I-cell Disease and Cellular Structures

I-cell Disease

• Characterized by defective physical growth and intellectual disabilities
• Caused by a deficiency in GlcNac-1-phosphotransferase
• The enzyme deficiency occurs in the Golgi apparatus
• Lysosomal enzymes aren't properly phosphorylated
• Unphosphorylated lysosomal enzymes are released into the bloodstream instead of being directed to lysosomes
• Lysosomes accumulate undegraded proteins

Plasma Membrane

• Composed of lipid, protein, and carbohydrate components
• Key function is selective permeability, allowing specific substances to cross
• Contains embedded proteins that move laterally through diffusion
• Lipid bilayer is mostly impermeable to ions and larger polar molecules
• The major ion found inside a cell is potassium
• The membrane is a fluid structure

Golgi Apparatus

• Modifies, sorts, and packages proteins for secretion
• Primarily responsible for secretion functions and directing molecules to appropriate destinations within the cell.
• Located near the nucleus and the endoplasmic reticulum (ER)
• The golgi apparatus receives transport vesicles from the ER

Peroxisomes

• Small, membrane-bound vesicles
• Similar to lysosomes
• Involved in oxidative reactions within the cell
• Primary function is to convert hydrogen peroxide to water and oxygen, protecting the cell from the toxic effects of hydrogen peroxide.
• Peroxisomes contain oxidative enzymes.
• Abundant in liver and kidney cells.

Mitochondria

• Involved in energy production by producing ATP
• Contain their own DNA (mtDNA)
• Have inner and outer membranes
• Inner membrane has folds called cristae, which increase its surface area for more ATP production
• Mitochondrial DNA has a higher mutation rate compared to nuclear DNA.
• The typical outcome of Zellweger syndrome within the first year of life is usually fatal.

Zellweger Syndrome

• Characterised by impaired brain development and lesions in organs
• A consequence of peroxisomal dysfunction, resulting in an accumulation of very long chain fatty acids
• Diagnosed by detecting elevated levels of very long-chain fatty acids in the blood

Lysosomal Storage Diseases

• Caused by a defect in a lysosomal enzyme
• Results in the abnormal accumulation of substances within the cell
• Children are predominantly affected
• Typically result in a shortened lifespan

Tay-Sachs Disease

• Caused by a deficiency in the enzyme Hex A (hexosaminidase A)
• Causes an accumulation of gangliosides in neurons
• Neurological deterioration typically begins around 3-6 months of age
• Associated with a cherry-red spot on the retina.

Hurler Syndrome

• Caused by a deficiency in the enzyme α-L-iduronidase
• Results in the accumulation of undigested glycosaminoglycans (GAGs), leading to several symptoms, including intellectual disabilities and skeletal abnormalities
• Confirmed diagnostically through detecting nondegraded glycosaminoglycans (GAGs) in the urine

Unfolded Protein Response (UPR)

• Serves as a quality control mechanism for secretory proteins
• Involved in protein processing and transfer through the ER and golgi
• Occurs in response to misfolded or unfolded proteins in the endoplasmic reticulum (ER)

Explore the complexities of I-cell disease, including its genetic causes, and the role of cellular structures like the plasma membrane and Golgi apparatus. Understand how enzyme deficiencies impact cellular function and the significance of selective permeability in membranes. Test your knowledge on these essential biology topics.