1. 1

2. The cell 2 © Zanichelli editore 2015

3. Cells are complex microsystems 3 © Zanichelli editore 2015

4. From biomolecules to cells 4 There is a hierarchical organization in cells: atoms constitute biomolecules; biomolecules and water are used to build up structures that work together so that the cell can grow, develop and reproduce. © Zanichelli editore 2015

5. Why are cells small? /1 5 Cells are small in order to have a large surface compared to their volume. This ratio allows for efficient exchanges with the external environment. Same volume but different surface © Zanichelli editore 2015

6. Why are cells small? /2 6 Volume64 cm 3 Surface96 cm 2 192 cm 2 384 cm 2 Surface/Volume96/64 = 1.5192/64 = 3384/ 64 = 6 © Zanichelli editore 2015

7. Observing cells 7 Cells can be observed with the light microscope or the electron microscope which has a higher resolving power. © Zanichelli editore 2015

8. Prokaryotic cells /1 8 Prokaryotes are unicellular organisms that belong to Archaea or Bacteria domains. Prokaryotic cells always present four structures: plasma membrane; cytoplasm; nucleoid with a circular DNA molecule; ribosomes. © Zanichelli editore 2015

9. Prokaryotic cells /2 9 Many prokaryotic cells present additional structures: cell wall; capsule; flagella; fimbriae or pili. © Zanichelli editore 2015

10. Eukaryotic cells 10 Eukaryotes are organisms that can be unicellular or multicellular. Eukaryotic cells, besides the base structures of prokaryotic cells, have membrane-bound organelles and a nucleus. © Zanichelli editore 2015

11. Animal and plant cells /1 11 Both animal and plant cells have common structures: mitochondria; Golgi apparatus; nucleus; endosplamic reticulum; cytoskeleton. Animal cells also have lysosomes and centrioles. © Zanichelli editore 2015

12. Animal and plant cells /2 12 Plant cells also present a cell wall, vacuoles and chloroplasts. © Zanichelli editore 2015

13. Organelles in eukaryotic cells 13 © Zanichelli editore 2015

14. Nucleus and nucleolus 14 The nucleus contains the DNA with the genetic information of the organism. The DNA controls the synthesis of proteins and it replicates during cell division. The subunits of ribosomes are assembled in the nucleolus. The synthesis of proteins takes place in the cytoplasm, on ribosomes. © Zanichelli editore 2015 nucleus nucleolus

15. Mitochondria and cell energy 15 The energy necessary for the cell is produced by cell respiration in the mitochondria. These organelles contain their own DNA and ribosomes. © Zanichelli editore 2015 They are divided into compartments: the outer membrane; the intermembrane space; the inner membrane; the matrix. outer membrane inner membrane matrix Intermembrane space

16. The endoplasmic reticulum: rough and smooth 16 The main function of the rough endoplasmic reticulum is to store and modify proteins. The smooth endoplasmic reticulum is important for the synthesis of many lipids and for the degradation of toxic substances and metabolic waste. © Zanichelli editore 2015

17. The Golgi apparatus 17 The Golgi apparatus is a membrane system. It receives the molecules synthesized in the endoplasmic reticulum, modifies them and stores them in vesicles. The vesicles transport the molecules to different parts of the cell. © Zanichelli editore 2015

18. Lysosomes 18 © Zanichelli editore 2015 nucleus (green colored) Lysosome (red colored) Lysosomes are vesicles formed in the Golgi apparatus. They contain enzymes which degrade macromolecules and metabolic waste or destroy bacteria.

19. Cytoskeleton, cilia and flagella 19 The cytoskeleton consists of a dense network of filaments and microtubules. It provides shape and support to the cell and an anchoring site for organelles. It is involved in the transport of organelles and molecules inside the cell. © Zanichelli editore 2015 Many cells can present external, mobile structures, called cilia and flagella. They are involved in cell movement and they can be used to move the external fluids.

20. Plant cells: the cell wall 20 The cell wall in plant cells provides support and protection and reduces water loss. It is mainly made up of cellulose and surrounds the cell membrane. © Zanichelli editore 2015

21. Plant cells: vacuoles 21 Up to 90% of a plant cell’s volume may be occupied by the vacuole. © Zanichelli editore 2015 This organelle stores nutrients, degrades waste, accumulates toxic substances that repel herbivores and insects, contains pigments that attract pollinators and provides mechanical support for the plant.

22. Plant cells: chloroplast 22 The chloroplast, which is present in plants and algae, is the organelle responsible for photosynthesis - the transformation of light energy into chemical energy. It contains chlorophyll and possesses its own DNA. © Zanichelli editore 2015 outer membrane thylakoids stroma inner membrane granum

23. Cell adhesion and communication 23 © Zanichelli editore 2015

24. Cells communicate each other /1 24 Nearly all the cells of multicellular organisms are connected to, and communicate with, other cells. In animal cells, the main types of cell adhesion are: tight junctions – they form a thin watertight layer to keep the cells locked together; desmosomes – they connect cells in robust layers and bundles; gap junctions – they form open channels between two cells and are important for intercellular communication. © Zanichelli editore 2015

25. Cells communicate to each other /1 25 In plants, cells can exchange substances through plasmodesmata: they are microscopic channels that enable communication and transportation between cells. © Zanichelli editore 2015