Lecture 1: Fluid Compartments, Cell Membranes, Diffusion

Question 1

What percentage of the Total Body Weight is water?

Answer 1

60%

Question 2

What proportion of the Total Body Water is found in Intracellular Fluid? Extracellular Fluid?

Answer 2

2/3 ICF. 1/3 ECF

Question 3

How is the ionic composition of ICF and ECF different (in terms of Na+ and K+)?

Answer 3

ECF has high [Na] and low [K]
ICF has low [Na] and high [K]
remember 3 Na+ out of the cell and 2 K+ in.

Question 4

What are the two fluid compartments of ECF?

Answer 4

Blood Plasma- 20%

Interstitial- 80% (btwn cells)

Question 5

How is ICF compartmentalized?

Answer 5

cytosolic fluid and organellar fluid

Question 6

What are the major components of the Cell Membrane? (were looking for 3 main ones)

Answer 6

phospholipid bilayer, cholesterol, proteins

Question 7

Name the differences between Integral (transmembrane and single sided), peripheral and glycoproteins.

Answer 7

Integral proteins are those that are buried within the phospholipid membrane. Transmembrane span the entire membrane, while single-sided extend midway. Peripheral proteins are those that can be associated with the bilayer or other integral proteins. Glycoproteins are have extracellular carbohydrate that’s attached to membrane proteins– they are used to detect self from nonself cells.

Question 8

What does the Fluid Mosaic Model of membrane structure propose?

Answer 8

integral membrane proteins are associated with the hydrophobic phase of the bilayer (REMEMBER * integral membrane proteins MUST be associated with both the hydrophilic and hydrophobic portions of the bilayer)

Question 9

The four types of membrane junctions are: junctional proteins, desmosomes, tight junctions, and gap junctions. Name the function of each type of junction.

Answer 9

Junctional proteins (integrins)-- transmembrane proteins that link cells to one another and to the extracellular matrix.
Desmosomes-- provide mechanical linkage btwn cells (connects cells to cytoskeleton and allows for flexibility)
Tight junctions-- provide an impermeant barrier by closely linking adjacent cells producing a "sidedness" to the cells so that substances moving from one side to the other MUST CROSS THROUGH CELLS (apical cell membrane @ junction)
Gap Junction-- integral proteins that allow for cell to cell communication- allow ions and electrical charges to go through neighboring cells

Question 10

Why is diffusion considered a random process?

Answer 10

Well, because the thermal motion is random and because the probability of directional movement depends upon concentration. [the probability of particles to move in a certain direction increases when there are more particles i.e. high to low]

Question 11

What is “net flux”?

Answer 11

Net Flux refers to the difference in probability of movement of particles from one compartment to another.. increase conc. = increase flux

Question 12

Which of the following DOES NOT contribute to the magnitude of flux?

a. Concentration difference of the molecule on both sides of the membrane
b. temperature of the solutions
c. size of the molecule
d. area of the membrane
e. none of the answer choices above are correct

Answer 12

E.

Answers A-D all contribute to the magnitude of flux. get it in your head.

Question 13

What is Fick’s Equation? (in layman’s terms)

Answer 13

Diffusion as a function of time and distance. The Flux (J) of a particle is proportional to the concentration gradient of the particle. This proportionality constant is the DIFFUSION COEFFICIENT (D) that is measured in cm2/sec.
diffusion over short distances is fast and over long distances its slow.

Question 14

How has Fick’s Equation adapted?

Answer 14

It incorporates the presence of a cell membrane or barrier where Co is the concentration OUTSIDE the cell and Ci is the concentration INSIDE the cell. (Co-Ci)
Net Flux is dependent of the surface area of the membrane (A)
The constant of proportionality that relates flux (J) to the concentration difference and the membrane area is the PERMEABILITY COEFFICIENT (kp).
J= kp x A x (Co-Ci)

Question 15

At what rate would a hydrophilic substance move across a hydrophobic membrane?

Answer 15

Very slowly because permeability coefficient (kp) is small.

Question 16

T/F: Hydrophobic substances and gases have a much higher permeability coefficient.

Answer 16

True. Those substances can pass through a cell membrane easier that hydrophilic substances therefore they have a HIGHER PERMEABILITY coefficient.

Question 17

What can “selectively” increase the permeability coefficient for particular substances, ie ions?

Answer 17

Integral membrane proteins– channels or pores allow for free diffusion via a semi-aqueous path
[H]–> [L]
Transporters provide protein mediated transport which can couple the transport of another substance “down” its flux gradient – can be regulated

Question 18

What types of gates can channels have?

Answer 18

electrical activity
ligand binding
modification by enzymes
mechanical deformation

Question 19

how does an “electrochemical gradient” influence flux?

Answer 19

the separation of charge across a membrane affect the diffusion of ions because opposites attract and contrastingly like charges repel.
Therefore, an electrical force may pull an ion in a direction opposite its chemical force (or gradient).

Question 20

What are the 5 properties of protein mediated transport?

Answer 20

1) faster than diffusion through the membrane
2) specific for a particular chemical species
3) is saturable (limited number of carriers)
4) can be competitively inhibited by similar substances
5) inhibitable by drugs and other like substances

Question 21

What determines the flux magnitude across a membrane?

Answer 21

1) number of transporters
2) degree of saturation of transporters
3) rate of conformational change of the transporter
4) extracellular solute concentration– mediated transport can reach MAX FLUX regardless of amount of solute because it can reach full capacity and not be able to extend further (as oppose to diffusion).. theres no room in the inn.