Endoplasmic Reticulum

The Endoplasmic Reticulum (ER)

• accounts for more than half the total membrane in many eukaryotic cells

• ER consists of membranous channels

• saccules (flattened vesicles)

The ER membrane

is continuous with the nuclear envelope

Two types of ER

1. Smooth ER, which lacks ribosomes

2. Rough ER, which contains ribosomes

Smooth ER

• has no ribosomes

• makes and stores lipids and steroids

Rough ER

• covered in ribosomes

• makes and stores proteins

Both …

make cellular materials 

The Rough Endoplasmic Reticulum

Rough ER is studded with ribosomes on the side of the membrane that faces the cytoplasm

Also modifies proteins

• enzymes in rough ER add carbs to proteins - Glycoproteins

• other ER enzymes help fold proteins - Chaperonins

• proteins are distributed through out the cell by transport vesicles

The Smooth Endoplasmic Reticulum

• the smooth ER is continuous with rough ER

• lacks ribosomes

• synthesizes lipids

• Phospholipids and steroids

• testosterone in the testes

• metabolizes carbs

• stores calcium

• in liver detoxifies drugs

Smooth ER in alll cells

• smooth ER forms vesicles in which molecules are transported

• to the plasma membrane

• or the Golgi apparatus

The Golgi Apparatus Structure

• 3 to 20 slightly curved saccules called cisternae

• like a stack of pancakes

• inner face is directed toward the ER

• cis face

• outer face is directed towards the plasma membrane

• trans face

The Golgi Apparatus

• Receives many of the transport vesicles produced in the ER

• Vesicles contain protein or lipid

Functions of the Golgi apparatus include

• manufacture of macromolecules

• modification of the products of the rough ER

• produces vesicles that give rise to lysosomes and vacuoles

Enzymes in the Golgi

• alter the carbs chains attached to proteins in the rough ER

• or a phosphate may be added to the protein