Animal cell definition, Diagram, Function, Organelles, Parts
What is an animal cell?
Animal cells are the basic unit of life in organisms in the Animalia kingdom. They are eukaryotic cells, which means they have a true nucleus and specialized structures called organelles that carry out different functions. Animal cells do not have plant-specific organelles like cell walls, which support the plant cell, or chloroplasts, the organelle that carries out photosynthesis.
Animal cell Explain
All cells are surrounded by a cell membrane (also called a plasma membrane). The cell membrane is the boundary that separates the inside of the cell from the outside of the cell. The plasma membrane encloses all the cellular components, which are suspended in a gel-like fluid called cytoplasm. The cytoplasm is the location of the organelles.
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. Prokaryotic cells do not have a defined nucleus (instead, a region of the cytoplasm, called the nucleotide, contains the genetic material). They also lack membrane-bound organelles.
All animals are multicellular, which means that several cells work together to form the entire organism. In complex organisms, such as humans, these cells may be highly specialized to perform different functions. As such, they often look and function very differently from each other, even though they are all human cells.
Animal cell definition
- Animals are a large group of diverse living organisms that make up to three-quarters of all species on earth. With their ability to move, respond to stimuli, respond to environmental changes, and adapt to different feeding modes, defense, and reproduction mechanisms, all these mechanisms are reinforced by their constituent elements in the body. However, animals cannot make their food like plants and are therefore dependent on plants in one way or another.
- All living things are made up of cells that make up the structure of your body. Some of these living things are unicellular (unicellular) and other organisms are made up of more than one cell (multicellular).
- A cell is the smallest structural-functional unit of life (microscopic) of an organism. The cells that make up an animal are called animal cells, and the cells that makeup plants are known as plant cells.
- Most cells are covered by a protective membrane known as the cell wall that gives cells their shape and stiffness.
- An animal cell is a eukaryotic cell that lacks a cell wall and is enclosed by the plasma membrane. Cellular organelles are enclosed by the plasma membrane, including the cell nucleus. Unlike the animal cell that lacks the cell wall, plant cells have a cell wall.
- Since animal cells lack a rigid cell wall, it allows them to develop a wide variety of cell, tissue, and organ types. Nerves and muscles are made up of specialized cells that plant cells cannot evolve to form, therefore these nerve and muscle cells can move.
Animal cell Diagram
Animal cell size and shape
- Animal cells come in all kinds of shapes and sizes, ranging in size from a few millimeters to micrometers. The largest animal cell is the ostrich egg which is 5 inches in diameter, weighing approximately 1.2-1.4 kg, and the smallest animal cells are neurons approximately 100 microns in diameter.
- Animal cells are smaller than plant cells and generally have irregular shapes that take various forms, due to the lack of the cell wall. Some cells are round, oval, flattened, or rod-shaped, spherical, concave, rectangular. This is due to the lack of a cell wall. Note: Most cells are microscopic, so they can only be seen under a microscope to study their anatomy.
- But animal cells share other cell organelles with plant cells, since both have evolved from eukaryotic cells.
- As noted above, animal cells are eukaryotic cells with a membrane-bound nucleus. therefore they have their genetic material in the form of DNA locked in the nucleus. They also have various structural organelles within the plasma membrane that perform various specific functions for proper cellular function and, in general, to maintain normal body mechanisms.
Animal cell structure
The animal cell is made up of several structural organelles enclosed in the plasma membrane, which allow it to function properly, causing mechanisms that benefit the (animal) host. The joint work of all cells gives the animal the ability to move, reproduce, respond to stimuli, digest, and absorb food, etc. Generally, the combined effort of all animal cells is what allows the normal functioning of the body.
Animal cell organelles
The main cell organelles include:
Plasma membrane (cell membrane)
Definition of the plasma membrane (cell membrane)
It is a thin layer of semipermeable protein membrane that surrounds an animal cell.
Structure of the plasma membrane (cell membrane)
- Semi-permeable thin membrane
- It contains a percentage of lipids that form a semipermeable barrier between the cell and its physical environment.
- It has some protein components to
- It is very consistent around the cell.
- All living cells have a plasma membrane.
Functions of Plasma membrane (Cell membrane)
- To enclose and protect cellular content
- To regulate also the molecules that enter and leave the cell, through the plasma membrane. Therefore, it controls homeostasis.
- Proteins actively participate in the transport of materials through the membrane.
- Proteins and lipids allow cell communication, and carbohydrates (sugars and sugar chains), which decorate proteins and lipids and help cells recognize each other.
Definition of Nucleus
- This is a spherical structured organelle that is located primarily in the center of a cell surrounded by a double-layered nuclear membrane that separates it from the cytoplasm.
- It is held together with the cytoplasm with the help of filaments and microtubules.
- It contains other cell organelles, including the nucleolus, nucleosomes, and chromatins.
- A cell has a nucleus that divides into multinucleated cells, e.g. Skeletal muscle cell fibers.
- Some cells lose their nuclei after maturation, e.g. red blood cells
Structure of Nucleus
- The double-layered membrane is a continuous membranous channel of the endoplasmic reticulum network.
- The membrane has pores that allow large molecules to enter.
- Nucleoli (Singular; nucleolus) are small/small bodies found in the nucleus
- The nucleus and its component organelles are suspended in the nucleoplasm (House of chromosomal DNA and genetic materials)
Functions of Nucleus
- The main role of the nucleus is to control and regulate cellular growth activities and to maintain cellular metabolism.
- It also carries genes that have hereditary information from the cell.
- Chromosomal DNA and genetic materials, which are made up of a genetic code, ultimately form the amino acid sequences of its proteins for use by the cell.
- Therefore, the nucleus is the information center.
- It is the site for transcription (formation of mRNA from DNA) and the mRNA is transported to the nuclear envelope.
Definition of Cytoplasm
- This is a gel-like material that contains all the cell organelles, enclosed within the cell membrane.
- These organelles include; Mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, intermediate filaments, microfilament microtubules, vesicles.
Definition of Mitochondria
- These are membrane-bound organelles located in the cytoplasm of all eukaryotic cells.
- The number of mitochondria found in each cell varies widely depending on the function of the cell it performs.
- For example, erythrocytes do not have mitochondria, while liver and muscle cells have thousands of mitochondria.
Structure of Mitochondria
- They are rod-shaped or oval or spherical, with a size of 0.5 to 10 μm.
- Mitochondria have two special membranes: outer and inner membranes.
- They have a mitochondrial gel-matric in the central mass.
- The membranes fold into folds known as ridges.
Functions of Mitochondria
- Their main function is to generate energy for the cell, that is, they are energy generators, which produce energy in the form of adenosine triphosphate (ATP), converting nutrients and oxygen into energy that allows the cell to perform its function and also release the excess energy. From the cell.
- Mitochondria also store calcium, which aids cellular signaling activity, generating cellular and mechanical heat, and mediating cell growth and death.
- The outer membrane is permeable, allowing the transport of small molecules and a special channel to transport large molecules.
- The inner mitochondrial membrane is less permeable, allowing very small molecules in the mitochondrial gel matrix in the central mass. The gel matrix is made up of the DNA of the mitochondria and the enzymes for the tricarboxylic acid (TCA) cycle or the Kreb cycle.
- The TCA cycle uses nutrients, turning them into by-products that the mitochondria use to produce energy. These processes take place in the inner membrane because the membrane is folded into folds called ridges, where the protein components are used for the main cells of the energy production system, known as the electron transport chain (ETC). ETC is the main source of ATP production in the body.
- ETC involves several sequences of oxidation-reduction reactions to transport electrons from one protein component to another, thereby producing energy that is used for phosphorylation of ADP (adenosine diphosphate) to ATP. This process is called the chemosmotic coupling of oxidative phosphorylation. This mechanism provides energy to most cellular activities, including muscle movement, and powers general brain function.
- Some, if not all, of the proteins and molecules that make up the mitochondria, come from the cell nucleus. The mitochondrial nucleus genome has 37 genes, of which 13 of these genes produce the majority of the ETC components. However, mitochondrial DNA is highly vulnerable to mutations because it does not have a large DNA repair mechanism, a common element found in other nuclear DNA.
- Furthermore, reactive oxygen species (ROS) also called free radicals to occur in the mitochondria, due to the preference for abnormal production of free electrons. These electrons are neutralized by antioxidant proteins in the mitochondria. However, some of the free radicals can damage mitochondrial DNA (mtDNA).
- Likewise, alcohol consumption can cause damage to mtDNA because excess ethanol in the body saturates detoxifying enzymes that lead to the production and leakage of highly reactive electrons in the cytoplasmic membrane and in the mitochondrial matrix, combining with others cellular molecules forming numerous radicals that cause significant cellular damage.
- Most organisms inherit their mtDNA from their mother. This is because the maternal ovum donates most of the cytoplasm to the embryo, while the mitochondria inherited from the father’s sperm are destroyed. This causes the origin of inherited and acquired mitochondrial diseases due to mutations transmitted to the embryo from maternal and paternal DNA or maternal mtDNA. Such diseases include Alzheimer’s disease and Parkinson’s disease. When mutated mtDNA accumulates over time it has been linked to aging and the development of certain cancers and diseases.
- Naturally, mitochondria play an important role in programmed cell death (apoptosis), and due to mutations in mtDNA, they can inhibit cell death and cause cancer development.
Definition of Ribosomes
- They are small organelles formed mainly by 60% of RNA cytoplasmic granules and 40% of proteins.
- All living cells contain ribosomes, which can freely circulate in the cytoplasm, and some are attached to the endoplasmic reticulum.
- It is the site for protein synthesis.
Structure of Ribosomes
- Ribosomes are made up of ribosomal proteins and ribosomal RNA (rRNA). In a eukaryotic cell, ribosomes make up half of ribosomal RNA and half of the ribosomal proteins.
- Each ribosome is made up of two subunits i. The large subunit and the small subunit with their own distinct shapes. These subunits are designated as the 1940s and 1960s in the animal cell.
Functions of Ribosomes
- Ribosomes that are produced as free particles bind to the membrane of the endoplasmic reticulum and are produced in large numbers and represent about a quarter of the cell organelles. A single replicated cell has around 10 million ribosomes.
- Ribosomal subunits are the site for genetic coding in proteins. In ribosomes, mRNA helps determine the encoding of transfer RNA (tRNA) that also determines the amino acid sequences of the protein. This leads to the formation of the rRNAs that are involved in the catalysis of peptidyl transferase by creating the peptide bond that is between the amino acid sequences that proteins develop. The proteins formed detach from the ribosomes, migrating to other parts of the cell for use by the cell.
Endoplasmic Reticulum (ER)
Structure of Endoplasmic Reticulum (ER)
- This is a continuous folded membranous organelle found in the cytoplasm formed by a thin network of interconnected flattened compartments (sacs) that connect from the cytoplasm to the cell nucleus.
- Within its membranes, there are membrane spaces called crystalline spaces, and the folding of the membrane is called cristae.
- There are two types of ER depending on their structure and the function they perform, including the rough endoplasmic reticulum and the smooth endoplasmic reticulum.
Functions of Endoplasmic Reticulum (ER)
- Manufacture, processing, and transport of proteins for cellular use both inside and outside the cell. This is because it is directly connected to the nuclear membrane and provides a passage between the nucleus and the cytoplasm.
- The ER has more than half the content of membranous cells, therefore it has a large surface area where chemical reactions take place. They also contain the enzymes for almost all cellular lipid synthesis, therefore they are the site for lipid synthesis.
Variation in physical and functional characteristics differentiate the emergency room into two types, that is, rough endoplasmic reticulum and smooth endoplasmic reticulum.
Types of Endoplasmic Reticulum
- Rough Endoplasmic Reticulum (Rough ER): Rough ER is called “rough” because its surface is covered with ribosomes, giving it a rough appearance. The role of ribosomes in rough ER is to synthesize proteins and they have a signaling sequence, which directs them to the endoplasmic reticulum for processing. Rough ER transports proteins and lipids through the cell to the ridges. They are then either sent to the Golgi bodies or inserted into the cell membrane.
- Smooth endoplasmic reticulum (smooth ER): Smooth ER is not associated with ribosomes and its anointing is different from that of the rough endoplasmic reticulum, despite being adjacent to the rough endoplasmic reticulum. Its function is the synthesis of lipids (cholesterol and phospholipids) that are used to produce new cell membranes. They are also involved in the synthesis of steroid hormones from cholesterol for certain types of cells. It also contributes to the detoxification of the liver after the intake of drugs and toxic chemicals.
There is also a specialized type of soft ER known as the sarcoplasmic reticulum. Its function is to regulate the concentration of calcium ions in the cytoplasm of muscle cells.
Structure of Golgi apparatus (Golgi bodies)
- These are membrane-bound cellular organelles found in the cytoplasm of a eukaryotic cell, next to the endoplasmic reticulum and near the nucleus.
- Golgi bodies are supported together by cytoplasmic microtubules and supported by a protein matrix.
- It is made up of flattened stacked bags known as cisterns.
- These cisterns can be 4 to 10 in number for Golgi bodies of animal cells, although some organisms such as single-celled organisms have approximately 60 cisterns.
- They have three primary compartments known as cis (cisterns closest to the endoplasmic reticulum), medial (central layers of cisterns), and trans (cisterns furthest from the endoplasmic reticulum).
- Animal cells have very few (1-2) Golgi bodies, while plants have a few hundred.
Functions of Golgi apparatus (Golgi bodies)
- Its main function is to transport, modify and package proteins and lipids in the Golgi vesicles to take them to their target sites. Animal cells contain one or more Golgi bodies, while plants have a few hundred.
- The cis and trans-Golgi network make up the outer layer of cisterns on the cis and trans sides and are responsible for classifying the proteins and lipids received on the cis side and released by the trans side, by the Golgi bodies.
- The cis side collects proteins and lipids from the fused vesicles in groups. The fused vesicles move along the microtubules through a specialized compartment known as the vesicular-tubular group. This compartment is located between the endoplasmic reticulum and the Golgi apparatus.
- The vesicle clusters fuse with the cis Golgi network, delivering proteins and lipids to the cis-face cisterns, and as they move from the cis-face to the trans-face, they are modified to functional units. These functional units are delivered to the intracellular and extracellular components of the cell.
-Modification mechanisms include:
-Cleavage of oligosaccharide chains
-Fixation of sugar residues from different side chains.
- Add fatty acids and/or phosphate groups by phosphorylation and/or remove monosaccharides, eg. the removal of mannose residues is carried out in the cis and the medial cisterns, while the addition of galactose is carried out in the trans cisterns.
- Sorting of the modified proteins and lipids occurs in the trans-Golgi network and is packaged in the trans vesicles, which then send them to the lysosomes or sometimes to the cell membrane for exocytosis. Assisted by ligands bound to receptors that trigger protein fusion and secretion.
Also known as cell vesicles; Lysosomes were discovered by Christian Rene de Duve, a Belgian cytologist in the 1950s.
Structure of Lysosomes
- They are round subcellular organelles found in almost all eukaryotic cells.
- Lysosomes are highly acidic organelles that contain digestive enzymes, and therefore each lysosome is surrounded by a membrane to protect it from the outside environment.
Functions of Lysosomes
- This is the site for cellular nutrient digestion, excretion, and cell turnover.
- Lysosomes break down macromolecule components from outside the cell into simpler elements that are transported to the cytoplasm through a proton pump to build new cell materials.
- These macromolecule components include old cells and parts, cell waste products, microorganisms, and cell waste.
- The digestive enzymes found in lysosomes are called hydrolytic enzymes or acid hydrolases, breaking down large molecules into smaller molecules that can be used by the cell.
- These enzymes also break down large molecules e. g proteins, carbohydrates, lipids, in small molecules, e.g. amino acids and simple sugars, fatty acids, respectively.
- Note: Enzymes are active only inside the acid lysosome and their acidity protects the cell from breaking down when there is a lysosomal leak because the cell’s pH is neutral to slightly alkaline.
Structure of Cytoskeleton
- This is a fibrous network that is formed from different proteins with long amino acid chains.
- These proteins are found in the cell cytoplasm of eukaryotic cells.
- They are also made up of 3 types of small filaments:
- Actin filaments (microfilaments), microtubules, intermediate filaments.
Functions of Cytoskeleton
- The cytoskeleton works to create a network that organizes the components of the cell and also to maintain the shape of the cell.
- It also provided the smooth movement of the cell and its organelles, through the network of the filament system found in the cell’s cytoplasm.
- It also organizes some of the cellular components that maintain cellular shape.
- It plays an important role in the movement of the cell and some cell organelles in the cytoplasm.
The tiny filaments include:
- Actin filaments; also known as microfilaments; It is a network of fibers that run parallel to each other and play a major role in shaping the cell; they constantly change, helping the cell to move and also mediating certain cellular activities, such as the ability to adhere to substrates and cleavage mechanisms during mitotic cell division
- Microtubules: These are long filaments that help mitosis move the daughter chromosomes to the new daughter cell’s information.
- Intermediate filaments: they are more stable filaments compared to actin and microtubules. They form the true skeleton of the cell and hold the nucleus in its correct position within the cell.
- It also allows the elasticity factor of the cell to allow it to withstand physical stress.
Other proteins that can be added as part of the cell’s cytoskeleton include septin ((assembles the filaments) and spectrin (help maintain cell structure by binding the cell membrane to the cell’s intracellular surface).
Structure of Microtubules
- These are long, straight, hollow cylinder filaments that are built from 13-15 sub-filament filaments (protofilament) of a special globular protein called tubulin, found only in eukaryotic cells.
- They are found throughout the cytoplasm of the animal cell.
Functions of Microtubules
- Transport of some organelles such as mitochondria and vesicles, that is, the transport of vesicles from the body of the neuronal cell to the tips of the axons and back to the cell body.
- Structural support, they give characteristic support to the Golgi bodies, keeping them inside the gel matrix of the cytoplasm.
- They provide the rigid and organized component of the cell’s cytoskeleton, allowing a cell to take on a particular shape.
- They are the main elements that make up the locomotive projections of a cell (cilia and flagella)
- They also play a role in the formation of the spindle fibers of the cell’s chromosome during mitotic cell division.
This is clearly found in the animal cell, which has the ability to replicate or make copies of itself. It is made up of 9 microtubule packages and its main function is to help organize the process of cell division.
Structure of Centrioles
- It is a small structure that is made up of 9 sets of microtubules, placed in groups of three, therefore they are triplet microtubules.
- As triplets, they remain very strong together, therefore they have been found to be found in structures such as cilia and flagella.
- Triple microtubules are held together by proteins, shaping the centriole.
- They are found in the centrosome, creating and maintaining microtubules within the cell.
- Triple microtubules are surrounded by a pericentriolar matrix that contains molecules that make up the microtubules.
- Each microtubule within the triplet microtubule complex is composed of tubulin subunits that join together to form long, hollow, straw-like tubes (microtubules).
Functions of Centrioles
- Centriole microtubules allow the transport of substances that are linked with a glycoprotein to any cellular location. The glycoprotein bond acts as a signaling unit to move specific proteins.
- The centrioles anchor the microtubules that extend from there and contain the factors necessary to create more tubules.
- Mitosis is accomplished by replicating each centriole that makes duplicates of each centriole (4 centrioles). The newly formed centrioles are divided into two centrosomes, each centriole at an angle to the second centriole. The microtubules between the centrosomes separate the pairs of centrioles towards the opposite ends of the cell. When the centrioles are in place, the microtubules extend into the cell cytoplasm to search for the chromosome. The microtubules bind to the chromosome at the centromere. The microtubules are disassembled from the centriole that separates the chromosomes.
Structure of Peroxisomes
- They are spherical in shape, are bound by a membrane, and are the most common microorganisms in the cell cytoplasm.
Functions of Peroxisomes
The functions of peroxisomes include:
- Lipid metabolism
- Chemical detoxification by moving hydrogen atoms from various oxygen molecules to produce hydrogen peroxide, thereby neutralizing body poison like alcohol.
- Its mechanism in reactive oxygen species is very essential.
Cilia and Flagella
These are locomotive projections found on the surface of the cell.
Structure of Cilia and flagella
- They are made of strands of filaments. These filaments have complete, partial microtubules that extend the projections. Partial microtubules do not extend to the tip of the cilium and complete microtubules extend to the tip of the cilium.
- Microtubules also have motor proteins known as dynein that make a link between partial microtubules and complete microtubules.
- The entire collection is combined as extensions on the plasma membrane of the cell.
Functions of Cilia and flagella
- Sperm have flagella that allow them to swim to the eggs for fertilization. For individual cells, like sperm, this allows them to swim.
- The cilia in the animal cell help move fluids away from stationary cells and pass them.
- The cilia help move particles from the surface, especially in the epithelial lining of the nostrils and move mucus over the cell’s surface.
These are vesicles joined by membranes and formed by an endocytosis mechanism. They are found in the cell cytoplasm.
Structure of Endosome
They are membranous organelles that are attached to the cell membrane.
Functions of Endosome
- Its main function is to fold the plasma membrane. The folding allows the diffusion of molecules through extracellular fluids.
- Its main function is to remove waste materials from the cell through endocytic processes such as exocytosis and phagocytosis.
These are liquid-filled cell organelles enclosed by a membrane.
Structure of Vacuoles
- They are membrane-bound sacs found within the cell cytoplasm.
- The vacuole sac has a unique membrane surrounding it known as a tonoplast, and this membrane resembles the plasma membrane.
Functions of Vacuoles
- Its main function is to store food, water, carbohydrates in the form of sugars and waste materials.
- Tonoplast is a regulator that controls the entry and exit of children through a protein pump.
- acts as a guard of what kind of matter is allowed to pass into and out of vacuoles
- They also remove toxic substances and waste materials from the cell as a protection strategy.
- They also remove misfolded proteins from the cell.
- Vacuums can also change their functionality to provide the necessary roles that adapt to the cell by being able to change shape and size.
These are superficial bumps found on the intestinal lining, on the surfaces of the ovules, and on white blood cells.
Structure of Microvilli
- These are surface bumps formed from accessory proteins in the actin filaments. Accessory proteins clump together to form microvilli on the surface of the cell membrane.
Functions of Microvilli
- In the small intestine, they increase the surface area for the absorption of digested food and water. Some microvilli can be found in the ear to detect sound and transmit sound waves to the brain through an electrical signal.
- They also help anchor sperm to the egg to facilitate fertilization.
- In white blood cells, they also act as anchors that allow freely moving white blood cells in the circulatory system to attach to potential pathogens.
Animal Cells vs. Plant Cells
Animal cells, unlike plant and fungal cells, do not have a cell wall. Instead, multicellular animals have other structures that support their tissues and organs, such as the skeleton and cartilage. Furthermore, animal cells also lack chloroplasts found in plant cells. Chloroplasts are specialized organelles that trap energy from the sun and use it as fuel to produce sugars in a process called photosynthesis.
Furthermore, while plant cells tend to have a large central vacuole, animal cells lack this feature. Some animal cells have small vacuoles, but their function is to aid in the storage and transport of large molecules.
Animal cell definition, Diagram, Function, Organelles, Parts