Wednesday May 1, 2013

Forming Life's Building Blocks

• Concerns have been raised about the "primordial soup" hypothesis
• No oxygen=> no protective ozone layer
• therefore, the UV light would have been destroyed and the essential ammonia and methane gases
• Louis Lerman, in 1986, proposed the bubble model
• When the experiment is done one of the things formed is urisil which is found in RNA 

The First Cells

• The first step may have been the formation of tiny bubble termed microspheres 

Structure of Prokaryote

• Prokaryotes are small, simpily organized, single cells that lack a nucleus
• Include bacteria and archaea
• have a cell wall
• composed of peptidoglycan 
• network of polysaccharides linked by peptide cross-links

• bacteria are separated into two groups based on membranes
• Peptidoglycan are in either a thick layer with no outer membrane that will stain (gram-positive) or in a thin layer with an outer membrane that won't stain (gram-negative)
• Hans Christian Gram developed a stain to differentiate between the two
• When cells are stressed they pass their plasmid DNA following cell-to-cell contact
• Based on carbon and energy sources, prokaryotes can be divided into four categories
• 1. Photoautotrophs: Photosynthesizes, or plants. 
• Cyanobacteria: when a lake suddenly has an algae bloom and turns pea soup green, it's not algae, its cyanobacteria

• 2. Chemoautotrophs: use inorganic fuels as their food. 
• For example: nitrogen-fixing bacteria, nitrifiers oxidize ammonia or nitrite

• 3. Photoheterotrophs: Use light as energy and pre-formed organic molecules as carbon sources
• Purple nonsulfur bacteria
• Very Rare

• 4. Chemoheterotrophs: Use organic molecules and energy sources 
• Decomposers and most other types of bacteria.