Understanding Cells: A Comprehensive Overview of Cell Structure and Function

1. Chapter 6 A Tour of the Cell

2. Overview: The Importance of Cells • All organisms are made of cells • The cell is the simplest collection of matter that can live

3. 10 µm • Cell structure is correlated to cellular function Figure 6.1

4. Concept 6.1: To study cells, biologists use microscopes and the tools of biochemistry

5. 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Light microscope Chicken egg 1 cm Frog egg 1 mm 100 µm Most plant and Animal cells Electron microscope 10 µ m NucleusMost bacteriaMitochondrion 1 µ m Electron microscope Smallest bacteria 100 nm Viruses 10 nm Ribosomes Proteins Lipids 1 nm Small molecules Figure 6.2 Atoms 0.1 nm • Different types of microscopes • Can be used to visualize different sized cellular structures Unaided eye Measurements 1 centimeter (cm) = 102 meter (m) = 0.4 inch 1 millimeter (mm) = 10–3 m 1 micrometer (µm) = 10–3 mm = 10–6 m 1 nanometer (nm) = 10–3 mm = 10–9 m

6. Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions • Two types of cells make up every organism • Prokaryotic • Eukaryotic

7. Comparing Prokaryotic and Eukaryotic Cells • All cells have several basic features in common • They are bounded by a plasma membrane

8. They contain a semifluid substance called the cytosol • They contain chromosomes • They all have ribosomes

9. Prokaryotic cells • Do not contain a nucleus • Have their DNA located in a region called the nucleoid

10. Pili: attachment structures on the surface of some prokaryotes Nucleoid: region where the cell’s DNA is located (not enclosed by a membrane) Ribosomes: organelles that synthesize proteins Plasma membrane: membrane enclosing the cytoplasm Cell wall: rigid structure outside the plasma membrane Capsule: jelly-like outer coating of many prokaryotes Bacterialchromosome 0.5 µm Flagella: locomotion organelles of some bacteria (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) Figure 6.6 A, B

11. Eukaryotic cells • Contain a true nucleus, bounded by a membranous nuclear envelope • Are generally quite a bit bigger than prokaryotic cells

12. The logistics of carrying out cellular metabolism sets limits on the size of cells

13. Surface area increases while total volume remains constant 5 1 1 Total surface area (height  width  number of sides  number of boxes) 6 150 750 Total volume (height  width  length  number of boxes) 125 125 1 Surface-to-volume ratio (surface area  volume) 6 1.2 6 • A smaller cell • Has a higher surface to volume ratio, which facilitates the exchange of materials into and out of the cell Figure 6.7

14. Outside of cell Hydrophilic region TEM of a plasma membrane. The plasma membrane, here in a red blood cell, appears as a pair of dark bands separated by a light band. (a) Inside of cell 0.1 µm Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane • The plasma membrane • Functions as a selective barrier • Allows sufficient passage of nutrients and waste Carbohydrate side chain Figure 6.8 A, B

15. A Panoramic View of the Eukaryotic Cell • Eukaryotic cells • Have extensive and elaborately arranged internal membranes, which form organelles

16. Plant and animal cells • Have most of the same organelles

17. Nuclear envelope ENDOPLASMIC RETICULUM (ER) NUCLEUS Nucleolus Rough ER Smooth ER Chromatin Flagelium Plasma membrane Centrosome CYTOSKELETON Microfilaments Intermediate filaments Ribosomes Microtubules Microvilli Golgi apparatus Peroxisome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Lysosome Mitochondrion • A animal cell Figure 6.9

18. Nuclear envelope Rough endoplasmic reticulum Nucleolus NUCLEUS Chromatin Smooth endoplasmic reticulum Centrosome Ribosomes (small brwon dots) Central vacuole Tonoplast Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell • A plant cell CYTOSKELETON In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Figure 6.9

19. Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes

20. The Nucleus: Genetic Library of the Cell • The nucleus • Contains most of the genes in the eukaryotic cell

21. Nucleus Nucleus 1 µm Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Rough ER Surface of nuclear envelope. 1 µm Ribosome 0.25 µm Close-up of nuclear envelope Nuclear lamina (TEM). Pore complexes (TEM). • The nuclear envelope • Encloses the nucleus, separating its contents from the cytoplasm Figure 6.10

22. Ribosomes: Protein Factories in the Cell • Ribosomes • Are particles made of ribosomal RNA and protein

23. Ribosomes Cytosol Free ribosomes Bound ribosomes Large subunit Small subunit 0.5 µm TEM showing ER and ribosomes Diagram of a ribosome • Carry out protein synthesis ER Endoplasmic reticulum (ER) Figure 6.11

24. Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell • The endomembrane system • Includes many different structures

25. The Endoplasmic Reticulum: Biosynthetic Factory • The endoplasmic reticulum (ER) • Accounts for more than half the total membrane in many eukaryotic cells

26. Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Ribosomes Transitional ER Transport vesicle 200 µm Smooth ER Rough ER • The ER membrane • Is continuous with the nuclear envelope Figure 6.12

27. There are two distinct regions of ER • Smooth ER, which lacks ribosomes • Rough ER, which contains ribosomes

28. Functions of Smooth ER • The smooth ER • Synthesizes lipids • Metabolizes carbohydrates • Stores calcium • Detoxifies poison

29. Functions of Rough ER • The rough ER • Has bound ribosomes • Produces proteins and membranes, which are distributed by transport vesicles

30. The Golgi Apparatus: Shipping and Receiving Center • The Golgi apparatus • Receives many of the transport vesicles produced in the rough ER • Consists of flattened membranous sacs called cisternae

31. Functions of the Golgi apparatus include • Modification of the products of the rough ER • Manufacture of certain macromolecules

32. cis face (“receiving” side of Golgi apparatus) 5 3 4 6 2 1 Vesicles coalesce to form new cis Golgi cisternae Vesicles move from ER to Golgi 0.1 0 µm Vesicles also transport certain proteins back to ER Cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion trans face (“shipping” side of Golgi apparatus) Vesicles transport specific proteins backward to newer Golgi cisternae • Functions of the Golgi apparatus Golgi apparatus Figure 6.13 TEM of Golgi apparatus

33. Lysosomes: Digestive Compartments • A lysosome • Is a membranous sac of hydrolytic enzymes • Can digest all kinds of macromolecules

34. 1 µm Nucleus Lysosome Hydrolytic enzymes digest food particles Food vacuole fuses with lysosome Lysosome contains active hydrolytic enzymes Digestive enzymes Lysosome Plasma membrane Digestion Food vacuole (a) Phagocytosis: lysosome digesting food • Lysosomes carry out intracellular digestion by • Phagocytosis Figure 6.14 A

35. Lysosome containing two damaged organelles 1 µ m Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion (b) Autophagy: lysosome breaking down damaged organelle • Autophagy Figure 6.14 B

36. Vacuoles: Diverse Maintenance Compartments • A plant or fungal cell • May have one or several vacuoles

37. Food vacuoles • Are formed by phagocytosis • Contractile vacuoles • Pump excess water out of protist cells

38. Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm • Central vacuoles • Are found in plant cells • Hold reserves of important organic compounds and water Figure 6.15

39. The Endomembrane System: A Review • The endomembrane system • Is a complex and dynamic player in the cell’s compartmental organization

40. 1 Nuclear envelope is connected to rough ER, which is also continuous with smooth ER Nucleus Rough ER 2 Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi Smooth ER cis Golgi Nuclear envelop 3 Golgi pinches off transport Vesicles and other vesicles that give rise to lysosomes and Vacuoles Plasma membrane trans Golgi 4 5 6 Lysosome available for fusion with another vesicle for digestion Transport vesicle carries proteins to plasma membrane for secretion Plasma membrane expands by fusion of vesicles; proteins are secreted from cell • Relationships among organelles of the endomembrane system Figure 6.16

41. Concept 6.5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria • Are the sites of cellular respiration • Chloroplasts • Found only in plants, are the sites of photosynthesis

42. Mitochondria: Chemical Energy Conversion • Mitochondria • Are found in nearly all eukaryotic cells

43. Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 µm • Mitochondria are enclosed by two membranes • A smooth outer membrane • An inner membrane folded into cristae Figure 6.17

44. Chloroplasts: Capture of Light Energy • The chloroplast • Is a specialized member of a family of closely related plant organelles called plastids • Contains chlorophyll

45. Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid • Chloroplasts • Are found in leaves and other green organs of plants and in algae Figure 6.18

46. Chloroplast structure includes • Thylakoids, membranous sacs • Stroma, the internal fluid

47. Chloroplast Peroxisome Mitochondrion 1 µm Peroxisomes: Oxidation • Peroxisomes • Produce hydrogen peroxide and convert it to water Figure 6.19

48. Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell

49. Microtubule Microfilaments 0.25 µm Figure 6.20 • The cytoskeleton • Is a network of fibers extending throughout the cytoplasm Figure 6.20

50. Roles of the Cytoskeleton: Support, Motility, and Regulation • The cytoskeleton • Gives mechanical support to the cell