Chapter 3


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Chapter 3

  1. 1. Types of Cells Nerve cells: surface is sensitive to stimuli. Long extensions. Muscle cells: contain tiny fibers that slide together forcefully. Elongated and threadlike. Red blood cells: contains hemoglobin that attracts and releases oxygen. Gland cells: contains sacs that release a secretion to the outside of the cell. Immune cells: recognize and destroy “nonself” cells such as bacteria and cancer.
  2. 2. Cell Structure Cytoplasm: gel like substance inside the cell. This gel contains the cell organelles. Plasma membrane: the outer boundary of the cell. Membranous organelles also have these membranes. Primary structure of a cell membrane is a double layer of phospholipids molecules. Heads are hydrophilic (water loving) Tails are hydrophobic (water fearing) Double layer is called a bilayer. The bilayer allows the heads to face the water and the tails to face away.
  3. 3. Fluid Mosaic Model Molecules that comprise a cell membrane are arranged in a sheet. Molecules are able to slowly float around the membrane like icebergs because it is fluid. Membrane proteins have many different structural forms that allow them to serve various functions. Some have a carbohydrate attached to their outer surface forming glycoprotein molecules which act as identifying markers.
  4. 4. Fluid Mosaic Model Membrane channel proteins have openings like gates in a fence that only allow certain kinds of molecules to pass through. Other membrane proteins are receptors that can react to the presence of a hormone or other regulatory chemicals thereby triggering a change in the cell.
  5. 5. Cell Organelles Organelles: “little organs”. Two classifications: Membranous organelles: organelles that are specialized sacs or canals made of a cell membrane. Nonmembranous organelles: are not made of a membrane but of microscopic filaments or other nonmembranous material.
  6. 6. Cell Organelles Endoplasmic reticulum: protein synthesis and intracellular transportation. Rough ER: ribosomes are attached to the ER and synthesize proteins Smooth ER: synthesizes lipids, steroid hormones and certain carbohydrates. Ribosomes: site of protein synthesis. A cell’s “protein factory”. Nonmebranous.
  7. 7. Cell Organelles Golgi Apparatus: synthesizes carbohydrates, combines it with protein and packages the product as globules of glycoprotein. Membranous. Lysosome: bags of digestive enzymes break down worn cell parts and ingest particles. A cell’s “digestive system”. Membranous. Peroxisomes: contain enzymes that detoxify harmful substances. Membranous. Contain peroxidase and catalase.
  8. 8. Cell Organelles Mitochondria: ATP synthesis. A cell’s “power plant”. Membranous. Centrosome: area of cytoplasm near the nucleus that coordinates the building and breaking of microtubules in the cell. Nonmembranous. Plays an important role during cell division when the “spindle” moves chromosomes around the cell.
  9. 9. Nucleus Nucleus is one of the largest cell organelles. Houses the genetic code which in turn dictates protein synthesis. It’s membrane the Nuclear envelope consists of: Nucleoplasm: nuclear substance Nuclear pores: selectively permeable Nucleolus: the most prominent structure visible in the nucleus. Plays an essential role in the formation of ribosomes. Synthesizes ribosomal RNA. Nonmembranous.
  10. 10. Cell Extensions Cilia and Flagella: hair like extensions that serve to move substances over a cells surface (cilia) or to propel sperm cells (flagella). Microvilli: like tiny fingers crowded against each other. Cover surfaces where absorption is important. Example: epithelial cells that line the intestines.
  11. 11. Cell Fibers Microfilaments: serve as “cellular muscles”. They are thin, twisted strands of protein molecules and usually form bundles that lie parallel to the long axis of a cell. Intermediate filaments: are twisted protein stands that are slightly thicker than microfilaments.  Thought to form much of the supporting framework in many types of cells. Microtubules: are the thickest cell fibers. They are tiny, hollow tubes made of protein subunits arranged in spiral fashion.  Called the “engines” of cells because they often move things around.
  12. 12. Cell Connections Gap Junctions: are formed when membrane channels of adjacent plasma membranes adhere to each other.  They form gaps or “tunnels”. This allows certain molecules to pass directly from one cell to another.  Example: heart muscle cells- allows for impluses to travel. Tight Junctions: occurs in cells that are joined by “collars” of tightly fused membrane. This is important for tissues that need to control what gets past. Molecules can not penetrate this membrane.  Example: lining of the intestines. Desmosomes: are small “spot welds” that hold adjacent cells together.  Example: adjacent skin cells are held together this way.