Exam 3 - Cell Membrane And Transport

Question 1

Passive movement across cell membrane

Answer 1

• Will move passively if lipid soluble

- If not…need to move via channel or carrier proteins (selective)

Question 2

Simple Diffusion

Answer 2

• Movement driven by a gradient

- carrier proteins can move in both directions

Question 3

Facilitated

Answer 3

• Driven by a gradient but helped by movement of another molecule
• carrier proteins can move in both directions
• used by glucose and amino acids

Question 4

Active transport

Answer 4

• 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)

Question 5

Brownian motion

Answer 5

• random motion in all directions

- affected by temperature (or KE)

Question 6

Factors that affect rate of diffusion

Answer 6

• Gradient (direct)
• Surface Area (direct)
• Solubility (direct)
• Distance (indirect)
• Sqrt of MW (indirect)

Question 7

Gradients that affect rate of diffusion

Answer 7

• [ ]
• Electrical
• Pressure (hydrostatic / osmosis)

Question 8

Movement of water given osmolarity

Answer 8

• Water will move toward area of higher osmolarity

- Osmolairty is measure of [solute]

Question 9

Substances that passively diffuse

Answer 9

• Oxygen
• CO2
• N2
• Alcohol
• For gases…solubility always the same unless disease is present

Question 10

Osmosis

Answer 10

• 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

Question 11

Na channels

Answer 11

• 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

Question 12

Gated channels

Answer 12

• 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)

Question 13

If we say potential of cell is negative….

Answer 13

• The cell is more negative on the inside relative to outside

Question 14

K gates

Answer 14

• Gate is on inside

- opens when inside of cell becomes positive

Question 15

Maximum facilitated diffusion rate

Answer 15

• Depends on # of channels available
• Depends on time it takes channel to complete cycle
• V max

Question 16

Na/K pump

Answer 16

• 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

Question 17

Four gradients created with Na/K pumps

Answer 17

• Increase in [Na] on outside
• Increase in [K] on inside
• More negative on inside
• More osmotic particles on outside….so H2O moves out

Question 18

Na/K pump proteins

Answer 18

• 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

Question 19

Energy required for active transport

Answer 19

Energy = (1400)*( log([new or in]/[old or out]))

Units: calories/osmole

Question 20

Co-transport

Answer 20

• using Na gradient to move amino acids/glucose down gradient into the cell

Question 21

Counter-transport

Answer 21

• using Na gradient to move Ca/H in opposite direction out of cell

Question 22

Nernst equation

Answer 22

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

Question 23

Starling forces acting on capillary

Answer 23

• 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

Question 24

Edema

Answer 24

• Build up of fluid in tissues if lymph system cannot remove fluid coming out of capillaries fast enough

Question 25

Normal Osmolality of ECF/ICF

Answer 25

300 milliosmoles/Kg of H2O

Question 26

Normal Osmolarity

Answer 26

285 - 300 mOsm/L - Long term: equilibrium will be reached - Short term: movement can happen between compartments

Question 27

Calculate Osmolarity

Answer 27

- 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)

Question 28

Pressure created by 1 osmole / L

Answer 28

19,300 mmHg or 19.3 mmHg (mOsm/L)

Question 29

Common cell resting Membrane potential

Answer 29

- Most cells are negative

Question 30

Stable voltage / potential

Answer 30

- No net current across the membrane | - Potential WILL NOT change unless there is a net movement of ions

Question 31

Nernst Potential

Answer 31

- Like the equation but + or - depends on ion - + for NEGATIVE ions and - for POSITIVE ions - Put the sign in front of the 61.5

Question 32

Number of ions needed to move to create a potential

Answer 32

- Very few number of ions | - Number of ions needed to start potential has no effect on overall gradient

Question 33

Equation for multiple permeable ions

Answer 33

EMF = (P% of Na)(EMF of Na) + (P% of K)(EMF of K) + .....

Question 34

Normal RMP for cardiac cells

Answer 34

- -90mV - Created by leaky K+ channels (move out of the cells) - Leaky channels polarize the membrane - Some effect caused by small amount of Na