Endoplasmic Reticulum

Rough Endoplasmic Reticulum (RER) 

• Structure 
  • composed of a lipid membrane with membrane bound ribosomes
  • lipid membrane is continuous with nuclear membrane
• Function
  • synthesis of secretory proteins  
    • e.g. peptide hormones
  • addition of N-linked oligosaccharides to peptides
• Cell biology
  • RER is found in high concentration in
    • neurons
      • termed Nissl bodies
        • stain basophilic 
      •  
        • synthesize/secrete peptide neurotransmitters in prepackaged vesicles
    • pancreatic acinar cells
• synthesize/secrete digestive enzymes

Smooth Endoplasmic Reticulum (SER)

• Structure
  • lipid membrane without membrane bound ribosomes
• Function 
  • steroid synthesis 
  • detox of chemicals
    • makes compounds water soluble
    • two mechanisms
      • hydroxylation
        • via cytochrome P450 hydroxylase complex
      • conjugation
        • involves binding of polar moiety (e.g. glucuronate via glucuronyl transferase) to toxin
  • lipid metabolism
    • release of fatty acids from triglycerides
    • assembles lipoproteins for release
  • carbohydrate metabolism
    • gluconeogenesis
      • allows free glucose to be released into circulation during fasting by removing phosphate from glucose-6-phosphate
      • mediated by glucose-6-phosphatase
        • deficient in von Gierke’s disease
          • glycogen storage disease type I
          • presentation
            • accumulation of glycogen in kidney and liver
              • hepatomegaly
            • hypoglycemia
• Cell biology
  • found in high concentrations in
    • hepatocytes
    • kidney
    • adrenal cortex
    • corpus luteum
    • muscle
      • modified SER = sarcoplasmic reticulum
• stores and releases calcium to mediate muscle contraction