TOPICS

• Review of major compartments/fluids

• Movement among compartments

• Review of Plasma Membrane permeability

• Passive Transport– Diffusion

• Simple diffusion

• Facilitated diffusion

– Osmosis

– Filtration

• Active Transport– Ion pumps

– Secondary active transport

– Endocytosis

– exocytosis

Body-Fluid Compartments

• Intracellular (67% of total body fluids)

• Extracellular (33% of total body fluids)

– blood plasma (6.6% of total body fluids)

– interstitial fluid or tissue fluid (26.4% of total body fluids)

1-45

AB C

ECF

ICF

Solution = solvent + solutes

water non-water

Extracellular (outside cell)

Intracellular (inside cell)

Lipid bilayer Non-polar tail region

Prevents passage of ions and polar

molecules (except water)

Water and lipid soluble substances

pass through

6

or channel

Membrane permeability summary

TRANSPORT PROTIENS OF THE PLASMA MEMBRANE

Have binding sites-- specific-- competition-- saturation-- facilitate diffusion

• Facilitated Diffusion• Ion Pumps

Always open-- ions-- some specificity

• facilitated diffusion

Open and Close--ions-- some specificity-- condition specific

• facilitated diffusion

All matter is in motion diffusion

Diffusion:• movement (inherent in all chemicals) results in substances spreading from where they are

more highly concentrated to where they are less concentrated• Resulting in uniformly distributed substances that are still in motion (but evenly spread out)*

*at least in the absence of other factors/influences

Diffusion Across a Membrane:Results in a net change in concentrations, but movement never stops dynamic equilibrium

Diffusion Times

Time it takes the “average” molecule to diffuse a given distance.

Distance Time1 ųm 0.5 msec

10 ųm 50 msec

100 ųm 5 sec

1 mm 8.3 min

1 cm 14 hr

ųm = 1/1000 of a millimeter

msec = 1/1000 of a second

too slow; if a substance had to diffuse this distance the cell would die waiting for needed materials

size range of “typical” cells and typical distance from a blood vessel

DIFFUSION RELATED TOPICS

• Random movement of all matter is why/how– substrates find/bind enzymes– chemical signals find/bind receptors

• Concentrations power the net movement of these substances onto and off of the chemicals they bind– Higher concentrations drive substances to bind

receptors/enzymes– Low concentrations will drive substances off

receports/enzymes (or at least slow binding)

• Concentration gradient influences rate of interactions

Fig. 6.2

Diffusion subtypes and classes of molecules transported

Simple Diffusion Through lipids:

•nonpolar molecules—O2, CO2, fatty acids, steroid hormones

•Water

Facilitated diffusion Through channel proteins:

• ions

• water (through aquaporins)

Facilitated Diffusion through carrier proteins:

• e.g., glucose, amino acids

Example of Simple Diffusion through membrane lipids

Fig. 6.6 Gated Channels:

• open and close under different conditons/stimuli• Ligand Gate, voltage gated, mechanically gated, etc….

Fig. 6.16 Facilitated Diffusion through a carrier protein

Different Carriers for different substances

expandsshrinksNo change

Fig. 6.13

Issues in Osmosis:

• glycogen is the stored form of glucose

• diarrhea

glucose

glucose glycogen

A B

Filtration

pre

ssu

re

pre

ssu

re

Filtration:--Size determines what passes through membrane--more pressure more filtration

Fig. 6.18

Active Transport: ion pumps

pump

Fig. 6.19

Active Transport: sodium/potassium pump (exchange)

Carrier-Mediated Transport: facilitate transport and primary active transport/pumps

• Protein carriers exhibit:– Specificity for specific (sometimes single) molecules NOTE: specificity can also be true of ion

channels

– Competition among compatible substrates for transport• Competition reduces the transport rate of any single substance

– Saturation when all carriers are occupied• There is a maximum transport rate

6-24

Fig. 6.15

Saturation, competition, and maximum transport

Fig. 6.20 Cotransport/symport: Diffusion of one substance powers uphill movement of another

Fig. 6.20

Cotransport/symport: Diffusion of one substance powers uphill movement of another

Fig. 6.23

Receptor mediated endocytosis

Fig. 6.21