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1 Chapter 3 Cell Structure Introduction: 1. You will distinguish eukaryotic and prokaryotic cells. 2. You will learn the structure and function of the plasma membrane. 3. You will relate the structure of cell parts to their functions. 4. You will recognize the 5 scientists that discovered the nature of cells. CH. 3.1 Looking at Cells 1. All living things are made of cells. 2. Cells are often too small to be seen with the naked eye. Discovery of Cells 1. Prior to the discovery of microscopes people believed that curses and supernatural forces caused diseases. 2. The invention of microscopes in the early 1600s allowed people to start seeing things too small to be observed by the naked human eye. 3. A compound light microscope uses a series of lenses to magnify objects in steps. 4. 1665 – Robert Hooke used a compound microscope to look at cork. He described the tiny box-like structures as cells. (They reminded him of the cells in a monastery. His microscope had multiple lenses but the lens quality was poor allowing him to only see things about 20 times bigger.) 5. Anton van Leeuwenhoek described cells seen through 2 a simple light microscope from 1668 to 1700. His microscope had only one lens. (He was a lens maker and his single lens could see things up to 200 times bigger.) He was the first person to see unicellular organisms (He was the first person to see single cell organisms like protists. He was the first person to see sperm and blood cells.) 6. By the 1800’s microscopes and lenses had been perfected so scientists could see things up to 1500 times bigger. 7. 1830’s – Matthais Schleidan observed a variety of plants and concluded they were made of cells. 8. 1830’s – Theodore Schwann made similar observations about animals. 9. 1858 – Rudolf Virchow determined that cells come from other cells. 10.The work of Schleidan, Schwann, and Virchow formed the modern cell theory. Cell Theory 1. All organisms are composed of cells. 2. The cell is the basic unit of organization of organisms. 3. All cells come from pre-existing cells. Cells divide to form two identical cells (mitosis or binary fission). Types of microscopes 1. A compound light microscope uses light passing through two or more lenses to enlarge an image of a specimen. 2. Developed in the 1600’s and perfected over 200 years the CLM can magnify objects up to 1500 times. 3. An electron microscope uses a beam of electrons instead of light to produce pictures of the specimen. Developed in the 1940’s, the electron microscope can magnify objects 500,000 times their original size. Object must be in a vacuum. Organisms cannot survive in the vacuum of an EM. 3 Cells must be small 1. Small cells work more efficiently than large ones. 2. The human body is composed of 100 trillion cells. 3. Small cells exchange substances more readily than large cells because of surface-area-to-volume ratio. 4. The higher the surface-area-to-volume ratio the shorter the distance an object has to travel to reach the center of the cell. 5. Small things and flat things have more surface area compared to the volume inside. 4 Common features of the cell (all cells have these) 1. All cells share some common features. 2. All cells have a plasma membrane that is an outer boundary of the cell. (plasma membrane is also called the cell membrane) 3. The plasma membrane regulates what comes in and goes out of the cell. 4. All cells contain cytoplasm that is the “interior fluid” of the cell. 5. All cells have a cytoskeleton that acts like a scaffold and supports the cell as well as the interior structures. 6. All cells have ribosomes which are the structures on which proteins are made. 7. All cells have DNA and RNA which contain all the instructions for making proteins, regulating cellular activities, and reproduction. Prokaryotes do not contain internal compartments 1. The smallest and simplest cells are prokaryotes or bacteria. 2. Prokaryotes do not have a nucleus. They also do not have endoplasmic reticulum, mitochondria, chloroplasts, vacuoles, Golgi apparatus, or any other membrane bound structures. 3. The genetic material in bacteria is a single circular strand of DNA. 4. Bacteria grow and divide very rapidly. 5. Some bacteria cause human disease. 6. Bacteria have a cell wall made of simple polysaccharides that surrounds the plasma membrane. 7. Antibiotics break down the cell wall causing the bacteria to explode. 8. Many bacteria have long flagella that enable them to move. Eukaryotic Cells are organized 1. Eukaryotic cells have a nucleus. 2. The nucleus is an internal membrane bound structure that contains the cell’s DNA. 3. The DNA is in open ended strands. 4. Eukaryotic cells have many other membrane bound structures that enable them to function in ways bacteria cannot. 5. Some single celled eukaryotes have flagella or cilia that allows them to move. 5 6. Flagella are long whip-like projections. 7. Cilia are short hair-like projections. 8. Some cells have cilia designed to move other materials from place to place. Cell Membranes 1. Are selectively permeable meaning some things can pass through while others cannot. 2. Are flexible instead of being hard like a shell. (like a water balloon) 3. Are primarily composed of phospholipids. 4. A phospholipid is composed of a polar head and two non-polar tails. 5. The polar head is a phosphate group and is hydrophilic. 6. The non-polar tails are fatty acids and are hydrophobic. 7. This hydrophilic / hydrophobic nature creates an inner non-polar layer to the membrane with two polar layers on the outside of the membrane. Proteins are embedded in the lipid bilayer 1. Surface marker proteins often have a carbohydrate head that allows cells to recognize each other. 2. Receptor proteins recognize and bind to specific substances. 3. Enzymes assist chemical reactions inside the cell. 4. Transport proteins help substances move across the membrane. Cell Organelles are membrane bound structures with specialized functions. The Nucleus 1. The nucleus houses the DNA and controls most functions of the cell. (This is the boss’ office and the Boss DNA has all the information needed make proteins) 2. The DNA in eukaryotic cells is shaped like elongated thin strands. 3. The nuclear membrane has pores called nuclear pores which allow the RNA to pass from the nucleus into the cytoplasm. 4. The RNA carries a message from the DNA to the ribosomes where the message is translated and turned into proteins. (The RNA is the supervisor who carries the message to the Ribosome Workers who make the protein) 6 The Endoplasmic Reticulum 1. In addition to free floating ribosomes found in all cells, eukaryotic cells have ribosomes attached to the endoplasmic reticulum. 2. The ER moves proteins through the cell. 3. The two main parts of the ER are Rough ER and Smooth ER. 4. The rough ER contains ribosomes. 5. The smooth ER does not contain ribosomes. 6. After the proteins are made, a part of the ER pinches off forming a vesicle (little bag) containing the proteins. (The ER is the conveyor belt in the protein factory) Golgi Apparatus 1. The Golgi apparatus packages and distributes proteins. (Fed Ex) (Pimped Out) 2. Vesicles from the ER travel to the Golgi apparatus delivering crude proteins. 3. Enzymes in the Golgi apparatus modify these proteins. 4. The proteins are then repackaged into new vesicles and then ships them out to other parts of the cell or to the outside of the cell. 5. Lysosomes are vesicles produced by the Golgi apparatus that contain digestive enzymes. (Recycle Bin) Mitochondria 1. The mitochondria make ATP, the energy currency of the cell. (Power Plant) 2. Mitochondria are a unique organelle in that they contain a separate nucleus with separate DNA and free floating ribosomes. 3. The mitochondrial DNA allow them to reproduce independent of cell division. 4. This is one piece of evidence in the theory on the origin of eukaryotic cells from prokaryotic cells. Specialized Plant Structures and Organelles 1. Cell Wall 2. Chloroplasts 3. Central Vacuole Cell Wall 1. Plant cells have a thick cell wall that surrounds the cell 7 membrane and gives the cell support and protection. 2. The cell wall is made of a complex polysaccharide called cellulose. 3. Most animals cannot digest cellulose without the help of symbionts. (mutualism) Chloroplasts 1. Chloroplasts are organelles that trap light energy to make carbohydrates from CO2 and H2O. 2. Chloroplasts, like mitochondria, contain their own DNA and are thought to be descendants of prokaryotic cells. Central Vacuole 1. The central vacuole is the largest organelle in the plant cell. 2. The central vacuole stores water, nutrients, ions, and waste. 3. When the central vacuole is full of water, it presses tight against the cell wall making the cell rigid. 4. This rigidity is called turgor pressure and allows soft tissue plants to stand upright.
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