1 4 Endoplasmic reticulum ER The principle functions

1. 4. Endoplasmic reticulum (ER) The principle functions of ER 1) Synthesizing, processing, and sorting proteins 2) Adding N-linked glycans 3) Synthesizing a diverse array of lipid molecules 4) Anchoring sites for actin filaments bundles

1. 4. 1 The ER gives rise to the endomembrane system

1. 4. 2. The ER forms a dynamic net work, the organization of which changes during the cell cycle and development. A living onion epidermal cell taken 5 min apart

Rough ER

Rough ER

Smooth ER

The cortical ER

Extra functions of ER - In mitosis, spindle activity and cell plate assembly - Gravity sensing in columella cells of roots - Accumulation of storage protein in seeds - Accumulation of lipophilic substances (terpenes, cutins, flavonoids)

Oil Body in ER

Protein body in ER Ex) Proamines (alcohol soluble) Cf) Globulin (water soluble) in storage vacuoles

Transport vesicles budding from ER cisterna in the vicinity of a Golgi stack

1. 5 Golgi apparatus The function of Golgi apparatus 1) receiving newly synthesized proteins and lipids from the ER 2) directing them to cell surface or vacuoles 3) assembling complex polysaccharides of cell wall matrix 4) synthesizing and processing the O-linked oligosaccharide side chains of membrane 5) processing the N-linked oligosaccharide side chains of membrane 6) producing glycolipids for plasma membrane and tonoplast

Golgi stack of a pea root tip cell

Mannosidase 1 -GFP protein in BY-2 cells

A dividing golgi stack in a root cell of pea

Subdivision of golgi stacks- cis, medial, trans, TGN

The functions of glycosylation (N-linked, O-linked) 1. Protect proteins against proteolysis 2. Specify PM-cell wall interaction 3. Prevent premature activation of lectins 4. Contribute to protein folding or assembly of multiful protein comple

N-linked glycan: 1. Starts in ER with 14 sugar oligosaccharide in dolichol 2. transferred to selected asparagine residue 3. Most of processing occur in Golgi O-linked glycan: 1. Starts in Golgi 2. Occur in hydroxylproline, serine, threonine

Spatial organization of the xyloglucan (A) and pectic polysaccaraide (B)