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Cell Structure: Organelles, Prokaryotes vs Eukaryotes
- 1. 1 Cell Structure Prof.ssa Patrizia Mauri ISISS Cicognini- Rodari - Prato
- 2. 2 The cell Cell means “little room” The first cells were observed in the 1655 by Robert Hook, with a rudimentary Optical Microscope – they were cork cells, a plant tissue. Then Antony Van Leewenhoek observed for the first time Protozoa (unicellular animals), Sperm Cells and Bacteria.
- 3. 3 Cork tissue Paramecium Sperm Cells Escherichia Coli
- 4. 4 Cell Theory (19th century) • All organisms are composed of one or more cells. • Cells are the smallest living units of all living organisms. • Cells are generated only by the division of previously existing cells.
- 5. 5 Cell Characteristics Plasma membrane encloses the cell Cytoplasm fills cell interior, it contains organelles and any kind of molecules Genetic material – DNA - prokaryotes: single circular molecule - eukaryotes: more linear molecules (enclosed into a nucleus) Phospholipid Membrane proteins
- 7. 7 Cell Size •Most cells are relatively small because as size increases, volume increases much more ---> longer diffusion time
- 9. 9 Prokaryotic Cell • Simplest organisms (unicellular) commonly called Bacteria – Cytoplasm is surrounded by plasma membrane and encased in a rigid cell wall NO distinct interior compartments – no nucleus (DNA is free in the cytoplasm) - no organules
- 10. 10 Prokaryotic Cell • Some use a flagellum for locomotion – threadlike structures protruding from cell surface Bacterial cell wall Flagellin Rotary motor Sheath
- 13. 13 Eukaryotic Cell • Bigger and more complex. It is characterized by an endomembrane system which forms organules. There are: - NUCLEUS (DNA) - Cytoskeleton (internal protein scaffolding) - Organules , Vesicles - Cell wall – Only plant and fungi cells
- 14. 14
- 15. 15
- 16. 16 Nucleus • It is the repository for genetic material (DNA) • It directs activities of the cell • Usually is single, some cells have several, RBC none - Nucleolus – a region of intensive ribosomal RNA synthesis - Nuclear envelope - is the surface of nucleus made by two phospholipidic bilayer membranes Nuclear pores – protein gatekeepers
- 17. 17 Nucleus
- 18. 18 Chromosomes • DNA of eukaryotes is divided into linear chromosomes. – It exists as strands of chromatin, except during cell division – Is associated with packaging proteins - histones - to form nucleosomes
- 19. 19
- 20. 20 Cytoskeleton • It is network of protein fibers supporting cell shape and anchoring organelles – Actin filaments cell movement – Microtubules Hollow tubes Facilitate cell movement – Intermediate filaments Stabilize – support cell structure Actin Microtubules Intermediate filaments
- 21. 21 Cytoskeleton
- 22. 22 Endomembrane System An inner system of organelles linked one to the other by a stream of molecules. It includes: - Endoplasmic Reticulum - Golgi Apparatus - Vesicles and Lysosomes
- 23. 23 Endomembrane System – Endoplasmic Reticulum: an inner labyrinth Rough ER - studded with ribosomes Smooth ER - no ribosomes
- 24. 24 Endoplasmic Reticulum • Composed of a membranes system • Functions in storage and secretion • Rough ER is “rough” because of associated ribosomes (sites of protein synthesis) • Smooth ER - lacks associated ribosomes – synthesis of carbohydrate and lipid molecules
- 25. 25 Endomembrane System • Golgi Apparatus > Cisternae – stacked membrane tanks > Front - cis , Back – trans > Collect, package, and distribute molecules synthesized in ER
- 26. 26 Endomembrane System • Vesicles Trasport vesicles -transfer molecules from ER to Golgi Apparatus and from there to the Membrane Lysosomes - vesicles containing digestive enzymes – from Golgi Apparatus
- 27. 27 Cytoplasm Phagocytosis Food vesicle Golgi apparatus Lysosomes Plasma membrane Digestion of phagocytized food particles or cells Endoplasmic reticulum Transport vesicle Old or damaged organelle Breakdown of old organelleExtracellular fluid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
- 28. 28 Ribosomes • Ribosomes are RNA-protein complexes composed of two subunits that join each other - they are assembled in nucleolus - they are the site of protein synthesis
- 29. 29 Mitochondria (in all eukaryotic cells) Powerhouse of the cell ( through the degradation of sugars and fats) Structure- outer and inner membranes, cristae Have their own DNA
- 30. 30 Chloroplasts (only in photosynthetic cells) Thet are the site of Photosyntesis Chloroplasts are larger and more complex than mitochondria. Outer and inner membranes Thylakoids, disc-shaped structures, with light capturing pigments, they form grana Have their own DNA
- 31. 31 Theory of Endosymbiosis • Endosymbiotic theory suggests that engulfed prokaryotes became hosts within an eukaryotic cell, providing advantages associated with specialized metabolic activities
- 33. 33 Evidence for the endosymbiont theory is that mitochondria and chloroplasts: - Are appropriate size to be descendants of ancestral bacteria - Replicate by splitting, as prokaryotes - DNA is circular and different from the DNA of the cell nucleus - Have ribosomes similar to prokaryotes
- 34. 34 Plant Cells - Central vacuole It is often found in the center of the cell and serves as a storage for water and other materials - Cell wall It is made of cellulose. It supports the cell and glues cells together - Chloroplasts They are the sites of Photosyntesis which provides nutrition to the cell (glucose)
- 35. 35
- 36. 36 Fungal cell
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- 38. 38
- 39. 39 See you after Christmas with two more topics: 1. MEMBRANE TRANSPORT 2. OPTICAL MICROSCOPE
- 40. 40 Merry Christmas and Happy New Year !!