Transport Across Cell Membranes-Active transport + Co transport Flashcards
(9 cards)
Describe how movement across membranes occurs by active transport
● Substances move from area of lower to higher concentration / against a concentration gradient
● Requiring hydrolysis of ATP and specific carrier proteins
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport (4)
- Complementary substance binds to specific carrier protein
- ATP binds, hydrolysed into ADP + Pi, releasing energy
- Carrier protein changes shape, releasing substance on side
of higher concentration - Pi released → protein returns to original shape
Describe how movement across membranes occurs by co transport
● Two different substances bind to and move simultaneously via a
co-transporter protein (type of carrier protein)
● Movement of one substance against its concentration gradient is often
coupled with the movement of another down its concentration gradient
Describe an example that illustrates co-transport (Absorption of sodium ions and glucose( or amino acids) by cells lining the mammalian ileum
- ● Na
+ actively transported from
epithelial cells to blood (by
Na+/K+ pump)
● Establishing a conc. gradient
of Na+(higher in lumen than
epithelial cell) - ● Na+ enters epithelial cell down
its concentration gradient with
glucose against its concentration gradient
● Via a co-transporter protein - ● Glucose moves down a conc.
gradient into blood via
facilitated diffusion
PROCESS OF ACTIVE TRANSPORT
A molecule binds to a receptor complementary to its shape on the carrier protein. Each carrier protein is specific and will only transport one type of molecule/ ion.
ATP binds to carrier protein from inside of the cell.
ATP hydrolysed into ADP and Pi
Pi attached to protein causing phosphorylation.
This produces a conformational change of the protein/change in tertiary structure so the molecule is released on the other side of the membrane.
Carrier protein returns to its original shape when inorganic phosphate ions are released after the molecule/ ion is transported.
ENERGY FOR ACTIVE TRANSPORT
A lot of ATP (metabolic energy) is required. This is released in mitochondria during respiration so lots of mitochondria will be present in cells undergoing lots of active transport.
ATP → ADP + Pi
Hydrolysis reaction, Pi attaches to protein causing change in tertiary structure due to phosphorylation.
After transport, the Pi is released and ADP and Pi ion will later reform during respiration
CO-TRANSPORT
Transport of two molecules, one going down concentration gradient and one against concentration gradient. Energy for active transport indirectly from the conc gradient of the other molecule.
Type of secondary active transport
SYMPORT
If the two molecules are transported in the same direction.
Sodium-glucose cotransporter
ANTIPORT
If the two molecules are transported in opposite directions.
Sodium-calcium exchangers.
Explain the adaptations of some specialised cells in relation to the rate of
transport across their internal and external membranes
● Cell membrane folded eg. microvilli in ileum → increase in surface area
● More protein channels / carriers → for facilitated diffusion (or active transport - carrier proteins only)
● Large number of mitochondria → make more ATP by aerobic respiration for active transport
Describe how surface area number of channel/carrier proteins and differneces in gradient of conc or water potential affect the rates of movement across cell membarnes
● Increasing surface area of membrane increases rate of movement
● Increasing number of channel / carrier proteins increases rate of facilitated diffusion / active transport
● Increasing concentration gradient increases rate of simple diffusion
● Increasing concentration gradient increases rate of facilitated diffusion
○ Until number of channel / carrier proteins becomes a limiting factor as all in use / saturated
● Increasing water potential gradient increases rate of osmosis
