Plasma membrane, PM proteins, Crossing membranes, Receptors

Question 1

Mechanisms for molecule movement across membranes

Answer 1

$ basic mechanisms by which molecules move across membranes:

Simple diffusion
Diffusion through a channel
Facilitated diffusion
Active transport

Question 2

Simple diffusion

Answer 2

Very small molecules
Uncharged
High to low concentration
O2, CO2, H2O (osmosis)

Question 3

Diffusion through a channel

Answer 3

Small molecules
Charged molecules (ions)
High to low concentration
Channels are made of integral membrane proteins
E.g. Na, K, Ca, Cl

Question 3

Facilitated diffusion

Answer 3

Molecule binds to integral membrane protein called a “facilitative transporter”

Transporter changes conformation which allows molecule to be released on the other side

Downhill flow

No energy required

E.g. Glucose

Question 4

Passive Mechanisms

Answer 4

Passive movements of substances across cell membranes from higher to lower concentrations does not require energy

Question 5

Ion channels

Answer 5

Formed by integral membrane proteins
They are GATED and can be opened or closed in response to different signals
Examples: Voltage-Gated, Ligand-gated channels

Question 6

Voltage Gated (Na and K channels)

Answer 6

Some channels can respond to changes in charge across membrane

Question 7

Ligand-gated channels

Answer 7

The channel responds to the binding of a specific molecule (a ligand)

Binding of a ligand causes a conformational change in the structure of the receptor/channel

Question 8

Active Transport

Answer 8

Molecule binds specifically to integral membrane protein called an active transporter

Transporter conformation change caused by the hydrolysis of an ATP molecule allows the molecules to be released on the other side.

Energy requires