Chapter 16 Flashcards
Early Earth
Forma5on of earth—4.5 bya
• Microbial life—found in fossils 3.5 billion years old
Stromatolites
Microbial mats
of layers of filamentous
microbes and minerals
Subsurface origin of life hypothesis
Life originated at hydrothermal springs on
ocean floor • Stable condi5ons
• Steady and abundant supply of energy (e.g., H2
and H2S)
RNA world and lipid vesicles
RNA world theory
– RNA can bind small molecules (e.g., ATP, other nucleo5des)
– RNA has cataly5c ac5vity; may have catalyzed its own synthesis
• Lipid vesicles
Last universal common ancestor (LUCA)
Possible scheme for energy genera5on in primi5ve cells
Abundant H2 and FeS
Endosymbio5c hypothesis
Mitochondria and chloroplasts of eukaryotes arose from engulfment of bacteria into other cells
• Prokaryo5c ribosomes (70S) • Bacterial 16S ribosomal RNA • Ribosomes inhibited by same an5bio5cs • Covalently closed, circular DNA
Endosymbio5c hypothesis #2—hydrogen hypothesis
Accounts for • Bacterial lipids • Archaeal
transcrip5on and transla5on
• Bacterial energy genera5on
• Favored hypothesis
Evolu5on
Descent with modifica5on
Fitness
survival capacity or reproduc5ve ability
– Harmful muta5ons—lower fitness – Beneficial muta5ons—increase fitness – Neutral muta5ons—do not affect fitness,
accumulate in genome
Gene duplica5on • Gene loss
obligate symbionts and parasites • Horizontal gene transfer
Environments select organisms that
survive and successfully compete and reproduce
Evolution occurs rapidly in microbes because of
Large popula5ons – Fast reproduc5on
Phylogeny
Inferred evolu5onary history • Assump5ons:
– All organisms descended from LUCA – Sequence of DNA is record of organism’s ancestry
Genes used in phylogene5c analysis
Small subunit rRNA (SSU rRNA)
– 16S rRNA in prokaryotes – 18S in eukaryotes
– Universally distributed – Func5onally constant – Sufficiently conserved
– Adequate length
Genes used in phylogene5c analysis
EF-‐‐Tu• Hsp60 • tRNA synthetases
• gyrB • recA