Lecture 2: Chapter 21

1. Lecture 2: Chapter 21 Viruses, Bacteria, and Archaea

2. Outline • Viruses • Structure • Classification • Reproduction • Prokaryotes • Structure • Reproduction • Nutrition • Bacteria • Archaea

3. The Viruses • Virus (poison) is chemical complexes of RNA or DNA protected by protein. • They are noncellular and thus cannot be classified with cellular organisms.

4. The Viruses

5. The Viruses • Each type of virus has at least two parts. • Capsid: Outer layer composed of protein subunits. • Nucleic acid core: the inner most portion is made of DNA or RNA.

6. The Viruses

7. Viral Reproduction • Viruses gain entry into host because portions of capsid adhere to a specific receptor on the host cell’s outer surface. • Viral nucleic acid enters the cell and once inside, the nucleic acid codes for the protein units inside the capsid. • Virus takes over metabolic machinery of the host cell.

8. Lytic Cycle

9. Viral Infections • Viruses are best known for causing infectious diseases in plants and animals. • Herpes, HIV, cancer (carrying oncogenes) • Viruses lack enzymes; thus, antibiotics have no effect. • Retrovirus: may cause cancer or AIDS,

10. The Prokaryotes • The prokaryotes include bacteria and archaea, which are fully functioning cells. • They contain a single circular DNA molecule as the genetic material.

11. Prokaryote Structure • Lack a eukaryotic nucleus. • Have outer cell wall containing peptidoglycan. • Lack membranous organelles. • Contain nucleoid. • May have accessory ring of DNA (plasmid). • Move by flagella

12. Reproduction in Prokaryotes • Prokaryotes reproduce asexually by means of binary fission. • Variation in a strain of bacteria mainly occurs from mutations, which are rapidly replicated and selected in a haploid

13. Binary Fission

14. Reproduction in Prokaryotes • Transformation occurs when bacterium picks up free pieces of DNA from other prokaryotes. • Transduction occurs when bacteriophages carry portions of bacterial DNA from one cell to another. • When faced with unfavorable conditions, some bacteria form endospores.

15. Prokaryotic Nutrition • Anaerobes -grow in the presence of oxygen. • Facultative anaerobes - grow in either the presence or absence of oxygen. • Aerobics - grow only in the presence of oxygen

16. Autotrophic Prokaryotes • Photoautotrophs - use solar energy to reduce carbon dioxide to organic compounds. • Chemoautotrophs - oxidize inorganic compounds to obtain the necessary energy to reduce O2 to an organic compound.

17. Heterotrophic Prokaryotes • Most prokaryotes are chemotrophs that take in organic nutrients. • Chemotrophs – take in organic nutrients

18. The Bacteria • Groups of bacteria are commonly differentiated from one another using the Gram stain procedure. • Gram-positive bacteria retain dye and appear purple. • Gram-negative bacteria do not retain dye and appear pink.

19. The Bacteria Bacteria can be classified based on their shape: • Spiral (spirilli), Rod (bacilli), and Round (cocci).

20. Cyanobacteria • Cyanobacteria are Gram-negative bacteria that photosynthesize. • Believed to be responsible for introducing oxygen into the primitive atmosphere.

21. Cyanobacteria

22. Archaea Structure and Function • Their plasma membranes contain unusual lipids that allow them to function at high temperatures. • Most are chemoautotrophs. • They are not photosynthetic.

23. Types of Archaea • Methanogens • Found in anaerobic environments. • Halophiles • Require high salt concentrations for growth. • Thermoacidophiles • Reduce sulfides and survive best at temperatures above 80oC.