Introduction to Cell: The Unit of Life
The most fundamental, structural, and functional unit of all living beings is the cell. A cell is a structure containing organelles that perform essential processes to survive. Not all cells, though, are the same. Plants and animals have cells that are substantially different. The absence of cell walls in animal tissue is one of the most significant differences. The egg and female ovum is the largest cell within the human body, with the egg and female ovum being the smallest. It’s around 1 mm long and 1 millimetre wide. The smallest is the granule cell, which is present in the human cerebellum and measures around 4.5 micrometres in diameter.
Types of Cells
Let’s learn the major difference between the two types of cells: Prokaryotic and Eukaryotic cells.
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Prokaryotic cells
Microorganisms that belong to the prokaryotic cell family include bacteria, blue-green algae, mycoplasma, and PPLO. There are many types of bacterial cells, including Bacillus (rod-shaped), Coccus (sphere), Vibrio (comma-shaped), and Spirillum (spirillum) (spiral).
Except for Mycoplasma, all prokaryotic cells have a cell wall that surrounds the cell membrane. Plasmid DNA is found in certain bacteria and is responsible for several unique characteristics, such as antibiotic resistance. Prokaryotes lack cell organelles such as mitochondria, Golgi bodies, and similar structures. A cell envelope surrounds each bacterial cell and is composed of three layers in the case of bacteria. The glycocalyx is the outermost layer, the intermediate layer is the cell wall, and the innermost layer is the cell membrane. The glycocalyx is a loose sheath called a slime layer, as hard as a capsule. The plasma membrane of the mesosome contains vesicles, tubules, and lamellae. They aid in cell wall construction, DNA replication, and cell division. Flagella are made up of filaments, hooks, and basal bodies. Pili and fimbriae help bacteria connect to hosts and other things.
Prokaryotic ribosomes are composed of two subunits: 50S and 30S. Ribosomes synthesise protein. Polyribosomes are ribosomes linked together by mRNA.
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Eukaryotic cells
Protists, plants, animals, and fungi all contain eukaryotic cells. Organelles that are membrane-bound cause the cytoplasm to be segmented. A nuclear membrane surrounds the nucleus in Eukaryotic cells. Plant cells vary from animal cells in that they have a cell wall, plastids, and a large central vacuole. In contrast to plant cells, which lack centrioles, animal cells contain these structures. The Eukaryotic cells have 80 ribosomes.
Parts of cells
Cell: The unit of life has four vital parts, which are given below
- Cell Membrane
- Cell Wall
- Endomembrane system
- Nucleus
Now that you have become familiar with the parts of cells. Let’s understand each part in detail.
Cell Membrane
The cell membrane is made up of bilayers of lipids. Phosphoglycerides dominate the lipid component. Proteins can be integral or peripheral. Peripheral protein is found on the surface of the integral protein, while the integral protein remains buried. Singer and Nicolson proposed the fluid mosaic concept in 1972. The quasi-fluid property of lipids allows lateral protein mobility inside the lipid bilayer. The movement of molecules across the plasma membrane is the membrane’s primary function.
There are two types of transport in a cell membrane.
- Active Transport
In active transport, the cells spend energy as they transfer material. It happens against the gradient of concentration. More simply, active transport can be defined as the transportation or movement of molecules in a cell membrane from a lower concentration region to a higher concentration region.
- Passive Transport
Passive transport refers to the transportation inside the cell membrane, which does not require any energy. The movement in this transport follows the second law of thermodynamics. It works along the concentration gradient. Therefore, no energy is consumed.
It consumes no energy for the cells. Examples of Passive transport are osmosis, simple diffusion, and facilitated diffusion.
Cell wall
Plant and fungal cells have a cell wall. Algae contain cellulose, galactans, and calcium carbonate in their cell walls. It is composed of cellulose, hemicellulose, pectin, and proteins in plants. Plasmodesmata link adjacent cytoplasm.
Endomembrane system
The endomembrane system contains the endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles. The Endoplasmic Reticulum is a tubular structure found throughout an organism’s cytoplasm.
Endoplasmic reticulum types include:
Rough Endoplasmic Reticulum
- Ribosomes are connected to the outer surface.
- It is involved in the production and secretion of proteins.
Endoplasmic Reticulum Smooth
- Absence of ribosomes
- Lipid synthesis site
Parts of the endoplasmic reticulum:
Golgi Apparatus
Camillo Golgi discovered the Golgi apparatus in 1898. They are made up of multiple parallel flat disc-shaped sacs called cisternae. The Golgi apparatus holds the function of making packages and transporting materials. The Golgi apparatus synthesises glycoproteins and glycolipids.
Lysosomes
These membrane-bound vesicles are produced during the Golgi apparatus packaging process. In addition, lipases, proteases, and carbohydrates, all active at low pH, are found in abundance in these organisms. These enzymes may digest proteins, lipids, and nucleic acids.
Vacuole
The membrane-bound spaces that hold water, sap, and excretion are called vacuoles. A single membrane connects them all. Many species use them to create contractile vacuoles and food vacuoles.
Mitochondria
The mitochondrial lumen is divided by an outer and an inner membrane and has a two-compartment structure. Cristae are infoldings of the inner membrane that point toward the matrix. Each enzyme found inside a membrane is unique. Aerobic respiration occurs inside mitochondria. As ATP is the primary source of the cell, the unit of life’s energy, it has been termed its ” powerhouse.”
Plastids
Plastids are present in euglenoids and plant cells. The chloroplast captures sunlight energy for photosynthesis. Plants use chromoplasts to produce yellow, orange, and red hues. Amyloplasts (carbohydrates), elaioplasts (oils), and aleurops (proteins) are stored in leucoplasts (proteins). Chloroplasts have two membranes. The inner membrane space is termed the stroma. Stacks of thylakoids termed “grana” are seen in the stroma. Protein and carbohydrate synthesis enzymes are found in the stroma. Circular DNA and ribosomes are also found in the stroma.
Centrioles
Centrioles can be defined as two cylindrical structures that make up the centrosome, an organelle. The Tubulin protein fibrils make up each centriole. The hub and spokes are the central and peripheral portions, respectively.
Nucleus
The nucleus contains chromatin, nuclear matrix, and nucleoli, which are complex nucleoprotein fibres. It is disc-shaped kinetochores found on both sides of the centromere of every chromosome. The nucleus is further divided based on their centromere location, chromosomes as:
- Metacentric: the centromere is located at the centre.
- Submetacentric: Located closer to one end of a chromosome.
- Acrocentric: Located near the axis’s end.
- Telocentric: having a centromere at the end.
Conclusion
Cell biology is the study of cells, starting with their fundamental structure and progressing through the activities of each cell organelle. Cells are made up of various organelles, each of which performs a specific job to carry out the activities of life. Every organelle has a unique structure. The genetic material of the organisms may also be found in the cells of the organisms.