Ion Flux

Question 1

What is the major extracellular cation?

Answer 1

Sodium

Question 2

What is the major intracellular cation?

Answer 2

Potassium

Question 3

What is the major extracellular anion?

Answer 3

Chloride

Question 4

________ transport is energy independent, and depends upon a downhill concentration gradient

Answer 4

Passive

Question 5

______ transport is energy-dependent, and moves againt a concentration gradient

Answer 5

Active

Question 6

_______ diffusion is unaided, passive transport of smaller uncharged molecules

Answer 6

Simple

Question 7

________ diffusion is aided by transmembrane proteins required by large and/or charged molecules

This type of diffusion requires:

__________, which likely have polar core residues and allow diffusion down a concentration gradient

OR

_________, which bind a molecule on one side of the membrane and conformational change moves the molecule to the other side. The conformational change is induced by the binding event itself, or ______ hydrolysis

Answer 7

Facilitated

Channels

Transporters

ATP

Question 8

Channels and transporters are characterized based on what 2 factors?

Answer 8

Directionality of molecular diffusion

Number of molecules transported (uniporter, symporter, antiporter)

Question 9

Defects in the uptake system of dimeric amino acid cystine leads to the autosomal recessive disorder ___________; there are also likely to be defects in the uptake of dibasic amino acids ______, ______, and __________. This results in cystine crystals forming in the kidneys (renal calculi) identified by a positive nitroprusside test.

Patients usually present with _______ _______, or abdominal pain that comes in waves. Kidney stones are soluble in _________ urine, so they are typically dissolved by dietary changes.

Answer 9

Cystinuria
Arg, Lys, and ornithine

Renal colic
Alkaline

Question 10

What disease is an autosomal recessive disorder caused by a defect in the transporter of nonpolar or neutral amino acids like tryptophan?

Answer 10

Hartnup disease

Question 11

What disease manifests in infancy as failure to thrive, nystagmus, intermittent ataxia, tremor, and photosensitivity? What is another name for it?

Answer 11

Hartnup disease aka pellagra-like dermatosis

Question 12

Tryptophan is particularly problematic in Hartnup disease. Trp is usually primarily found in the _________ and intestines. It is a precursor for serotonin, __________, and ___________ (which is a precursor for NAD)

Answer 12

Kidneys
Melatonin
Niacin

Question 13

It has been established that a Hartnup disease “attack” is often preceded by a period of poor nutrition. Knowing this, what is the typical treatment for this disease?

Answer 13

A high protein diet, which can usually overcome the deficient transport of neutral amino acids

Question 14

What is the difference between ligand-gated ion channels and voltage-gated ion channels?

Answer 14

Ligand-gated: ligand binding opens the channel by an orthosteric mechanism (ligands such as NTs or hormones)

Voltage-gated: open/close in response to changes in membrane potential; often found in neurons

Question 15

In the example of neurotransmission, the neurotransmitter acts as the __________. Drugs, poisons, or therapies act as ____________ that prevent the electrochemical signal propagation. ___________ can up-regulate or down-regulate these neuronal firings.

Answer 15

Agonists
Antagonists
Modulators

Question 16

What are the 3 possible states in which you might find a ligand-gated ion channel?

Answer 16

Resting (no ligand bound, channel is closed)

Open (ligand bound, channel is open)

Desensitized (ligand bound for too long, channel is closed)

Question 17

Define depolarization as it relates to voltage-gated ion channels

Answer 17

Increased membrane potential due to influx of positively charged ions - this triggers the channel to open

Question 18

What type of transport is the Na+/K+ ATPase, where is it found, and how does it maintain the intracellular environment?

And how much potassium vs. sodium per molecule of ATP?

Answer 18

Primary active transport

Antiporter found in ALL plasma membranes

Maintains high K+ and low Na+ in intracellular environment

[transports 2 K+ in and 3 Na+ out per ATP]

Question 19

What specific transporter is involved in the primary active transport in the sarcoplasmic reticulum of muscle cells? It exists as a uniporter in MOST plasma membranes.

Answer 19

Ca2+ ATPase (maintains low intracellular Ca)

Question 20

Describe secondary active transport

Answer 20

Protein assited and energy-dependent, but does not directly use ATP

It utilizes the molecular gradient established by another primary active transporter which DOES use ATP

Question 21

What is the primary example of a secondary active transporter that exists as a symporter in the body?

Answer 21

Sodium-glucose transporter (SGLT1)

Imports 2 Na+ to transport in 1 glucose based on the sodium gradient previously established by Na+/K+ ATPase

Question 22

What is the primary example of a secondary active transporter that exists as an antiporter in the body?

Answer 22

Na+/Ca+ exchanger (NCX) in the plasma membranes and mitochondria and ER of excitable cells

Imports 3 Na+ to remove 1 Ca++

Question 23

What type of drugs are used to treat weak myocardial contractions due to conditions like CHF or MI?

Answer 23

Cardiotonic drugs, which inhibit the Na+/K+ ATPase and the NCX antiporter

This acts to increase myocardial intracellular Ca++, which increases the strength of cardiac muscle contraction

Question 24

Describe the transport of dietary saccharides from the intestinal lumen across the enterocyte and into the bloodstream

Answer 24

SGLT1 transports D-glucose and D-galactose with Na+ into the intestinal epithelial cells (via secondary active transport using gradient created by Na/K pump). At the same time, GLUT5 transport fructose into the enterocyte via facilitated diffusion.

GLUT2 then transports D-glucose, D-galactose, and fructose across the cell surface to the bloodstream via facilitated diffusion

Question 25

Defective transport of what ion leads to cystic fibrosis?

Answer 25

Cl-

Question 26

Describe the clinical presentation of cystic fibrosis

Answer 26

Thick mucous secretion in the lungs, which leads to secondary microbial infections

Fibrosis and cysts in the pancreas due to insufficient digestive enzymes leads to failure to thrive and insulin-dependent diabetes

Question 27

Describe how defective Cl- transport leads to cystic fibrosis

Answer 27

CFTR misfolds and never leaves the ER

Or, a defect (loss of F508) in the CFTR transmembrane protein affects Cl- transport from inside of cells to outside in the airways using ATP hydrolysis energy

The buildup of Cl- in the airway epithelial cells and sweat is compensated by an increase of Na+, water follows salt, which decreases the water content of the mucous

Question 28

What are some of the complications caused by thickened mucous in cystic fibrosis patients?

Answer 28

Labored respiration
Inflammation
Scarring
Continuous or recurrent infections leading to overall loss of lung function
Blockage of intestines by thick feces