CELL STRUCTURE

1. BIOLOGY CELL STRUCTURE

2. A Liver cell

3. Liver cell TEM x9400

4. Lily Parenchyma cell x.s. (TEM x7210)

5. Cell and Organelle All living organisms are made of cells. A cell is made of living material called protoplasm. Different kinds of cells vary in size, shape, colours and internal structures.

9. Prokaryotic Cell

11. Subatomic particle atomic molecule molecular complex organelle Virus Cell Tissue Organ System Organism Organization of a cell

12. Cell Structure • Cell wall • Cell membrane • protoplasm - the living contents within the cell: nucleus and cytoplasm • The cytoplasm contains many subcellular organelles. •  Sub cellular organelles revealed are: Golgi apparatus, mitochondrion, food granules, centriole, secretary granules and chromatin in nucleus.

15. Cell membrane • Chemical components :consists of protein and lipid • Structure: Two layers of phospholipid sandwiched between two protein layers

16. Davson and Danielli model

17. Unit membrane hypothesis ( proposed by Robertson )u  Under electron microscopy, membrane shows a characteristic trilaminar appearance.u   The 3 layers are arranged as that of Davson Danielli’s model.

18. trilaminar appearance

19. Fluid mosaic model of cell membrane

20. A mosaic of protein molecules floats in a fluid lipid layer.u      In this model, lipid bilayer remains as the main backbone of the unit membrane.u      The lipids spontaneously form a bilayer owing to their polar heads and non-polar tails.u      Proteins act as islands floating in the lipids. Some proteins move about freely while others are fixed in position.

21. Some proteins penetrate only part of the way into the membrane while others penetrate all the way through.u      Proteins are variable in function.u      Sugars are incorporated with protein of lipid to form glycoprotein or glycolipid respectively. These sugars are important in recognition mechanism.u      Both lipids and proteins show rapid lateral diffusion in the plane of the membrane.u      Fluidity and permeability of the cell membrane are determined by the degree of saturation and the hydrocarbon chain of the lipids.

25. Function of cell membrane • Protein components: • Act as a partially permeable barrier controlling the movement of substances between the cell and the surrounding • Channels or pores are formed within a protein or between adjacent protein molecules • Act as support to give strength • Act as enzyme which catalyzes the chemical reaction within the cell membrane • Act as carriers in transporting substance across the membrane • Act as recognition center • As a pump moving things across it

26. uLipid component:X  The presence of unsaturated lipids can prevent close packing of the molecules so as to make membrane fluid.X  Fluidity is also increased with decreasing length of the fatty acid tails.u      Some membranes are folded to increase surface area to facilitate exchange with environment. e.g. microvilli of intestinal epithelial cells.

27. uCell membrane can also separate the contents of cells from their external environments, i.e. form compartments for individual metabolic reaction to take place within the cell.u      Cell membrane is differentially permeable because cell membrane allows glucose, amino acid, fatty acid, glycerol to diffuse slowly and actively control what substances to pass through.u      The ability of infolding and extension to form vesicles allows endocytosis and exocytosis to take place.

28. Nucleus • Contains chromatin which is involved in nuclear division • Contains a nucleolus

29. Structure of Nucleus • Enclosed by and envelope of two membranes that is perforated by nuclear pores

30. Function of Nucleus • Necessary for survival of a cell • Controls all the activities of the cell, cellular function, cell division and heredity

31. Nuclear membrane • Doubled layer • Similar structure as cell membrane • Continuous with E.R. • With microscopic pores for exchange of materials between nucleus and cytoplasm

32. Nucleus with nuclear pores

33. Nucleoplasm • Nuclear sap • Gel-like • Denser than cytoplasm • Contains proteins, nucleotides and ions

34. Chromatin • Consists of DNA and protein ( histone ) • Condense to rod-shape chromosome just prior to nuclear division • Carry genetic materials which determine organisms’ characteristics and transmit these characteristics to next generations

35. Nucleolus • Composed of DNA mainly • Act as the manufacturing site of ribosomal DNA (rDNA) and ribosomes

36. Endoplasm Reticulum ( E.R.) • A system of parallel flattened membrane-bounded sacs called cisternae • Continuous with the outer membrane of the nuclear envelope • Act as an intracellular transport system • There are two types of E.R - Rough ER and smooth ER

38. Rough E.R. • Ribosomes are attached to its surface • Transports proteins made by the ribosomes through the cisternae to smooth ER and then to Golgi appartus for futher modification

39. Smooth E.R. • Without ribosomes attached to its surface • Transport lipids • Synthesis of lipids and steriod

40. Diagram of Golgi

45. Golgi Apparatus • Usually located near the nucleus • consists of stacks of flattened membrane bounded sacs called cisternae and many vesicles • At one end of the stacks new cisternae are constantly formed by fusion of vesicles pinched from smooth ER; at the other end, small Golgi vesicles are pinched off constantly • Transport in vesicles of many cell materials, such as enzymes form ER • Involved in secretion and lysosome formation

46. Ribosomes • Particles synthesis in nucleolus and then pass through the nuclear pores to the cytoplasm • Made of protein and rDNA • The site for protein synthesis

48. Ribosomes and Polysomes