CELL

1. CELL 2010

2. What is a cell? • “ Life is a dynamic equilibrium of hundreds and thousands and millions of chemical and biochemical reactions going on between non-living substances at ionic and molecular level”. -Panday S.N & SinhaB.K,Plant Physiology Is the structural and functional unit of a living body.

3. History • Term “Cell”- coined by Robert Hooke (1665). • Nucleus – Robert Brown (1831). • Mirbel (1819)-” plants are formed by a membranous cellular tissue”. • White Lamarck (1819)- “nobody can have life, if its constituent parts are not cellular tissue or not formed by cell”. • M.J Scheleiden and Theodore Schwann 91839)- propounded cell theory- “ The cells are organisms; animals as well as plants are aggregates of these organisms arranged in accordance with definite laws”.

4. Virchow (1855)- Omnis cellula-e-cellula, i.e., new living cells arise only by reproduction of pre-existing living cells. • Von Mohl (1846)- protoplasm is the physical basis of life. • Purkinje (1840) introduced the term Protoplasm.

5. Cell Theory • All living things are composed of cells and their products. • All cells arise from pre-existing cells. • All cells are basically alike in chemical composition and metabolic activities. • The function of an organization as a whole is the outcome of the activities and interactions of the constituents cells.

6. Criticisms of cell theory • Viruses do not fit in the definition of a cell and these are therefore often described as living chemicals. • Among other examples, coenocytic forms such as vaucheria (alga) and Rhizopus (fungus) may also be found placed outside the definition limit. • Their living substances are enclosed in a wall and there is hardly any organization like that of a cell. • It is therefore difficult to accommodate these kinds of units in the context of cell theory.

7. Differences Prokaryote Eukaryote Cell is not covered with a sheath or capsule. Chloroplast are present as double membrane strs. Present as double membrane str. Mesosome absent. 5. Present. 6. Cytoplasmic streaming is often found. • Cell is covered with gelatinous sheath or capsule • Lacks chloroplasts. • Lacks mitochondria. • Mesosome present. • Golgi bodies, ER, lysosomes, vacuoles are absent. • Cytoplasmic streaming is absent

8. Nucleus, nuclear membrane and nucleolus are absent • Chromosomes of prokaryotes are referred to a genophores. DNA not associated with protein. • Ribosomes are of 70S type • DNA is circular and double stranded • Muramic acid is present in almost all prokaryotic cell walls • Present • Chromosomes are made of DNA and histone proteins • Ribosomes are of 80S type • DNA is spirally coiled, helical and double stranded. • Muramic acid is absent

9. PLANT CELL

10. Cell wall

11. Cell wall • Is the non-living component of a cell and is secreted and maintained by the living portion of the cell, called protoplasm. • Synthesis- controlled by golgi bodies. • Typical cell wall is composed of three different regions: • Middle lamella • Primary cell wall • Secondary cell wall

12. Middle lamella: • works as a cementing layer between the two daughter cells. • Consist of Ca and Mg pectate. • Primary wall: • is the first layer of individual cell, synthesized by protoplasm. • Composed of hemcellulose 50%, cellulose- 25%, and smaller amount of pectic substances, non-cellulosic polysaccharides, fats and proteins.

13. 3. Secondary cell wall: • formed next to primary wall towards the protoplasm. • Mainly consist of cellulosic or varying mixture of cellulose and non-cellulosic material. • Gives structural independence to the cell and provides rigidity to the wall.

14. Function: • Mechanical support, definite shape, protection to cell & cellular content. • Being hydrophilic in nature- imbibing water & helps in movement of water & solutes towards protoplasm. • Molecular mechanism of auxins action through proton extrusions • has adsorption sites for cation • Cutin and suberin deposition on the wall reduce the rate of water loss through transpiration

15. Cell Membrane

16. Cell Membrane • Outer most covering of the protoplast • Living and differentially permeable membrane. Chemical composition: • Proteins- 42% • Lipids – 32% • Carbohydrate – 6% • Water – 20%

17. Structure of cell membrane Fluid Mosaic Model: • Proposed by Singer & Nicholson (1972). • Central bilipid layer is composed of phosplolipids, with their spherical polar head group on the outer surface, form the basic str. of a membrane. • The two non-polar trails of each molecule point inwards. • This arrangements forms a water resistant barrier through which lipid soluble substance can pass through.

18. They described the model as protein ice berg in a sea of lipids. • In fact, proteins are found in the form of discrete particles which may either be embedded in the lipid layer – integral protein or intrinsic protein . • Superficially attached – peripheral or extrinsic proteins.

19. Functions • Permeability barrier • Cytoskeleton- provide mechanical frame on which enzymes can be superficially oriented. • Participate in biogenesis of cell wall

20. Chloroplasts

21. Plastids • Schimper (1885)- derived from Greek word Plastikas. • Discoid organelles about 5µm in diameter and 3 µm in thickness • Free cytoplasm in plant cell. Three types: • Chromoplast- red, yellow and orange • Leucoplast • Chloroplast

22. Chloroplasts • Chloroplast are plastids that contain the green pigment chlorophyll • along with other photosynthetic pigments. • Chloroplasts perform photosynthesis. • Chloroplasts are double membrane-bounded organelles present in plant cells. • In the stromachloroplast DNA and ribosomes can be found

23. Functions • Main site of photosynthesis in which both light and dark reactions are found • Participates in photorespiration and a site of glycolic acid production which functions as the substrate of photorespiration. • Some amt. of protein synthesis takes place. • Carries out lipid metabolism to synthesis pigment molecules • Has its own genetic system and self replicating

24. Peroxysomes • Isolated by Tolbert et al in 1968 from broken choloroplast. • Are microbodies and range from 0.5- 1µm in diameter. • Transitory Lifespan of 4-5 days. • Oval, single membraned str. enclosing dense homogenous stroma. • Associated with chloroplast or ER. • Found in C3 and CAM plants. • Peroxysomes originates from ER. • Site for photorespiration. • Contain enzymes catalase, urateoxidase etc. • Protective function – oxidises accumulated substance hydrogen peroxide.

25. Central Vacuole

26. Vacuole • Non-living reservoir and are enveloped by unit membrane str. • The envelop of a vacuole- tonoplast • Vacuole contains cell sap contains mineral salts, sugars, organic acids and at times anthocyanin pigment. • The various colour of petals are due to the presence of various dissolved anthocyanin pigments present in vacuoles. Function: • Cell metabolism • Storage compartment • Turgor pressure • Detoxification • Movement of gametes in spirogyra

27. Ribosomes

28. Ribosomes • First observed by Robinson and Brown (1953) in plant cell & Palade in animal cell. • about 150-200 Å • two types are recognized • 70 S in Prokaryotes • 70 S and 80 S in Eukaryote • 70 S has (i) smaller unit 30S and (ii) larger unit 40 S • 80S has ( i) smaller unit 40S and (ii) larger unit 60 S Function: • Protein synthesis

29. Nucleus

30. Nucleus • First discovered by Robert brown in 1931 in orchid cell • More or less spherical embedded in cytoplasm. • 5-10µm in diameter. Consists of four different components: • Nuclear membrane/ nuclear envelop • Karyolymph / nucleoplasm • Chromatin • Nucleolus

31. Functions • It contains the genetic information in its chromatin for reproduction, development, metabolism as well as behavior of organisms. • Controls all cellular activities in the cell. • Nucleolus takes part in the production of ribosome.

32. Endoplasmic Reticulum (ER)

33. Endoplasmic Reticulum (ER) • The ER is a membrane bounded organelle. • The smooth and rough regions of the ER are interconnected. Smooth ER. • lacks ribosomes. • It is a network of pipe-like interconnected tubes. Functions of the SER • include synthesis of lipids, processing of sugars, and detoxification of drugs and poisons.

34. Rough ER • has bound ribosomesattached to the outside. • The RERis in fact an extension of the outer nuclear membrane. Functions: • RER include anchorage of newly synthesize proteins, and the finishing of proteins

35. Golgi Apparatus

36. Golgi Apparatus • The Golgi Apparatus is a single membrane-bounded organelle constituted of piled sac-like cisternae. • Both animal and plant cells have Golgi Apparatus Functions: • To finally process the immature enzymes into functional forms and to secrete them in a closed vesicle. Thus , secretion is the main functions of the golgi complex. • Participates in the transfer of glyco proteins.

37. Participates in cell plate formations by releasing vesicles which actively organize cell plate orientation with the help of phragmoplasts ( microtubules). • Plays roles in giving rise to the primary lysosomes. • Suppose play role in regulation of fluid balance. 6. Believe to play role in phospholipids synthesis and lipid absorption

38. Lysosomes

39. lysosomes • Named in 1955 by Christain de Duve on the basis of composition. • Contain about 50 hydrolytic enzymes & as a matter of fact these are the lytic bodies functioning as suicidal bags. • Structurally, polymorphic, sub-microscopic bodies ranging in size from 0.4 – 0.8 microns. • Has a single limiting membrane composed of lipoprotein, densely granulated stroma and a large vacuole. • Chemically a lysosome is a bag filled with acid hydrolases functioning at acid pH.

40. Functions: Intracellular digestion: • digestion of particles that are taken into the cell by phagocytosis. Autophagy: • begin to digest the other cell inclusions such as mitochondria and ER. • A process of obtaining the needful energy by making use of these constituents as a source.

41. Ageing: • produce autolytic enzymes, that slowly disrupt the delicate intracellular machines. • Produce some biproduct that clog the gears of metabolic machinery. • They may digest some functional elements and then produce insoluble residues. Autolysis: • removing of dead or degenerating cells. • During the process, the lysosomes membrane ruptures and • enzymes are set free to digest the dead cells and to get rid of the cell debris- Autolysis. Seedlings: • in seedling, they are involved in the hydrolysis and removal of protein and starch during germination.

42. Mitochondria

43. Mitochondria • Named by C. Benda in 1897. • Derived from Greek word Mitos- filaments and chondros– granules. • Shape variable. • Occasionally influenced by environment and physiological conditions. • However, they may be granular, club-shaped, tennis-racket shaped, vesicular or rod-shaped. • Size also varies. • Rod shaped are 0.5µ to 2µ but may attain a maximum length of 7µ.

44. Outer membrane: • smooth and contains about 40% lipid content with lipid/protein ratio of 0.8 • proteins are of intrinsic type which appears to have channels for passage of solutes. Such proteins are called porins. Inner membrane: • Show complex infoldings called mitochondrial crest or cristae. • On its inner surface towards matrix are found F1 particles ( oxysomes) Matrix: • Contains RNA, DNA, ribosomes and enzymes involved in nucleic acid metabolism and protein synthesis.

45. Functions of mitochondria • Major part of ATP is synthesized in mitochondria by oxidation of food stuffs. • Provide raw materials for synthesis of chlorophyll. Cytochrome, pyrimidine, alkaloid and steroids. • Site for amino acid and fatty acid synthesis.

46. Task Differentiate between the following: • 70S and 80S ribosome. • Mitochondrial DNA and nuclear DNA. • Plant cell and animal cell