Zero to Genetic Engineering Hero - Chapter 3 - Growing E. coli Cells 83
Summary and What’s Next?
In this chapter, you grew real lab-strain K12 Escherichia
coli (E. coli) cells on LB agar petri dishes. Congratula-
tions! Knowing how to grow the organism you plan to
engineer is the rst step towards learning the genetic
engineering process. This fundamental skill is used
in virtually all your genetic engineering experiments.
You will quickly become an expert at making LB agar
plates and streaking microorganisms.
In the Fundamentals section, we dug deeper into where
K12 E. coli come from and how they differ from the E.
coli bacteria that live in your large intestine and the
dangerous ones that can make you sick. We compared
the K12 E. coli to factories and looked into the phys-
ical make-up of their cells: the capsule layer, outer
membrane, intermembrane space, peptidoglycan,
inner membrane, and the cytoplasm. Knowing the
architecture of the cells is very important in your jour-
ney to becoming a Genetic Engineering Hero.
In addition to the physical structure of E. coli cells,
you learned about the macromolecules that form
them. You used the knowledge of nucleic acids gained
in Chapter 1 to become familiar with sugars (a.k.a
saccharides or carbohydrates), lipids, and proteins.
Collectively, these macromolecules are made up of
CHOPNS, a group of atoms that scientists call organic
In the upcoming chapters, the four different types
of macromolecules (nucleic acids, lipids, sugars,
proteins) will repeatedly come up. Your understand-
ing of them will continue to grow and become more
sophisticated. In Chapter 4, you will do your first
genetic engineering experiment where you will take
the skills you learned in this chapter to the next level
by genetically engineering K12 E. coli cells with DNA
plasmids, making them your own microfactories!
In the Fundamentals of Chapter 4, you will step one
layer deeper into E. coli cells. You will go beyond simply
what they are made of and more into how they func-
tion. Specifically, you will discover how cells read
DNA blueprints to create other products through a
process called transcription. Transcription requires
some knowledge of all the macromolecules, so hang
onto what you learned in the Fundamentals from this
Figure 3-31. What causes bacteria to be spherical or rod shaped?
Why are E. coli rod-shaped? Going Deeper 3-8
Proteins can determine cell structure. Why are E. coli bacteria rod-shaped and not spherical like other bacte-
ria? It was thought that peptidoglycan and the outer cell membrane are responsible for the bacterium’s
rod shape. However, it has now been shown that several proteins, including one called “MreB”, regulate
the shape of E. coli. Genetically engineered E. coli that lack MreB becomes spherical in shape! A follow-up
question is, why does E. coli benet from being rod-shaped? Why has it evolved to have this characteristic?
The answer is still unknown!
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