Transport Mechanisms Flashcards
Cell Membrane is what kind of barrier to what kind of molecules?
These allow diffusion in gram negative bacteria?
CM is a hydrophobic barrier to most hydrophilic molecules.
Porins in gram negative bacteria allow diffusion of hydrophilic compounds to the periplasm.
Which compounds can diffuse through outer and inner membranes without hindrance?
Goal is to?
how many groups of general transport mechanisms?
Oxygen, Carbon Dioxide, Ammonia, and water
Goal: concentration of nutrients inside the cell that may be in short supply externally (require energy)
4 groups of general transport mechanisms
the four groups of transport mechanisms:
1) facilitated diffusion
2) Chemiosmotic-driven transport
3) binding protein-dependent transport
4) group translocation
Facilitated diffusion’s two ways:
Aquaporin-Z
Mechanosensitive Channels
(abrupt changes in extracellular osmolality)
Mechanosensitive Channels work by?
Turgor pressure; which permits inward and outward flow of ions and lowers turgor.
concentration of intracellular solutes: glutamate (K)
Chemiosmotic-driven transport: (3)
symport (opposite or neutral charges)
Antiport (two like charged {Na+/H+}
Uniport (independent of ion coupling)
Binding protein-dependent transport:
ATP-binding cassette transporter family (AKA traffic ATPases)
Energized by ATP or other high energy P-compounds (acetyl phoshate)
ATP hydrolysis leads to pore opening, and its unidirectional diffusion.
OMPs=
Outer membrane proteins aka porins
water filled pores, about 1-2 diameter in size
which regulates the access of hydrophilic solutes to the CM
Which compounds have specific transport proteins or specific pores:
Maltose example:
Vitamin B12, oligosaccharides, iron chelates have specific transport proteins or specific pores
Maltose makes the journey via a maltoporin.
Porins, or Beta-barrel membrane proteins:
can be _____ diffusion pores, ______ pores, as well as:
can be non-specific diffusion pores, specific pores, active transporters
enzymes
lipases
acyltransferases
OmpA=
OmpT=
NalP=
FadL=
PhoE=
ScrY=
OmPIA=
FhuA and BtuB=
small ion channel
protease
autotransporter
long chain fatty acid transporter
diffusion pore
sucrose specific porin
phospholipase
active transporters for ferrichrome iron and vitabin B12 uptake
porins are also involved transport of?
transport of antibiotics, toxins, and other secreted compounds, and enzymes and those compounds used to cope with osmotic pressure.
Omp C and Omp F levels are:
Omp C increased:
Omp F decreased:
reciprocal
osmolarity
osmolarity
Why are establishing of ion gradients important:
proton and sodium gradients for energy production and transport
charged ions and cell membrane
interrelated series of ion circulations
F-type and P-type ATPases
Ionophores:
two models of ionophores:
Ionophores: ion carriers/proteins small, lipid soluble molecules that allow specific ions to permeate the membrane.
1) Mobile Carrier model
- Valinomycin
2) Pore model (channel-forming)
- gramicidin A
-valinomycin is highly selective for? rather than and why?
how does the K+–valinomycin complex look?
valinomycin is highly selective for K+ relative to Na+.
and this is because it is less energentically favorable for Na+ to shed its waters of hydration to form a complex with valinomycin.
K+ in the middle of a complex of 6 valinomycin units.
Gramicidin A structure:
Valinomycin structure:
(valine-gramicidin A; as well as an ethanolamine)
valinomycin has L-lactic acid, D-valine, D-hydroxy isovaleric acid, and L-valine and is in a circular complex of 3 molecules.
Simple diffusion:
Facilitated diffusion:
simple: concentration gradient without energy expenditure
Facilitated diffusions: carrier proteins
Active transport:
solute transport coupled with energy expenditure is divided into two categories:
1) primary transport
2) secondary transport
1) Primary transport:
2) Secondary Transport:
1) uses energy directly; light or chemical which is then converted to electrochemical energy as electrochemical potential of the substances to be transported. (photosynthetic electron transport, light driven ion pumps, redox energy dependent respiratory chains, transport ATPases and Na+ pumps utilzing decarboxylation energy.)
2) electrochemical energy originates from the electrochemcial potential of another substance that is used up in symport or antiport.
ATP-dependent transport: ATP-binding cassette pathway (ABC):
subunits?
identical vs nonidentical?
NBDs?
what is the signature seq of amino acids residues within the nucleotide?
- 4 subunits
- two nonidentical (hydrophobic transmembrane moieties)
- two are identical (hydrophilic)
- NBDs= nucleotide-binding domain that binds ATP on the cytoplasmic side of the membrane. NBDs bind and hydrolyse ATP to power the transport cycle.
- characterized by LSGGQ motif
