Lecture 6: What is Life? Flashcards
What are the 4 requirements of life?
- maintain internal homeostasis
- respond to external stimuli
- consume & produce energy
- reproduce and have some form of heredity
what does maintaining homeostasis mean?
Living organisms must be able to maintain an interior environment that is thermally and chemically distinct from the external environment.
- Maintained by selectively permeable membranes
what does responds to external stimuli mean?
Physical or chemical response to a change in the external environment (ex: hormones, movement)
What does consume and produce energy mean?
living things must use energy and consume nutrients to carry out the chemical reactions that sustain life. this energy must either be capture (autotrophs) or eaten (heterotrophs)
How does energy circulate in our bodies?
Through ATP via chemiosmosis
What is reproduction and heredity?
Process by which living things give rise to offspring and transmit hereditary information
Asexual vs sexual reproduction?
asexual: simple organism clones itself (bacteria, archaea, etc)
secual: cells from new parents unite to form first cell of new organism - offspring is different than parent
How do organisms pass on hereditary information?
Living things pass their traits to their offspring through genes (sequence of DNA and RNA) made up of nucleotides.
What are the necessary ingredients for life?
Chemical building blocks (oxygen, hydrogen, carbon, nitrogen, sulphur, phosphorous)
Energy source (solar, electrical from lightning, chemical)
What are the four main macromolecules?
Carbohydrates
Lipids
Proteins
Nucleic Acids
How are macromolecules formed?
Enzymes catalyze reaction rates.
What are the three common theories for the creation of life?
Primordial soup
RNA world theory
Hydrothermal deep sea vent theory
What is the primordial soup theory?
the earth had high concentrations of compounds needed for life. The highly chemically reducing atmosphere (no oxygen), exposed to energy from the sun or lightning, produced simple organic monomers. These accumulated in a “soup” and eventually combined to form complex polymers, which created life.
What is the support of the primordial soup theory?
Miller-Urey experiment: tons of amino acids produced under early primitive earth conditions (without oxygen).
What are the issues with the primordial soup theory?
- There is no mechanism for the generation of complex polymers from simple monomers
- There is no mechanism for the evolution of cells from monomers and polymers
- Constant sustained energy is needed for life to develop
What is the RNA world theory?
RNA formed first and then led to DNA and protein formation. RNA can store replication information, can replicate itself, can act as an enzyme, could have provided heredity and catalysis before DNA.
- does not preclude primordial soup theory
What is the support of the RNA world theory?
- Nucleic acid precursors and nucleotides have been made in the lab from compounds common on early earth and UV light
- Some viruses contain only RNA (viruses are considered to be an ancient form of life)
What are the issues with the RNA world theory?
- how does a combination of DNA, RNA and proteins lead to cell formation?
- how are membranes produced?
- attempts to recreate RNA formation under early earth conditions have failed
- RNA is unstable in water
What is the deep sea hydrothermal vent theory?
Involves the generation of electrochemical gradients and metal-containing enzymes as the first precursors to life –> allowed for the generation of (chemical) energy
Alkali vent water meets acidic ocean water, creating a proton gradient, thus generating energy and macromolecules, which would combine behind a membrane, exits the vent and spreads throughout the ocean.
What is the support of the deep sea hydrothermal vent theory?
- artificial hydrothermal vents have generated proton gradients
- most old enzymes contain iron and sulfur (which would have come from the vents)
What are the issues with the hydrothermal vent theory?
- no clear mechanism yet for how biomolecules actually developed
What is the evidence for the last common ancestor (LUCA) theory?
all life is:
- carbon based
- similar enzymes and genetics
passes hereditary info through RNA/DNA
- has only left-handed amino acids and only right handed amino acids
