrier proteins can move in both directions
- used by glucose and amino acids
Active transport
- Primary: energy provided directly by energy source
- Secondary: energy stored in gradient that was created via use of energy source
- Carrier proteins move in only one direction
- Against gradient (usually electrochemical…Na, K, Ca, H, Cl)
Brownian motion
- random motion in all directions
- affected by temperature (or KE)
Factors that affect rate of diffusion
- Gradient (direct)
- Surface Area (direct)
- Solubility (direct)
- Distance (indirect)
- Sqrt of MW (indirect)
Gradients that affect rate of diffusion
- [ ]
- Electrical
- Pressure (hydrostatic / osmosis)
Movement of water given osmolarity
- Water will move toward area of higher osmolarity
- Osmolairty is measure of [solute]
Substances that passively diffuse
- Oxygen
- CO2
- N2
- Alcohol
- For gases…solubility always the same unless disease is present
Osmosis
- Movement of water through channel protein across membrane
- not membrane itself - Very rapid
- Aquaporins: water selective channel proteins (other ions can’t pass)
- Ions move across via other channels if water soluble and small
Na channels
- small diameter
- strong negative charge inside channel (attracts Na+)
- gradient across Membrane determines movement
- gate is on outside
- opens when inside of cell becomes less negative
Gated channels
- can control permeability (really low to really high)
- gates can be on outside or inside or both)
- conformational change of protein causes opening or closing
- Can be voltage or chemical (ligand) gated
- voltage will open if voltage gradient changes…
- ligand will open if bonded to ( ACH is common)
If we say potential of cell is negative….
- The cell is more negative on the inside relative to outside
K gates
- Gate is on inside
- opens when inside of cell becomes positive
Maximum facilitated diffusion rate
- Depends on # of channels available
- Depends on time it takes channel to complete cycle
- V max
Na/K pump
- ATP required
- 3 Na out / 2 K in
- Establishes negative voltage inside of cell
- Made of two proteins (large and small…small function unknown)
- maintains normal cell volume (w/o pump…cell would swell due to high [protein] on inside)
- increase activity if increase in cell volume/osmolarity
- creates a -4mV membrane potential
Four gradients created with Na/K pumps
- Increase in [Na] on outside
- Increase in [K] on inside
- More negative on inside
- More osmotic particles on outside….so H2O moves out
Na/K pump proteins
- Large and Small
- Large: 3 Na binding sites on inside
2 K binding sites on outside
ATP binding site on inside - Breakdown of ATP and release of energy causes change in shape
Energy required for active transport
Energy = (1400)*( log([new or in]/[old or out]))
Units: calories/osmole
Co-transport
- using Na gradient to move amino acids/glucose down gradient into the cell
Counter-transport
- using Na gradient to move Ca/H in opposite direction out of cell
Nernst equation
EMF (mV) = (-61.5/charge of ion)*(log([ion in]/[ion out]))
- Tells us the potential charge that would be created if ions were to move across their gradients
Starling forces acting on capillary
- Capillary Hydrostatic P: pushes out of capillary
- Interstitial Hydrostatic P: pushes into cap (+) or pulls out (-)
- Plasma Oncotic P: Pulls into Cap
- Interstitial Oncotic P: Pull out of Cap
Edema
- Build up of fluid in tissues if lymph system cannot remove fluid coming out of capillaries fast enough
Normal Osmolality of ECF/ICF
300 milliosmoles/Kg of H2O
Normal Osmolarity
285 - 300 mOsm/L
- Long term: equilibrium will be reached
- Short term: movement can happen between compartments
Calculate Osmolarity
- Determine g/L from %
- Find number of moles using MW
- Multiply by i factor if needed
- note units (usually should end up in milliosmoles/L)
Pressure created by 1 osmole / L
19,300 mmHg
or
19.3 mmHg (mOsm/L)
Common cell resting Membrane potential
- Most cells are negative
Stable voltage / potential
- No net current across the membrane
- Potential WILL NOT change unless there is a net movement of ions
Nernst Potential
- Like the equation but + or - depends on ion
- for NEGATIVE ions and - for POSITIVE ions
- Put the sign in front of the 61.5
Number of ions needed to move to create a potential
- Very few number of ions
- Number of ions needed to start potential has no effect on overall gradient
Equation for multiple permeable ions
EMF = (P% of Na)(EMF of Na) + (P% of K)(EMF of K) + …..
Normal RMP for cardiac cells
- -90mV
- Created by leaky K+ channels (move out of the cells)
- Leaky channels polarize the membrane
- Some effect caused by small amount of Na
