Animal cells included in eukaryotic cells because it has a nuclear cell membrane. Animal cells also have a smaller size compared to plant cells. Besides that, what are the characteristics of animal cells? And what do these cells specialize in? To answer this question, let’s look at and understand the discussion below.

Characteristics of Animal Cells

Following are the characteristics of animal cells, namely:

1. It has no cell walls and no plastids.
2. Cell shape is not fixed.
3. Just like plant cells, animal cells also have vacuoles but are smaller in size and almost invisible.
4. Has centrioles which are not found in plant cells. Animal cells have two centrioles within the centrosome organelle. When cell division occurs, each centriole separates from each other towards the opposite pole and forms threads that will stick to the chromosomes.

Animal Cell Organelles and their Functions

Animal Cell Skeletal Structure

Animal cells do not have a cell wall, so these cells have many variations in shape. To maintain the integrity of the cells, animal cells have a modification in the form of a cytoskeleton and extracellular matrix which function as cell walls for animal cells. To find out more about the explanation, let’s look at the explanation in the sub-chapters below.

A. Cytoskeleton

The cytoskeleton has the same function as the plant cell wall, which maintains the shape and structure of the cell. The cytoskeleton is composed of three types of fibers, namely microfilaments, microtubules and intermedia filaments.

Three types of fibers make up the cytoskeleton, namely:

1. Microfilament

• Microfilaments are thin, interconnected double chains of proteins that have a diameter of 7 nm.
• Myrofilaments are composed of actin and myosin proteins.
• Microfilaments are found in many muscle cells.
• The function of microfialmen, namely to maintain cell shape, cell contraction, cell movement, and cell division.

Microfilament Structure
Image Source: Campbell, N. (2005)

2. Microtubules

• Microtubules are protein chains that form an elongated spiral like a hollow tube with a diameter of 25 nm.
• Microtubules are composed of tubulin protein.
• The largest and largest number of fibers in the cytoskeleton.
• The function of microtubules, namely directing the movement of chromosomes to each pole during cell division, maintaining cell shape, cell movement, and assisting cells in mitotic division.

Microtubule Structure
Image Source: Campbell, N. (2005)

3. Intermedia filaments

• Intermedia filaments are chains of protein molecules that form strands and are wrapped around one filament to another, and have a diameter of about 8-12 nm.
• The intermedia filament is composed of fimentin protein, but not all parts of the intermedia filament cells are composed of these proteins, for example in filamentous skin cells which are composed of keratin protein.
• The function of the intermedia filament is to maintain the shape of the cell, to which the nucleus and organelles are attached, and to form the nuclear lamina.

Intermedia Filament Structure
Image Source: Campbell, N. (2005)

B. Extracellular Matrix in Animal Cells

Apart from the cytoskeleton, animal cells also have an extracellular matrix to protect the plasma membrane and the intracellular parts of the cell. The main components of the extracellular matrix in animal cells are glycoproteins and molecules resulting from cell secretion that contain carbohydrates.

The constituent parts of the extracellular matrix in animal cells, namely:

1. Collagen, the largest and largest number of fibers in the extracellular matrix.
2. Proteoglycans, bind to polysaccharide molecules non-covalently to form proteoglycan complexes.
3. Fibronectin, located attached to the integrin protein.
4. Integrin protein, a protein located on the plasma membrane which functions to transmit signals between the extracellular matrix and the cytoskeleton.

Extracellular Matrix Structure