Cell Biology & Origin of Life

Seven Characteristics of Life
Display Order
Arranged in a highly ordered manner
Cell: fundamental unit of life
Harness & Utilize Energy
Acquire energy from the environment and use it to maintain state
Reproduce
Have the ability to make more of their own kind
Respond to Stimuli
Can make adjustments to their structure, function and behavior in response to changes to external environment
Exhibit Homeostasis
Regulate internal environment so that conditions stay relatively constant
Growth & Development
Increase their size by increasing the size/number of cells
Evolve
Populations change over generations to become better adapted to the environment
The Fundamental Unit of Life
Cell Theory
All organisms are composed of one or more cells
The cell is the smallest unit that has the properties of life
Cells arise only from the growth and division of preexisting cells
LUCA
Last Universal Common Ancestor
Evidence:
Lipid membranes
Genetic system based on DNA
Reproduction
ETC – ATP & Glucose
DNA to RNA to Protein transfer of information
Common system of protein assembly: ribosomes, mRNA, tRNA
Earliest Life
Stromatolites dated to 3.5 billion years ago represent the earliest fossil evidence of life
Layered rock that is formed when microorganisms bind articles of sediment together, forming thin sheets
Formed by cyanobacteria – modern – posses a sophisticated metabolism
Panspermia is the hypothesis that very simple forms of life are present in space and seeded the earth soon after it cooled
Stages of Prebiotic Evolution
So what do you need?
Abiotic synthesis
Heritable Information
Formation of Cells
Assembly of complex organic molecules from simple molecules, including protein, RNA or both
Aggregation of complex organic molecules inside membrane-bound protobionts
Geophysical Stage
Conditions On Young (Primordial) Earth
Chemicals: H2O, H2, CH4, NH3, H2S
Energy Sources: ultraviolet light, lightening
Reducing atmosphere
Allow for building up of highly reduced compounds (electrons)
Miller-Urey experiment demonstrated that abiotic synthesis of biologically important molecules such as amino acids, sugar, nucleotide bases, lactic, acetic, formic acid, is possible
1953: Miller and Urey tested this theory and produced organic molecules from inorganic ingredients
Life may have evolved in deep sea vents, atmosphere or surface of earth
Chemical Stage
Abiotic Synthesis: organic molecules from inorganic molecules
No abiotic synthesis today – oxidizing environment
Reactants
Water vapor
Ammonia
Methane gas
Hydrogen gas
Conditions
Heating by sun
Cooling at night
Radiation from the sun
Energy from electrical storms
Results (after 1 week)
Aldehydes, carboxylic acids formed
Glycine and alanine formed
Amino acids
Sugars
Purines & pyrimidines
Chirality
Chiral molecule: not superimposable on its mirror image (come in two forms)
Two enantiomers (optical isomers)
Handedness
Same chemical and physical properties
Different biological properties
Thalidomide
Used as a “morning sickness” drug in 1960s
Antiemetic & readily convert to the other chiral form (teratogen causing birth defects)
Approved in 20 European countries not in NA
Side effect: deformed children
Chirality Problem
Miller-Urey experiment = racemic (50% of both chiral forms mixture)
Biology is homochiral (only one form, no mixture)
L amino acids, D sugars
Origin of Homochirality
Homochirality
Essential to the evolution of life
Specificity is required = one chiral form
Random chance
Extraterrestrial origin
Murchison meteorite
Contains 7 amino acids
9% more L isomer (bias led to life)
Biological Stage
Development of DNA, RNA and protein triad
Synthesis of polymers
Monomers not polymers – first cells (Miller-Urey experiment)
The Origins of Information & Metabolism
All organisms contain deoxyribonucleic acid (DNA)
DNA is copied onto ribonucleic acid (RNA)
RNA directs the production of protein molecules
Enzymes catalyze all reactions
Enter RNA World
RNA: information, structure, catalysis
Speed up rate of reaction
How can RNA catalyze?
RNA can fold
Complementary base pairing
Ribosome
Ancient organelle – required for all cells
2/3 RNA, 1/3 protein
Ribozymes
RNA molecule that has catalytic properties
Self-splicing introns – catalyze own excision
Can catalyze reactions on the precursor RNA molecules that lead to their own synthesis, as well as on unrelated RNA molecules
Ribosome aminotroinferase activity
Can fold into very specific shapes and are single-stranded
Function depends on folding
RNA was the first molecule from which both DNA and proteins developed
Ribosome aminotransferase activity
Evolution of Information Transfer
RNA
Information, catalysis & structure
Proteins
Structure & catalysts
Diversity (20 amino acids)
DNA
DNA is more stable than RNA
Deoxyribose more stable then ribose
Base uracil found in RNA is not found in DNA; replaced by thymine – common mutation in DNA is the conversion of cytosine into uracil – by utilizing thymine in DNA, any uracil is easily recognized as a damaged cytosine and can be repaired
DNA is double-stranded – complementary strand can be used to repair the damaged strand
The First Cells
Monomers -> polymers: abiotic synthesis of cell molecules
Hypothesis
Clay particles creating a surface upon which polymerization reactions could occur
Accelerated spontaneous reaction by clay particles (montmorillionite)
High surface area & charged surface
Charged components of the molecules are attracted to the charged surface of the clay
Facilitate formation of SHORT nucleotide/amino acid chain (still function and have a selective advantage)
Flourescent Dye Evidence
Purpose: how long fluorescent dye is retained in an abiotically synthesized vesicle
Separates biological environment from outside environment
Retain macromolecules inside so their concentrations are higher inside

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Protobionts: The First Cells
Abiotically produced organic molecules that are surrounded by a membrane or membrane-like structure
Formation allowed for an internal environment to develop that was different than external environment

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