Cells

1. Cells Chapter 4

2. Cells • Cellsare the smallest unit of life. • Because they are so small, no one observed them until the microscope was invented. Robert Hooke was the first to describe a cell in 1665.

3. Cell Theory • Cell Theory– idea that all organisms are composed of cells. • All organisms composed of 1+ cells within which life processes occur. • Cells are the smallest living things. • Life evolved only once, 3.5 billion years ago. • Cells arise only by division of a previously existing cell.

4. Tiny Cells • Cells are usually very small because larger cells can’t function as efficiently. • Larger cells have a smaller surface area to volume ratio.

5. Cell Structure Polar areas of protein Phospholipids Polar hydrophilic heads Nonpolar hydrophobic tails • Cells have a delicate cell (plasma) membranesurrounding them that controls permeability to water and dissolved substances. • A semi-fluid matrix called cytoplasmfills the inside of the cell. Polar hydrophilic heads Cholesterol Nonpolar areas of protein Phospholipid Protein channel Cholesterol Receptor protein Cell identity marker

6. Plasma Membrane • Plasma membrane is made up of a variety of proteins in a lipid framework – the fluid mosaic model. • All cells have the same basic type of outer membrane. http://www.youtube.com/watch?v=Qqsf_UJcfBc

7. Phospholipids • The lipid layer is composed of phospholipids. • Polar phosphate group on one end. • Two nonpolar fatty acid chains on the other.

8. Phospholipid Bilayer • When lots of phospholipids are placed in water, they form a bilayer with fatty acid tails pointing in together – away from water. • Note that the layer is double – no fatty acid tails in contact with water. • Polar molecules can’t pass through nonpolar area without assistance.

10. Membrane Proteins • Proteins float in the lipid bilayer and provide channels that will allow certain molecules to pass through.

11. Cell Surface Proteins • Cell surface proteinsproject up from the membrane surface and may have carbohydrates or lipids attached to them. • Identify type of cell. • Binding sites for particular hormones or proteins.

12. Transmembrane Proteins • Transmembrane proteinsspan the entire lipid bilayer providing channels for polar ions and molecules.

13. Prokaryotic Cells • Cytoplasm is not compartmentalized. • Prokaryotesinclude the two kingdoms of bacteria. • Bacteria are the simplest cellular organisms. • Ribosomesfor protein construction are present. They are not organelles – no membrane.

14. Prokaryotic Cells • Bacteria have a plasma membranelike all cells. • Cell wall(different than that found in plants or fungi) • Capsuleencloses cell wall sometimes.

15. Prokaryotic Cells • Bacteria have diverse array of shapes. • They can adhere in chains and masses, although the cells remain separate.

16. Eukaryotic Cells • Eukaryotesinclude all protists, fungi, plants, and animals. • Much larger than prokaryotic cells – complex internal compartmentalization. • Membrane bound organelles– specialized structures where particular cell processes occur. • Largest organelle is usually the nucleus. • Cells Alive!

19. Cytoskeleton • Cytoskeleton– a dense network of protein fibers which supports the shape of the cell and anchors organelles in place.

20. Cytoskeleton • Three types of protein fibers make up the cytoskeleton. • Long, slender microfilamentsmade of actin. • Hollow tubes called microtubulesmade of tubulin. • Thick ropes called intermediate fibers.

21. Cytoskeleton • Cytoskeleton is important in determining the shape of an animal cell (no cell wall). • Filaments can form and dissolve quickly so the shape of an animal cell can change rapidly.

22. Nucleus • The nucleusis the control center of the cell and genetic library where hereditary information is stored.

23. Nucleus • The nuclear envelopeis actually 2 membranes. • Nuclear poresare depressions where the two membranes pinch together. • The pores contain many embedded proteins that permit proteins and RNA to pass into or out of the nucleus.

24. Nucleus • In bacteria and eukaryotes, all hereditary information is encoded in DNA. • In eukaryotes, the DNA is divided into several segments and is associated with protein, forming chromosomes. • The protein allows the condensing of the chromosomes during cell division. • Uncoiled, threadlike strands of DNA are called chromatin.

25. Nucleus • The darkest region of the nucleus is called the nucleolus. • Ribosomal subunit assembly. • Subunits leave through nuclear pores – ribosomes are assembled in cytoplasm.

26. Ribosomes • Ribosomesread the RNA copy of a gene and uses the information to construct a protein. • Ribosomes are made up of several special forms of RNA – ribosomal RNA (rRNA) bound up with proteins.

27. Endoplasmic Reticulum – The Transportation System • Endoplasmic Reticulum- “Little net within the cytoplasm” - an extensive system of internal membranes. • Sometimes forms membrane enclosed sacs called vesicles.

28. Endoplasmic Reticulum • Carbohydrates and lipids are manufactured on the surface of the ER. • Manufacture of proteins intended for export occurs on ER that is studded with ribosomes and called rough ER. • ER with few ribosomes is called smooth ER.

29. Golgi Complex – The Delivery System • New molecules made on the ER surface are passed through the ER membrane and into flattened stacks of membranes called Golgi bodies. • Function – collection, packaging, and distribution of molecules manufactured in the cell. • Collectively Golgi bodies are called the Golgi complex.

31. Golgi Complex • Proteins & lipids manufactured on ER membranes are transported through the channels of the ER or as vesicles budded off of it and passed into Golgi bodies. • Inside Golgi bodies, carbohydrates may be attached.

32. Golgi Complex • Vesicles pinch off the Golgi and carry molecules to other parts of cell or to the plasma membrane so they can be released outside the cell.

33. Lysosomes – Recycling Centers • Lysosomesarise from the Golgi complex and contain a concentrated mix of powerful enzymes that break down macromolecules. • They act as recycling centers by digesting worn out cell components to make way for newly formed ones while recycling the proteins of the old components.

34. Lysosomes • They also eliminate particles engulfed by the cell. • Enzymes that occur inside a lysosome digest cell parts that are engulfed – if not confined to the lysosome, they would digest the cell!

35. Organelles That Contain DNA • Eukaryotic cells contain some organelles derived from ancient bacteria assimilated by ancestral eukaryotes. • Mitochondria– occur in all but a few eukaryotes. • Chloroplasts– occur only in plants & some protists (algae). • Centrioles– relict organelles with no membrane that occur in all animals & most protists.

36. Mitochondria – Powerhouses of the Cell • Eukaryotic organisms extract energy from food through a complex series of chemical reactions called oxidative metabolismwhich takes place in mitochondria.

37. Mitochondria • Mitochondria have two membranes • Outer membrane is smooth • Inner membrane bent into numerous folds called cristae. • Cristae partition mitochondrion into two compartments, an inner matrixand an outer compartment – the intermembrane space.

38. Mitochondria • Mitochondria still have some of their original genes, contained in a circular, closed molecule of DNA (mtDNA). • This DNA loop contains genes that code for proteins essential to oxidative metabolism.

39. Chloroplasts – Energy Capturing Centers • All photosynthesisin plants and algae takes place within chloroplasts. • Likely derived from an ancient symbiotic bacteria.

40. Chloroplasts • Two membranes, as in mitochondria. • Inner membranes are fused to form stacks of closed vesicles called thylakoids. • Light powered reactions of photosynthesis take place within thylakoids. • Stacks of thylakoids are called grana. • Interior fluid is called the stroma.

41. Chloroplasts • Like mitochondria, chloroplasts contain a circular DNA molecule containing genes that code for proteins essential to the process of photosynthesis.

42. Centrioles • Centriolesassemble microtubules from tubulin subunits in animals and most protists.

43. Centrioles • Centrioles occur in pairs in the cytoplasm. • Often at right angles • Usually near nuclear envelope • Cilia and flagella are anchored by a type of centriole called a basal body.

44. Centrioles • Centrioles lack a membrane, but contain a circular DNA molecule involved in the production of structural proteins. • They resemble a type of bacteria. • May have originated as symbiotic bacteria.

45. Cell Movement • Cell motion is tied to movement of actin filaments, microtubules, or both. • Actin filaments form and dissolve quickly.

46. Cell Movement - Crawling • The arrangement of actin filaments in the cell cytoplasm allow a cell to crawl. • Motion essential to inflammation, clotting, wound healing, and the spread of cancer. • White blood cells move this way. • Produced in bone marrow, released in circulatory system, they crawl out of capillary into tissue to destroy pathogens.

47. Cell Movement • During animal cell reproduction, chromosomes move to opposite sides of a dividing cell because they are attached to shortening microtubules. • Cells pinch in two because the belt of actin filaments contracts. • Also essential for muscle contraction.

48. Flagella • Flagellaare long, threadlike organelles protruding from the cell surface. • Each flagellum is anchored at a basal bodyand consists of 9 microtubule pairs surrounding 2 central microtubules (9+2 arrangement). • 9+2 arrangement is fundamental feature of eukaryotes. • Examples: human sperm cell, many single celled organisms - used for locomotion.

50. Cilia • When flagella are very numerous and organized in dense rows they are called cilia. • Cilia have the same structure as flagella, but are usually short. • Examples: lining of human trachea to move dust and mucus out of the respiratory tract to the throat, protists such as the Paramecium.