Biology Fall 2009--Rozema
Unit 2: Cell Structure & Function
“Where did cells come from?” Notes
Formation of Macromolecules:
- Earth is about 7billion years old.
- There existed biological molecules. There is no way science can “prove” exactly how these biological molecules came “into existence”.
- We know that all things like planets and stars are made of matter (atoms), and we know that atoms undergo many chemical reactions (forming different molecules) in order to gain stability in their environment.
- Scientists can prove that gases such as carbon dioxide, methane, ammonia and hydrogen gas all existed within the ocean. Through laboratory tests, scientists were able to find that when reacting these gases with water and extreme temperatures, the various biological molecules were formed.
- The most crucial biological molecule was nucleic acid. While DNA or RNA did not “spontaneously” form, simpler monomers (nucleotides) did exist. Because of the instability of nucleotides (attractions between the pentose sugars and phosphates, and between opposing nitrogenous bases), nucleotides bound together.
- Sure, at first, nucleic acid polymers would be formed, and unsuccessful (would prove to have no purpose). But as they gained the ability to self replicate and sustain function, the successful compounds continued to replicate.
Formation of Cell Membranes & Close Cells:
- Again remember this is about 5billion years ago, and the oceans are scalding hot, and spewing with gases and biomolecules.
- Also remember that phospholipids (one of the types of biomolecules) form micelles when mixed in water (polar) solutions.
- Imagine now that a series of phospholipids form a micelle, capturing a variety of biomolecules inside. Essentially, this is a primitive cell.
- Can we prove this? No, no one will ever be able to prove it or disprove it. Science does not try and say this is the only answer, but run tests in order to find out possible explanations/answers.
Formation of the First Cells—Prokaryotic Cells:
- Prokaryotic means that the cells had NO high-tech nucleus, NO high-tech organelles and what not.
- Prokaryotic cells are literally a phospholipids membrane, with water and biomolecules floating around inside.
- Many scientists propose that complex organelles such as mitochondria were once prokaryotic cells. (THIS IS CALLED THE ENDOSYMBIOTIC THEORY)
- The endosymbiotic theory states that primitive prokaryotic cells (now mitochondria) once freely existed. Because they could provide large quantities of energy to other prokaryotes, they formed a symbiotic relationship with other cells. This means that other cells lived together with mitochondria, providing shelter and nutrients to the mitochondria, and in return the mitochondria provided energy to the other cell.
- Many organisms today live in symbiotic relationships. Humans are full of bacteria that help brake down inorganic compounds. It is called the “endosymbiotic theory” because the mitochondria live INSIDE (endo) the other cells.
- Mitochondria + other Prokaryote à First Eukaryotic cell!
Evidence for the Endosymbiotic Theory:
- Both chloroplasts + mitochondrion have their own DNA (nucleic acid)
- Both chloroplasts + mitochondrion have their own cell membranes
- Both chloroplasts + mitochondrion can reproduce on their own through binary fission (like bacterial cells)
- Both chloroplasts + mitochondrion have their own ribosomes, to produce their own protein
- Chloroplats + Mitochondria have everything present day prokaryotic cells have!