Molecules move from an area of high concentration to an area of lower concentration
Only very small molecules like H2O and CO2 - non-polar only
Does not involve carrier proteins
Moves along the concentration gradient
ATP not required
Reversible movement
Shows saturation
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Facilitated Diffusion
Diffusing involving carrier proteins (permeases)
Rate of diffusion increases with the concentration gradient
Major intrinsic proteins (MIPs) facilitate diffusion
Small, polar molecules eg. glycerol
ATP not required
Shows saturation
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Active Transport
Transport of solute molecules to a higher concentration
ATP is needed
Involves use of permeases
Against the concentration gradient
Shows saturation
Irreversible
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Group Translocation
Molecule is chemically modified as it is brought into the cell
Type of active transport
Well known example is the PTS system - in this system when a sugar is taken up it gets phosphorylated using PEP as the phosphate donor, yielding pyrivate
Most aerobes except Bascillus lack a PTS system
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Iron Uptake - Gram Negative Bacteria
Numerous pathways, unlcuding uptake from transferrin, siderophores or heme
All require an outer membrane receptor, a Periplasmic Binding Protein or an inner membrane ATP Binding Cassetle
Not all bacteria have all 3, but some have more than 1 type
Outer membrane receptor (very specific) to get through to periplasm ---> once in need PBP ---> need an ATP transporter to get through to cytoplasm
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Iron Uptake - Gram Positive Bacteria
Uptake of iron from heme, siderophore or transferrin
Involves membrane Anchored Binding Protein and a membrane associated ATP Binding Cassetle
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