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Yr 1 - Membranes, Lipids, Signalling > Active Transport > Flashcards

Active Transport Flashcards

1
Q

What characterises active transport?

A

Requires input of metabolic energy (can be ATP-driven or ion-driven)

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2
Q

What is Na+, K+, Ca2+ and H+ transport directly coupled to during ATP-driven active transport?

A

ATP hydrolysis

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3
Q

What is Na+/K+ gradient of mammalian cells?

A

Have high [K+] and low [Na+] inside cell and opposite outside cell

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4
Q

What is purpose of Na+/K+ gradient?

A
  1. Controls cell volume

2. Electrochemical gradient –> makes nerve and muscle cells electrically excitable

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5
Q

How is Na+/K+ gradient maintained?

A

By Na+/K+ ATPase (an integral membrane protein)

Pumps 3 Na+ ions out and 2 K+ ions into cell –> polarises cell membrane (net +ve charge on outside)

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6
Q

Why is an input of energy required with Na+/K+?

A

Working against concentration gradient

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7
Q

How is Na+/K+ and ATP a coupled system?

A

ATP not hydrolysed unless Na+ and K+ are transported an vice versa

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8
Q

What is ion-driven active transport?

A

Movement of molecule is coupled to movement of ion (Na+ or H+) down its concentration gradients –> cotransporters

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9
Q

What are the 2 examples of cotransporters?

A
  1. Symport

2. Antiport

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10
Q

What is Na+/glucose transporter an example of?

A

Symport

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11
Q

What is Na+/Ca2+ exchanger an example of?

A

Antiport

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12
Q

What is a symport?

Explain in relation to Na+/glucose

A

Both molecules travelling in same direction

  1. Glucose comes across membrane in company with Na+
  2. Concentration gradient of Na+ is used to drive active transport of glucose
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13
Q

What is an antiport?

Explain in relation to Na+/Ca2+

A

Molecules travelling in different direction

  1. Na+ movement into cell can be coupled to movement of Ca2+ out of cell
  2. Na+/Ca2+ exchanger helps maintain a low concentration of Ca2+ inside cell (3 Na+ in and 1 Ca2+ out)
  3. Energy comes from electrochemical gradient
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14
Q

What is heart contraction caused by?

A

An increase of [Ca2+] within cell

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15
Q

What is needed to maintain [Ca2+] gradient?

A

Na+/K+ ATPase

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16
Q

How does inhibition of Na+/K+ ATPase affect heart?

A
  1. Inhibition leads to increased [Na+] inside cell and decreased Na+ gradient across membrane (due to initial low [Na+] inside cell)
  2. Leads to increased [Ca2+] inside cell (as Na+ gradient is required for Na+/Ca2+ exchanger to move Ca2+ out of cell)
  3. Increased [Ca2+] inside cell of cardiomyocytes
  4. Leads to enhanced strength of contractions
17
Q

How was digitalise (foxglove) used to treat heart failure?

A

Inhibits Na+/K+ ATPase –> strengthens heartbeat

18
Q

Where are intestinal epithelial cells found?

A

Line the lumen of small intestine

Similar cells found in kidney tubules that are involved in reabsorption of molecules from urine

19
Q

What is function of intestinal epithelial cells and how are they adapted for this?

A

Absorb nutrients from digested food into blood

There are villi on intestinal folds which increase SA for absorption

20
Q

These intestinal epithelial cells are polarised. What does this mean?

A

They have 2 distinct sides:

  1. Apical
  2. Basolateral
21
Q

What is the apical side of intestinal epithelial cells?

A

Apical (brush border) membrane that faces the lumen of gut.

Has finger-like projections of the membrane –> increase SA

22
Q

What is the basolateral surface of intestinal epithelial cells?

A

Faces blood stream

23
Q

How do these intestinal epithelial cells take up glucose?

A
  1. Glucose transporter (GLUT2)

2. Na+/glucose transporter

24
Q

Where is GLUT2 present in intestinal epithelial cells?

A

Only in basolateral membrane

25
Q

What is purpose of GLUT2 in intestinal epithelial cells?

A
  1. Enables glucose that has built up in intestinal epithelial cells to move down concentration gradient into blood
  2. Moves via facilitated diffusion
26
Q

Where is Na+/glucose transporter found in intestinal epithelial cells?

A

Only in apical membrane

27
Q

What is purpose of Na+/glucose transporter in intestinal epithelial cells?

A
  1. Moving glucose across concentration gradient across apical membrane (from low conc in lumen of intestine to high conc in cytosol of epithelial cells)
  2. Requires energy –> ion-driven active transport
28
Q

How is low conc of Na+ maintained inside epithelial cells?

A

By Na+/K+ ATPase on the basolateral membrane (example of ATP driven active transport)

29
Q

Why is sodium required for uptake of glucose?

A

Provides electrochemical gradient in order to allow uptake of glucose

30
Q

What are the 2 methods by which glucose can move across the cell membrane?

A

Active transport and facilitated diffusion

31
Q

What are oral rehydration therapies made of?

A

Solution of glucose and Na+

32
Q

How do oral rehydration solutions work?

A

Movement of Na+ and glucose from lumen of intestine across the epithelial cell to blood sets up difference in osmotic pressure (increases osmotic pressure in epithelial cells)

Water flows through cell by simple diffusion

Yr 1 - Membranes, Lipids, Signalling (24 decks)

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