Lecture 10 PMB

Question	Answer
What determines phospholipid "identity"?	The hydrophilic head group and the length of the tail determines this
Intercalaters of cell membranes:	eukaryotes: cholesterol prokaryotes: hopanoids
How can bacteria attack eukaryotic cell membranes?	Bacteria can secrete pore forming toxins to bind to CHOLESTEROL, not hopanoids
What percent of proteins of bacteria reside in the cell membrane?	10-20% of prokaryotic proteins reside here
major functions of cytoplasmic membrane	permeability barrier protein anchor energy conservation
comparative permeabilities of membrane to various molecules	water >>>> Na+ or K+
What is the proton gradient used to power? (IN GENERAL)	Powers ATP synthesis, transport reactions, flagellar rotation
hallmarks of all protein mediated transport:	1) transport rate is saturable (finite) 2) inactivation of an individual protein can block transport
What do ACTIVE transport systems specially allow for?	Allow for the accumulation of solutes in the cell to be >>> than surrounding fluid
How does glycerol enter the cell?	Enters through the GlpF protein by facilitated diffusion --> transporter will work to keep levels on inside and out of cell always even
What are the three families of energy dependent transport?	1) Simple transport 2) Group translocation 3) ABC system
simple transport	Driven by energy used in proton motive force
group translocation/transport	substrate enters by facilitated diffusion, is modified by an energy using reaction to prevent reverse transfusion
ABC system	periplasmic binding proteins involved, energy comes directly from ATP also known as ATP binding cassette transporters
simple transport example	use energy from proton motive force/existing ion gradient (Na+)
symport	two solutes go the same way (in simple transport) EX: H+ and lactose
antiport	two solutes go the same way (in simple transport) EX: Na+ and H+
group transport example	El and HPr gain a phosphate when PEP forms pyruvate, these then phosphorylate sugars and block them from entering IIC
ABC transport examples	reverse: no use of periplasmic binding protein, pump OUT substrates (antibiotics) G+: PBP = lipoprotein anchored in cytoplasmic membrane
TonB dependent transporters	Also known as TBDT used when a substrate is too large for a nonspecific OM protein TBDT interacts with TonB box which interacts with TonB, ExbB, ExbD, proton motive force powers uptake of substrate which is then carried by PBP in periplasm to ABC transporter and into the cytoplasm
Two pathways that lead to SecY, SecE, and Sec G transmembrane transport channel	1) SecB chaperone binds fully synthesized protein and keeps it unfolded, export powered by SecA ATPase 2) SRP binds to signal sequences from ribosome & halts translation, this complex is transferred to SecYEG and continued translation pushes protein across membrane
What types of proteins is SecB used for?	Used to transport OM, lipo, and periplasmic proteins (hydrophilic)
What types of proteins is SRP used for?	Used for integral IM proteins (hydrophobic)
Twin Arginine Transport (Tat) pathway	proteins that cant fold outside of cytoplasm are folded within it, and then transported using proton motive force
Why might proteins not fold properly in the periplasm?	Protein needs 1: a complex cofactor built by cytoplasmic assembly factors 2: Cytoplasmic chaperones 3: another protein to bind to in the cytoplasm for stability
Difference between Sec signal peptides and Tat signal peptides	Tat signal peptides have an RR motif 3 to 5 amino acids away from the N terminus of the hydrophobic region AND can transport larger substrates
Similarities between Sec and Tat pathways	both pathways use the proton motive force for energy and dispel similar amounts of protons
TatABC mechanism	1) TatB and C make a dimer 2) TatC binds Tat signal peptide, this + PMF allows TatA to polymerize and bind to BC 3) Substrate crosses through TatA complex 4) Signal peptide cleaved, TatA disassembles (can no longer maintain a permeability barrier)

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	Created by Candice Young over 6 years ago