The animal cell is the building block of all animal structures. It is a type of eukaryotic cell, which is characterized by presenting a nucleus where the genetic material is enclosed in the form of deoxyribonucleic acid or DNA.
The animal cell has different parts with specific functions, as shown in the following table:
Parts of the
animal cell
Plasma membrane function
Protects the interior of the cell
Allows the entry of nutrients
Detect external conditions
establish communication between cells
Nucleus Synthesizes DNA and RNA Cytoplasm
Allows movement of molecules and organelles
Endoplasmic reticulum
Assembles and processes proteins
Regulates intracellular calcium
synthesize lipids
Ribosome Synthesizes proteins Golgi apparatus Stores and distributes proteins and lipids
Form vesicles Mitochondria
Synthesizes ATP (biological energy molecule)
Oxidizes fatty acids Lysosome Digests material ingested by the cell Peroxisome Oxidizes fatty acids
synthesizes myelin lipids
Removes hydrogen peroxide Centrosome Organizes and assembles microtubules Cytoskeleton Gives structure and support to the cell
Allows cell movement
Each of the parts of the animal cell and what they are used for are described below.
plasma membrane
The plasmatic membrane or cell membrane is the outermost part of the cell that limits and closes its content, separating the extracellular environment from the cell interior. Its structure is fluid and dynamic, made up of a double layer of lipids, mainly phospholipids and cholesterol, and proteins.
One third of the cell’s proteins are found in the plasma membrane. These are responsible for perceiving external conditions or signals and sending that information inside, so that the cell can respond to the stimulus. Other proteins allow the passage of elements such as sodium and calcium, so that the cell can carry out its activities.
The cytoskeleton is attached to the plasma membrane, in order to maintain the shape of the cell and the movement of intracellular structures.
The plasma membrane separates the intracellular space from the outside, made up of phospholipids and proteins.
Core
The nucleus is the part of the cell where the genome or genetic information such as deoxyribonucleic acid (DNA) is concentrated. It concentrates the functions of DNA and ribonucleic acid (RNA) synthesis, cell division and control of cell activities.
The nucleus can be distinguished thanks to the nuclear envelope, formed by two membranes with holes or nuclear pores. During cell division, the nuclear envelope disappears until new cells are formed and it is rebuilt.
In the nucleus, chromatin can also be distinguished, which is nothing more than DNA attached and packaged to nuclear proteins.
Within the nucleus is the nucleolus, present in all animal cells except those that have lost their nucleus, such as red blood cells. The main function of the nucleolus is the production of ribosomes. In growing or cancer cells, the nucleolus increases in size.
Electron microscope image of the nucleus of a cell.
Cytoplasm
The cytoplasm is the space that surrounds the nucleus up to the membrane. Within the cytoplasm are submerged the cell’s organelles and the microtubule skeleton.
The cytoplasm is composed of:
the cytosol: the semi-gelatinous internal fluid where nutrients and wastes are dissolved.
inclusions: are insoluble particles in the cytosol, such as glycogen and fat granules.
organelles: are “small organs” formed by membrane with specific functions, such as mitochondria and lysosomes.
protein fibers: made up of polymers of small proteins, including actin microfilaments and tubulin microtubules.
Endoplasmic reticulum
The endoplasmic reticulum is the largest organelle in the cell. It is a membrane structure that is constantly changing. It participates in the modifications that proteins and lipids have during their synthesis and after they are synthesized. It also has a role in cellular calcium homeostasis.
The endoplasmic reticulum can be divided into:
The rough endoplasmic reticulum: is a continuation of the nuclear envelope. It consists of stacked sacs of membranes with attached ribosomes, giving it a rough appearance. Participates in protein synthesis, transfer and folding of the same.
The smooth endoplasmic reticulum: is devoid of ribosomes and participates in the synthesis of lipids. Cells such as those that synthesize steroid hormones and liver cells have a large amount of smooth endoplasmic reticulum.
ribosome
Ribosomes are small, dense granules of RNA and protein. Its main function is the synthesis of proteins following the directions of the DNA.
There are free ribosomes in the cytoplasm and ribosomes attached to the membrane of other organelles, for example, the endoplasmic reticulum. Some free ribosomes form groups of 10 to 20 forming polyribosomes.
Golgi apparatus
The Golgi apparatus or Golgi complex consists of a series of stacked curved sacs that continues into the endoplasmic reticulum. It is responsible for receiving the proteins synthesized in the rough endoplasmic reticulum, modifying them and packaging them in vesicles for transport to the sites where their function is required.
Mitochondria
Mitochondria is a double membrane organelle, the outer mitochondrial membrane and the inner mitochondrial membrane, which delimits the matrix. It is responsible for the production of adenosine triphosphate or ATP, the energy molecule of the cell. In addition, the cell cycle and apoptosis are regulated in mitochondria.
Muscle cells form long networks of mitochondria for rapid, coordinated energy production. In the neuron, the mitochondria in the postsynaptic dendrites are larger and interconnected.
lysosome
Lysosomes are a heterogeneous group of vesicles of different sizes and contents. Their main function is the digestion of the external or internal material of the cell, which is why they are considered a kind of “cellular stomach”. It does this thanks to several enzymes that break down proteins, carbohydrates, lipids, and nucleic acids.
Lysosomal enzymes are produced in the endoplasmic reticulum, matured in the Golgi apparatus, and transported to the cytoplasm in small vesicles, known as primary lysosomes. Mature lysosomes fuse and divide, making them a dynamic compartment.
Lysosomes exist in all animal cells except the red blood cell. Degradation of endocytosed or autophagocytosed materials takes place within lysosomes that have an acidic pH between 4 and 5. After the encased material is degraded, the lysosomes enter a “resting” state.
peroxisome
The peroxisome is a membranous organelle that participates in oxidative metabolism. In mammals, abundant peroxisomes are found in liver and kidney cells.
Peroxisomes participate in the oxidation of fatty acids, in the synthesis of myelin lipids, and in the removal of hydrogen peroxide from cells.
When there are failures in the functioning of the peroxisomes or they do not exist, a disease called Zellweger syndrome occurs.
centrosome
The centrosome is a non-membranous organelle that serves as the microtubule organizing center. Facilitates cell motility, polarity, shape maintenance, cell division, vesicle transport. In the interphase or phase of the cell where it is not dividing, the centrosome is close to the nucleus.
The centrosome of a mammalian animal cell consists of a protein scaffold surrounding a pair of cylindrical centrioles.
You may also be interested in seeing Mitosis and meiosis.
cytoskeleton
The cytoskeleton is a flexible three-dimensional structure made up of protein filaments. Depending on the thickness of the filament, they are classified into microfilaments (7 nanometers (nm)), intermediate filaments (10 nm), and microtubules (25 nm).
The cytoskeleton maintains the shape of the cell, allows the movement of cilia and flagella, and participates in the intracellular transport of organelles.
You may also be interested in seeing:
References
Goodman, S.R. (2019). Cell (biology). AccessScience. Retrieved January 25, 2022, from https://doi.org/10.1036/1097-8542.116000
Hettema, E., Gould, S. (2017). Organelle formation from scratch. Nature 542: 174–175. https://doi.org/10.1038/nature21496
Islinger, M., Voelkl, A., Fahimi, D., Schrader, M. (2018). The peroxisome: an update on mysteries 2.0. Histochemistry and Cell Biology 150:443. https://doi.org/10.1007/s00418-018-1722-5
Kurz, T., Terman, A., Gustafsson, B., Brunk, UT (2008). Lysosomes in iron metabolism, aging and apoptosis. Histochemistry and Cell Biology 129: 389