SWOT with Narayankar

I.  Centrioles and centrosomes play significant role in formation of spindle apparatus during cell division.  ii.  Centrosome is usually found near the nucleus of an animal cell. iii.  It contains a pair of cylindrical structures called centrioles.  iv.  The cylinder (centriole) are perpendicular to each other and are surrounded by amorphous substance called pericentriolar material. V. Each cylinder of centriole is made up of nine sets of triplet microtubules made up of tubulin. Vi. Evenly spaced triplets are connected to each other by means of non-tubulin proteins. Vii. At the proximal end of centriole, there is a set of tubules called hub. viii. The peripheral triplets are connected to hub by means of radial spokes. Due to this proximal end of centriole looks like a cartwheel. Ix. Centriole forms basal body of cilia and flagella.

i. Cilium or flagellum helps in locomotion of unicellular organisms. ii. They consist of basal body, basal plate and shaft. iii. Basal body is placed in outer part of cytoplasm. It is derived from centriole. It has nine peripheral triplets of fibrils.  iv. Shaft is exposed part of cilia or flagella. It consists of two parts- sheath and axoneme. V.  Sheath is covering membrane of cilium or flagellum. vi. Core called axoneme possesses 11 fibrils (microtubules) running parallel to long axis. vii. It shows 9 peripheral doublet microtubules and two single central microtubules (9+2). viii. The central tubules are enclosed by central sheath. IX.  This sheath is connected to one of the tubules of peripheral doublets by a radial spoke.  X.  Central tubules are connected to each other by bridges. xi. The peripheral doublet microtubules are connected to each other through linkers or inter-doublet bridge.

1. The cytoskeleton is microfilaments. a supportive structure built from microtubules, intermediate filaments, and ii. Microtubules are made up of protein- tubulin. iii. Microfilaments are made up of actin. IV. Intermediate filaments are composed of fibrous proteins.

I. Nucleus contains genetic information in the form of chromosomes which are DNA molecules associated with proteins. ii. In a non-dividing cell, the chromosomes appear as thread like network and cannot be identified individually. This network is called chromatin material. iii. The chromatin material contains DNA,  histone and non-histone proteins and RNA. Iv. In some regions of chromatin, DNA is more and is genetically active called euchromatin Some regions that contain more of proteins and less DNA and are genetically inert, are called heterochromatin .

Nucleus is known as the master cell organelle as it regulates various metabolic activities through synthesis of various proteins and enzymes. The nucleus in eukaryotic cell is made up of nuclear envelope, nucleoplasm, nucleolus and chromatic networks.

i. Ribosomes are protein factories of cell and were first observed as dense particles in electron micrograph of a cell by scientist Palade in 1953. ii. Ribosomes lack membranous covering around them and are made up of Ribosomal RNA and proteins. iii. In a eukaryotic cell, ribosomes are present in mitochondria, plastids (in plant cells) and in cytosol. IV. Ribosomes are either found attached to outer surface of Rough Endoplasmic Reticulum and nuclear membrane or freely suspended in cytoplasm. V. Both are of 80S type. Each ribosome is made up of two subunits- a large (60S) and a small (40S) subunit.  Vi.  Bound ribosomes generally produce proteins that are transported outside the cell after processing in ER and Golgi body. e.g. Bound ribosomes of acinar cells of pancreas produce pancreatic digestive enzymes. Vii.  Free ribosomes come together and form chains called polyribosomes for protein synthesis. Viii.  Free ribosomes generally produce enzymatic proteins that are used up in cytoplas

i. In plants, chloroplast is found mainly in mesophyll of leaf. ii. Chloroplast is lens shaped but it can also be oval, spherical, discoid or ribbon like.  iii. A cell may contain single large chloroplast as in Chlamydomonas (type green algae) or there can be 20 to 40 chloroplasts per cell as seen in mesophyll cells(makes mesophyll layer in plant leaves).  iv. Chloroplasts contain green pigment called chlorophyll along with other enzymes that help in production of sugar by photosynthesis. V. Inner membrane of double membraned chloroplast is comparatively less permeable. vi. Inside the cavity of inner membrane, there is another set of membranous sacs called thylakoids. vii. Thylakoids are arranged in the form of stacks called grana (singular: granum). viii. The grana are connected to each other by means of membranous tubules called stroma lamellae.  ix. Space outside thylakoids is filled with stroma. X. The stroma and the space inside thylakoids contain various enzymes essential for pho

Plastids are double membraned organelles containing DNA, RNA and 70S ribosomes. i.  Plastids are classified according to the pigments present in it. Three main types of plastids are - leucoplasts, chromoplasts and chloroplasts. ii. Leucoplasts do not contain any photosynthetic pigments they are of various shapes and sizes. These are meant for storage of nutrients:  a. Amyloplasts store starch.  b. Elaioplasts store oils. c. Aleuroplasts store proteins. iii. Chromoplasts contain pigments like carotene and xanthophyll etc. a. They impart yellow, orange or red colour to flowers and fruits.  b. These plastids are found in the coloured parts of flowers and fruits. iv.  Chloroplasts are plastids containing green pigment chlorophyll along with other enzymes that help in production of sugar by photosynthesis. They are present in plants, algae and few protists like Euglena.

a. Mitochondria are found in nearly all eukaryotic cells, including plants, animals, fungi, and most unicellular eukaryotes. b. Some of the cells have a single large mitochondrion, but frequently a cell has hundreds of mitochondria.  C. The number of mitochondria correlates with the cell's level of metabolic activity. For e.g. cells that move or contract have proportionally more mitochondria than metabolically less active cells. d. However, mature red blood cells in humans lack mitochondria.

Mitochondrion is known as the power house of the cell. It plays significant role in aerobic respiration Mitochondria are absent in prokaryotic cells and red blood corpuscles (RBCs). The structure of mitochondrion:  i. Shape of the mitochondria may be oval or spherical or like spiral strip. ii. It is a double membrane bound organelle. i. Outer membrane is permeable to various metabolites due to presence of a protein-Porin or Parson's particles. IV. Inner membrane is selectively permeable to few substances Both membranes are separated by intermembrane space. only. vi. Inner membrane shows several finger like or plate like folds called as cristae which bears numerous particles oxysomes & cytochromes/electron carrier. vii. Inner membrane encloses a cavity called inner chamber, containing a fluid-matrix. viii. Matrix contains few coils of circular DNA, RNA, 70S types of ribosomes, lipids and various enzymes of Krebs' cycle and other pathways.

Glyoxysomes are membrane bound organelles containing enzymes that convert fatty acids to sugar. They are observed in cells of germinating seeds where the cells utilize sugar (formed by conversion of stored fatty acids) till it starts photosynthesising on its own.

The organelle which helps in maintaining turgidity of the cell and a proper internal balance of cellular contents is known as vacuole.  i. The vacuoles are bound by semipermeable membrane, called tonoplast membrane. This membrane helps in maintaining the composition of vacuolar fluid (cell sap), different from that of the cytosol. ii. Composition of cell sap differs in different types of cells.  iii. In vacuoles along with excretory products other compounds are stored that are harmful or unpalatable to herbivores, thereby protecting the plants. iv. Attractive colours of the petals are due to storage of such pigments in vacuoles.  v. Generally, there are two or three permanent vacuoles in a plant cell. vi. In some large plant cells, a single large vacuole occupies the central part of the cell. It is called central vacuole. In such cells, vacuole can occupy about 90% of the total volume of the cell. vii. The cell sap of central vacuole is a store house of various ions and thus is hyperto

i. Lysosomes are considered as dismantling and restructuring units of a cell.  ii. These are membrane bound vesicles containing hydrolytic enzymes . The enzymes in lysosomes are used by most eukaryotic cells to digest (hydrolyse) macromolecules. iii. The lysosomal enzymes show optimal activity in acidic pH. iv. Lysosomes arise from Golgi associated endoplasmic reticulum. v. Lysosomes are polymorphic in nature and are classified as primary lysosomes, secondary or hybrid lysosomes, residual body and autophagic vesicle. The list of lysosomal enzymes includes: All types of hydrolases viz, amylases, proteases and lipases. Reason for been called as Suicidal bags: i. Lysosomes which bring about digestion of cell's own organic material like a damaged cell organelle are called autophagic vesicle (suicide bags). ii. An autophagic vesicle essentially consists of lysosome fused with membrane bound old cell organelle or organic molecules to be recycled. iii. Thus, lysosomes are cap

Golgi complex or Golgi apparatus or Golgi body act as a assembly, manufacturing cum packaging & transport unit of cell. i. Structure of Golgi complex: a. Golgi complex consists of stacks of membranous sacs called cisternae. b. Diameter of cisternae varies from 0.5 to 1μm. c. A Golgi complex may have few to several cisternae depending on its function. d. The thickness and molecular composition of membranes at one end of the stack of a Golgi sac differ from those at the other end. e. The Golgi sacs show specific orientation in the cell. f. Each cisterna has a forming or 'cis' face (cis: on the same side) and maturing or 'trans' face (trans: the opposite side). g. Transport vesicles that pinch off from transitional ER merge with cis face of Golgi cisterna and add its contents into the lumen. ii. Location of Golgi complex: Golgi bodies are usually located near endoplasmic reticulum. iii. Functions of Golgi complex: a. Golg

Smooth endoplasmic reticulum (SER):  i. Depending on cell type, it helps in synthesis of lipids for e.g. Steroid secreting cells of cortical region of adrenal gland, testes and ovaries.  ii. Smooth endoplasmic reticulum plays a role in detoxification in the liver and storage of calcium ions (muscle cells).  Rough Endoplasmic Reticulum (RER): i. Rough ER is primarily involved in protein synthesis. For e.g. Pancreatic cells synthesize the protein insulin in the ER. ii. These proteins are secreted by ribosomes attached to rough ER and are called secretory proteins. These proteins get wrapped in membrane that buds off from transitional region of ER. Such membrane bound proteins depart from ER as transport vesicles. iii. Rough ER is also involved in formation of membrane for the cell. The ER membrane grows in place by addition of membrane proteins and phospholipids to its own membrane. Portions of this expanded membrane are transferred to other components of endomembrane system.

i. Endoplasmic reticulum is a network present within the cytosol. ii. It is present in all eukaryotic cells except ova (female reproductive cell/egg cell)  and mature red blood corpuscles. iii. Under the electron microscope, it appears like network of membranous tubules (ERs) and sacs called cisternae. iv. This network of ER divides the cytoplasm in two parts viz. one within the lumen of ER called laminal cytoplasm and non-laminal cytoplasm that lies outside ER. v. Membrane of ER is continuous with nuclear envelope at one end and extends till cell membrane. It thus acts as intracellular supporting framework and helps in maintaining position of various cell organelles in the cytoplasm. vi. Depending upon the presence or absence of ribosomes, endoplasmic reticulum is called rough endoplasmic reticulum (RER) or smooth endoplasmic reticulum (SER) respectively.

i. The cell contains ground substance called cytoplasmic matrix or cytosol. ii. This colloidal jelly like material shows streaming movements called cyclosis. iii. The cytoplasm contains water as major component along with organic and inorganic molecules like sugars, amino acids , vitamins, enzymes , nucleotides , minerals and waste products. iv. It also contains various membrane bound cell organelles like endoplasmic reticulum, Golgi complex, mitochondria, plastids , nucleus, microbodies and cytoskeletal elements like microtubules . v. Cytoplasm acts as a source of raw materials as well as seat for various metabolic activities taking place in the cell. vi. It helps in distribution and exchange of materials between various cell organelles.

Fluid Mosaic Model: i. Fluid mosaic model was proposed by Singer and Nicholson (1972). ii. This model states that plasma membrane is made up of phospholipid bilayer and proteins. iii. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids. iv. Phospholipid bilayer is fluid in nature. v. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity vi. Based on organization of membrane proteins they are of two types, as: a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water. b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.

Eukaryotic plasma membrane/ Cell membrane/ Biomembrane: i. It is thin, quasi-fluid structure present both extracellularly and intracellularly.  ii. Extracellularly, it is present around protoplast and intracellularly, it is present around most of the cell organelles in eukaryotic cell. It separates cell organelles from cytosol.  iii. Thickness of bio-membrane is about 75Å. iv. Cell membrane appears trilaminar (made up of three layers) when observed under electron microscope. It shows presence of lipids (mostly phospholipids) arranged in bilayer. v. Lipids possess one hydrophilic polar head and two hydrophobic non-polar tails. Therefore, phospholipids are amphipathic. vi. Lipid molecules are arranged in two layers (bilayer) in such a way that their tails are sandwiched in between heads. Due to this, tails never come in direct contact with aqueous surrounding.  vii. Cell membrane also shows presence of proteins and carbohydrates. viii. Ratio of proteins and lipids varies in different cel

i. Middle lamella: It is thin and present between two adjacent cells. It is the first structure formed from! cell plate during cytokinesis. It is mainly made up of pectin, calcium and magnesium pectate. Softening of ripe fruit is due to solubilization of pectin. ii. Primary wall: In young plant cell, it is capable of growth. It is laid inside to middle lamella. It is the only wall seen in meristematic tissue, mesophyll, pith, etc. iii.  Secondary wall: It is present inner to primary wall. Once the growth of primary wall stops, secondary wall is laid. At some places thickening is absent which leads to formation of pits.