active membrane transport

Question 1

active transport

Answer 1

Carrier proteins transport substances across a membrane from regions of lower solute concentration to regions of higher solute
concentration (against concentration gradient)

Question 2

energy sources

Answer 2

– Primary active transport – energy obtained from ATP hydrolysis
– Secondary active transport – energy stored in ionic concentration gradient

Question 3

primary active transport

Answer 3

Energy derived from ATP changes shape of carrier protein pumps a substance
across the membrane against its concentration gradient
– Carrier proteins often called pumps
* Most prevalent primary active transport mechanism is called the sodium-
potassium pump (aka Na+/K+ ATPase)

Question 4

sodium-potassium pump

Answer 4

-activated on opposite sides by both elements
-moves two potassium ions into the cell where potassium levels are high, and pumps three sodium ions out of the cell and into the extracellular fluid

Question 5

secondary active transport

Answer 5

• Moves substance against concentration gradient
• Uses energy from movement of second substance down its gradient
  – Kinetic energy providing “power” to pump other substance
• Two types:
  – Symporters move two substances in the SAME direction
  – Antiporters move two substances in OPPOSITE directions

Question 6

vesicular transport

Answer 6

Substances are transported in vesicles from one structure to
another

Question 7

exocytosis

Answer 7

substances move OUT of a cell by the fusion of a
vesicle with the plasma membrane

Question 8

endocytosis

Answer 8

substances move INTO a cell in a vesicle formed from the plasma membrane

Question 9

phagocytosis

Answer 9

“Cell Eating”
* Cells engulf (take in) large solid particles from their surroundings

• Only a few cell types perform this
  – Main types are macrophages and
  neutrophils

Question 10

how phagocytosis works

Answer 10

– Forms large extensions called pseudopodia
– They surround particle, enclosing it in a membrane sac
– Sac is internalized and fuses with lysosome to form phagolysosome
– Contents digested and released from cell (undigested materials remain in cells as residual bodies)

Question 11

pinocytosis

Answer 11

“Cell Drinking”
* Cells take in liquids from their surroundings
– No receptor proteins involved
– Internalization of droplets of interstitial fluid containing dissolved solutes
– Multiple, small vesicles formed
* Enables the cell to obtain bulk quantities of substances
* Occurs in most cells, especially absorptive cells of intestines & kidneys

Question 12

Receptor-Mediated Endocytosis

Answer 12

• Highly selective type of endocytosis
• Cells take up specific ligands

Question 13

how receptor mediated endocytosis works

Answer 13

1. LDL particle binds to LDL receptors located on plasma membrane in
   clathrin-coated pits.
2. Invaginated edges of membrane fuse and small pieces of the membrane pinch
   off to form vesicles
3. Vesicle loses clathrin coat and becomes
   uncoated.
4. Uncoated vesicle fuses with an endosome. LDL separates from receptor
5. Accumulating receptors pinch off, forming transport vesicles
6. Large proteins and lipids of LDL particle are broken down and recycled