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Chapter 6
A Tour of the Cell
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
1
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
What?
 A microscope is an
instrument for
viewing objects that
are much too small
to be seen with the
naked eye
 It uses one or more
glass lenses which
magnify the objects
2
How?
Lens makers
ground “beads” of
glass into lenses
Compound
microscopes use
more than one lens
By the mid 1600’s
microscopes could
magnify an object
270 times
3
Who?
 Zacharias Janssen- who
was credited with trying to
create lenses with stronger
magnification for people
with poor eyesight (which
evolved into a lens for a
scope)
 Robert Hooke- important in
the development of the
fields of astronomy,
physics, biology and
medicine (just to name a
few). He was the first
person to have seen cork
cells (using a microscope)
4
Who?
 Probably most
important was:
Anton Van
Leeuwenhoek
whom discovered:
bacteria, free-living
and
parasitic microscopic
protists, sperm cells,
blood cells, microscopic
nematodes and
rotifers, and much more
5
What happened next?
 The advances made by these scientists by the 1600’s
later lead to the formulation of one of the MAJOR
theories in science:
The Cell Theory
6
The modern beliefs of the Cell Theory
include:
1. all known living
things are made up
of cells.
2. the cell is the basic
structural &
functional unit of all
living things.
7
The modern beliefs of the Cell Theory
include:
3. all cells come from preexisting cells by
division.
(Spontaneous Generation does not
occur).
4. cells contain hereditary
information which is
passed from
cell to cell during cell
division
8
The modern beliefs of the Cell Theory
include:
5. All cells are
basically the same in
chemical
composition.
6. all energy flow
(metabolism &
biochemistry) of life
occurs within cells.
9
Fig. 6-1
3 IMPORTANT BIOLOGY EXPERIMENTS
10
Microscopy
 Scientists use microscopes to visualize cells too small to see with the
naked eye
 In a light microscope (LM), visible light passes through a
specimen and then through glass lenses, which magnify the image
 The quality of an image depends on
 Magnification, the ratio of an object’s image size to its real size
 Resolution, the measure of the clarity of the image, or the minimum
distance of two distinguishable points
 Contrast, visible differences in parts of the sample
11
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10 m
1m
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
1 cm
Unaided eye
Fig. 6-2
Frog egg
Most plant and
animal cells
10 µm
Nucleus
Most bacteria
1 µm
100 nm
10 nm
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
1 nm
Small molecules
12
0.1 nm
Atoms
Electron microscope
100 µm
Light microscope
1 mm
 LMs can magnify effectively to about 1,000 times the size of the
actual specimen
 Various techniques enhance contrast and enable cell components to
be stained or labeled
 Most subcellular structures, including organelles (membraneenclosed compartments), are too small to be resolved by an LM
13
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Cell Fractionation
 Cell fractionation takes cells apart and
separates the major organelles from one
another
 Ultracentrifuges fractionate cells into
their component parts
 Cell fractionation enables scientists to
determine the functions of organelles
 Biochemistry and cytology help correlate
cell function with structure
14
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Fig. 6-5
TECHNIQUE
Homogenization
Tissue
cells
Homogenate
1,000 g
(1,000 times the
force of gravity)
Differential centrifugation
10 min
Supernatant poured
into next tube
20,000 g
20 min
Pellet rich in
nuclei and
cellular debris
80,000 g
60 min
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
15
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
Fig. 6-5a
TECHNIQUE
Homogenization
Tissue
cells
16
Differential centrifugation
Homogenate
Fig. 6-5b
TECHNIQUE (cont.)
1,000 g
(1,000 times the
force of gravity)
10 min
Supernatant poured
into next tube
20,000 g
20 min
80,000 g
60 min
Pellet rich in
nuclei and
cellular debris
150,000 g
3 hr
Pellet rich in
mitochondria
(and chloroplasts if cells
are from a plant)
17
Pellet rich in
“microsomes”
(pieces of plasma
membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
Concept 6.2: Eukaryotic cells have
internal membranes that
compartmentalize their functions
 The basic structural and functional unit of every organism is one of
two types of cells: prokaryotic or eukaryotic
 Only organisms of the domains Bacteria and Archaea consist of
prokaryotic cells
 Protists, fungi, animals, and plants all consist of eukaryotic cells
18
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Two “kinds” of cells:
First kind:
Cells that DO NOT
have their hereditary
information (DNA)
located within a
MEMBRANE BOUND
nucleus
These are called
“Prokaryotic” cells
19
Prokaryotic cells:
 Prokaryotes include the
kingdoms of Monera
(simple bacteria) and
Archaea.
 They are molecules
surrounded by a
membrane and cell wall.
 They do not have
organelles (“mini
organs”)
 They might have
photosynthetic pigments
(like cyanobacteria)
 They might have flagella
for locomotion or hair20like pili for adhesion
Shapes of bacteria
 Bacteria can be found as
 Cocci (spheres), Baccilli (rods) or Spirilla (spirals).
21
Prokaryote Reproduction
 Bacteria and archaea reproduce by a process called
binary fission.
 The DNA is copied and the cell grows.
 Once the cell gets large enough it pinches itself off into
two daughter cells
 What kind of cellular reproduction is this?
22
Binary Fission
23
http://www.youtube.com/watch?
v=7stZk6TesKk
bacterial conjugation
24
Comparing Prokaryotic and Eukaryotic
Cells
 Basic features of all cells:
Plasma membrane
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)
25
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Fig. 6-6
Fimbriae
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 µm
(a) A typical
rod-shaped
bacterium
26
Flagella
(b) A thin section
through the
bacterium
Bacillus
coagulans (TEM)
Prokaryote parts:
 The capsule is outside of the cell wall and is made of
polysaccharides, it is a virulent factor meaning it
enhances the ability for the bacteria to cause disease
 Fimbria are protein structures that allow bacteria to cling
to each other or to other organisms
 Nucleoid (nucleus like) structure contains the DNA of the
bacterial cell
 Ribosomes large complex of RNA and protein that is
used to catalyze translation (making protein from RNA)
27
 Cell wall- acts as protective barrier, structural support
and filter
 Cell membrane-selectively permeable, allows things
in/out of cell
28
• Eukaryotic cells are
characterized by having
DNA in a nucleus that is
bounded by a membranous
nuclear envelope
Membrane-bound
organelles
Cytoplasm in the region
between the plasma
membrane and nucleus
 Eukaryotic cells are generally
much larger than prokaryotic
29
cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
 The plasma membrane is a selective
barrier that allows sufficient passage of oxygen,
nutrients, and waste to service the volume of every
cell
 The general structure of a biological membrane is a
double layer of phospholipids (more on this in
chapter 7)
30
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-7
Outside of cell
Inside of
cell
0.1 µm
(a) TEM of a plasma
membrane
Carbohydrate side chain
Hydrophilic
region
Hydrophobic
region
31
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
 The logistics of carrying out cellular metabolism
sets limits on the size of cells
 The surface area to volume ratio of a cell is critical
 As the surface area increases by a factor of n2, the
volume increases by a factor of n3
 Small cells have a greater surface area relative to
volume
32
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Ratio of Surface Area to Volume
33
 As the cell grows, its volume increases
much more rapidly than the surface
area.
The cell might have difficulty supplying
nutrients and expelling enough waste
products.
34
Transport of Substances
 Substances move by diffusion or by motor
proteins.
 Diffusion over large distances is slow
and inefficient.
 Small cells maintain more efficient
transport systems.
35
Cellular Communications
 The need for signaling proteins to
move throughout the cell also limits cell
size.
 Cell size affects the ability of the cell
to communicate instructions for cellular
functions.
36
Fig. 6-8
Surface area increases while
total volume remains constant
5
1
1
Total surface area
[Sum of the surface areas
(height  width) of all boxes
sides  number of boxes]
Total volume
[height  width  length 
number of boxes]
37
Surface-to-volume
(S-to-V) ratio
[surface area ÷ volume]
6
150
750
1
125
125
6
1.2
6
A Panoramic View of the Eukaryotic Cell
 A eukaryotic cell has internal membranes that
partition the cell into organelles (some of the
chemical reactions need to be isolated from each
other because the environment wouldn’t be
conducive to them happening in one jumble)
 Plant and animal cells have most of the same
organelles
BioFlix: Tour Of An Animal Cell
38
BioFlix: Tour Of A Plant Cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-9a
Nuclear
envelope
ENDOPLASMIC RETICULUM (ER)
Flagellum
Rough ER
NUCLEUS
Nucleolus
Smooth ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Microtubules
Ribosomes
Microvilli
Golgi
apparatus
Peroxisome
39
Mitochondrion
Lysosome
Fig. 6-9b
NUCLEUS
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma
membrane
Cell wall
Plasmodesmata
40
Wall of adjacent cell
CYTOSKELETON
Concept 6.3: The eukaryotic cell’s
genetic instructions are housed in the
nucleus and carried out by the
ribosomes
 The nucleus contains
most of the DNA in a
eukaryotic cell (there is
also some DNA found in
the mitochondria called
mtDNA)
 Ribosomes use the
information from the DNA
to make proteins
41
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The Nucleus: Information Central
 The nucleus contains most of the cell’s
genes and is usually the most
conspicuous organelle
 The nuclear envelope encloses the
nucleus, separating it from the
cytoplasm
 There are pores in the nuclear
envelope
 The pore complex lines each pore and
regulates the passage of proteins,
RNAs and large macromolecules
 The nuclear membrane is a double
membrane; each membrane consists of
a lipid bilayer
42
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Fig. 6-10
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Surface of
nuclear envelope
Rough ER
Ribosome
1 µm
0.25 µm
Close-up of nuclear
envelope
43
Pore complexes (TEM)
Nuclear lamina (TEM)
 The shape of the nucleus is
maintained by the nuclear
lamina, which is composed of
protein
 It is a “net like” array of protein
filaments (on the inside of the
nuclear membrane; think of
mesh) that helps not only in
maintaining the shape of the
nucleus, but also helps to
mechanically support the nuclear
envelope
 It also helps regulate important
cell events like DNA replication
and cell division
44
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 In the nucleus, DNA and proteins form
genetic material called chromatin (a
thin threadlike form of
chromosomes) the nuclear lamina
also helps in this chromatin
organization
 Chromatin condenses to form discrete
chromosomes (several different
forms we will learn in cell reproduction
chapters)
 The nucleolus is located within the
nucleus and is the site of ribosomal
RNA (rRNA) synthesis
Nucleolus
chromatin
45
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Ribosomes: Protein Factories
 Ribosomes are particles made of
ribosomal RNA and protein (made by
the nucleolus)
 Ribosomes carry out protein
synthesis in two locations:
 In the cytosol (free ribosomes);
these make proteins that are
used in the cell
 On the outside of the
endoplasmic reticulum or the
nuclear envelope (bound
ribosomes); if a ribosome makes
a protein that is needed for
another organelle the ribosome
becomes embedded in the ER
and it inserts the new protein
into the ER; it is then transported
to its destination via the
secretory pathway
46
They are structurally identical and
can alternate between the ER and
cytosol
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-11
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
TEM
showing ER and ribosomes
47
Small
subunit
Diagram of a ribosome
Concept 6.4: The endomembrane
system regulates protein traffic and
performs metabolic functions in the cell
 Components of the endomembrane system:
 Nuclear envelope (already talked about this)
 Endoplasmic reticulum
 Golgi apparatus
 Lysosomes
 Vacuoles
 Plasma membrane
•
These components are either related through direct physical
continuity or via transfer of membrane segments by tiny vesicles
48
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The Endoplasmic Reticulum:
Biosynthetic Factory
 The endoplasmic reticulum (ER)
accounts for more than half of the
total membrane in many eukaryotic
cells
 The ER membrane is continuous
with the nuclear envelope
 There are two distinct regions of
ER:
 Smooth ER, which lacks ribosomes
 Rough ER, with ribosomes studding
its surface
49
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Fig. 6-12
Smooth ER
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
50
Nuclear
envelope
Transitional ER
Rough ER
200 nm
Functions of Smooth ER
 The smooth ER
 Synthesizes lipids
 Metabolizes carbohydrates
 Detoxifies poison
 Stores calcium
THE FUNCTION DEPENDS ON
THE TYPE OF CELL IT IS FOUND
IN:
In liver cells the smooth ER
produces enzymes (enzymes are
proteins) that help to detoxify
certain compounds. This usually
involves adding a hydroxyl group
to drugs to make them more
water soluble
51
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In muscles the smooth ER assists in the contraction of muscle
cells. It stores calcium ions that are released across the ER
into the cytosol and triggers muscle contraction.
In brain cells it synthesizes male and female hormones
(hormones are proteins).
52
Functions of Rough ER
 The rough ER
 Has bound ribosomes, which
secrete glycoproteins (proteins
covalently bonded to carbohydrates)
 Once a protein is made it distributes
the protein to where it is needed by
transport vesicles, proteins
surrounded by membranes
 Is a membrane factory for the cell
 http://www.youtube.com/watch?v=
VB3PTN05b5U
 Biosynthetic secretory pathway
53
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The Golgi Apparatus: Shipping and
Center
Receiving
The Golgi apparatus
consists of
flattened membranous sacs called
cisternae; the cisternae are not believed
to be directly connected so a series of
budding, vesicle formation and fusion
with the next golgi sac
 Functions of the Golgi apparatus:
 Modifies products of the ER (like proteins
and phospholipids)
 Manufactures certain macromolecules
 Sorts and packages materials into
transport vesicles (it tags them so they are
sorted correctly)
 The cis face is the “receiving” end and is
closely associated with the ER
54
 The trans face is the “shipping” end
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-13
cis face
(“receiving” side of
Golgi apparatus)
0.1 µm
Cisternae
trans face
(“shipping” side of
Golgi apparatus)
55
TEM of Golgi apparatus
Lysosomes: Digestive Compartments
 A lysosome is a membranous sac of hydrolytic enzymes that can
digest macromolecules
 Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides,
and nucleic acids
 Made by the ER and golgi
 If they are compromised wouldn’t do a terrible amount of damage
because the cytosol is neutral
 Act as the recyclers of the cell (trashmen)
 Believed to be a part of programmed cell death (apoptosis)
 If defective can cause 50 different diseases because substances
destined for recycling just accumulate in the cell; Tay-sach’s is one
of these disorders
56
Animation: Lysosome Formation
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 Some types of cell can engulf another cell by phagocytosis; this
forms a food vacuole
 A lysosome fuses with the food vacuole and digests the molecules
 Lysosomes also use enzymes to recycle the cell’s own organelles and
macromolecules, a process called autophagy
 http://www.youtube.com/watch?v=aWItglvTiLc
 Amoeba engulfing paramecium by phagocytosis
57
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Fig. 6-14
Nucleus
1 µm
Vesicle containing
two damaged organelles
1 µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Lysosome
Digestive
enzymes
Plasma
membrane
Lysosome
Peroxisome
Digestion
Food vacuole
Vesicle
(a) Phagocytosis
58
(b) Autophagy
Mitochondrion
Digestion
Vacuoles: Diverse Maintenance
Compartments
 A plant cell or fungal cell may have
one or several vacuoles
 You won’t see as many in animal cells
 Food vacuoles are formed by
phagocytosis
 Contractile vacuoles, found in
many freshwater protists, pump
excess water out of cells in order to
maintain ion concentrations
 Central vacuoles, found in many
mature plant cells, hold organic
compounds and water, store
pigments to attract pollinators, store
wastes, store poisons to keep
animals from consuming
59
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Fig. 6-15
Central vacuole
Cytosol
Nucleus
Central
vacuole
Cell wall
Chloroplast
60
5 µm
The Endomembrane System: A Review
 The endomembrane system is a complex and dynamic player in the
cell’s compartmental organization
61
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Fig. 6-16-3
Nucleus
Rough ER
Smooth ER
cis Golgi
62
trans Golgi
Plasma
membrane
Concept 6.5: Mitochondria and
chloroplasts change energy from one
form to another
 Mitochondria are the sites of cellular respiration, a metabolic
process that generates ATP (found especially in areas that require a
lot of energy)
 Chloroplasts, found in plants and algae, are the sites of
photosynthesis
 Peroxisomes are oxidative organelles
63
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Mitochondria and chloroplasts
Are not part of the endomembrane
system
Have a double membrane
Have proteins made by free ribosomes
Contain their own DNA
WHY?
64
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Mitochondria: Chemical Energy
Conversion (we will learn about this in
chapter 9)
 Mitochondria are in nearly all
eukaryotic cells (their membranes
are made by free ribosomes;
considered to be semiautonomous)
 They have a smooth outer
membrane and an inner membrane
folded into cristae
 The inner membrane creates two
compartments: intermembrane
space and mitochondrial matrix
 Some metabolic steps of cellular
respiration are catalyzed in the
mitochondrial matrix
 Cristae present a large surface area
for enzymes that synthesize ATP;
the folding increases the surface
65
area
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Chloroplasts: Capture of Light Energy
 The chloroplast is a member of a
family of organelles called plastids
 Chloroplasts contain the green
pigment chlorophyll, as well as
enzymes and other molecules that
function in photosynthesis
 Chloroplasts are found in leaves
and other green organs of plants
and in algae
66
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 Chloroplast structure includes:
 Thylakoids, membranous sacs, stacked to form a granum to increase
surface area and efficiency for photosynthesis
 Stroma, the internal fluid
67
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Fig. 6-18
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
68
1 µm
Peroxisomes: Oxidation
 Peroxisomes are specialized metabolic compartments bounded by a
single membrane
 Peroxisomes produce hydrogen peroxide (it moves H from
substances to oxygen and makes peroxide as a byproduct) and
convert it to water
 Oxygen is used to break down different types of molecules (like fatty
acids, alcohol)
69
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Fig. 6-19
Chloroplast
Peroxisome
Mitochondrion
70
1 µm
Concept 6.6: The cytoskeleton is a
network of fibers that organizes
structures and activities in the cell
 The cytoskeleton is a network
of fibers extending throughout
the cytoplasm
 It organizes the cell’s structures
and activities, anchoring many
organelles
 It is composed of three types of
molecular structures:
 Microtubules
 Microfilaments
 Intermediate filaments
71
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Fig. 6-20
Microtubule
0.25 µm
72
Microfilaments
Roles of the Cytoskeleton: Support,
Motility, and Regulation
 The cytoskeleton helps to support the cell and maintain its shape
 It interacts with motor proteins to produce motility
 Inside the cell, vesicles can travel along “monorails” provided by the
cytoskeleton
 Recent evidence suggests that the cytoskeleton may help regulate
biochemical activities
73
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Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
74
(b)
Vesicles
0.25 µm
Components of the Cytoskeleton
 Three main types of fibers make up the cytoskeleton:
 Microtubules are the thickest of the three components of the cytoskeleton
 Microfilaments, also called actin filaments, are the thinnest components
 Intermediate filaments are fibers with diameters in a middle range
75
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Table 6-1
10 µm
10 µm
10 µm
Column of tubulin dimers
Keratin proteins
Actin subunit
Fibrous subunit (keratins
coiled together)
25 nm
76
7 nm


Tubulin dimer
8–12 nm
Microtubules
 Microtubules are hollow rods about 25 nm in diameter and about
200 nm to 25 microns long
 Functions of microtubules:
 Shaping the cell
 Guiding movement of organelles
 Separating chromosomes during cell division
77
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Centrosomes and Centrioles
 In many cells, microtubules grow out from a centrosome near
the nucleus
 The centrosome is a “microtubule-organizing center”
 In animal cells, the centrosome has a pair of centrioles, each
with nine triplets of microtubules arranged in a ring
 Centrioles give rise to spindle fibers which attach to chromosomes and move them
around during cell reproduction
78
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Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
79
Longitudinal section Microtubules Cross section
of one centriole
of the other centriole
Cilia and Flagella
 Microtubules control the beating of cilia and flagella, locomotor
appendages of some cells
 Cilia and flagella differ in their beating patterns
 Help in locomotion, or directing the flow of substances
80
Video: Chlamydomonas
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Video: Paramecium Cilia
Fig. 6-23
Direction of swimming
(a) Motion of flagella
5 µm
Direction of organism’s movement
Power stroke Recovery stroke
81
(b) Motion of cilia
15 µm
Fig. 6-27bc
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Nonmoving cortical
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
91
(c) Cytoplasmic streaming in plant cells
Cell wall
•
Localized contraction brought about by actin and myosin also drives
amoeboid movement
•
Pseudopodia (cellular extensions) extend and contract through the
reversible assembly and contraction of actin subunits into
microfilaments
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 Cytoplasmic streaming is a circular flow of cytoplasm within cells
 This streaming speeds distribution of materials within the cell
 In plant cells, actin-myosin interactions and sol-gel transformations
drive cytoplasmic streaming
 http://www.youtube.com/watch?v=pFsty-XyLZc
 http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter4/animation__cytoplasmic_streaming.html
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Video: Cytoplasmic Streaming
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Concept 6.7: Extracellular components
and connections between cells help
coordinate cellular activities
 Most cells synthesize and secrete materials that are external to the
plasma membrane
 These extracellular structures include:
 Cell walls of plants
 The extracellular matrix (ECM) of animal cells
 Intercellular junctions
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Cell Walls of Plants
 The cell wall is an
extracellular structure that
distinguishes plant cells from
animal cells
 Prokaryotes, fungi, and some
protists also have cell walls
 The cell wall protects the
plant cell, maintains its
shape, and prevents
excessive uptake of water
 Plant cell walls are made of
cellulose fibers embedded in
other polysaccharides and
protein
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 Plant cell walls may have multiple layers:
 Primary cell wall: relatively thin and
flexible (made first)
 Middle lamella: thin layer between
primary walls of adjacent cells (has pectin
in it to “glue” adjacent cells together)
 Secondary cell wall (in some cells):
added between the plasma membrane and
the primary cell wall
•
Plasmodesmata are channels between
adjacent plant cells that allow passage of
materials
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 Functions of the ECM:




Support
Adhesion
Movement
Regulation
Break down of collagen as
we age: facial creams with
copper peptides; foods rich
in lysine and proline amino
acids; foods high in vitamin
C, eat garlic
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Intercellular Junctions
Neighboring cells in tissues, organs, or
organ systems often adhere, interact, and
communicate through direct physical
contact
Intercellular junctions facilitate this
contact
There are several types of intercellular
junctions
 Plasmodesmata (talked about in cell wall structure)
 Tight junctions
 Desmosomes
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 Gap junctions
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Plasmodesmata in Plant Cells
 Plasmodesmata are channels that perforate plant cell walls
 Through plasmodesmata, water and small solutes (and sometimes
proteins and RNA) can pass from cell to cell
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Fig. 6-31
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
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Plasmodesmata Plasma membranes
Tight Junctions, Desmosomes, and Gap
Junctions in Animal Cells
At tight junctions, membranes of
neighboring cells are pressed together,
preventing leakage of extracellular fluid
Desmosomes (anchoring junctions) fasten
cells together into strong sheets
Gap junctions (communicating junctions)
provide cytoplasmic channels between
adjacent cells
Animation: Tight Junctions
Animation: Desmosomes
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Animation: Gap Junctions
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Fig. 6-32
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
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Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
Fig. 6-32b
Tight junction
Used to maintain a tight
barrier between cells; hold
cells together; makes sure
the ions have to pass into
the cell instead of the spaces
between the cells
110
0.5 µm
Fig. 6-32c
Acts to adhere cells
to each other;
mutations can
cause
Arrythmogenic right
ventricular
cardiomyapothy;
associated with
blistering diseases
if not functioning
Desmosome
correctly
111
1 µm
Fig. 6-32d
Connect the
cytoplasm
Between
different cells
Allowing ions
and other
Substances to
pass; allows
Electrical
Gap junction
communication
Between cells
and chemical
Communication
between
cells
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0.1 µm
The Cell: A Living Unit Greater Than the
Sum of Its Parts
 Cells rely on the integration of structures and organelles in order to
function
 For example, a macrophage’s ability to destroy bacteria involves the
whole cell, coordinating components such as the cytoskeleton,
lysosomes, and plasma membrane
 http://www.youtube.com/watch?v=Ao9cVhwPg84&feature=related
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Fig. 6-UN1
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Structure
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Nucleus
Function
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit of
materials.
(ER)
Two subunits made of riboProtein synthesis
somal RNA and proteins; can be
free in cytosol or bound to ER
Ribosome
Concept 6.4
The endomembrane system
regulates protein traffic and
performs metabolic functions
in the cell
Concept 6.5
Mitochondria and chloroplasts change energy from
one form to another
Extensive network of
membrane-bound tubules and
sacs; membrane separates
lumen from cytosol;
continuous with
the nuclear envelope.
Smooth ER: synthesis of
lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons
Golgi apparatus
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of Golgi
products, which are then
released in vesicles.
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Vacuole
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Mitochondrion
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Cellular respiration
Endoplasmic reticulum
(Nuclear
envelope)
Chloroplast
Peroxisome
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Rough ER: Aids in synthesis of
secretory and other proteins from
bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Breakdown of ingested substances,
cell macromolecules, and damaged
organelles for recycling
Typically two membranes
Photosynthesis
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
Specialized metabolic
compartment bounded by a
single membrane
Contains enzymes that transfer
hydrogen to water, producing
hydrogen peroxide (H2O2) as a
by-product, which is converted
to water by other enzymes
in the peroxisome
You should now be able to:
1.
Distinguish between the following pairs of terms: magnification
and resolution; prokaryotic and eukaryotic cell; free and bound
ribosomes; smooth and rough ER
2.
Describe the structure and function of the components of the
endomembrane system
3.
Briefly explain the role of mitochondria, chloroplasts, and
peroxisomes
4.
Describe the functions of the cytoskeleton
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5.
Compare the structure and functions of microtubules,
microfilaments, and intermediate filaments
6.
Explain how the ultrastructure of cilia and flagella relate to their
functions
7.
Describe the structure of a plant cell wall
8.
Describe the structure and roles of the extracellular matrix in
animal cells
9.
Describe four different intercellular junctions
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