Cell Structure - Cell Membrane Flashcards
How thick is the plasma membrane that separates living cells from surroundings?
8nm thick
What are the P. Membranes 3 main functions?
1.It has selective permeability
2.Maintenance of cell integrity
3.Transport and cell signalling
4 components of the cell membrane
1.Phospholipid bilayer
2.Cholesterol
3.Carbohydrates
4.Proteins
Describe the polarity and structure of a phospholipid
The negatively charged phosphate head makes it hydrophilic, whereas the non polar fatty acid chains are hydrophobic, making it an amphipathic
Name 4 prominent phospholipids found in animals
1.phosphatydlcholine (PC)
2.Phosphatydlethanolamine (PE)
3.Phosphatydlserine (PS)
4.Sphingomyelin
What are michelles like
Michelles in water face hydrophobic heads outside and form a sphere interior can be aqueous
What phospholipids does the outer leaflet of bilayers usually contain?
Phosphotydlcholine
Sphingomyelin
What phospholipids does the inner bilayer contain?
Phosphatydlethanolamine
Phosphatydlserine
How is fluidity of the phospholipid bilayer affected by temperature?
Governed by adjacent hydrocarbon chain interacting
High temp: interactions are overcome and fluidity (double bonds lower Mt)
Low temp: high degree of interaction, membrane is more solid
How is fluidity affected by the saturation of fatty acids?
saturated FAs only = Less fluidity
Saturated and mono saturated mixed= more fluidity
What is the major sterol of mammalian membranes?
Cholesterol (ampipathic) like PL molecules
What does cholesterol do to fluidity of the bilayer?
1.Makes lipid bilayer less deformable
2.Decreease it’s penalty to small water soluble molecules
3.prevents phase shifts
Low temp:stops tight packing of PL in bilayer
High temp:Holds PL together
What does cholesterol do to the movement of PLs?
Limits movements of PLs and keeps membrane stabilised
Describe the movements of phospholipids and how often they occur
Lateral movements occur 10^7 times/sec
Flip flop movement occurs once a month
Describe membrane carbohydrates
Usually <15 units, short and branched
Covalent bound to lipids and proteins to form glycolipids/proteins and vary amongst species, and cell types
Name 3 functions of membrane carbohydrates
They are involved in cell-cell recognition
Cell sorting to form tissues and organs
Detection of foreign cells (P-selectin)
Also can tell us certain blood types so used as identification markers
Describe a membrane protein
Collage of proteins embedded into bilayer and determines a cells specific functions
Integral proteins : transmembrane and partially embedded proteins
Peripheral proteins: usually attached to PL head or other integral proteins
What are 4 types of functions membrane proteins can have?
1.Transporters
2.Anchors
3.Receptors
4.Enzymes
Membranes proteins are very mobile, what bonds hold membrane molecules in place?
Membrane molecules are held in place by weak hydrophobic interactions
What is FRAP?
A technique developed by Axelrod used to study protein mobility in living cells using intense laser
Describe plasma membrane permeability?
P. Membranes are selectively permeable
free movement of a molecule through membrane depends on interaction of a molecule with the hydrophobic core of the membrane
What type of molecules can diffuse through the lipid bilayer?
Hydrophobic molecules such as CO2, O2, hydrocarbons can diffuse through bilayer
What type of molecules require the aid of membrane proteins to cross the membrane?
Ions, polar molecules (water), and large molecules (glucose) require membrane proteins to cross the membrane
What does molecule movement through the membrane depend on (what gradients)?
Internal vs external concentration /electricochemical gradients
What is a uniporter,symporter and an anti porter?
Uniporters move one molecule at a time and are passive
Symporter moves two molecules at the same time requires ATP
Antiporter move one molecule in and one out at the same time like calcium potassium channel requires ATP
How many ions does passive move and how many does active transport move?
Passive - 10^7 ions per sec
Active Transport - 450 ions per second
Two examples of uniporters and what they move
Aquaporin - moves water
Gated sodium ion channel - moves Sodium
What do antiporters and symporters move?
Antiporters - sodium/potassium channel (muscles)
Symporter - sodium/glucose channel
