Page 7 - Cell biology PDG 2024

Figure 2:prokaryotic and eukaryotic cells

Components of the cell

1) Cell membrane:
• The cell membrane (also known as the plasma membrane, or
cytoplasmic membrane, and historically referred to as the
plasmalemma) is the semipermeable membrane of a cell that
surrounds and encloses its contents of cytoplasm.
• It separates the cell from the surrounding extracellular fluid.
• It controls the movement of substances in and out of cells and
organelles. In this way, it is selectively permeable to ions and
organic molecules.
• It is involved many cellular processes such as cell adhesion, ion
conductivity and cell signalling beside serving as the attachment
surface for the cell wall

Structure of the cell membrane:
1) The cell membrane consists of a lipid bilayer (bilayer of
phospholipids). These phospholipids have a polar head group
and two hydrophobic hydrocarbon tails. The tails are usually
fatty acids, and they can differ in length
The phospholipid molecules spontaneously form bilayers in
aqueous environments. In which, the hydrophilic heads face the
water at each surface of the bilayer, and the hydrophobic tails
are shielded from the water in the interior

This structure alone makes it a selectively permeable membrane. Only
relatively small, nonpolar materials can cross the lipid bilayer at
biologically relevant rates and enter inside the cell ex: water, carbon

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