Chapter 2: Origins of Life
Ch. 2.1b The Fundamental Unit of Life is the Cell
• Cell Theory:
1. All organisms are composed of one or more cells
• Prokaryotes are composed of a single cell
• In unicellular organisms, the one cell is functionally
independent, capable of life activities.
• In more complex cells, life activites are divided among
○ Individual cells of multicellular organisms are
potentially capable of surviving alone if placed in a
chemical medium that can sustain them
• Metabolic processes occur in cells
1. The cell is the smallest unit that has the properties of
• Opening cells destroys the property of life and all life
activities cease to occur.
1. Cells arise only from the growth & division of pre-
• Cells carry hereitable information:
○ DNA & RNA contain the info required to
manufacture a vast array of biological molecules.
• New cells can arise only from the division of pre-existing
Ch. 2.3a The Origin of the Information System
• All organisms contain DNA, a large, double stranded, helical
molecule that contains a unique alphabet that provides the
instructions to assemble important cell components from simpler
molecules • DNA functions similarly in all organisms:
○ Info in DNA is copied onto molecules of RNA, which then
directs the production of protein molecules
○ Even simple cells contain thousands of proteins coded from
a DNA sequence.
• Enzymes are required to catalyze the replication of DNA, the
transcription of DNA into RNA & finally the translation of RNA into
• Info is preserved from generation to generation by the ability of
DNA to direct its own replication so offspring receive the same
molecular instructions their parents have.
Ch. 2.3d The Development of Energy Harnessing Reaction Pathways
• Oxidation-reduction rxns were the first E releasing rxns of the
• Humans oxidize food molecules & use liberated E (electrons) to
reduce other molecules (ex. Those needed to synthesize
• Electrons removed in an oxidation rxn in a primitive cell would be
transferred directly to the OA in a 1 step process.
○ Changed over time b/c it wastes too much E into a multi
step process where E from oxidation is released slowly.
• ATP links E releasing rxns to those requiring E
○ May have 1 entered early cells as one of the organic
molecules absorbed from the primitive environment,
initially hydrolyzed into ADP & Pi causing a release of E
○ E releasing during electron transfer was used to synthesize
ATP from ADP & Pi.
Ch. 2.4 Early Life
Ch. 2.4a Earliest Evidence of Life • Stromalites are a type of layered rock that is formed when
microorganisms bind particles of sediment together, forming thin
• Modern day stromalites are formed by the action of a group of
photosynthetic prokaryotes called cyano bacteria
• Evidence of early life is given from carbon composition in rocks
as these organisms would have the ability to take CO2 from the
atmosphere & fix it by incorporating it into various forms (sugar,
• Panspermia is the hypothesis that very simple forms of life are
present in space & seeded Earth soon after it cooled
• Both Prokaryotic & eukaryotic cells share common features:
○ Plasma membrane: separates external environment from
the cytoplasm consisting of the cytosol and organelles
○ Electron transport chains: used to link the oxidation of
molecules to the synthesis of ATP.
○ Transcription translation machinery that relies on
ribosomes for the synthesis of proteins from RNA
○ Both DNA is organized in chromosomes.
DNA of a prokaryote lacks a nucleus, and is localized
into the nucleoid
• Some early cells developed the capacity to carry out
photosynthesis using water as an electron donor; the oxygen
produced as a by-product accumulated, and the oxidizing
character of Earth’s atmosphere increased. From this time on,
organic molecules produced in the environment were quickly
broken down by oxidation, and life could arise only from
preexisting life, as in today’s world.
○ Photosynthesis that relies on the oxidation of water is
called oxygenic photosynthesis ○ In aerobic respiration, E is extracted from food molecules,
with O2 acting as the final electron acceptor.
○ Aerobic respiration allows organisms to extract a much
greater amount of E from food then anerorbic respiration.
Ch. 2.5 Eukaryotic Cells
• Eukaryotic cells possess an endomembrane system (collection
of interrelated membranous sacs that divide the organelle) that
probably evolved from infolding of the plasma membrane.
○ Consists of the nuclear envelope, the ER, and the Golgi
○ Infolding of the plasma membrane is believed to be
responsible for the evolution of organelles explained by
pockets of the plasma membrane extending inward &
surrounding the nuclear region to fuse around DNA and
form the nuclear envelope & nucleus
Remaining membranes formed vesicles giving rise to
the ER & golgi complex
• Membranes of the endomembrane system are connected by
vesicles, which are small membrane bound compartments that
transfer substances b/w parts of the system • Cytoplasm: cytosol & extra nuclear organelles
• Lumen: interior of organelle
• Cytosol: cell contents excluding organelles
• The ER occurs in 2 forms:
○ Smooth: synthesizes lipids & breaks down toxic
substances ○ Rough: makes proteins that become part of cell
membranes or are released to the cell surface within
vesicles that pinch off from the ER and join the golgi
○ Proteins made by freely suspended ribosomes in the
cytosol pass through the nuclear pores to enter the
nucleus or become parts of other structures.
• The Golgi complex chemically modifies proteins made in the
rough ER and sorts finished proteins to be secreted from the cell
or embedded in the plasma membrane
○ Proteins secreted from the cell are transported to the
plasma membrane by secretory vesicles that release
their contents to the exterior via exocytosis. Cells may
also enter the cell via endocytosis.
• Lysosomes budding from the golgi membrane contain
hydrolytic enzymes that digest damaged organelles or contents
of endocytic vesicles that fuse with them.
• The E transducing organelles-chloroplasts & mitochondria-
are thought to have been derived from free-living prokaryotic
• Eukaryotic Nucleus:
○ Contains DNA & associated proteins, machi