Human Physiology: "Transport across the plasma membrane." (Transmembrane Transport)

What is an inotropic effect?

*Something that effects HEART CONTRACTILITY (i.e. stroke volume) *Can be a positive inotropic effect (increases heart contractility) *Can be a negative inotropic effect (decreases heart contractility)

What is the intracellular concentration (in moles per liter = mM) of magnesium (Mg+) ions?

0.5

What is the extracellular concentration (in moles per liter = mM) of calcium (Ca++) ions?

1-2

What is the extracellular concentration (in moles per liter = mM) of magnesium (Mg+) ions?

1-2

What three (3) types (or classes) of transmembrane proteins enable IONS and other water-soluble molecules to traverse (i.e., move across) cell membranes?

1. Ion channels: form a pore to allow the passage of specific ions by passive diffusion. 2. Symporters: proteins that simultaneously transport two molecules across a membrane in the same direction. & Antiporters: transport molecules in opposite directions. 3. Pumps: transmembrane proteins that actively move ions and/or solutes against a concentration or electrochemical gradient across biological membranes.

What are the two kinds of active transport? How do they differ?

1. Primary (Direct): Directly uses a source of chemical energy (ATP) to move molecules across a membrane against their gradient. 2. Secondary (Indirect): Uses an electrochemical gradient generated by active transport as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP.

List six (6) features of the Sodium/Potassium pump.

1. Pumps: 3 Na+ ions out of the cytosol and 2 K+ ions into the cytosol for each ATP hydrolyzed. 2. Electrogenic: contributes - 5 mV to the transmembrane voltage. 3. Ubiquitous & abundant: It is present in every cell type. 4. Consumes: about 33% of the total ATP consumed by our cells. 5. Generates: Considerably metabolic heat from ATP cleavage. 6. Maintains: osmotic balance and stabilizes cell volume by regulating intracellular (Na+)

What are the three (3) factors that determine whether a molecule can pass directly through a pure (i.e., synthetic) phospholipid bilayer?

1. The size of the molecule. 2. The electrical charge on the molecule (if any). 3. Whether the molecule is lipophilic or hydrophilic.

One cycle of the Na+/K+ pump requires ________ milliseconds.

10

Once an ion channel's pore has been OPENED, ions flow through the pore at high rates by _____________ ________________ of the ion down its electrochemical gradient.

10 million ions per second

What is the intracellular concentration (in moles per liter = mM) of calcium (Ca++) ions?

10-4 = (100nM)

What is the extracellular concentration (in moles per liter = mM) of chloride (Cl-) ions?

110

What is the intracellular concentration (in moles per liter = mM) of potassium (K+) ions?

140

What is the extracellular concentration (in moles per liter = mM) of sodium (Na+) ions?

145

The Na+/Ca2+ exchanger allows ___________ (how many?) sodium ions (Na+) to enter the cytosol, and ejects ________ (how many?) calcium ions (Ca2+) from the cytosol, per cycle.

3, 1

One Na+/K+ ATPase protein pumps _______ (how many?) sodium ions (Na+) out of the cytosol per cycle, and pumps _________ (how many?) potassium ions (K+) into the cytosol per cycle?

3, 2

Over the course of one second, a Na+/K+ pump proteins transports ___________ (how many?) Na+ ions out of the cytosol, and __________ (how many?) K+ ions into the cytosol, and converts ___________ (how many?) molecules of ATP into ADP?

300, 200, 100

What is the extracellular concentration (in moles per liter = mM) of hydrogen (H+) ions?

4 x 10-5

What is the extracellular concentration (in moles per liter = mM) of potassium (K+) ions?

5

What is the intracellular concentration (in moles per liter = mM) of chloride (Cl-) ions?

5-15

What is the intracellular concentration (in moles per liter = mM) of sodium (Na+) ions?

5-15

What is the intracellular concentration (in moles per liter = mM) of hydrogen (H+) ions?

7 x 10-5

What is a LIGAND? What does 'ligand-gated' mean in regard to ion channels?

A molecule that physically binds to the channel. The Ligand acts as a "key" and can unlock the ion channel, or in other words, open the gate.

Transport of Na+ and K+ ions across the plasma membrane by the Sodium/Potassium Pump (aka the Na+/K+ pump or the Na+ ATPase) is an example of __________________________ transport.

Active

What is an electrochemical gradient? How is it different from a chemical (or concentration gradient) across the plasma membrane?

An electrochemical gradient is the combination of the electrical gradient and the chemical gradient that act on an electrically-charged molecule like an ion.

The intracellular concentration of sodium ions (Na+) is lower than the extracellular concentration of Na+ ions. Which specific membrane transport protein is responsible for this?

Antiporter

A solution in which the solvent is water is known as an ______________ solution.

Aqueous

For a ligand-gated ion channel, does the ligand bind the extracellular region of the channel, or the intracellular region?

Both

How does the Na+/K+ pump create a voltage (i.e., by separating electrical charges)?

By pumping against the electrochemical gradient the ions want to go back to equilibrium but since they cant it creates a voltage

The sodium/calcium (Na+/Ca2+) exchanger (aka Na+/Ca2+ antiporter) is an example of a _____________ transporter protein.

Coupled

Substances that cannot be chemically interconverted or broken down into simpler substances are known as ________________.

Elements

True or False? A pure (i.e., synthetic) phospholipid bilayer has transmembrane transport proteins imbedded within it.

False

True or False? IONS can easily diffuse directly through a pure (i.e., synthetic) phospholipid bilayer.

False

True or False? Large, uncharged, polar molecules can easily diffuse directly through a pure (i.e., synthetic) phospholipid bilayer.

False

True or False? Pure (synthetic) phospholipid bilayers (these lack membrane transport proteins) are highly permeable to ions and large, uncharged, polar molecules such as glucose.

False (Highly impermeable)

The protein-lined tunnel (or pore) of an ion channel shields ions that are diffusing across the bilayer from contacting the _____________________ ________ of phospholipids in a bilayer.

Hydrocarbon tails

Word meaning that a molecule loves water (and is water-soluble):

Hydrophilic

Word meaning that a molecule fears water (and is NOT water-soluble):

Hydrophobic

What does 'gating' mean for an ion channel?

Ion channels often possess a "gate" that can either be open or closed by various stimuli.

How does an increase in the intracellular concentration of calcium ions (Ca2+) affect heart function?

It creates a build up of Ca2+ in the cytosol, and increases the force of contraction of the heart and prolongs the duration of the diastolic phase of the cardiac cycle, which results in increased filling of the ventricles. Both of the above effects increase the stroke volume of the heart and increase the volume of blood pumped by the heart per unit time.

How do the drugs digitoxin & digoxin affect the ability of the Na+/Ca2+ exchanger to eject calcium ions from the cytosol?

It decreases the efficiency of the antiporter, so less Ca2+ is ejected into the cytoplasm.

How do the drugs digitoxin & digoxin affect the ability of the Na+/K+ pump to operate?

It inhibits it. Increased intracellular Na+ reduces the electrochemical gradient for Na+ across the PM.

What will happen to the intracellular concentration of potassium ions (K+) if you eat Purple Foxglove flowers?

It will decrease

Which types of molecules can freely diffuse across the plasma membrane (PM) without using membrane transport proteins?

Lipid-soluble molecules

Word meaning that a molecule loves lipids (i.e., fats) and is lipid-soluble:

Lipophilic

Word meaning that a molecule fears lipids and is NOT lipid-soluble:

Lipophobic

What type of proteins are embedded within the phospholipid bilayer of the plasma membrane?

Membrane transport proteins

What will happen to the intracellular concentration of sodium ions (Na+) if you eat Purple Foxglove flowers?

Na+ concentration increases.

Kidney tubule cells each contain (within their plasma membrane) several million _______________ pump proteins.

Na+/K+ ATPase

The ability of the Na+/Ca2+ exchanger to function is completely dependent upon the electrochemical gradient for sodium ions (Na+), which is created by the _______________ pump.

Na+/K+ ATPase

Which specific membrane transport protein consumes about 33% of the total ATP consumed by our cells.

Na+/K+ pump

Name the three (3) transmembrane transport proteins required to transport glucose across intestinal epithelial cells (from gut lumen into interstitial fluid).

Na/K pump Na/glucose symporter Glucose uniporter (GLUT)

Does passive transport (i.e., movement) of a molecule across a cell membrane (such as the plasma membrane) require energy input?

No

Does the flow of potassium (K+) ions through an open K+ selective ion channel requires energy input?

No (Passive transport)

Would you expect STRETCH to open or gate a mechanically-gated ion channel?

Open

Does the oxygen atom in a water molecule have a FULL electric charge, or a PARTIAL electric charge?

PARTIAL

What physical feature must an ion channel possess in order to be opened and/or closed by voltage (i.e., a difference in electrical potential) across the plasma membrane?

Passive Conduction

Glucose molecules have no electric charge. Is the transport of glucose molecules across the plasma membrane affected by an electrochemical gradient for glucose? Why or why not?

Secondary (Coupled) transport of glucose can be powered by the energy stored within the electrochemical gradient for sodium ions (Na+).

The Na+/Ca2+ exchanger performs _____________________ active transport and it (does or does not?) directly consume ATP.

Secondary, does not

Name the six (6) major physiological IONS.

Sodium, Potassium, Magnesium, Calcium, Chloride, Hydrogen

The liquid component of a solution is known as the:

Solvent

What does "selective permeability" mean?

Some molecules can get across the plasma membrane of cells, whereas other molecules cannot.

The Secondary Active (Coupled) Transport proteins relies on what to work?

The concentration or electrochemical gradient of one solute must be created and maintained by a primary active transport protein such as the Na+/K+ pump.

What provides the energy for transport of glucose by the Na+/glucose symporter?

The electrochemical gradient for Na+

How does the 'selectivity filter' of a potassium-selective ion channel prevent sodium ions (Na+) from flowing through the pore?

They fit into a certain spot, and will stay in the spot if it fits right.

What are the differences between a uniporter, a symporter and an antiporter?

Uniporter: One molecular species transported down its concentrated gradient. Symporter: 2 molecular species transported in the same direction. Antiporter: 2 molecular species transported in opposite directions.

Which molecules require membrane transport proteins in order to cross the PM?

Water-soluble molecules

Does active transport (i.e., movement) of a molecule across a cell membrane (such as the plasma membrane) require energy input?

Yes (Because it transports molecules against the concentration gradient)

Why must the Na+/K+ pumps be confined within the basolateral domain of the plasma membrane?

because it is important to keep a low concentration of Na in the cell because that is what is driving Na and K in through Na driven glucose symporter

Why does the hydration shell that surrounds IONS dissolved in an aqueous solution prevent the ions from diffusing across a pure (i.e., synthetic) phospholipid bilayer?

because of their watery hydration shells, ions CANNOT get across the plasma membrane simply by diffusing directly through the lipid bilayer.

Why do water molecules form a 'sphere of hydration' around IONS such as Sodium (Na+)?

because the Oxygen atom of the water molecule has a partial negative charge that is electrostatically attracted to the positively charged Na+ (cation).

In secondary active transport (aka Coupled Transport), one solute is transported uphill against its chemical (concentration) or electrochemical gradient, and the other solute is transported _________________ its chemical or electro-chemical gradient.

down

Rheogenic' means that the Na+/Ca2+ exchanger creates an ________________ current.

electrical

The Na+-K+ pump is an ATPase ________________.

enzyme

With the Na+/Ca2+ exchanger, there is a NET MOVEMENT OF (how many?) ________ positive electric charge into the cytosol per cycle.

one

Molecules dissolved in a solution are known as:

solutes

Speaking of Electrochemical gradients: what kinds of molecules are influenced by an electrical gradient (i.e., voltage)?

solutes such as ions

Name at least two (2) solutes in Mountain Dew.

sugar, sodium, and caffeine.

How does the Na+/K+ pump create an electric current?

they maintain a low intracellular Na+ concentration, that then drives Na+ into the cytosol

What is the solvent in Mountain Dew?

water