CHAPTER 4 The Organization of Cells

1. CHAPTER 4The Organization of Cells

2. The Cell: The Basic Unit of Life • All cells come from preexisting cells and have certain processes, molecules, and structures in common. • Surrounded and separated from external environment by a lipid bilayer membrane

3. The Cell: The Basic Unit of Life • Microscopes are needed to visualize most cells • Eggs notable exception • Light or electron microscopes allow observation of greater detail than light microscopes do.

4. Categories of Cells • Eukaryotic • membranous organelles • nucleus, ER, Golgi, vesicles, mitochondria, plastids • cytoskeleton • actin, myosin, tubulin • Prokaryotic • circular chromosome • no membranous organelles

5. Prokaryotic Cell Features • Prokaryotic cell organization is characteristic of the kingdoms Eubacteria and Archaebacteria. Prokaryotic cells lack internal compartments. • All prokaryotes have • plasma membrane • nucleoid region with DNA • cytoplasmic ribosomes • Some prokaryotes have • cell wall • outer membrane and capsule • photosynthetic membranes • mesosomes.

6. Prokaryotic Organelles • Ribosome • Large & small subunits • 3 core molecules of RNA (rRNAs) and ~40 proteins • 23S rRNA + 5S rRNA = 50S large ribosomal subunit • 16S rRNA = 30S small ribosomal subunit • Assembles on mRNA • Associates with tRNAs to decode mRNA and synthesize proteins • 23S rRNA molecule is catalytic component that joins amino acids to for polypeptides

7. Some prokaryotes have rotating flagella for movement. Pili are projections by which prokaryotic cells attach to one another or to environmental surfaces. Prokaryotic Cells

8. The Cell: The Basic Unit of Life • Eukaryotic cell organization is characteristic of the other four kingdoms – animalia, protista, plantae, fungi. • Eukaryotic cells have many membrane-enclosed compartments, including a nucleus containing DNA.

9. Figure 4.7 – Part 1 Animal Eukaryotic Cell figure 04-07a.jpg

10. Figure 4.7 – Part 2 Plant Eukaryotic Cell figure 04-07b.jpg

11. Eukaryotic Organelles - Nucleus • Contains most of the cell’s DNA • Chromatin – DNA bound by proteins • Discrete units - chromosomes • Surrounded by nuclear envelope • Double membrane system • Pores • Outer membrane contiguous with ER • Nucleolus • Subdomain where transcription rRNA and assembly of ribosomes occurs

12. Eukaryotic Organelles - Endomembrane System • The endomembrane system groups together interrelated membranes and compartments. • Coordinated function to produce, process, and transport materials

13. Endoplasmic Reticulum • Contiguous with the outer nuclear membrane • Rough endoplasmic reticulum • Associated with ribosomes synthesize proteins to be transported out of the cell or into other cellular membranes • Smooth endoplasmic reticulum • Not associated with ribosomes • Location of lipids biosynthesis

14. Golgi Apparatus • Modifies proteins to be secreted or incorporated into lysosomes/endosomes • Proteins enter the Golgi in vesicles from the ER • Three subregions of Golgi – cis, medial, trans

15. Golgi, Lysosomes & Endosomes • Lysosomes • Contain hydrolytic enzymes to break down biomolecules into constitutive monomeric units • Endosomes • Bud off from plasma membrane • Contain materials to be degraded or to be incorporated into the cell

16. Mitochondria and Chloroplasts figure 04-14.jpg

17. Energy Processing Organelles • Mitochondria • Enclosed by an outer membrane and an inner membrane • Inner membrane highly convoluted to provide large surface area • Cristae • Contain enzymes that carry out cellular respiration and generate ATP • Chloroplasts • Enclosed by an outer membrane and an inner membrane • 3rd internal membrane system – thylakoid • Contain pigments and enzymes that carry out photosynthesis • Generate ATP, NADPH, & O2 • Synthesize sugars from ATP, NADPH & CO2

18. Organelles that Process Energy • Mitochondria and chloroplasts contain their own DNA and ribosomes and can make most of their own tRNAs and some of their own proteins.

19. Organelles that Process Energy • The endosymbiont theory of the evolutionary origin of mitochondria and chloroplasts • originated when large prokaryotes engulfed, but did not digest, smaller ones. • Mutual benefits permitted symbiotic relationship to evolve into eukaryotic organelles of today. • Mitochondria – eubacterial origin • Chloroplast - cyanobacterium • Chromosome • Circular, intron-less genes • bacterial-like ribosomes • Sensitivity to antibiotics, bacterial size • double membrane

20. Other Membraneous Organelles • Peroxisomes • Glyoxysomes • contain special enzymes and carry out specialized chemical reactions inside the cell. • Vacuoles • a membrane-enclosed compartment of water and dissolved substances. • They take in water and enlarge, providing pressure to stretch the cell wall and structural support for a plant.

21. The Cytoskeleton • The cytoskeleton within the cytoplasm of eukaryotic cells provides shape, strength, and movement. It consists of three major types of protein fibers.

22. The Cytoskeleton – Actin cytoskeleton • Microfilaments consist of two chains of actin units forming a double helix. • Microfilaments strengthen cellular structures and provide movement in animal cell division, cytoplasmic streaming, and pseudopod extension. • They occur as individual, bundled, or networked fibers.

23. The Cytoskeleton • Intermediate filaments are formed of keratins and add strength to cell attachments in multicellular organisms.

24. The Cytoskeleton - Microtubules • Chains of dimers of the protein tubulin, • Cilia and flagella both have a characteristic 9 + 2 pattern of microtubules.

25. The Cytoskeleton - Microtubules • Movements of cilia and flagella are due to binding of the motor protein dynein to microtubules. Microtubules also bind motor proteins that move organelles through the cell. • Centrioles, made up of triplets of microtubules, are involved in the distribution of chromosomes during nuclear division.

26. Extracellular Structures • Materials external to the plasma membrane provide protection, support, and attachment for cells in multicellular systems. • Cell walls of plants consist principally of cellulose. They are pierced by plasmodesmata that join the cytoplasm of adjacent cells • In multicellular animals, the extracellular matrix consists of different proteins many of which are proteoglycans. • Collagen - bone and cartilage • Fibronectin – basal membranes of epithelia • Laminin

27. CHAPTER 5Cellular Membranes

28. Biological membranes consist of lipids, proteins, and carbohydrates. fluid mosaic model describes a phospholipid bilayer in which membrane proteins move laterally within the membrane. Membrane Composition and Structure

29. Figure 5.2 Lipid Bilayer Structure figure 05-02.jpg

30. Membrane Composition and Structure • Membrane Proteins • Integral membrane proteins are inserted into the phospholipid bilayer. • Peripheral proteins attach to its surface by ionic bonds, H-bonds, and/or polar interactions.

31. Membrane Composition and Structure • The two surfaces of a membrane can have different properties due to different phospholipid compositions, exposed domains of integral membrane proteins, and peripheral membrane proteins. • Defined regions (rafts) of a plasma membrane may have different membrane proteins. • Proteins projecting from the external surface of the plasma membrane function in communication & recognition signals between cells.

32. Cell Adhesion • Cells recognize and bind to each other by means of membrane proteins protruding from the cell surface.

33. Cell Adhesion - Categories of Adhesive Junctions • Tight junctions • prevent passage of molecules around cells • define functional regions of the plasma membrane • ZO-1, actin cytoskeleton • Desmosomes • Allow strong adhesion between cells • Desmin, intermediate filaments • Adherins Junctions • Allow strong, but reversible adhesion between cells of the same type • Cadherin, catenins, actin cytoskeleton • Focal Adhesions • Allow temporary attachment to ECM for motility • Integrins, actin cytoskeleton • Gap junctions • provide channels for chemical and electrical communication between cells • Connexins

34. 5.6 – Part 1 figure 05-06a.jpg Tight junction Figure 5.6 – Part 1 Desmosome Adherins junction similar to desmosome

35. 5.6 – Part 2 figure 05-06b.jpg Figure 5.6 – Part 2 Focal adhesions

36. Transmembrane Movement of Substances table 05-01.jpg

37. Passive Processes of Membrane Transport • Two types of passive movement • unaided diffusion through the lipid bilayer, • facilitated diffusion through protein channels, or by means of a carrier protein • Solutes diffuse across a membrane from a region of greater solute concentration to a region of lesser concentration. Equilibrium is when the concentrations are equal • The rate of diffusion of a solute across a membrane is directly proportional to the concentration gradient across the membrane. • For unaided diffusion to occur requires lipid solubility

38. Passive Processes of Membrane Transport • Osmosis • Diffusion of water • Osmosis occurs when the solutes on either side of a membrane can not pass through the membrane • H2O is slightly lipid soluble • H2O passes through membrane toward equilibrium

39. Passive Processes of Membrane Transport • Tonicity • Relative concentrations of two solutions • Hypo – lower [solute] relative to some solution • Hyper – higher [solute] relative to some solution • Iso – equal [solute] relative to some solution • Often tonicity of solution is relative to tonicity of cell • For a cell: • hypotonic solutions - cells tend to take up water • hypertonic solutions – cells tend to lose water • isotonic equal rate of water movement (dynamic equilibrium)

40. 5.8 figure 05-08.jpg Figure 5.8

41. Passive Processes of Membrane Transport • The cell walls of plants and some other organisms prevent cells from bursting under hypotonic conditions. Turgor pressure develops under these conditions and keeps plants upright and stretches the cell wall during cell growth.

42. Passive Processes of Membrane Transport • Channel proteins

43. Passive Processes of Membrane Transport figure 05-10.jpg • Carrier proteins

44. Active Transport • Active transport means that energy is required to move substances across a membrane • Any movement against a concentration gradient will require active transport • Energy sources • ATP • Counter gradient

45. Active Transport • Active transport requires integral membrane proteins • Active transport proteins • uniports, • symports, • antiports

46. Primary Active Transport • Energy from the hydrolysis of ATP • Binding of ATP alters protein configuration allowing binding to substrate on one side of membrane • Hydrolysis of ATP is possible after substrate bound • Hydrolysis of ATP alters configuration of protein to release substrate on opposite side of membrane

47. Secondary Active Transport • Couples the passive movement of one solute down its concentration gradient to the movement of another solute up its concentration gradient. • Energy from ATP is used indirectly to establish the concentration gradient of the counter gradient resulting in movement of the first solute.

48. Endocytosis and Exocytosis • Endocytosis • transports macromolecules, large particles, and small cells into eukaryotic cells by means of engulfment and vesicle formation from the plasma membrane. • Exocytosis • materials in vesicles are secreted from the cell when vesicles fuse with the plasma membrane. • In receptor-mediated endocytosis, a specific membrane receptor binds to a particular macromolecule

49. Other Membranes Functions • Sites for recognition and processing of extracellular signals, • Sites for energy transformations, • Sites for organizing chemical reactions.

50. Membranes Are Dynamic • Although not all cellular membranes are identical, ordered modifications in membrane composition accompany the conversions of one type of membrane into another type.