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The Plant Cell and the Cell Cycle

The Plant Cell and the Cell Cycle. Chapter 3. Cell. Basic unit of plant structure and function Robert Hooke Looked at cork tissue under microscope “little boxes or cells distinct from one another ….that perfectly enclosed air” Nehemiah Grew

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The Plant Cell and the Cell Cycle

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  1. The Plant Cell and the Cell Cycle Chapter 3

  2. Cell • Basic unit of plant structure and function • Robert Hooke • Looked at cork tissue under microscope • “little boxes or cells distinct from one another ….that perfectly enclosed air” • Nehemiah Grew • Recognized leaves as collections of cells filled with fluid and green inclusions

  3. Cell Theory

  4. Basic Similarities of Cells • Cells possess basic characteristic of life • Movement • Metabolism • Ability to reproduce • Organelles • “little organs” • Carry out specialized functions within cells

  5. Light Microscope • View cells 20-200 µm in diameter • Can view living or stained specimens • Resolution (resolving power) • Ability to distinguish separate objects • Limited by lenses and wavelengths of light used • Smallest object that can be resolved is ~ 0.2 µm in diameter

  6. Confocal Microscope • Laser illumination • Detecting lens focuses on single point at a time • Scans entire sample to assemble picture • No reduction in contrast due to scattered light • Can generate 3-D images

  7. Transmission Electron Microscope • Responsible for discovery of most of smaller organelles in cell • Greater resolution • Uses beams of electrons rather than light • Magnets for lenses • Ultrathin section examined in vacuum • View image on fluorescent plate or photographic film

  8. Scanning Electron Microscope • Collected electrons used to form picture in television picture tube • High resolution view of surface structures • Requires vacuum • Recent refinements • Can operate in low vacuum • Can view live plant cells and insects

  9. Microscope Comparisons

  10. Generalized Plant Cell

  11. Boundaries Between Inside and Outside the Cell Plasma Membrane and Cell Wall

  12. Plasma Membrane • Surrounds cell • Controls transport into and out of cell • Selectively permeable

  13. Plasma Membrane • Composed of approximately half phospholipid and half protein, small amount of sterols • Phospholipid bilayer • Separates aqueous solution inside cell from aqueous layer outside cell • Prevents water-soluble compounds inside cell from leaking out • Prevents water-soluble compounds outside cell from diffusing in

  14. Plasma Membrane • Proteins in bilayer • Perform different functions • Ion pumps • Move ions from lower to higher concentration • Require ATP energy • Proton pump – moves H+ ions from inside to outside of cell • Ca+2 pump – moves Ca2+ to outside of cell • Channels – allow substances to diffuse across membrane

  15. Plasma Membrane • Plasmodesmata • Connects plasma membranes of adjacent plant cells • Extends through cell wall • Allows materials to move from cytoplasm of one cell to cytoplasm of next cell • Symplast – name for continuous cytoplasm in set of cells

  16. Plasma Membrane • Apoplast – • Space outside cell • Next to plasma membrane within fibrils of cell wall • Area of considerable metabolic activity • Important space in plant but questionable as to whether it is part of the plant’s cells

  17. Cell Wall • Rigid structure made of cellulose microfibrils • Helps prevent cell rupture • Process of osmosis allows water to enter cell • Inflow of water expands cell • Expansion forces cell membrane against cell wall • Resistance of cell wall to expansion balances pressure of osmosis • Stops flow of water into cell • Keeps cell membrane from further expansion

  18. Cell Wall • Osmotic forces balanced by pressure exerted by cell wall • Creates turgor pressure • Causes cells to become stiff and incompressible • Able to support large plant organs • Loss of turgor pressure – plant wilts

  19. Cell Wall • Place cell in salt solution • Water leaves cytoplasm • Protoplast (space inside plasma membrane) shrinks • Plasma membrane pulls away from cell wall • Cell lacks turgor pressure - wilts

  20. Cell Wall Structure • Primary cell wall • Cell wall that forms while cell is growing • Secondary cell wall • Additional cell wall layer deposited between primary cell wall and plasma membrane • Generally contains cellulose microfibrils and water-impermeable lignin • Provides strength to wood

  21. Cell Wall Structure • Specialized types of cell walls • cutin covering cell wall or suberin imbedded in cell wall • Waxy substances impermeable to water • Cutinized cell walls • Found on surfaces of leaves and other organs exposed to air • Retard evaporation from cells • Barrier to potential pathogens

  22. Organelles of Protein Synthesis and Transport Nucleus, Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus

  23. Nucleus • Ovoid or irregular in shape • Up to 25 µm in diameter • Easily stained for light or electron microscopy

  24. Nucleus • Surrounded by double membrane – nuclear envelope • Protein filaments of lamin line inner surface of envelope and stabilize it • Inner and outer membranes connect to form pores • Nucleoplasm • Portion of nucleus inside nuclear envelope

  25. Nucleus • Nucleoli (singular, nucleolus) • Densely staining region within nucleus • Accumulation of RNA-protein complexes (ribosomes) • Site where ribosomes are synthesized • Center of nucleoli • DNA templates • Guide synthesis of ribosomal RNA

  26. Nucleus • Chromosomes • Found in nucleoplasm • Contain DNA and protein • Each chromosome composed of long molecule of DNA wound around histone proteins forming a chain of nucleosome • Additional proteins form scaffolds to hold nucleosomes in place

  27. Nucleus • DNA in chromosomes • Stores genetic information in nucleotide sequences • Information used to direct protein synthesis • Steps in protein synthesis • Transcription – DNA directs synthesis of RNA • Most RNA stays in nucleus or is quickly broken down • Small amount of RNA (mRNA) carries information from nucleus to cytoplasm

  28. Nuclear Components

  29. Ribosomes • Small dense bodies formed from ribosomal RNA (rRNA) and proteins • Function in protein synthesis • Active ribosomes in clusters called polyribosomes • Attached to same mRNA • All ribosomes in one polyribosome make same type of protein

  30. Ribosomes • In living cell, ribosomes are not fixed • Move rapidly along mRNA • Read base sequence • Add amino acids to growing protein chain • At end of mRNA, ribosome falls off, releasing completed protein into cytoplasm

  31. Endoplasmic Reticulum • ER • Branched, tubular structure • Often found near edge of cell • Function • Site where proteins are synthesized and packaged for transport to other locations in the cell • Proteins injected through membrane into lumen

  32. Endoplasmic Reticulum • Packaging of proteins by ER • Considered to be packaged when separated from cytoplasm by membrane • Sphere (vesicle) of membrane-containing proteins may bud off from ER • Vesicle carries proteins to other locations in cell

  33. Endoplasmic Reticulum • Types of ER • rough ER – ribosomes attached to surface • smooth ER – does not have attached ribosomes • Carbohydrate transport • Often attached to proteins in ER • Helps protect carbohydrate from breakdown by destructive enzymes

  34. Golgi Apparatus • Also called a dictyosome • Consists of stack of membranous, flattened bladders called cisternae

  35. Golgi Apparatus • Directs movements of proteins and other substances from ER to other parts of cell • Cell wall components (proteins, hemicellulose, pectin) pass through cisternae • Move to plasma membrane inside membranous sphere • Sphere joins with plasma membrane • Membrane of sphere becomes part of plasma membrane • Protein, hemicellulose, and pectin contents released to outside the cell

  36. Endomembrane System • Complex network that transports materials between Golgi apparatus, the ER, and other organelles of the cell • Movement • Rapid • Continuous

  37. Organelles of Energy Metabolism Plastids and Mitochondria

  38. Plastids • Found in every living plant cell • 20-50/cell • 2-10 µm in diameter • Surrounded by double membrane • Contain DNA and ribosomes • Protein-synthesizing system similar to but not identical to one in nucleus and cytoplasm

  39. Plastids • Proplastids • Small plastids always found in dividing plant cells • Have short internal membranes and crystalline associations of membranous materials called prolamellar bodies • As cell matures, plastids develop • Prolamellar bodies reorganized • Combined with new lipids and proteins to form more extensive internal membranes

  40. Plastids • Types of plastids • Chloroplasts • Leukoplasts • Amyloplasts • Chromoplasts

  41. Plastids • Chloroplasts • Thylakoids • Inner membranes • Have proteins that bind to chlorophyll • Chlorophyll • Green compound that gives green plant tissue its color • Stroma • Thick solution of enzymes surrounding thylakoids

  42. Plastids • Chloroplasts • Function • Convert light energy into chemical energy (photosynthesis) • Accomplished by proteins in thylakoids and stromal enzymes • Can store products of photosynthesis (carbohydrates) in form of starch grains

  43. Chloroplast

  44. Leukoplasts • leuko – “white” • Found in roots and some nongreen tissues in stems • No thylakoids • Store carbohydrates in form of starch • Microscopically appear as white, refractile, shiny particles

  45. Amyloplasts • amylo – “starch” • Leukoplast that contains large starch granules

  46. Chromoplasts • chromo – “color” • Found in some colored plant tissues • tomato fruits, carrot roots • High concentrations of specialized lipids – carotenes and xanthophylls • Give plant tissues orange-to-red color

  47. Plastids

  48. Mitochondria • Double-membrane structure • Contain DNA and ribosomes • Inner membrane infolded • Folds called cristae • Increase surface area available for chemical reactions

  49. Mitochondria • Matrix • Viscous solution of enzymes within cristae • Function • source of most ATP in any cell that is not actively photosynthesizing • Site of oxidative respiration • Release of ATP from organic molecules • ATP used to power chemical reactions in cell

  50. Other Cellular Structures Vacuoles, Vesicles, Peroxisomes, Glyoxysomes, Lysosomes, and Cytoskeleton

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