Animal Cell:

Introduction:

• Animal cells are typical of the eukaryotic cell, enclosed by a cell membrane having membrane-bound organelles and a well-defined nucleus.

• An Animal cell is comparatively smaller in size approx. 1-100mm.

• The cell wall is absent in animal cells therefore, lack of cell wall allowed animals to develop a greater diversity of cell types, tissue, and organs.

• The animal kingdom is unique among eukaryotic organisms because most animal tissues are bound together in an extracellular matrix by a typical helix of protein known as collagen.

• The animal cell possesses locomotory organ and cytoskeleton structure (help to maintain the structure of cell).

Structure of Animal cell:

There are various components that are found in the animal cells:

1. Cell Membranes:

• Discovered by Swiss Botanist Carl Naegeli and C. Cramer in 1855.

• Animal cells have only cell membranes to contain and protect their contents.

• The cell membranes also regulate the passage of molecules in and out of the cells.

2. Micro-villi:

• Micro-villi are the foldings present on the cell's membrane which help to increase the surface area of the cell when needed.

• Micro-villi also help in the absorption, secretion, and attachment of cells.

3. Nucleus:

• The nucleus is a highly specialized organelle that serves as the information processing and administrative center.

• Nuclear Membrane: The nucleus is enclosed in a distinct nuclear membrane which is made up of Lipoprotein about 40nm thick.

• It bears some pores which remain attached to the Endoplasmic Reticulum while others are free through which the nucleus maintains direct communication with the surrounding cytoplasm.

• Chromosome: It is mainly composed of DNA (deoxyribonucleic acid) and proteins which are chiefly concerned with heredity.

• Nucleolus:

4. Endoplasmic Reticulum:

• It is a network of sacs that manufacture, process, and transport chemical compounds for use inside and outside of the cell.

• The endoplasmic reticulum is connected to the double-layered nuclear envelope, which provides a pipeline between the nucleus and the cytoplasm.

• Depending upon the nature of its membrane, the endoplasmic reticulum is of two types:-

1. Smooth Endoplasmic reticulum: It does not bear ribosomes over the surface of its membrane, and it is engaged in the synthesis of glycogen, lipid, and steroid. The most important role of the smooth endoplasmic reticulum is it has enzymes for detoxification.

2. Rough Endoplasmic reticulum: It possesses ribosomes attached to its membrane. The membrane of the rough endoplasmic reticulum bears a fine pore below its ribosomes for the passage of synthesized polypeptide into the endoplasmic reticulum channel.

5. Golgi Body:

• It is the distribution and shipping department for the cells chemical products.

• It modifies proteins and fat which are built in the endoplasmic reticulum and prepared them for export to the outside of the cell.

• Golgi bodies manage the protein transport system.

6. Lysosomes:

• It breaks down the cellular waste products and debris from outside the cell into simple compounds which are transferred to the cytoplasm as new cell-building materials.

• The main function of these micro-bodies is digestion.

7. Mitochondria:

• Mitochondria are the main power generators that help in converting oxygen and nutrients into energy.

• They contain their own DNA and Ribosomes.

• They are the sites of cellular respiration, hence providing energy for the vital activities of living cells.

• They store energy which releases during the reaction in the form of ATP ( Adenosine triphosphate).

8. Vesicles:

• It acts as transport vesicles in which materials are Transported from one cell organelles to another cell organelles.

9. Microtubule:

• These are hollow-straight cylinders found throughout the cytoplasm and carry many varieties of functions, ranging from transport to structural support.

10. Microfilament:

• It is a solid structure and is made up of a globular protein called actin.

11. Centriole:

• Self-replicating organelles are made up of nine bundles of microtubule and tubulin protein.

• They help in cell division.

Cilia and Flagella:

Generally differentiated based on size and number. Cilia are usually small and occur together in much greater numbers than flagella which are often solitary.

Endocytosis/Phagocytosis:

The transport of solid matter such as food, foreign particles, pathogens, etc. across the plasma membrane by forming detachable vesicles. The vesicles ate called phagosomes.

Exocytosis/Pinocytosis:

The transport of bulk fluid matter and substances dissolved in it across the plasma membrane inside the cell.

Secretive vesicles:

It also helps in transportation. Made up of Lipoprotein. Secretive vesicles and cell membranes are both made up of Lipoprotein so that the materials to be transported through the membrane can easily diffuse.