Transport Across Membranes

Question 1

What is passive membrane transport?

Answer 1

The movement of a substance across a membrane without the use of chemical energy. Diffusion drives passive transport.

Question 2

What does the rate of diffusion depend on?

Answer 2

It depends on the concentration gradient that exists between the two areas of concentration or across a membrane. The larger the gradient the faster the rate of diffusion. However, there is no net change in concentration, this is an example of dynamic equilibrium.

Question 3

What are the 2 types of passive transport?

Answer 3

Simple diffusion and facilitated diffusion

Question 4

What factors determine the ease with which a molecule can cross a membrane?

Answer 4

Charge and size

Question 5

What is simple diffusion?

Answer 5

The ability of a substance to move across a membrane unassisted

Question 6

What molecules can use simple diffusion?

Answer 6

Very small polar molecules (O@ and CO2) are readily soluble in the hydrophobic membrane interior, and move rapidly from one side to the other. Non-polar steroid hormones and drugs. Small uncharged molecules such as water and glycerol.

Question 7

What is facilitated diffusion?

Answer 7

Protein complexes that span the membrane facilitate diffusion of high-demand compounds across a membrane

Question 8

Facilitated diffusion is carried out by transport proteins, what are the 2 types of transport proteins?

Answer 8

Carrier and channel proteins

Question 9

What do channel and carrier proteins do?

Answer 9

Channel proteins form hydrophilic pathways in the membrane for water and certain ions to pass through, these channels are often voltage-gated
Carrier proteins form pathways through the membrane and protein binds to specific solute, such as glucose or a particular amino acid, the protein then changes shape to allow the solute to pass from one side to the other.

Question 10

Hypertonic, Hypotonic, Isotonic

Answer 10

Hyper - when there is too much water in the cell
Hypo - when there is not enough water in the cell
Iso - state of equilibrium

Question 11

What is active membrane transport

Answer 11

When molecules are carried across a membrane against their concentration gradient, using chemical energy.

Question 12

How does active membrane transport work?

Answer 12

Using “pumps” active transport is able to concentrate specific compounds inside cells and push others out. ex: muscle cells sometimes need calcium concentrations up to 30 000 higher than in another compartment.

Question 13

Explain primary active transport

Answer 13

primary active transport uses pumps to move positively charged ions (H+, Ca+, K+, Na+) across membranes. The movement of these ions in one direction causes a difference in charge on the two sides of the plasma membrane. The combined effects of voltage and ion concentration difference create an electrochemical gradient. The secondary active transport system uses this gradient as its energy source.

Question 14

Explain secondary active transport

Answer 14

The secondary active transport system uses this gradient as its energy source. For example, animal cells use the high outside/low inside Na+ gradient set up by the sodium-potassium pump. Secondary active transport is facilitated by symport and anti port.

Question 15

Symport vs Antiport

Answer 15

Symport - solute moves through membrane channel in same direction as driving ion.
Antiport - driving ion moves through membrane in one direction, providing energy for active transport of another molecule in the opposite direction, many ions, such as Na+ are exchanged by antiport.

Question 16

Endocytosis and exocytosis

Answer 16

Carried out by vesicles, use ATP.
Endocytosis - import of larger molecules such as proteins, larger aggregates of molecules or whole cells. Carried out by three different pathways.
Exocytosis - export of larger molecules such as secretory proteins and waste materials.

Question 17

Pinocytosis

Answer 17

Means cell drinking. Takes in water as well as any molecules that may be in the water. No binding by surface receptors takes place.

Question 18

Receptor-mediated endocytosis

Answer 18

Molecules to be taken in bind to outer cell surface by receptor proteins. Primarily binds to proteins or molecules carried by proteins. After binding receptors collect into a pit coated with a net-work of proteins called clathrin, that reinforce the cytosol side. The coated pit breaks free of the membrane to form a vesicle which loses the clathrin coating and may find a lysosome to digest its contents, breaking them down into molecules that are useful to the cell.

Question 19

Phagocytosis

Answer 19

Cells engulf bacteria, parts f dead cells, viruses, and other foreign particles. Most commonly used by a macrophage - a type of white blood cell.