1.1.1 Pre-Midterm Biochem - Membrane Structure And Transport

Front 1

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Back 1

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Front 2

What factors effect membrane fluidity?

Back 2

Phospholid chain length
Degree of acyl unsaturation
Transition temperature
Presence of cholesterol

Front 3

The Fluid Mosaic Model
The general complex lipid composition of the plasma membrane
The function of cholesterol in the plasma membrane
Active and passive transport

Back 3

If you don't know these things, God help you. 8(

Front 4

Discuss facilitated diffusion using the families of glucose transporters GLUT 1-5 as examples

Back 4

Glucose is polar and can not freely diffuse across membranes. The GLUT family or transporters use facilitated diffusion to get it across.
GLUT1 - most mammalian tissues
GLUT2 - Insulin Independent. High Km for glucose such that glucose only enters during the fed state. - Liver, kidney, pacreatic β-cells, serosal side of enterocytes
GLUT3 - low Km for glucose but responsible for continuous transport - Brain
GLUT4 - insulin-sensitive. Low Km for glucose - Heart, muscle, adipose tissue
GLUT5 - Primarily a fructose transporter - Small intestine

Front 5

What does it mean to be Insulin-Stimulated?

Back 5

In an unstimulated cell, glucose transporters remain pooled in the cell rather than on the membrane. If insulin stimulates the cell, a signal causes relocalization these receptors to the membrane allowing glucose to quickly diffuse in.

Front 6

Distinguish between Primary active transport and secondary active transport

Back 6

Primary - Solute accumulation is coupled directly to an exergonic reaction

Secondary - Occurs when an endergonic transport of one solute is coupled with an exergonic flow of another solute. The exergonic solute has been pumped out with Primary active transport so Secondary active transport uses that energy indirectly.

Front 7

Explain Na+/K+ -ATPase Primary active transport.

Back 7

Na+ ions bind to the transport and when it is phosporylated, it undergoes a conformational change releasing them out of the cell against their gradient. Outside the cell, two K+ ions then bind with the transport, dephosphorylating it, and are released into the cell in a return conformational change, against their concentration gradient.

Front 8

Explain Sodium-linked glucose transporters (SGLT), a form of Secondary active transport

Back 8

SGLTs are integral membrane proteins that bring Na+ across the luminal side of enterocytes with glucose via a symport mechanism. The enterocyte then utilizes Na/K ATPase primary transport to send the Na+ across the basolateral membrane, against its gradient.

Front 9

Where are the transports on intestinal epithelial cells?

Back 9

Glucose facilitative transporters and SGLTs are on the luminal sides of enterocytes.
GLUT2 facilitated transports are on the serosal side.
Fructose enters and leaves enterocytes via GLUT5 facilitated difussion.

Front 10

What are ABC transporters? What pathologies do they involve?

Back 10

ATP-binding cassette transporters are molecules with ATP binding regions. Involved in transporting peptides, drugs and Cl- as part of the immune response. They are also involved in transporting very long chain fatty acids (VLCFAs) across peroxisomal membranes.
This system is defective in Cystic Fibrosis, Zellweger's Syndrome, Tangier disease, Adrenoleukodystrophy, Sitosterolaemia, Cholera.

Front 11

Describe the pathology of Cystic Fibrosis.

Back 11

The CF gene codes for the cystic fibrosis tansmembrane conductance regulator (CFTR) Cl- channel.
The most common mutation is the deletion of phenylalanine causing a misfolding of the protein.
In the lumen of a sweat duct, Cl- can not enter the cell, keeping Na+ with it. The NaCl is then flushed with the sweat increasing its viscosity.
In the lungs, Cl- can not leave the cell, drawing Na+ in, accompanied by water. This dehydrates mucus in the lumen and the higher viscosity fights mucal clearance.
A similar mechanism causes pancreatitis, reduced pancreatic secretions that lead to steatorrhea, malnutrition and fat-soluble vitamin deficiency.

Front 12

Where is the CF gene expressed?

Back 12

The CF gene is expressed in epithelial cells of sweat glands, bile ducts, vas deferens, pancreatic ducts and the pulmonary passages.