BOT 6516 Plant Metabolism

Lecture 2

Membrane Structure and Membranous Organelles

Cell membranes possess common structural and functional properties

The nature of all cell membranes is inherited

The driving forces for self organization of membrane lipids into membrane bilayers derives from the thermodynamics of amphipathic molecules in a strongly polar solvent

Membranes are best described by the Fluid-Mosaic Model

Movement and inversion of lipids between bilayers within membranes does occur

Membrane fluidity is a function of environment and lipid composition

Membranes interact with associated proteins in a variety of ways

Plants have cytosol to cytosol connections via plasmodesmata

The plasma membrane possesses P-type proton ATPases for the generation of cross-membrane proton gradient that can power transport of metabolites and inorganic elements/ion across the membrane against a concentration gradient into and out of the cell

Naturally, the plasma membrane of the plant cell possesses a variety of receptor proteins

The plasma membrane of plant cells are covalently linked to the inside surface of the cell wall presumably by protein connectors

Endomembranes arise from the ER/Golgi complex, as do some oil bodies and protein bodies

Turgor pressure affects membrane processes linked with exocytosis and endocytosis and membrane recycling

Vacuoles are important plant organelles and the tonoplast membrane contains V-type proton ATPases that create a proton gradient across the membrane for much the same purpose as the P-type proton ATPases of the plasma membrane

The nuclear membrane is a double membrane structure separated by the perinuclear space

The nuclear membrane contains rather large pores composed of a complex of components that give rise to its function as a transporter and molecular sieve

Chloroplasts are derived from precursor proplastids

Like mitochondria, chloroplasts possess a double membrane structure and inner and outer membrane known as the chloroplast envelope

Each of these membranes have different lipid compositions and transport functions

The inner membrane gives rise to thylakoid membranes which can organize into grana structures that support photosynthetic functions of ATP synthesis, light harvesting and electron transport

Mitochondrial inner membranes function in a manner similar to thylakoidmembranes of chloroplast in electron transport and ATP synthesis

Glyoxysomes and peroxisomes are single membrane organelles of similar nature, one linked with the glyoxylate cycle of fatty acid fueled gluconeogenesis and the other linked with photorepiration, ROS metabolism and amino acid biosynthesis