3.2 - The Cell Membrane and Transport Flashcards
How much of the genome codes for membrane proteins?
1/3 of the genome
What are the two main types of membrane proteins
(1) Integral proteins
(2) Peripheral proteins
What are integral membrane proteins?
Integral membrane proteins are permanently attached to the membrane. They are embedded within the protein layer and cannot be removed easily. Integral proteins float rather freely within the bilayer.
What is the typical type of integral protein?
Transmembrane proteins which extend through the lipid bilayer so that one end is in contact with the outside of the cell while the other is in contact with the interior
Which part of integral protein is hydrophobic and which part is hydrophilic?
The portion of the protein in the hydrophobic region is hydrophobic whilst the extended parts of the protein are hydrophilic.
What are peripheral membrane proteins?
Peripheral membrane proteins are temporarily attached either to the lipid bilayer or to integral proteins through a combination of hydrophobic, electrostatic and other non-covalent interactions. They are easily seperable and are less mobile than integral proteins
Which between integral and peripheral proteins can be post-translationally modified?
Both
What are some types of membrane proteins?
(1) Membrane proteins
(2) Transport proteins
(3) Enzymes
(4) Cell adhesion molecules
(5) Structural support proteins
How does ATP synthase work?
There are a lot of protons in the inner membrane space of mitochondria. These protons flow through ATP synthase. Since protons are flowing down their concentration gradient e free energy released from their transport will lead to the rotation of a c ring in the ATP synthase. This drives the rotation of the gamma subunit which rotates beta modules. This generates 3 ATP.
What are the two types of transport?
(1) Passive transport: movement of molecules down a concentration gradient
(2) Active transport: movement of molecules against their concentration gradient
Examples of molecules that use passive transport
Weak acids and weak bases like aspirin, penicillin
Examples of molecules that use active transport
Vitamin B12
What do lipids do in membranes?
Provide fluidity to membranes.
What do all lipids have in common?
They are all not soluble in water
What constitutes phospholipids?
A glycerol with an ester link to two fatty acid chains and a phosphoryl polar head group
What constitutes a fatty acid?
A carboxyl group which is hydrophilic and a long hydrocarbon chain which is hydrophobic
Why are lipids special?
Their upper parts interact strongly with water (hydrophilic) whereas the lower part (the tail) stays away from water (hydrophobic)
Which part of the lipid points away from water?
The hydrophobic fatty acid tails
What does the fluidity and permeability of membranes depend on?
The saturation of the fatty acid tails
How can you get a membrane to be more fluid permeable
Unsaturated fatty acids have double bonds in their hydrocarbons which causes kinks in the tail since there are no rotations around double bonds. As a result, the fatty acid tails cannot interact as easily together as if they were all straight (saturated) and the membrane becomes more fluid permeable.
What does the enhances fluidity of a kinked phospholipid do?
Improve the function of the membrane at lower temperatures.
What does the degree of saturation of fatty acids depend on?
(1) Temperatures
(2) Growth phases
What should the membrane be like during the exponential phase (rapid growth)?
The membrane needs to be fluid so we have double bonds in the fatty acids.
What happens during the stationary phase (no growth) ?
Cells will produce enzymes that will react with these double bonds and produce a propane cycle.