Study Notes on Cell The Unit of Life
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Study Notes on Cell The Unit of Life
- Cell theory
Cell theory was formulated by schleiden and Schwann, and was modified by Rudlof Virchow.Cell theory states.
- All living organisms are composed of cells and products of cells.
- All cells arises from pre-existing cells.
Prokaryotic cell:
Modification of cell envelope
- Slime layer: Glycocalyx in form of loose sheath.
- Capsule: Glycocalyx in form of thick and tough sheath.
- Mesosomes: Extension of plasma membrane.
These can be in form of vesicles and lamellae.
Function:
- cell wall formation, DNA replication and distribution to daughter cells, respiration, secretion process, to increase surface area of plasma membrane and enzyme content.
- Flagella: Extension of cell wall. It is composed of three structure- filament, hook and basal body. It help in motility of bacteria.
- Pili and fimbriae: Surface structure of some bacteria which attaches them to rocks in streams and to host tissues.
Genetic material:
- It is not covered by nuclear envelope. In addition to the genomic DNA ( the single chromosome/ circular DNA) , many bacteria have small circular self replicating , double standard DNA which is called as plasmid, plasmid contain genes like antibiotic resistance.
EUKARYOTIC CELLS
- Possess an organised nucleus with nuclear envelope and have a variety of complex locomotory and cytoskeletal structures.
Cell membrane
- Singer and Nicolson (1972) gave ‘fluid mosaic model’ .
- According to this the quasi-fluid nature of lipid enable lateral movement of proteins within the overall bilayer , two types of proteins (peripheral and integral proteins) with cholesterol, glycolipids and glycoprotein.
- Erythrocyte membrane has 52% protein and 40% lipids.
Function
- It is semi permeable and transport of molecule across it.
Passive transport
- Transport of molecules from higher to lower concentration.
Active transport
It do not utilise energy (ATP) .eg., diffusion.
- Transport of molecules from lower to higher concentration.
- It utilise energy (ATP).eg. Na+/k+ ATPase Pump.
(fluid mosaic model of plasma membrane)
CELL WALL
- Cell wall is non-living rigid structure which gives shape to the cell and protects cell from mechanical damage and infection, which in cell-to-cell interaction and provides barrier to undesirable macromolecules.
- Cell of algae is made of cellulose, galactose, mannose and mineral like calcium carbonate. •Plant cell wall consists of cellulose, hemicellulose, pectins and proteins.
- middle lamella is made of calcium pectate which holds neighbouring cells together.
- Plasmodesmata connect the cytoplasm of neighbouring cells.
Endoplasmic Reticulam(ER)
- Consists of network of tiny tubular structure.ER divides the intracellular space into two distinct compartments-luminal (inside ER) and extra luminal (cytoplasm).
(1)Rough Endoplasmic Reticulum (RER):
- Ribosomes attached to outer surface.
Function
- Involved in Protein synthesis and secretion.
(2) Smooth Endoplasmic Reticulum (SER)
- Lack ribosomes.
Function
Site for synthesis of lipid.
Golgi apparatus
- First observed by Camilio Golgi in (1988)
- Consists of cisternae stacked parallel to each other.
- Two faces of the organelles are convex/sis or forming face and concave/ trans or maturing face.
- Function:
- perform packaging of material, to be delivered either to the intra-cellar targets or secreted outside of the cell.
- Important site of formation of glycoprotein and glycolipids.
Lysosomes:
- Membrane bound vesicular structure formed by the process of packaging in the Golgi apparatus. Contain hydrolysing enzymes(lipase, protease, carbohydrose) Which are active in acidic PH.
- Also called ‘suicidal Bag’.
Function:
- Intracellular digestion.
Vacuoles:
- Member bound space found in the cytoplasm.
- Contain water, sap, excretory products, etc.
- In plant cell vacuole occupies 90% of the space.
Function:
- In plants tonoplast (single membrane of vacuoles ) facilites transport of ions and other substances.
- Contractile vacuole for excretion in amoeba and food vacuoles formed formed in protists for digestion of food.
Mitochondria:
- Doubled membrane structure.
- Outer membrane smooth and inner membrane forms a number of infolding called cristae.
- The cristae increase the surface area.
Function:
- Sites of aerobic respiration.
- Called power house of the cell which produce cellular energy in the form of ATP.
- Matrix possess single circular DNA molecule, a few RNA molecules, ribosomes (70s).
- It divides by binary fission.
Plastids:- Found in plant cells and euglenoides.
- Chloroplasts, chromoplasts, leukoplasts are 3 types of Plastids depending on pigments contained.
- Choloroplast which is green coloured Plastids contain chlorophyll, double standard DNA and 70s ribosomes.
- Chromoplast which give colour to plant parts .
- Leucoplast ,amyloplast (starch),Elaioplasts(oil+fat).
Function:
- Site of photosynthesis, and imparts colour to fruits and flowers.
Chloroplasts:-
- organelles that conduct photosynthesis where the photosynthetic pigment chlorophyll capture
the energy from sunlight, converts it and store it in the form of ATP.
Ribosomes:
- Composed of RNA and proteins; without membrane. Eukaryotic ribosomes are 80s .(s-svedberg’s unit)
Function:
- Site of protein synthesis.
Cytoskeleton:
- Network of filaments.
- Proteinaceous structure in cytoplasm made up of microtubules and micro filaments.
Function:
- Mechanical support, motility, maintenance of the shape of the cell.
Cilia and Flagella:
- Cilia are small structure which work like a oars which help in movement.
- Flagella are longer and responsible for cell movement. They are covered with a plasma membrane. Core is called axoneme which has 9+2 arrangement of axonemal microtubules.
Centrosome and centriole
- Centrosome contain two cylindrical structure called centrioles.
- Surrounded by amorphous pericentriolar materials.
- Centrioles from the basal body of cilia or Flagella and spindle fibres for cell division in animal cell.
- They produces spindle apparatus during cell division.
Nucleus:
- with double membrane with perinuclear space and nuclear pores has chromatin ,nuclear matrix and nucleoli (site for RNA synthesis) .
- Named by Robert Brown in 1831.
- chromatin is consists of DNA and non histone proteins which is named by Flemming.
- centrosomes in which primary constriction disc is known as kinetochore.
- Satellite is some chromosome have non straining secondary construction at a constant location , which gives the appearance of small fragment called satellite.
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