Lecture 2

Question 1

Membranes

Answer 1

-Membranes are dynamic structures with many functions
Function: Import/export of molecules, regulate the interaction between cells with other cells and the environment, transfer info from outside into cell, and define mechanical properties, movement and growth

Question 2

Membranes

Answer 2

1) receiving info
2)import and export molecules
3) capcity for movement and expansion

Question 3

Internal membrane

Question 4

Lipid Bilayer

Answer 4

-This is the universal basis for membrane strucure
-main constituents are lipids and proteins, held with non covalent bonds
-Lipids form impermeable barrier to water soluble molecules and proteins act as transporters, sensors and binding agents with extracellular matrix
-it is double layer dynamic and fluid

Question 5

Major types of membrane lipid molecules

Answer 5

-glycerophospholipids, sphingolipids, sterols (glycolipids discussed later is a 4th)

Question 6

Glycerophospholipid parts

Answer 6

-Main part is called phphatidylcholine
-two sites of glycerol link to fatty acid residues
-third site link to phosphate group
-phosphate links to organic substance like choline

Question 7

4 major phospholipids in mammal plasma membrane

Answer 7

-the head groups vary in size shape and sharge
-phophatidylserine is the only negative charge
-4 groups end in ethnolamine, serine, choline and spingomyelin
-the polar head contain the choline or whatever amino acid, then the phosphate, then glycerol then has two tails

Question 8

Sterols

Answer 8

-smaller but rigid rings
-single polar hydroxyl group
-variable side chains
-cholesterol is an example

Question 9

Lipids= Amphilic

Answer 9

-structure of the bi-layer membrane is specified by the amphiphilic nature of lipid molecules and their shape
-hydrophilic= water love
-hydrophobic= water fearing

Question 10

Lipids self assemble

Answer 10

These properties make is energy favor for lipids to suddenly assemble bilayers in aqeous solutions
-polar environment at surface facing exterior
-polar envionrment at surface of cytosolic leaflet
-all next to water except for the hydrophobic interior
-interior has chlesterol and phospholipids

Question 11

Sealed compartments

Answer 11

-The self assembly properties of lipds lead to formation of sealed compartments
-energy favored are circle=sealed compartment
-2 consequences of this, it will quickly re seal if there is damage but the vesicles will fuse and the diffusion barrier means that polar molecules cannot move freely in the membrane

Question 12

Two dimension fluid=Lipid bilayer

Answer 12

-individual lipid molecules diffuse freely in the bilayer
-fludity has to be precise regulated to maintain enzyme activities and transport activities of proteins
-the extent of memrane fludity is defined by phase transition
-phase transition is the temperature where the bilayer changed from liquid to crystal
-the phase transition of lipid bilayer depends on its composition