Chapter 6: A Tour of the Cell

1. Chapter 6:A Tour of the Cell

2. Technology to study cells

3. light microscopes – pass visible light through specimen and lenses

4. magnification – ratio of image size to actual size

5. resolution – clarity of image; minimum distance between two distinguishable points

6. electron microscopes – focus beams of electrons through or onto specimen– resolution 100x better than light microscopes

7. scanning electron microscope (SEM) – studying external structures

8. transmission electron microscope (TEM) – studying internal structures

9. Cell Fractionation – take cells apart and isolate organelles

10. Uses a centrifuge; spin test tubes very fast, separates cell components by size and density

12. Surface are to volume ratio:– limits cell size because as cells get bigger, their volume increases faster than their surface area

13. – surface area important for transport of substances through the membrane microvilli in intestine increases surface area for absorption

14. All cells have: • cytosol– semifluid substance containing organelles and dissolved nutrients • plasma membrane – selective barrier • chromosomes – packaged DNA • ribosomes – make proteins

15. Prokaryotic Cells

16. Prokaryotic Cells • smaller than eukaryotic cells • no membrane-bound organelles • no nucleus (nucleoid – region containing prokaryotic DNA) • small ribosomes • circular DNA • plasmids

17. Bacterial conjugation using pili

19. Eukaryotic Cells

20. nucleus – contains DNA • nuclear envelope – double membrane that encloses nucleus • nuclear pores – holes in the nuclear envelope. Allow passage of large molecules.

21. chromosomes – made of chromatin, a complex of proteins and DNA • nucleolus – rRNA synthesized, ribosomes assembled

22. ribosomes – synthesize proteins • made of ribosomal RNA (rRNA) and protein • cells that synthesize many proteins have many ribosomes • either free-floating in cytosol (make proteins for cell’s use) or bound to rough ER (make proteins for secretion)

23. endomembrane system • more than half the total membrane of the cell • consists of membranous tubules and sacs (cisternae) • lumen – interior cavity of cisternae

25. smooth endoplasmic reticulum (ER) • no bound ribosomes • synthesizes lipids (phospholipids, oils, steroids) • stores calcium ions, especially in muscles (important to muscle contraction)

26. Enzymes detoxify drugs and poisons, especially in the liver • add hydroxyl groups to drugs; makes them more soluble • drug tolerance due to proliferation of smooth ER in addicts; higher doses required to achieve the same effect

27. rough endoplasmic reticulum (ER) • has bound ribosomes • continuous with nuclear envelope

28. helps in synthesis of secretory proteins (proteins made for secretion), especially glycoproteins – proteins that have carbohydrates on them • adds carbohydrates to glycoproteins, sends them in transportvescicles (sacs of membrane) to Golgi

29. Also the membrane factory of cell; makes new membrane for itself that becomes vescicles; these eventually become part of cell membrane

30. Golgi apparatus – products of ER modified, stored and then shipped • flattened sacs (cisternae) • cis face – receiving side • trans face – shipping side

31. vescicles from ER fuse with cis face and empy contents into lumen of cisternae • products of ER modified in Golgi: – modifies carbohydrates – alters protein structure

32. Golgi makes some macromolecules • products transferred from one cisternae to another, eventually arrive at trans face. • products sorted and “addressed” for where they will go

33. vescicles bud off trans face and carry contents to cell membrane for export or to different parts of the cell

35. Lysosomes – digest • membrane sac of hydrolytic enzymes • digests molecules and worn-out cell parts (autophagy)

36. phagocytosis – food particle engulfed by cell and contained in vescicle– vescicle merges with lysosome and is digested

38. Tay-Sachs disease – lysosomal disorder in humans, allows lipids to accumulate in cells.

39. Tay-Sachs • Lipids accumulate in nervous tissue • Degeneration of mental and physical abilities • Seizures, paralysis • Death before age 4 Cherry-red spot on retina identifies Tay-Sachs

40. Vacuoles • membrane-bound sacs • central vacuole – in plants, storage for nutrients and wastes, water – membrane: tonoplast

41. food vacuoles – formed by phagocytosis • contractile vacuoles – in protists, pump excess water out of cell

42. Mitochondria – make cell energy • change molecular energy to cellular energy; cell respiration

43. double membrane • outer membrane is smooth • Inner membrane has folds called cristae • intermembrane space – between outer and inner membrane • mitochondrial matrix – lumen within the inner membrane

44. Chloroplasts – make carbohydrates • a plastid (other plastids are amyloplasts (store starch in plants) and chromoplasts (contain pigments that color fruit and flowers) • contain pigment chlorophyll

45. double membrane – outer membrane smooth – inner membrane is stacks of sacs called thylakoids • a stack of thylakoids is a granum • fluid between granum and outer membrame is stroma

46. Peroxisomes • sac containing enzymes that transfer hydrogen to oxygen, producing H2O2 • digestion of fats, detoxification of alcohol • not part of endomembrane system (lysosomes are)

47. Cytoskeleton • support, maintain cell shape • cell motility (movement): both movement of whole cell and parts of cell within. • motor proteins – help cytoskeleton accomplish movement

48. Microtubules • hollow tubes of 13 columns of tubulindimers • 25 nm • -tubulin and -tubulin • cell shape (reists compression), cilia and flagella, move chromosomes during cell division, organelle movement

49. Microfilaments (actin filaments) • 2 intertwined strands of actin • 7 nm • cell shape (resist force), muscle contraction, cytoplasmic streaming, pseudopodia in amoeboid movement

50. Intermediate filaments • thick cables of fibrous protein • 8-12 nm • fibrous Keratin protein • cell shape (resist force), anchorage of nucleus and organelles