Chapter 4 A Tour of the Cell

1. Chapter 4 A Tour of the Cell SC 101 General Biology Essential Biology CM Lamberty

2. The Microscopic World of Cells • Cells are marvels of complexity • Trillions of cell in human body • Many specialized types • Main tool for exploration--Microscope

3. Microscopes as Windows on the World of Cells • Light Microscope (LM) • Visible light projected through specimen • Lenses enlarge the image and project to eye • View living cells • Magnification • Increase in size, depends on lens • Resolving Power • Clarity of magnified image • Electron Microscope (EM) beam of electrons • Scanning Electron Microscope (SEM) • View cell surfaces • Transmission Electron Microscope (TEM) • View internal structures

4. Microscopes as Windows on the World of Cells

5. Microscopes as Windows on the World of Cells

6. The 2 Major Categories of Cells The countless cells on earth fall into two categories: • Prokaryotic cells — Bacteria and Archaea • Eukaryotic cells — plants, fungi, and animals All cells have several basic features. • They are all bound by a thin plasma membrane. • All cells have DNA and ribosomes, tiny structures that build proteins

7. The 2 Major Categories of Cells Prokaryotic and eukaryotic cells have important differences. Prokaryotic cells are older than eukaryotic cells. • Prokaryotes appeared about 3.5 billion years ago. • Eukaryotes appeared about 2.1 billion years ago. Prokaryotes • Are smaller than eukaryotic cells • Lack internal structures surrounded by membranes • Lack a nucleus • Have a rigid cell wall

8. Idealized Prokaryotic Cell

9. The 2 Major Categories of Cells Eukaryotes • Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions. • The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA.

10. Idealized Eukaryotic Cell

11. Overview of Eukaryotic Cells • Eukaryotic cells are fundamentally similar. • The region between the nucleus and plasma membrane is the cytoplasm. • The cytoplasm consists of various organelles suspended in fluid. • Unlike animal cells, plant cells have • Protective cell walls • Chloroplasts, which convert light energy to the chemical energy of food

12. Membrane Structure • Separates living cell from nonliving surroundings • Regulates traffic of chemicals in and out of cell • Key to how it works is the structure

13. Plasma Membrane: Lipids & Proteins • Phospholipids • Related to dietary fats • Only 2 fatty acid tails not 3 • hydrophobic • Phosphate group in 3rd position • Charged, hydrophilic • Phopholipid bilayer • 2-layered membrane • Proteins embedded in bilayer • Regulate traffic

14. Plasma Membrane: Lipids & Proteins • Fluid Mosaic • Not static (fluid) • Diverse proteins (mosaic) • Phospholipids and proteins free to drift about in the plane of the membrane • Illness can result if membrane is compromised • Superbugs: staphylococcus aureus • MRSA • Flesh eating disease!!

15. Cell Surfaces • Plant cells have rigid cell wall surrounding plasma membrane • Made of cellulose • Protect the cells • Maintain cell shapes • Keep cells from absorbing too much water • Cells connected via channels through cell walls • Join cytoplasm of each cell to neighbor • Allow water and small molecules to move between cells

16. Cell Surfaces • Animal cells lack cell wall • Extracellular matrix • Sticky coating to hold cells together • Protects and supports cells • Cells junctions • Connect cells togther • Allow cells in tissue to function in coordinated way

17. Genetic Control of Cell • Nucleus chief of the cell • Genes store information necessary to produce proteins • Proteins do most of the work of the cell

18. Structure and Function of Nucleus • Nuclear Envelope • Double membrane that surrounds nucleus • Similar in structure to plasma membrane • Pores allow transfer of materials • Nucleolus • Prominent structure • Where ribosomes are made • Chromatin • Fibers formed from long DNA and associated proteins • Chromosome • One chromatin fiber

19. The nucleus

20. DNA, chromatin and chromosomes

21. Ribosomes • Responsible for protein synthesis • In eukaryotic cells, ribosomes make in nucleus and transported into cytoplasm • Suspended in fluid making proteins that remain in fluid • Attached to outside of endoplasmic reticulum, making proteins incorporated into membranes or secreted by cell

22. How DNA Directs Protein Production • DNA programs protein production in cytoplasm via mRNA • mRNA exits through pores in nuclear envelope, travels to cytoplasm, and binds to ribosomes • As ribosomes move along mRNA, genetic message translated into protein with specific amino acid sequence.

23. How DNA Directs Protein Production DNA RNA Protein

24. The Endomembrane System • Cytoplasm of eukaryotic cells partitioned by organelle membranes • Some are connected • Directly by membranes • Indirectly by transfer of membrane segments • Together form endomembrane system • Includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles

26. Endoplasmic Reticulum (ER) • Main functioning facility in cell • Rough ER • Ribosomes stud the surface • Produce membrane and secretory proteins (i.e. salivary glands) • Products transferred via transport vesicles • Smooth ER • Lacks ribosomes on surface • Synthesis of lipids (steroids) • Helps liver detoxify drugs

27. Endoplasmic Reticulum (ER)

28. The Golgi Apparatus • Refinery, warehouse and shipping center • Products made in ER reach Golgi in transport vehicles • Receiving dock and shipping dock • Modifications by enzymes as products move from receiving to shipping • Phosphate groups added as tags for different destinations

29. The Golgi Apparatus

30. Lysosomes • Sac of digestive enzymes (animal cells) • Proteins • Polysaccharides • Fats • Nucleic acids • Develop from vesicles budding from Golgi • Food vacuoles • fuse with lysosomes, exposing food to enzymes for digestion • Small molecules from digestion leave the lysosome and nourish the cell. • Breakdown damaged organelles • Sculpturing feature • Digest webbing between fingers and toes

31. Lysosomes

32. Vacuoles • Sacs that bud from ER, Golgi or plasma membranes • Variety of size and function • Contractile vacuoles of protists pump out excess water in the cell. • Central vacuoles of plants • Store nutrients • Absorb water • May contain pigments or poisons

33. Vacuoles

34. Review of Endomembrane System

35. Chloroplasts and Mitochondria • Energy Conversion • Cellular power stations

36. Chloroplasts • Photosynthetic cells of plants and algae • 3 compartments • Space between membranes that surround chloroplast • Stroma: thick fluid • Network of disks and tubes • Grana: interconnected stacks of disks • Solar power pack

37. Chloroplasts

38. Mitochondria • Site of cellular respiration • Harvest E from food MQ and converts to ATP • Found in all eukaryotic cells • Structure • Enveloped by 2 membranes filled with matrix • Inner membrane has several infoldings (cristae) • Contain DNA that encodes their own protein

39. Mitochondria

40. The Cytoskeleton • Network of fibers extending throughout cytoplasm • Skeleton and muscles • Support and movement

41. Maintaining Cell Shape • Series of fibers • Microtubules • Straight hollow tubes composed of proteins • Guide movement of chromosomes when cells divide • Intermediate filaments and Microfilaments • Both thinner and solid • Anchorage and reinforcement for organelles • Dynamic cytoskeleton (amoeboid movements)

42. Maintaining Cell Shape

43. Cilia and Flagella • Mobile appendages • Aid in movement • Flagella • Generally occur singly • Propel cell • Undulating whiplike motion • Cilia • Shorter and more numerous than flagella • Promote movement by back and forth motion • Some function to move fluid over tissue surfaces

44. Cilia and Flagella