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Chapter 3

Chapter 3. Cells: The Living Units Intro and Membrane. Cell. The basic structural and functional unit of all living things. 4 Concepts of Cell Theory. Cell is the basic structural and functional unit of life

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Chapter 3

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  1. Chapter 3 Cells: The Living Units Intro and Membrane

  2. Cell • The basic structural and functional unit of all living things

  3. 4 Concepts of Cell Theory • Cell is the basic structural and functional unit of life • The activity of an organism depends on the individual and collective activities of cells • The function of the cell depends on its organelles (principle of complementarity) • Continuity of life has a cellular basis

  4. Characteristics of Cells • Cells vary greatly in their size, shape, and function • A cells shape reflects its function • All cells are composed of carbon, hydrogen, nitrogen, oxygen and trace amounts of other elements • A generalized human cell contains the plasma membrane, cytoplasm, and nucleus

  5. 3 Main Parts of Human Cells • Plasma membrane • Cytoplasm • Nucleus

  6. Plasma Membrane • Membrane, composed of phospholipids, cholesterol, and proteins, that encloses cell contents; outer limiting cell membrane

  7. Plasma Membrane • Intracellular fluid • Fluid inside the cell • Extracellular fluid • Fluid outside of the cell

  8. Plasma Membrane • Fluid Mosaic Model • Because the proteins that float in the lipid bilayer form a constantly changing mosaic pattern

  9. Plasma Membrane • Composition • Phospholipids – most • Cholesterol – small • Glycolipids – small

  10. Plasma Membrane • Phospholipids • Head – polar  hydrophilic (water loving) – faces the intra/extracellular fluid • Tail – nonpolar hydrophobic (water fearing) – tails are facing towards the inside

  11. Plasma Membrane • Glycolipids • Phospholipids with attached sugar groups • Only found on the outer surface of the plasma membrane

  12. Plasma Membrane • Lipid Rafts • Groups of saturated phospholipids that are packed tightly together. Associated with shphingolipids and cholesterol. • More stable and less fluid that the rest of the membrane • Assumed that they are needed for cell signaling

  13. Plasma Membrane • Integral Protein • Protein that is inserted into the lipid bilayer. • They have both hydrophobic and hydrophilic regions so that they can interact with the different regions of the lipid bilayer.

  14. Plasma Membrane • Integral Protein • Can protrude from one surface, but most are transmembrane which means that they go through the entire membrane.

  15. Plasma Membrane • Integral Protein • Transmembrane proteins are mainly involved with transport – when many cluster together they form channels or pores so “stuff” can flow into and out of the membrane (water soluble ions or molecules) • Also act as carries that bind a substance and then move it through the membrane

  16. Plasma Membrane • Peripheral Protein • Proteins that aren’t embedded in the lipid bilayer; attached loosely to integral proteins or membrane lipids. Removed easily without disrupting the plasma membrane

  17. Plasma Membrane • Peripheral Protein • Some are enzymes and others are involved in mechanical functions (changing cell shape during mitosis, muscle cell contraction, or linking cells together).

  18. Plasma Membrane • Glycocalax • “sugar covering” • Fuzzy sticky carbohydrate rich area surrounding the cell

  19. Plasma Membrane • Microvilli • “little shaggy hairs” • Small fingerlike projections of the plasma membrane. • Increase the surface area. • Found in areas where lots of absorption take place (intestine and kidneys)

  20. Factors that Join Cells • Glycoproteinsact as an adhesive • Wavy contours of the membranes of adjacent cells fit together in a tongue and groove fashion • Special membrane junctions (tight junction, desmosomes, gap junctions)

  21. Special Membrane Junctions • Tight Junction • Integral proteins of adjacent cells fuse together to form an impermeable junction that encircles the cell. • Help to prevent molecules from passing through the extracellular space between cells. • Found in lining of the digestive tract.

  22. Special Membrane Junctions • Desmosomes • “binding bodies” or anchoring junctions • Like rivets to prevent cells from separating and distributes tension throughout a cellular sheet to reduce the chance of tearing. • Present in skin and heart muscle

  23. Special Membrane Junctions • Gap Junction • “bond” or nexus • Communicating junction between adjacent cells • Cells are connected by hollow cylinders called connexons. • Small molecules pass through the water filled channels from one cell to the next. • Present in electrically excitable tissues like heart and smooth muscle

  24. Functions of the Plasma Membrane • Cells are bathed in an extracellular fluid called interstitial fluid. • Derived from the blood. • Contains thousands of ingredients • Amino acids, sugars, fatty acids, vitamins, hormones, neurotransmitters, salts, waste products, etc. • Cells “take” from the interstitial fluid what they need when they need it.

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