Saran's Learn Microbiology

  CYTOSKELETON ·        The Cytoplasm is the substance in which various Cellular components are found. ·        The term Cytosol refers to the fluid portion of Cytoplasm. ·        A major difference between Eukaryotic and Prokaryotic cytoplasm is that Eukaryotic cytoplasm has a complex internal structure, consisting of exceedingly Small rods (Microfilaments and Intermediate filaments) and Cylinders (Microtubules). Together, they form the Cytoskeleton. ·      Microfilaments or Actin filaments are smaller, about 7 nm in diameter, and are polymers of two intertwined strands of the protein Actin. Microfilaments function in ü   Maintaining or changing cell shape ü   Cell motility by cells that move by amoeboid movement, and during cell division. ·       Intermediate filaments are role like structures made up of fibrous Keratin proteins that form into fibers 8 – 12 nm in diameter. Their name comes from their intermediate size between Actin filaments and Microtubule. Its functio

  CENTROSOMES ·       Centrosome located near the Nucleus, consists of two components: (i) Pericentriolar area and (ii) Centrioles. ·     The Pericentriolar material is a region of the Cytosol composed of a dense network of small protein fibers. This area is the organizing center for the mitotic spindle, which plays a critical role in Cell division, and for Microtubule formation in nondividing cells. ·     Within the Pericentriolar material is a pair of cylindrical structures called Centrioles, each of which is composed of nine clusters of three microtubules (triplets) arranged in a circular pattern. Functions of Centrosomes ·        Helps in Eukaryotic cell division. ·        Maintain the Chromosome number during Cell division. ·        Stimulate the changes in the shape of the Cell membrane by Phagocytosis In mitosis, it helps in organizing the microtubules ensuring that the Centrosomes are distributed to each daughter

  PEROXISOMES ·        Peroxisomes are the organelles similar in structure to Lysosomes, but smaller. ·      Peroxisomes are found in all types of Eukaryotic cells but are especially prominent in the kidney and liver cells of mammals. ·      Peroxisomes were once thought to form by budding off the Endoplasmic Reticulum’ but now it is agreed that they form by the division of preexisting Peroxisomes. Functions of Peroxisomes ·     Peroxisomes contain one or more enzymes that can oxidize various Organic substances. For example, substances such as Amino acids and Fatty acids are oxidized in Peroxisomes as part of normal metabolism. ·        Peroxisomes take part in Lipid metabolism. ·        Peroxisomes also involved in catabolism of Amino acids, Polyamines and Bile acids. ·     Peroxisomes contain Oxidase and Catalase, which are enzymes that degrade poisonous metabolic wastes such as Free radicals (Oxidase) and Hydrogen peroxide (Catalase) resulting from some oxygen-depend

LYSOSOMES ·        Lysosomes are present only in Eukaryotes. Also called as “Suicide bags” of the cell. ·      The term was coined by Christian de Duve, a Belgian biologist, who discovered it and ultimately got a Nobel Prize in Medicine or Physiology in the year 1974. ·        Lysosomes are roughly spherical and enclosed in a Single membrane. ·      The sizes of Lysosomes vary with the largest ones measuring in more at than 1.2 μ m. But, they typically range from 0.1 μ m to 0.6 μ m. ·      Lysosomes are involved in intracellular digestion and contain the enzymes (nearly 50 enzymes) needed to digest all types of Macromolecules. These enzymes, called Hydrolases, catalyze the hydrolysis of molecules and function best under slightly acidic conditions (usually around pH 3.5 to 5.0). ·        Lysosomes maintain an acidic environment by pumping protons into their interior. ·      Lysosomes are called as “Suicide bags” because t

  EUKARYOTIC RIBOSOMES ·     Ribosome, particle that is present in large numbers in all living cells  and serves as the site of Protein  synthesis. ·       The small particles that came to be known as Ribosomes were first described in 1955 by Romanian-born American Cell  Biologist George E. Palade , who found them to be frequently associated and attached with the endoplasmic reticulum in eukaryotic cells. ·        A single actively replicating Eukaryotic cell may contain as many as 10 million Ribosomes. ·     The size of Ribosomes ranging from 3.5 MDa in lower Eukaryotes to 4.0 MDa in higher Eukaryotes. ·        Ribosomes are made up of Ribosomal proteins (50 %) and rRNA (50 %). ·        Ribosomes are usually made up of three or four rRNA molecules and anywhere from about 40 to 80 different Ribosomal proteins. ·        80 S type of Ribosomes are present in Eukaryotes. Each Ribosome is composed of two sub-units, a larger sub-unit 60 S and a smaller sub-unit 40 S. The sub-u

  GOLGI APPARATUS ·      Golgi apparatus or Golgi body is present in Eukaryotic cells as one or more groups of flattened, membrane-bounded compartments or sacs. ·        This organelle was named after its discoverer, Camillo Golgi. ·     Golgi apparatus are located very near the Rough Endoplasmic Reticulum and hence near the Nucleus. ·        Golgi apparatus measures about 15 – 20 nm thick. ·        The Golgi apparatus is present in most eucaryotic cells, but many fungi and ciliate protozoa lack a well-formed structure. ·      Golgi apparatus is a discrete organelle consisting of a stack of several flattened, disc-shaped sacs called Cisternae. ·       Sometimes the Golgi consists of a single stack of Cisternae. However, many cells may contain up to 20, and sometimes more, separate stacks. These stacks of Cisternae, often called Dictyosomes, can be clustered in one region or scattered about the cell. ·      The Golgi body packages secretions in Sacs called Secretory vesi

  ENDOPLASMIC RETICULUM ·     Continuous with the outer membrane of the nuclear envelope is a netlike arrangement of flattened hollow tubules called Endoplasmic Reticulum (ER). ·        It is around 40 to 70 nm in diameter. ·        Many flattened sacs called Cisternae are present in Endoplasmic Reticulum. ·     Two types of Endoplasmic Reticulum are (i) Rough Endoplasmic Reticulum (RER) and (ii) Smooth Endoplasmic Reticulum (SER). i) Rough Endoplasmic Reticulum ·     Rough Endoplasmic Reticulum (RER)  is named for its Rough appearance, which is due to the Ribosomes  (site of Protein synthesis) attached to its outer (cytoplasmic) surface. ·       RER lies immediately adjacent  to the cell Nucleus , and its membrane is continuous with the outer membrane of the nuclear envelope. ·        Proteins produced by Ribosomes on the RER are inserted into the Lumen (central canal) of the RER and transported throughout the cell.