Cell Membranes : Structure And Function Flashcards
Describe the chemical compositions of cell membrane
Membranes are dynamic structures in which proteins float in a sea of lipids
Eukaryotic cells contain internal membranes that form boundaries of the organelles
Membranes are sheet-like 60-100 angstroms
How are bacteria classified and how do the membranes differ
Bacteria are classified into gram negative which has 2 membranes
And gram positive which has a single membrane
What properties do fatty acids present in lipids?
Hydrophobic properties
It may be saturated or unsaturated
What are the 3 common types of membrane lipids?
Phospholipids
Glycolipids
Cholesterol
What are the properties of membrane lipids
Amphipathic - form bimolecular sheets in solution.
Polar heads - hydrophilic
Non polar hydrocarbon tails- hydrophobic
What are peripheral and integral membrane proteins?
Peripheral membrane proteins bind to the surface of integral proteins
The integral proteins interact with the hydrocarbon region
where is alpha helices found in membrane
Found in bacteriohodopsin
Certain non-polar amino acid and very few are charged
How are beta strands found in membrane
Found I porin
Each strand is diagonally hydrogen bonded to its neighbour- antiparallel
Forms a single beta sheet which curls to form a hollow cylinder
Porin has hydrophilic and hydrophobic AA in adjacent positions
Hydrophilic residues tend to lie outside the structure
How come sometimes detergents are needed to release proteins and in what protein
Eg prostaglandin and synthase-1
Lies along the outset studrgace of the membrane bound by alpha helices
The alpha helices extend into the membrane
The linkage is strong enough that only detergents can release the proteins
Technically integral, although not membrane spanning
What is the fluid mosaic model
All is lateral no event but not rotation though the membrane
Lateral diffusion of proteins is rapid
Spontaneous rotation/ flip flop is slow
How is membrane fluidity controlled
Fatty acid composition and cholesterol content
Cholesterol is the key regulator and disrupts interactions between fatty acid chains
- also forms specific complexes with soem phospholipid
Makes membrane more rigid and less subject to phase transition s
Fatty acids composition - number of double bond or chain length
Packing of fatty acid chains is disrupted by cis double bonds
Increased chain length decrease membrane fluidity
What is the role of cell membrane
- prevent molecules generated from cell to leak out
- barriers that define inside and outside of cells
-prevent unwanted molecules from diffusing into a cell - contain transport systems that allow spruced molecules to be taken up and removed
How does receptor-mediated endocytosis (LDL)?
- LDL. binds to a specific receptor
- The complex invaginates to form an internal vesicle
-The vesicle separates from its receptors and fuses with a lysosome
-LDL is degraded and it’s cholesterol is released
Name the different types of secondary transporter
Anti-porter - eg. Sodium-calcium exchanger - molecules flow in opposite directions
Symporters- eg. Sodium-glucose symporter - molecules flow in the same direction
What does eversions means?
Turning inside out
what are phospholipids made up of
Made up of two fatty acids, glycerol, phosphate and an alcohol
what is cholesterol formed from
four linked hydrocarbon rings
▪ Oriented parallel to fatty acid chains in membranes
▪ Hydroxyl group interacts with nearby phospholipid heads
what can be predicted from the AA sequence
Transmembrane proteins can be predicted from amino acid sequences
Amino acids with more negative transfer free energy values are more likely
to be located in an aqueous environment
what do hydropathy plots predict
Hydropathy plots can predict the window of 20 residues from which the
transmembrane domain originates
what a lipid bilayers held by and what are its properties
Lipid bilayers are held by covalent bonds
o No exposed hydrocarbon chains – form compartments
o Self-sealing – holes are energetically unfavourable
what transports require a mixture of ATPase and secondary transporters:
Na+/K+ ATPase converts free energy into a sodium ion gradient
o This gradient is used to pump other materials into cells using secondary transporters
▪ E.g. sodium-glucose symporter
The mechanism of P-type ATPase action
describe the the mechanism of P-type ATPase
- The Na+
/K+ ATPase binds with ATP and 2 calcium ions - Phosphorylation then occurs and the ATP converts to ADP and is lost leaving the Phosphate attached onto the complex.
- eversion occurs
- the calcium molecules are released
- hydrolysis occurs removing the phosphate
In a phospholipid what bond is present
Ester bond bewteren phosphate and alcohol
What is cholesterols
Membrane lipid based on steroid nucleus
