The Secret of Ping-Pong

To get to where you want to go, it helps to know where you have come from

Life is a self-organizing complex phenomenon that occurs (sometimes) in places where energy is flowing from a hotter object to a cooler object.

The natural state of the universe is for energy to move from a state of order to chaos.

What we call life is a process by which order is maintained amidst chaos

Basic parts of the cell: 1. Cell membrane 2. Proteins 3. DNA 4. RNA

Just like DNA, but single stranded. Communicates between DNA and proteins

Flow of energy is used to maintain balance and order

Universe comes into existence

Solar system is formed

First fossil evidence of life. Single celled bacteria

Explosion of multicellular life

 What came first? The chicken or the egg?  Where did the seed that gave rise to the tree of life come from?  What is the origin of life?

1. Where did the organic molecules come from? 2. How did polymerization arise spontaneously? 3. How did the first polymers begin self-replication? 4. How can all this occur in water, which by nature dissolves these molecules?

Remember, a theory cannot be proven true, only false

 Reducing atmosphere: very little oxygen around (modern metabolism not yet evolved)  High Temperatures: oceans were between degrees Centigrade  UV radiation: no oxygen, no ozone  Lots of lightning

Heat + gases + water + lighting = amino acids

 Based on possible pre-biotic conditions of earth it is possible that amino acids and other vital organic molecules were present.  But how would these molecules have become something so complex as the cell?

 Replication of macromolecules is a significant requirement for life.  What came first? DNA, RNA, or Proteins?  The RNA World Theory

 The RNA world hypothesis proposes that a world filled with RNA (ribonucleic acid) based life predates current DNA (deoxyribonucleic acid) based life.  RNA can store information like DNA and catalyze reactions like proteins (enzymes).  Hypotheses presents RNA-based catalysis and information storage as the first step in the evolution of cellular life.

 The living RNA theory has created a whole new set of problems that need a solution. 1) The building blocks for RNA are harder to synthesize under plausible prebiotic conditions than amino acids. In fact, cytosine has never been synthesized. Cytosine is also absent from meteorites. 2) Unlike amino acids, two of the building blocks required for RNA (cytosine and ribose) are not stable and have very short lifetimes. It is unlikely that these molecules existed in the soup.

 Assume that the first cells did indeed arise out of a solution of organic molecules.  Where is it likely the necessary conditions would have occurred?

Life could have started in the primordial soup of early earth.

Bacteria living near the warm, energy rich ocean vents are the basis of whole ecosystems and do not require the suns energy

 The theory that life was seeded here on Earth from outside our world.  Possibilities include meteorites, comets, aliens, etc.

 Protobionts are systems that are considered to have possibly been the precursors to prokaryotic cells.  A protobiont is an aggregate of abiotically produced organic molecules surrounded by a membrane or a membrane-like structure.

 Protobionts exhibit some of the properties associated with life, including simple reproduction, metabolism and excitability, as well as the maintenance of an internal chemical environment different from that of their surroundings.

 Early earth’s atmosphere consisted almost entirely of carbon dioxide and nitrogen.  The first prokaryotes were anaerobes converting naturally occurring organic molecules into ATP.  Then some prokaryotes began collecting sunlight energy and releasing oxygen.  Anaerobic respiration first, then photosynthesis, then aerobic respiration

 The endosymbiotic theory states that chloroplasts and mitochondria originated as free living prokaryotes that were endocytosed, but not digested, by primitive proto-eukaryotes and over time the cells developed a mutual dependency upon one another.

Mitochondria and Chloroplasts… 1. Have a double membrane (results of endocytosis) 2. Have circular, naked DNA (like prokaryotes) 3. Have 70s ribosomes (like prokaryotes) 4. Divide by binary fission (like prokaryotes)