Our Journey to Cosmos of the Cell  -  Origins of Life

  
Cells are a Unifying Concept of Biology...  the Unity of LIFE...
& CMB is the study of the Molecular Chemistry of cells

  
      the basic unit of LIFE is the
CELL…

            an inanimate mixture of  biomoleculesmwking  which have been selected    

            for their fitness to perform certain biochemical reactions...
            reactions that characterize and define life.
                                                [web-biomolecule databases]

                  Every living thing is cellular…
             
"The only life we know for certain is cellular..."  
                       
                                           H.J. Morowitz -biologist & philosopher

                                                                                                                          all class readings: are on the class web pages 


 

 

       

 

 
but, have you ever seen an individual living cell  ?   [ pics of cells* ]
                             
 
  
    ATCC-CCL 2
- HeLa cells   in frozen ampuoles @ -321 0F  
       frozen cultured cells show no signs of life, not even simple chemical metabolism, if warmed to room temp...
         "
resurrection - seem to come back to life"...  they move about, feed and metabolize, maybe reproduce

   

             
                                                                           American Type Culture Collection - Manassas, VA
 
          Human Life...  for centuries, life was defined in the unit of the whole organism,  
                                                                                     a cat,  a bird,  a human being...
         but today life is sum of the lives of many individual cells making up a human body... 
  
        
             Life may be best defined in terms of the individual CELL,
                                                        and its molecular constituents.
                                                                                                                       some ideas about life through the scientific age

 

 

 

 
Universal Characteristics of Cells (all Life)

   
1.  all cells store their hereditary information in DNA
  

2.  all cells replicate their hereditary info via templated polymerization*
          templated replication                templated transcription      
  

3.  all cells transcribe hereditary info into intermediate RNA via templated transcription
  

4.  all cells translate RNA in same mechanistic way via codon:anticodon "Chargaff" pairing

     chargaff pairing A  :  T   or   A  :  U

G  :  C 

 
                                               







5.  all cells regulate rate of gene transcription/translation, so only a portion of full
         repertoire of possible RNA's/proteins are copied, thus hereditary info dictates
         not only nature of cell's proteins, but also when/where they are to be made
         so called, differential gene activity.
 6.  all cells use protein catalysts (enzymes) to make/break covalent bonds
                                      E  +  
S    <--->    ES    <--->   E  +   P
 7.  all cells metabolize - consume free energy and are far from chemical equilibrium.
     consumption of free energy creates covalent bonds (which resist the disordering
     effects of thermal motion), thereby creating hereditary info in a DNA sequence.
          the methods that cells have evolved to obtain free energy include:
                 heterotrophy - oxidation of foods (covalent bonds)
                 autotrophy - capture of light energy via pigments (photosynthesis)
                 lithotrophy - chemical electron donors provide energy
           N2 & CO2 are stable and unreactive & reduction to NH2 & CH2O uses energy.
8.  all cells are enclosed in a spontaneously aggregating amphiphilic phospholipid bilayer:
     membranes regulate nutrient/water transfer, concentrate molecules internally,
     all membrane have embedded protein transport molecules             
 a text description of the PROPERTIES of  LIVING CELLS* read this
 
 

 

 

 

 

 

 

 

 

 
So what exactly defines Life
 ?

  Most biologists agree: life exhibits certain "QUALITIES" that equate to the living state and many
  prefer to use an operational description of what living entities can do and perform rather than to
 
use a strict
definition of life... thus we describe the Attributes of the Living State
:

  
  1) Autonomous Replication - Self-Replication of cells by cell division (Mitosis  &  Meiosis)  pics*
         two whole copies of genome: maternal & paternal hereditary info: a backup-redundancy
         all cells store their hereditary information in DNA, coded as genes. (table of sequenced genomes*)
  
       based in the semi-conservative replication of DNA (complementary templated polymerization)
              
  most defining trait of the living state…
  
  2) Life had an Origin - Life begets Life... "all cells are derived from preexisting cells"...
          ►  Prime Directive:   Rudolph Virchow states (1858) this as a prime directive of life.
                  all individual organisms come from a single cell & all individual cells in an
                  organism are descended from fertilized egg.
                                   
       eliminates Spontaneous Generation [ Redi &  Pasteur  experiments ]
 

 

 

        
 

  
     
   All living things have evolved from a common ancestral cell, through processes that include
   natural selection and genetic drift acting on heritable genetic variation. 

   
   LUCA - Last Universal Common Ancestor* -

          supporting evidence that all cells are derived from a single PRIMORDIAL cell
...
                 This hypothesis is based upon the
circumstantial evidence...
                  mostly the
commonality that occurs in all current known living organisms, such as:
           1.  all living things are composed of very
similar organic molecules:
                     the same proteins, lipids, carbohydrates, similar nucleic acids etc...

           2.  all proteins, the biological catalysts responsible for life's chemical reactions,
                     are made from
one set of 20 standard amino acids...
a-amino acids &  L-stereoisomers...

           
3.  all contemporary organisms carry their genetic information in nucleic acids [DNA/RNA]
                     and use the
same genetic CODE.

   
   


 
 
       

                                      
 

 

 

              
  
3) Life exhibits EMERGENT PROPERTIES...     a large scale, group behavior in a system,
        which doesn't seem to have any clear explanation in terms of the system's constituent parts.

                     ex:  oxygen - colorless, odorless, tasteless, reactive GAS that supports combustion
                  
     hydrogen - colorless, odorless, tasteless, reactive GAS that is flammable
                        water - H2O - a non-flammable chemically reactive polar LIQUID that exist in 3 phases
                   ex: metal Na is explosive & gas chlorine is poisonous --> edible table salt NaCl
*
           Emergent properties are unexpected, nontrivial results of relatively simple interactions by
           relatively simple components. Emergent properties seem to be a
consequence of complexity
           from which unpredicted behaviors and patterns emerge.
     
   
      from a mix of biomolecules thus emerges a complexity that exhibits properties we call life:
    

  4) Life requires a Critical Level of COMPLEXITY...
           Structural complexity and information content are built up according to current paradigm
           by combining simpler subunits into multiple complex combinations.
 
                        elements --> stable monomers --> polymers --> metabolism --> supramolecular complexes --> organelles --> cells*
    A single cell has no concept of the whole. A cell runs by the chemical rules built into its molecules.
    A single cell can't do much without interaction with other cells, but
in combination cells can
    produce complex results such as
consciousness.
 

 
   

 

 

 

 

 

 
 
 5)  Life exhibits biochemical autonomy, i.e., it carries on & regulates METABOLISM:   
         
biochemical activities in cells transform energy (ATP)   &   molecules to sustain cells
          
cellular energetics occurs via a few basic molecular reaction mechanisms in all cells...
 
                                1.   cellular redox reactions,
                               
2.   
capture of light energy in photosynthesis
                               
3.   electron flow through carrier proteins, 
                            
   4.   H+ ion pumps
.

                                5.   concentration gradients across interfaces.
 
      

      Life is a chemical
system far from equilibrium.
          it consumes free energy, largely derived from photosynthesis, which is stored in
             high-energy bonds
or ionic concentration gradients. The release of this energy
             is coupled to thermodynamically unfavorable reactions to drive biological processes:



                                there are no unique Laws of chemistry or physics just for the Living State...
                                       
ΔG   =   ΔH  -  T ΔS

   
 


 

 

 

 

 
 
 
7)  Life is manifest by the absence of the living condition...
            
a lack of the properties of the living state is itself definitional of living state.
         
  death is
a deterministic event, because all living beings will eventually die.   [death & taxes]
  
        Cells 
DIE - When metabolism ceases with no prospect of starting again; 
                                    
Cell death is the collapse of the quantum state which has allowed living matter to take energy from the
                  environment, while preventing an increase local entropy and delaying the
the tendency of energy to be
                 
dispersed or diffused
.
Thus, death is an irreversible final state Dead organisms will never return to life
                  because they would be violating the Law of Entropy.
THE LAW OF ENTROPY CAN BE TEMPORARILY
                  BLOCKED
(Life), BUT IT CAN NEVER BE VIOLATED.
  
       senescence is process of aging.  Cellular senescence is a phenomena where isolated cells show
       a limited ability to divide in culture. The successive shortening of the chromosomal telomeres
       with each cell cycle is also believed to influence the vitality of the cell, thus contributing to aging.
          cell death plays a considerable role during physiological processes of multicellular organisms,
          particularly during embryogenesis and metamorphosis
...     
              
programmed cell death is known as...     apoptosis*  &  definition
    

 

 

 

 

 

 

 

  

    thus, the attributes of life are manifest in the Definition of a Cell...
  
    A living cell may be described as a(n)...
        ... self contained...  self assembling...  self adjusting...  self perpetuating... 
                  
 isothermal (steady & ambient) mix of biomolecules,
        ... held in a 3-D conformation by
weak non-covalent forces,
        ... that can
extract raw materials (precursors) & free energy from its surroundings,
        ... & that can
catalyze reactions with specific biocatalysts (enzymes), 
                    which it makes itself ,
        ... & that shows great efficiency & economy of
metabolic regulation,
        ... & that maintains a
dynamic steady state far from equilibrium,
        ... & can
self-replicate, using the linear information in the "molecule of life"…   DNA,

   But where did the first cells come from?  
   next lecture. Universal Characteristics of Cells*  A practice topic test - Properties of Life