Chapter 13 - The Nature and Origins of Life Flashcards
What is life?
cells, energy, reproduction, heredity, growth, self-maintenance
No real dividing line between living and non-living
life energy
The miracle of life
Chance of life evolving - Probability of virus forming by chance in a billion years is 10^2,000,000 to 1, but fossils of algae far more complex were laid down 3.5 billion years ago, 1b years after Earth formed
Complexity of simplest forms
How information encoded in genes came into existence - Second law of thermodynamics states that info can’t spontaneously spring into being any more than object can spontaneously heat up
DNA molecues
Made of 4 bases, A-T, C-G
If ladder pulled apart, each half becomes template which grows into new DNA molecules and new appropriate bases attach themselves facilitated by enzymes
Enzyme
unzip and rejoin DNA and guide right bases into position
Amino acids
Three rungs combined form 64 “words” from which all protein molecules are made
All organisms use only 20 different amino acids
Changing just one “word” would change proteins containing amino acid with fatal results
Chains of up to 4 form naturally in volcanoes
Protein
Long chains of 100 or more amino acids
Every cell in higher organisms contain 30,000 different proteins
Represent 30 million bits of info
Gene
contains proteins in DNA
mRNA
messenger RNA
reads proteins and takes it to one of thousands ribosome “factories”
Ribosome
Where proteins are assembled from amino acids
tRNA
transfer RNA
Gather amino acids in protein
Once chain of amino acids is complete, protein folds into precise 3-D shape
Origins of life
First complex organic molecules form
From these, simple self-replicating molecules like proteins or RNA must emerge that have potential to evolve into life
Complex soup of chemical reagents must be isolated from surroundings to facilitate self-organizing reactions
Genetic code can’t be reduced to simple model like other complex chemical systems
Evolutionary trend towards ever-greater complexity
Cells may act as quantum computers that have ability to generate info
Psi field could inform living things about what has happened in other parts of spacetime, enabling genetic info to be shared across universe
Peptide
chain of amino acids, forming these is more challenging than forming amino acids because appropriate energy must be supplied
To create proteins, first must sort between 10^130 combos of amino acid chains, of which life only uses a fraction. Odds against appropriate set being selected by chance is 1 in 10^40,000; molecules of diff composition have similar shapes, so only needed to find ones of right shape
self replicating systems
one virus that uses RNA molecules instead of both DNA and enzymes might have formed spontaneously, but doesn’t demonstrate energence of life because it probably wouldn’t have been available in primeval soup. RNA evolved relatively late so unlikely to be original self-replicating molecule
Alternative possibility is simple protein molecule which can replicate and correct errors
Protecting self-organizing chemical reactions from risruption by environment
Molecules can form membrane around bubble of liquid and catalyst that facilitates reaction
Catalyst molecues trapped inside when membrane formed
If membrane is punctured it will be repaired when ctalyst tries to escape
Bubbles grow by absorbing “food” molecules and reproduce by dividing when they reach critical size
If chemical composition inside each bubble were slightly different after division, evolution would begin towards bubbles that grow more efficiently
Problem with protection of self-organization theory
Unfit environment for formation and survival of bubbles; earth was almost completely covered in hot water in huge tides, atmosphere was dense and unbreathable, thick clouds, and UV radiation, molten rock, asteroids,etc.
Earliest living things were extremophiles, most likely place for them to exist is pores of spongy under-water basalt rocks
