Eukaryotes and prokaryotes

 Eukaryotes and prokaryotes:

Definition of Prokaryotic Cells

                     Prokaryotes (pro-KAR-ee-ot-es) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. -otes; also spelled "procaryotes") are organisms without a cell nucleus (= karyon), or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular.

Generalized structure of Prokaryotic cell consists of the following:

1. Glycocalyx: This layer function as a receptor, the adhesive also provide protection to the cell wall.
2. Nucleoid: It is the location of the genetic material (DNA), large DNA molecule is condensed into the small packet.
3. Pilus: Hair like hollow attachment present on the surface of bacteria, and is used to transfers of DNA to other cells during cell-cell adhesion.
4. Mesosomes: It is the extension of the cell membrane, unfolded into the cytoplasm their role is during the cellular respiration.
5. Flagellum: Helps in movement, attached to the basal body of the cell.
6. Cell Wall: It provides rigidity and support for the cell.
7. Fimbriae: Helps in attachment to the surface and other bacteria while mating. These are small hair-like structure.
8. Inclusion/Granules: It helps in storage of carbohydrates, glycogen, phosphate, fats in the form of particles which can be used when needed.
9. Ribosomes: Tiny particles which help in protein synthesis.
10. Cell membrane: Thin layer of protein and lipids, surrounds cytoplasm and regulate the flow of materials inside and outside the cells.
11. Endospore: It helps cell in surviving during harsh conditions.

In terms of peptidoglycan present in the cell wall, prokaryotes can be divided into Gram-positive and Gram -negative bacteria. The former contains a large amount of peptidoglycan in their cell wall while the latter have the thin layer.

Definition of Eukaryotic Cells

                       Eukaryotes (IPA: [juːˈkæɹɪɒt]) are organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane bound structure is the nucleus. This feature gives them their name, (also spelled "eucaryote,") which comes from the Greek ευ, meaning good/true, and κάρυον, meaning nut, referring to the nucleus. Animals, plants, fungi, and protists are eukaryotes.

                   This kind of cells are found in algae, fungi, protozoa, plants, and animals and can be single-celled, colonial or multicellular. Among them, fungi and protists (algae and protozoa) are the major kingdoms.

The general structure of Eukaryotic cells contain:

• Nucleus: Eukaryotic cells have a well-defined nucleus where DNA (genetic material) is stored, it helps in the production of protein synthesis and ribosomes also. The chromosome is present inside the nucleus, which is surrounded by the nuclear envelope. It is a bi-lipid layer and controls the passage of ions and molecules.
• Cytoplasm: It is the location where other organelles are located, and other metabolic activities of the cell also take place here. It consists of –
  • Mitochondria: It is called ‘the powerhouse of the cell,’ and is responsible for making ATP. Mitochondria has its own DNA and ribosomes.
  • Chloroplast: These are found in algae and plants, it is one of the most important organelles in the plant which helps in converting energy sunlight into chemical energy through photosynthesis. They resemble mitochondria.
  • Golgi Apparatus: It consists of a stack of many flattened, disc-shaped sacs known as cisternae. The exact nature of Golgi varies, but it helps in the packaging of materials and in secreting them.
    • Lysosomes and Vacuoles – The most important function of Endoplasmic reticulum and Golgi apparatus is the synthesis of Lysosomes, which helps in digestion of intracellular molecules with the help of the enzyme called hydrolase.
    • Vacuoles are the membrane-bound cavities containing fluid as well as solid materials, and they engulf materials through endocytosis.
  • Endoplasmic Reticulum: It transport lipids, proteins, and other materials through the cell. They are of two types of smooth endoplasmic reticulum and rough endoplasmic reticulum.
  • Appendages: Cilia and Flagella are locomotory attachments, helps in the movement of a cell towards positive stimuli. Cilia are shorter than flagella and numerous.
  • Surface structure: Glycocalyx is a kind of polysaccharide, and it is the outermost layer of the cell which helps in cell adherence, protection and in receiving signals from other cells.
  • Cell Wall: Cell Wall provides shapes, rigidity, and support to the cell. Compositions of the cell wall may vary of different organisms but which can be of either cellulose, pectin, chitin or peptidoglycan.
  • Cytoplasmic Membrane/Plasma Membrane: It is a thin semipermeable, surrounding the cytoplasm, it acts as the barrier of the cell which regulates entry and exit of the substances inside and outside the cell. This layer is made up of two layers of phospholipids embedded with proteins. In Plant cell, this layer is present below the cell wall whereas in the Animal cell it is the outermost layer.
  • Ribosomes: Though small in size but are present in numbers, they help in protein synthesis. Eukaryotes have 80S ribosomes which are further divided into two subunits which are 40S and 60S (S stands for Sedverg unit).
  • Cytoskeleton: It is supporting framework of the cells, which is of two types Microtubules and Microfilaments. Microtubules have a diameter of about 24 nanometers (nm), made up of a protein called tubulin, while Microfilaments has a diameter of 6nm, made of the protein called actin. Microtubules are the largest filament and Microfilament the smallest one.