15. Cell membrane and glycocalix. Cell membrane models

Question 1

Cell membrane? Func? Size? Visibility? Phospholipids?

Answer 1

• The PCM func as selective barrier reg passage of materials in/out of cell - facilitating the transport of specific molecules
• keeps constant ion content of cytoplasm (differs from extracellular fluid)
• spec recognition and signalling functions (role in interactions of cell and its environment)
• Size: 7.5 - 10 nm thick
• visible from only EM, yet plasma mem proteins and extracellular material can reach some visibility in LM
• Phospholipids are amphipathic (with both hydrophobic and hydrophilic components) - with hydrophilic head and two hydrophobic fatty tails
• PL are more stable - organised into bilayer (tails inside)
• Cholesterol can be inserted - restricting movement - modulating fluidity and movement of components

Question 2

Glycocalyx

Answer 2

• Each half of BL is diff
• Some of outer lipids –> glycoplipids incl oligosaccharide chains
• The OGSC extend from surface making up a delicate cell surface coating = GLYCOCALYX (glycoprotein-polysaccharide covering)
• Under EM looks like a fuzzy coat on the cell
• Made from Lipids (PL, GL, Cholesterol), proteins and carbohydrates
• Carbohydrates on the surface have many functions
• Cell- cell recognition
• Protections
• Immunity to infection
• Cell adhesion
• Inflammation regulation

Question 3

Integral and peripheral proteins? Extraction?

Answer 3

• IP - directly incorporated w/in LB - can be only extracted by detergents to disrupt lipid
• PP - looser association - loosely bound PP are easily extracted from CM w/ salt solutions

Question 4

Fluid Mosaic Model basic comp?

Answer 4

The common cell membrane model is that of the Fluid Mosaic Model. Basic components are:

•Phospholipid bilayer
oHydrophilic phosphate heads (Polar), hydrophobic lipid tails (non-polar)

•Embedded proteins
o Either integral or peripheral
o Can have Carbohydrates attached 
o Can form different types of protein
Globular proteins
Glycoprotines
Alpha-helix proteins

•Filaments of cytoskeleton are also present

Note, the phospholipid molecules are not chemically bound to each other and therefore free to move independently providing flexibility.