Lecture 2 - Membrane Transport

Question 0

Describe osmotic forces

Answer 0

Two ways.
force/pressure of water entering a cell with semi-impermeable memb.

or force/pressure required to stop water from entering this cell with s.p memb.

aka measure of tendancy to take on water.

Question 1

Describe the methods of molecular movement.

Answer 1

simple molecular movement, not movement across membrane comes from the normal Kinetic energy aka. kinetic motion of matter, this is also a measure of its temperature.

Question 2

Describe mechanisms used by substances to cross cellular membranes

Answer 2

•Energy independent (except for kinetic energy)
Diffusion -
-simple diffusion - thru memb, which osmosis is.
-facilitated - uses protein
2 types of which each have 2 mechs.
(non gated: aquaporins, ion channels)
(gated: voltage and ligand/chemical gated)
•Energy dependent:
Active: Primary (atpase) and Secondary sym/antiporters)

Question 3

3 Factors affecting rate of diffusion

Answer 3

• Proportional to concentration difference across membrane (aka. conc. grad.)
• Membrane electric potential (Nernst potential)
• Pressure difference

Question 4

Facilitated diffusion differs from Simple in what important way?

Answer 4

Facilitated has a max rate, dependent on the carrier protein’s ability/rate of diffusion.

Question 5

The most important things that used facilitated diffusion are?

Answer 5

Glucose and most A.A.

Question 6

3 factor that determine the net rate of diffusion for a substance that can diffuse both directions

Answer 6

permeability
conc grad
elec. potential

Question 7

Ligands are typically what type of molecule

Answer 7

Neurotransmitter like ACH or

a hormone

Question 8

the rate of diffusion of a substance through a cell memb. is directly proportional to its what?

Answer 8

Lipid solubility

Question 9

when facilitated diffusion plateaus, its called the

Answer 9

Vmax

Question 10

All Cells have what Family/type of transport proteins?

Answer 10

GLUT Family

glucose transporters

Question 11

Voltage is in reference to the inside or outside of the cell membrane?

Answer 11

inside

Question 12

When can gated channels allow only partial flow of the substance through them?

Answer 12

Never!, they are all or none.

Question 13

Challenging question

why do both Na and separate K ion channels (non gated) have such specificity?

Answer 13

B/c of their selectivity filters
and largely due to size
K - larger - the Carbonyl O’s on K ion channel are spaced further that they dehydrate K allowing it through 1000:1 K:Na
Na - smaller - So the strong Neg charges on Na ion channel are able to pull it in. then diffuses due to conc. grad.

Question 14

Uniporter is what

Answer 14

a channel carrier protein that allows for Facilitated diffusion of 1 substance AT A TIME! and not necessarily always the same substance. Also there are binding sites that are alternately available on either side of the membrane. MEANING: the transport of substance can go BOTH ways B/C IT IS DIFFUSION (& based on conc. gradient)

Question 15

Active Transport utilizes what energy source from what enzyme?

Answer 15

ATP

ATPase transporters

Question 16

define multiporter
what type of transport does in take part in
2 examples and define them

Answer 16

carrier protein that carries 2 substances at once across a membrane.

its Secondary active Transport

Symporter (co transport) 2 same way & time
Antiporter - (counter transport) 2 opp way same time

Question 17

Na/K pump creates a positive or negative charge inside the cell?

Answer 17

Net -1 charge INSIDE the cell for each round of pumping

Question 19

the Na/K pump is important for controlling what?

Answer 19

The cell volume

Question 20

where is there a higher concentration of the following ions

1. Na
2. Ca
3. K

and why?

Answer 20

1. extracellularly
2. same
3. intracellulary

Primary active transports through the Ca and Na/K pumps

Question 21

What Ion is often involved in secondary active transport?

Answer 21

Na

Question 22

for the Na/K pump…

how many binding sites are there for Na and K and where are they located?

Answer 22

Na 3 binding sites intracellularly

K 2 binding sites extracellularly

Question 23

If sodium moves down its electrochemical
gradient, why is this referred to as secondary active
transport?

Answer 23

the conc grad for Na was originally created by primary active transport.

Question 24

Sodium/calcium antiporters move three
sodium ions per calcium ion. Why does it take three
sodium ions to move one calcium ion?

Answer 24

bc it takes more E to move Ca

Question 25

a conformational change in a membrane protein is caused by

Answer 25

Liberated or Freed energy from ATPase activity during active transport.

Question 26

Say there is an excess of ADP. Whats unique about the Na/K pump?

Answer 26

It can run in reverse and used to generate ATP or pump the ions in opposite directions, depending on the relative
concentrations of ATP, ADP, phosphate, sodium, and potassium ions

Question 27

in secondary active transport, at least one substance is moving which direction?

Answer 27

down its concentration. This is why its secondary. The Gradient that this substance is flowing down, was where the initial primary active transport took place.

Question 28

Sodium glucose pump is what type of transport

Answer 28

Secondary active transport

and a symporter. aka co transport

Question 29

What type of transport does Na/K pump provide?

Answer 29

Primary Active transport

Question 30

Glucose Transporters (GLUT) employ which form of transport

Answer 30

Facilitated Diffusion

Question 31

Na/H pump is what type of multiport

Answer 31

Antiport aka counter transport (active)

Question 32

Na/Ca pump is what type of multiport

Answer 32

Antiport

aka counter transport (active)

Question 33

Explain the role of the cell membrane in establishingintra- and extracellular environments.

Answer 33

We have no way to move water directly, ie. no proteins that move water. If we need to move water we can move ions so that osmosis occurs.