Membrane Structure and Function. Chapter 7. TEM of Phospholipid Bilayer. Hydrophobic region of protein. Hydrophilic regions of protein. Membrane Structure. Basic fabric of membranes is a phospholipid bi-layer
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Hydrophilic regions of proteinMembrane Structure
(Oligosaccharide added in the Golgi body)
(Part of cytoskeleton)The fluid mosaic model
Membranes have the consistency of cooking oil!
When mouse and human cells were fused, their phospholipid bi-layers, along with their membrane proteins intermingled within one hour – creating a chimeric plasma membrane.
A transmembrane protein
For example: Enzymes embedded in the inner membrane of mitochondria play a role in cellular respiration
For example: insulin binding to membrane proteins, which starts a signaling pathway that stimulates cells to take up more glucose from the bloodstreamTypes of membrane proteins – and their roles
For example: cells of the immune system need to bind to glycoproteins on cell surfaces, in order to decide if the cell belongs to the body or is foreignTypes of membrane proteins – and their roles, cont’d.
Integrins are an example of cell surface receptor proteins that adhere to and interact with the ECM. Integrins also coordinate activities inside and outside cells via signal transduction.
Selective permeability glycoproteins on cell surfaces, in order to decide if the cell belongs to the body or is foreignTraffic Across Membranes
-70 mV (It can range from -50 to -200 mV)
Low free energy – stable system
High free energy
Low solute glycoproteins on cell surfaces, in order to decide if the cell belongs to the body or is foreign
(Also a form of Passive Transport)
solute and solvent balanced
(of water molecules)
As solute concentration increases, “free” water concentration decreases – so water potential decreases
Water then moves from an area of high water potential to an area of low water potential
Water will therefore move out of the cell to an area of lower (Net movement is outwards)
Water molecules always move from an area of higher water potential to an area of lower water potential, so water rushes into the “cell” from the outside (Net movement is inwards)
Is equal on both sides, so no net movement
Is the “cell” hypertonic, hypotonic or isotonic with respect to its environment?
Osmosis & Plant cells
1.) solute concentration
2.) physical pressure (cell wall)
can be measured as Water Potential
Water = pressure + solute
Potential potential potential
S = - iCRT
i = # particles molecule makes in water
C = Molar concentration
R = pressure constant 0.0831 liter bar mole oK
T = temperature in degrees Kelvin
= 273 + oC
= P + S
In an open container, P = 0
1. Remember water always moves from [hi] to [lo].
2. Water moves from hypo hypertonic.
3. [Solute] is related to osmotic pressure. Pressure is related to pressure potential.
4. Pressure raises water potential.
5. When working problems, use zero for pressure potential in animal cells & open beakers.
6. 1 bar of pressure = 1 atmosphere
In the absence of aquaporins, cells do not swell osmotically!
1. open channel – (water uses this method -aquaporins)
2. gated channel
3. carrier proteins – (glucose uses this method)
1. outside has more solute particles
Na+ binds to the transport protein at specific binding sites
Phosphorylation causes conformational change in protein, which moves the Na+ out of the cell
Na+ binding causes ATP to phosphorylate protein
When K+ exits its binding site, it causes the release of the inorganic phosphate group
When Na+ exits the binding site, the binding site for K+ is made accessible and K+ binds to sites
When K+ binds, it causes another conformational change, which moves K+ into cellActive Transport Cont’d.
Proton Pumps helps move H+ against their gradient (out of cell) – this build-up of H+ outside the cell is VERY important, because it is a high-energy/ unstable system that can be used to energize other cellular processes
Pinocytic vesicle forming outside has more solute particlesEndocytosis = Phagocytosis + Pinocytosis
Endocytosis is active transport – needs energy expenditure
TEM of lymphocyte – E.coli being ingested
SEM of stained prep.