Origin of Life on Earth Flashcards
Oparin-Haldane Hypothesis (4 Requirements of Life on Early Earth)
- formation of organic molecules, the building blocks of cells (AA, nucleotides, simple sugars)
- formation of polymers (longer chains) of organic molecules, that can function as enzymes to carry out metabolic reactions and possibly replicate (proteins, RNA strands)
- encoding hereditary information (RNA strands)
- formation of protocells
SPECIFIC HYPOTHESIS THAT FUFILLS THE REQUIREMENTS OF THE FOUR REQUIREMENTS FOR THE ORIGIN OF LIFE ON EARTH
Miller-Urey Experiment
- tested the first step of the Oparin-Haldane hypothesis by investigating the formation of organic molecules from inorganic molecules
- produced a number of organic molecules, such as AA, cyanide, formaldehyde
- simulated early Earth reducing atmosphere (methane, ammonium, hydrogen), an ocean, and a hydrologic cycle
- energy inputs via heating and electrical discharge
3 Major Sources of Organic Molecules of Pre-Life Earth
- atmospheric synthesis of organic molecules by Miller-Urey chemistry
- synthesis of deep sea hydrothermal vents
- in-fall of organic molecules synthesized in outer space
RNA World Hypothesis
self-replicating RNA molecules eventually led to the evolution of a hereditary system in the first cells/protocells
- CREATED A SYSTEM LIKE DNA BEFORE DNA EXISTED
- system of RNA molecules to encode codons to specify AA
- tRNA-like molecules to encode matching AA
- catalytic RNAs to create peptide bonds
Transition from RNA to DNA
- at some point leading to the last universal common ancestor, DNA became the preferred long-term storage molecule for genetic info
- DNA is more chemically stable than RNA
- DNA serves as a template for replication (2 complementary strands) of its partner strand, providing some innate redundancy
Modern RNA
- used to read genetic info to synthesize proteins
- rRNA does key catalytic activity of forming peptide bonds to link 2 AA
- ribosome organelle
Leading up to the RNA World Hypothesis
Thomas Cech discovered some RNA molecules can catalyze their own site-specific cleavage, led to:
1. term RIBOZYMES to denote catalytic RNA molecules
2. revival of a hypothesis that RNA molecules were the original hereditary molecules (pre-dating DNA)
Four Requirements for the Origin of Life on Earth
- ability to reproduce
- replication of hereditary information
- enclosure in membranes to form cells
- the use of energy to accomplish growth and reproduction
REQUIREMENTS FOR A HYPOTHESIS FOR ORIGIN OF LIFE
Catalytic RNA Molecules
- a single molecule could potentially store genetic info + replicate themselves, with no proteins needed initially
- populations of such RNA would undergo a molecular evolution - RNA molecules would make copies of each other, making mistakes and generating variants
- variants would continue to self-replicate, leading in an increase in frequency in the population of catalytic RNA molecules
Formation of organic polymers
- AA link together to form polypeptide chains, and the chains fold to become protein molecules
- Ribose, 5 carbon sugar, nitrogenous base, and phosphate bond to form nucleotides. Nucleotides link together to form nucleic acids (DNA and RNA0
Protocells
membrane bound droplets, lipid vesicles that enclosed RNA ; enclosed reactants, emitted products and helped growth ; some had primitive metabolism
- may have been precursors of cellular life
When did evolutionary process begin to drive the origin of the first cells?
- RNA World Hypothesis envisions evolutionary processes driving pops of self-replicating RNA molecules of protocells with such molecules
- RNA molecules that replicated imperfectly would produce daughter molecules with slightly diff sequences, one that’s replicated better/improve growth replication of host protocells WOULD HAVE MORE PROGENY
MOLECULAR EVOLUTION OF SELF-REPLICATING RNA MOLECULES/PROTOCELL POPULATIONS DONTAINING SUCH RNA WOULD FAVOR THE EVENTUAL FORMATOIN OF THE FIRST CELLS
What is the correct sequence of these major events in the origin of life?
- Formation of protocells (protobionts)
- Synthesis of organic monomers
- Synthesis of organic polymers
- Development of a hereditary mechanism
synthesis of organic monomers < synthesis of organic polymers < formation of protocells < development of a hereditary mechanism
The first genetic material was most likely a(n):
a. protein (a polymer of amino acids)
b. RNA (a polymer of ribonucleotides)
c. DNA (a polymer of deoxyribonucleotides) with enzymatic activity
d. ribonucleotide (a monomeric unit of RNA)
e. DNA (a polymer of deoxyribonucleotides)
RNA (polymer of ribonucleotides)
The Cambrian explosion describes:
an adaptive radiation
