sodium potassium pump

sodium potassium pumps in and out how much Na and K?

3 Na out of cell and 2 K into cell

what is role of Na/K pump?

1. provides energy for coupled transport of other molecules

2. produces electrochemical membrane potential in neuron and muscle cells

3. maintains osmolality

secondary active transport

• also called coupled transport

• the energy this needs to move molecules against their concentration gradient is acquired by moving sodium back into the cell, creating high pressure. This pressure is what causes glucose to bind to transport proteins to move against its concentration gradient

• Na was originally pumped outside the cell using ATP, which is why this is considered active transport

• not primary active transport because there’s no use of a pump to transport molecules

• symport

  • the other molecule is moved with Na

  • common way to transport glucose

• antiport

  • other molecule is moved in the opposite direction from Na

    • ex., uphill extrusion of Ca2+ from a cell

transport across epithelial membranes

• absorption

  • transportation of digestive products across intestinal epithelium into the blood

  • first time something enters the body

• reabsorption

  • transport of molecules out of the urinary filtrate back in to the blood

  • second time something enters the body, usually from the kidneys

• involves transcellular transport

  • movement of molecules through the cytoplasm of the epithelial cells

exocytosis

• how large molecules such as proteins, hormones, and neurotransmitters are secreted

• secretes and drifts away

• requires ATP

• trafficking of vesicle inside cell and fuses with membrane to diffuse away

transcellular transport

movement of molecules through cytoplasm of epithelial cells

endocytosis

• required to move large molecules such as cholesterol into the cell

• transpo. protein interacts with plasma membrane proteins to trigger endocytosis

• opposite exocytosis

• cell eating

• brings things inside cell

pinocytosis

• cell drinking

  • cell gets more water and electrolytes at a higher volume than normal

• fluid

• uses active transpo.

paracellular transport

• movement of molecules through intercellular space between the epithelial cells

• does not go directly through the cells themselves (this is transcellular transpo.)

• passive

• uses tight junctions

what is a potential difference and how is it made?

• potential difference is a difference in the charge of the molecules inside versus outside the cell

• The inside o the cell in negative compared to the outside

• it is made due to:

  • the permeability of the membrane

  • action of Na/K pumps

    • puts the more positive molecules outside the cell

  • negatively charged molecules inside the cell

    • anions are trapped inside the cell

    • the cations are not pumped inside the cell to even out the negative charge

inner leaflet

inner layer of ECM

outer leaflet

outer layer of ECM

cytosolic side

inside the cell, not outside in the ECM

why does K accumulate at high concentrations in the cell?

• Na/K pump actively brings in K

• membrane is very permeable to K

  • default setting of all cells

• negative anions inside the cell attract cations outside the cell

• limited by strong concentration gradient

what is the K+ concentration inside the cell?

150mM

what is the K+ concentration outside the cell?

5 mM

what is the potential difference between the outside and inside leaflets?

-90 mM

how do we find and calculate the equilibrium potentials of cells?

Nernst equation

based on ion concentrations

what is the Na+ concentration inside the cell?

12 mM

what is the Na+ concentration outside the cell?

145mM

what is the Na equilibrium potential?

+66mM

what is the membrane potential if it is perfectly permeable to K?

-90 mV

what does the change in voltage of a cell’s membrane potential do?

its a signal for the cell to do something (we haven’t learned yet)

what impacts the resting membrane potential?

• K+, Na+, Ca 2+, and Cl- contribute to resting potential

• a change in the permeability of the membrane for any ion will change the cell’s resting potential

• a change in the concentration of any ion inside or outside the cell will change the resting potential of the cell

• key to how neurons and other tissues work

neuron resting potential

usually -70 mV

what does a neuron change its permeability to when it sends an impulse?

Na

it drives the membrane potential closer to the equilibrium potential for Na

how do cells communicate?

• using chemical signals

• types:

  • gap junctions

  • paracrine signaling

  • synaptic signaling

  • endocrine signaling

gap junctions

allow adjacent cells to pass ions and regulatory molecules through a channel between the cells

paracrine signaling

• cells within an organ secrete molecules that diffuse across the extracellular space to nearby target cells

• often called local signaling

synaptic signaling

involves neurons secreting neurotransmitters across a synapse to target cells

endocrine signaling

• involves glands that secrete hormones into the bloodstream

• can reach multiple target cells

how does a target cell receive a signal?

• A target cell has receptor proteins on the plasma membrane that are specific to that signal

• nonpolar molecules can penetrate the plasma membrane and interact with receptors inside the cell

• large, polar signal molecules bind to receptors on the plasma membrane (cell’s surface)

  • from here, second messengers are sent inside the cell to affect change

  • may be ions (Ca 2+) or molecules

cAMP

• stands for cyclic adenosine monophosphate

• common second messenger

• steps to activate it:

  1. a signaling molecules binds to a receptor

  2. this activates an enzyme that produces cAMP from ATP

  3. cAMP activates other enzymes

  4. cell activities change in response

what are G-proteins, why do we need them, and how do they work?

• We need G-proteins because receptor proteins that bind to a signal and enzyme proteins that produce a second messenger are rarely together. They need something to shuttle between them, which is were G-proteins come in

• made up of 3 subunits: alpha, beta, and gamma

  • one subunit dissociates when a signal molecule binds to the receptor and travels to the enzyme or ion channel