1. Alberts, Bray, Hopkins, Johnson Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Professor: Dr. Barjis Room: P313 Phone: (718)2605285 Email: ibarjis@citytech.cuny.edu General Biology Sylvia S Mader 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. 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 O 2 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 80 o C.