1. Reshef Meshulam reshefm87@gmail.com
GRE Exam
Biochemistry, Cell and Molecular Biology
Preparation course
Cell Biology – Membrane bilayer
Reshef Meshulam

2. Lipid Bilayer

3. Lipid Bilayer
The membrane determines the interaction between the cell and its environment.
The membrane is composed from a mix of various types of phospholipids and cholesterol molecules

4. Lipid Bilayer Sterols
Cholestrol
Amphipatic
Four Fused rings

5. Lipid Bilayer Sphingolipids

6. Phospholipids

7. Lipid Bilayer Outer leaflet
Sphingomyelin (SPH) is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds nerve cell axons.
Phosphatidylcholine is more commonly found in the exoplasmic or outer leaflet of a cell membrane. It is thought to be transported between membranes within the cell by  Phosphatidylcholine Transfer Protein (PCTP).

8. Lipid Bilayer Inner leaflet
Phosphatidylserine – during apoptosis phosphatidyl serine is no longer restricted to the cytosolic part of the membrane, but becomes exposed on the surface of the cell. Many cells maintain asymmetric distributions of phospholipids between their cytoplasmic and exoplasmic membrane leaflets. The loss of asymmetry, in particular the appearance of the  phosphatidylserine  on the exoplasmic face, can serve as an early indicator of apoptosis
Phosphatidylinositol  is a negatively charged phospholipid and a minor component in the cytosolic side of eukaryotic cell membranes. The inositol can be phosphorilated to form phosphatidylinositol phosphate (PIP),  phosphatidylinositol biphosphate  (PIP2) and phosphatidylinositol triphosphate  (PIP3). PIP, PIP2 and PIP3 are collectively called phosphoinositides.
Phosphatidylethanolamine (cephalin) is found in all living cells, although in human physiology it is found particularly in nervous tissue such as the white matter of brain, nerves, neural tissue, and in spinal cord.

9. Membrane Fluid Mosaic Phospholipids movement
Lateral movement and rotation are done without the usage of energy or enzymatic activity.
Flip-Flop movement is aided by flippasses (Phospholipid translocators).

10. Membrane permeability
Different factors, with different physical qualities have a different ability to cross the membrane.
The ones that cannot cross the membrane in a direct way – do it via transport proteins
Water can:
Enter the cell via osmosis
Enter the cell via channels called aquaporins

11. Membrane proteins
Proteins can be bounded to the membrane in different ways; direct or indirect (integral & peripheral respectively)

12. Membrane proteins
Membrane proteins have various roles in the living cell

13. passive transport
active transport
fig. 12-4/9

14. Coupled transport - gradients provide energy

15. Transportation
Example – the mechanism of glucose intake via digestive system.

16. sodium – potassium ion pump
The Na+/K+-ATPase helps maintain resting potential, avail transport, and regulate cellular volume. It also functions as signal transducer/integrator to regulate MAPK pathway, as well as intracellular calcium. For most animal cells, the Na+/K+-ATPase is responsible for 1/3 of the cell's energy expenditure. For neurons, the Na+/K+-ATPase is responsible for 2/3 of the cell's energy expenditure

17. Quick Question I What fact is correct concerning transport proteins:
a. In sodium - potassium ATPase pump – the same number of ions is transferred from each side
b. There is more than one way in which water can get into the cell
c. Ions channels control the direction of ion migration and allow ions to cross the membrane only in one direction
d. Transporters and channels are ligand independent
e. Phosphorilation never effect transporters ב

18. Na+/K+-ATPase