Cell - The Fundamental Unit of Life.
Biology is study of living Organism.
*Cytology :- The medical and scientific study of cells. Cytology refers to a branch of pathology, the medical specialty that deals with making diagnoses of diseases and conditions through the examination of tissue samples from the body.
*Cell:- the smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.
Discovery :-
Cell was first discovered by Robert Hooke in 1665. Leuweenhook state that cell was living .Robert Breown discovered nucleus .
CELL THEORY :
Schieiden and Schwann together formulated the cell theory.
=All living organisms are composed of cells.
=Cell is the fundamental unit of life.
=All new cells come from pre-existing cells.
*Rudolf Virchow (1855) he modified and gives the final shape to the cell theory.
All living organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
Shape and Size of Cells
Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped, or totally irregular like the nerve cell. The Size of cell also varies in different animals and plants. Most of the cells are microscopic in size like red blood cells (RBC) while some cells are fairly large like nerve cells. Average size of cells varies from 0.5 to 20 μ.
Types of Cells:
The cells can be categorized in two types :
1. Prokaryotic Cell
2. Eukaryotic Cell
PROKARYOTIC CELLS :
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EUKARYOTIC CELL :
Cell envelope and its Modifications :
Most prokaryotic cell have characteristic complex cell envelope.
The cell envelops consists of tightly bound three layer structure;
*The outermost glycocalyx.
*Middle cell wall
*Inner plasma membrane.
=According to the nature of the cell wall and behavior towards the stain developed by Gram, bacteria are Gram positive or Gram negative.
*Gram positive bacteria : Bacteria that take up gram stain.
*Gram negative bacteria : Bacteria that do not take up gram stain.
=Glycocalyx may for a loose sheath called slime layer.
=Glycocalyx may be thick and tough called the capsule.
=The cell wall determines the shape of the cell, strong structural support to prevent the bacterium from bursting and collapsing.
=Plasma membrane is semi-permeable in nature and interacts with outside world.
=A special membranous structure is the mesosome which is formed by extensions of plasma membrane into the cell.
=These extensions are in the form of vesicles, tubules and lamellae.
=They help in cell wall formation, DNA replication and distribution to the daughter cell.
=They also help in respiration and secretion.
=Some bacteria have filamentous extensions called flagella.
=Bacterial flagellum has three parts – filament, hook and basal body.
=Pili are elongated tubular structures made of a special protein.
=Fimbriae are small bristle like fibres sprouting out of the cell. Play role in adhesion.
Cell Structures
Cell is composed of some basic structures:
=Cell membrane :
*The cell membrane composed of lipids that arranged in bilayer.
*Lipids are arranged within the membrane with the hydrophilic polar head towards the outer sides and the hydrophobic tails towards the inner part.
*Non polar tail of saturated hydrocarbons is protected from the aqueous environment.
*The lipid component of the membrane mainly consists of phophoglycerides.
*Cell membrane also possesses protein and carbohydrates.
*Ratio of protein and lipids varies from cell to cell.
*Human erythrocyte plasma membrane contains 52 % protein and 40 % lipids.
*Membrane protein may be integral or peripheral.
*Peripheral protein lie on the surface and integral proteins are partially or totally buried in the membrane.
*The improved model of the structure of plasma membrane was proposed by singer and Nicolson (1972) widely accepted as fluid mosaic model.
*According to this the quasi fluid nature of lipid enables the lateral movement of proteins within the overall bilayer.
Function :
*Passive transport:-Transport of molecules across a membrane along the con- centration gradient, i.e., from higher to lower concentration without the consumption of energy.
*Simple diffusion :- The process by which solutes are moved along a concentration gradient in a solution or across a semipermeable membrane.
*Facilitated diffusion:- In the cell, examples of molecules that must use facilitated diffusion to move in and out of the cell membrane are glucose, sodium ions, and potassium ions.
*Active transport :- Transport of molecules against concentrataion gradient, i.e., from lower to higher concentration with the consumption of energy (ATP).
*Phagocytosis :- Process by which certain living cells called phagocytes ingest or engulf other cells or particles. The phagocyte may be a free-living one-celled organism, such as an amoeba, or one of the body cells, such as a white blood cell.
*Exocytosis :- Exocytosis is a process by which a cell transports secretory products through the cytoplasm to the plasma membrane. Secretory products are packaged into transport vesicles (membrane-bound spheres). ... Secreted protein - enzymes, peptide hormones, and antibodies. Neurotransmitters from nerve cells.
*Pinocytosis:- The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
=Cell wall :
*A non-living rigid structure called cell wall present outside the plasma membrane of plant and fungal cell.
*Algae have a cell wall made of cellulose, galactans, mannans and minerals like calcium carbonate.
*Plant cell wall consists of cellulose, hemicelluloses, pectins and proteins.
*The cell wall of young plant is called primary cell wall.
*On maturity secondary cell wall formed inner to it.
*The middle lamella is a layer of calcium pectate which holds or glues the neighboring cells.
*The cell wall and middle lamella may traversed by plasmodesmata; the cytoplasmic connection between two adjacent cell.
=Protoplasm:
*It is a jelly-like, viscous, colourless semi-fluid substance in various cell organelles present in colloidal form.
*Protoplasm consists two parts: cytoplasm and nucleoplasm.
#Cytoplasm is that part of protoplasm which surrounds the nucleus.
#Nucleoplasm is that part of protoplasm which is located inside the nucleus.
Functions:
*Protoplasm acts as a store of vital chemicals like amino acids, proteins, sugars etc.
*It is the site of some metabolic reactions.
The endomembrane system :
=Endoplasmic reticulum :
*Network or reticulum of tiny tubular structures scattered in the cytoplasm, called endoplasmic reticulum.
*It divides the intracellular space into two distinct compartments:
Luminal (inside the ER)
Extra luminal (cytoplasm).
*The ER shows ribosomes attached to their outer surface called Rough Endoplasmic reticulum (RER).
*Endoplasmic reticulum without ribosome called SER (smooth endoplasmic reticulum)
Function:
*RER present in the cell actively involved in protein synthesis.
*SER is the site for synthesis of lipid, glycogen and steroid hormones.
=Golgi apparatus:
*Camillo Golgi (1898) first observed this organelle, and named after him.
*It consists of many flat, disc shaped sacs or cisternae.
*These are staked parallel to each other.
*The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cisor the forming face and concave transor the maturing face.
Function:
*Principally responsible for packing of materials to be delivered intra-cellular target or intercellular target.
*Materials are packed in the form of vesicles, from the ER fuse with the cis face of the Golgi apparatus and move towards the trans face.
*Important site for the formation of glycoprotein and glycolipids.
=Lysosomes:
*Membrane bound vesicular structure.
*Formed by Golgi body.
*Rich in all type hydrolytic enzymes, optimally active in acidic pH.
*These enzymes are capable to digesting carbohydrates, proteins, lipids and nucleic acids.
=Vacuoles:
*The vacuole is the membrane-bound space found in the cytoplasm.
*It contains water, sap, excretory product.
*Vacuole is bounded by a single membrane called tonoplast.
*In plant cells the vacuole can occupy 90% of the volume.
*Tonoplast facilitates active transport of material from cytoplasm into the vacuole.
*In Amoeba the contractile vacuole is important for excretion and osmoregulation.
*In many protists, food vacuoles are formed by engulfing the food particles.
=Mitochondria:
*The number of mitochondria varies according to the physiological activity of the cell.
*Each mitochondrion is a double membrane bound structure with outer and inner membrane, dividing its lumen into two aqueous compartments
*Outer compartment.
*Inner compartment.
*The inner compartment is called the matrix.
*The inner membrane forms a number of infoldings called the cristae towards the matrix.
*The cristae increase the surface area.
*Two membranes have their own specific enzymes associated with the mitochondrial function.
*Mitochondria are the site of aerobic respiration.
*They produce cellular energy in the form of ATP, hence called ‘power house’ of the cell.
*The matrix also possess single circular DNA molecule and a few RNA molecules, ribosomes (70S), they synthesize their own protein.
Mitochondria divide by fission.
=Plastids :
*Plastids are found in all plant cells and in Euglenoids.
*They bear some specific pigment, impart specific colour to the plants.
Based on the type of pigments plastids can be classified into:-
1.Chloroplasts: Green coloured plastids containing chlorophyll. 2.Chloroplasts manufacture food by the process of photosynthesis.
3.Chromoplasts: Colourful plastids. They provide colour to flowers and fruits.
4.Leucoplasts: Colourless plastids. They help in the storage of various substances like starch, proteins and fats.
*The chloroplasts contain chlorophyll and carotenoid pigments, traps solar energy for photosynthesis.
*In the chromoplasts fat soluble carotenoid pigments like carotene, xanthophylls are present.
*The leucoplasts are colourless plastids of varied shapes and size with stored nutrients.
#Amyloplast - store carbohydrates.
#Elaioplasts – store oils and fats.
#Aleuroplast – store proteins and minerals.
*Chloroplasts are found in the mesophyll cells of the leaves.
*These are oval, spherical, discoid or even ribbon like organelles.
*Chloroplast is a double membrane organelle.
*The space limited by inner membrane is called stroma.
*A number of organized flattened membranous sacs called thylakoid are present in the stroma.
*Thylakoids are arranged like stakes of coins to form grana.
*There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
*They thylakoids enclose a space called lumen.
*Chlorophyll pigments are located in the thylakoids.
*Chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
*Stroma contains small circular DNA and ribosomes.
=Ribosomes :
*Ribosomes are granular structure first observed by George Palade (1953).
*Composed of ribonucleic acid (RNA) and proteins.
*Non-membranous cell organelles.
*Eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S.
*‘S’ stands for sedimentation coefficient; measure of density and size.
*Both 70S and 80S ribosomes consists of two subunits.
*Primary function is protein synthesis hence called protein factory of the cell.
=Cytoskeleton :
*An elaborate network of filamentous proteinaceous structures present in the cytoplasm is collectively known as cytoskeleton.
*Cytoskeleton involved in many function such as mechanical support, motility, maintenance of the shape of the cell.
=Cilia and Flagella :
*Cilia and flagella are hair-like outgrowths of the cell membrane.
*Cilia are small help in the movement of cell or surrounding fluid.
*Flagella are longer and responsible for cell movement.
*Cilia and flagella covered by plasma membrane.
*Their core called axoneme, possess a number microtubules running parallel to the long axis.
*The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules and a pair of centrally located microtubules.
*The central tubules are connected by bridges and are also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublet by radial spoke.
*The peripheral doublets are also interconnected by linkers.
*Both cilia and flagella emerge from centrioles-like structure called basal bodies.
=Centrosome and centrioles :
*Centrosome is an organelle usually containing two cylindrical structures called centrioles.
*They are surrounded by amorphous pericentriolar materials.
*Both centrioles in a Centrosome lie perpendicular to each other.
*Each centriole has an organization like the cartwheel.
*They are made of nine evenly spaced peripheral fibrils of tubulin.
*Each of the peripheral fibril is a triplet.
*The adjacent triplets are also linked to each others.
*The central part of the centriole is called hub.
*The hub connected to peripheral triplets by radial spokes.
*The centriole forms the basal body for cilia, flagella and form spindle fibres during cell division.
=Nucleus :
*Nucleus as a cell organelle was first described by Robert Brown in 1831.
*Materials inside the nucleus was stained by Flemming and named as chromatin.
*The interphase nucleus has highly extended and elaborates nucleoprotein fibres called chromatin.
*The nucleus also contains nuclear matrix and one or two spherical bodies called nucleoli.
*Nuclear envelope consists of two membranes with perinuclear space (10- 50 nm).
*The outer membrane remains continuous with endoplasmic reticulum.
*Presence of nuclear pore due to fusion of two membranes.
*Nuclear pores allow the movement of RNA and protein in both directions.
*The nuclear matrix or nucleoplasm contains nucleolus and chromatin.
*Nucleolus is the site for active ribosomal RNA synthesis.
*During cell division the chromatins condensed to form chromosomes.
*Chromatin contains DNA and some basic proteins called histones, non-histone proteins and some RNA.
*A single human cell contains approximately two meter long thread of *DNA in 46 chromosomes.
*Each chromosome essentially has a primary constriction or the centromere.
*On each side of centromere there is disc shaped structures called kinetochores.
#Based on the position of the centromere chromosomes are classified into four types:-
*Metacentric: centromere at the middle with two equal arms.
*Sub-Metacentric: one short arm and one long arm.
*Acrocentric: with extremely short arm and a very long arm.
*Telocentric: with terminal centromere.
*A few chromosomes have non-staining constrictions at a constant location. This gives the appearance of a small fragment called the satellite.
=Transport of Substances through Plasma Membrane
Substance can pass through plasma membrane by two processes: Diffusion and Osmosis.
*Diffusion: It is the process of movement of substances from its high concentration to low concentration.
During the respiration, carbon dioxide is given out a waste product and accumulates in higher concentration inside the cell compared to outside. Due to the difference in concentration inside and outside the cell, CO2 start moving out of the cell.
*Osmosis : It is the process of movement of water from its high concentration to its low concentration through semi-permeable membrane.
Points to learn :-
centriole and ribosomes are not membrane bounded organelles .
Centriole help in cell division.Centriole are presented in chromosome in a pair.
Membrane bound organelles ER,Golgi Appratus ,plastids,lysosomes,vacuoles, and Chloroplast and mitochondria are double membrane .
Bacteria peptidoglycan have NAG and NAM are bounded with glycosidic bound and it is break by the lysosomes that why it is called anti-bacterial .
Biology is study of living Organism.
*Cytology :- The medical and scientific study of cells. Cytology refers to a branch of pathology, the medical specialty that deals with making diagnoses of diseases and conditions through the examination of tissue samples from the body.
*Cell:- the smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.
Discovery :-
Cell was first discovered by Robert Hooke in 1665. Leuweenhook state that cell was living .Robert Breown discovered nucleus .
CELL THEORY :
Schieiden and Schwann together formulated the cell theory.
=All living organisms are composed of cells.
=Cell is the fundamental unit of life.
=All new cells come from pre-existing cells.
*Rudolf Virchow (1855) he modified and gives the final shape to the cell theory.
All living organisms are composed of cells and products of cells.
All cells arise from pre-existing cells.
Shape and Size of Cells
Cells vary in shape and size. They may be oval, spherical, rectangular, spindle shaped, or totally irregular like the nerve cell. The Size of cell also varies in different animals and plants. Most of the cells are microscopic in size like red blood cells (RBC) while some cells are fairly large like nerve cells. Average size of cells varies from 0.5 to 20 μ.
Types of Cells:
The cells can be categorized in two types :
1. Prokaryotic Cell
2. Eukaryotic Cell
PROKARYOTIC CELLS :
- Represented by bacteria, blue-green algae, mycoplasma and PPLO.
- Smaller and multiply more rapidly than eukaryotic cells.
- Four basic shape of bacteria are
- Bacillus (rod like):-Escherichia ,Bacillus anthracis
- Coccus (spherical) :- Staphylococcus
- Vibrio (comma shaped):-Vibrio cholerae
- Sprillum (spiral) :-Spirilla
- All prokaryotes have a cell wall surrounds the plasma membrane.
- There is no well defined nucleus.Nucleoid present .
- Chromosome is single and circular, not enveloped by nuclear membrane.
- Presence of many small, circular, extra chromosomal and self replicable DNA called plasmid.
- Plasmid provides unique characteristic to the bacteria.
- One of the characteristic is antibiotic resistant.
- No membrane bound cell organelles.
- A specialized differentiated form of cell membrane called mesosome is present.
EUKARYOTIC CELL :
- Eukaryotes include all the Protists, plants, animals and fungi.
- Extensive compartmentalization due to membrane bound cell organelles.
- Possess an organized nucleus with nuclear envelope.
- Have a variety of complex locomotory and cytoskeletal structure.
- Genetic materials are organized into chromosomes.
- The plant cell possess cell walls, plastids and a large central vacuole, which are absent in animal cell.
- Animal cells have centrioles which absent in plant cells.
Cell envelope and its Modifications :
Most prokaryotic cell have characteristic complex cell envelope.
The cell envelops consists of tightly bound three layer structure;
*The outermost glycocalyx.
*Middle cell wall
*Inner plasma membrane.
=According to the nature of the cell wall and behavior towards the stain developed by Gram, bacteria are Gram positive or Gram negative.
*Gram positive bacteria : Bacteria that take up gram stain.
*Gram negative bacteria : Bacteria that do not take up gram stain.
=Glycocalyx may for a loose sheath called slime layer.
=Glycocalyx may be thick and tough called the capsule.
=The cell wall determines the shape of the cell, strong structural support to prevent the bacterium from bursting and collapsing.
=Plasma membrane is semi-permeable in nature and interacts with outside world.
=A special membranous structure is the mesosome which is formed by extensions of plasma membrane into the cell.
=These extensions are in the form of vesicles, tubules and lamellae.
=They help in cell wall formation, DNA replication and distribution to the daughter cell.
=They also help in respiration and secretion.
=Some bacteria have filamentous extensions called flagella.
=Bacterial flagellum has three parts – filament, hook and basal body.
=Pili are elongated tubular structures made of a special protein.
=Fimbriae are small bristle like fibres sprouting out of the cell. Play role in adhesion.
Cell Structures
Cell is composed of some basic structures:
=Cell membrane :
*The cell membrane composed of lipids that arranged in bilayer.
*Lipids are arranged within the membrane with the hydrophilic polar head towards the outer sides and the hydrophobic tails towards the inner part.
*Non polar tail of saturated hydrocarbons is protected from the aqueous environment.
*The lipid component of the membrane mainly consists of phophoglycerides.
*Cell membrane also possesses protein and carbohydrates.
*Ratio of protein and lipids varies from cell to cell.
*Human erythrocyte plasma membrane contains 52 % protein and 40 % lipids.
*Membrane protein may be integral or peripheral.
*Peripheral protein lie on the surface and integral proteins are partially or totally buried in the membrane.
*The improved model of the structure of plasma membrane was proposed by singer and Nicolson (1972) widely accepted as fluid mosaic model.
*According to this the quasi fluid nature of lipid enables the lateral movement of proteins within the overall bilayer.
Function :
*Passive transport:-Transport of molecules across a membrane along the con- centration gradient, i.e., from higher to lower concentration without the consumption of energy.
*Simple diffusion :- The process by which solutes are moved along a concentration gradient in a solution or across a semipermeable membrane.
*Facilitated diffusion:- In the cell, examples of molecules that must use facilitated diffusion to move in and out of the cell membrane are glucose, sodium ions, and potassium ions.
*Active transport :- Transport of molecules against concentrataion gradient, i.e., from lower to higher concentration with the consumption of energy (ATP).
*Phagocytosis :- Process by which certain living cells called phagocytes ingest or engulf other cells or particles. The phagocyte may be a free-living one-celled organism, such as an amoeba, or one of the body cells, such as a white blood cell.
*Exocytosis :- Exocytosis is a process by which a cell transports secretory products through the cytoplasm to the plasma membrane. Secretory products are packaged into transport vesicles (membrane-bound spheres). ... Secreted protein - enzymes, peptide hormones, and antibodies. Neurotransmitters from nerve cells.
*Pinocytosis:- The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
=Cell wall :
*A non-living rigid structure called cell wall present outside the plasma membrane of plant and fungal cell.
*Algae have a cell wall made of cellulose, galactans, mannans and minerals like calcium carbonate.
*Plant cell wall consists of cellulose, hemicelluloses, pectins and proteins.
*The cell wall of young plant is called primary cell wall.
*On maturity secondary cell wall formed inner to it.
*The middle lamella is a layer of calcium pectate which holds or glues the neighboring cells.
*The cell wall and middle lamella may traversed by plasmodesmata; the cytoplasmic connection between two adjacent cell.
=Protoplasm:
*It is a jelly-like, viscous, colourless semi-fluid substance in various cell organelles present in colloidal form.
*Protoplasm consists two parts: cytoplasm and nucleoplasm.
#Cytoplasm is that part of protoplasm which surrounds the nucleus.
#Nucleoplasm is that part of protoplasm which is located inside the nucleus.
Functions:
*Protoplasm acts as a store of vital chemicals like amino acids, proteins, sugars etc.
*It is the site of some metabolic reactions.
The endomembrane system :
=Endoplasmic reticulum :
*Network or reticulum of tiny tubular structures scattered in the cytoplasm, called endoplasmic reticulum.
*It divides the intracellular space into two distinct compartments:
Luminal (inside the ER)
Extra luminal (cytoplasm).
*The ER shows ribosomes attached to their outer surface called Rough Endoplasmic reticulum (RER).
*Endoplasmic reticulum without ribosome called SER (smooth endoplasmic reticulum)
Function:
*RER present in the cell actively involved in protein synthesis.
*SER is the site for synthesis of lipid, glycogen and steroid hormones.
=Golgi apparatus:
*Camillo Golgi (1898) first observed this organelle, and named after him.
*It consists of many flat, disc shaped sacs or cisternae.
*These are staked parallel to each other.
*The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cisor the forming face and concave transor the maturing face.
Function:
*Principally responsible for packing of materials to be delivered intra-cellular target or intercellular target.
*Materials are packed in the form of vesicles, from the ER fuse with the cis face of the Golgi apparatus and move towards the trans face.
*Important site for the formation of glycoprotein and glycolipids.
=Lysosomes:
*Membrane bound vesicular structure.
*Formed by Golgi body.
*Rich in all type hydrolytic enzymes, optimally active in acidic pH.
*These enzymes are capable to digesting carbohydrates, proteins, lipids and nucleic acids.
=Vacuoles:
*The vacuole is the membrane-bound space found in the cytoplasm.
*It contains water, sap, excretory product.
*Vacuole is bounded by a single membrane called tonoplast.
*In plant cells the vacuole can occupy 90% of the volume.
*Tonoplast facilitates active transport of material from cytoplasm into the vacuole.
*In Amoeba the contractile vacuole is important for excretion and osmoregulation.
*In many protists, food vacuoles are formed by engulfing the food particles.
=Mitochondria:
*The number of mitochondria varies according to the physiological activity of the cell.
*Each mitochondrion is a double membrane bound structure with outer and inner membrane, dividing its lumen into two aqueous compartments
*Outer compartment.
*Inner compartment.
*The inner compartment is called the matrix.
*The inner membrane forms a number of infoldings called the cristae towards the matrix.
*The cristae increase the surface area.
*Two membranes have their own specific enzymes associated with the mitochondrial function.
*Mitochondria are the site of aerobic respiration.
*They produce cellular energy in the form of ATP, hence called ‘power house’ of the cell.
*The matrix also possess single circular DNA molecule and a few RNA molecules, ribosomes (70S), they synthesize their own protein.
Mitochondria divide by fission.
=Plastids :
*Plastids are found in all plant cells and in Euglenoids.
*They bear some specific pigment, impart specific colour to the plants.
Based on the type of pigments plastids can be classified into:-
1.Chloroplasts: Green coloured plastids containing chlorophyll. 2.Chloroplasts manufacture food by the process of photosynthesis.
3.Chromoplasts: Colourful plastids. They provide colour to flowers and fruits.
4.Leucoplasts: Colourless plastids. They help in the storage of various substances like starch, proteins and fats.
*The chloroplasts contain chlorophyll and carotenoid pigments, traps solar energy for photosynthesis.
*In the chromoplasts fat soluble carotenoid pigments like carotene, xanthophylls are present.
*The leucoplasts are colourless plastids of varied shapes and size with stored nutrients.
#Amyloplast - store carbohydrates.
#Elaioplasts – store oils and fats.
#Aleuroplast – store proteins and minerals.
*Chloroplasts are found in the mesophyll cells of the leaves.
*These are oval, spherical, discoid or even ribbon like organelles.
*Chloroplast is a double membrane organelle.
*The space limited by inner membrane is called stroma.
*A number of organized flattened membranous sacs called thylakoid are present in the stroma.
*Thylakoids are arranged like stakes of coins to form grana.
*There are flat membranous tubules called the stroma lamellae connecting the thylakoids of the different grana.
*They thylakoids enclose a space called lumen.
*Chlorophyll pigments are located in the thylakoids.
*Chloroplast contains enzymes required for the synthesis of carbohydrates and proteins.
*Stroma contains small circular DNA and ribosomes.
=Ribosomes :
*Ribosomes are granular structure first observed by George Palade (1953).
*Composed of ribonucleic acid (RNA) and proteins.
*Non-membranous cell organelles.
*Eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S.
*‘S’ stands for sedimentation coefficient; measure of density and size.
*Both 70S and 80S ribosomes consists of two subunits.
*Primary function is protein synthesis hence called protein factory of the cell.
=Cytoskeleton :
*An elaborate network of filamentous proteinaceous structures present in the cytoplasm is collectively known as cytoskeleton.
*Cytoskeleton involved in many function such as mechanical support, motility, maintenance of the shape of the cell.
=Cilia and Flagella :
*Cilia and flagella are hair-like outgrowths of the cell membrane.
*Cilia are small help in the movement of cell or surrounding fluid.
*Flagella are longer and responsible for cell movement.
*Cilia and flagella covered by plasma membrane.
*Their core called axoneme, possess a number microtubules running parallel to the long axis.
*The axoneme usually has nine pairs of doublets of radially arranged peripheral microtubules and a pair of centrally located microtubules.
*The central tubules are connected by bridges and are also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublet by radial spoke.
*The peripheral doublets are also interconnected by linkers.
*Both cilia and flagella emerge from centrioles-like structure called basal bodies.
=Centrosome and centrioles :
*Centrosome is an organelle usually containing two cylindrical structures called centrioles.
*They are surrounded by amorphous pericentriolar materials.
*Both centrioles in a Centrosome lie perpendicular to each other.
*Each centriole has an organization like the cartwheel.
*They are made of nine evenly spaced peripheral fibrils of tubulin.
*Each of the peripheral fibril is a triplet.
*The adjacent triplets are also linked to each others.
*The central part of the centriole is called hub.
*The hub connected to peripheral triplets by radial spokes.
*The centriole forms the basal body for cilia, flagella and form spindle fibres during cell division.
=Nucleus :
*Nucleus as a cell organelle was first described by Robert Brown in 1831.
*Materials inside the nucleus was stained by Flemming and named as chromatin.
*The interphase nucleus has highly extended and elaborates nucleoprotein fibres called chromatin.
*The nucleus also contains nuclear matrix and one or two spherical bodies called nucleoli.
*Nuclear envelope consists of two membranes with perinuclear space (10- 50 nm).
*The outer membrane remains continuous with endoplasmic reticulum.
*Presence of nuclear pore due to fusion of two membranes.
*Nuclear pores allow the movement of RNA and protein in both directions.
*The nuclear matrix or nucleoplasm contains nucleolus and chromatin.
*Nucleolus is the site for active ribosomal RNA synthesis.
*During cell division the chromatins condensed to form chromosomes.
*Chromatin contains DNA and some basic proteins called histones, non-histone proteins and some RNA.
*A single human cell contains approximately two meter long thread of *DNA in 46 chromosomes.
*Each chromosome essentially has a primary constriction or the centromere.
*On each side of centromere there is disc shaped structures called kinetochores.
#Based on the position of the centromere chromosomes are classified into four types:-
*Metacentric: centromere at the middle with two equal arms.
*Sub-Metacentric: one short arm and one long arm.
*Acrocentric: with extremely short arm and a very long arm.
*Telocentric: with terminal centromere.
*A few chromosomes have non-staining constrictions at a constant location. This gives the appearance of a small fragment called the satellite.
=Transport of Substances through Plasma Membrane
Substance can pass through plasma membrane by two processes: Diffusion and Osmosis.
*Diffusion: It is the process of movement of substances from its high concentration to low concentration.
During the respiration, carbon dioxide is given out a waste product and accumulates in higher concentration inside the cell compared to outside. Due to the difference in concentration inside and outside the cell, CO2 start moving out of the cell.
*Osmosis : It is the process of movement of water from its high concentration to its low concentration through semi-permeable membrane.
- If the medium surrounding the cell has higher water concentration than in cell, cell will gain water by osmosis. Such dilute solution is called Hypotonic solution. Though water molecules pass across plasma membrane in both sides but more water will enter inside the cell. The cell is therefore, swell up and increase in volume. This process is called Endosmosis.
- If the medium surrounding the cell is exactly the same water concentration as inside the cell, there will no net movement of water across membrane resulting in no change in size of cell. Such solution is called Isotonic solution.
- If the medium surrounding the cell has lower water concentration than inside the cell, the cell will lose water through osmosis. Such concentrated solution is called Hypertonic solution. The cell will therefore, shrink and reduce in volume. This process is known as Exosmosis.
Points to learn :-
centriole and ribosomes are not membrane bounded organelles .
Centriole help in cell division.Centriole are presented in chromosome in a pair.
Membrane bound organelles ER,Golgi Appratus ,plastids,lysosomes,vacuoles, and Chloroplast and mitochondria are double membrane .
Bacteria peptidoglycan have NAG and NAM are bounded with glycosidic bound and it is break by the lysosomes that why it is called anti-bacterial .
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