Prelim 1 Biog1440 Flashcards
Cell membrane
membrane that separates the cell from its environment
Phospholipids
Synthesized from glycerol & two fatty acid side chains in ester linkage. The third alcohol (-OH) functional group is linked to a phosphate containing head group.
Amphipathic
Contain both hydrophobic and hydrophilic molecules
Hydrophobic
Not soluble with water
Hydrophilic
Polar, soluble with water
4 major phospholipids
Phosphatetidylcholine, phosphateidylethanolamine, phosphatidylserine, sphingomyelin *additional: Phosphatidylinositol
Entropy
The measure of randomness of a system
High entropy: high disorder & low energy
Low entropy: Lower disorder & greater energy
Hydrophobic effect
Hydrophobic molecules mix well in hydrophobic solvents & hydrophilic molecules with hydrophilic solvents (water) LIKE MIXES WITH LIKE
Phospholipids will spontaneously assemble into bilayers due to hydrophobic effect. Hydrophobic molecules with water tend to form cage like shells (altercate) separating water which forms an ice like layer.
Which is chaotic=entropy which is favorable though it goes against thermodynamics
Fluid mosaics
Phospholipids are not covalently linked to one another, they’re held together by weak hydrophobic forces. So these phospholipids can diffuse around in the plane of the membrane from side to side.
Chemical composition can change to maintain membrane fluidity. A model of membrane structure in which proteins are inserted in a fluid phospholipid biolayer
Fluidity
Controlled by the introduction of a double bond into a fatty acid side chain which leads to bends or kinks in the fatty acid chain which weakens the intra & intermolecular packing interactions (ex. cholesterol)
Cholesterol
At warm temperatures (37 degrees) it limits excess fluidity. At cool temperatures cholesterol maintains fluidity, prevents tight packing of FA chains.
Laterally
Lipids and proteins can drift laterally but the size of the proteins & their interactions often limit their movement.
Peripheral membrane
Surface of the membrane but don’t actually extend into the membrane. Operationally defined as proteins that dissociate from the membrane following treatments with polar reagents, such as solutions of extreme pH or high salt concentration that DO NOT disrupt the phospholipid bilayer
Integral membrane
Extends through the bilayer and usually peaks out of both sides. Proteins can be released only by treatments that disrupt the phospholipid bilayer (ex. detergents)
Outer leaflet
Mainly phosphatidylcholine & sphingomyelin
Inner leaflet
Phosphatidylethanolamine & phosphatidylserine
Why is the phospholipid important?
- The interior phospholipid bilayer uses hydrophobic fatty acid chains which makes it impermeable to water
- Bilayers of phospholipids are fluid so the fatty acids of phospholipids have one or more double bonds which introduce kinks into the hydrocarbon chains & makes them difficult to pack together; therefore the long hydrocarbon chains move freely in the interior of the membrane so its flexible.
Cells can vary the properties of their membranes in two ways:
- They can change the type of polar head group (chlorine-serine-glycerol-ethanolamine) which changes the charge & properties of the membrane
- Change the length & shape of fatty acids
Homeoviscous Adaptation
Cells actively regulate membrane fluidity by changing the shape of their fatty acids depending on the temp they are grown
Transmembrane Proteins
Typically require assistance to integrate into membranes
SecYEG Translocon
Proteins that help other proteins cross or move into the membrane where they become integrated into the membrane. Once the protein is integrated, it can be modified.
Osmosis
The net movement of water (solvent) across a selectively permeable membrane into a region of higher solute concentration.
Facilitated diffusion
Speeds the passive movement of solutes across the membrane.
When transport proteins speed the passive movement of molecules across the plasma membrane (down a concentration gradient).
Active transport
Requires the energy of ATP or the energy available in other gradients (e.g. PMF) & leads to the accumulation of solutes against their gradients.
Uses energy to move solutes against (up) their gradients.
Can also use energy stored in chemical gradients