Chapter 3
Cell Structure
All life on Earth have a plasma membrane that separates the interior of the cell from the outside
environment. What is the function of the plasma membrane? What is the function of the proteins
embedded in the plasma membrane? Can any type of molecule pass through the plasma membrane?
A cell wall gives a bacteria its shape but what is the main function of the cell wall? What are the two
main types of cell wall?
The bacterial cell wall is made of peptidoglycan, which is a structure unique to bacteria. What are
the two types of “bricks” that make up the peptidoglycan wall? How are peptidoglycan layers linked
together? Medically speaking, why do we care that peptidoglycan is only found in bacteria?
Describe the Gram-positive cell wall.
Staphylococcus aureus, Streptococcus pyogenes, and Clostridium difficile are three examples of
pathogenic bacteria with a Gram-positive cell wall. What is an example of a disease each bacteria
causes?
Describe the Gram-negative cell wall.
Escherichia coli, Salmonella enterica, and Helicobacter pylori are three examples of pathogenic
bacteria with a Gram-negative cell wall. What is an example of a disease each bacteria causes?
The outer membrane of Gram-negative bacteria contains a sugar called lipopolysaccharide (LPS).
Why can LPS be dangerous? What is the dangerous structure on LPS called?
E. coli O157:H7 is an example of a Gram-negative bacteria that is a major cause of food poisoning.
The O stands for the O antigen. What does the H stand for? (H is mentioned in a later slide). Where
does the bacteria naturally live and how can one ingest the pathogen? There have even been
vegetable recalls due to E. coli O157:H7 contamination. How did the bacteria get there?
In April and December 2018, there were massive E. coli O157:H7 outbreaks affecting the United
States. What produce was contaminated? Where did the bacteria come from? According to a 2015
estimate from the CDC, approximately what percentage of food-borne illnesses were caused by
produce?
Peptidoglycan makes for a good target since it is unique to bacteria. Compare and contrast the
actions of lysozyme and penicillin. Penicillin is an antibiotic, what is lysozyme? Where is lysozyme
found?
Not all bacteria have a cell wall. Mycoplasma are a unique exception. How are they able to survive in
an environment without a cell wall? What is an example of a Mycoplasma species that causes
disease? What disease does it cause? Are lysozymes and penicillin effective against it?
Many bacteria have structures external to their cell wall that gives them a competitive advantage.
One example is a sticky, sugary layer called a capsule; why is it advantageous for bacteria to have a
capsule? What are the dental concerns with this type of structure? How do encapsulated bacteria in
the mouth result in dental plaque and cavities?
Run your tongue over the sides of your molars. Feel that film? What is it and why do you want to get
rid of that film?
What is flagella and what is its function? What is the flagella anchored to in the cell and how does it
move? What are some examples, discussed in class, of arrangements of flagella around a bacterial
cell? Drawing these arrangements may help.
Do bacteria have eyes? Bacteria move via chemotaxis. What is chemotaxis? Bacteria move through a
series of runs and tumbles. What would bacteria want to run to? Away from?
What is fimbriae and what is its purpose? What is an example of a pathogen that uses it fimbriae to
cause disease? What is that disease and what is happening that causes the characteristic
symptoms?
The sex pilus is a single protein strand that functions to help a bacterial cell grab and pull another
bacterial cell. What happens when the two cells touch? What type of DNA can be transferred? Even
though it’s called the sex pilus, are bacteria having sex?
A single bacterial cell is called a bacterium. Bacteria is plural. In the PowerPoint gif, the bacterium is
using its sex pilus to pick up something specific from its environment. What is it grabbing?
Bacterial cells have a variety of essential structures within the cell, such as a chromosome,
plasmids, ribosomes, and endospore.
What is the function of the circular bacterial chromosome? All bacteria have 1 chromosome, how
many do we have? In a bacterial cell, the chromosome is not in a nucleus but forms a tightly packed
mass called the nucleoid that is sloshing around the inside of the cell.
Plasmids are circular pieces of DNA that have a similar function to the chromosome, but are
smaller, separate, and numerous. Including specific examples, what is the function of plasmids?
How can plasmids be transferred from cell to cell?
What are ribosomes responsible for? What does it mean when bacterial ribosomes are 70S and
eukaryotic ribosomes are 80S? Medically speaking, why are these differences very important to
know?
Some bacteria turn into an endospore, which is a unique type of dormant bacterial cell. How long
can these “hibernating” cells remain alive? What do endospores form in response to? What is an
endospore protecting?
Endospores makes bacteria extremely resistant to harsh environments such as high heat, drying,
and chemical treatment. Are endospores indestructible? What are two genera of bacteria capable of
producing endospores? Any of them potential human pathogens? What diseases do they cause?
Provide a general description of how a Clostridium difficile endospore can exit one host and infect
another person.
Generally speaking, eukaryotic cells (plants, animals, fungi) are more complex than bacterial cells
and contain organelles. Two organelles we will talk about are mitochondria and chloroplasts.
What is the function of the mitochondria within our cells? What is unique about them relative to
our other organelles? What are some fun facts that describes the importance of mitochondria?
Chloroplasts are organelles that are the sites of photosynthesis. What does photosynthesis do?
What types of organism have chloroplasts? Do those organisms also have mitochondria to make
energy? What is unique about chloroplasts relative to other organelles?
Endosymbiosis is the scientific theory of why mitochondria and chloroplasts resemble bacteria.
What does that theory describe? What type of organism was mitochondria? Chloroplasts?
The cells involved in endosymbiosis were in symbiosis, meaning they worked together. How was
the relationship mutually beneficial? How long ago did the endosymbiosis events occur? What types
of organism only exist because of endosymbiosis?
In class we discussed four lines of evidence that supports this endosymbiosis theory. What is that
evidence?
Endosymbiosis of mitochondria and chloroplasts can be broken down into four distinct stages.
Describe what is happening in each stage. Which stage gave rise to all animal and fungi organisms
and which stage gave rise to all plant and algae organisms.
Describe how penicillin and lysozyme act differently in how they target the cell wall.
The antibiotic penicillin is not effective at killing Gram-negative bacteria. Why do you think that is?
Using terminology discussed in class, explain how a sugary diet can lead to tooth decay.
If endosymbiosis never occurred, what would life on this planet look like?
You can use this space to draw the structures of a bacterial cell.