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  1. Chapter 15 The Basic Unit of Life- The Cell Principles of Science II
  2. This lecture will help you understand: 1. Characteristics of Life 2. Macromolecules Needed for Life 3. Cell Types: Prokaryotic and Eukaryotic 4. The Microscope 5. Tour of a Eukaryotic Cell 6. The Cell Membrane 7. Transport into and out of Cells 8. Cell Communication 9. How Cells Reproduce 10.How Cells Use Energy 11. ATP and Chemical Reactions in Cells 12.Photosynthesis 13.Cellular Respiration and Fermentation
  3. Characteristics of Life • All living things – use energy. – develop and grow. – maintain themselves. – have the capacity to reproduce. – are parts of populations that evolve.
  4. Characteristics of Life • All living things use energy. – Plants take electromagnetic energy from sunlight and convert it to chemical energy. – Animals convert energy from food into chemical energy. – Living things use this chemical energy to build structures and fuel their activities. – How living things use energy is consistent with the laws of physics.
  5. Characteristics of Life • All living things develop and grow, changing over time. • Living things maintain themselves. – They build structures (bones, stems). – They repair damage (heal wounds). – They maintain their internal environments (body temperature, water balance).
  6. Characteristics of Life • All living things have the capacity to reproduce. – Asexual reproduction occurs when an organism reproduces by itself. – Sexual reproduction occurs when organisms produce sperm and eggs that join to develop into new individuals.
  7. Characteristics of Life • All living things are parts of populations that evolve. – Populations do not remain constant. – Populations change over time, across generations. – Populations may evolve in response to their environments.
  8. Macromolecules Needed for Life • Proteins (amino acid Leucine) • Carbohydrates (Glucose) • Lipids (Palmitric Acid) • Nucleic acids (Guanine DNA)
  9. Cell Types: Prokaryotic and Eukaryotic • Prokaryotic cells have no nucleus. • Prokaryotes are almost always single-celled, microscopic organisms. Their DNA is found in a single circular structure. They usually have an outer cell wall.
  10. Cell Types: Prokaryotic and Eukaryotic • Eukaryotic cells have a nucleus and may be single-celled or multicellular. They – have their DNA inside the nucleus. – have linear chromosomes. – have various organelles. – are larger than prokaryotic cells.
  11. The Microscope • Light microscopes allow people to view cells and make out the larger features within them. • Electron microscopes allow people to view even smaller structures within cells.
  12. The Microscope Light microscope
  13. The Microscope Electron microscope
  14. Tour of a Eukaryotic Cell • Eukaryotic cells contain many parts, including: – Cell membrane – Nucleus – Cytoplasm – Cytoskeleton – Organelles • All the parts of the cell have specific functions.
  15. Tour of a Eukaryotic Cell • Plant cells also contain (animal cells do NOT) – a cell wall to make the cell rigid. – chloroplasts that perform photosynthesis.
  16. The Cell Membrane • The cell membrane – defines a cell's boundary. – controls what moves into and out of the cell. – consists of a phospholipid bilayer, membrane proteins, and short carbohydrates.
  17. The Cell Membrane • The fluid mosaic model describes the structure of the cell membrane, a mosaic of proteins and phospholipids, almost all of which can move fluidly around the membrane.
  18. Transport into and out of cells • Cells take in many resources, including water, oxygen, and organic molecules. • Cells also discard wastes. • Transport occurs through: – Diffusion – Facilitated diffusion – Active transport – Endocytosis and exocytosis
  19. • Diffusion is the tendency of molecules to move from an area of high concentration to an area of low concentration. – Molecules diffuse across the phospholipid bilayer of the cell membrane. – Diffusion requires no energy from the cell. It is a form of passive transport. Transport into and out of cells
  20. Transport into and out of cells • Facilitated diffusion occurs when a transport protein binds to a molecule and moves it down a concentration gradient. – Facilitated diffusion requires no energy from the cell. It is a form of passive transport.
  21. Transport into and out of cells • Active transport occurs when a transport protein moves a molecule against its concentration gradient. – Active transport requires energy from the cell.
  22. Transport into and out of cells • Larger amounts of material can be transported into and out of cells through endocytosis and exocytosis. – In endocytosis, a vesicle pinches off from the cell membrane. – In exocytosis, a vesicle fuses with the cell membrane.
  23. Cell Communication • Cells communicate with one another using special molecules. • Communication between adjacent cells occurs when molecules move from one cell to another through special "doorways." – Animal cells have gap junctions. – Plant cells have plasmodesmata.
  24. Cell Communication • Long-distance communication relies on message molecules traveling through the bloodstream. – Receptors are membrane proteins. – A receptor binds a message molecule with a lock- and-key fit. – The binding of the receptor to a message molecule initiates a series of chemical reactions that results in the target cell's response to the message.
  25. Cell Communication
  26. How Cells Reproduce • In mitosis, one parent cell divides into two daughter cells that have the same genetic information as the parent cell.
  27. How Cells Reproduce • A dividing cell goes through the stages of the cell cycle: 1. Gap 1 2. Synthesis 3. Gap 2 4. Mitosis/cytokinesis
  28. How Cells Reproduce • The phases of mitosis: 1. Prophase: Chromosomes condense, and nuclear membranes break down. 2. Metaphase: Chromosomes line up along the equatorial plane. 3. Anaphase: Sister chromatids are pulled apart and move to opposite poles of the cell. 4. Telophase: New nuclear membranes form around each set of chromosomes. • After mitosis, cytokinesis occurs: The cytoplasm divides, completing cell division.
  29. How Cells Reproduce
  30. How Cells Use Energy • Two things are necessary for a chemical reaction to occur: – Must be consistent with the law of conservation of energy. • Exothermic (energy-releasing) reactions occur spontaneously. • For all other reactions, cells rely on usable energy stored in molecules of ATP. – Activation energy needed for initial breaking of bonds.
  31. How Cells Use Energy • ATP provides energy for chemical reactions in cells. • Cells obtain energy from ATP when one phosphate group is removed, leaving ADP.
  32. How Cells Use Energy • Cells eventually turn ADP back into ATP by adding a phosphate group during cellular respiration.
  33. How Cells Use Energy • The sodium-potassium pump uses active transport to control the levels of sodium ions (Na+ ) and potassium ions (K+ ) in cells. This process uses one molecule of ATP.
  34. How Cells Use Energy • Reacting molecules must collide with an activation energy that is needed for the initial breaking of bonds. • The activation energy for many essential chemical reactions is very high. • A catalyst is a substance that lowers the activation energy, allowing a reaction to happen more quickly. • The catalysts in cells are enzymes—large, complex proteins.
  35. How Cells Use Energy • An enzyme binds the reactants at its active site and releases the products. • In the process, the enzyme is not altered or destroyed; it can be used again and again.
  36. How Cells Use Energy • Cells regulate enzymes – Cells control the synthesis and degradation of enzymes. – Enzyme function depends on temperature, pH, and other features of the environment. – Inhibitors can block the function of enzymes.
  37. How Cells Use Energy • Two types of enzyme inhibition – In competitive inhibition, the inhibitor binds to the active site of an enzyme so that the enzyme cannot bind its substrate. – Noncompetitive inhibition occurs when an inhibitor binds to a different part of the enzyme, changing the active site so that the enzyme can no longer bind to its substrate.
  38. Photosynthesis • The process organisms use to convert light energy from the Sun into chemical energy. • Conducted in the chloroplasts of plants. • Occurs in two stages: the light-dependent reactions and the light-independent reactions. • Photosynthesis is the ultimate source of (practically) all organic molecules on Earth.
  39. Photosynthesis Light-dependent reactions
  40. Photosynthesis • Light-independent reactions – The light-independent reactions make use of stored energy from the light-dependent reactions. – Carbon is fixed, moved from atmospheric CO2 to the sugar glucose. – The molecules produced during photosynthesis are used as a starting point for building all of the macromolecules of life.
  41. Cellular Respiration and Fermentation • Cells break down glucose to produce ATP. • Cellular respiration is aerobic (uses oxygen). • Cellular respiration yields 38 molecules of ATP from every molecule of glucose.
  42. Cellular Respiration and Fermentation • Cellular respiration occurs in three steps: – Glycolysis – The Krebs cycle – Electron transport
  43. Cellular Respiration and Fermentation • Glycolysis takes place in the cytoplasm of cells. – The glucose molecule is split into two molecules of pyruvic acid, releasing two molecules of ATP.
  44. Cellular Respiration and Fermentation • The Krebs cycle occurs in the cell's mitochondria. – In the Krebs cycle, pyruvic acid is converted to acetic acid and bound to a molecule of coenzyme A. The result—acetyl-CoA—is broken down into CO2. – Two molecules of ATP are harvested. Additional energy is stored in the molecules NADH and FADH2.
  45. Cellular Respiration and Fermentation • In electron transport, electrons carried by NADH and FADH2 are sent down electron transport chains. – In the process, the electrons lose energy, which is used to pump hydrogen ions across a membrane inside the mitochondria. – At the end of the chain, the electrons combine with O2 to make water. – The concentration gradient generated by pumping hydrogen ions is used to make ATP.
  46. Cellular Respiration and Fermentation • In certain cells, under certain conditions, glycolysis is followed by fermentation. – Fermentation uses no oxygen and generates no ATP. – But, fermentation regenerates the molecules necessary to keep glycolysis going, so cells can continue to obtain energy through glycolysis. • Alcoholic fermentation by yeast is used to bake bread and make beer and wine. • Lactic acid fermentation occurs in muscle cells when there is not enough oxygen for cellular respiration to continue. It is also used by red blood cells. Lactic acid fermentation by bacteria and yeast is used to make yogurt and cheese.