Transport Mechanisms

Question 1

Cell Membrane is what kind of barrier to what kind of molecules?

These allow diffusion in gram negative bacteria?

Answer 1

CM is a hydrophobic barrier to most hydrophilic molecules.

Porins in gram negative bacteria allow diffusion of hydrophilic compounds to the periplasm.

Question 2

Which compounds can diffuse through outer and inner membranes without hindrance?

Goal is to?

how many groups of general transport mechanisms?

Answer 2

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

Question 3

the four groups of transport mechanisms:

Answer 3

1) facilitated diffusion
2) Chemiosmotic-driven transport
3) binding protein-dependent transport
4) group translocation

Question 4

Facilitated diffusion’s two ways:

Answer 4

Aquaporin-Z

Mechanosensitive Channels

(abrupt changes in extracellular osmolality)

Question 5

Mechanosensitive Channels work by?

Answer 5

Turgor pressure; which permits inward and outward flow of ions and lowers turgor.

concentration of intracellular solutes: glutamate (K)

Question 6

Chemiosmotic-driven transport: (3)

Answer 6

symport (opposite or neutral charges)

Antiport (two like charged {Na+/H+}

Uniport (independent of ion coupling)

Question 7

Binding protein-dependent transport:

Answer 7

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.

Question 8

OMPs=

Answer 8

Outer membrane proteins aka porins

water filled pores, about 1-2 diameter in size

which regulates the access of hydrophilic solutes to the CM

Question 9

Which compounds have specific transport proteins or specific pores:

Maltose example:

Answer 9

Vitamin B12, oligosaccharides, iron chelates have specific transport proteins or specific pores

Maltose makes the journey via a maltoporin.

Question 10

Porins, or Beta-barrel membrane proteins:

can be _____ diffusion pores, ______ pores, as well as:

Answer 10

can be non-specific diffusion pores, specific pores, active transporters

enzymes

lipases

acyltransferases

Question 11

OmpA=

OmpT=

NalP=

FadL=

PhoE=

ScrY=

OmPIA=

FhuA and BtuB=

Answer 11

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

Question 12

porins are also involved transport of?

Answer 12

transport of antibiotics, toxins, and other secreted compounds, and enzymes and those compounds used to cope with osmotic pressure.

Question 13

Omp C and Omp F levels are:

Omp C increased:

Omp F decreased:

Answer 13

reciprocal

osmolarity

osmolarity

Question 14

Why are establishing of ion gradients important:

Answer 14

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

Question 15

Ionophores:

two models of ionophores:

Answer 15

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

Question 16

-valinomycin is highly selective for? rather than and why?

how does the K+–valinomycin complex look?

Answer 16

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.

Question 17

Gramicidin A structure:

Valinomycin structure:

Answer 17

(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.

Question 18

Simple diffusion:

Facilitated diffusion:

Answer 18

simple: concentration gradient without energy expenditure

Facilitated diffusions: carrier proteins

Question 19

Active transport:

Answer 19

solute transport coupled with energy expenditure is divided into two categories:

1) primary transport
2) secondary transport

Question 20

1) Primary transport:
2) Secondary Transport:

Answer 20

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.

Question 21

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?

Answer 21

• 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