Chapter 6 A Tour of the Cell

1. Chapter 6A Tour of the Cell

2. How We Study Cells Microscopes opened up the world of cells Characteristics of Microscopes • magnification: ability to make an image larger than actual size • resolution: power to show details clearly while enlarged (if poor, objects seem fuzzy) • constrast: accentuates different parts of the sample

3. Types of Microscopes • compound light - light passes through one or more lenses - object must be sliced thinly enough to be transparent - upper limitation is 2000X or 0.5 microns (um) in diameter - resolution limitation: 0.2 microns

4. II. Electron Microscopes (1950’s) - limited by physical characteristics of light - can magnify an image up to 200,000 X - beams of electrons produces enlarged image - resolution limitation: 0.002 nm across object

5. Types of Electron Microscopes • transmission electron microscope (TEM) - used to study internal structures - transmits a beam of electrons through very thinly sliced specimen stained with heavy metals - change density of cellular structures and electron transmission - dead specimens - 200,000 X magnification - black and white only Plant Cell

6. scanning electron microscope (SEM) - used to study surface structures - surface covered with thin film of gold - beam excites electrons on surface - produces three dimensional images - 100,000 X mag. - dead specimens only

7. Isolating organelles • Cell fractionation - take apart cells, separate major organelles • Ultracentrifuge - applies force 1 million times the force of gravity to separate further the cell organelles with the most dense at the bottom

8. CELL THEORY • all living things are composed of cells • cells are basic units of structure and function 3. all cells come from pre- existing cells

9. Activities of Life • Most everything you think of a whole organism needing to do, must be done at the cellular level… • reproduction • growth & development • energy utilization • response to the environment • homeostasis

10. Common features of all cells - plasma membrane (cell membrane) - cytosol: semi-fluid substance, holds cellular structures - cytoplasm: cystsol + organelles - cytoskeleton: microscopic protein fibers that keep cells shape - ribosomes: make proteins - DNA: controls all cell activities

11. Prokaryote vs Eukaryote

12. Cell Size - most cells are 5-50 microns surface area ratio (limits size of cells) inside of cell grows faster: cubed (V = L x W x H) outside of cell grows slower: squared (A = L x W)

13. Relationship of Surface Area to Volume

14. Surface Area Example • Cells must be small to maintain a large surface area to volume ratio • Large S.A. allows  rates of chemical exchange between cell and environment Small Intestine: highly folded surface to increase absorption of nutrients • Villi: finger-like projections on small intestine wall • Microvilli: projections on each cell

15. Surface Area ExampleRoot hairs increase surface area for water and mineral absorption

16. Limits to Cell Size • Metabolic requirements set uper limit of size • In large cell, cannot move material in and out fast enough to support life

17. How to get Bigger • Become multi-cellular

18. - most spherical or cuboidal - different shapes reflect function dermal epidermal cells white blood cells goblet cell red blood cells nerve cell Cell Shape

19. Eukaryotic CellsAnimal Plant Cytoplasmic channels- Connnect adjacent Cell’s cytoplasm

20. Cell Structure Main components of eukaryotic cells • cell membrane (outer boundary) • nucleus (control center) • cytoplasm (material between nucleus and membrane)

21. Nucleus - control center of cell: directs all cell activities - contains DNA - continuous with rough ER - site of DNA and RNA synthesis - located in center of most cells

22. Structure: - nuclear matrix - protein skeleton helps maintain nucleus shape - nuclear envelope (double membrane) - contains chromatin: combination of strands of DNA and protein - nuclear pores: control substance movement - nucleoplasm: dense, protein rich - nucleolus: region that forms ribosomal subunits

23. Cytosol(between membrane and nucleus) - Cytoplasm = cytosol + organelles • gel like material between • contains water, salts, organic molecules • in constant motion (cytoplasmic streaming) • holds organelles animation amoeba animation

24. Organelles Organelle: tiny structure that performs special functions in the cell to maintain life

25. Mitochondria • powerhouse of cell (cell respiration) • provides energy for cell in form of ATP • membrane bound • double membrane: • most numerous in cells which use a lot of energy (muscle) • self replicating, contain their own DNA - cristae: folds of inner membrane greatly enlarge surface area of inner membrane (more area for chemical reactions of respiration) - matrix: fluid filled inner compartment

26. Ribosomes • spherical structures which make proteins • not surrounded by membrane • composed of protein and rRNA • site of protein synthesis • free ribosomes: float in cytosol- make proteins used within cell • bound ribosomes: attached to rough ER- make proteins for export from cell (secretion)

27. Rough ER - ribosomes stuck to membrane surface - package proteins for secretion and inserted into ER - can be stored or exported to smooth ER - prominent in cells that make a lot of protein Smooth ER - no ribosomes - also stores and acts as an intercellular highway for proteins and enzymes involved in: - synthesis of steroids in gland - cell regulation of Ca levels in muscle - cells break down toxic substances in liver cells Endoplasmic reticulum: (ER)intercellular highwaycomplex membrane system of folded sacs and tunnels regulates protein traffic and performs metabolic functions

28. Golgi Apparatus • flattened system of membranes and sacs piles on each other (like pancakes) • very close to ER • processes, packages, and secretes proteins for transport (o other parts of cell (vesicles) and produce lysosomes • Cis face: receives vesicles • Trans face: ships vesicles animation

29. Steps of Protein Production and Transport • ribosomes make proteins on the rough ER- packaged into vesicles • vesicles transport the newly made proteins from the rough to the Golgi apparatus • in Golgi, proteins are processed and then packaged into NEW vesicles • vesicles move thru Golgi to cell membrane and release contents outside cell animation 2

30. Lysosomes • small round vesicles that contain digestive hydrolytic enzymes • formed from Golgi Apparatus • digest and remove waste from cell (old organelles, byproducts, bact., viruses) animation

31. Vacuoles • Storage of materials (food, water, minerals, pigments, poisons) • Membrane bound • Ex: food vacuoles, contractile vacuoles

32. Peroxisomes • contain different oxidative enzymes than lysosomes • break down toxic substances into H2O2 (remove H from substances and transfer them to O2) then converts H2O2 to H2O - detox alcohol and drugs - break down fatty acids • formed from proteins in cytosol, not Golgi • Glyoxysomes (fat tissues of plant seeds) FA  sugar

33. Cytoskeleton (cell framework) • maintains shape and size of cell • composed of network of long protein strands located in cytosol • provides movement for organelles within cytosol • regulate biochemical activities

34. Cytoskeleton Structure • Intermediate Filaments (medium size fibers) - protein fibers coiled into cables - maintain shape of cell - permanent fixtures - anchor nucleus and organelles

35. Cytoskeleton Structure B. Microtubules (largest fibers) - long hollow coiled protein tubes (tubulin) - maintain shape and support cells - internal cell highways – move organelles thru cell - form centrioles, spindles (cell division) - motility (cilia and flagella)

36. flagella: long whip-like structures used for movement (motility) • cilia: short numerous hair like projections - movement - transport of substances across cell - signal receiving antenna for ex: ear drum: transmits sound waves respiratory tract: moves mucus etc. Motility requires interaction Basal body- anchors of cytoskeleton fibers with cilia/flagella to cell motor proteins.

37. Internal Organization 9 + 2 Arrangement dynein animation respiratory system animation

38. Centrosomes: region near nucleus • Microtubule organizing center • Contains centrioles • Used in cell division • Not found in plants or fungi • 9 + 0 arrangement

39. Cytoskeleton Structure C. Microfilaments (smallest fibers) - two strands fine protein (actin) intertwined - used in cytoplasmic streaming, muscle contraction, ameboid movement - smallest strands of cytoskeleton cytoplasmic streaming

40. Extracellular Matrix (ECM) • Outside plasma membrane • Composed of glycoproteins (collagen/ proteoglycans) • Strengthens tissues and transmits external signals to cell • Fibronectins/integrins: attach cells to ECM

41. Intercellular Junctions (Animal Cells) • Tight junctions: 2 cells are fused to form watertight seal • Desmosomes: “rivets” that fasten cells into strong sheets • Gap junctions: channels through which ions, sugar, small molecules can pass

42. Intercellular Junctions (Plant Cells) Plasmodesmata • Channels in plant cell walls that attach plasma nmembranes of bordering cells connect • Water, solutes, some proteins, RNA move through channels

43. Contain the same organelles as animal cells plus the following: 1. cell walls 2. vacuoles 3. plastids Plant Cells

44. Plant Cell wall • rigid covering of plant cells, algae, and some bacteria • composed of long chains of cellulose embedded in hardened lignin and pectin • very porous (O, H2O, CO2 easily pass through) • function: support & protection

45. - middle lamella laid first, formed from the cell plate during cytokenesis pectin: gluey substance holds cells together - primary cell wall forms next, expanded inside the middle lamella cellulose: structure and support - secondary wall constructed between the plant cell and primary wall after a maximum size has been reached and stops growing lignin: very stiff and hard, in woody plants in bark structure and support Structure

46. PlastidsConvert solar energy into chemical energy to be stored. 3 types (arise from proplastids) 1. chloroplasts- chlorophyll (green pigment) used in photosynthesis • chromoplasts- synthesize and store red, orange, and yellow pigments (give plants unusual colors) • leucoplasts- store starches, proteins, and lipids colorless