Unit-2

Symport - It is kind of co-transporter (transport two different substrates) integral membrane protein that helps in transport of different types of molecules across the membrane. E.g. Na+/K+ transporter.

Diffusion or passive diffusion - Is a kind of molecular movement, in which atoms or molecules move across the concentration gradient i.e. from a region of high concentration to low concentration.

Facilitated diffusion – A kind of transport in which molecules are transported by passive movement (move from region of higher concentration to low concentration), however transport is effected by carrier protein. E.g. transport of glucose, sodium  

Uniport - It is an integral membrane protein that transports only a single substrate at a time across the cell membrane, transport is effected by facilitated diffusion or secondary active transport mechanism. E.g. glucose transport  

Antiport – It is a co-transporter (transport two different substrates) integral membrane protein that is involved in transporting two different molecules or ions across a plasma membrane in opposite directions with input of energy in the form of secondary active transport. E.g. Na+/H+

Group translocation – Also called as phosphor transferase system, involving multiple component of proteins, it is a distinct transport mechanism in which the functional group was altered (e.g. glucose altered to glucose-6-phosphate) to effect translocation, and energy for this transport mainly comes from phosphoenol pyruvate.

Active transport – It refers to movement of ions or molecules across a membrane, against concentration gradient (from the region of low concentration to the region of high concentration), cell energy as ATP is used in this process and the transport is effected by several integral membrane proteins. E.g. ABC (ATP binding cassette) transport system transporting several molecules. E.g. E. coli transport several sugars (arabinose, maltose, galactose, ribose) and amino acids (glutamate, histidine, leucine).

Nutrient Any substance, whether in elemental or molecular form that must be provided to an organism, that could facilitate growth and metabolism. E.g.H20, O2

Osmosis – Refers to diffusion or movement of water molecules across a semi permeable membrane from region of less concentrated solutes to region of more concentrated solutes, mainly to balance the osmotic pressure.

Bulk transport - A kind of active transport commonly takes place in eukaryotes, it involves mass transport of large particles, cells and liquids by engulfment and vesicle formation. The various kind of bulk transport are exocytosis, pinocytosis etc.  

Periplasmic binding proteins - Periplasmic binding proteins (PBPs) are members of a widely distributed protein superfamily found in Bacteria and Archaea, and are involved in the cellular uptake of solutes or substrates (sugar, amino acids and ions) mainly through ABC systems.

Permease - It refers to any kind of protein that are acting as carrier proteins, and involved in the transport of molecules or ions across the membrane as facilitators

Porins -They are trimeric, beta barrel proteins that allows passive diffusion that forms water filled transmembrane channel that permits the passage of certain ions, sugars and small molecules, allows molecules below 1500 daltons. e.g. OmpF (Aquaglyceroporin) - glycerol, CO2, ammonia and urea across outer membrane

 Osmoregulatory proteins - Refers to diverse biosynthetic enzymes, transporters and channel proteins that are involved in the maintenance of osmotic balance of the cells. E.g. aquaporins and K transporters.

Aquaporins - water specific channels embedded in the membrane that accelerate the transmembrane water fluxes, mostly they are involved in controlling water fluxes in eukaryotic cells.

Osmoprotectants - They are also called as osmolytes or compatible solutes that refers to several compounds, when present within a cell or externally, play role in maintaining cell volume and fluid balance and can stimulate bacterial growth rates under hyperosmotic conditions. e.g. trimethylamine n oxide (TMAO), trehalose, betaine, glycine betaine

Mechanosensitive channels - channels present in the cytoplasmic membrane which responds to increases in the cell’s turgor pressure by increasing in pore size, effecting inward or outward movement of water. Thus they facilitate efflux of water and certain solute, these channels seems to have low ion selectivity but high conductance.

Secondary active transport - refers to transport of molecules across the cell membrane utilizing energy in forms other than ATP. (e.g. as proton gradient or sodium gradient) e.g. of transport like Symport and Antiport