1. Cell structure and Function
1.4.Animal cell
Animal cell
Dr V Malathi and Mrs Sushumna Rao
Animal cells are the fundamental units of animal tissues and organs.
They are eukaryotic cells and therefore have membrane-bound organelles suspended in the cytoplasm enveloped by a.
Animal cells have (or a pair of centrioles), and which the plant cells do not possess.
A typical structure of an animal cell includes Organelles ( We will discuss about this in chapter 1.5) , cytoplasmic structures, Cytosol and Cell membrane .
The cell organelles like Centrosomes and lysosomes are found only in animal cells, but do not exist within plant cells
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Cell Membrane or the Plasma membrane
The cell membrane of an animal cell is a lipid bilayer which is embedded with other molecules like proteins, cholesterol and with some carbohydrates attached.
It separates the interior of the cell from the outside environment.
The cell membrane is semipermeable. The cell membrane regulates the transport of materials entering and exiting the cell.
The plasma membrane as it is other wise called permits the entry of small non polar molecules with ease, while large , polar molecules requires the help of transporters like membrane proteins .
The cholesterol embedded in the membrane provides structural integrity and support. Furthermore, the presence of cholesterol makes the membrane fluid rather than rigid, and renders them the capability of movement.
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The membrane proteins are of two categories namely Integral membrane proteins and peripheral membrane proteins
Integral membrane proteins
These are otherwise called as Intrinsic proteins . These are proteins that are permanently attached to the cell membrane.
Their functions include : channeling or transport molecules across the membrane , cell receptors, cell adhesion
They are further classified as
- Transmembrane proteins : these span the entire plasma membrane and are found in all types of biological membranes
- Integral monotypic proteins : these are permanently attached to the membrane from only one side.
Peripheral membrane proteins
These are proteins that are only temporarily associated with the membrane.
They can be easily removed,
Peripheral proteins can also be attached to integral membrane proteins or they can be stick to the lipid bilayer.
They are mostly hydrophilic.
Their functions include cell signaling, they are often associated with ion channels and transmembrane receptors.
The Fluid Mosaic Model
This model about membrane structure was proposed by S.J.Singe and G.L.Nicolson in the year 1972.
This model is now widely accepted .
The postulates of this model are:
- The plasma membrane comprises a phospholipid bilayer
- The integral membrane proteins are embedded in the phospholipid bilayer,
- Some of these proteins extend all through the bilayer ( Integral proteins), and some only partially acro