Exam 2 Material (Chap. 16) Flashcards
Chapter 16 Material (29 cards)
The Earliest Life
first evidence can be found in rocks ~3.86 billion years old
Stromatolites
Fossilized microbial mats consisting of layers of filamentous prokaryotes and trapped sediment
- found in rocks 3.5 billion years old
- Ancient formed from Anoxygenic phototrophic filamentous bacteria
- Modern formed from oxygenic phototrophic cyanobacteria
Origins of Cellular Life
Early Earth was anoxic and much hotter than present day
First biochemical compounds were made by abiotic systems that set the stage for the origin of life
-amino acids
-nucleic acids
Subsurface origin hypothesis
Life originated at hydrothermal springs on the ocean floor
- more stable conditions
- steady and abundant supply of energy (H2 and H2S)
RNA World Theory
Prebiotic chemistry of early Earth set stage for self-replicating systems
-First self-replicating systems may have been RNA-based; RNA can bind small molecules (ATP, nucleotides, etc.)
~RNA has catalytic activity; may have catalyzed its own synthesis
~RNA is an informational molecule
Transition to DNA
DNA, a more stable molecule than RNA, eventually became genetic repository
- protein took over most catalysis jobs
- Three-part systems (DNA, RNA, and protein) evolved and became universal among cells
Last Universal Common Ancestor (LUCA)
Population of early cells from which cellular life may have diverged into ancestors of modern-day Bacteria and Archaea
-Characteristics:
~Early Earth was anoxic, thus energy-generating metabolism of primitive cells almost DEFINITELY was: anaerobic, chemlithotrophic, and obtained carbon from CO2
~LIKELY: obtained energy from H2, generated by FeS resting with H2S or UV light, and Thermophilic
Chemoorganotrophy
- Early forms of life was chemolithotrophic (produced large amounts of organic compounds)
- organic material provided abundant, diverse, and continually renewed source of reduced organic carbon –> stimulating evolution of chemoorganotrophic metabolisms
Basic Timeline of Life
- Early forms of life: Chemolithotrophs
- ~4 billion years ago: ancestors of archaea and bacteria
- 2.7 billion years ago: development of oxygenic photosynthesis by cyanobacteria (carbon dioxide + water –> glucose + oxygen)
- 2.4 billion years ago: Rise of oxygen: spurred evolution of organelle-containing eukaryotic microorganisms
- ~2 billion years ago: oldest eukaryotic microfossils
- 1.9-1.4 billion years ago: fossils of multicellular and more complex eukaryotes found in rocks
Endosymbiosis
contends that mitochondria and chloroplasts arose from symbiotic association of prokaryotes within another cell type
-well supported hypothesis for origin of eukaryotic cells; 2 hypotheses
2 Hypotheses of Endosymbiotic Origin of Eukaryotes
- Eukaryotes began as nucleus-bearing lineage that later acquired mitochondria and chloroplasts by endosymbiosis
- Eukaryotic cell arose from intracellular association between oxygen-consuming bacterium (the symbiont), which gave rise to mitochondria, and an archaeal host
-Both hypotheses suggest eukaryotic cell is chimeric
-supported by several features:
~ Eukaryotes have similar lipids and energy metabolisms to Bacteria
~Eukaryotes have transcription and translational machinery most similar to Archaea
Mutations
- Changes in the nucleotide sequence of an organism’s genome
- Occur because of errors in replication, UV radiation, and other factors
- Adaptative: improve fitness of an organism, increasing its survival
Other genetic changes besides Mutations
- gene duplication
- horizontal gene transfer
- gene loss
Phylogeny
- Evolutionary history of a group of organisms
- Can be inferred indirectly from nucleotide sequence data
Molecular clocks (chronometers)
- Certain genes and proteins can act as measures of evolutionary change
- Major assumptions of this approach: Mutations occur at a constant rate, are generally neutral, and are random
SSU rRNA genes
- Most widely used molecular clocks are small subunit ribosomal RNA genes
- Found in all domains of life (16S rRNA in prokaryotes and 18S rRNA in eukaryotes)
- Functionally constant
- Sufficiently conserved (change slowly)
- Sufficient length
- Has more and less conserved regions
Carl Woese
- Pioneered the use of SSU rRNA for phylogenetic studies in 1970s
- Established the presence of 3 domains of life: Bacteria, Archaea, and Eukarya
- Provided a unified phylogenetic framework for Bacteria
Ribosomal Database Project (RDP)
- A large collection of rRNA sequences (currently contains >409,000 sequences)
- Provides a variety of analytical programs
Comparative rRNA sequencing
-a routine procedure that involves:
~ amplification of gene encoding SSU rRNA
~ sequencing of amplified gene
~ analysis of sequence in reference to other sequences
-the first step in sequence analysis involves aligning sequence of interest with sequences from homologous (orthologous) genes from other strains or species
BLAST (Basic Local Alignment Search Tool)
- Web-based tool of the National Institutes of Health
- Aligns query sequences with those in GenBank database
- Helpful in identifying gene sequences
Bacterial Phylogeny
- Contains at least 80 major phyla
- many groups defined from environmental sequences alone (no cultured representatives)
- many groups are phenotypically diverse
Eukaryotic Phylogeny
-organelles originated within bacteria
~mitochondria arose from Proteobacteria
~Chloroplasts arose from cyanobacteria
Archaea Phylogeny
Consists of two major groups:
- Crenarchaeota
- Euryarchaeota
Species
A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding
