Introduction
• In 1665, Hooke examined a piece of cork under a crude microscope and identified “little rooms” as cells.
• Leeuwenhoek, working at about the same time,
used more refined lenses to describe living cells from blood, sperm, and pond water.
• Since the days of Hooke and Leeuwenhoek,
4.1 Microscopes reveal the world of the cell
• A variety of microscopes have been developed for a clearer view of cells and cellular structure.
• The first microscopes were light microscopes. In a
light microscope (LM), visible light passes
through a specimen, then through glass lenses, and finally is projected into the viewer’s eye.
4.1 Microscopes reveal the world of the cell
• Magnification is the increase in an object’s image size compared with its actual size.
4.1 Microscopes reveal the world of the cell
• Microscopes have limitations.
• The human eye and the microscope have limits of
resolution—the ability to distinguish between small structures.
• Therefore, the light microscope cannot provide the
4.1 Microscopes reveal the world of the cell
• Using light microscopes, scientists studied
• microorganisms,
• animal and plant cells, and
• some structures within cells.
• In the 1800s, these studies led to cell theory,
which states that
• all living things are composed of cells and
• all cells come from other cells.
Figure 4.1e-0
Human height Length of some nerve and muscle cells Chicken egg Frog egg Paramecium Human egg
Most plant and animal cells Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosome Proteins U n a id ed e ye L ig h t m ic ro sc o p e E le c tr o n m ic ro s co p e 10 m 1 m 100 mm (10 cm) 10 mm (1 cm) 1 mm 100 nm 10 nm 100 μm
10 μm
4.1 Microscopes reveal the world of the cell
• Beginning in the 1950s, scientists started using a very powerful microscope called the electron
microscope (EM) to view the ultrastructure of cells.
• Instead of light, EM uses a beam of electrons.
• Electron microscopes can
• resolve biological structures as small as 2
nanometers and
4.1 Microscopes reveal the world of the cell
• Scanning electron microscopes (SEMs) study the detailed architecture of cell surfaces.
• Transmission electron microscopes (TEMs) study the details of internal cell structure.
4.2 The small size of cells relates to the need
to exchange materials across the plasma
membrane
• Cell size must
• be large enough to house DNA, proteins, and
structures needed to survive and reproduce, but
• remain small enough to allow for a
Figure 4.2a
Total volume 3
3
1
1
2 6
Total surface area
Surface-to-volume ratio
27 units3 27 units3
4.2 The small size of cells relates to the need
to exchange materials across the plasma
membrane
• The plasma membrane forms a flexible boundary between the living cell and its surroundings.
• Phospholipids form a two-layer sheet called a
phospholipid bilayer in which
• hydrophilic heads face outward, exposed to water,
and
4.2 The small size of cells relates to the need
to exchange materials across the plasma
membrane
• Membrane proteins are embedded in the lipid bilayer.
• Some proteins form channels (tunnels) that shield
ions and other hydrophilic molecules as they pass through the hydrophobic center of the membrane.
• Other proteins serve as pumps, using energy to
4.3 Prokaryotic cells are structurally simpler
than eukaryotic cells
• Bacteria and archaea are prokaryotic cells.
• All other forms of life are composed of eukaryotic
cells.
• Eukaryotic cells are distinguished by having
• a membrane-enclosed nucleus and
• many membrane-enclosed organelles that perform
specific functions.
4.3 Prokaryotic cells are structurally simpler
than eukaryotic cells
• Prokaryotic and eukaryotic cells have
• a plasma membrane,
• an interior filled with a thick, jellylike fluid called the
cytosol,
• one or more chromosomes, which carry genes
made of DNA, and
4.3 Prokaryotic cells are structurally simpler
than eukaryotic cells
• The inside of both types of cells is called the
cytoplasm.
4.3 Prokaryotic cells are structurally simpler
than eukaryotic cells
• In a prokaryotic cell,
• the DNA is coiled into a region called the nucleoid
(nucleus-like) and
4.3 Prokaryotic cells are structurally simpler
than eukaryotic cells
• Outside the plasma membrane of most prokaryotes is a fairly rigid, chemically complex cell wall, which
• protects the cell and
• helps maintain its shape.
• Some prokaryotes have surface projections.
• Short projections help attach prokaryotes to each
other or their substrate.
• Longer projections called flagella (singular,
Figure 4.3-1
Fimbriae
Ribosomes
Nucleoid
Plasma membrane
Cell wall
Capsule Bacterial
chromosome
A typical rod-shaped
4.4 Eukaryotic cells are partitioned into
functional compartments
• A eukaryotic cell contains
• a membrane-enclosed nucleus and
• various other organelles (“little organs”), which
4.4 Eukaryotic cells are partitioned into
functional compartments
• The structures and organelles of eukaryotic cells perform four basic functions.
1. The nucleus and ribosomes are involved in the
genetic control of the cell.
2. The endoplasmic reticulum, Golgi apparatus,
4.4 Eukaryotic cells are partitioned into
functional compartments
3. Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing.
4. Structural support, movement, and
4.4 Eukaryotic cells are partitioned into
functional compartments
• The internal membranes of eukaryotic cells partition it into compartments.
4.4 Eukaryotic cells are partitioned into
functional compartments
• Almost all of the organelles and other structures of animals cells are present in plant cells.
• A few exceptions exist.
• Lysosomes and centrosomes containing centrioles
are not found in plant cells.
• Only the sperm cells of a few plant species have
4.4 Eukaryotic cells are partitioned into
functional compartments
• Plant but not animal cells have
• a rigid cell wall that contains cellulose,
• plasmodesmata, cytoplasmic channels through cell
walls that connect adjacent cells,
• chloroplasts, where photosynthesis occurs, and
• a central vacuole, a compartment that stores water
Figure 4.4b Rough endoplasmic reticulum Smooth endoplasmic reticulum NUCLEUS Nuclear envelope Nucleolus Chromatin Ribosomes Plasma membrane Peroxisome Mitochondrion Microfilament Microtubule CYTOSKELETON
Cell wall of
adjacent cell Golgi
4.5 The nucleus contains the cell’s genetic
instructions
• The nucleus
• contains most of the cell’s DNA and
• controls the cell’s activities by directing protein
synthesis by making messenger RNA (mRNA).
• DNA is associated with many proteins and is organized into structures called chromosomes.
4.5 The nucleus contains the cell’s genetic
instructions
• The double membrane nuclear envelope has pores that
• regulate the entry and exit of large molecules and
• connect with the cell’s network of membranes
4.5 The nucleus contains the cell’s genetic
instructions
• The nucleolus is
• a prominent structure in the nucleus and
Figure 4.5
Nucleolus Nuclear
envelope
Endoplasmic reticulum
Ribosome
4.6 Ribosomes make proteins for use in the
cell and export
• Ribosomes are involved in the cell’s protein synthesis.
• Ribosomes are the cellular components that use
instructions from the nucleus, written in mRNA, to build proteins.
• Cells that make a lot of proteins have a large
4.6 Ribosomes make proteins for use in the
cell and export
• Some ribosomes are free ribosomes; others are bound.
• Free ribosomes are suspended in the cytosol.
• Bound ribosomes are attached to the outside of the
Figure 4.6
Rough ER
Bound ribosome
Endoplasmic reticulum
Protein
4.7 Many organelles are connected in the
endomembrane system
• Many of the membranes within a eukaryotic cell are part of the endomembrane system.
• Some of these membranes are physically connected, and others are linked when tiny
4.7 Many organelles are connected in the
endomembrane system
• Many of these organelles interact in the
• synthesis,
• distribution,
• storage, and
4.7 Many organelles are connected in the
endomembrane system
• The endomembrane system includes the
• nuclear envelope,
• endoplasmic reticulum (ER),
• Golgi apparatus,
• lysosomes,
• vacuoles, and
4.7 Many organelles are connected in the
endomembrane system
4.8 The endoplasmic reticulum is a
biosynthetic workshop
• There are two kinds of endoplasmic reticulum, which differ in structure and function.
1. Smooth ER lacks attached ribosomes.
Figure 4.8a
Rough ER
Smooth ER
4.8 The endoplasmic reticulum is a
biosynthetic workshop
• Smooth ER is involved in a variety of metabolic processes, including
• the production of enzymes important in the
synthesis of lipids, oils, phospholipids, and steroids,
• the production of enzymes that help process drugs,
alcohol, and other potentially harmful substances, and
4.8 The endoplasmic reticulum is a
biosynthetic workshop
• Rough ER makes
• additional membrane for itself and
4.9 The Golgi apparatus modifies, sorts, and
ships cell products
• The Golgi apparatus serves as a molecular warehouse and processing station for products manufactured by the ER.
• Products travel in transport vesicles from the ER to
the Golgi apparatus.
• One side of the Golgi stack serves as a receiving
4.9 The Golgi apparatus modifies, sorts, and
ships cell products
• Products of the ER are modified as a Golgi sac
progresses through the stack.
• The “shipping” side of the Golgi functions as a
Figure 4.9 Golgi apparatus 1 2 3 4
“Receiving” side of Golgi apparatus Transport vesicle
from the ER
Transport vesicle from the Golgi
4.10 Lysosomes are digestive compartments
within a cell
• A lysosome is a membrane-enclosed sac of digestive enzymes
• made by rough ER and
4.10 Lysosomes are digestive compartments
within a cell
• Lysosomes
• fuse with food vacuoles and digest food,
• destroy bacteria engulfed by white blood cells, or
• fuse with other vesicles containing damaged
Figure 4.10a-4
Digestive enzymes
Lysosome
Food vacuole
Plasma membrane
Figure 4.10b-3
Lysosome
Digestion Vesicle containing
4.11 Vacuoles function in the general
maintenance of the cell
• Vacuoles are large vesicles that have a variety of functions.
• Some protists have contractile vacuoles, which help
to eliminate water from the protist.
• In plants, vacuoles may
• have digestive functions,
• contain pigments, or
Figure 4.11a
Contractile vacuoles
Figure 4.11b
Central vacuole
4.12 A review of the structures involved in
manufacturing and breakdown
Figure 4.12
Nucleus
Smooth ER
Rough ER
Transport vesicle
Lysosome
Nuclear envelope
Golgi apparatus
Plasma membrane
4.12 A review of the structures involved in
manufacturing and breakdown
• Peroxisomes are metabolic compartments that do not originate from the endomembrane system.
• How they are related to other organelles is still
unknown.
• Some peroxisomes break down fatty acids to be
4.13 Mitochondria harvest chemical energy
from food
• Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells.
4.13 Mitochondria harvest chemical energy
from food
• Mitochondria have two internal compartments.
1. The intermembrane space is the narrow region
between the inner and outer membranes.
2. The mitochondrial matrix contains
• the mitochondrial DNA,
• ribosomes, and
4.13 Mitochondria harvest chemical energy
from food
• Folds of the inner mitochondrial membrane, called
Figure 4.13
Mitochondrion
Intermembrane space
Outer
membrane
Inner
membrane
4.14 Chloroplasts convert solar energy to
chemical energy
• Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar
molecules.
• Chloroplasts are the photosynthesizing
4.14 Chloroplasts convert solar energy to
chemical energy
• Chloroplasts are partitioned into compartments.
• Between the outer and inner membrane is a thin
intermembrane space.
• Inside the inner membrane is a thick fluid called
stroma, which contains the chloroplast DNA, ribosomes, many enzymes, and a network of
interconnected sacs called thylakoids, where green
chlorophyll molecules trap solar energy.
Figure 4.14
Chloroplast
Granum
Stroma
Inner and
outer membranes
4.15 EVOLUTION CONNECTION:
Mitochondria and chloroplasts evolved by
endosymbiosis
• Mitochondria and chloroplasts contain
• DNA and
• ribosomes.
• The structure of this DNA and these ribosomes is
4.15 EVOLUTION CONNECTION:
Mitochondria and chloroplasts evolved by
endosymbiosis
• The endosymbiont theory states that
• mitochondria and chloroplasts were formerly small
prokaryotes and
Figure 4.15-3
Endoplasmic
reticulum Nucleus
Ancestor of
eukaryotic cells (host cell)
Mitochondrion Engulfing of photosynthetic prokaryote Mitochondrion Chloroplast Nonphotosynthetic eukaryote At least one cell
4.16 The cell’s internal skeleton helps
organize its structure and activities
• Cells contain a network of protein fibers, called the
4.16 The cell’s internal skeleton helps
organize its structure and activities
• Microtubules (made of tubulin)
• shape and support the cell and
• act as tracks along which organelles equipped with
motor proteins move.
• In animal cells, microtubules grow out from a
region near the nucleus called the centrosome,
4.16 The cell’s internal skeleton helps
organize its structure and activities
• Intermediate filaments
• are found in the cells of most animals,
• reinforce cell shape and anchor some organelles,
and
4.16 The cell’s internal skeleton helps
organize its structure and activities
• Microfilaments (actin filaments)
• support the cell’s shape and
Figure 4.16-0
Nucleus
Nucleus
Microtubule
25 nm
Intermediate filament
10 nm
Microfilament
Figure 4.16-1
Nucleus
Figure 4.16-2
Nucleus
Intermediate filament
Figure 4.16-3
4.17 SCIENTIFIC THINKING: Scientists
discovered the cytoskeleton using the tools
of biochemistry and microscopy
• In the 1940s, biochemists first isolated and identified the proteins actin and myosin from muscle cells.
• In 1954, scientists, using newly developed techniques of microscopy, established how
filaments of actin and myosin interact in muscle contraction.
• In the next decade, researchers identified actin
4.17 SCIENTIFIC THINKING: Scientists
discovered the cytoskeleton using the tools
of biochemistry and microscopy
• In the 1970s, scientists were able to visualize actin filaments using fluorescent tags and in living cells.
• In the 1980s, biologists were able to record the
4.18 Cilia and flagella move when
microtubules bend
• The short, numerous appendages that propel protists such as Paramecium are called cilia
(singular, cilium).
• Other protists may move using flagella, which are
longer than cilia and usually limited to one or a few per cell.
• Some cells of multicellular organisms also have
4.18 Cilia and flagella move when
microtubules bend
• A flagellum, longer than cilia, propels a cell by an undulating, whiplike motion.
• Cilia work more like the oars of a boat.
• Although differences exist, flagella and cilia have a
4.18 Cilia and flagella move when
microtubules bend
• Both flagella and cilia are composed of
microtubules wrapped in an extension of the plasma membrane.
• In nearly all eukaryotic cilia and flagella, a ring of
nine microtubule doublets surrounds a central pair of microtubules.
• This arrangement is called the 9 2 pattern.
• The microtubule assembly is anchored in a basal
Figure 4.18c-0
Outer
microtubule doublet
Central
microtubules
Cross-linking proteins
Motor proteins (dyneins)
4.18 Cilia and flagella move when
microtubules bend
• Cilia and flagella move by bending motor proteins called dynein feet.
• These feet attach to and exert a sliding force on an
adjacent doublet.
4.19 The extracellular matrix of animal cells
functions in support and regulation
• Animal cells synthesize and secrete an elaborate
extracellular matrix (ECM), which
• helps hold cells together in tissues and
4.19 The extracellular matrix of animal cells
functions in support and regulation
• The ECM may attach to the cell through other
glycoproteins that then bind to membrane proteins called integrins.
• Integrins
• span the membrane and
• attach on the other side to proteins connected to
Figure 4.19
Collagen fiber
EXTRACELLULAR FLUID
CYTOPLASM
Glycoprotein
complex with long polysaccharide
Connecting glycoprotein
Integrin
Plasma membrane
4.20 Three types of cell junctions are found in
animal tissues
• Adjacent cells adhere, interact, and communicate through specialized junctions between them.
• Tight junctions prevent leakage of fluid across a
layer of epithelial cells.
• Anchoring junctions fasten cells together into
sheets.
• Gap junctions are channels that allow small
Figure 4.20
Tight junction
Anchoring junction
Gap junction
Plasma membranes of adjacent cells
Ions or small molecules Extracellular matrix
4.21 Cell walls enclose and support plant
cells
• A plant cell, but not an animal cell, has a rigid cell wall that
• protects and provides skeletal support that helps
keep the plant upright and
• is primarily composed of cellulose.
• Plant cells have cell junctions called
plasmodesmata that allow plants tissues to share
• water,
Figure 4.21
Vacuole
Plant cell walls
Plasmodesmata
Primary cell wall Secondary cell wall Plasma membrane
4.22 Review: Eukaryotic cell structures can
be grouped on the basis of four main
functions
• Eukaryotic cell structures can be grouped on the basis of four functions:
1. genetic control,
2. manufacturing, distribution, and breakdown of
materials,
3. energy processing, and
4. structural support, movement, and intercellular
You should now be able to
1. Describe the importance of microscopes in understanding cell structure and function.
2. Describe the two parts of cell theory.
3. Distinguish between the structures of prokaryotic and eukaryotic cells.
4. Explain how cell size is limited.
You should now be able to
6. Explain why compartmentalization is important in eukaryotic cells.
7. Compare the structures of plant and animal cells. Note the function of each cell part.
8. Compare the structures and functions of chloroplasts and mitochondria.
You should now be able to
10. Compare the structures and functions of
microfilaments, intermediate filaments, and microtubules.
11. Relate the structure of cilia and flagella to their functions.
12. Relate the structure of the extracellular matrix to its functions.
You should now be able to
14. Relate the structures of plant cell walls and plasmodesmata to their functions.
