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# AS Level Biology - 2) Cell Structures

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Cell Structures
- Microscopy... Cytology
- Prokaryotes vs. Eukaryotes
- Cell structures/ Organelles
Nucleus
Endoplasmic Reticulum
Mitochondria
- The Endosymbiont theory

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### AS Level Biology - 2) Cell Structures

1. 1. BIOLOGY AS LEVEL REVISION 01
2. 2. 2. Cell Structures
3. 3. Cells  ALL organisms are made up of cells  Simplest collection of LIVING matter  Cell structure correlate to their functions  All cells are related to earlier cells that they descend from
4. 4. MICROSCOPY
5. 5. Microscopy  Microscope is an instrument that magnifies objects too small to be seen, producing an image that appears larger.  Photographs/ pictures of cells derived from the microscope - Micrographs
6. 6. Magnification  A measure how much larger a microscope can cause an object to appear  The Ratio of the object to its actual size (Magnification = measured length[of image]/ actual length of object)
7. 7. Resolution  A measure of clarity – the smallest distance by which two points can be distinguished in an image.  Limited by the physical properties of light
8. 8. Light Microscope  Commonly used  Visible light passes through the specimen  Bent through the lens system – producing magnified image  X1000 magnification  Uses blue light – 400 nm  Lowest Resolution = 200nm
9. 9. The Electromagnetic Spectrum  The resolution depends on the wavelength of the light/ radiation being used on the specimen
10. 10. Light Colors  Light with the largest wavelength is red = 700 nm  Light with smallest wavelength is blue = 400 nm  With the magnification, resolution is actually half the wavelength  Light microscope uses blue – 200 nm resolution
11. 11. Electron microscope  Uses electron – has a shorter wavelength  X-ray is hard to control – electron can be controlled using magnets  Electron can only function in vacuum – oxygen molecules may cause the electron to be knocked around  False-coloring by computer
12. 12. SEM  Scanning Electron microscope  Electron bounce back and forth across specimen’s surface  Creating a detailed 3D image  Resolution smaller that TEM
13. 13. TEM  Transmission Electron Microscope  Electron passes through the surface  Used to inspect the inner structures of cell  Resolution can go down to 0.5 nm
14. 14. Light Vs. Electron Similarities  Both uses Lens Differences  One uses visible light, another uses electron molecule (electron vs. photon)  Resolution, one is 200, the other is 0.5  With SEM – 3D image is possible  Electron is more expensive  One focuses light with lens, the other focuses light by electromagnetic control  One uses electron gun, the other uses low voltage bulb  On magnifies up to 1500, the other up to 500000  One uses air as medium, another uses vacumm
15. 15. Cell Fractionation  Takes cell apart and separates organelles  Cells are centrifuged where the heavier components will sink to the bottom  Ultracentrifuges – fractionates them into components
16. 16. Cell Sizes/ Scale  Red Blood Cell: 7 micrometer (7000 nm)  Egg cell: 100 micrometer (100000 nm)  A virus: 20 – 400 nanometer  Prokaryote: 0.1 – 5 micrometer (100 – 5000 nm)  Nucleus: 6 – 7 micrometer (6000 nm)  Ribosomes: 25 nanometer  Cell Membrane: 7 nm  Microtubules: 25 nm  Microfilaments: 6 nm
17. 17. Extra read: http://peer.tamu.edu/curriculum_modules/Cell_Biology/module_1/whatweknow. htm
18. 18. Kingdom of living things  Eukaryote 1. Animal 2. Plant 3. Fungi 4. Protists  Prokaryote 1. Bacteria 2. Archea
19. 19. PROKARYOTE VS. EUKARYOTE
20. 20. Prokaryotic  Prokaryote – a simple organism e.g. Bacteria  No nucleus  No membrane-bound organelles  Has Cell Walls  Has Circular chromosomes  Common cell structures: Plasma membrane, Cytoplasm, DNA, Ribosomes
21. 21. Animal Cells
22. 22. Animal Cell Structure  Nucleus: Contains chromosomes/ DNA – code for the synthesis of proteins that control the function of the cell – hence the nucleus commands the cell  Cell Surface membrane: Holds the cell content, controls the ins/outs, structural forms, cell recognition, adhesion, signaling, transport of substances, endo/exocytosis  Cytoplasm: the liquid where all the cell metabolic activities take place  Mitochondria: Produces energy in the form of ATP through respiration
23. 23. Animal Cell Structure  Ribosomes: Receiving mRNA coded for Protein synthesis  Lysosome: Engulfs materials and destroy them with enzymes  Rough ER: Has ribosomes on it – involved in protein synthesis – transport network for protein  Smooth ER: Synthesis of lipid – involved in cell detoxification  Golgi bodies: Process the finished proteins
24. 24. Nucleus  Double nuclear envelope – encloses/ protect DNA  Nuclear pore – received substances for DNA Replication(extra phosphate), exits for mRNA  small molecules pass through by diffusion, large ones get in actively  in micrographs – RNA/protein complex can be seen plucking the pore
25. 25. Nucleus  Nucleoplasm – contains chromatin granules, DNA/associated proteins: during cell division, they condense to form chromosomes  Nucleolus – produces rRNA part of ribosomes, proteins, coenzymes, enzymes for nucleic acid synthesis, RNA  Outer membrane continuous with ER – easier transport
26. 26. Endoplasmic Reticulum  A system of hollow tubes/ sacs – transportation purpose nucleus Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum
27. 27. Rough ER  Covered with ribosomes  Interconnected system of flattened sacs  Ribosomes on surface synthesize proteins which are then transported through the interconnected system  RER is abundant in cells which needed to produce a lot of proteins for exports e.g. Digestive enzymes/ growth
28. 28. Smooth ER  Lacks ribosomes  A system of interconnected tubules  Carbohydrate/ lipids metabolism  Synthesizes: triglycerides, phospholipid, cholesterol  Modification of steroid hormones  High percentage in cells involved with metabolism of lipids/drugs
29. 29. Golgi Body  Flattened cisternae  Invaginate/ fuse to form vesicles  Internal transports by vesicles  Vesicles protect molecules  In case of enzymes – protect the cells
30. 30. Cell Membrane  Fluid mosaic bilayers which surround the cell content  Control the ins/outs of the cell  Gives the cell stability during temperature changes  Endocytosis/ exocytosis  Important in cell recognition  Cell signaling  Cell adhesion
31. 31. Cytoplasm  Makes up of liquid: Cytosol  Where the metabolism takes place  Contains water/ solution  Most organelles float here  Osmoregulation
32. 32. Mitochondria  Double Membrane – isolate certain reaction – high concentration of enzymes/ substrates can be maintained  Outer membrane – permeable to salt, sugar, nucleotides  Inner membranes – selectively permeable (control chemical composition of the matrix – optimizes enzyme activity)
33. 33. Mitochondria  Porins on inner membranes – entry of oxygen/pyrovic acid – exit of ATP/ Carbon dioxide  Folded inner membrane (cristae) – increases surface area for enzymes/ coenzymes  70s ribosomes – protein manufacturing  Loop of circular DNA – codes for protein  Enzymes
34. 34. Endosymbiosis theory  States that mitochondria’s ancestors were bacterial ingested by a eukaryote  The eukaryote kept it as it is useful for respiration  Evidences: 70s vs. 80s ribosomes  Evidences: Own DNA  Evidences: Divides by itself
35. 35. Ribosomes  2 subunits  Made of rRNA/ Protein  rRNA – formed in nucleus – moves out via pores  Protein part – assembled in the cytoplasm  Found as dense clusters (polysomes)  On membranes of RER
36. 36. Lysosomes  Vesicles that contains hydrolytic enzymes  Break down old organelles – recycle the materials  Break down storage molecules  Break down whole cell when it dies
37. 37. Cytoskeleton  Microtubules – tubulin proteins : Thickest fo the three – around 25 nm  Microfilaments – actin proteins  Intermediate filaments
38. 38. Microfilament  Rods of about 7nm in diameter  Made up of a twisted double chain of actin subunits
39. 39. Microfilaments  Create tension  Support the shape of the cell  3-D Cortex inside plasma membrane  Bundles of microfilaments indie the microvilli
40. 40. Microtubules
41. 41. Microtubules  25 nm wide  Made up of tubulin proteins  Arranged in dimers (alpha tubulin/ beta tubulin)  This dimer repeat in vertical format – forming a protofilament  13 protofilaments arrange around a hollow core  MICROTUBULES FORM
42. 42. Microtubules  Shapes the cell  Guide the movements of cells/ organelles – with help of motor proteins  Make up spindles that separate chromosomes during cell division
43. 43. Centrosome  Contains 2 centrioles  The location for MTOC (Microtubules organizing center)  MAY have a role in regulating the cell division
44. 44. Centrioles  Microtubules form triplets (1 complete microtubule, 2 partial microtubules)  These triplets then arrange into a cylinder  200 nm in diameter, 500 nm long  Two of these line up perpendicular to form centriole  Not sure of its function yet  Some believe it might be MTOCs for spindles during cell division
45. 45. Cilia/ Flagella  Long structures projecting out of a cell membrane  A core of microtubules sheathed by the plasma  Flagellum – longer and for movement of cell  Cilia – shorter – usually to beat up things
46. 46. Plant Cells
47. 47. Cell Wall  Cellulose fiber embedded in other polysaccharides/ proteins  Pectin and cellulose fiber (strong)  Permeable  Space between cells above the wall: middle lamella  Things like wood may have secondary cell wall
48. 48. Cell Wall  The osmotic pressure vs. the pressure from cell wall gives the plant its structure  Structure of Cellulose – resistant to degradation and enzymes – only cellulase – Protects the cell  Prevent bursting
49. 49. Cell Wall  May have multiple layers 1. Primary Cell Wall – thin and flexible 2. Middle lamella – a thin layer between primary walls and adjacent cells 3. Secondary cell wall (only found in certain cells) : between plasma membrane and primary cell wall – on the inside where it grows
50. 50. Cell Wall  Tunnels between cells: Plasmodesmata  Protoplast: A plant, bacterial or fungal cell with its cell wall removed
51. 51. Vacuoles  Enclosed membrane compartments – filled with water content/ enzymes/ proteins etc.  Storage for waste, harmful materials  Storage for water  Hydrostatic pressure controlled  Work with cell wall to maintain turgidity  The membrane around it: Tonoplast
52. 52. Chloroplasts  Plant organelles specialized in conducting photosynthesis  Larger than mitochondria  Double membrane  Has its own DNA  Endosymbiosis theory applied to it as well
53. 53. Chloroplast  Inner/ Outer membrane  Stroma: The liquid inside the inner membrane  Grana: Made up of stacks of thylakoid  Thylakoid: Has chlorophyll on the surface
54. 54. Virus  Size: 20 – 750 nm  We are not sure if virus is considered an organism  As it is unable to fully function without a host  Nevertheless, virus is a fascinating component to Biology worthy of studies
55. 55. Virus Structure  Consists of an RNA molecule protected by a protective protein coat called capsid  Capsid made up of proteins called capsomere  On the outside a protein envelope gives it another layer of protection  Glycoproteins/lipids stuck out from the envelope
56. 56. Plant Cell Vs. Animal Cell Common  Nucleus  ERs/ Golgi body  Plasma membranes  Phospholipid bilayer  Mitochondria  Gap between cells (gap junction/ Plasmodesmata)  Both have cytoskeleton  Peroxisomes Differences  Cell Wall  Cell membrane: Glycolipid/ Glycoprotein  Centrioles  Central vacuoles  Chloroplasts