membrane lipids and proteins

Question 1

what are the functions of the cell membrane

Answer 1

1. define cell boundary and serve as permeability barriers
2. represent sites of specific functions
3. regulate the transport of solutes
4. detect and transmit electrical and chemical signals.
5. mediate cell to cell communication

Question 2

describe the fluid mosaic model

Answer 2

the membrane is a two-dimensional sea of mobile lipid in which proteins diffuse or float

Question 3

why can proteins move about the membrane

Answer 3

because they usually carry an electric charge and so they migrate towards regions of the opposite charge within the membrane

Question 4

what are the two types of membranes

Answer 4

1. plasma membrane
2. internal membranes (ER, golgi, intracellular vesicles)

Question 5

what do membranes contain

Answer 5

1. lipids
2. proteins
3. carbohydrates

Question 6

what are the major membrane lipids

Answer 6

1. phospholipids
2. steroids
3. neutral fats
4. glycolipids

Question 7

describe the structure of a phospholipid

Answer 7

polar (hydrophilic head) with a non-polar (hydrophobic) tail
they usually begin with an amino acid, then a phosphate, then glycerol and finally the fatty acid chain

Question 8

what does amphipathic mean

Answer 8

contains both hydrophilic and hydrophobic portions

Question 9

how do phospholipids form bilayers in aqueous solutions

Answer 9

spontaneously
polar hydrophilic head groups orient toward the polar water, and the nonpolar (hydrophobic) tails orient away from the water

Question 10

the formation of bilayers allows what to occur

Answer 10

exocytosis and endocytosis

Question 11

what are the different types of membrane proteins

Answer 11

1. integral (intrinsic)
2. peripheral (exofacial/endofacial)
3. signal spans
4. multiple spans
5. multimeric protein complexes

Question 12

what are the receptor subunits of cys-loop receptors composed of

Answer 12

• extracellular N-terminus
• small intracellular loop
• small extracellular loop
• large intracellular loop
• 4 hydrophobic transmembrane domains
• extracellular C-terminus

Question 13

what are the different charges that amino acid residues may have

Answer 13

• neutral
• cationic
• anionic

Question 14

why would electric charge distribution vary along a protein

Answer 14

depends upon primary structure
- regions of high chagre density are relatively hydrophilic
- regions of low charge density are relatively hydrophobic
- prediction of protein structure can be obtained using a “HYDROPATHY PLOT”

Question 15

evidence of the fluid mosaic model

Answer 15

• lipid area
• x-ray and neutron diffraction
• transmission electron microscopy
• freeze-etching
• ESR
• phase-transition
• protein-tagging

Question 16

explain transmission electron microscopy

Answer 16

• all cell membranes share a characteristic trilaminar appearance
• two electron-dense layers seperated by a less dense central region

Question 17

explain freeze-etching

Answer 17

basically frozen tissue is fractured with a knife, which causes the membrane to separate in half
if proteins are left sticking out of the membrane, it reveals that they were embedded in the lipid bilayer