solute protein transport ch 17

Types of secondary transporters?

Symport
Antiport
Uniport

What kind of substances can cross by simple diffusion? And why

Substances that dissolve in the hydrophobic interior of the membrane (like H20, H2, CO2, O2).

What is simple diffusion, and what kind of transport is it?

Simple diffusion is the random and passive movement of molecules from high to low concentrations.
It is a type of passive transport.

What are the characteristics of simple diffusion?

No competition between substances,

net flux of molecules are proportional to the concentration difference and the permeability of the membrane,

No saturation kinetics.

What type of transport is facilitated diffusion?

Passive transport

What is facilitated diffusion?

Movement of substances from high to low concentration through pores (protein channels of carrier proteins).

These substances cannot diffuse directly through the cell membrane.

What are the characteristics of facilitated diffusion?

Related substrates can compete for the same carrier protein or pore.

Can become fully saturated (Tm) due to lack of available pores.

What type of molecules are transported through facilitated diffusion?

Only a few molecules, like glycerol.

Glycerol uptake via aquaglycerolporins such as E. coli GlpF.

What are secondary transporters?

Transporters that use electrochemical gradients of H+ or Na+

Often, mediated by a single polypeptide.

What is passive transport?

A type of solute transport that does not require energy.

What are the two types of passive transport?

Simple diffusion and facilitated diffusion.

What is secondary transport?

A type of solute transport that relies on an electrochemical gradient.

What is primary transport?

A type of solute transport that requires energy.

What is group translocation?

A type of primary transporter known as the PEP phosphotransferase system.

What are ABC transporters?

A type of primary active transporter.

How does symport work in secondary transport?

Uses energy stored in an ion gradient to move both molecules in the same direction.

How does antiport work in secondary transport?

Uses energy stored in an ion gradient to move two molecules in opposite directions across the membrane.

How does uniport work in secondary transport?

Uses only the concentration gradient of the molecule being transported. transports a single type of molecule or ion across the membrane in one direction.

What are the types of primary transport?

primary active transport, and group translocation

What is primary active transport?

Uses ATP to move substances against their concentration gradient using specific pump proteins.

Examples of primary active transport.

ATP synthase

ATP binding cassette

Bacteriorhodopsin

Oxaloacetate (OAA) decarboxylase

What is group translocation?

Energy dependent transport mechanism where a molecule is transported across a membrane while being chemically modified.

What is a type of group translocation system?

Phosphotransferase (PTS) system

What does the phosphotransferase system (PTS) do?

Accumulate carbohydrates as phosphorylated derivates (glucose-6-P, mannitol-1-P, mannose-6-P)

Look at a picture of the phosphotransferase system (PTS). Explain what is happening.

1. PEP donates phosphoryl group to E1 enzyme.

2. E1, now phosphorylated, is now a high energy molecule. Transfers phosphoryl group to HPr.

3. Now that Histidine protein is phosphorylated, it is available for transferring to a variety of E2 proteins, linked to transporters of PTS sugars (mannitol, glucose, mannose).

PTS system is common in what types of microbes?

Common in strict and facultative anaerobes.

What is ATP-binding Cassette (ABC) Transporter?

ATP used to drive transport of substrates/solutes across cell membranes.

What substrates are included in ATP binding cassette (ABC) transporter?

Metabolites, lipids, sterols, and drugs.

What is ATP binding cassette (ABC) transporter involved in the uptake of?

Metabolites like maltose, tumor resistance, bacterial multi-resistance, antigen presentation and inherited human disease like cystic fibrosis

What is a characteristic of ATP binding cassette (ABC) transporter?

Ancient/large superfamily of proteins, found in all three domains.

Components of ATP-binding Cassette (ABC) Transporter

1. Solute binding protein
2. Transmembrane spanning domain
3. Nucleotide binding domain

Description of solute binding protein

G(-) often located in periplasm.

G(+) and others are associated with the cell membrane.

Description of transmembrane spanning domain

Typically heterodimer of 2 different subunit. spans the membrane.

What motifs are present in the nucleotide binding domain?

Walker A and B motifs

What is the structure of the nucleotide binding domain?

It is a dimeric protein complex.

What is the function of the nucleotide binding domain?

It drives solute uptake via conformational change in protein mediated by ATP binding and hydrolysis.

ABC transporters in Gram Negative bacteria

Non-energy depende rxn, porin allows facilitated diffusion of maltose via Omp porin.

Maltose binding protein binds maltose. to reduce overall free form amount of maltose (to minimize concentration of maltose).

TMD allows uptake of maltose into cell.

Transition state for ATP hydrolysis causes conformational change so that maltose can be taken into cell.

What happens when cell becomes low on K+

Cell switches on Kdp system, with a high affinity for uptaking K+.

Two component phosphrelay system, that is stimulated when low K+.

The relay system is involved in transcriptional regulation that turns on transcription of high affinity Kdp system,.

K+ uptake, used to maintain osmotic/pH homeostasis.

K+ is preferred over Na+ by organisms.

What transporter system is activated when cell is under low K+ conditions

Kdp system

What transporter system is activated when cell is under high K+ conditions

TrK system

Explain how transporter systems are linked with precursor/product antiporters.

fermentation of end products with the uptake of nutrients.

What are examples of transporter systems in which:

The energy generated by the accumulation of fermentation of end-products in cell drives the antiport-like uptake of nutrients

1. Cell grows on malate, and produces lactate.

2. Cell grows on arginine, and produces ornithine.

3. Cell grows on lactose, and produces galactose.

What is a siderophore?

Small molecules that have an extremely high affinity for iron and are secreted by microbes to chelate iron.

What is a essential trace metal for all living organisms (besides some lactobacilli and bacilli)?

Iron

What is considered the "critical determinant" in deciding the outcome of host-pathogen interactions?

And why?

Iron acquisition

Because extracellular iron is low in the host environment.

Siderophore-iron complexes.

Recognized by specific receptors on the bacterial surface for uptake.

Name the types of siderophores.

1. Catecholate
2. Phenolate
3. Hydroxamate
4. Carboxylate

How does S. aureus partake in iron acquisition

Has 2 types of siderophores

FhuC ATPase powers uptake.

Xenosiderophores produced by other bacteria.

Heme acquisition mediated by Isd System.

Either IsdDF or HtsBC permeases mediate uptake via membrane.

Isd enzymes degrade heme to iron and staphylobilin.

How does Gram negative bacteria partake in iron acquisition in a gerneral model?

Use a TonB dependent transporter in an energy dependent mechanism, to take iron through the outer membrane.

Transports ferric siderophore across the OM derives energy from the PMF of IM via energy -transducing TonB complex, that binds the TonB box of TBDTs.

Extracytoplasmic function sigma factors are common to bacteria and typically regulated by an anti-sigma factor. under low iron.

What happens when cell is under high K+ conditions.

Cell is under constitutive, low affinity for K+ in the Trk System.

uses a K+ ion driven by PMF, to uptake K+ ions into cell in energy dependent mechanism.