Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Unit 14: Review Prokaryotes Lab I. Bacteria These are the three domains, Bacteria, Archaea, and Eukarya. We examined the Bacteria domain. Some of the structures below are always found in bacteria and some are not. The typical bacterium contains: cytoplasm, nuclear material, ribosomes, a cell wall, plasma membrane, pili, flagellum, and capsule. Found in all bacteria The cytoplasm is a region within the cell filled with a jelly-like fluid called the cytosol. The nuclear material is dsDNA (double-stranded DNA). The nuclear material is located in the cytosol of the cell in a region called nucleoid. Ribosomes of bacteria are smaller, less dense than eukaryotic ribosomes but they serve the same function; to synthesize protein. The cell wall of bacteria is made of peptidoglycan. The amount of peptidoglycan can vary. The plasma membrane lies between the cell wall and the cytoplasm. This structure regulates what enters and leaves the organism. Found in some bacteria Some bacteria form pili (pilus, singular). These fingerlike projections are found on the surface of the body. Their function is for attachment. Bacteria with pili can attach to teeth, rocks, roots, each other, etc. Some bacteria can have one or more flagella (flagellum, singular). Flagella are for locomotion. Some bacteria can form capsules. The capsule lies outside the cell wall and protects the bacteria from destruction. Continue Bacteria continued II. Bacterial Shapes and Arrangements Labeled typical bacterium One way to classify bacteria is by examining its shape. Bacteria appear in many different shapes. We will examine the three basic shapes but note that others exist. Three basic shapes of bacteria (refer back to unit 7) • Bacilli (bacillus, singular) are rod-shaped • Cocci (coccus, singular) are spherically-shaped • Spirilla (spirillum, singular) are spiral-shaped Continue Continue III. Gram Staining Gram Staining continued In 1884 Hans Christian Gram developed a staining procedure, Gram Staining. The composition of the cell wall of bacteria vary among species. Due to this difference (diagram on next slide) bacteria can be divided into two groups; Gram positive and Gram negative. Gram positive bacteria have thick peptidoglycan cell walls and retain a purple color when stained with crystal violet. Gram negative bacteria have double cell walls. A thin peptidoglycan inner wall and outer wall made of carbohydrates, proteins and lipids. These cells retain the red color when stained with safranin. Continue Continue Gram staining bottles 1 Gram Staining continued Gram stain procedure (abridged) 1. Obtain a slide 2. Add one drop of water and place in a staining tray 3. Sterilize a loop Gram Staining continued 4. Transfer bacteria to your slide and mix it with the drop of water on your slide Slide 5. Heat-fix the slide by passing the slide over an open flame several times Staining tray Touching bacteria with loop Continue Continue Gram Staining continued Heat-fixing slide Gram Staining continued 6. Flood smear with crystal violet (purple stain) for 1 minute Next step is most important. It will differentiate Gram positive from Gram negative bacteria. 7. Rinse off the stain 10. Decolorize with ethanol. Ethanol must be added drop-wise to a slanted slide. Stop when first clear drop is seen. Rinse slide with water. 8. Flood smear with iodine for 1 minute 9. Rinse off the iodine Mixing bacteria with water At this point, Gram positive bacteria remain purple because they do not decolorize but Gram negative bacteria decolorize. At this point all bacteria will appear purple because of the crystal violet. Decolorizing Continue Continue Gram Staining continued 11. Flood smear with safranin (counterstain) for 1 minute. Only decolorized cells will stain red. Gram Staining continued 12. Rinse slide off with water and blot slide dry between sheets of bibulous paper At this point Gram negative bacteria stain red in color. Gram positive bacteria remain purple. Packet of bibulous paper 13. Slide can be examined Slide with safranin Continue Continue 2 Gram Staining continued Gram positive (purple) • Bacilli • Cocci • Spirilla Continue Gram negative (red) IV. Bacteriology A single bacterium multiples to form a colony. A colony consists of millions of cells that all arise from one cell. Each colony exhibits specific colonial morphology (characteristic size, shape, consistency, texture and color). End of Lab Review ☺ 3