Animal Cell

3D illustration of an animal cell

What is an animal cell?

Animal cells are the cells that make up human beings and all other living things that we know as animals: dogs and cats, cows and horses, ants and spiders, worms and birds, dolphins and crabs, snails and beetles, among others.

Cells can be defined as the fundamental basic units of living beings , since they are the smallest living parts in which a living being can divide.

Animal cells are eukaryotic cells, that is, they are cells with a defined nucleus and different internal compartments such as mitochondria, the endoplasmic reticulum, the Golgi complex, peroxisomes and lysosomes, among others that we will explain later.

The main difference between animals and plants is in the type of cells that compose them: plants are made up of plant cells and animals are made up of animal cells. Both are two types of eukaryotic cells , that is, cells with a defined nucleus and internal compartments.

Characteristics of animal cells

Animal cells have several characteristics:

  • They are eukaryotic cells , so they have a sac or compartment surrounded by a membrane where the genetic material (DNA) is enclosed.
  • They have internal structures or “organs” surrounded by membranes, which could be considered analogous to the organs of our body.
  • They are made up of a cell membrane and have no wall of any kind.
  • They are heterotrophic cells , which means that they are not capable of producing their own food, but have to feed on what they can obtain in the environment around them.
  • They are generally cells with the capacity for movement and / or displacement.
  • They establish close communications with adjacent cells, by direct or indirect contact through the plasma membrane

Parts of the animal cell (organelles)

Animal Cell Anatomy
Animal cells, like all eukaryotic cells, have different parts that perform special functions, fundamental for cell life. Let’s see, next, what are the main parts of animal cells:

Plasma membrane

The plasma membrane is a common structure for all cells in nature. It is extremely important, as it provides the “barrier” that delimits cells and separates what is inside them from the external environment.

It is generally described as a semi- permeable or selectively permeable structure , which means that it allows the passage of certain substances and prevents the passage of others in and out.

It is made up mainly of molecules called lipids , but it also contains many proteins and carbohydrates that have important functions.

The cytoskeleton

Just as our body has a skeleton made up of bones that support our weight, protect our organs and facilitate some of our movements, many cells also have a system of internal molecular scaffolds that help them maintain their structure.

Such is the case of animal cells, where these scaffolds make up what we call the cytoskeleton (the cell skeleton), which provides structural support and allows the internal organization and movement of vesicles and substances from one side of the cell to the other.

Cytosol

The cytosol is a kind of fluid that is found inside the plasma membrane, where all the membranous organelles are suspended and where there is a large amount of water, proteins, sugars, ions and other types of molecules.

Numerous chemical reactions occur in the cytosol that cells need to survive. This fluid also contributes to the shape of cells and their communication with the environment that surrounds them.

Nucleus: nuclear envelope, nucleoplasm and nucleolus

One of the most attractive organelles or compartments of animal cells is the nucleus. This, in addition, is the compartment that defines eukaryotic cells, that is, cells of plants, fungi and animals.

All the information that a cell needs to be a cell is stored in the nucleus; it is more or less like the brain of our body.

This information is stored in the form of chromosomes, which are structures made up of a complex of proteins and deoxyribonucleic acid called chromatin .

Deoxyribonucleic acid (DNA) is the molecule that contains all the information in a cell. During cell division, this molecule is duplicated and a faithful copy is transferred to the daughter cell.

  • Nuclear envelope or lamina

The nucleus has its own organellar membrane, which separates it from the rest of the components of the cytosol. This membrane is known as the envelope, lamina or nuclear envelope and, like the plasma membrane, allows the passage of certain substances and prevents the passage of others.

In the nuclear envelope there are pores, known as nuclear pore complexes , which allow the nucleus to communicate with the rest of the components in the cytosol.

  • The nucleoplasm and nucleolus

The interior of the nucleus contains what is known as the nucleoplasm or lumen, which is analogous to the cytosol. It is in the nucleoplasm that chromatin and nucleolus are found, which is the place where ribosomes are produced (the “organelles” responsible for making proteins).

Endoplasmic reticulum

This organelle is a system of membranes that are connected to the membrane that forms the nuclear envelope. Its job is to process and distribute many cellular proteins, especially those that must be sent to the different membranes.

Golgi complex or apparatus

It is also a membranous organelle, but it is made up of a pile of flattened “sacs” in the shape of cisterns . It is not associated with the membrane of the nucleus, but it also participates in the processing and modification of some proteins.

This organelle is also important for the transport of different substances inside and outside cells.

Mitochondria

They are the cellular energy centers, the power sources of all eukaryotic cells. They have an elongated shape, very similar to that of some bacteria. In its interior, chemical reactions take place that allow cells to breathe and obtain energy from the food they acquire from around them.

Mitochondria are one of the most important organelles in a cell. They have their own DNA, but some of the proteins inside them are produced by the DNA in the nucleus.

Lysosomes

Lysosomes are like the “dump” for animal cells. Inside it, a large amount of waste is found that the cells have to eliminate because its accumulation can be toxic.

Within these organelles – which do not have their own DNA – there are a large number of enzymes that help digest different types of molecules, such as proteins, lipids, carbohydrates, etc.

Peroxisomes

They are organelles smaller than lysosomes, that is why they are classified as microbodies . They do not have their own DNA and their function also has to do with the elimination of toxic substances, specifically hydrogen peroxide.

They are also responsible for the metabolism of some fats, certain amino acids and some sugars.

Centrosomes

Illustration of a centrosome
These are characteristic “organelles” of animal cells. They participate in cell division and are made up of two centrioles, which are the structures responsible for the formation of microtubules, the molecules that separate DNA copies during cell division.

Cell functions

Animal cells have many functions:

Medium

Animal cells make up the tissues and organs of animals, in the same way that bricks make up the walls that make up a building.

In addition, some cells serve as nutritional support for others, such as glial cells in the brain. This means that its function is to provide the necessary energy and nutrients for other cells with different functions.

On the other hand, there are cells that support the development of others, such as Sertoli cells in the testes, and of many other cells that are responsible for producing the molecular factors necessary for the correct development of certain cells.

Cellular division

All cells in an animal’s body divide and it is cell division that allows tissues to maintain and constantly renew themselves.

The cells of the human body, for example, with the exception of germ cells, divide by mitosis generating copies of themselves, which favors the maintenance of cell lines in each particular tissue, as well as the growth of the animal body (in the multicellular animals).

Germ cells divide by meiosis, and thanks to this division, gametes are produced, which are sex cells specialized in reproduction.

Movement

Almost all animal cells are capable of some kind of movement.

Animals normally have cells equipped with cilia and / or flagella that allow them to carry out different types of movements and, thus, different activities.

The movement of different sets of hair cells is essential in the small intestine for digestion, as well as in the inner ear it is essential for hearing and in the respiratory system it is essential for filtering the particles contained in the air.

On the other hand, vertebrate animals have muscle tissues made up of cells capable of contracting and relaxing in unison. The cells of these tissues facilitate the movement of these animals -including humans- to carry out multiple activities.

Defending

There are many animal cells that participate in the defense of the organism to which they belong.

For example, in mammals the specialized cells of the immune system are capable of recognizing invading microorganisms or dangerous foreign substances and eliminating them with some speed and efficiency.

Communication

Communication is essential for all cells in nature, and animals are no exception.

In unicellular animals, the communication function involves the “awareness” of the environment that surrounds them, because in order to find food, water, detect potential dangers and respond to changes that occur, it is necessary to establish constant exchanges with the outside environment. .

In multicellular animals, communication between cells is essential for the functioning of the tissue and the organism to which they belong.

Examples of animal cells

Let’s look at several common examples of animal cells:

Red blood cells

Illustration of red blood cells in blood vessels
Red blood cells or erythrocytes are the animal cells that are responsible for the transport of oxygen through the blood. These cells, in mammals, do not have a nucleus and are full of a protein called hemoglobin , which is responsible for carrying oxygen.

Neurons

Illustration of a synapse between two neurons
They are the main cells of the animal nervous system. They are formed by a body -soma- that has a series of extensions that look like the hair of Medusa (Greek mythology) -dendrites- and a long projection -axon- that establishes contact with other cells of the body.

Neurons specialize in transmitting messages in the form of nerve impulses. Those that are connected to the musculoskeletal system, for example, tell the muscles of the body when and how to move.

Hepatocytes

They are the cells that form the tissue that makes up the liver, one of the organs of the body of vertebrate animals.

Myocytes

Myocytes in muscle tissue
They are the cells that make up the muscle tissues of animals. Some are cylindrical and very elongated and inside they have proteins capable of sliding over each other to shorten their length and contract the tissue to which they belong.

Immunoglobulins

They are very important cells of the immune system of mammalian animals. About 5 different types have been described, the most important of which function in the detection of foreign substances and the production of antibodies , some of which are capable of “neutralizing” or “marking” invaders for elimination.

Other topics of interest

Cell types 

Plant cell

Eukaryotic cell

Prokaryotic cell

References

  1. Alberts, B., Bray, D., Hopkin, K., Johnson, AD, Lewis, J., Raff, M.,… & Walter, P. (2013). Essential cell biology . Garland Science.
  2. Cooper, GM, Hausman, RE, & Hausman, RE (2000). The cell: a molecular approach (Vol. 10). Washington, DC: ASM press.
  3. Gartner, LP, & Hiatt, JL (2006). Color textbook of histology ebook . Elsevier Health Sciences.
  4. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). New York: McGraw-Hill.
  5. Solomon, EP, Berg, LR, & Martin, DW (2011). Biology (9th edn). Brooks / Cole, Cengage Learning: USA.
  6. Villanueva, JR (1970). The living cell.

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