Review of Cell Structure

Question 1

Integral Membrane Proteins when membrane is split

Answer 1

When a frozen piece of membrane is split mechanically between the outer and inner lipid layers, the outer face is called the external face and the inner leaflet is the protoplasmic face.

Integral membrane swill associate with protoplasmic face because these rpoteins are stablizied by attachment to cytoskeleton.

In RBCs, the integral membrane proteins are associated with actin and spectrin

i.e Mutations in spectrins in RBCs lead to spherical rather than biconcave RBCs that are sensitive to mild hypertonic solution.

Question 2

Microvilli

Answer 2

• Microvilli are modifications on enterocytes that increase the surface area for absorption.
• Microvilli have an actin cytoskeleton
• Terminal web at base of microvilli contain actin and intermediate filaments.

When viewed in EM–> Microvilli

When viewed in light microscopy –> Brush border

Question 3

Smooth ER

Answer 3

1. Function
   
   1. Lipid storage
   2. Detox
   3. Metabolism of drugs
      
      1. Site of many heme-linked proteins like cytochrome p450
   4. Storage of Ca2+

Question 4

Constitutive secretion vs. regulated secretion

Answer 4

Cells undergoing constitutive secretion are characterized by absence of storage/secretory granules.

Question 5

Lysosomes

Answer 5

• Function
  
  • Intracellular digestion
  • Processing of molecules that enter the cell from external environment
  • Removal of worn-out intracellular organelles
• Often the lysosomes (*) of eosinophils (but not other cell types) have crystalline inclusions as shown in the right micrograph.