Animal cells are the basic structural and functional unit of all animal organisms. These cells are diverse in their structure and function, but all share certain characteristics that define them as animal cells.
In this blog post, we will explore the different components of animal cells, including the cell membrane, cytoplasm, and various organelles such as the nucleus, mitochondria, and endoplasmic reticulum.
We will also discuss the various functions and types of animal cells and how they work together to maintain the overall health and survival of an organism.
Whether you’re a student studying biology or simply curious about the inner workings of animal cells, this post is sure to provide valuable insights and information.
Animal cell Definition
Animal cells are the basic structural and functional units of animal tissues and organs. They are eukaryotic cells, meaning that they are cells that have a defined nucleus and membrane-bound organelles suspended in the cytoplasm enveloped by a plasma membrane.
This fundamental feature is not exclusive to animal cells, as both animal cells and plant cells are eukaryotes, and therefore a plant cell has this feature as well.
However, plant cells can be easily distinguished from animal cells by the presence of a cell wall. Apart from the presence of a cell wall, another notable difference between animal cells and plant cells is that animal cells lack plastids, especially chloroplasts. Chloroplasts are organelles that are found in plant cells, algae, and some protists, and they are responsible for photosynthesis.
What is an animal cell?
Animals, plants, fungi, and protists are all made up of at least one eukaryotic cell, while bacteria and archaea are made up of a single prokaryotic cell.
All cells, whether eukaryotic or prokaryotic, are surrounded by a cell membrane, also called a plasma membrane. The cell membrane acts as the boundary that separates the inside of the cell from the outside of the cell.
It encloses all the cell components, which are suspended in a gel-like fluid called the cytoplasm. The cytoplasm is the location of the organelles, which are specialized structures that carry out specific functions within the cell.
Eukaryotic cells are distinguished from prokaryotic cells by the presence of a defined nucleus and other membrane-bound organelles, such as the mitochondria, endoplasmic reticulum, and Golgi apparatus.
The mitochondria are the powerhouses of the cell, responsible for producing energy, the endoplasmic reticulum is responsible for protein synthesis and transport, and the Golgi apparatus is responsible for the sorting, modification, and packaging of molecules.
Prokaryotic cells, on the other hand, do not have a defined nucleus (instead, a region of the cytoplasm – called the nucleotide – holds the genetic material) and they also lack membrane-bound organelles.
Animals are multicellular organisms, meaning that multiple cells work together to form the whole organism. In complex organisms, such as humans, these cells can be highly specialized to perform different functions.
As such, they often look and function very differently from one another, even though they are all human cells.
For example, nerve cells are specialized for transmitting electrical signals, muscle cells are specialized for contraction, and blood cells are specialized for transportation and defense. This specialization of cells allows for the efficient functioning of the organism as a whole.
Animal cell diagram
The animal cell diagram is a visual representation of the different parts of an animal cell and their respective functions. This diagram is often used in examinations as a way to understand the structure and functions of an animal cell.
The different parts of an animal cell include centrioles, cilia, and flagella, endoplasmic reticulum, endosomes and endocytosis, Golgi apparatus, intermediate filament, lysosomes, microfilaments, Microtubules, Mitochondria, Nucleus, Peroxisomes, plasma membrane, and Ribosomes.
The diagram of an animal cell typically includes all these structures and is labeled to show the name of each part and its specific location within the cell.
By studying the animal cell diagram, students can gain a better understanding of the structure and functions of an animal cell, which is an essential part of understanding the overall functioning of organisms.
Animal cell structure
Animal cells are a type of eukaryotic cell, which means they have a membrane-bound nucleus and organelles. The plasma membrane, also known as the cell membrane, surrounds the cell and acts as a barrier, controlling what enters and exits the cell. The nucleus, which is the cell’s control center, contains the cell’s genetic material in the form of DNA.
Organelles are specialized structures within the cell that perform specific functions. Some common organelles found in animal cells include:
Centrioles
Centrioles are self-replicating organelles that are found only in animal cells. They are made up of nine bundles of microtubules, which are protein structures that provide support and shape to the cell. Centrioles play an important role in organizing cell division, but they are not essential for the process.
During the process of cell division, centrioles help to organize the formation of the mitotic spindle, which is a structure that pulls the chromosomes apart during cell division. The microtubules of the centrioles help to form the spindle fibers that attach to the chromosomes and pull them apart.
However, recent studies have shown that centrioles are not essential for cell division. Some animal cells, such as some types of stem cells, can divide without centrioles. Additionally, some cells that have centrioles, like somatic cells, can divide without them.
This means that centrioles are important in organizing cell division, but they are not absolutely essential to the process.
Cilia and Flagella
Cilia and flagella are structures found on the surface of eukaryotic cells that are essential for the movement of individual organisms. These structures are made up of microtubules and are powered by the energy produced by the cell.
In single-celled eukaryotes, protozoa, cilia, and flagella are used for the locomotion of the organism. They work by beating in a coordinated manner to propel the organism through the environment, allowing it to move in search of food or to avoid predators.
In multicellular organisms, cilia have different functions. They are found on the surface of cells and work to move fluid or materials past an immobile cell. For example, cilia in the respiratory system help to move mucus and debris out of the lungs, while cilia in the reproductive system help to move the egg or sperm toward the uterus or vas deferens.
Additionally, cilia can also be found on the surface of cells that are part of a group of cells called cilia, that move as a coordinated group, allowing the movement of a cell or group of cells. For example, cilia on the surface of cells in the brain help to move cerebrospinal fluid through the brain and spinal cord, providing nourishment and removing waste products.
Endoplasmic Reticulum
The endoplasmic reticulum (ER) is a network of flattened sacs and tubules that is present in the cytoplasm of eukaryotic cells. It acts as a complex system that plays a key role in the manufacturing, processing, and transport of chemical compounds for use inside and outside of the cell.
The ER is divided into two parts: the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER). The RER is studded with ribosomes, which are responsible for the synthesis of proteins.
The newly synthesized proteins are then transported to the lumen of the RER for further processing and modification before being transported to different destinations.
The SER, on the other hand, lacks ribosomes, and it is responsible for the synthesis of lipids and carbohydrates, detoxification of drugs and xenobiotics, and the regulation of intracellular calcium levels.
The ER is connected to the double-layered nuclear envelope, which surrounds the nucleus. This connection provides a pipeline between the nucleus and the cytoplasm, allowing the transport of molecules between the two compartments.
This connection is essential for the correct functioning of the cell, as it ensures that the right molecules are transported to the right place at the right time.
Endosomes and Endocytosis
Endosomes are membrane-bound vesicles that are formed via a complex family of processes collectively known as endocytosis. They are found in the cytoplasm of virtually every animal cell. Endocytosis is the process by which a cell takes in molecules or particles from the extracellular environment.
The basic mechanism of endocytosis is the reverse of what occurs during exocytosis or cellular secretion. Exocytosis is the process by which a cell releases molecules or particles into the extracellular environment.
Endocytosis involves the invagination (folding inward) of a cell’s plasma membrane to surround macromolecules or other matter diffusing through the extracellular fluid. This process forms a vesicle, which is then pinched off from the plasma membrane and transported into the cytoplasm.
There are different types of endocytosis, such as phagocytosis, pinocytosis, and receptor-mediated endocytosis. Each of these types of endocytosis has a specific function and involves different mechanisms.
Phagocytosis is the process of engulfing large particles, such as bacteria or debris, pinocytosis is the process of taking in droplets of extracellular fluid, and receptor-mediated endocytosis is a specific mechanism that allows cells to selectively take in specific molecules.
Golgi Apparatus
The Golgi apparatus, also known as the Golgi complex, is a complex system of flattened stacks of membrane-bound vesicles found in the cytoplasm of eukaryotic cells. It plays a key role in the modification, sorting, and transport of chemical compounds and macromolecules within the cell.
The Golgi apparatus receives proteins and lipids that are synthesized in the endoplasmic reticulum and modifies them. This modification process can include the addition of sugars to proteins, forming glycoproteins, or the addition of phosphates to lipids, forming phospholipids.
These modifications can change the chemical and physical properties of the molecules, providing them with new functions, such as targeting them to specific destinations.
After modification, the molecules are sorted and packaged into vesicles that are then transported to different destinations. The Golgi complex is divided into three regions, the cis-Golgi, medial-Golgi, and trans-Golgi, each responsible for specific modifications and sorting functions.
The cis-Golgi is the region where the newly synthesized proteins and lipids are received and modified. The medial Golgi is responsible for further modification, such as the formation of lysosomal enzymes, and sorting of the molecules.
The trans-Golgi is responsible for the final sorting and packaging of the molecules into vesicles that are then transported to the plasma membrane, lysosomes, or the extracellular space.
Intermediate Filaments
Intermediate filaments are a very broad class of fibrous proteins that play an important role as both structural and functional elements of the cytoskeleton. The cytoskeleton is a network of protein fibers that provides cells with their shape and mechanical strength.
Intermediate filaments are one of the three main components of the cytoskeleton, along with microtubules and microfilaments. They are made up of different types of proteins, such as keratins in epithelial cells, vimentin in mesenchymal cells, and neurofilaments in nerve cells.
Intermediate filaments are intermediate in size between microfilaments (7nm) and microtubules (25nm) and range in size from 8 to 12 nanometers. These fibers are relatively stable and long-lived and function as tension-bearing elements to help maintain cell shape and rigidity.
They are located in the cytoplasm and provide structural support to the cell by connecting the cell membrane to the nucleus, and other organelles, and also help to resist mechanical stress.
Intermediate filaments also have functional roles. They help to maintain the shape of the cell, protect the cell from damage and act as a scaffold for the attachment of other cytoskeletal elements. They also participate in cell movement, cell division, and cell signaling.
Lysosomes
Lysosomes are membrane-bound organelles that are found in the cytoplasm of eukaryotic cells. They are often referred to as the “garbage disposals” of the cell because their main function is the digestion of cellular waste products and debris from outside the cell.
Lysosomes are formed by the Golgi apparatus, which packages enzymes and other molecules into vesicles that then fuse with the plasma membrane, forming a lysosome.
Lysosomes are filled with a variety of hydrolytic enzymes that can break down a wide range of biomolecules, including proteins, lipids, carbohydrates, and nucleic acids.
The lysosomes are responsible for breaking down cellular waste products and debris from outside the cell into simple compounds. These compounds are transferred to the cytoplasm as new cell-building materials.
They also help to break down large molecules that are brought into the cell by endocytosis, such as bacteria or cellular debris.
Lysosomes are also responsible for the removal of unnecessary or damaged organelles, such as old mitochondria, by a process called autophagy. Additionally, they can also play a role in the removal of abnormal or abnormal cells by a process called apoptosis.
Microfilaments
Microfilaments are one of the three main components of the cytoskeleton, along with intermediate filaments and microtubules. They are made up of a protein called actin and are responsible for maintaining the shape of the cell, as well as its mechanical strength and resistance to stress.
Microfilaments are very thin, measuring around 7nm in diameter. They are composed of two main types of actin, G-actin, and F-actin. G-actin is a globular protein that polymerizes to form F-actin, which is a long, linear polymer.
These filaments can be found throughout the cytoplasm and are responsible for maintaining the shape of the cell, as well as its mechanical strength and resistance to stress.
The actin filaments form a network that provides mechanical support for the cell and helps to resist mechanical stress. They also play a critical role in cell movement, by providing the force needed for the cell to contract, change shape or move. In addition, they also participate in cell division, cell signaling, and intracellular transport.
Microtubules
Microtubules are one of the three main components of the cytoskeleton, along with intermediate filaments and microfilaments. They are straight, hollow cylinders that are made up of a protein called tubulin and are found throughout the cytoplasm of all eukaryotic cells. They are not found in prokaryotic cells, which lack a cytoskeleton.
Microtubules are relatively large, measuring around 25nm in diameter, and are composed of repeating units of tubulin. They form a network that provides mechanical support for the cell, helps to resist mechanical stress and plays a critical role in cell movement and intracellular transport.
One of the main functions of microtubules is to provide a structural framework for the cell. They help to maintain the shape of the cell and provide a scaffold for the attachment of other cytoskeletal elements. They also participate in cell division by helping to move chromosomes during cell division.
Microtubules are also involved in intracellular transport. They form a network of tracks that run throughout the cell and allow for the movement of vesicles and organelles from one part of the cell to another. This is important for the delivery of nutrients, hormones, and other important molecules to different parts of the cell.
Mitochondria
Mitochondria are small, oblong-shaped organelles found within the cytoplasm of eukaryotic cells. They are often referred to as the “powerhouse” of the cell, as they play a crucial role in the production of energy through a process called cellular respiration.
During cellular respiration, oxygen and nutrients are taken in by the cell and are converted into a form of energy called adenosine triphosphate (ATP) through a series of chemical reactions that take place within the mitochondria.
This energy is then used by the cell to perform various functions, such as maintaining the cell’s structure and carrying out metabolic processes. In animal cells, mitochondria are the main site for energy production.
Nucleus
The nucleus is a large, spherical organelle found in eukaryotic cells, and it serves as the “brain” or “control center” of the cell. It plays a crucial role in the cell’s overall function by controlling and coordinating the activities of the cell, such as growth, metabolism, protein synthesis, and reproduction.
One of the main functions of the nucleus is to store the cell’s genetic material, or DNA. DNA is the blueprint that contains all the genetic information needed for the cell to function and for an organism to develop and function correctly. The DNA is packaged into structures called chromosomes, which are located inside the nucleus.
The nucleus also plays a key role in controlling the cell’s activities through the process of gene expression. This is the process by which the information stored in the DNA is used to produce proteins and RNA, which are responsible for carrying out specific functions within the cell.
The nucleus also coordinates cell division, which is the process by which a single cell divides into two or more daughter cells. This is essential for the growth, repair, and reproduction of the organism.
Peroxisomes
Microbodies are a group of organelles found in the cytoplasm of eukaryotic cells. They are small, roughly spherical structures that are bound by a single membrane, which separates their contents from the rest of the cytoplasm. There are several types of microbodies, each with its own unique function.
Peroxisomes are the most common type of microbody. They are similar in structure to lysosomes, another type of organelle, but they have different functions. Peroxisomes are involved in a variety of metabolic reactions, including the breakdown of fatty acids and amino acids, and the detoxification of harmful substances.
They contain enzymes that catalyze specific reactions, such as the breakdown of fatty acids to generate energy. They also contain enzymes that detoxify harmful substances such as alcohol and formic acid, by converting them into less toxic compounds.
Peroxisomes are particularly important in liver cells where they participate in the detoxification of drugs, toxins, and other harmful substances. They also play a role in the synthesis of plasmalogens, which are important structural components of the cell membrane.
Plasma Membrane
The plasma membrane, also known as the cell membrane, is a thin layer of lipids and proteins that surrounds all living cells, both prokaryotic and eukaryotic. It acts as a barrier between the cell’s internal environment and the external environment and plays a crucial role in maintaining the cell’s homeostasis.
In prokaryotic cells, such as bacteria, the plasma membrane is the inner layer of protection and is surrounded by a rigid cell wall. The cell wall provides an additional layer of protection for the cell and gives it shape and rigidity.
Eukaryotic animal cells, on the other hand, have only the plasma membrane as a layer of protection. The membrane is composed of a double layer of phospholipids, which form a barrier that keeps the cell’s contents inside and the outside environment separate.
The plasma membrane also regulates the passage of molecules in and out of the cell. The membrane is selectively permeable, meaning that it only allows certain molecules to pass through.
It does this through a variety of transport mechanisms, such as facilitated diffusion, active transport and endocytosis, and exocytosis. These mechanisms allow the cell to take in essential nutrients, get rid of waste products, and communicate with the external environment.
Ribosomes
Ribosomes are tiny organelles that are found in all living cells, both prokaryotic and eukaryotic. They are composed of approximately 60 percent RNA (ribonucleic acid) and 40 percent protein. RNA is a type of nucleic acid that plays a key role in the production of proteins.
Ribosomes are responsible for the synthesis of proteins, a process called translation. They do this by reading the genetic code of the mRNA (messenger RNA) and linking together amino acids to form a protein. The sequence of bases in the mRNA determines the sequence of amino acids in the protein.
In eukaryotic cells, ribosomes are composed of four strands of RNA. These ribosomes are usually found in the cytoplasm and are known as cytoplasmic ribosomes. They are responsible for synthesizing proteins that will be used within the cell, including enzymes and structural proteins.
Types of animal cell
Animal cells are diverse and complex, and each animal cell type is specialized to perform specific functions within the body. There are many different types of animal cells, but some of the most common include:
Skin Cells
Skin cells make up the largest organ in the human body, and there are several different types of skin cells that work together to protect the body from external threats. Melanocytes produce the pigment melanin, which gives color to the skin, hair, and eyes.
Keratinocytes produce the protein keratin, which forms the protective outer layer of the skin. Merkel cells and Langerhans cells are involved in sensing touch and pressure.
Muscle Cells
Muscle cells, also known as myocytes, are responsible for movement and are grouped into three types: skeletal, smooth, and cardiac muscle cells.
Myosatellite cells are a type of muscle cell that is responsible for repairing damaged muscle tissue. Tendon cells and cardiac muscle cells are specialized muscle cells that have distinct functions.
Blood Cells
Blood cells are essential for maintaining the health of the body. Leukocytes are white blood cells that are involved in the immune response, while erythrocytes, also known as red blood cells, transport oxygen throughout the body. Platelets are involved in blood clotting.
Nerve Cells
Nerve cells, also known as neurons, are specialized cells that transmit electrical signals throughout the body. Schwann cells and glial cells are types of supportive cells that protect and support neurons.
Fat Cells
Fat cells, also known as adipocytes, are specialized cells that store energy in the form of lipids. They also play a role in maintaining body temperature and cushioning organs.
Animal Cells vs. Plant Cells
Animal cells and plant cells are both eukaryotic cells, meaning they have a defined nucleus and other membrane-bound organelles. However, there are some fundamental differences between the two types of cells.
One of the main differences is that animal cells do not have a cell wall, while plant and fungi cells do. The cell wall provides structural support and protection for plant cells, but multicellular animals have other structures that provide support to their tissues and organs, such as skeleton and cartilage.
Another difference is that animal cells lack chloroplasts, which are specialized organelles found in plant cells that are responsible for trapping energy from the sun and using it as fuel to produce sugars in a process called photosynthesis.
Additionally, plant cells tend to have a large, central vacuole, which is a membrane-bound organelle that stores water, ions, and other molecules. On the other hand, animal cells lack this feature. Some animal cells do have small vacuoles, but their function is to assist in the storage and transport of large molecules.
Reference
- Molecular Expressions Cell Biology: Animal Cell Structure. (2019). Retrieved Fsu.edu website: https://micro.magnet.fsu.edu/cells/animalcell.html
- Plant and Animal Cells Grade 4 Unit 3 Lesson 1. (n.d.). Retrieved from https://coast.noaa.gov/data/SEAMedia/Presentations/PDFs/Grade 4 Unit 3 Lesson 1 Plant & Animal Cells.pdf
- Cell Structure and Function. (2019). Retrieved from Msu.edu website: https://msu.edu/~potters6/te801/Biology/biounits/cellstructure&function.htm
- Alberts B., Johnson A., Lewis J., et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. The Compartmentalization of Cells. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26907/
- Lodish H., Berk A., Zipursky S.L., et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 5.4, Organelles of the Eukaryotic Cell. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21743/
