Download Chapter 4 Cell Structure

CHAPTER 4
A Tour of the Cell
Key Terms
cell theory
cell wall
cellular metabolism
central vacuole
centrosome
chloroplasts
chromatin
chromosome
cilia
crista (plural, cristae)
cytoplasm
cytosol
cytoskeleton
electron microscope (EM)
endomembrane system
endoplasmic reticulum (ER)
endosymbiont theory
eukaryotic cell
extracellular matrix (ECM)
flagellum (plural, flagella)
glycoprotein
Golgi apparatus
granum (plural, grana)
integrins
intermediate filaments
light microscope (LM)
lysosome
microfilaments
microtubules
mitochondrial matrix
mitochondrion (plural,
mitochondria)
nuclear envelope
nucleoid
nucleolus
nucleus (plural, nuclei)
organelles
peroxisomes
plasma membrane
plasmodesma (plural,
plasmodesmata)
prokaryotic cell
ribosome
rough endoplasmic reticulum
scanning electron
microscope (SEM)
smooth endoplasmic
reticulum
stroma
thylakoid
transmission electron
microscope (TEM)
transport vesicle
vacuoles
vesicle
Lecture Outline
I. Introduction
A. Cells have a cytoskeleton that
1. provides support and
2. allows some cells to crawl and others to swim.
B. Our understanding of nature often goes hand in hand with the invention and refinement of instruments that extend our senses.
C. Leeuwenhoek, working at about the same time, used more refined lenses to describe
living cells from blood, sperm, and pond water.
D. Since the days of Hooke and Leeuwenhoek, improved microscopes have vastly
expanded our view of the cell.
II. Introduction to the Cell
A. 4.1 Microscopes reveal the world of the cell
1. A variety of microscopes have been developed for a clearer view of cells and cellular structure.
2. The first microscopes were light microscopes. In a light microscope (LM), a visible light passes
through a specimen, then through glass lenses, and finally is projected into the viewer’s eye.
3. Specimens can be magnified by up to 1,000 times.
4. Magnification is the increase in an object’s image size compared with its actual size,
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5. Resolution is a measure of the clarity of an image. In other words, it is the ability of an instrument to show two close objects as separate.
6. Microscopes have limitations.
a. The human eye and the microscope have limits of resolution—the ability to
distinguish between small structures.
b. Therefore, the light microscope cannot provide the details of a small cell’s
structure.
7. Using light microscopes, scientists studied
a. microorganisms,
b. animal and plant cells, and
c. some structures within cells.
8. In the 1800s, these studies led to cell theory, which states that
a. all living things are composed of cells and
b. all cells come from other cells.
9. Beginning in the 1950s, scientists started using a very powerful microscope called the electron
microscope (EM) to view the ultrastructure of cells.
10. Instead of light, EM uses a beam of electrons.
11. Electron microscopes can
a. resolve biological structures as small as 2 nanometers and
b. magnify up to 100,000 times.
12. Scanning electron microscopes (SEMs) study the detailed architecture of cell
surfaces.
13. Transmission electron microscopes (TEMs) study the details of internal cell
structure.
14. Differential interference light microscopes amplify differences in density so that
structures in living cells appear almost three-dimensional.
B. 4.2 The small size of cells relates to the need to exchange materials across the plasma membrane
1. Cell size must
a. be large enough to house DNA, proteins, and structures needed to survive and
reproduce, but
b. remain small enough to allow for a surface-to-volume ratio that will allow adequate exchange
with the environment.
2. The plasma membrane forms a flexible boundary between the living cell and its
surroundings.
3. Phospholipids form a two-layer sheet called a phospholipid bilayer in which
a. hydrophilic heads face outward, exposed to water, and
b. hydrophobic tails point inward, shielded from water.
4. Membrane proteins are embedded in the lipid bilayer.
5. Some proteins form channels (tunnels) that shield ions and other hydrophilic
molecules as they pass through the hydrophobic center of the membrane.
6. Other proteins serve as pumps, using energy to actively transport molecules into or out of the
cell.
C. 4.3 Prokaryotic cells are structurally simpler than eukaryotic cells
1. Bacteria and Archaea are prokaryotic cells.
2. All other forms of life are composed of eukaryotic cells.
3. Eukaryotic cells are distinguished by having
a. a membrane-enclosed nucleus and
b many membrane-enclosed organelles that perform specific functions.
4. Prokaryotic cells are smaller and simpler in structure.
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5. Prokaryotic and eukaryotic cells have
a. a plasma membrane,
b. an interior filled with a thick, jellylike fluid called the cytosol,
c. one or more chromosomes, which carry genes made of DNA, and
d. ribosomes, tiny structures that make proteins according to instructions from the genes.
6. The inside of both types of cells is called the cytoplasm.
7. However, in eukaryotic cells, this term refers only to the region between the nucleus and the
plasma membrane.
8. In a prokaryotic cell,
a. the DNA is coiled into a region called the nucleoid (nucleus-like) and
b. no membrane surrounds the DNA.
9. Outside the plasma membrane of most prokaryotes is a fairly rigid, chemically
complex cell wall, which
a. protects the cell and
b. helps maintain its shape.
10. Some prokaryotes have surface projections.
a. Short projections help attach prokaryotes to each other or their substrate.
b. Longer projections called flagella (singular, flagellum) propel a prokaryotic cell through its
liquid environment.
D. 4.4 Eukaryotic cells are partitioned into functional compartments
1. A eukaryotic cell contains
a. a membrane-enclosed nucleus and
b. various other organelles (“little organs”) that perform specific functions in the cell.
2. The structures and organelles of eukaryotic cells perform four basic functions.
a. The nucleus and ribosomes are involved in the genetic control of the cell.
b. The endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes are involved in the manufacture, distribution, and breakdown of molecules.
c. Mitochondria in all cells and chloroplasts in plant cells are involved in energy
processing.
d. Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane, and cell wall.
3. The internal membranes of eukaryotic cells partition it into compartments.
4. Cellular metabolism, the many chemical activities of cells, occurs within organelles.
5. Almost all of the organelles and other structures of animal cells are present in plant cells.
6. A few exceptions exist.
a. Lysosomes and centrosomes containing centrioles are not found in plant cells.
b. Only the sperm cells of a few plant species have flagella.
7. Plant but not animal cells have
a. a rigid cell wall that contains cellulose,
b. plasmodesmata, cytoplasmic channels through cell walls that connect adjacent cells,
c. chloroplasts, where photosynthesis occurs, and
d. a central vacuole, a compartment that stores water and a variety of chemicals.
III. The Nucleus and Ribosomes
A. 4.5 The nucleus is the cell’s genetic control center
1. The nucleus
a. contains most of the cell’s DNA and
b. controls the cell’s activities by directing protein synthesis by making messenger RNA
(mRNA).
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2. DNA is associated with many proteins and is organized into structures called
chromosomes.
3. When a cell is not dividing, this complex of proteins and DNA, called chromatin,
appears as a diffuse mass within the nucleus.
4. The double membrane nuclear envelope has pores that
a. regulate the entry and exit of large molecules and
b. connect with the cell’s network of membranes called the endoplasmic reticulum.
5. The nucleolus is
a. a prominent structure in the nucleus and
b. the site of ribosomal RNA (rRNA) synthesis.
B. 4.6 Ribosomes make proteins for use in the cell and export
1. Ribosomes are involved in the cell’s protein synthesis.
a. Ribosomes are the cellular components that use instructions from the nucleus,
written in mRNA, to build proteins.
b. Cells that make a lot of proteins have a large number of ribosomes.
2. Some ribosomes are free ribosomes; others are bound.
a. Free ribosomes are suspended in the cytosol.
b. Bound ribosomes are attached to the outside of the endoplasmic reticulum or
nuclear envelope.
IV. The Endomembrane System
A. 4.7 Many cell organelles are connected through the endomembrane system
1. Many of the membranes within a eukaryotic cell are part of the endomembrane
system.
2. Some of these membranes are physically connected, and others are linked when tiny vesicles
(sacs made of membrane) transfer membrane segments between them.
3. Many of these organelles interact in the
a. synthesis,
b. distribution,
c. storage, and
d. export of molecules.
4. The endomembrane system includes the
a. nuclear envelope,
b. endoplasmic reticulum (ER),
c. Golgi apparatus,
d. lysosomes,
e. vacuoles, and
f. plasma membrane.
5. The largest component of the endomembrane system is the endoplasmic reticulum (ER), an extensive network of flattened sacs and tubules.
B. 4.8 The endoplasmic reticulum is a biosynthetic factory
1. There are two kinds of endoplasmic reticulum, which differ in structure and function.
a. Smooth ER lacks attached ribosomes.
b. Rough ER has bound ribosomes that stud the outer surface of membrane.
c. Although physically interconnected, smooth and rough ER differ in structure and function.
2. Smooth ER is involved in a variety of metabolic processes including
a. the production of enzymes important in the synthesis of lipids, oils, phospholipids, and steroids.
b. the production of enzymes that help process drugs, alcohol, and other potentially harmful substances.
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c. the storage of calcium ions.
3. Rough ER makes
a. additional membrane for itself and
b. secretory proteins.
C. 4.9 The Golgi apparatus finishes, sorts, and ships cell products
1. The Golgi apparatus serves as a molecular warehouse and processing station for products manufactured by the ER.
a. Products travel in transport vesicles from the ER to the Golgi apparatus.
b. One side of the Golgi stack serves as a receiving dock for transport vesicles
produced by the ER.
c. Products of the ER are modified as a Golgi sac progresses through the stack.
d. The “shipping” of the Golgi functions as a depot where products in vesicles bud off and travel
to other sites.
D. 4.10 Lysosomes are digestive compartments within a cell
1. A lysosome is a membrane-enclosed sac of digestive enzymes
a. made by rough ER and
b. processed in the Golgi apparatus.
2. Lysosomes
a. fuse with food vacuoles and digest food,
b. destroy bacteria engulfed by white blood cells, or
c. fuse with other vesicles containing damaged organelles or other materials to be
recycled within a cell.
E. 4.11 Vacuoles function in the general maintenance of the cell
1. Vacuoles are large vesicles that have a variety of functions.
a. Some protists have contractile vacuoles that help to eliminate water from the protist.
b. In plants, vacuoles may
i. have digestive functions,
ii. contain pigments, or
iii. contain poisons that protect the plant.
F. 4.12 A review of the structures involved in manufacturing and breakdown
1. Peroxisomes are metabolic compartments that do not originate from the endomembrane system.
a. How they are related to other organelles is still unknown.
b. Some peroxisomes break down fatty acids to be used as a cellular fuel.
V. Energy-Converting Organelles
A. 4.13 Mitochondria harvest chemical energy from food
1. Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells.
2. Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine
triphosphate).
3. Mitochondria have two internal compartments.
a. The intermembrane space is the narrow region between the inner and outer
membranes.
b. The mitochondrial matrix contains
i. the mitochondrial DNA,
ii. ribosomes, and
iii. many enzymes that catalyze some of the reactions of cellular respiration.
4. Folds of the inner mitochondrial membrane, called cristae, increase the membrane’s surface area,
enhancing the mitochondrion’s ability to produce ATP.
B. 4.14 Chloroplasts convert solar energy to chemical energy
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1. Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar
molecules.
2. Chloroplasts are the photosynthesizing organelles of plants and algae.
3. Chloroplasts are partitioned into compartments.
4. Between the outer and inner membrane is a thin intermembrane space.
5. Inside the inner membrane is a thick fluid called stroma that contains the chloroplast DNA, ribosomes, many enzymes, and a network of interconnected sacs called thylakoids, where green
chlorophyll molecules trap solar energy.
6. In some regions, thylakoids are stacked like poker chips. Each stack is called a granum.
C. 4.15 EVOLUTION CONNECTION: Mitochondria and chloroplasts evolved by
endosymbiosis
1. Mitochondria and chloroplasts contain
a. DNA and
b. ribosomes.
2. The structure of this DNA and these ribosomes is very similar to that found in
prokaryotic cells.
3. The endosymbiont theory proposes that
a. mitochondria and chloroplasts were formerly small prokaryotes and
b. they began living within larger cells.
VI. The Cytoskeleton and Cell Surfaces
A. 4.16 The cell’s internal skeleton helps organize its structure and activities
1. Cells contain a network of protein fibers, called the cytoskeleton, which organize the structures
and activities of the cell.
2. Microtubules (made of tubulin)
a. shape and support the cell and
b. act as tracks along which organelles equipped with motor proteins move.
3. In animal cells, microtubules grow out from a region near the nucleus called the centrosome, which
contains a pair of centrioles, each composed of a ring of microtubules.
4. Intermediate filaments
a. are found in the cells of most animals,
b. reinforce cell shape and anchor some organelles, and
c. are often more permanent fixtures in the cell.
5. Microfilaments (actin filaments)
a. support the cell’s shape and
b. are involved in motility.
B. 4.17 SCIENTIFIC THINKING: Scientists discovered the cytoskeleton using the tools of biochemistry and microscopy
1. In the 1970s, scientists were able to visualize actin filaments using fluorescent tags and living
cells.
2. In the 1980s, biologists were able to record the changing architecture of the
cytoskeleton.
C. 4.18 Cilia and flagella move when microtubules bend
1. The short, numerous appendages that propel protists such as Paramecium are called cilia (singular, cilium).
2. Other protists may move using flagella, which are longer than cilia and usually limited to one or a
few per cell.
3. Some cells of multicellular organisms also have cilia or flagella.
4. A flagellum, longer than cilia, propels a cell by an undulating, whiplike motion.
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5. Cilia work more like the oars of a boat.
6. Although differences exist, flagella and cilia have a common structure and mechanism of movement.
7. Both flagella and cilia are composed of microtubules wrapped in an extension of the plasma
membrane.
8. In nearly all eukaryotic cilia and flagella, a ring of nine microtubule doublets
surrounds a central pair of microtubules.
a. This arrangement is called the 9 + 2 pattern.
b. The microtubule assembly is anchored in a basal body with nine microtubule
triplets arranged in a ring.
9. Cilia and flagella move by bending motor proteins called dynein feet.
a. These feet attach to and exert a sliding force on an adjacent doublet.
b. This “walking” causes the microtubules to bend.
D. 4.19 The extracellular matrix of animal cells functions in support and regulation
1. Animal cells synthesize and secrete an elaborate extracellular matrix (ECM), which
a. helps hold cells together in tissues and
b. protects and supports the plasma membrane.
2. The ECM may attach to a cell through glycoproteins that then bind to membrane
proteins called integrins. Integrins span the plasma membrane and connect to
microfilaments of the cytoskeleton.
E. 4.20 Three types of cell junctions are found in animal tissues
1. Adjacent cells communicate, interact, and adhere through specialized junctions
between them.
a. Tight junctions prevent leakage of fluid across a layer of epithelial cells.
b. Anchoring junctions fasten cells together into sheets.
c. Gap junctions are channels that allow molecules to flow through protein-lined pores between
cells.
F. 4.21 Cell walls enclose and support plant cells
1. A plant cell, but not an animal cell, has a rigid cell wall that
a. protects and provides skeletal support that helps keep the plant upright against
gravity and
b. is primarily composed of cellulose.
2. Plant cells have cell junctions called plasmodesmata that allow plant tissues to share
a. water,
b. nourishment, and
c. chemical messages.
G. 4.22 Review: Eukaryotic cell structures can be grouped on the basis of four main
functions
1. Eukaryotic cell structures can be grouped on the basis of four functions:
a. genetic control,
b. manufacturing, distribution, and breakdown of materials,
c. energy processing, and
d. structural support, movement, and communication.
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CHAPTER 4
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Word Roots
chloro- = green; -plast = molded (chloroplast: the site of photosynthesis in plants and algae)
cili- = hair (cilium: a short hairlike cellular appendage with a microtubule core, specialized for locomotion)
cyto- = cell; -plasm = fluid (cytoplasm: everything inside a cell between the plasma membrane and the nucleus, consisting of a semifluid medium and organelles)
-ell = small (organelle: a membrane-enclosed structure with a specialized function within a cell)
endo- = inner; sym- = together; bios- = living (endosymbiosis: when one organism lives inside another organism; the process by which the mitochondria and chloroplasts of eukaryotic cells probably evolved)
eu- = true; karyo- = nucleus (eukaryotic cell: a cell with a membrane-enclosed nucleus and other membraneenclosed organelles)
extra- = outside (extracellular matrix: the substance in which animal tissue cells are embedded)
flagell- = whip (flagellum: a long whip-like cellular appendage specialized for locomotion)
glyco- = sweet (glycoprotein: a macromolecule consisting of one or more polypeptides linked to short chains
of sugars)
lyso- = loosen (lysosome: a digestive organelle containing hydrolytic enzymes used by eukaryotic cells to
digest food and wastes)
micro- = small; -tubul = a little pipe (microtubule: a straight, hollow tube of globular proteins in the cytoskeleton of eukaryotic cells that support the structure and movement of cilia and flagella)
nucle- = nucleus; -oid = like (nucleoid: a dense region of DNA in a prokaryotic cell); a band or bond (plasmodesmata: an open channel in a plant cell wall)
pro- = before (prokaryotic cell: a cell that has no nucleus)
-soma = a body (chromosome: the structure carrying the genetic material found in the nucleus of a eukaryotic
cell)
thylaco- = sac or pouch (thylakoid: a flattened membranous sac inside the chloroplast that serves as the site of
the light reactions of photosynthesis)
trans- = across; -port = a harbor; vesic- = sac or bladder (transport vesicle: a membranous
compartment used to enclose and transport materials from one part of a cell to another)
vacu- = empty (vacuole: a membrane-enclosed sac that is part of the endomembrane system of a eukaryotic
cell)
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