Chapter 5

Membrane Dynamics

Outline

Cell Membranes

Movement across membranes

Distribution of water and solutes in the body

Osmosis Lab

Proteins: role in communication

Proteins act as “passageways”

Channel Proteins Open Gated*

Carrier Proteins

Open and Gated Channels

Norm

ally

clo

sed

Norm

ally

op

en

These are types of “gates”

Chemical gates

Voltage gates

Mechanical gates

Gated channels almost always closed

Cystic Fibrosis Trans-membrane Receptor

CFTR mutationBlocks Cl-

CF: autosomal recessive

Carrier Proteins

Like a revolving door!

Movement across membranes

I. Passive transport: no ATP Non-carrier mediated Carrier mediated

Diffusion: passive

Without membrane Across membrane: no carrier

Passive transportPassive diffusion

Passive movement can require a carrier

SpecificCan saturate

II. Active Transport

Active Transport

Requires a TRANSPORTER

AND

Requires ENERGY

Primary Active Transport

Is this a symport or antiport?

Let’s look at both primary and secondary together!

Figure 5-28 (insert)

Na+ gradient is potential energy

NOTICE

Distribution of water and solutes in the body

Osmosis

Movement of water across a semi-permeable membrane

Compare osmolarity of one solution to another solution.

Isosmotic

Hyperosmotic

Hyposmotic

Number of particles are

ABA

Particle #

BParticle #

Term Used

300 300 A & B are Isomotic

#>300 300 A Hyperosmotic to B

#<300 300 A Hyposmotic to B

A B

Now, look at the following terms

Isotonic

Hypotonic

Hypertonic

Tonicity defines what a solution would do to the cell volume (size).

To cell size and tonicity: You must understand the terms

Non-penetrating versus Penetrating solutes

But I’m so tired…

3 Beakers with various concentrations of non-penetrating solutes and RBCs

Here’s your experiment: You place red blood cells in the threeBeakers and view them later under themicroscope. Now what will you observe?

200 mOsm600 mOsm 300 mOsm

Tonicity defines the affect on cell size or shape.

Crenation SwellingNo change

Hypertonic Isotonic Hypotonic600 mOsm 300 mOsm 200 mOsm

Non Penetrating

What if…

A cell of 6 Osm is placed in a solution also of 6 Osm then what is the tonicity?

Oops, that’s tricky! There is no way to know the tonicity with the information given! Why??

But what eventually happens to H20?

Look and penetrating versus non-penetrating

Clinical Application

A. 0.9% saline

SMC

Physio

0.9% saline is non penetrating= 300 mOsm

A. 0.9% saline: is isosmotic and isotonic

Transport of Macromolecules

Transport of Macromolecules White blood cells

Phagocytosis

Receptor-Mediated Endocytosis

all cells can carry out endocytosis

Transport errors…

Membrane Potential

Cell charge and cell function are related

The cell membrane separates charges

Measurement of this charge

What ions may cause this charge?

Nernst Equation: You can calculate this answer.

Eion= 61/z log [ion]out/[ion]in

61 is a constant Z is charge of ion

Ion K+mM

Na+mM

ICF 150 15

ECF 5 150

Now let’s now integrate the concept of cell membranes and a physiological process…

Cell function and Charge