EL 3 Cell Structures and Functions PDF

# Cell: Structure and Function ## Introduction * **Fundamental unit of life.** * **Self replicating structure.** * **The first cells were observed and named by Robert Hooke in 1665 from slice of cork.** * **Some organisms consist of a unicellular organism, others are multicellular.** * **Diamete...

# Cell: Structure and Function ## Introduction * **Fundamental unit of life.** * **Self replicating structure.** * **The first cells were observed and named by Robert Hooke in 1665 from slice of cork.** * **Some organisms consist of a unicellular organism, others are multicellular.** * **Diameter- 2-120 μm.** ## Diagram of a Plant and Animal Cell ### Animal Cell * **Nucleus** * **Cytoplasm** * **Cell membrane** * **Mitochondria** ### Plant Cell * **Cell wall** * **Chloroplasts** * **Vacuole** ## Diagram of a Animal Cell ### Nucleus * **Cell's control center** ### DNA * **Contains coded information that passes on every single inherited characteristic.** ### Mitochondrion * **Produces energy for cells to use by breaking down substances during oxidative metabolism.** ### Golgi complex * **Collects, packages and distributes molecules made in the cell.** ### Endoplasmic reticulum * **Smooth and rough tubes that move and store materials made by the cell.** ### Lysosome * **Where digestion of cell nutrients takes place.** ### Cytoplasm * **Jelly-like fluid between cell membrane and the nucleus. This is where all the organelles (little organs) are found.** ### Ribosome * **Tiny protein producing factories. Proteins produce chemical messages that run a cell.** ### Vacuole * **Storage area from fats and other substances.** ### Peroxisome * **Vesicle that contains enzymes that carry out particular reactions, such as detoxifying potentially harmful molecules.** ### Cell membrane * **Made up of a double layer of fatty material. It allows some materials to pass into and out the cell at thousands of places across the surface. It allows foods to pass into the cell and waste to pass out of the cell.** ### Centriole * **Tiny organs that help the cell divide** ## Subcellular Structures **Major Structures Present in a cell are:** * **Cell Membrane** * **Cytoplasm and its Organelles** * **Nucleus** ## Cell Membrane * **Thin pliable elastic outermost structure which envelops the cell.** * **It consists of bilipid layer with embedded proteins that are:** * **Integral Proteins** * **Peripheral proteins** ## Functions of Cell Membrane * **Protective:** Forms outermost boundary of the cell organelles. * **Digestive:** Takes in food and excretes waste products. * **Selective Permeability:** * **a) Non-Polar Molecules** - Gases (like O2, CO2, N2), Lipids, Steroid Hormones, Alcohols can dissolve in the non-polar regions of the membrane and move rapidly across the membrane. * **b)Polar molecules:** H2O soluble ions, Glucose, urea etc. have much lower solubility. Therefore Penetrate the membrane much more slowly. * **c)Chemical and Physical Properties of membrane control the free passage of ions in and out of cell. This property helps in maintaining components in ICF and ECF.** * **Links adjacent cells together by junctional complexes to form tissues.** * **Insulating Properties:** It acts as dielectric material of a charged condenser, thus cell membrane have very high insulating value. ## Cytoplasm * **Thick, gel-like semitransparent fluid that is found in both plant and animal cell.** * **The constituent parts of cytoplasm are cytosol, cell organelles and cytoplasmic inclusions.** * **Bounded by the plasma membrane, and contains many organelles in a eukaryotic cell (cell containing membrane bounded nucleus).** ## Cytosol * **The cytosol, the aqueous part of the cytoplasm outside all of the organelles, also contains its own distinctive proteins.** * **It accounts for almost 70% of the total cell volume.** * **Gelatinous substance consisting mainly of cytoskeleton filaments, organic molecules, salt and water.** * **Chemically, the cytoplasmic matrix is composed of many chemical elements in the form of atoms, ions and molecules.** ## Organelles * **Following organelles are present in the Cytoplasm:** * **i) Mitochondria** * **ii) Endoplasmic Reticulum** * **iii) Lysosomes** * **iv) Golgi Apparatus** * **v) Peroxisomes** * **vi) Vacuole** * **Each organelle is bounded by a lipid membrane, and has specific functions.** ## Mitochondria * **The mitochondria were first observed by Kolliker in 1850 as granular structures in the striated muscles.** * **Mitochondria are called the 'powerhouse of the cell'.** ### Structure: * **Length: 5-12 μm** * **Diameter: 0.5-1 μm** * **Filamentous or globular in shape.** * **Components of Mitochondria are:** * **i)Outer membrane** * **ii)Inner membrane** * **iii)Intermediate Space:** Space between outer and inner membranes * **iv)Cristae:** Infoldings of inner membrane * **v)Matrix:** The space enclosed by inner membrane * **The membranes are made up of phospholipids and proteins.** ### Function: * **Power generating units of the cells.** * **Important to maintain proper concentration of calcium ions within the various compartments of the cell.** * **Energy transduction through respiration.** * **Responsible for thermogenesis.** ## Endoplasmic Reticulum * **Network of tubular and flat vesicular structures in the cytoplasm.** * **An extensive network of closed, flattened membrane-bounded sacs called cisternae.** * **Space inside the tubules is filled with Endoplasmic Matrix.** ### Two Types * **Smooth Endoplasmic Reticulum:** * **Ribosomes absent.** * **Site of synthesis of lipid and steroid hormones.** * **Mainly present in lipid forming cells such as adipocytes, interstitial cells of testis, glycogen storing cells of liver, adrenal cortex cells, muscle cells, leucocytes etc.** * **Rough Endoplasmic Reticulum** * **Contains ribosomes.** * **Site of protein synthesis, processing and packaging.** * **Mainly present in protein forming cells such as pancreatic acinar cells, Goblet cells, antibody producing plasma cells, Nissl's granules of nerve cells etc.** ## Function * **Synthesis of proteins.** * **Protein segregation.** * **Unsaturation of fatty acid.** * **Muscle contraction.** ER is commonly known as Sarcoplasmic Reticulum in muscle fibers. ## Golgi Bodies * **Golgi Bodies is a collection of membrane enclosed sacs composed of four or more stacked layers of thin, flat enclosed vessels lying near the side of the nucleus.** * **Consist of multiple discrete compartments.** * **Consist of four functionally distinct regions:** * **i)The cis Golgi network** * **ii)Golgi stack:** Which is divided into * **a) The medial and** * **b)Trans sub compartments** * **iii)The trans Golgi network.** ## Function * **Wrapping and Packaging department of the cell.** * **Produces secretion granules i.e. membrane enclosed complexes, which store hormones and enzymes in the protein secreting cells, it packages proteins.** * **Site of formation of lysosomes i.e. large irregular structures surrounded by membrane which are present in the cytoplasm.** * **It adds certain carbohydrates to form glycoproteins, which play an important role in the association of the cells to form tissues.** ## Lysosomes * **Diameter: 250-750 nm** * **These are the irregular structures surrounded by the unit membrane.** * **More acidic than rest of the cytoplasm and external bacteria as well as worn out cell components are digested in them.** * **The interior is kept acidic(near pH 5.0) by the action of proton pump or H+ or ATPase.** * **Lysosomes are cell hydrolases and they function best at the acidic pH.** ## Function * **Acts as a form of digestive (lytic) system or the cell, because enzymes present in it can digest essentially all macromolecules.** * **Engulf worn out components of the cells in which they are located.** * **Engulf exogenous substances e.g. bacteria and degrade them.** * **When a cell dies, lysosomal enzymes causes autolysis of the remanant. Thats why lysosomes are called as Suicidal Bags.** ## Nucleus * **The nucleus contains chromatin, RNAs, and nuclear proteins move freely in aqueous solution.** * **Nucleus has an internal structure that organizes the genetic material and localizes nuclear functions.** * **A loosely organized matrix of nuclear lamins extends from the nuclear lamina into the interior of the nucleus.** ## Continued * **These lamins serve as sites of chromatin attachment and organize other proteins into functional nuclear bodies.** * **Chromatin within the nucleus is organized into large loops of DNA, and specific regions of these loops are bound to the lamin matrix by lamin-binding proteins in the chromatin.** ## Nuclear Envelope * **Complex structure consisting of two nuclear membranes, an underlying nuclear lamina, and nuclear pore complexes.** * **Two concentric membranes, called the inner and outer nuclear membranes. ** * **The outer membrane is continuous with the endoplasmic reticulum, so the space between the inner and outer nuclear membranes is directly connected with the lumen of the endoplasmic reticulum.** ## Function * **Serves both as the repository of genetic information and as the cell's control center.** * **The presence of a nucleus thus allows gene expression to be regulated by posttranscriptional mechanisms, such as alternative splicing.** * **The nuclear envelope provides novel opportunities for the control of gene expression at the level of transcription.** ## Summary | **COMPARTMENTS** | **MAJOR FUNCTIONS** | |-----------------------------|---------------------------------------------------------| | Plasma Membrane | Transport of ions and molecules | | Cytosol | Metab. of carbohydrate, lipids and amino acids | | Mitochondria | Energy production | | Endoplasmic Reticulum | Synthesis of proteins and lipids | | Golgi apparatus | Modification and sorting of proteins | | Lysosomes | Cellular digestion | | Peroxisomes | Utilisation of H2O2 | | Cytoskeleton | Cell Morphology and cell motility | | Nucleus | DNA synthesis and Repair |