DLA #4: Membrane Structure and Transport

Question 1

Lipid Rafts are:

Answer 1

Dynamic assemblies of lipids and proteins

Question 2

Lipid Rafts play a role in:

Answer 2

Signal transduction and virus infections

Question 3

Planar lipid rafts are:

Answer 3

• formed by cholesterol, glycolipids and sphingomyelin
• they are short lived

Question 4

Caveola are

Answer 4

• Also lipid rafts
• Form invagination of the pm
• Long lived -Stabilized by caveolins

Question 5

Explain what happens to fatty acid tails when exposed to a cold environment. What homeostatic response occurs

Answer 5

• Fatty acid tails stiffen up
• Cholesterol will intercalate itself b/w phospholipids and increase membrane fluidity.

Question 6

Explain what happens to fatty acid tails when exposed to a hot environment. What homeostatic response occurs

Answer 6

• Fatty acid tails begin to loosen up and become more fluid.
• Cholesterol will use its steroid ring system to decrease fluidity.

Question 7

What are lipoproteins

Answer 7

Proteins that transport nonpolar lipids through the blood/lymph.

Question 8

Describe the characteristic traits of a lipoprotein

Answer 8

• Hydrophobic core
• Hydrophillic shell.
• Transfers TAG and cholesteryl ester.

Question 9

How do membranes inside the cell regulate fluidity

Answer 9

Membranes inside the cell DO NOT have cholesterol.

Therefore, regulation of fluidity is based upon the fatty acid composition of that membrane.

Question 10

Passive transport through a membrane includes:

Answer 10

1) Simple Diffusion (Moves down gradient through pm)
2) Faciliated DIffusion (Moves down gradient through a channel/transporter)

Question 11

Cell w/in out body take in Glucose via:

Answer 11

Glucose Transporters aka GLUT

(multiple in body for select area)

Question 12

GLUT is a good example of what type of diffusion

Answer 12

Faciliated.

Question 13

List out the high affinity GLUT transporters:

Answer 13

GLUT-1, GLUT-3, GLUT-4

Question 14

List out the low affinity transporters

Answer 14

-GLUT-2 and GLUT-5

Question 15

During normal or lower blood glucose levels in general circulation we expect

Answer 15

-GLUT-1 and GLUT-3 to be working at a constant rate

Question 16

GLUT-1 is found in

Answer 16

RBC’s, BBB and Kidneys

Question 17

GLUT-3 is found in:

Answer 17

Neurons and the brain

Question 18

What is hereditary GLUT-1 deficiency

Answer 18

• form of metabolic encephalopathy
• as infants develop growth of brain and skull is slowed
• Symptoms include:
• Epileptic-Seizures
• Ataxia
• Delayed psychomotor development
• Movement disorder
• Speech Disorder

***Symptoms become more prevalent w/ age

Question 19

What is a way in which we can evaluate if someone has GLUT-1 Deficiency

Answer 19

Taking a sample of the RBC’s

Question 20

What is really unique about GLUT-2:

Answer 20

Its a TWO way transporter.

Question 21

Where are GLUT-2 transporters usually found:

Answer 21

1) Intestinal Mucousal cells => Glucose gets transferred via GLUT-2 into the portal vein
2) Hepatocytes => Liver is the glucose banks. It both stores glucose during levels of high glucose in circulation and gives off stored glucose during fasting. It can even make new glucose during serious starvation. Therefor we expect a two way GLUT portal to be available.
3) Pancreatic B-cells => Beta cells have GLUT - 2 in order to test the amount of glucose in general circulation and determine if release of insulin is necessary.
4) Renal tubular cells. => In the renal syste, both reasorption and secretion of glucose occurs. Therefore, a two way portal is needed. Not only that, kidneys do very little gluconeogensis, therefore we expect the kidney’s to also have GLUT-2.

Question 22

Explain a little more about why GLUT-2 is used to measure glucose levels in regards to B-cell functioning:

Answer 22

GLUT-2 is used by Beta cells of the pancreas to “taste” glucose levels in the general circulation.

These GLUT-2 are so important b/c the pancreas needs to know when it’s the right time to release insulin for uptake of glucose into our adipose and skeletal tissue cells.

****Document attached goes even more in depth

Question 23

Where is GLUT-4 found and what is its function

Answer 23

• Adipose
• Skeletal
• Heart

Question 24

What signals can cause a cell to release GLUT-4

Answer 24

• High levels of Glucose in general circulation
• ALSO, during vigorous excercise

Question 25

Where is GLUT-5 and function

Answer 25

- GLUT-5 is the "fructose transporter" - Transports fructose from the lumen of the intestinal mucousa through hepatic portal. - GLUT-5 is also found in seminal vesicles Fructose supplies energy to the sperm.

Question 26

Define Primary Active transport

Answer 26

Transport that **requires ATP** in order to move a substance **against** its concentration gradient.

Question 27

Give a poster child example of primary active transport

Answer 27

Na+/K+ - Atpase (sodium-potassium pump) found on pm

Question 28

How does the sodium-potassium work.

Answer 28

Pumping of 3 Na+ out of cell and 2 K+ into cell. Keep in mind this requires ATP and we are moving against the concentration gradient.

Question 29

Define/explain secondary active transport

Answer 29

A transporter that is dependent upon the concentration gradient generated by a primary active transporter. Typically we see this coupled to a sodium-potassium pump

Question 30

What is SGLT-1 and what does it do

Answer 30

SGLT-1 is a **Secondary active transporter (symporter).** SGLT-1 bring in either **Na+ - Glucose** or **Na+ - Galactose** into the intestinal mucousal cell.

Question 31

What is SGLT-2 and what does it do

Answer 31

SGLT-2 is a **Secondary Active Transport (symporter).** **Also Is dependent upon sodium-potassium Atpase** SGLT-2 is found in the kidney and its job is to **transport Na+ -Glucose for** **reuptake**

Question 32

What type of inhibitors are used in the treatmen of diabetes and why.

Answer 32

**SGLT-2 inhibitors** Rather than re-uptaking glucose back into the blood stream and jeapordize a diabetics blood sugar, SGLT-2 inhibitors can allow the patient to excrete out glucose instead.

Question 33

What are ATP Binding Cassette (ABC) transporters

Answer 33

- They are a form of active transport - Pumping of molecules from the cytosol to the extracellular space occur - Requires ATP - Solutes transported tend to be lipid compounds: * Bile * Cholesterol * Bilirubin

Question 34

Describe CFTR:

Answer 34

- Voltage-gated ion channels that faciliates the movement of chloride. - **Considered a "special" type of ABC transporter** - Chloride flow with gradient like a channel rather than a pump - Mainly present in **epithelial cells** on the **luminal membrane** * **P**ancreatic ducts * **A**irway ducts * **R**eproductive ducts * Mnemonic: "*CFTR on **PAR**"*

Question 35

Describe Cystic Fibrosis

Answer 35

- Disease with which there is a **deficiency** in _CFTR._ - Known in infants as "salty baby syndrome" - Patient will have: * Poor Growth * Low weight * Lung infection * Pancreatis * Male infertitility * Steatorrhea (oily-foul stool)

Question 36

What unique property does CFTR **ONLY** have in the epithelial cells of the skin.

Answer 36

- The CFTR can re-open and bring back Cl- from the the ecs back into the cytosol. - Done in order to salvage sweat for future cooling