Chapter 9 Flashcards
What are the 6 functions of biological membranes?
- Separate cells from external medium and intracellular compartments
- Facilitate transport of substrates and ions in the cell
- Membranes for mitochondria, chloroplasts and plasma membrane of bacteria are sites of energy conversion
- Neural signal transduction
- Involved in cell-cell interaction
- Membranes contain receptors for hormones and other signals
What are the 3 forms of membrane?
Micelle- where individual units are wedge-shaped (big circle) (fatty acids and detergents)
Bilayer- individual units are cylindrical (flat stacks) (glycerophospholipids and sphingolipids)
Liposome- bilayer wrapped in a circle like micelle
Pictures on slide 3
Why are liposomes more useful than bilayers?
They have no exposed hydrocarbon tails so they are more stable and energetically favourable
What is a peripheral protein and an integral protein (single transmembrane helix and multiple trans membrane helix)?
Peripheral protein- attaches to outside membrane wall or other proteins in membrane using lipid anchors (inside or outside cell)
Integral protein- embedded into the membrane and can be detached using detergents
Single helix- has just one row embedded into membrane
Multiple helix- has multiple rows embedded into helix
Diagram on slide 5
What are the two types of lipid diffusion across membranes and what is the relative time to complete each?
- Uncatalyzed transverse (flip flop) diffusion- lipid molecule flips sides of the membrane
T1/2 is in days length - Transverse diffusion catalyze by flippase- flippase embeds in the membrane and the lipid uses it to flip to the other side of membrane
T1/2 is in seconds length
What are the two ways acyl groups are ordered in the lipid bilayer interior?
What changes these states from one to the other?
Paracrystalline state (gel)- ordered state below phase transition temperature Fluid state- at temperatures well above phase transition, the hydrocarbon chains are disordered and membrane is fluid Heat changes paracrystalline state to fluid state
What state is the lipid membrane in at intermediate temperatures?
Liquid-ordered state (between paracrystalline state and fluid state)
Hydrocarbon chains are partially ordered, but lateral diffusion is possible
How is the percentage of total fatty acids affected by temperature for saturated and unsaturated?
Saturated- As temperature goes up, more fatty acids are needed and used
Unsaturated- as temperature goes up, less fatty acids are needed
How does the percentage of total fatty acids change as you get more carbons?
More double bonds?
More carbons - higher fatty acid percentage
More double bonds- higher fatty acids percentage
How do sphingolipids create lipid tarts in biological membranes?
Sphingolipids associate with cholesterol to form lipid rafts that are domains of liquid ordered lipid surrounded by largely disordered fluid phospholipid
Picture on slide 9
How are lipid rafts stabilized?
Interactions between the cholesterol ring and long saturated hydrocarbon tails of sphingolipids
What are lipid rafts?
Attachment points for peripheral membrane proteins that are anchored to the membrane by two covalently attached saturated acyl chains or glycosylated phosphoinositol derivatives (GPI)
What are the 3 types of covalent attachment inside the cell?
- Using palmitoyl group on internal Cys or Ser
- Using N-Myristoyl group on amino-terminal Gly (amide bond)
- Using farnesyl group on carboxyl-terminal Cys
Picture on slide 11
What is the one type of covalent attachment outside the cell?
Using GPI anchor on carbonyl terminus
Picture on slide 11
How do you know if a protein is bonded outside the cell or inside the cell based on what it’s bonded to?
Proteins anchored by Glycosylated phosphoinositol (GPI) are always outside the cell
Proteins anchored by fatty acyl or prenyl chains are always inside the cell
How are amino acids distributed (inside or outside the cell) in integral membrane proteins?
Charged residues (Asp, Glu, Arg, Ltd) are locates mostly outside the membrane with some exceptions for interactions Resides with apolar side chains dominate inside the hydrophobic slab of the bilayer Tryptophan and tyrosine are inbetween the hydrocarbon chain and polar headgroup
What are the two archetypes of membrane transport protein structure?
α-helices- coiled up tightly knit through the membrane
β-barrel- membrane spanning strands
Pictures on slide 13
How are carbonyl and amide groups of the protein backbone inside the bilayer bonded? Why?
That are bonded with hydrogen bonds so that the transfer of uncompensated electric dipoles on the protein backbone into the apolar core of bilayer won’t have a high energy penalty
All peptide groups inside bilayer cores are hydrogen bonded in secondary regular structures
What are the 8 biological processes the membrane fusion is a result of?
- Budding of vesicles from golgi complex
- Exocytosis
- Endocytosis
- Fusion of endosome and lysosome
- Viral infection
- Fusion of sperm and egg
- Fusion of small vacuoles
- Separation of two plasma membranes at cell division
How does membrane fusion play a role in neural transmission?
Neurotransmitter release in neural synapses involves fusion of membrane vesicles loaded with neurotransmitter with plasma membrane. Requires SNAP and SNARE proteins
Diagram on slide 16 and 17
How does concentration gradient drive diffusion across the membrane?
(Equation)
ΔG=2.3RT*log[C2]/[C1]
R=8.32 J/molK
Concentration will always move to the side with less (always find equilibrium m)
How does electric potential drive diffusion across the membrane?
(Equation)
ΔG=-mFΔΨ
F= 96480 J/Vmol
ΔΨ= electric potential difference between two compartments
What is the entire equation that connects the concentration gradient and electric potential for finding diffusion across a membrane?
What is the equation for protons?
ΔG=-mFΔΨ+2.3RT*[Cin][Cout]
For protons:
ΔG=-FΔΨ+2.3RT*ΔpH(out-in)
What are the 6 types of membrane transport?
- Simple Diffusion (nonpolar only) Sout->Sin (down conc gradient)
- Facilitated Diffusion- Sout->Sin with help of embedded protein (down electrochemical gradient)
- Primary Active Transport- uses ATP (against electrochemical gradient)
- Secondary active transport- driven by ion moving down its gradient (electrochemical gradient)
- Ion channel- may be gated by a ligand or ion
(Down electrochemical gradient) - Ionophoremediated ion transport- ion bonded to ionophore goes through membrane (down electrochemical gradient)
Slide 20
What are primary active transporters?
Couple endergonic transport of X against its electrochemical gradient (ΔG>0) to an exergonic chemical reaction (ΔG<0)
What are secondary active transporters?
Couple endergonic transport of X against X electrochemical gradient (ΔG>0) to exergonic transport of Y down Y electrochemical gradient (ΔG<0)
What are passive transporters?
Can only transport X down it’s electrochemical gradient (ΔG<0)
