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Chapter 2

BIOL 1000 Chapter Notes - Chapter 2: Cytoplasmic Streaming, Exocytosis, Secretion


Department
Biology
Course Code
BIOL 1000
Professor
Nicole Nivillac
Chapter
2

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Origins of Life
Chapter 2
Cell Theory states that:
1. All organisms are composed of one or more cells
- prokaryotes are unicellular organisms capable of carrying out all of life’s activities and
biological processes.
- multicellular organisms carry of life’s activities and biological processes by dividing it among
many specialized cells
2. The cell is the smallest unit of life
- If the cell is broken, all activities of life cease. This includes growth, reproduction and response
to stimuli.
3. Cells come from pre-existing cells that have gone through growth and cellular division.
The origins of Information and Metabolism
Two systems must be active so that the cell may carry out its life activities:
1. One system devoted to protein synthesis
[This includes replication, storage, and translation]
2. The second system devoted to capturing and harnessing energy for metabolism
The Information System
DNA is found in every organism. It’s responsible for assembling the important components of
the cell from simpler molecules.
The information from DNA is copied onto RNA, which is responsible for the production of
protein molecules.
Proteins each have their own unique DNA sequence that is coded differently from the rest.
Enzymes:
1. Catalyze the replication of DNA
2. Transcription of DNA into RNA
3. Translation of RNA into protein molecules.
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The Development of Energy-Harnessing Reaction Pathway
Redox reactions have always been a form of energy-releasing processes. The consumption of
food is oxidized and that energy is reduced (or supplemented) to other molecules that require the
energy to synthesize proteins. However, this is not a one step process or else a lot of energy will
be wasted. The energy is distributed in a multistep process that is slowly released (cellular
respiration)
Adenosine Triphosphate (ATP) is the compound that links energy releasing reactions to those
that need energy.
Earliest Evidence of Life
Stromatolites are a type of layered rock with thin sheets that have formed due to
microorganisms binding sediment particles to each other. This is the earliest evidence of life,
dating back to 3.5 billion years ago.
Modern day stromatolites are formed by cyanobacteria – a group of photosynthetic prokaryotes.
The cyanobacteria provide evidence that due to their sophisticated metabolism, earlier life forms
must have preceded their evolution.
Panspermia is the name of a hypothesis that suggests life on Earth came from an extraterrestrial
origin. There are two pieces of evidence that support this statement:
1. Although Earth was formed 4.6 billion years ago there is chemical evidence of life that dates
back to 3.9 billion years ago. Scientists argue that the window for the development of life is very
narrow; hence, life must have formed relatively quickly after the formation of the Earth.
2. Life organisms are far more resilient than previously thought and could possible survive for
many years in space. Extremophiles are prokaryotes that can thrive under very harsh conditions
of temperature, pressure and can survive in a dormant state in interstellar space. Spores, for
example are highly resistant to change and can be restored to active growth after being exposed
to high level radiation. Given the complexity of these organisms, the idea of life forms from
space coming to Earth to initiate the evolution of life is highly possible.
Prokaryotes
Prokaryotic organisms can be found in two main domains of life:
1. Bacteria
2. Archaea
Although prokaryotes do not have a nucleus, it is important to know that they share similar
fundamental features to eukaryotes.
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They have a selective permeable plasma membrane which separates the external environment
from the cytoplasm (liquid substance + organelles) of the cell. The cytoplasm contains cytosol
– a substance that contains water, salts and various organic molecules. The cytoplasm also
holds organelles in place.
The selective permeable plasma membrane controls what goes in and out of the cell run by
protein complexes that control the electron transport chains that are used to link the oxidation of
energy rich molecules to the synthesis of ATP. In photosynthetic prokaryotes, the internal
membranes are the sites of photosynthetic electron transport chains which harvest light
energy for the synthesis of ATP and energy-rich molecules.
In eukaryotes, the synthesis of energy rich molecules occurs in the mitochondria and
chloroplasts.
Prokaryotes and Eukaryotes have their DNA in the form of chromosomes but the structures of
chromosomes differ distinctly from each other. The DNA of a prokaryote is found in the
nucleoid, since it lacks a nucleus. The process of transcription and translation are similar as well
as both need ribosomes to synthesize proteins from an RNA template.
Prokaryotes [MORE FEATURES IN CHAPTER 21]
1. are 10 times smaller than a eukaryotic cell
2. have less internal membrane organization in their cells
3. display remarkable metabolic flexibility – they can use a variety of substances as energy and
carbon sources to synthesize necessary organic molecules in order to survive
4. biochemically more versatile than eukaryotes
5. abundant in the world and can life in almost all regions of the Earth
The most primitive form of metabolism used anaerobic respiration, fermentation and
photosynthesis. These processes relied on hydrogen sulfide (H2S) and ferrous iron, which would
be oxidized to reduce CO2 into sugars.
Prokaryotes called cyanobacteria eventually used electrons from water by oxidizing it. By
oxidizing water, electrons, protons and O2 were released over time which accumulated in the
atmosphere. Photosynthesis that relies on oxidized water is referred to oxygenic photosynthesis.
This is a biological breakthrough as water is not easily oxidized.
What made cyanobacteria so abundant back in prehistoric times was that water was plentiful and
as long as there was sunlight, they could grow and thrive. Oxygenic photosynthesis remains the
dominant form of photosynthesis used by all plants and algae including modern day
cyanobacteria.
A rise in oxygen levels allowed prokaryotes to evolve and undergo aerobic respiration, which
gave them much more energy than anaerobic respiration. The development of oxygenic
photosynthesis paved the way for the development of eukaryotic cells.
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