Sept 17th: Transport of Substances across Compartments

What are the four functions of the membrane proteins?

1. Membrane transport

2. Cellular comms via receptors

3. Cellular reactions via enzymes

4. Cell structure via structural proteins

Simple Diffusion def.

Passive or Active?

selectivity?

competitive inhibition?

How do they cross membrane?

What crosses in simple diffusion?

• Passive transport (high to low)

• Not selective

• not competitively inhibited

• Molecules move unassisted through membrane

• Small, non polar

5 factors that affect the rate of simple diffusion

1. Surface area

• greater surface area = faster rate

2. Lipid solubility

3. Size

4. Thickness of membrane

5. Conc. gradient

• better diffusion if greater gradient

What is Ficks Law of simple diffusion

Surface area x Conc. gradient / membrane thickness

Define Channel Mediated Diffusion

Passive or Active?

Selectivity?

Comp. inhibition?

How do they cross membrane?

What crosses in channel mediated?

Conformational change?

• Passive (high to low)

• fairly selective

• Can be comp. inhibited

• Use transmembrane protein to cross

• small, hydrophilic/charged

• no conformational change

What are the 4 factors that affect channel mediated diffusion

Concentration gradient

Number of channels

Size of substance

Charge on substance

Define osmosis

• how does osmosis cross?

• what is the property of the water crossing?

high water conc. to low water conc.

• crosses through aquaporins

• small, hydrophilic

What two factors affect rate of osmosis

Conc. gradient

Number of of Channels

Define Osmole

Concentration = number of particles dissolved

unit used for this is osmole

Define osmolarity

Number of particles per litre of solution

What is facilitated diffusion?

• type of transport?

• selectivity?

• comp. inhibition?

• what does it transport?

• conformational change?

• passive transport (high to low)

• very selective

• can be comp. inhibition

• large, charged/hydrophilic

• conformational change

what are the 3 key points regarding facilitated diffusion?

1. very selective

2. can be completely inhibited

3. rate of sat. stays the same regardless of conc.

Define primary active transport

• type of transport?

• selectivity?

• comp. inhibition?

• what does it transport?

• conformational change?

• Uses ATP to power pumps by changing conformation when atp binds to the transport protein

• active transport (low to high)

• selective

• yes comp. inhibition

• ions

• conformation changes

For every ATP used, how many ions does the Sodium-Potassium pump move, and in which direction?

• It pumps 3 Sodium (Na⁺) ions OUT of the cell and 2 Potassium (K⁺) ions INTO the cell.

Define secondary active transport

• type of transport?

• selectivity?

• comp. inhibition?

• what does it transport?

• movement using energy stored in an electrochemical gradient created by primary active transport.

• Active

• highly selective

• can be competitively inhibited

• transports ions

How does secondary active transport get its energy if it doesn't break down ATP directly?

• It relies on the downhill movement of a driver ion (usually Na⁺ or H⁺) to pull a second substance uphill against its own concentration gradient.

What is a symporter (or cotransporter)?

membrane protein that moves two different substances in the same direction

What is an antiporter (or countertransporter)?

• membrane protein that moves two different substances in opposite directions