1 Chap 27 Prokaryotes and the Origins of Metabolic Diversity Current nucleotide analysis of a specific RNA molecule called 16S has classified life on Earth into 3 lineages or Domains: i.Eukarya ii.Bacteria iii.Archaea The purpose of this chapter is to compare and contrast the prokaryotes, the bacteria and Archaea.

2 Figure 27.2 The three domains of life

3 Universal Ancestor Extreme Halophiles Extreme Thermophiles Methanogens Bacteria Archaea Cyanobacteria Proteobacteria Spirochetes Major Groups of Prokaryotes

4 Domain Archaea Structural Differences Cell Wall A: only protein B: peptidoglycans Gram positive and gram negative: stain acts on the peptidoglycans and gram positive bacteria have more peptidoglycans so pick up more stain. E: plants have polysaccharides; animals have no cell walls and fungi have chitin

5 Figure 27.5x Gram-positive and gram-negative bacteria

6 Figure 27.5 Gram-positive and gram-negative bacteria

7 Cell Membrane B & E: straight chain fatty acids connected to glycerol A: HC’s linked to glycerol molecules (no fatty acids) Molecular Biology Comparisons Organization of the genome similar to bacteria chromosome is a single piece of circular DNA plasmids are present thermal denaturation resistance: provided by the presence of a high salt concentration and DNA binding proteins

8 DNA Replication DNA polymerases resemble eukaryotic polymerases in their primary protein sequence. some proofreading that occurs during replication topoisomerases and restriction restriction enzymes are present. Transcription RNA polymerase is more closely related to euk. polymerase in terms of genes. There are several kinds of RNA polymerases and therefore several genes. E. coli RNA polymerase (bacterial) can initiate transcription whereas the archaea RNA polymerase cannot when in vitro (transcription factors are needed.) Archaea promoter regions are rich in A’s and T’s like the TATA box of eukaryotes.

9 Gene Organization Introns have been found in rRNA and tRNA genes of archeal genomes. functionally related genes are often organized in operon-like structures. Reproduction Prokaryotes reproduce asexually by binary fission Neither mitosis nor meiosis occurs (as it does sin eukaryotes) Three Mechanisms of Gene Transfer (not sexual) 1.Transformation 2.Conjugation: direct transfer by sex pili 3.Transduction: viral transfer from one prokaryote to another. Endospores: resistant cells that can withstand most high heat.

10 Figure 27.x1 Prokaryotic conjugation

11 Table 27.2 A Comparison of the Three Domains of Life

12 Archaea Diversity Extremophiles: a general term to describe the “extreme” environments in which the archaea inhabit Methanogens methane or marsh gas is produced CO 2 + H 2 produces CH 4 + H 2 O they hate oxygen strict anaerobes they are decomposers at sewage plants, inhabit the guts of herbivores (cattle), termites.

13 Extreme Halophiles Great Lake, Dead Sea Some tolerate the high salt, others require it. They photosynthesize using a pigment called bacteriorhodopsin. Extreme Thermophiles most enjoy the warm of a 60 – 80 o C environment some will obtain energy from sulfur compounds hot springs and thermal vents

14 Figure An anthrax endospore

15 Evolution of Photosynthesis Very first prokaryotes were heterotrophs. That is, they required an organic compound such as glucose to make energy. Photoheterotrophs: obtain carbon from some organic compound but make ATP with the help of light. Chemoheterotroph: breakdown organic compounds for ATP and to obtain their carbon. Most widely for of nutrition in prokaryotes Glycolysis was probably the first metabolic pathway used to make ATP. The fact that almost every modern organism has this pathway supports the idea that glycolysis was one of the earliest pathways to make ATP.

16 What selection pressure would have begun to favor some sort of organism that could make its own energy? The ability to make their own food required the: harnessing of the sun to make ATP creation of reducing power too convert CO 2 into organic cpds.

17 Evidence the PS evolved early on 1.Many different prokaryotes possess this ability. The researches think because of the complexity of PS, that it developed in a common ancestor. 2.PS may have been present and then lost in organisms related to those that still are photosynthetic. 3.Cyanobacteria These are the only autotrophic prokaryotes that release oxygen with the splitting of water. Cyanobacteria have been shown to be a major part of environment when oxygen was present Fossils of prokaryotes, some 3.5 billion years old, look like modern cyanobacteria

18 Evidence the PS evolved early on 4.The complexity of PS Recall that it requires two photosystems Some prokaryotes use a single photosytem involving hydrogen sulfide. The H 2 S gets split instead of water. 5.The evolution of cyanobacteria with their oxygen production changed the entire environment from a reducing one to an oxidizing one. The use of oxygen in respiration increases the efficiency of breaking down fats and carbos. Electron transport chains and proton gradient mechanisms as well as ATP synthesis proteins are thought to have evolved from PS machinery.

19 Table 27.1 Major Nutritional Modes