Membrane Transport BSCI 420 421 Trust your gut

Membrane Transport BSCI 420, 421 “Trust your gut” Lecture 17 -Barbara Walters Oct 2002

Living cells maintain concentration membranes. E. g. : (Table II-I) OUT Protein < Na+ > K+ < Ca+ > H+ > Cl> gradients across their IN PROTEIN Na+ K+ Ca+ H+ Cl- They maintain these gradients by the passive and active transport properties of their membranes.

Four major ways molecules or ions get across membranes:

Transport is either with or against the electochemical gradient

Simple diffusion: 1/ size & proportional to solubility In lipids

2. Carrier Mediated Transport: Carrier proteins undergo a conformational change

Carrier-mediated diffusion obeys Michaelis-Menton Kinetics Reaches a Vmax, lim by no. of transporters and rate each can transport; Also char. By M-M constant KM

Three types of carrier mediated transport And also active transport:

4. Active transport is the transport of a solute against its Electochemical gradient. Secondary (indirect) or Primary (direct) active transport

The glucose transporter: Glucose uptake is driven by a Na+ gradient

Lactose permease, indirect AT driven by an H+ gradient

Glucose transport across intestinal epithelium 2 transporters kept separate by tight j(x)s

Direct active transport: The Na+-K+ pump (a P-class pump)

The S. R. calcium pump

An ABC transporter e. g. the multidrug resistance transporter