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AP BIOLOGY Chapter 6
Cell Structure & Function
WHAT’S NEW you didn’t learn in BIO I?
Slide shows combined and modified from:
http://gbs.glenbrook.k12.il.us/Academics/gbssci/bio/apbio/Lecture/lecture.htm;
http://www.explorebiology.com/
http://home.att.net/~tljackson/neville.html
NUCLEAR ENVELOPE
http://cellbio.utmb.edu/cellbio/nuclear_envelope.htm
DOUBLE MEMBRANE is
fused in spots forming
NUCLEAR PORES
NUCLEAR LAMINA- netlike array of protein
filaments on nuclear side of envelope that
maintains the shape of the nucleus
(Play a role in reforming nuclear membrane after cell division,
if you inject antibodies to lamina proteins, nucleus can’t
reform after mitosis)
NUCLEAR ENVELOPE
Nucleus
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Pore
complex
Rough ER
Surface of nuclear
envelope.
1 µm
Ribosome
0.25 µm
Close-up of
nuclear
envelope
Figure 6.10
Pore complexes (TEM).
Nuclear lamina (TEM).
ENDOMEMBRANE SYSTEM
Regulates protein traffic and performs
metabolic functions in the cell
Includes:
Plasma membrane
Nuclear membrane
Endoplasmic reticulum
Golgi apparatus
Vacuoles
Lysosomes
INSULIN being released by pancreas cells
using exocytosis
http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x26.jpg
Golgi apparatus
Cisternae = Flattened membrane sacs
(look like stacked pancakes)
2 sides = 2 functions
 cis = (receives vesicles by fusion)
 trans = buds off vesicles to send to
other places (shipping face)
Animation from: http://www.franklincollege.edu/bioweb/A&Pfiles/week04.html
See a Golgi movie
EVERYTHING’S CONNNECTED!
LYSOSOMES:
Uncontrolled release of lysosome contents into the
cytoplasm can also cause cell death (necrosis)
• APOPTOSIS (self-destruct mechanism)
“cell suicide”
Embryonic development
Removes damaged cells
Cancer cells and AIDS virus over-ride destruct signals
LYSOSOMES
(common in animal cells but rare in plant cells)
Contain hydrolytic enzymes for intracellular
digestion
• Food (Phagocytosis)
See movie
• Damaged organelles
AUTOPHAGY
~ “eating self”
WHITE BLOOD CELLS USE LYSOSOMES TO
DIGEST ENGULFED BACTERIA
(Phagocytosis)
http://fig.cox.miami.edu/~cmallery/255/255ion/fig14x28.jpg
PEROXISOMES
Other digestive enzyme sacs
in both plants and animals
In fat storing seeds (called GLYOXYSOMES)
Break down fatty acids → sugars
transport to mitochondria for energy
In LIVER CELLS
Detoxify alcohol & other poisons
PRODUCE HYDROGEN PEROXIDE (TOXIN)
but have enzyme (CATALASE) to break this down
H2O2 → H2O + O2
PLASTIDS
CHLOROPLASTS- contain pigment
chlorophyll for photosynthesis
CHROMOPLASTS- contain pigments
that give fruits and flowers colors
AMYLOPLASTS- store starch (amylose)
in roots and tubers (colorless)
http://www.jonathanwald.com/800x600/images/Red-Apple.jpg
http://en.wikipedia.org/wiki/Image:Potato_-_Amyloplasts.jpg
ANIMAL VACUOLES & VESICLES
“transport vehicles”
• FOOD VACUOLES
Phagocytosis fuse with lysosomes
• CONTRACTILE VACUOLES
Freshwater organisms pump
out excess water
http://www.microscopy-uk.org.uk/mag/imgjun99/vidjun1.gif
PLANT VACUOLES (Central Vacuole)
Surrounded by membrane
= TONOPLAST
Selectively permeable
– controls what goes in & out
STORAGE
• Water
• Stockpile proteins/inorganic ions
• Deposit metabolic byproducts
• Store pigments
• Store defensive compounds against herbivores
25
26
27
Pili: attachment structures on
the surface of some prokaryotes
Nucleoid: region where the
cell’s DNA is located (not
enclosed by a membrane)
Ribosomes: organelles that
synthesize proteins
Plasma membrane: membrane
enclosing the cytoplasm
Cell wall: rigid structure outside
the plasma membrane
Capsule: jelly-like outer coating
of many prokaryotes
Bacterial
chromosome
(a) A typical
rod-shaped bacterium
Figure 6.6 A, B
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
Prokaryotic Cells
Some use flagellum for locomotion
– Pilli- threadlike structures protruding
from cell surface; help in attachment
Bacterial cell wall
Rotary
motor
Flagellin
Sheath
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cytoplasm
Endoplasmic
reticulum
Phagocytosis
Food
vesicle
Golgi
apparatus
Lysosomes
Plasma
membrane
Extracellular
fluid
Digestion of
phagocytized
food particles
or cells
Transport
vesicle
Old or damaged
organelle
Breakdown
of old
organelle
Chloroplasts
•Chloroplasts are larger and more complex than
mitochondria
•Grana – closed compartments of stacked membranes
•Thylakoids – disc shaped structure – light capturing
pigment
•Stroma – fluid matrix
Cytoskeleton
•
Network of protein fibers supporting cell shape and
anchoring organelles
–
Actin filaments

–
Microtubules





–
cell movement
Microtubules
Intermediate
filaments
Hollow tubes
Facilitate cell movement
Centrioles – barrel shaped
organelles occur in pairs –
help assemble animal cell’s microtubules
Intermediate filaments

Stable - don’t break down
Actin
Cytoskeleton
Plant Cells
•
•
Central vacuole
– often found in the center of a plant, and
serves as a storage facility for water and
other materials
Cell wall
– primary walls – laid down while cell is
growing
– middle lamella – glues cells together
– secondary walls – inside the primary cell
walls after growth
Plant Cell
Animal Cells
•
Animal cells lack cell walls.
– form extracellular matrix
 provides support, strength, and resilience
Modified from: http://www.coe.unt.edu/ubms/documents/classnotes/ Fall2005/Chapter%205%20-%20Cell%20Structure.ppt
Endomembrane system, II




Golgi apparatus
•ER products are modified, stored, and
then shipped
Cisternae: flattened membranous sacs
trans face (shipping) & cis face (receiving)
Transport vesicles
Endomembrane system, III




Lysosomes
•sac of hydrolytic
enzymes; digestion of
macromolecules
Phagocytosis
Autophagy: recycle cell’s
own organic material
Tay-Sachs disease~
lipid-digestion disorder
Endomembrane system, IV




Vacuoles
•membrane-bound
sacs (larger than
vesicles)
Food (phagocytosis)
Contractile (pump excess
water)
Central (storage in plants)
•tonoplast membrane
• Eukaryotic cells
– Contain a true nucleus, bounded by a
membranous nuclear envelope
– Are generally quite a bit bigger than
prokaryotic cells
• A smaller cell
– Has a higher surface to volume ratio, which
facilitates the exchange of materials into and
out of the cell
Surface area increases while
total volume remains constant
5
1
1
Figure 6.7
Total surface area
(height  width 
number of sides 
number of boxes)
6
150
750
Total volume
(height  width  length
 number of boxes)
1
125
125
Surface-to-volume
ratio
(surface area  volume)
6
12
6
A Panoramic View of the Eukaryotic Cell
• Eukaryotic cells
– Have extensive and elaborately arranged
internal membranes, which form organelles
• Plant and animal cells
– Have most of the same organelles
EVERYTHING’S CONNNECTED!
The Nucleus: Genetic Library of the Cell
• The nucleus
– Contains most of the genes in the
eukaryotic cell
Ribosomes: Protein Factories in the Cell
• Ribosomes
– Are particles made of ribosomal RNA
and protein
– Carry out protein synthesis
Ribosomes
ER
Cytosol
Endoplasmic reticulum (ER)
Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
TEM showing ER and ribosomes
Figure 6.11
Small
subunit
Diagram of a ribosome
Concept 6.4: The endomembrane system
regulates protein traffic and performs metabolic
functions in the cell
• The endomembrane system
– Includes many different structures
The Endoplasmic Reticulum: Biosynthetic Factory
• The endoplasmic reticulum (ER)
– Accounts for more than half the total
membrane in many eukaryotic cells
• The ER membrane
– Is continuous with the nuclear envelope
Smooth ER
Rough ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
Smooth ER
Rough ER 200 µm
Figure 6.12
• There are two distinct regions of ER
– Smooth ER, which lacks ribosomes
– Rough ER, which contains ribosomes
Functions of Smooth ER
• The smooth ER
– Synthesizes lipids
– Metabolizes carbohydrates
– Stores calcium
– Detoxifies poison
Functions of Rough ER
• The rough ER
– Has bound ribosomes
– Produces proteins and membranes, which are
distributed by transport vesicles
The Golgi Apparatus: Shipping and
Receiving Center
• The Golgi apparatus
– Receives many of the transport vesicles
produced in the rough ER
– Consists of flattened membranous sacs called
cisternae
• Functions of the Golgi apparatus include
– Modification of the products of the rough ER
– Manufacture of certain macromolecules
• Functions of the Golgi apparatus
Golgi
apparatus
cis face
(“receiving” side of
Golgi apparatus)
1 Vesicles move
2 Vesicles coalesce to
6 Vesicles also
form new cis Golgi cisternae
from ER to Golgi
transport certain
Cisternae
proteins back to ER
3 Cisternal
maturation:
Golgi cisternae
move in a cisto-trans
direction
Figure 6.13
5 Vesicles transport specific
proteins backward to newer
Golgi cisternae
0.1 0 µm
4 Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma membrane for secretion
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Lysosomes: Digestive Compartments
• A lysosome
– Is a membranous sac of hydrolytic enzymes
– Can digest all kinds of macromolecules
• Lysosomes carry out intracellular digestion by
– Phagocytosis
Nucleus
1 µm
Lysosome
Lysosome contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Digestive
enzymes
Lysosome
Plasma membrane
Digestion
Food vacuole
Figure 6.14 A
(a) Phagocytosis: lysosome digesting food
• Autophagy
Lysosome containing
two damaged organelles
1µm
Mitochondrion
fragment
Peroxisome
fragment
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Lysosome
Vesicle containing
damaged mitochondrion
Figure 6.14 B
Digestion
(b) Autophagy: lysosome breaking down damaged organelle
Vacuoles: Diverse Maintenance Compartments
• A plant or fungal cell
– May have one or several vacuoles
• Food vacuoles
– Are formed by phagocytosis
• Contractile vacuoles
– Pump excess water out of protist cells
• Central vacuoles
– Are found in plant cells
– Hold reserves of important organic
compounds and water
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
Figure 6.15
5 µm
The Endomembrane System: A Review
• The endomembrane system
– Is a complex and dynamic player in the cell’s
compartmental organization
• Relationships among organelles of the
endomembrane system
1 Nuclear envelope is
connected to rough ER,
which is also continuous
with smooth ER
Nucleus
Rough ER
2
Membranes and proteins
produced by the ER flow in
the form of transport vesicles
to the Golgi
Smooth ER
cis Golgi
Nuclear envelop
3
Golgi pinches off transport
Vesicles and other vesicles
that give rise to lysosomes and
Vacuoles
Plasma
membrane
trans Golgi
4
Lysosome available
for fusion with another
vesicle for digestion
Figure 6.16
5 Transport vesicle carries 6
proteins to plasma
membrane for secretion
Plasma membrane expands
by fusion of vesicles; proteins
are secreted from cell
• Concept 6.5: Mitochondria and chloroplasts
change energy from one form to another
• Mitochondria
– Are the sites of cellular respiration
• Chloroplasts
– Found only in plants, are the sites of
photosynthesis
Mitochondria: Chemical Energy Conversion
• Mitochondria
– Are found in nearly all eukaryotic cells
• Mitochondria are enclosed by two membranes
– A smooth outer membrane
– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Figure 6.17
Mitochondrial
DNA
100 µm
Chloroplasts: Capture of Light Energy
• The chloroplast
– Is a specialized member of a family of closely
related plant organelles called plastids
– Contains chlorophyll
• Chloroplasts
– Are found in leaves and other green organs of
plants and in algae
Chloroplast
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Figure 6.18
Thylakoid
• Chloroplast structure includes
– Thylakoids, membranous sacs
– Stroma, the internal fluid
Peroxisomes: Oxidation
• Peroxisomes
– Produce hydrogen peroxide and convert it to
water
Chloroplast
Peroxisome
Mitochondrion
Figure 6.19
1 µm
• The cytoskeleton
– Is a network of fibers extending throughout the
cytoplasm
Microtubule
Figure 6.20
0.25 µm
Microfilaments
Roles of the Cytoskeleton: Support, Motility, and Regulation
• The cytoskeleton
– Gives mechanical support to the cell
– Is involved in cell motility, which utilizes motor
proteins
ATP
Vesicle
Receptor for
motor protein
Motor protein
Microtubule
(ATP powered)
of cytoskeleton
(a) Motor proteins that attach to receptors on organelles can “walk”
the organelles along microtubules or, in some cases, microfilaments.
Vesicles
Microtubule
0.25 µm
Figure 6.21 A, B
(b) Vesicles containing neurotransmitters migrate to the tips of nerve cell
axons via the mechanism in (a). In this SEM of a squid giant axon, two
vesicles can be seen moving along a microtubule. (A separate part of the
experiment provided the evidence that they were in fact moving.)
Components of the Cytoskeleton
• There are three main types of fibers that make
up the cytoskeleton
Table 6.1
Microtubules
• Microtubules
– Shape the cell
– Guide movement of organelles
– Help separate the chromosome copies in
dividing cells
Centrosomes and Centrioles
• The centrosome
– Is considered to be a “microtubule-organizing
center”
– Contains a pair of centrioles
Centrosome
Microtubule
Centrioles
0.25 µm
Figure 6.22
Longitudinal section
of one centriole
Microtubules
Cross section
of the other centriole
Cilia and Flagella
• Cilia and flagella
– Contain specialized arrangements of
microtubules
– Are locomotor appendages of some cells
• Flagella beating pattern
(a) Motion of flagella. A flagellum
usually undulates, its snakelike
motion driving a cell in the same
direction as the axis of the
flagellum. Propulsion of a human
sperm cell is an example of
flagellatelocomotion (LM).
Direction of swimming
Figure 6.23 A
1 µm
• Ciliary motion
(b) Motion of cilia. Cilia have a backand-forth motion that moves the
cell in a direction perpendicular
to the axis of the cilium. A dense
nap of cilia, beating at a rate of
about 40 to 60 strokes a second,
covers this Colpidium, a
freshwater protozoan (SEM).
Figure 6.23 B
15 µm
• Cilia and flagella share a common
ultrastructure
Outer microtubule
doublet
Dynein arms
0.1 µm
Central
microtubule
Outer doublets
cross-linking
proteins inside
Microtubules
Radial
spoke
Plasma
membrane
Basal body
(b)
0.5 µm
(a)
0.1 µm
Triplet
(c)
Figure 6.24 A-C
Cross section of basal body
Plasma
membrane
• The protein dynein
– Is responsible for the bending movement of
cilia and flagella
Microtubule
doublets
ATP
Dynein arm
(a) Powered by ATP, the dynein arms of one microtubule doublet
grip the adjacent doublet, push it up, release, and then grip again.
If the two microtubule doublets were not attached, they would slide
relative to each other.
Figure 6.25 A
ATP
Outer doublets
cross-linking
proteins
Anchorage
in cell
(b) In a cilium or flagellum, two adjacent doublets cannot slide far because
they are physically restrained by proteins, so they bend. (Only two of
the nine outer doublets in Figure 6.24b are shown here.)
Figure 6.25 B
1
3
2
(c) Localized, synchronized activation of many dynein arms
probably causes a bend to begin at the base of the Cilium or
flagellum and move outward toward the tip. Many successive
bends, such as the ones shown here to the left and right,
result in a wavelike motion. In this diagram, the two central
microtubules and the cross-linking proteins are not shown.
Figure 6.25 C
Microfilaments (Actin Filaments)
• Microfilaments
– Are built from molecules of the protein actin
– Are found in microvilli
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
Figure 6.26
0.25 µm
• Microfilaments that function in cellular motility
– Contain the protein myosin in addition to actin
Muscle cell
Actin filament
Myosin filament
Myosin arm
Figure 6.27 A
(a) Myosin motors in muscle cell contraction.
• Amoeboid movement
– Involves the contraction of actin and myosin
filaments
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
Figure 6.27 B
(b) Amoeboid movement
• Cytoplasmic streaming
– Is another form of locomotion created by
microfilaments
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Parallel actin
filaments
Figure 6.27 C
(b) Cytoplasmic streaming in plant cells
Cell wall
Intermediate Filaments
• Intermediate filaments
– Support cell shape
– Fix organelles in place
Concept 6.7: Extracellular components and
connections between cells help coordinate
cellular activities
Cell Walls of Plants
• The cell wall
– Is an extracellular structure of plant cells that
distinguishes them from animal cells
• Plant cell walls
– Are made of cellulose fibers embedded in
other polysaccharides and protein
– May have multiple layers
Central
vacuole
of cell
Plasma
membrane
Secondary
cell wall
Primary
cell wall
Central
vacuole
of cell
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Figure 6.28
Plasmodesmata
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
• The ECM
– Is made up of glycoproteins and other
macromolecules
EXTRACELLULAR FLUID
Collagen
A proteoglycan
complex
Polysaccharide
molecule
Carbohydrates
Core
protein
Fibronectin
Plasma
membrane
Integrin
Figure 6.29
Integrins
Microfilaments
CYTOPLASM
Proteoglycan
molecule
• Functions of the ECM include
– Support
– Adhesion
– Movement
– Regulation
Intercellular Junctions
Plants: Plasmodesmata
• Plasmodesmata
– Are channels that perforate plant cell walls
Cell walls
Interior
of cell
Interior
of cell
Figure 6.30
0.5 µm
Plasmodesmata
Plasma membranes
Animals: Tight Junctions, Desmosomes, and Gap Junctions
• In animals, there are three types of intercellular
junctions
– Tight junctions
– Desmosomes
– Gap junctions
• Types of intercellular junctions in animals
TIGHT JUNCTIONS
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
At tight junctions, the membranes of
neighboring cells are very tightly pressed
against each other, bound together by
specific proteins (purple). Forming continuous seals around the cells, tight junctions
prevent leakage of extracellular fluid across
A layer of epithelial cells.
DESMOSOMES
Desmosomes (also called anchoring
junctions) function like rivets, fastening cells
Together into strong sheets. Intermediate
Filaments made of sturdy keratin proteins
Anchor desmosomes in the cytoplasm.
Tight junctions
Intermediate
filaments
Desmosome
Gap
junctions
Space
between Plasma membranes
cells
of adjacent cells
Figure 6.31
1 µm
Extracellular
matrix
Gap junction
0.1 µm
GAP JUNCTIONS
Gap junctions (also called communicating
junctions) provide cytoplasmic channels from
one cell to an adjacent cell. Gap junctions
consist of special membrane proteins that
surround a pore through which ions, sugars,
amino acids, and other small molecules may
pass. Gap junctions are necessary for communication between cells in many types of tissues,
including heart muscle and animal embryos.
The Cell: A Living Unit Greater Than the Sum of Its Parts
5 µm
• Cells rely on the integration of structures and
organelles in order to function
Figure 6.32