The animal cell is the basic building unit of animal organisms . It is a type of eukaryotic cell, like plant cells, this means that it has a nucleus, plasma membrane and cytoplasm.
Characteristics of the animal cell
- They are cells of the eukaryotic type , that is, their genetic content is enclosed in a membranous structure called the nucleus.
- They have variable shapes and sizes.
- They do not have a cell wall, unlike the plant cells.
- They have organelles that are compartments with a membrane inside the cell, with specific functions.
- They have centriole, centrosome and lysosomes, which are not found in the plant cell.
- They get the nutrients from the outside.
Basic structures of the animal cell
The animal cell is fundamentally composed of a plasma membrane, a nucleus and a cytoplasm. Next, we will explain each one in detail.
The plasma membrane is the outer covering of the cell, through which contact is made with the external environment. It consists of two sheets of lipids, or lipid bilayer, and membrane proteins. The most abundant lipids are phospholipids and cholesterol.
The proteins allow the passage of compounds from the outside to the interior of the cell, and vice versa. There are also proteins in the membrane called receptors . These recognize compounds outside the cell and activate signals within it, causing specific responses.
Among the functions of the plasma membrane are:
- regulation of the transport of substances: water and ions (such as sodium, chlorine and potassium), organic molecules (such as hormones), and gases (such as oxygen and carbon dioxide), and
- the recognition of substances abroad by means of the receivers, in order to send signals to the cellular interior.
Nucleus and nucleolus
The nucleus is the part of the cell that stores the genetic information in the form of deoxyribonucleic acid or DNA. It is delimited by the nuclear envelope , which is a double membrane, with openings or nuclear pores , through which compounds enter and leave. The inner liquid where the nuclear compounds float is the nucleoplasm .
The nucleus is the control and reproduction center of the cell. DNA is bound to proteins and forms chromatin . The information obtained for the operation of the cell is obtained from the DNA.
In the nucleus is a region where chromatin and ribonucleic acid (RNA) are concentrated. This region is called a nucleolus and is the center of production of ribosomes.
The cytoplasm is the aqueous-gelatinous medium where most cellular activities occur. It is composed of water, salts, ions and proteins and comprises approximately 70% of the volume of the cell.
The cytoplasm comprises the space through which cellular components move.
Organelles of the animal cell
To fulfill the different functions, the animal cell presents different organelles and structures.
The ribosome is one of the organelles of the cell that does not have a membrane. It is composed of proteins and RNA and is formed in the nucleolus within the nucleus. It has two parts or subunits: a major subunit or 60S, and a minor subunit or 40S.
The ribosome is the factory for the production of proteins . Between the major and minor subunits, messenger RNA, transfer RNA and amino acids are coupled to form the polypeptide chains.
The ribosome of animal cells consists of two subunits: 60S and 40S.
The endoplasmic reticulum is a membrane system formed by sacs and vesicles that is adjacent to the nucleus. The interior or central space is called lumen.
The rough endoplasmic reticulum is named after the presence of ribosomes on its external surface. Its main function is the synthesis and packaging of proteins.
Synthesis of membrane lipids occurs in the smooth endoplasmic reticulum. In muscle cells there is a smooth endoplasmic reticulum called sarcoplasmic reticulum , which is where the calcium necessary for muscle contraction is stored.
In the Golgi apparatus, materials that are produced in the endoplasmic reticulum are classified and packaged. The vesicles from the endoplasmic reticulum fuse in the cis face of the Golgi apparatus and there they deposit the material they transport.
In the lumen of the Golgi apparatus, proteins and lipids are modified or “adorn”; in this way they are identified, classified and routed to their destination site. They come out through the trans face of the Golgi apparatus enclosed in secretory vesicles.
The mitochondria is the organelle responsible for the production of energy in the animal cell, from glucose and other molecules. The chemical energy of the cells is in the form of adenosine triphosphate or ATP.
The mitochondria is composed of two membranes: internal and external. The inner membrane folds into the interior forming the mitochondrial crests.
The mitochondria have their own DNA and ribosomes for the synthesis of specific proteins. Possibly they originated from a bacterium that was swallowed by a eukaryotic cell.
The centrosome is the area of the animal cell where the microtubules are produced. It is found in the cytoplasm in a region close to the nucleus. Here centrioles are formed, which are present only in the animal cell.
The centrosome is the area where the centrioles are located in the cytoplasm.
Lysosomes are vesicles or membrane sacs that are produced in the Golgi apparatus. They are one of the characteristic organelles of the animal cell, as they are not found in plant cells. They contain compounds that degrade or digest various materials.
Enzymes that act in an acid medium and break proteins, nucleic acids, polysaccharides and lipids that are no longer necessary for the cell are present within lysosomes. One could say that lysosomes are the processors of intracellular “garbage”.
Once the lysosomes have acted, the cell can recycle the amino acids, nucleotides and other elements for the construction of new cellular materials.
The lysosomes also participate in the destruction of invading agents, especially in the cells of the immune system, which are in charge of the defense of the organism.
The lysosome contains in its interior material for intracellular digestion.
Peroxisomes are simple membrane vesicles, that is, with a single layer of lipids. Its name is due to the production of hydrogen peroxide or hydrogen peroxide, as we commonly know it.
These organelles are important in the elimination of intracellular toxins and in the oxidation of fatty acids. Liver cells are especially rich in peroxisomes.
Flagella and cilia
The flagella are structures similar to small whips that are found on the outside of the plasma membrane. They allow the movement of certain cells, such as sperm and some protozoa.
Cilia are shorter structures, like hairs, that also serve to move the cell or to move substances away from the cell, such as in the airways.
The flagellum is a structure that allows the movement of the cell.
Basic functions of the animal cell
Each animal cell fulfills certain basic functions such as cellular respiration, metabolism and cell division.
The process by which the cell picks up oxygen from the outside and expels carbon dioxide from the inside is known as cellular respiration.
The animal cell, unlike the plant cell, can not capture carbon dioxide to produce new compounds, such as sugars.
They are all chemical reactions that take place inside the cell. This includes the synthesis ( anabolism ) and degradation ( catabolism ) of substances.
The cells reproduce by mitosis or meiosis to give rise to new cells. To divide, each cell undergoes a series of transformations through its cell cycle.
The cells multiply by the process of mitosis.
Within multicellular organisms there are cells with specific functions; This is achieved thanks to cell differentiation .
There are cells in animals that are responsible for protection against invading agents, such as bacteria or viruses. Cells of the immune system, such as white blood cells and macrophages, patrol the body for pathogens to eliminate them.
A macrophage captures a bacterium and destroys it.
Muscle cells are specialized cells in contraction and relaxation. By acting in a coordinated manner, they allow movement.
Smooth muscle cells produce movement of internal organs, such as the gastrointestinal tract, while heart cells produce movement of the heart.
The skeleton of vertebrates and the exoskeleton of invertebrates is armed thanks to specialized cells, which give structure and shape to the animal.
Gametes or sex cells, unlike somatic cells, have half the genetic load. When a male gamete is combined with a female gamete, the zygote forms, giving rise to a new individual of that species.
Animal cell examples
There is a great diversity of cells in animals, with different shapes, sizes and functions. Let’s see examples of cells with special characteristics.
The eggs are probably the largest cells in the animal kingdom. The egg of an ostrich can weigh 1.5 kg.
When an egg is fertilized, it will give rise to a new animal under the appropriate conditions.
Neurons are the specialized cells of the nervous system. They are designed to receive information, transform it into electrical signals and transmit it by chemical signals, all within a network of other neurons.
The neurons form a network of nervous intercommunication.
Red blood cells
Red blood cells or erythrocytes are the cells responsible for transporting oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs.
The red blood cells travel in the blood through the blood vessels, spreading throughout the body, to reach all cells.