membrane transport part 1

Question 1

Membrane diffusion

Answer 1

Different molecules diffuse through the membrane at different rates:
-small, nonpolar molecules rapidly diffuse across membrane
-small, uncharged. polar, molecules diffuse across membrane
-Large, uncharged, polar molecules rarely diffuse across membrane
-charged ions cannot cross the membrane

Question 2

Why can’t hydrophilic molecules diffuse through the membrane? How can they?

Answer 2

The hydrophobic interior of the lipid bilayer prevents the passage of hydrophilic, water-soluble molecules. They are able to pass through the membrane with transmembrane protein (hydrophilic pore and hydrophobic interior)

Question 3

Transporters (carriers)

Answer 3

transmembrane proteins that change shapes to transport specific molecules/ions
-binds solute and undergoes shape change to push source to the other side

Question 4

Channels

Answer 4

transmembrane proteins that form pores which can open and close to transport ions or water.
-provides passageway (hydrophilic core)
-multipass transmembrane protein

Question 5

Ion concentrations within the cell

Answer 5

Sodium (Na+) low conc. inside cell, high conc. outside cell.
Potassium (K+) high conc. inside cell, low conc. outside cell

Question 6

Passive transport

Answer 6

when solutes spontaneously travel from high to low concentration.
-no energy input needed (concentration gradient)

Question 7

Active transport

Answer 7

when solute travels from low to high concentration.
-energy input required and is carried out by transporters

Question 8

Electrochemical gradient

Answer 8

-ions have two gradients : electrical and concentration
-electrical gradient determines if passive or active transport happens for the ion and at what rate.

Question 9

Sodium electrical gradient

Answer 9

High electrical gradient because concentration and voltage work in the same direction.
-inside our cell we have negative membrane resting potential
-Na+ wants to go inside because of the negative charge and concentration gradient
-causes cell to store power for whenever it needs it

Question 10

Potassium electrical gradient

Answer 10

low electrical gradient because concentration and voltage work in opposite directions
-concentration gradient is different so it wants to go outside (but every time it leaves it makes cell more negative)

Question 11

Glucose transporters

Answer 11

-glucose can usually be done through passive transport
-liver cells helps regulate glucose from bloodstream

Question 12

After a meal: glucose

Answer 12

glucose transporter transports glucose from extracellular space to cytosol (high to low conc)
-glucose is high in bloodstream

Question 13

Fasting/Hunger pains : glucose

Answer 13

-glucose is low in bloodstream
-transporter transports glucose from cytosol to extracellular space (high to low conc)

Question 14

Coupled transporter

Answer 14

transports two different polar molecules where one provides energy for the second to be transported
-can use electrochemical gradient to power active transport
-one travels down the gradient and the other goes against

Question 15

ATP-driven pump

Answer 15

uses energy from ATP to transport solutes against concentration gradient.
-hydrolyzes phosphate group (ATP to ADP)
-now pumps can move polar molecules against concentration gradient

Question 16

Na+/K+ pump

Answer 16

ATP-driven pump that transports Na+ outside of cell, and brings K+ inside cell (against gradient)
-> PumpKIn

Question 17

Glucose- Na+ symport pump

Answer 17

transports glucose into intestinal cells (against its gradient) by using high electrochemical gradient Na+ (with gradient)
-pump restricted to apical domain by tight junctions
-glucose transferred from gut lumen into the cell (against gradient, active transport)
-input of glucose (symport used) output of glucose (uniport used) goes with gradient