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Physiology of Cell

By Majeeda PT

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Cell

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Structural and functional unit of life capable of independent existence in the presence of appropriate nutritive environment.

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75-100 trillion cells in the human body

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Protoplasm; components that make up a cell

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Animal cell

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Composition of a cell

  • Water
  • Proteins
  • Lipids
  • Electrolytes
  • Carbohydrates

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Composition of a cell

  • Water;
    • 70-85%
    • Principal fluid medium
    • Cellular reactions occur in this medium-for dissolved substances
    • Suspended particles- for un-dissolved substances

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Composition of a cell

  • Electrolytes;
    • Sodium, potassium, chloride, magnesium, phosphate, calcium, sulphate, bicarbonate.
    • Required for cellular reactions and functions
    • Cellular control mechanisms

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  • Carbohydrates;
    • 1% of total cell
    • Nutritive function; glucose is readily available
    • Glycogen is the storage form in liver-utilized during fasting

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Composition of a cell

  • Proteins:
    • 10-20% of the total cell.
    • Structural proteins;
      • filaments of long chains of individual proteins
      • Provide a cytoskeleton to the cell (the microtubules),
      • Cilia, nerve fibers, extracellular proteins such as collagen and elastin
    • Functional proteins
      • Tubular rather than filamentous
      • Almost always in the form of enzymes
      • Control and catalyze cellular reactions

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Composition of a cell

  • Lipids
    • Approximately 2%
    • Soluble in fat solvents
    • Structural component of cell membranes and intracellular membrane compartments
    • Most important ones are phospholipids and cholesterol
    • Nutrition; triglycerides are the main storage form in adipose tissues.

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Components of cell

  • Cell Membrane
  • Cytoplasm
  • Nuclear membrane
  • Nucleus

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Cell Membrane

  • Outermost covering, 7.5-10 nm thick.
  • Thin, pliable and elastic
  • Mostly proteins (55%) and phospholipids (25%).
  • Others include cholesterol (13%), other lipids (4%), carbohydrates (3%)

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Cell Membrane

  • Composed of
    • Lipid bilayer
    • Membrane protein
    • Glycolipids and glycoproteins

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Cell Membrane

Integral protein

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The lipid bilayer

Phosphate Beads

Lipids

(Polar)

(Non-polar)

Amphipathic molecule; molecule with both hydrophilic (water-loving) and hydrophobic (water- avoiding) ends.

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The Phospholipid

Charged

and

polar

Un-charged

and

Non-polar

Prevents free movement of water- and water-soluble substances such as glucose and ions etc

Allows fat soluble substances such as oxygen, CO2

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Proteins of cell membrane

  • Integral proteins
    • Protrude all the way through the cell membrane
    • Act as channels and pores for ions and molecules
    • Carrier proteins for the transport of substances
    • Allow preferential diffusion of some molecules
    • May act as receptors for peptide hormones
    • Ligand-receptors-second messengers
  • Peripheral proteins
    • Usually on the inside of the cell membrane only.
    • Act as enzymes

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Glycoproteins/Glycolipids of cell membrane

  • Carbohydrates attached to lipids (glycolipids) or proteins (glycoproteins)
    • Glyco- portion protrude outside the cell
    • May act as charged molecules to repel other cells or materials
    • Part of the receptors of the cell
  • Glycocalyx
    • Carbohydrate coat on the surface of the cell membrane
    • Helps in the attachment of the cell