CELL STRUCTURES INVOLVED IN MANUFACTURING AND BREAKDOWN

1. CELL STRUCTURES INVOLVED IN MANUFACTURING AND BREAKDOWN

2. The Endomembrane System • This term refers to the organelles that are connected together by phospholipid membranes. • Prokaryotes don’t have an endomembrane system • The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, vacuoles, and the plasma membrane

4. Properties Transport system for moving molecules through interior of the cell. Lipid bi-layer Composition with proteins attached to either side or transversing them. Divides cell into organelles.

5. separates living cell from nonliving surroundings • thin barrier = 8nm thick • Controls traffic in & out of the cell • selectively permeable • allows some substances to cross more easily than others hydrophobic vs hydrophilic • Made of phospholipids, proteins & other macromolecules Cell Membrane

6. Phospholipids • Fatty acid tails • hydrophobic • Phosphate group head • hydrophilic • Arranged as a bi layer Phosphate Fatty acid

7. Phospholipidbilayer Polar hydrophilic heads Nonpolar hydrophobic tails Polar hydrophilic heads

8. Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Glycoprotein Glycolipid Phospholipids Trans membrane proteins Cholesterol Peripheral protein Filaments ofcytoskeleton Cytoplasm

9. Membrane fat composition • Fat composition affects flexibility • membrane must be fluid & flexible • % unsaturated fatty acids in phospholipidskeep membrane less viscous • cold-adapted organisms, like winter wheatincrease % in autumn • Cholesterol in membrane

10. Membrane Proteins • Proteins determine membrane’s specific functions • Peripheral proteins • loosely bound to surface of membrane • cell surface identity marker (antigens) • Integral proteins • penetrate lipid bi layer, usually across whole membrane • Trans membrane protein • Transport proteins • Channels, Permeases (pumps)

11. Examples Porin monomer H+ Retinal chromophore b-pleated sheets NH2 Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH Cytoplasm H+ Water Channels in Bacteria Proton pump channel in photosynthetic acteria Function through conformational change

12. Functions of Membrane Proteins Outside Plasma membrane Inside Enzyme Activity Cell surface Receptor Transporter Cell surface Identity marker Cell Adhesion Attachment to Cytoskeleton

13. Membrane carbohydrates • Play a key role in cell-cell recognition • important in organ & tissue development • basis for rejection of foreign cells by immune system

14. Movement across the Cell Membrane

15. Getting through cell membrane • Passive Transport • Simple diffusion • diffusion of non polar, hydrophobic molecules • lipids • high  low concentration gradient • Facilitated transport • diffusion of polar, hydrophilic molecules • through a protein channel • high  low concentration gradient • Active transport • diffusion against concentration gradient • low  high • uses a protein pump • requires ATP ATP

16. Getting through cell membrane ATP

17. Why an Endomembrane System? • Membranes provide compartmentalization, which allows different places in the cell to have different environments. • With this arrangement, the cell can “build” in some areas, “break down” in others, and reserve other areas for storage or other functions.

18. Let’s Follow a Protein… From the start of its existence through a few possible paths in the endomembrane system.

19. Protein structure is determined in the cell’s DNA, which is in the NUCLEUS. • The nucleus controls the cell’s activities and is responsible for inheritance • –Inside is a complex of proteins and DNA called chromatin, which makes up the cell’s chromosomes • –When it’s time to make a protein, the appropriate DNA is read and converted into RNA (transctiption) within the nucleus.

20. Once a chain of RNA gets made, it exits the nucleus via pores in the nuclear envelope. • The nuclear envelope is a double membrane with pores that allow material to flow in and out of the nucleus • –It is attached to a network of cellular membranes called the endoplasmic reticulum.

21. Two membranes of nuclear envelope Nucleus Nucleolus Chromatin Pore Endoplasmic reticulum Ribosomes See where the pores are? See how the nuclear envelope hooks up to the ER like a big maze?

22. Ribosomes make proteins for use in the cell and export • Ribosomes are involved in the cell’s protein synthesis • –Ribosomes are synthesized in the nucleolus, which is found in the nucleus • –Cells that must synthesize large amounts of protein have a large number of ribosomes Can you name a few cells that would have a lot of ribosomes?

23. Some ribosomes are free ; others are bound • –Free ribosomes are hanging out in the cytoplasm • –Bound ribosomes are attached to the endoplasmic reticulum (ER) which is connected with the nuclear envelope • Ribosomes are NOT made of membranes! • –They are made of protein and RNA. • –They are associated with the endomembrane system.

24. Cytoplasm Ribosomes ER Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Diagram of a ribosome TEM showing ER and ribosomes Small subunit Diagram of a ribosome

25. Many cell organelles are connected through the Endomembrane system • Some components of the endomembrane system communicate with others via the formation and transfer of small membrane “balloons” called vesicles • –One important result of communication is the synthesis, storage, and export of molecules

26. Proteins get created in The endoplasmic reticulum – A biosynthetic factory • There are two kinds of endoplasmic reticulum • smooth and rough • Smooth ER has no attached ribosomes • Rough ER is “studded” with attached ribosomes • –They differ in structure and function, but they are connected

27. Nuclear envelope Ribosomes Smooth ER Rough ER

28. The endoplasmic reticulum is a Bio-factory • Smooth ER is involved in a bunch of diverse metabolic processes • –For example, enzymes produced by the smooth ER are involved in synthesizing lipids, oils, phospholipids, and steroids. ROUGH ER USES LIPIDS FROM THE SMOOTH ER TO BUILD MEMBRANES. • Rough ER makes additional membrane for itself • It also makes all proteins destined for secretion (export) • –Once proteins are synthesized, they are transported in vesicles to other parts of the Endomembrane system.

29. 4 Transport vesicle buds off Transport vesicle With secretory Protein inside Ribosome making protein 3 1 Sugar chain added to a protein (glycosylation) 2 Glycoprotein Rough ER Polypeptide

30. Next Stop for our vesicle with protein inside: THE GOLGI.

31. The Golgi apparatus finishes, sorts, and ships cell products • The Golgi apparatus alongside the ER by modifying products of the ER • –Products travel in transport vesicles from the ER to the Golgi apparatus • –One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock • –Products are modified as they go from one side of the Golgi apparatus to the other. • –After going through the Golgi, the proteins (or other stuff) is shipped out in a new set of vesicles.

32. Golgi apparatus “Receiving” side of Golgi apparatus Golgi apparatus Transport vesicle from ER New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus

33. Where are the Proteins going?

34. If the proteins are digestive enzymes, they may go to LYSOSOMES. • A lysosome is a membranous sac containing digestive enzymes • –The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing • –The membrane serves to safely isolate these potent enzymes from the rest of the cell • –If it weren’t there, the cell would digest itself.

35. Lysosomes are digestive compartments within a cell • One of the several functions of lysosomes is to remove or recycle damaged parts of a cell • –The damaged organelle is first enclosed in a membrane vesicle • –Then a lysosome fuses with the vesicle, dismantling its contents and breaking down the damaged organelle

36. Digestive enzymes Lysosome Plasma membrane

37. Digestive enzymes Lysosome Plasma membrane Food vacuole

38. Digestive enzymes Lysosome Plasma membrane Food vacuole

39. Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole

40. Lysosome Vesicle containing damaged mitochondrion

41. Lysosome Vesicle containing damaged mitochondrion

42. Lysosome Digestion Vesicle containing damaged mitochondrion

43. Some proteins go to assist in the function of VACUOLES, which do maintenance jobs in the cell • Vacuoles are membranous sacs that are found in a variety of cells and possess an assortment of functions • –Examples: central vacuole in plants with hydrolytic (water-breaking) functions, • –pigment vacuoles in plants to provide color to flowers, and • –contractile vacuoles in some protists to expel water from the cell

44. Nucleus Contractile vacuoles Chloroplast Nucleus

45. Nucleus Nuclear membrane Rough ER Transport vesicle Smooth ER Transport vesicle Golgi apparatus Lysosome Vacuole Plasma membrane

46. Proteins can be exported out of the cell by EXOCYTOSIS • A cell uses two mechanisms for moving large molecules across membranes • –Exocytosis is used to export bulky molecules, such as proteins or polysaccharides • –Endocytosis is used to import substances useful to the livelihood of the cell • In both cases, material to be transported is packaged within a vesicle that fuses with the plasma membrane

47. Exocytosis and endocytosis transport large molecules across membranes • There are three kinds of endocytosis • –Phagocytosis is engulfment of a particle by wrapping cell membrane around it, forming a vacuole • –Pinocytosis is the same thing except that fluids are taken into small vesicles • –Receptor-mediated endocytosis is where receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle

48. Phagocytosis Phagocytosis Food being ingested CYTOPLASM EXTRACELLULAR FLUID Pseudopodium “Food” or other particle Food vacuole

49. Pinocytosis Pinocytosis Plasma membrane Vesicle Plasma membrane

50. Receptor-mediated endocytosis Plasma membrane Coat protein Receptors Coated vesicle Coated pit Coated pit Coated pit Specific molecule Material bound to receptor proteins