CHAPTER
3
Cell Structure and Function
Chapter Outline
Processes of Life (pp. 58)
Prokaryotic and Eukaryotic Cells: An Overview (pp. 58–59)
External Structures of Bacterial Cells (pp. 59–65)
Glycocalyces
Flagella
Bacterial Cell Walls (pp. 65–67)
Gram-Positive Bacterial Cell Walls
Gram-Negative Bacterial Cell Walls
Bacteria Without Cell Walls
Bacterial Cytoplasmic Membranes (pp. 68–73)
Structure
Cytoplasm of Bacteria (pp. 73–76)
Cytosol
Inclusions
Endospores
Nonmembranous Organelles
External Structures of Archaea (pp. 76–77)
Glycocalyces
Flagella
Archaeal Cell Walls and Cytoplasmic Membranes (p. 77-78)
Cytoplasm of Archaea (pp. 78)
External Structure of Eukaryotic Cells (p. 78-79)
Glycocalyces
Eukaryotic Cell Walls and Cytoplasmic Membranes (pp. 79–80)
Instructor’s Manual for Microbiology with Diseases by Body Systems, 5e
Cytoplasm of Eukaryotes (pp. 81-88)
Flagella
Cilia
Chapter Summary
Processes of Life (pp. 58)
All living things share four processes:
2. Reproduction: an increase in number
4. Metabolism: controlled chemical reactions
Prokaryotic and Eukaryotic Cells: An Overview (pp. 58–59)
All living things are composed of cells. Cells have a membrane and can carry out all the
processes of life. Cells can be classified as prokaryotic or eukaryotic. Organisms are categorized
into taxa. The taxa domain Archaea and domain Bacteria consist of prokaryotes. Prokaryotic
External Structures of Bacterial Cells (pp. 59–65)
The external structures of bacterial cells include glycocalyces, flagella, fimbriae, and pili.
Glycocalyces
A glycocalyx (plural, glycocalyces) is a gelatinous, sticky substance that surrounds the outside
of some cells. When the glycocalyx of a bacterium is composed of organized repeating units of
Chapter 3 Cell Structure and Function
Flagella
Some bacteria have structures responsible for cell motility that include flagella (singular,
flagellum) long extensions beyond the cell surface and glycocalyx that propel a cell through its
environment. Bacterial flagella are composed of a filament, a hook, and a basal body. Bacterial
flagella are composed of a protein called flagellin. The hook and basal body are composed of
several other proteins, and anchor the flagellum to the cell well and cytoplasmic membrane.
Fimbriae and Pili
Fimbriae (singular, fimbria) are short, sticky, proteinaceous bristlelike extensions of some
bacteria that help cells adhere to one another and to substances in the environment. Fimbriae
may also serve as motility structures by a mechanism somewhat like retracting a rope. In
Bacterial Cell Walls (pp. 65–67)
Most bacterial cells are surrounded by a cell wall that provides structure, shape, and protection
from osmotic forces. Characteristic bacterial shapes include cocci (spherical) and bacilli (rods).
Bacterial cell walls are composed of peptidoglycan, a complex polysaccharide composed of
Gram-Positive Bacterial Cell Walls
Gram-positive bacterial cells have thick layers of peptidoglycan that also contain teichoic
acids. Lipoteichoic acids anchor the wall to the cytoplasmic membrane. Their thick wall retains
Instructor’s Manual for Microbiology with Diseases by Body Systems, 5e
Gram-Negative Bacterial Cell Walls
Gram-negative bacterial cells have only a thin layer of peptidoglycan, outside of which is an
outer membrane containing lipopolysaccharide (LPS). Integral channel proteins, porins, permit
medium-sized molecules to cross the outer membrane. LPS is composed of sugars and a lipid
Bacteria Without Cell Walls
A few bacteria, such as Mycoplasma pneumoniae, lack cell walls entirely. However, they still
possess the other features of prokaryotic cells, such as prokaryotic ribosomes.
Bacterial Cytoplasmic Membranes (pp. 68–73)
Beneath the glycocalyx and cell wall is a cytoplasmic membrane (or cell membrane or plasma
membrane).
Structure
The cytoplasmic membrane is a double-layered structure, called a phospholipid bilayer,
composed of molecules with hydrophilic phosphate heads and hydrophobic lipid tails. Some
also contain hopanoids that help stabilize the structure. Proteins associated with the membrane
Function
The selectively permeable cytoplasmic membrane not only separates the contents of the cell
from the outside environment, it also controls the passage of materials into and out of the cell.
Although impermeable to most substances, its proteins act as pores, channels, or carriers to
Passive Processes
Passive processes require no cellular energy expenditure to move chemicals across the
cytoplasmic membrane. The electrochemical gradient provides the energy to transport substances
into or out of the cell. These processes include simple diffusion, which is the movement of
Chapter 3 Cell Structure and Function
chemicals down their concentration gradient, from an area of higher concentration to an area of
lower concentration. Only small or lipid-soluble chemicals diffuse across the membrane. In
Active Processes
Active processes require cells to expend energy, often in the form of ATP, to move materials
across the cytoplasmic membrane against their electrochemical gradient. Active transport
Cytoplasm of Bacteria (pp. 73–76)
Cytoplasm is the gelatinous, elastic material inside a cell. It is composed of cytosol, inclusions,
ribosomes, and in many cells a cytoskeleton. Some bacterial cells produce internal, resistant,
dormant forms called endospores.
Cytosol
The liquid portion of the cytoplasm is called cytosol. It is mostly water, plus dissolved and
Inclusions
Deposits called inclusions may be found within the cytosol of bacteria. These may be reserve
deposits of lipids, starch, or other chemicals. The lipid polymer polyhydroxybutyrate is a form
of carbon and energy storage found in some bacteria. Inclusions called gas vesicles store gases
for flotation.
Endospores
Some bacteria produce structures called endospores when one or more nutrients are limited.
Endospores are produced in the interior of the vegetative cell during a complex, hours-long
Instructor’s Manual for Microbiology with Diseases by Body Systems, 5e
Nonmembranous Organelles
Two types of nonmembranous organelles are found in direct contact with the cytosol of bacteria:
ribosomes and the cytoskeleton. Ribosomes are the sites of protein synthesis in cells. They are
External Structures of Archaea (pp. 76-77)
Archaeal cells have external structures similar to those of bacteria, including glycocalyces,
flagella, and fimbriae. Some have a novel external appendage called a hamus.
Glycocalyces
Flagella
Archaeal flagella function in a manner similar to those of bacteria, but are structurally distinct.
They are smaller, not hollow, are composed of different proteins, and frequently have sugar
Fimbriae and Hami
The fimbriae of archaea are structurally and functionally similar to those of bacteria. Some
archaea have unique structures called hami (singular, hamus), helical filaments with prickles
and a terminus that divide into three curved hooks. Both fimbriae and hami attach to surfaces.
Archaeal Cell Walls and Cytoplasmic Membranes (p. 77-78)
Most archaea have cell walls and all have cytoplasmic membranes. Archaeal cell walls are
composed of proteins or polysaccharides but lack peptidoglycan. Gram-positive archaea have thick
walls and stain purple with the Gram stain, while Gram-negative archaea have a layer of protein
Cytoplasm of Archaea (p. 78)
The cytoplasm of archaea is similar to that found in bacteria, including the presence of 70S
External Structure of Eukaryotic Cells (p. 78-79)
Glycocalyces
Animal and protozoan cells may have glycocalyces anchored to their cytoplasmic membranes. They
Eukaryotic Cell Walls and Cytoplasmic Membranes (pp. 79–80)
The eukaryotic cells of fungi, algae, plants, and some protozoa have a cell wall composed of
polysaccharides that provides protection from the environment. It also provides shape and
support against osmotic pressure. The cell walls of plants are composed of cellulose, whereas
fungal cell walls are composed of various polysaccharides, including cellulose, chitin, or
glucomannan. Algal cell walls are composed of various materials including cellulose, agar,
carrageenan, silicates, algin, calcium carbonate, or other chemicals.
All eukaryotic cells have cytoplasmic membranes. Like bacterial membranes, they are a fluid
Cytoplasm of Eukaryotes (pp. 81-88)
The cytoplasm of eukaryotes is more complex than that of prokaryotes, containing numerous
Flagella
Eukaryotic flagella are enclosed in the cytoplasmic membrane. The shaft of a eukaryotic
flagellum is composed of molecules of a globular protein called tubulin arranged in chains to
Instructor’s Manual for Microbiology with Diseases by Body Systems, 5e
Cilia
Some eukaryotic cells have cilia, which are structurally similar to eukaryotic flagella but are
much shorter and more numerous. Their coordinated rhythmic beating propels single-celled
Other Nonmembranous Organelles
Three nonmembranous organelles are found in eukaryotes: ribosomes, a cytoskeleton, and
centrioles. Eukaryotic ribosomes are 80S rather than 70S, are composed of 60S and 40S
subunits, and are found within the cytosol as well as attached to the membranes of the
Membranous Organelles
Eukaryotic cells contain a variety of organelles that are surrounded by phospholipid bilayer
membranes similar to the cytoplasmic membrane.
Nucleus
The nucleus is spherical to ovoid and is often the largest organelle in a cell. It contains most of
the cell’s genetic material in the form of DNA. The semiliquid matrix of the nucleus is called
Endoplasmic Reticulum
Continuous with the outer membrane of the nuclear envelope and traversing the cytoplasm is a
network of flattened hollow tubules called endoplasmic reticulum (ER). Smooth endoplasmic
Chapter 3 Cell Structure and Function
Golgi Body
Some cells have a Golgi body, a series of flattened, hollow sacs surrounded by phospholipid
bilayers. It receives, processes, and packages large molecules in secretory vesicles, which
release their contents from the cell via exocytosis.
Lysosomes, Peroxisomes, Vacuoles, and Vesicles
Vesicles and vacuoles are general terms for membranous sacs that store or carry substances.
Lysosomes of animal cells contain catabolic enzymes that damage the cell if they are released
Mitochondria
Mitochondria are spherical to elongated structures with two phospholipid bilayer membranes
and are found in most eukaryotes. The inner membrane is extensively folded into cristae. Often
Chloroplasts
Chloroplasts are light-harvesting structures found in photosynthetic eukaryotes. Like
mitochondria, chloroplasts have two phospholipid bilayer membranes, DNA, and ribosomes.
Endosymbiotic Theory
The endosymbiotic theory has been proposed to explain why mitochondria and chloroplasts
have 70S ribosomes, circular DNA, and two membranes. The theory states that the ancestors of
New Media Resources
Connecting Concepts: Cellular Structures and Dr. Ehrlich’s “magic bullets.”
Bacterial Cell Structures and Pathogen Characteristics