BIO 328 Lecture Notes - Lecture 2: Lipid Bilayer, Semipermeable Membrane, Chemical Polarity

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Published on 7 Aug 2018
Department
Course
Cell Physiology
The First Cells Protocells - cell membrane defines intracellular/extracellular space - Darwinian evolution
- don’t much about of how they became that. When the first cell membrain
first evolved, dawrin applied it. Self from non self. Immune system whats
what bactria, kills it.
- Iside cell self, outside not self
Physical Constraints on Protocells
1. Permeability of lipid bilayer - first cells leaky membrane - more transporters required as membrane
becomes less leaky
- leaky decline as traported increases
- deffusion was important for the first cell
Permeability of lipid bilayer
- useful solute they would tap there and cant diffusion out of the cell.
2. Diffusion - first cells were very small - high surface to volume ratio - diffusion times generally constrain
cell size
- small distance , 20 ms
I cm, takes 20 days?
Distance.- cell size. High serface to volume ratio
1 um takes 10 ms
******
3. Internal calcium ions disrupt many cellular processes - many calcium salts are insoluble e.g. calcium
phosphate - causes aggregation of nucleic acids and proteins - disrupts membrane structure - requires very
low Ca2+ concentration inside of cell
-cal salt insoluble . phosphates in nuclic acids, protiens. The first cells devolped with low cal consetration.
Had to figure out before moving out to make sure too much cal would kill them. Need ca to be really low.
Minimal Cell Physiological Properties mammual cells
1. Regulate membrane permeability
2. Regulate internal calcium concentration
3. Regulate internal pH
4. Regulate cell volume - osmolality - high internal K+ ion concentration
Water
- water molecules, 75% of total body weight
and 99% total number of molecules
- pure water, a poor conductor of electricity
- polar molecule, polar covalent bonds, electronegativity, dipole.
- hydrogen bonding between water molecules
- Because of its polar nature water is an excellent solvent for salts, acids and bases
- salts, acids, bases, dissociate into ions in water
- Na+ and Cl
- NaCl table salt
- uncharged, cannot carry a current
- hyrgoen bonding
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- red pic is hydration shell- water around the ions
salts in water have a election current.
( like sneesy, you know its coming, put you hand up, ready to go, react slowly so fast when your ready.
Cell Membrane
• barrier to diffusion of charged and polar molecules
made up of lipid bilayers which are made up of phospholipids
Phospholipids
• two distinct regions
• polar - hydrophilic, interact with water molecules
• nonpolar - hydrophobic, interacts with other hydrophobic molecules amphipathic
anitpathic molecular. Polor and non polar regins.
Lipid Bilayer- hydrophobic core like thin layer of oil
fluid mosaic model
integral membrane proteins- inbeded into the lipid core there are protiens “
intergral”.
Integral membrane proteins- amphipathic in phospholipid
- membrane 60Å (6 nm) thick hydrophobic core 30Å (3 nm) thick
- different domains keeping everything out or in the cell. Fragil . bild stabily by proteins and
interact with cytoskelten
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