Prokaryotic Cell Structure

Prokaryotic Cell Structure

They are the first organisms to be present on our planet earth. Organisms, with this cell type are known by the term prokaryotic organisms (or) prokaryotes. Bacteria, blue green algae and E.coli are few examples of this category. Prokaryotic cells are single-celled organisms, with the absence of nucleus and comprises of capsule, cell wall, cell membrane, cytoplasm, nucleiod, ribosome, plasmids, pili and flagella.

Prokaryotic Cell General Features

• The size of a cell ranges from 1-10 microns. Few prokaryotic cells vary in their size.
• They are single-celled (unicellular), which forms a colony or filamentous.
• The shape of the cell includes spherical, rod and flat shaped organisms.
• Mode of nutrients-- few organisms are photosynthetic (performing food with the help of sunlight), feed on living things and dead things.
• They reproduce asexually by the process called binary fission, transformation, conjugation, transduction.

Structure and Functions of a Prokaryotic Cell

Capsule: It is the slimy outer coating of the cell wall. It is composed of the polypeptide. The main function of the capsule is to protect the cell from getting dry and also helps in protecting cells from external pressures.

Cell wall: It is the tougher and a rigid structure, which provides the shape and protects the internal organelles of a cell. It is the middle layer, which is present in between the capsule and cell membrane.

Cell membrane: It is the inner delicate structure, which plays a vital role in regulating the entry and exits of materials in the cell. It acts a permeable membrane and separates the cell from its environment. It is of about 5-10nm in thickness, which helps in the secretion of proteins and elimination of waste products. It is also called by a name plasma membrane.

Cytoplasm: It is the liquid membrane, which is present in between the cell membrane and nucleiod. It plays a vital role in storing all types of materials, which are required for an organism to sustain the life.

Nucleiod: It is the cytoplasm region containing genetic material. The DNA of a prokaryotic organism is one big loop or a circular, which is located inside the nucleiod. It plays a vital role in cell division.

Ribosome: It  comprises of both RNA and proteins. It helps in protein synthesis in the cell. They are smallest membrane present inside the cytoplasm.

Plasmids: They are smallest membrane of a cell with double stranded DNA. Plasmids are rarely present in prokaryotic organisms. The main role of plasmids is it helps in DNA exchanging between the bacterial cells.

Pilli: It is the thinnest membrane of a prokaryotic cell. They are composed of protein complex called pilin and are mainly involved in sticking to the objects especially during sexual reproduction.

Flagella: It is the helical shaped membrane, whose sizes ranges from 19-20nm in diameter and plays a vital role in motility of an organism from one place to another place. It also helps in swimming, gliding, spinning and rotating both in clockwise and anti clockwise directions.

Eukaryotic Cell Structure

They are the cells with the presence of true nucleus. Organisms, with this cell type are known by the term eukaryotic organisms (or) eukaryotes. Animals, plants and other organisms excluding bacteria, blue green algae and E.coli have been grouped into this category. Eukaryotic cells are more complex than prokaryotic cells. These organisms have membrane bound nucleus with many cell organelles to perform several cellular functions within the system.

Eukaryotic Cell General Features

• The size of a eukaryotic ce

• ll ranges from 10-100 microns. Few eukaryotic cells vary in their size.
• They are large, advanced, multicellular and have membrane bound organelles.
• They reproduce both by sexually and by asexually.
• Mode of nutrients - Autotrophic and heterotrophic.
• Kingdom protozoa, algae, fungi, Plantae and Animalia are organisms with eukaryotic cell.

Structure and Functions of a Eukaryotic Cell

Plasma membrane: They are semi permeable membrane that acts as a boundary of a cell, which protects and separates the cell from the external environment.

Nucleus: It is surrounded by double layered of Phospho lipid bilayer called as nuclear envelope.  

They are the storehouse for the cell’s genetic materials in the form of DNA and store all the necessary information, which are required for a cell to control all types of activities. 

Nuclear membrane: It is the double membrane layer that surrounds the nucleus and it plays a role of entry and exits of materials within the nucleus.

Nucleolus: It is the non membrane bound organelles, which is present within the nucleus and is mainly involved in controlling all types of cellular activities including cellular reproduction.

Mitochondria: They are the double smooth membrane, which are present in all eukaryotic cells. They are the powerhouse of the cell. It plays a vital role in the synthesis of ATP and converts glucose to ATP.

Endoplasmic reticulum: They are the double membrane organelle, which divides the cell into compartments. It is connected to the nuclear membrane of the cell. It plays a vital role in protein synthesis, biosynthesis of lipids and steroids, stores and regulates calcium and metabolism of carbohydrates.  Endoplasmic reticulum is of two types – rough and smooth Endoplasmic reticulum.

Ribosome: It is present in the cytoplasm. They are the site for cell’s protein synthesis, which are composed of ribosomal RNA and proteins.

Golgi Bodies: It is the flattened membrane, which are mainly used to store the substances made by the cell. This membrane also helps in preserving, transporting materials within the cell. Hence it is also called as the post office of a cell.

Lysosomes: They are the membrane bound organelles, which contains digestive enzymes to break down macromolecules. Lysosome plays a vital role in protecting cell by engulfing or destroying foreign bodies entering the cell.

Cytoplasm: They are the jelly types of organelles, which are present in the inner region of a cell. It plays a vital role in keeping a cell in a stable and keeps the cell organelles separate from each other.

Chromosomes: The rod shaped structures, which are composed of proteins and DNA. Chromosomes also play a vital role in determining a sex of an individual. All human cells contain 46 numbers of chromosomes.

Plant Cell Structure

A plant cells are eukaryotic cells, with the presence of true nucleus, multicellular large and advanced membrane bound organelles. These plant cells are quite different from animal cells like in shape and other few organelles which are only found in animal cells but are absent in plant cells. Based on structure and functions, plant cells comprise of:

Cell wall: It is the outer layer of a plant cell, which helps a providing the shape and strength to the entire plant. A cell wall is composed of cellulose that protects and supports the plant to grow.

Cell membrane: It is a biological membrane that separates living cell organelles from non living structures. This membrane plays a vital role in helping a cell to communicate with the external environment and also in transporting proteins and other molecules throughout the cell.

Chloroplasts: They are green coloured oval shaped double membrane organelles, which are the sites of photosynthesis. The green colour pigment (chlorophyll) present in the leaves helps plants in absorbing solar energy to prepare food.

Cytoplasm: A jelly types double membrane organelles, which are present in the inner region of a cell. It helps by keeping a cell in stable and protects the cell organelles by separating them from each other.

Lysosomes: They are single membrane round organelles, which helps in digesting proteins, fats and carbohydrates. It also helps in excretion of undigested materials from the plant cells. It also helps in cell renewal and breakdown of large cells into smaller cells, old and dead cells.

Golgi Bodies (or) Gogi complex: The sac like structures, which are present in a cell to manufacture, store, packing and shipping the materials throughout the cell.

 Endoplasmic reticulum: The network of membrane, which helps in transporting materials around the cell. It forms a connection between nuclear envelope and the cell membrane of a cell.

Mitochondria: They are rod shaped organelles, plays an important role in releasing energy and they are the powerhouse of a cell. In plant cell, they are the sites of cellular respiration.

Nucleus: They are large, oval shaped organelle that contains one or more nucleoli with DNA. The main role of nucleus in plant cell is it controls all types of cellular activities.

Nucleolus: They are the spherical membranes, present inside the nucleus. This membrane contains RNA, which is used to build proteins. They are the sites of RNA synthesis.

Vacuole: They are the fluid sacs, which are present in large numbers in plant cells. The main function is this membrane is to store food and other waste materials. Vacuoles are the largest organelles present in the plant cells.

Animal Cell Structure

Animal cells are eukaryotic cells, with the presence of true nucleus; multicellular large and advanced membrane bound organelles. Like plant cells, animal cells have same organelles except the cell wall, chloroplasts, number of vacuoles and many more. Due to the absence of cell wall the shape of an animal cell is irregular. Based on structure and functions, animal cells comprise of:

Cell membrane: They are semi-permeable membrane surrounding the cell. It helps in holding the cell together and allows entry and exits of nutrients into the cell.

Nucleus: The largest organelle in the cell, which contains DNA and other cell's hereditary information. The main role of nucleus in animal cell is it controls all cellular activities.

Vacuole: They are the fluid sacs, which are present in less numbers in animal cells compared to plant cells. The main function is this membrane is to store food and other waste materials.

Golgi Bodies (or) Gogi complex: The sac like structures, which are present in a cell to manufacture, store, packing and shipping the selected particles throughout the cell.

Ribosome: It is present in the cytoplasm. They are the site of protein synthesis, which are composed of ribosomal RNA and proteins.

Endoplasmic reticulum: The network of membrane, which helps in transporting materials around the cell and also helps in the synthesis of lipids and proteins. It forms a connection between nuclear envelope and the cell membrane of a cell.

Mitochondria: They are rod shaped organelles, plays an important role in releasing energy and they are the powerhouse of a cell.

Cytoplasm: A jelly types double membrane organelles, which are present in the inner region of a cell. It helps by keeping a cell in stable and protects the cell organelles by separating them from each other.

Lysosomes: They are round single membrane round organelles, which helps in recycling of cell organelles. Lysosome of an animal cell contains some digestive enzymes that help in the digesting out the cell debris.

All types of cells eukaryotic and prokaryotic cell, animal and plant cells have many similarities and also differences in them, which all depends on its structure and functions of each cell organelles.