DLA1 Membrane Structure and transport: Integrated Basic Principles

Question 1

Why is the plasma membrane described as a fluid mosaic of lipids and proteins?

Answer 1

Because of the lateral movement

Question 2

What is a lipid raft?

Answer 2

Very small membrane patches of unique protein and lipid composition-used for signal transduction
-site of virus infection

Question 3

What are short lived planar lipid rafts composed of? (3)

Answer 3

1. Cholesterol
2. Glycolipids
3. Sphinogmyelin

Question 4

What are long lived signal conduction sites called?

Answer 4

Caveolae-form an invagination of the plasma membrane stabilized by caveolins

Question 5

Fluidity of plasma membrane determined by 2 things

Answer 5

1. Fatty acid composition
2. Amount of free cholesterol

Question 6

What happens at low temperatures in a plasma membrane?

Answer 6

Fatty acyl groups stiffen and cholesterol prevents decrease of membrane fluidity (separate acyl chains and prevent close packing)

Question 7

What happens at high temperature in the plasma membrane?

Answer 7

Fatty acyl groups are fluid and cholesterol prevents increaseof membrane fluidity by slowing down the movement of the esterified fatty acids.

Question 8

Composition of outer layer in the plasma membrane?

Answer 8

1. Mostly sphingomyelin (SM) and phosphatidylcholine (PC) (both have polar head)
2. Some Phosphatidylethanolamine (PE) and NO phosphatidylserine
3. Many glycosphingolipids which form together creating (glycocalyx)

Question 9

Inner layerof the plasma membrane is composed of what?

Answer 9

1. Mostly Phosphatidylethanolamine (PE) and Phosphatidylserine (PS)-negatively charged
2. Phosphatidylinositol (PI)-only found in the inner layer and can be used as PIP2 in the calcium messenger center

Question 10

What are the 6 functions of Integral Membrane Proteins?

Answer 10

1. Pumps/Carriers/Transporters-specific ions (Na, K), metabolic precursors (Sugars, AAs)
2. Channels-passive diffusion, aquaporins, gap junctions
3. Receptors
4. Linkers
5. Enzymes
6. Structural proteins

Question 11

What is the freeze fracture technique and what is it used for?

Answer 11

1. Tissue soaked in cyroprotectant eg glycerol-then frozen
2. Struck with a knife which fractures the hydrophobic part
3. Creates 2 faces (E and P)
4. Using EM we view integral membrane proteins

Question 12

What are the permeable molecules?

Answer 12

Hydrophobic, non-polar uncharged
Ex: N2, benzene, CO2, O2

Question 13

Less permeable molecules?

Answer 13

Small, polar, uncharged
Ex: H20, urea, glycerol

Question 14

Highly impermeable molecules

Answer 14

LARGE, CHARGED, POLAR
H+, glucose, sucrose

Question 15

GLUT-1 Tissue distribution and things to know

Answer 15

1. Found in most tissues-abundant in RBC and blood-brain barrier
2. High affinity glucose transporter
3. Basal glucose uptake remains constant (at low or normal glucose levels)

Question 16

GLUT-2 Tissue distribution and things to know

Answer 16

1. Liver, kidney, pancreatic beta cells, serosal side intestinal mucosa cells
2. High capacity, low affinity transporter
3. May be used as a BG sensor for insulin release from beta cells

Question 17

GLUT-3 Tissue distribution and things to know

Answer 17

1. Found in most tissues (abundant in brain neurons)
2. High affinity glucose transporter
3. Major transporter in the CNS

Question 18

GLUT-4 Tissue distribution and things to know

Answer 18

1. Found in fat cells, skeletal muscle and heart
2. High affinity glucose transport system that is INSULIN SENSITIVE-this leads to increase of GLUT-4 on the cell surface

Question 19

GLUT-5 Tissue distribution and things to know

Answer 19

1. Found on the mucosal side of intestinal mucosa cells (dietary fructose) and in semen
2. Preference for fructose transport and only transports glucose at very high concentrations

Question 20

How do we test for GLUT-1 deficiency?

Rare encephalopathy

Answer 20

Test RBCs!
Symptoms: epilepsy-like seizures in first few months of life. Also develop ataxia, delayed psychomotor development, movement disorders, impaired speech

Question 21

GLUT-2 transport in detail for small intestine

Answer 21

Facilitates release of all dietary monosaccharides from the intestinal mucusa cells on the serosal side into the hepatic portal vein

Question 22

What is the SGLT?

SGLT-1 and SGLT-2

Answer 22

Sodium-dependent glucose co-transporter
SGLT-1 found in intestinal mucosa for uptake of dietary glucose/galactose
SGLT-2: found in kidneys to reabsorb glucose into tubular system

Question 23

What is primary active transport by ABC transporters? What is an example?

Answer 23

ATP-Binding Cassette
Bile salts, cholesterol, conjugated bilirubin into the bile ducts

Form of Primary Active transport (ATP)

Question 24

What is the CFTR and why is it important?

Answer 24

Cystic Fibrosis Transmembrane conductance Regulator
Uses a gated channel with a ATP Binding Cassette-only opens or closes with stimulus using the cAMP messenger system
-CFTR does NOT pump chloride ions, they flow with the gradient when the channel opens

Question 25

Deficiency of CFTR leads to?

Signs/Symptoms

Answer 25

Cystic Fibrosis-Signs
1. Meconium ileus-requires immediate medical treatment
2. Salty skin-impaired reuptake of chloride ions
Symptoms:
1. Poor growth and low weight
2. Lung infections
3. Pancreatitis
4. Steatorrhea (excessive fluid in stools)
5. Infertitility