L1. Excitable Cells

Question 1

What is the composition of Extracellular fluid “interstitial fluid”

Answer 1

Primarily ions, proteins, and other molecules. Similar to plasma with respect to ionic composition. Therefore, has a high NaCl (high NA and CL).

Question 2

What are the 3 components of Cell excitation

Answer 2

ECF, intracellular fluid, membrane.

Question 3

What is the composition of Intracellular fluid “cytosol”

Answer 3

Ions, much higher concentrations of proteins and other molecules. Predominant salt: KCL (k & Cl) so, Inside and outside of cell are very different - this allows cells to communicate

Question 4

T/F the concentrations of predominant cations (Na vs. K) in the cytosol are the same in the inside and outside of a cell.

Answer 4

False. They’re different.

Question 5

What does the “membrane” consist of

Answer 5

Phospholipid bilayer and proteins. About equal amounts of protein and lipid, and a small (5%) amount of carbs.

Question 6

What characteristic is essential to cell excitation?

Answer 6

permeability

Question 7

The permeability of a membrane to an ion is an index of the ability of the ion _________

Answer 7

to cross the membrane.

Question 8

Changes in permeability that are ______ and _____, are essential to excitation in cells.

Answer 8

ion-specific and exquisitely timed

Question 9

During Simple diffusion. Non polar organic molecules diffuse rapidly through the membrane which is 50% _____.

Solubility in lipid is low or high? do you need energy?

Answer 9

50% lipid
is high
no energy

Question 10

During simple diffusion what do ions cross?

Answer 10

they cross protein channels (several subunits and ion specific) Ex: K channels and Na-Channels.

Question 11

what are some examples of non-polar substances:

Answer 11

02, CO2, fatty acids, steroid hormones

Question 12

____ = amount of substnace crossing a surface per unit of time

Answer 12

flux

Question 13

Diffusion between 2 compartments is always:

Answer 13

bi-directional

Question 14

Net flux is

Answer 14

the difference between the two unidirectional fluxes.

Question 15

What state is the system referred to as when the net flux = 0

Answer 15

diffusion equilibirum

Question 16

2 types of mediated transport

Answer 16

Facilitated diffusion & Active transport

Question 17

T/F

Facilitated Diffusion requires energy

Answer 17

FALSE

Question 18

What serves as a carrier to translocate a molecule across a membrane in faciliated diffusion?

Answer 18

Membrane protein

Question 19

Glucose is a ____ and ___ molecule

Answer 19

large and polar

Question 20

All cells have what transporters?

Answer 20

glucose

Question 21

Active transporters are referred to as

Answer 21

pumps

Question 22

What can energy affect?

Answer 22

Affinity of the transporter for the ligand on one side of the membrane more than on the other side & rate (of transporter conformational change)

Question 23

Describe the process of the primary active transport model

Answer 23

the energy source is the hydrolysis of atp –> transpoter becomes phosphorylated –> changes affinity for solute (ligand) –> increases transport rate.

Question 24

Give me 2 examples of primary active transport:

Answer 24

1. Transport of Na ions out of cells

2. Transport of K ions into cells

Question 25

Describe the process of the secondary active transport model

Answer 25

uses energy in ion conc. gradient across membrane. Transporter has two binding sites.
e.g. transport of amino acids, uses [Na] gradient.

Question 26

3 steps in mediated transport

Answer 26

1. Ligand binds to transporter
2. Transporter undergoes conformational change
3. Ligand is released on other side of membrane

Question 27

“osmalirty”

Answer 27

the total solute concentration in a solution. 1.0 osmol = 1.0 mole of solute. 1.0 mole of NaCl = 2.0 osmoles.

Question 28

What is the osmolarity of extracellular fluid?

Answer 28

300 mOsm

Question 29

Name the 3 types of EXTERNAL solutions?

Answer 29

Isotonic
hypotonic
hypertonic

Question 30

Isotonic external solution?

Is there a change in cell volume?

Answer 30

= 300 mOsm of non-penetrating solutes –> no change in cell volume

Question 31

Hypotonic external solution?

Is there a change in cell volume?

Answer 31

< 300 mOsm of non-penetrating solutes –> cells swell

Question 32

Hypertonic external solution?

Is there a change in cell volume?

Answer 32

> 300 mOsm of non-penetrating solutes –> cells shrink

Question 33

isoosmotic means what?

Answer 33

= 300 mOsm of non penetrating PLUS penetrating plus (this is the osmotic portion)

Question 34

what is a normal tonicity of a cell?

Answer 34

300 mosmol

Question 35

Lower concentration of mOsm =

Answer 35

higher concentration of water

ex: 200 mOsm non penetrating solutes in solution = the hypotonic solution and the cells swells.
ex: 300 mOsm non penetrating solutes = isotonic no change in volume
ex: 400 mOsm = hypoertonic –> cell shrinks because sol is higher and less water.

Question 36

Define:
Endocytosis
Pinocytosis
Phagocytosis

Answer 36

1. engulfment of fluid and particles from extra. space
2. drinking small particles with or without small volume of ECF; performed by all cell types
3. phagocytosis: engulfment of large particles or cellular debris; performed by specialized cells - phagocytes.

Question 37

In the distribution of ions across the plasma membrane the intracellular Ca2+ is ___________. The free Ca2+ is very ____.
The organic anions aka PROTEINS are where? why?

Answer 37

bound or sequestered; very low (

Question 38

Ohms law

Answer 38

V = IR 
V= voltage 
I = current 
R = resistance

Question 39

Conductance =

Answer 39

membrane property. Conductance does NOT = current
Conductance is the reciprocal of resistance: G=1/R
If the R is high then the G is low. if the R is low then the G is high.

Question 40

Diffusion potentials can be ______ ie. they can disappear over time. They are due to ______ ion flow which is ______________.

Answer 40

transient

they are due to asymmetric ion flow - an imbalance in the flow of an ion or several ions between two compartments. `