Co-transport

Question 1

Co-transport definition?

Answer 1

transport of 2 or more diff molecules at the same time in a coupled movement

Question 2

Na+/K+ pump?

Answer 2

1. binds 3 Na+ ions & 1 ATP molecule
2. hydrolysis of ATP provides energy to - change shape of channel - Na+ ions driven thru channel
3. Na+ ions r released to outside of membrane & new shape of channel allows 2 K+ ions to bind
4. release of Pi (phosphate) allows channel to revert to OG form - releasing K+ ions on inside of membrane

Question 3

Why is active/co-transport needed for glucose (with Na+ ions) in ileum?

Answer 3

• to absorb glucose from lumen to gut - must be higher conc. in lumen - compared to epithelial cell (for facilitated diffusion)
• BUT - usually more glucose in epithelial cell so - active/co- transport required
  *same as amino acids
  *how glucose absorbed from small intestine (ileum) -> blood
  *epithelial cells - lining ileum walls

Question 4

Co-transport of glucose & Na+ ions in ileum?

Answer 4

1. Na+ ions r actively transported out of epithelial cell into blood (K+ ions too)
2. this reduces Na+ ion conc. in epithelial cell
3. so - Na+ ions can then diffuse (by facilitated diffusion) from lumen down conc. gradient into epithelial cell
4. the protein that Na+ ions diffuse thru is co-transport protein so - glucose also attaches & transported into epithelial cell against its conc. gradient
5. glucose then moves by facilitated diffusion from epithelial cell to blood (down gradient)

Question 5

What maintains the concentration gradient of glucose between the epithelial cell & capillary?

Answer 5

blood flows and carries away absorbed glucose

Question 6

What increases the surface area for co-transporter proteins?

Answer 6

microvilli on epithelial cell
(as lots of co-transporter proteins embedded for max absorption)

Question 7

Bulk transport?

Answer 7

• into cells: endocytosis
• out of cells: exocytosis
• require energy so - both forms of active transport
• transport of large quantities of materials into/out of cells e.g…
• large molecules e.g. proteins/polysaccharides
• parts of cells
• whole cells e.g. bacteria’

Question 8

The endosymbiotic theory (Endosymbiosis)?

Answer 8

1. infoldings in plasma membrane of an ancestral prokaryote gave rise to endomembrane components - including nucleus & ER
2. 1st endosymbiotic event - ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria
3. 2nd event - the early eukaryote consumed photosynthetic bacteria that evolved into chloroplasts