Transport Across Cell Membranes-Active transport

Question 1

Describe how movement across membranes occurs by active transport

Answer 1

Substances move from an area of lower to higher concentration against a concentration gradient
Requiring hydrolysis of ATP and specific carrier proteins

Question 2

Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport

Answer 2

1. Complementary substances binds to specific carrier proteins
   ATP binds, hydrolyses ADP +Pi, releasing energy
   Carrier proteins changes shape, releasing substance on side of higher conc
   Pi released–>Protein returns to original shape

Question 3

Describe how movement across membranes occurs by co transport

Answer 3

Two different substances bind to and move simultaneously via a co transport protein (type of carrier protein)
Movement of one substance against its conc gradient is often coupled with the movement of another down its conc gradient

Question 4

Describe an example that illustrates co-transport (Absorption of sodium ions and glucose( or amino acids) by cells lining the mammalian ileum

Answer 4

1. Na+ actively transported from epithelial cells to blood (by Na+ pump)
   Establishing a conc gradient of Na+ (higher in lumen than epithelial cells)
2. Na+ enters epithelial cell down its conc gradient with glucose against its conc gradient
   VIa a co transporter protein
3. Glucose moves down a conc gradient into blood via facilitated diffusion

Question 5

PROCESS OF ACTIVE TRANSPORT

Answer 5

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.

Question 6

ENERGY FOR ACTIVE TRANSPORT

Answer 6

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

Question 7

CO-TRANSPORT

Answer 7

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.

Question 8

Describe the adaptations of some specialsed cells in relation to the rate of transport across their internal and external membranes

Answer 8

• Membranes folded e.g. microvilli in ileum –> increases surface area
• More protein channels/ carriers–> for facilitated diffusion
• Large numbers of mitochondria–> make more ATP by aerobis respiration for active transport

Question 9

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

Answer 9

• Increasing surface area of membrane increases rate of movement
• Increasing number of channel/carrier proteins incfreases rate of facilitated diffusion/active transport
• Increasing conc gradient incraeses rate of simple/faxcilitated and osmosis
• Increasing conc gradient incraeses rate of facilitated difssuion - until nhmber of channel/carrier proteins become a limitng factor as all in use /saturated
• Increasing water potential gradient creases rate of osmosis