Cells

1. Cells • What is a cell? A cell is a membrane bound unit containing hereditary material and other compounds that make metabolism, growth and reproduction possible. Hereditary material Plasma membrane Cytoplasm

2. Cells • Overview of cell structure • Cells are surrounded by a plasma membrane. • DNA the hereditary material is packaged in one or more chromosomes located in a nuclear region or nucleus. • The cytoplasm contains molecules and organelles needed for cellular activities. • Ribosomes are the factories in which proteins are manufactured.

3. Cells • How were cells discovered? • 1665 Robert Hooke Examined cork in simple microscope. Saw empty compartments and called them ‘cellulae’ (small rooms). • 1650 - 1700 Anton Van Leeuwenhoek Made his own microscope that could magnify 200 X. Observed living things. Called them ‘Animacules’ (little animals).

4. Cells • Formation of the cell theory • 1838 Matthias Schleiden Concludes that all plants are made of cells or their derivatives. He called this theory phytogenesis • 1839 Theodore Schwann All animal tissue is made of cells and within an organism these cells are identical. • The theory they presented from these observations is often called the Schleiden and Schwann Cell Theory

5. Cells • 1855 Rudolph Virchow Studied pathenogens and concluded ‘omnis cellula e cellua’ which means that all cells arise from pre-existing cells. • Principles of the Cell Theory • All organisms are composed of one or more cells. • Cells are the basic unit of life. • Cells arise only by division of a previously existing cell.

6. Cells • Cell size • Does small cell sizes have advantages? • The surface area increases as the square (10 )of the diameter of a sphere, but the volume increases as the cube (10 ). small cube - surface area small cube - volume 2 3 10 m 2 6 x (10 m x 10 m) = 600 m 3 10 m x 10 m x 10 m = 1000 m

7. Cells 2 6 x (30 m x 30 m) = 5400 m • big cell - surface area • big cell - volume 3 30 m x 30 m x 30 m = 27000 m

8. Cells 2 • Comparing different sizes • Surface area 1 small = 600 m 27 small = 16.200 m 1 big = 5400 m • Volume is the same for 1 big and 27 small • The ratio of surface to volume • 27 small 16200/27000 = 0,6 • 1 big 5400/27000 = 0,2 • surface area of small is 3X greater 2 2

9. Cell size • Why aren´t cells larger? • limitations of molecular diffusion • faster passage through small cells • more efficient communication • limitations of surface/volume ratio • with in size greater in volume • interaction occurs only at surface • insufficient exchange of materials at plasma membrane

10. Structure of prokaryotes • Strong cell wall made of carbohydrate matrix and peptide units. • Slime capsule (some times with pili), not always present.

11. Structure of prokaryotes • Simple interior organization • lack internal compartmentalization • reactions not separated, one metabolic unit • lack membrane-bound organelles • infolding of plasma membrane • Rotating flagella • cell movement - screw like motion

12. Structure of prokaryotes • Ribosomes in the cytoplasm • protein synthesis • Circular nuclear matter (DNA) • located in the nucleoid region • Plasmids • small independent circular DNA • Mesosome • infolding of plasma membrane often associated with photosynthesis

13. Structure of eukaryotes • More complex than prokaryotes • They are compartmentalized • possess internal membrane bound organelles • ribosomes • rough endoplasmic reticulum (rER) • lysosomes • Golgi apparatus (complex) • mitochondria • nucleus • chloroplasts

14. Structure of eukaryotes • Nucleus the largest organelle • the nuclear envelope • double layer of membranes, • outer continuous with ER • nuclear pores • restrict passage of molecules to proteins and RNA • chromosomes - chromatid • contain hereditary material • divided into linear chromosomes, associated with histone protein

15. Structure of eukaryotes • the nucleolus • an assembly plant for ribosomal subunits • ribosomal proteins are made in the cytoplasm • ribosomal RNA made in the nucleus

16. Organelles • Endoplasmic reticulum • Thin membrane not visible in the light microscope. • Divides interior into compartments. • Cytoskeleton, holds the cell shape. • Rough ER • covered with ribosomes • manufactures proteins for export • Smooth ER • lacks ribosomes • carbohydrate and lipid synthesis

17. Organelles • Ribosomes • Made of two parts. • Made in the nucleus. • Assist in the manufacture of proteins. • Golgi apparatus

18. Organelles • Mitochondrion • Lysosome

19. Organelles • Chloroplast

20. Cells • State two similarities between prokaryotic and eukaryotic cells. • State two differences between the eukaryotic nucleus and the prokaryotic nuclear material.

21. Endosymbiosis • Symbiosis is two organisms living in close association. • Mitochondria and chloroplasts are thought to be ancient bacteria that became incorporated into eukaryotic cells. • Evidence supporting Theory: • both are surrounded by double membranes • mitochondria and bacteria hvae similar size • mitochondrial ribosomes resemble bacterial ribosomes • both have circular DNA like bacteria • mitochondria divide by simple fission

22. The Plant Cell Wall