2.2 Transport Across the Cell Membrane

Membrane Proteins act as ______________. Account for almost 50% of the mass of the cell membrane.

Small, nonpolar molecules

• _________ are commonly gases, which do not have any charges.

• O2, CO2, & N2

• Steroid Hormones

concentrated to least concentrated

Diffusion is from __________ to ____________

concentration gradient

Small uncharged polar molecules can easily diffuse through the cell membrane as long as they've used the

facilitate their transfer

Larger uncharged polar molecules have a very hard time passing through our cell membrane, so you need the help of various proteins in order to _____________

True

True or False: Ions or charged molecules cannot pass through the cell membrane

specific concentration

It is very important that our ion have a ________ at different site of our cell membrane, outside and inside of the cell.

False, Other molecules inside the cell are POSITIVELY charged. That’s why there’s only one major ANION

True or False: Other molecules inside the cell are positively charged. That’s why there’s only one major cation

Cations

a positively charged ion

potassium ions (K+)

Intracellular: Inside the cell, you can find that there is a very high concentration of

sodium ions (Na+) and calcium ions (Ca+)

Extracellular: Outside the cell, we can find a very high concentration of

Anions

a negatively charged ion

chlorine (Cl-)

Anions or negatively charged ions, the major extracellular anion is ________. Inside the cell, most of the negative charges are negatively charged molecules inside the cell that are actually the different components of the cell like your amino acids and your nucleic acids.

Membrane Potential

Voltage difference across the cell membrane caused by an imbalance of charged molecules.

-20 and -200 millivolts (mV)

Resting membrane potential

• Transport of certain metabolites

• Cell-cell communication

Uses for Membrane Potential

Types of Transport

• Passive Transport

• Active Transport

• Facilitated Active Transport

Passive Transport

• Transfers molecules from very concentrated areas to less concentrated areas.

• It transports molecules along the concentration gradient.

• Does not require extra energy on the part of the cell.

• Channels

• Transporters

Two types of passive transport proteins:

Active Transport

• Moves molecules against their concentration gradient.

• From less concentrated areas to more concentrated areas.

• The cell has to expend energy in order to pump out these types of molecules.

pumps

Active transport proteins are called

Electrochemical Gradient

Our cell membranes have membrane potential. The outside is positively charged, and the inside is negatively charged.

• Concentration gradient

• Membrane potential

Net driving force of passive transport

• Channel

• Passive Transport

Classes of Membrane Transport Proteins

Channel

• Use size and electric charge

• Non- selective

Passive Transport

• Uses binding sites

• Selective

• Ion Selectivity

• Gated

Characteristics of Ion Channels

Active Transport

Transport solute against its electrochemical gradient.

• Gradient-driven pump

• ATP-driven pump

• Light-driven pump

Gradient- driven pump

Relies on the energy of the electrochemical gradient to transfer certain molecules.

ATP-driven pump

Uses energy from the breakdown of ATP

Light-driven pump

• Uses solar energy to transfer solutes against the electrochemical gradient.

• Only found in plant cells and other photosynthetic cells.

• Symport

• Antiport

• Uniport

Types of Gradient- Driven Pump

Symport

• Transports two molecules in the same direction.

• One molecule is the one following the electrochemical gradient and this is the molecule that produces energy as it passes through the pump.

• At the same time, the energy that is being produced by this molecule is used by the protein in order to co-transport another molecule.

Antiport

• You have one transported molecule along the concentration gradient (another term: downhill).

• This molecule is following downhill transport and the energy being produced by the transport of this molecule is then used to transport the other molecule against the concentration gradient or uphill, so this molecule is being transported uphill.

Uniport

These aren't really considered pumps because only one type of molecule is being transported and usually this molecule is going with the electrochemical gradient.

Aquaporins

• Channel proteins, used for the transport of water.

• They move water from the outside, where we can find a high water concentration and a low solute concentration to the inside of the cell, where we see high solute and low water concentration.

four

• Structure of the Aquaporins is a complex of _____ proteins.

True

True or False: If we just allowed water to keep on entering the cell eventually it would burst.

Use a discharging contractile vacuole

Combatting osmotic swelling for protozoans. Once the cell has detected that it is about to burst then it expels that water into its environment.

Combatting osmotic swelling for Plant Cells.

They have a very thick and very strong cell wall around the cell, so they are very resistant to osmotic pressure. In the case of the plant cell, it just allows water to keep going inside itself because it has a very strong cell wall to protect it from bursting.

Combatting osmotic swelling for Animal Cell

Instead of expelling the water directly, what they do is release ions outward into the extracellular space, and along with these ions, water will just naturally flow out of the cell.

False, sodium ions

True or False: In the extracellular space, you see an abundance of potassium ions. This means that the electrochemical gradient for your potassium ions goes from the outside of the cell to the inside of the cell.

Glucose Na+ Symport

Used for the transport of both sodium and glucose. We want to transport glucose against its electrochemical gradient or uphill, so in this case we would be using a symport.

True

True or False: Glucose actually has a higher concentration inside the cell rather than outside.

Two, one for your sodium ion and the other one for your Glucose

Glucose Na+ Symport has ____ binding sites.