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1. 3 Cells: The Living Units

2. Nuclear envelope Chromatin Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome Figure 3.2

3. Membranous Mitochondria Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Nonmembranous Cytoskeleton Centrioles Ribosomes Cytoplasmic Organelles

4. Outer mitochondrial membrane Ribosome Mitochondrial DNA Inner mitochondrial membrane (a) Cristae Matrix (c) Enzymes (b) Figure 3.17

5. Mitochondria • Double-membrane structure with shelflike cristae • Provide most of cell’s ATP via aerobic cellular respiration • Contain their own DNA and RNA

6. Ribosomes • Granules containing protein and rRNA • Site of protein synthesis

7. Nuclear envelope Chromatin Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome Figure 3.2

8. Smooth ER Nuclear envelope Rough ER Ribosomes (a) Diagrammatic view of smooth and rough ER Figure 3.18a

9. Endoplasmic Reticulum (ER) • Interconnected tubes and parallel membranes enclosing cisternae • Continuous with nuclear membrane • Two varieties: • Rough ER • Smooth ER

10. Rough ER • External surface studded with ribosomes • Manufactures all secreted proteins • Synthesizes membrane integral proteins and phospholipids

11. Smooth ER Nuclear envelope Rough ER Ribosomes (a) Diagrammatic view of smooth and rough ER Figure 3.18a

12. Smooth ER Functions: • In the liver—lipid and cholesterol metabolism, breakdown of glycogen, and, along with kidneys, detoxification of drugs, pesticides, and carcinogens • Synthesis of steroid-based hormones • In intestinal cells—absorption, synthesis, and transport of fats • In skeletal and cardiac muscle—storage and release of calcium

13. 1 Protein- containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. Rough ER Phagosome ER membrane Plasma mem- brane Proteins in cisterna Pathway C: Lysosome containing acid hydrolase enzymes 2 Proteins are modified within the Golgi compartments. Vesicle becomes lysosome 3 Proteins are then packaged within different vesicle types, depending on their ultimate destination. Secretory vesicle Pathway B: Vesicle membrane to be incorporated into plasma membrane Golgi apparatus Pathway A: Vesicle contents destined for exocytosis Secretion by exocytosis Extracellular fluid Figure 3.20

14. Golgi Apparatus • Modifies, concentrates, and packages proteins and lipids • Transport vessels from ER fuse with near face of Golgi apparatus • Proteins then pass through Golgi apparatus to far face and leave in secretory vesicles to particular parts of cell

15. Nuclear envelope Nucleus Smooth ER Rough ER Vesicle Golgi apparatus Plasma membrane Transport vesicle Lysosome Figure 3.22

16. Lysosomes • Digest ingested bacteria, viruses, and toxins • Degrade nonfunctional organelles • Break down bone to release Ca2+ • Destroy cells in injured or nonuseful tissue (autolysis)

17. Endomembrane System • Overall function • Produce, store, and export biological molecules • Degrade potentially harmful substances

18. Nuclear envelope Nucleus Smooth ER Rough ER Vesicle Golgi apparatus Plasma membrane Transport vesicle Lysosome Figure 3.22

19. Peroxisomes • Membranous sacs containing powerful oxidases and catalases • Detoxify harmful or toxic substances • Neutralize dangerous free radicals (highly reactive chemicals with unpaired electrons)

20. Nuclear envelope Chromatin Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome Figure 3.2

21. Cytoskeleton • Elaborate series of rods throughout cytosol • Microtubules • Microfilaments • Intermediate filaments

22. (a) Microfilaments Strands made of spherical protein subunits called actins Actin subunit 7 nm Microfilaments form the blue network surrounding the pink nucleus in this photo. Figure 3.23a

23. Microfilaments • Dynamic actin strands attached to cytoplasmic side of plasma membrane • Involved in cell motility, change in shape, endocytosis and exocytosis

24. (c) Microtubules Hollow tubes of spherical protein subunits called tubulins Tubulin subunits 25 nm Microtubules appear as gold networks surrounding the cells’ pink nuclei in this photo. Figure 3.23c

25. Microtubules • Dynamic hollow tubes • Most radiate from centrosome • Determine overall shape of cell and distribution of organelles

26. Motor Molecules • Protein complexes that function in motility (e.g., movement of organelles and contraction) • Powered by ATP

27. Vesicle ATP Receptor for motor molecule Motor molecule (ATP powered) Microtubule of cytoskeleton (a) Motor molecules can attach to receptors onvesicles or organelles, and “walk” the organellesalong the microtubules of the cytoskeleton. ATP Motor molecule (ATP powered) Cytoskeletal elements (microtubules or microfilaments) (b) In some types of cell motility, motor molecules attached to oneelement of the cytoskeleton can cause it to slide over anotherelement, as in muscle contraction and cilia movement. Figure 3.24

28. Centrosome • “Cell center” near nucleus • Generates microtubules; organizes mitotic spindle • Contains centrioles: Small tube formed by microtubules

29. Centrosome matrix Centrioles (a) Microtubules Figure 3.25a

30. Cellular Extensions • Cilia and flagella • Whiplike, motile extensions on surfaces of certain cells • Contain microtubules and motor molecules • Cilia move substances across cell surfaces • Longer flagella propel whole cells (tail of sperm) PLAY Animation: Cilia and Flagella

31. Outer microtubule doublet Dynein arms The doublets also have attached motor proteins, the dynein arms. Central microtubule Cross-linking proteins inside outer doublets The outer microtubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes. Radial spoke TEM A cross section through the cilium shows the “9 + 2” arrangement of microtubules. Microtubules Cross-linking proteins inside outer doublets Radial spoke Plasma membrane Plasma membrane Cilium Triplet Basal body TEM TEM Basal body (centriole) A longitudinal section of a cilium shows microtubules running the length of the structure. A cross section through the basal body. The nine outer doublets of a cilium extend into a basal body where each doublet joins another microtubule to form a ring of nine triplets. Figure 3.26

32. Power, or propulsive, stroke Recovery stroke, when cilium is returning to its initial position 1 2 3 4 5 6 7 (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity ofmany cilia acting together propels mucusacross cell surfaces. Figure 3.27

33. Cellular Extensions • Microvilli • Fingerlike extensions of plasma membrane • Increase surface area for absorption

34. Microvillus Actin filaments Terminal web Figure 3.28

35. Nucleus • Genetic library with blueprints for nearly all cellular proteins • Responds to signals and dictates kinds and amounts of proteins to be synthesized

36. Nuclear pores Nuclear envelope Nucleus Chromatin (condensed) Nucleolus Cisternae of rough ER (a) Figure 3.29a

37. Nuclear Envelope • Double-membrane barrier containing pores • Outer layer is continuous with rough ER and has ribosomes

38. Nuclear pores Nuclear envelope Nucleus Chromatin (condensed) Nucleolus Cisternae of rough ER (a) Figure 3.29a

39. Nucleoli • Dark-staining spherical bodies within nucleus • Involved in rRNA synthesis and ribosome subunit assembly

40. Chromatin • Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%) • Arranged in fundamental units called nucleosomes • Condense into barlike bodies called chromosomes when the cell starts to divide

41. 1 DNA double helix (2-nm diameter) Histones 2 Chromatin (“beads on a string”) structure with nucleosomes Linker DNA Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix) (a) 3 Tight helical fiber (30-nm diameter) 4 Looped domain structure (300-nm diameter) 5 Chromatid (700-nm diameter) Metaphase chromosome (at midpoint of cell division) (b) Figure 3.30

42. Protein Synthesis • DNA is the master blueprint for protein synthesis • Gene: Segment of DNA with blueprint for one polypeptide • Triplets of nucleotide bases form genetic library • Each triplet specifies coding for an amino acid PLAY Animation: DNA and RNA

43. Nuclear envelope DNA Transcription RNA Processing Pre-mRNA mRNA Nuclear pores Ribosome Translation Polypeptide Figure 3.34

44. Roles of the Three Main Types of RNA • Messenger RNA (mRNA) • Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm

45. Roles of the Three Main Types of RNA • Ribosomal RNA (rRNA) • A structural component of ribosomes that, along with tRNA, helps translate message from mRNA

46. Roles of the Three Main Types of RNA • Transfer RNAs (tRNAs) • Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis

47. Transcription • Transfers DNA gene base sequence to a complementary base sequence of an mRNA

48. Coding strand of DNA Rewindingof DNA Unwindingof DNA RNA nucleotides Direction oftranscription Templatestrand DNA-RNA hybrid region mRNA RNApolymerase The DNA-RNA hybrid: At any given moment, 16–18 base pairsof DNA are unwound and the most recently made RNA is stillbound to DNA. This small region is called the DNA-RNA hybrid. Figure 3.35 step 4

49. Translation • Converts base sequence of nucleic acids into the amino acid sequence of proteins • Involves mRNAs, tRNAs, and rRNAs

50. Genetic Code • Each three-base sequence on DNA is represented by a codon • Codon—complementary three-base sequence on mRNA