The Nature of Life Flashcards
Requirements to be Alive
- maintain internal homeostasis
- respond to external stimuli
- consume and produce energy
- reproduce and have a form of heredity
maintain homeostasis
- cells must be able to maintain their interior in the face of changing external conditions
- things to maintain: internal temp, internal pH, internal concentration of proteins, solutes
- maintained by: membranes, integral membrane proteins, and energy consumption
respond to external stimuli
- must be able to respond to a change in the environment external to the organism
- can be physical (movement) or chemical (hormones)
consume and produce energy
-all processes in life require energy
- unit of energy in cells: ATP
- -> produced through electrochemical gradients
electrochemical gradient
-difference in concentration or solutes and charges on two sides of a membrane
reproduction and heredity
- must have mechanism for reproduction
- heredity: DNA & RNA
- asexual or sexual
last universal common ancestor
- LUCA
- evidence from modern-day life suggests that all current life evolved from a single common ancestor
- evidence: all life is C-based, has similar enzymes, passes heredity through DNA or RNA
primordial soup theory
- proposed by Darwin
- amino acids formed first
-early earth environment consisted of high concentrations of compounds known to be abundant in life
(C, H, H2Ovap, NH3)
- atmosphere of Earth was reducing (preventing O buildup)
- energy entering atmosphere facilitated production of small organic monomer compounds (via lightning or UV light)
- organic monomers accumulated over time, becoming concentrated (SOUP)
- concentration led to eventual formation of complex organic compounds (polymers), from which life arose
- supported with Miller-Urey Experiment
issues with primordial soup theory
- no mechanism for generation of complex polymers from simple monomers
- no mechanism for evolution of cells from monomers and polymers
- need sustained energy for life to develop, not a one time spark
RNA World Theory
- RNA formed first
- RNA eventually lead to DNA and protein formation
- evidence: nucleic acid precursor and nucleotides have been produced from simple compounds and UV light
- also some viruses contain only RNA
issues with RNA World Theory
- how did combination of DNA, RNA and proteins lead to cell formation?
- how is energy produced?
- how are membranes produced?
Deep Sea Hydrothermal Vent Theory
-generation of electrochemical gradients and metal-containing enzymes as the first precursors to life, which allows for the generation of energy
- deep sea hydrothermal vents
- produce natural protein gradient
- once energy could be reliable generated, organic monomers and polymers would be formed naturally, RNA DNA and proteins would follow and eventually all would combine behind a membrane, which could safely leave the vent
-supported with artificial hydrothermal vents in lab, and the fact that many of the oldest enzymes contain Iron or Sulfur
issues with the Deep Sea Hydrothermal Vent Theory
-no clear mechanism for how RNA and DNA eventually developed
why isn’t life still evolving?
- competition (new primitive cells would have been outcompeted)
- rare occurrence (life was such a chance event
- oxygen being present in much higher concentration
Don’t know for sure!
