Download 4.3 What Are the Major Features of Eukaryotic Cells?

BIOLOGY Life on Earth
WITH PHYSIOLOGY Tenth Edition
Audesirk Audesirk Byers
4
Cell Structure
and Function
Lecture Presentations by
Carol R. Anderson
Westwood College, River Oaks Campus
© 2014 Pearson Education, Inc.
Chapter 4 At a Glance
 4.1 What Is the Cell Theory?
 4.2 What Are the Basic Attributes of Cells?
 4.3 What Are the Major Features of Eukaryotic
Cells?
 4.4 What Are the Major Features of Prokaryotic
Cells?
© 2014 Pearson Education, Inc.
4.1 What Is the Cell Theory?
 The cell theory states that cells are the basic units
of life
– Three principles comprise the cell theory
– Every living organism is made of one or more cells
– The smallest organisms are single cells, and cells are
the functional units of multicellular organisms
– All cells arise from preexisting cells
© 2014 Pearson Education, Inc.
4.2 What Are the Basic Attributes of Cells?
– Most cells range in size from about 1 to 100
micrometers in diameter
– Diffusion is the process whereby molecules dissolved
in liquids move from a highly concentrated region to a
lesser concentrated region
– Cells need to exchange nutrients and wastes with the
environment
– No part of the cell can be too far away from the
external environment
© 2014 Pearson Education, Inc.
Figure 4-1 Relative sizes
tallest trees
Size
100 m
visible with unaided
human eye
10 m
1m
10 cm
adult human
chicken egg
1 cm
1 mm
visible with
light microscope
frog embryo
100 m
10 m
most eukaryotic cells
1 m
10 nm
1 nm
visible with special
electron microscope
100 nm
visible with conventional
electron microscope
mitochondrion
most prokaryotic cells
virus
proteins
diameter of DNA
double helix
Units of measurement:
0.1 nm
© 2014 Pearson Education, Inc.
atoms
1 meter (m)  39.37 inches
1 centimeter (cm)  1/100 m
1 millimeter (mm)  1/1,000 m
1 micrometer (m)  1/1,000,000 m
1 nanometer (nm)  1/1,000,000,000 m
4.2 What Are the Basic Attributes of Cells?
 All cells share common features
– Include plasma membrane
– Include cytoplasm
– Use DNA as hereditary blueprint
– Use RNA to copy the blueprint and guide
construction of cell parts
© 2014 Pearson Education, Inc.
4.2 What Are the Basic Attributes of Cells?
 All cells share common features (continued)
– The plasma membrane encloses the cell and allows
interactions between the cell and its environment
– This structure is composed of lipid, protein, and
carbohydrate molecules, and regulates the passage
of ions and molecules in and out of cells
© 2014 Pearson Education, Inc.
Figure 4-2 The plasma membrane
interstitial fluid (outside)
carbohydrate
glycoprotein
A phospholipid bilayer
helps to isolate the
cell’s contents
Proteins help the cell
communicate with
its environment
channel protein
membrane protein
cytoskeleton
cytosol
© 2014 Pearson Education, Inc.
4.2 What Are the Basic Attributes of Cells?
 All cells share common features (continued)
– All cells contain cytoplasm
– The cytoplasm consists of all the fluid and structures
that lie inside the plasma membrane but outside of the
nucleus
– The fluid portion of the cytoplasm (cytosol) contains
water, salts, and organic molecules
– Most of the cell’s metabolic activities occur in the cell
cytoplasm
© 2014 Pearson Education, Inc.
Figure 4-3 A generalized animal cell
microfilaments
nuclear envelope
nuclear pore
nucleus
chromatin (DNA)
nucleolus
cytosol
microtubules
(cytoskeleton)
flagellum
(propels
sperm cell)
basal body
rough
endoplasmic
reticulum
vesicle
intermediate
filaments
(cytoskeleton)
cytoplasm
Golgi
apparatus
centriole
ribosomes
on rough
ER
polyribosome
lysosome
smooth
endoplasmic
reticulum
vesicles releasing
substances from
the cell
mitochondrion
© 2014 Pearson Education, Inc.
plasma
membrane
free ribosome
Figure 4-4 A generalized plant cell
nucleus
microtubules
(cytoskeleton)
nuclear envelope
nuclear pore
chromatin
nucleolus
ribosomes
intermediate
filaments
(cytoskeleton)
cell walls of adjoining
plant cells
chloroplast
cytoplasm
rough
endoplasmic
reticulum
smooth
endoplasmic
reticulum
Golgi apparatus
central
vacuole
vesicle
mitochondrion
cell wall
© 2014 Pearson Education, Inc.
plasma
membrane
plasmodesmata
cytosol
plastid
free
ribosome
© 2014 Pearson Education, Inc.
BioFlix Animation: Tour of a Plant Cell
© 2014 Pearson Education, Inc.
BioFlix Animation: Tour of a Animal Cell
4.2 What Are the Basic Attributes of Cells?
 All cells share common features (continued)
– All cells use DNA as a hereditary blueprint and RNA
to copy the blueprint and guide construction of cell
parts
– All cells use DNA (deoxyribonucleic acid) as a
hereditary blueprint
– All cells use RNA (ribonucleic acid) to copy the
blueprint and to guide construction of proteins
© 2014 Pearson Education, Inc.
4.2 What Are the Basic Attributes of Cells?
 There are two basic types of cells: prokaryotic and
eukaryotic
– Prokaryotic (“before the nucleus”) cells form the
bodies of bacteria and archaea, the simplest
forms of life
– Eukaryotic (“true nucleus”) cells form the bodies
of animals, plants, fungi, and protists
© 2014 Pearson Education, Inc.
4.2 What Are the Basic Attributes of Cells?
 There are two basic types of cells: prokaryotic and
eukaryotic (continued)
– The cytoplasm of eukaryotic cells includes a variety of
organelles, such as the nucleus and mitochondria
– The cytoskeleton gives shape and organization to
the cytoplasm of eukaryotic cells
© 2014 Pearson Education, Inc.
Table 4-1
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
– Eukaryotic cells make up the bodies of animals,
plants, protists, and fungi
– Eukaryotic cells are very diverse
– The cytoplasm of eukaryotic cells houses the nucleus
and mitochondria that perform specific functions
within the cell
– Plant and animal cells have structures that are unique
to each type of cell
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Some eukaryotic cells are supported by cell walls
– The outer surfaces of plants, fungi, and some protists
are covered with nonliving, relatively stiff coatings
called cell walls
– Plant cell walls are composed of cellulose and other
polysaccharides
– Fungal cell walls are made of polysaccharides and
chitin
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Some eukaryotic cells are supported by cell walls
(continued)
 Plant cells are surrounded by a cell wall
– Plant cells also have plastids and a central vacuole,
not found in animal cells
 Some animal cells possess vesicles, vacuoles, and
cilia, not found in plant cells
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Some eukaryotic cells are supported by cell walls
(continued)
– Cell walls are porous, allowing oxygen, carbon
dioxide, and water carrying dissolved molecules to
flow easily through them
– The plasma membrane is located just beneath the cell
wall
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The cytoskeleton provides shape, support, and
movement
– Organelles are attached to a network of protein fibers
that make up the cytoskeleton
– The cytoskeleton is composed of three types of
protein fibers
– Thin microfilaments
– Medium-sized intermediate filaments
– Thick microtubules
© 2014 Pearson Education, Inc.
Figure 4-5 The cytoskeleton
microtubules (red)
intermediate
filaments
microtubules
nucleus
microfilaments
microfilaments (blue)
Cytoskeleton
© 2014 Pearson Education, Inc.
Light micrograph showing
the cytoskeleton
Table 4-2
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The cytoskeleton provides shape, support, and
movement (continued)
– The cytoskeleton regulates the following cell
properties:
– Cell shape
– Cell movement
– Organelle movement
– Cell division
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Cilia and flagella move the cell through fluid or move
fluid past the cell
– Both cilia and flagella are hair-like structures that
propel cells through fluids or move fluids past cells
– They arise from a basal body, which anchors them to
the plasma membrane
– Basal bodies are derived from centrioles, which are
identical in structure to basal bodies
© 2014 Pearson Education, Inc.
Figure 4-6 Cilia and flagella
protein sidearms
central
pair of
microtubules
fused
microtubule
pair
section of cilium
0.1 micrometer
Paramecium
plasma membrane
basal body
(extends into
cytoplasm)
© 2014 Pearson Education, Inc.
cilium
4.3 What Are the Major Features of Eukaryotic
Cells?
 Cilia and flagella move the cell through fluid or move
fluid past the cell (continued)
– The force generated by cilia can be compared to that
created by oars on the sides of a rowboat
– The force generated by a flagellum can be compared
to that created by the engine on a motorboat
– Flagella are longer than cilia, and cells with flagella
usually have only one or two
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Cilia and flagella move the cell through fluid or move
fluid past the cell (continued)
– Some unicellular organisms, such as Paramecium,
use cilia to swim through water; others use flagella
– Ciliated cells line such diverse structures as the gills
of oysters, the oviducts of female mammals, and the
respiratory tracts of land vertebrates
– Most animal sperm rely on flagella for movement
© 2014 Pearson Education, Inc.
Figure 4-7 How cilia and flagella move
propulsion of fluid
cilia lining
trachea
mucus-secreting cells
Cilium
power stroke
plasma membrane
direction of locomotion
Flagellum
© 2014 Pearson Education, Inc.
return stroke
propulsion of fluid
continuous propulsion
flagellum of
human sperm
4.3 What Are the Major Features of Eukaryotic
Cells?
 The nucleus, containing DNA, is the control center
of the eukaryotic cell
– The nucleus is the control center of the eukaryotic
cell and has three major parts
– Nuclear envelope
– Chromatin
– Nucleolus
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The nucleus, containing DNA, is the control center of
the eukaryotic cell (continued)
– The nuclear envelope allows selective exchange of
materials
– The nucleus is isolated from the rest of the cell by a
nuclear envelope that consists of a double membrane
perforated by nuclear pores
– The membrane is perforated with tiny protein-lined nuclear
pores that allow water, ions, and small molecules to pass
freely
– Passage of proteins, pieces of ribosomes, and RNA are
regulated by gatekeeper proteins called the nuclear pore
complex that line each nuclear pore
© 2014 Pearson Education, Inc.
Figure 4-8 The nucleus
nuclear
envelope
nucleolus
nuclear
pores
ribosomes
nucleus
chromatin
nuclear pores with
nuclear pore complex
The nucleus
© 2014 Pearson Education, Inc.
Nucleus of a yeast cell
4.3 What Are the Major Features of Eukaryotic
Cells?
 The nucleus, containing DNA, is the control center
of the eukaryotic cell (continued)
– Chromatin consists of strands of DNA associated
with proteins
– Chromatin is a colored substance contained in the
nucleus
– During cell division, chromatin becomes compacted
into long strands called chromosomes
– The chromosomes contain genes that provide a
blueprint for a huge variety of proteins
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The nucleus, containing DNA, is the control center
of the eukaryotic cell (continued)
– Because proteins are synthesized in the cytoplasm,
copies of the protein blueprints on DNA must leave
the nucleus through the nuclear membrane
– To do this, genetic information in DNA is copied into
messenger RNA (mRNA), which travels through the
nuclear pores to the cytoplasm, where it directs
protein synthesis
© 2014 Pearson Education, Inc.
Figure 4-9 Chromosomes
chromatin
chromosome
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The nucleus, containing DNA, is the control center
of the eukaryotic cell (continued)
– The nucleolus is the site of ribosome assembly
– Eukaryotic nuclei contain at least one nucleolus, the
site of protein synthesis
– A ribosome is a small particle composed of ribosomal
RNA and proteins
– The nucleolus consists of ribosomal RNA, proteins,
ribosomes in various stages of synthesis, and DNA
© 2014 Pearson Education, Inc.
Figure 4-10 Ribosomes
ribosome
polyribosome
mRNA
growing
protein
amino acid
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system
– The endomembrane system segregates molecules
from the surrounding cytosol to ensure the orderly
occurrences of biochemical processes
– The endomembrane system includes the nuclear
envelope, endoplasmic reticulum, Golgi apparatus,
lysosomes, vesicles, and vacuoles
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– Vesicles are membranous sacs transporting
molecules to the various regions of the membrane
system
– Exocytosis is the process whereby vesicles fuse with the
plasma membrane as they export their contents outside
the cell
– Endocytosis is the process whereby the plasma
membrane extends and surrounds material just outside
the cell, fuses, and then pinches off to form a vesicle
inside the cell
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– The endoplasmic reticulum forms membraneenclosed channels within the cytoplasm
– The endoplasmic reticulum (ER) is a series of
interconnected membranes that form a labyrinth of
flattened sacs and channels within the cytoplasm
– The rough endoplasmic reticulum and smooth
endoplasmic reticulum are the two types of ER
– All the proteins and phospholipids of cell membranes
are synthesized in the ER
© 2014 Pearson Education, Inc.
Figure 4-11 Endoplasmic reticulum
ribosomes
smooth ER
rough ER
rough
ER
smooth ER
vesicles
Endoplasmic reticulum may be
rough or smooth
© 2014 Pearson Education, Inc.
Smooth and
rough ER
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– Rough endoplasmic reticulum is studded with
ribosomes and produces proteins destined for
other membranes or for secretion
– Smooth endoplasmic reticulum has no
ribosomes, detoxifies drugs, and synthesizes
lipids such as steroid hormones made from
cholesterol
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– The Golgi apparatus modifies, sorts, and packages
important molecules
– The Golgi apparatus modifies some molecules, such as
adding a carbohydrate group to proteins, and making
glycoproteins; it breaks some proteins into smaller
peptides
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– The Golgi apparatus modifies, sorts, and packages
important molecules (continued)
– It separates various proteins and lipids received from
the ER according to their destinations
– It packages the finished molecules into vesicles that
are then transported to other parts of the cell or to the
plasma membrane for export
© 2014 Pearson Education, Inc.
Figure 4-12 The Golgi apparatus
Protein-carrying
vesicles from the ER
merge with the Golgi
apparatus
Golgi
apparatus
Vesicles carrying
modified protein leave
the Golgi apparatus
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– Secreted proteins are modified as they move through
the cell
– Secreted proteins, like antibodies, are made in the
rough ER, travel through Golgi, and then are exported
through the plasma membrane
– Antibodies are glycoproteins produced by white blood
cells that attach to foreign invaders to destroy them
© 2014 Pearson Education, Inc.
Figure 4-13 A protein is manufactured and exported
(interstitial fluid)
Vesicles merge with the
plasma membrane and
release antibodies into the
interstitial fluid
(cytosol)
vesicles
Completed glycoprotein
antibodies are packaged
into vesicles on the opposite
side of the Golgi apparatus
Golgi apparatus
Vesicles fuse with the
Golgi apparatus, and
carbohydrates are added
as the protein passes
through the compartments
The protein is
packaged into vesicles
and travels to the Golgi
apparatus
forming
vesicle
Antibody protein is
synthesized on ribosomes
and is transported into
channels of the rough ER
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 The eukaryotic cytoplasm contains membranes that
form the endomembrane system (continued)
– Lysosomes serve as the cell’s digestive system
– Digestive proteins are made in the rough ER, travel
through the Golgi, and are packaged in membraneenclosed vesicles as lysosomes
– A lysosome fuses with a food vacuole and digests
food into basic nutrients
© 2014 Pearson Education, Inc.
Figure 4-14 Formation and function of lysosomes and food vacuoles via the endomembrane system
(interstitial fluid)
(cytosol)
food
food
vacuoles
A lysosome fuses
with a food vacuole,
and the enzymes
digest the food
The enzymes
are delivered to
the lysosome in
vesicles
lysosome
The Golgi
apparatus modifies
the enzymes for
export to the
lysosomes
Golgi apparatus
digestive
enzymes
The enzymes
are packaged into
vesicles and travel to
the Golgi apparatus
Digestive
enzymes are
synthesized on
ribosomes and
travel through
the rough ER
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Vacuoles serve many functions, including water
regulation, storage, and support
– Many freshwater organisms possess contractile
vacuoles composed of collecting ducts, a central
reservoir, and a tube leading to a pore in the plasma
membrane that carries excess water out of the
organism
– Cellular energy is used to pump salts from the
cytoplasm of the protist into collecting ducts
– A full contractile vacuole contracts, squirting water
out through a pore in the plasma membrane
© 2014 Pearson Education, Inc.
Figure 4-15 A contractile vacuole
contractile
vacuole
Paramecium
Water enters the collecting ducts
and fills the central reservoir
collecting
ducts
central
reservoir
pore
Contractile vacuole
© 2014 Pearson Education, Inc.
The reservoir contracts, expelling
water through the pore
4.3 What Are the Major Features of Eukaryotic
Cells?
 Vacuoles serve many functions, including water
regulation, storage, and support (continued)
– Plant cells have central vacuoles
– A large central vacuole occupies three-quarters or
more of the volume of most mature plant cells and has
several functions
– Central vacuoles provide support for plant cells
– Turgor pressure (water pressure), within the
vacuole, pushes the fluid portion of the cytoplasm
up against the cell wall
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Vacuoles serve many functions, including water
regulation, storage, and support (continued)
– Plant cells have central vacuoles (continued)
– The functions of the central vacuole include
– To maintain water balance
– To store hazardous wastes, nutrients, or pigments
– To provide turgor pressure on the cytoplasm to keep
cells rigid
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy
– All eukaryotic cells have mitochondria that capture
energy stored in sugar by producing high-energy
ATP molecules
– The cells of plants also have chloroplasts, which can
capture energy directly from sunlight and store it in
sugar molecules
– Biologists believe that both mitochondria and
chloroplasts evolved from prokaryotic bacteria that
became incorporated into the cytoplasm of other
prokaryotic cells (endosymbiont hypothesis)
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules, and
chloroplasts capture solar energy (continued)
– The endosymbiont hypothesis
– Both mitochondria and chloroplasts are about the size
of prokaryotic cells (1–5 micrometers in diameter)
– Both have a double membrane, the outer possibly
coming from the host cell and the inner from the
guest cell
– Both have enzymes to synthesize ATP
– Both possess DNA and ribosomes
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy (continued)
– Mitochondria are organelles that function as
“powerhouses of the cell”
– Mitochondria extract energy from food molecules
– The extracted energy is stored in high-energy bonds
of ATP
– The energy extraction process involves anaerobic
(“without oxygen”) and aerobic (“with oxygen”)
reactions
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy (continued)
– The inner membrane is folded into cristae
– The intermembrane compartment lies between inner
and outer membranes
– The matrix space is within the inner membrane
© 2014 Pearson Education, Inc.
Figure 4-16 A mitochondrion
outer
membrane
inner
membrane
intermembrane
space
matrix
cristae
0.1 micrometer
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy (continued)
– Chloroplasts are the sites of photosynthesis
– Chloroplasts are specialized organelles surrounded
by a double membrane
– The outer membrane separates the organelle from the
cytoplasm
– The inner membrane encloses the fluid stroma and
contains stacked, hollow, membranous sacs (grana)
made of individual thylakoids
© 2014 Pearson Education, Inc.
Figure 4-17 A chloroplast
outer membrane
inner membrane
stroma
thylakoid
channel
interconnecting
thylakoids
granum
(stack of thylakoids)
1 micrometer
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy (continued)
– Chloroplasts are the sites of photosynthesis
(continued)
– The thylakoid membranes contain the green pigment
chlorophyll and other pigments, which capture
sunlight and make sugar from CO2 and water
(photosynthesis)
© 2014 Pearson Education, Inc.
4.3 What Are the Major Features of Eukaryotic
Cells?
 Mitochondria extract energy from food molecules,
and chloroplasts capture solar energy (continued)
– Plants use plastids for storage
– Plastids are found only in plants and photosynthetic
protists
– They are surrounded by a double membrane
– Plastids are storage containers for various molecules,
such as pigments or starch
© 2014 Pearson Education, Inc.
Figure 4-18 A plastid
plastid
starch
globules
0.5 micrometer
© 2014 Pearson Education, Inc.
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells are small and possess specialized
surface features
 Prokaryotic cells have fewer specialized structures
within their cytoplasm
© 2014 Pearson Education, Inc.
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells are small and possess specialized
surface features (continued)
– Most prokaryotic cells (bacteria) are less than
5 µm long, with a simple internal structure compared to
eukaryotic cells
– They usually have a stiff cell wall
– Prokaryotic cells can take several shapes
– Rod-shaped bacilli
– Spiral-shaped spirilla
– Spherical cocci
© 2014 Pearson Education, Inc.
Figure 4-19 Prokaryotic cells are simpler than eukaryotic cells
chromosome
(within the
nucleoid region)
cell wall
plasma membrane
ribosomes
chromosome
(within the
nucleoid region)
Cocci
capsule
Internal structure
pili
ribosomes
Spirilla
food granule
prokaryotic
flagellum
capsule or
slime layer
cell wall
plasmid (DNA)
cytoplasm
plasma membrane
photosynthetic
membranes
Generalized prokaryotic cell (bacillus)
© 2014 Pearson Education, Inc.
Photosynthetic
prokaryote
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells are small and possess specialized
surface features (continued)
– Bacteria secrete polysaccharide coatings called
capsules and slime layers outside their cells
– Capsules and slime layers are similar except capsules
are harder to remove
– Capsules and slime layers assist in the formation of
bacteria on surface films
– Examples include tooth decay, diarrhea, and urinary
tract infections
– Both protect bacteria and keep them from drying out
© 2014 Pearson Education, Inc.
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells are small and possess specialized
surface features (continued)
– Pili (meaning hairs) are surface protein projections of
the cell walls in some bacteria that further enhance
adhesion
– Attachment pili are short and abundant; they help
bacteria adhere to structures
– Sex pili are few in number and long; one bacterium’s
sex pili binds it to a nearby bacterium of the same type
© 2014 Pearson Education, Inc.
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells have fewer specialized cytoplasmic
structures than do eukaryotic cells
– In the central region of the cell is an area called the
nucleoid, which is separate from the cytoplasm
– Within the nucleoid is a single, circular chromosome of
DNA
– Small rings of DNA (plasmids) are located in the
cytoplasm
© 2014 Pearson Education, Inc.
4.4 What Are the Major Features of Prokaryotic
Cells?
 Prokaryotic cells have fewer specialized cytoplasmic
structures than do eukaryotic cells (continued)
– Prokaryotic cells have no nuclear membrane or
membrane-bound organelles present
– Some have internal membranes used to capture light
– The cytoplasm may contain food granules and
ribosomes, the latter with a function similar to that of
ribosomes in eukaryotic cells
© 2014 Pearson Education, Inc.