96
A Tour of the Cell Ch. 6 5 μm Figure 6.32
A Tour of the Cell
Ch. 6
5 µ
m
Figure 6.32
Cell Types
Eukaryotic:
- internal membranes that
compartmentalize their
functions
- True nucleus
- Larger in size
Prokaryotic:
- Do not contain a nucleus
- Have their DNA located in
an area called the
nucleoid region
Common:
- bound by a plasma membrane
- semifluid substance called the cytosol
- contain chromosomes
- all have ribosomes
0.25 m
Virus
Animal
cell
Bacterium
Animal cell nucleus
Cell Size
The logistics of carrying out cellular
metabolism sets limits on the size of
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 to Volume RatioSurface area increases while
total volume remains constant
5
1
1
Total surface area
(height width
number of sides
number of boxes)
Total volume
(height width length
number of boxes)
Surface-to-volume
ratio
(surface area volume)
6
1
6
150
125
1.2
750
125
6
Cell Parts
Nucleus Mitochondria
Nucleolus Chloroplast
Endomembrane System Cytoskeleton
Endoplasmic Reticulum Cell Membrane
Golgi Apparatus Extracellular Matrix
Lysosomes
Vesicles
Nucleusmembrane bound structure that contains
most of the DNA in the cellNucleus
NucleusNucleolus
Chromatin
Nuclear envelope:Inner membraneOuter membrane
Nuclear pore
Rough ER
Pore
complex
Surface of nuclear
envelope.
Pore complexes (TEM). Nuclear lamina (TEM).
Close-up of
nuclear
envelope
Ribosome
1 µm
1 µm
0.25 µm
Nucleus Composition
1) - enclosed in a nuclear envelope which is a
phospholipid bilayer
- each side of the layer has specific proteinsembedded in the layer
- inside layer has protein filaments nuclear lamina - gives shape to nucleus
- envelope has sections where the bilayer pinches in forming pores that are surrounded by 8 protein granules
- pore regulates the flow of materials into and out of the nucleus
Flow in: ATP, nucleotides, enzymes
Flow out: ADP, PO4-3, ribosomes, RNA
Nuclear Contents
2) DNA
- organized into loose strands called chromatin
- mixed with proteins called histones
- controls DNA expression
- Condenses to form chromosomes(colored bodies)
- each species has a specific numberwith a specific gene sequence
Nuclear Contents
3) Nucleolus:
- concentration of proteins and RNA
- site of ribosome production
- produces ribosomal subunits (parts)
which are assembled in the cytoplasm
after they leave the nucleus via the
nuclear pore
NUCLEAR CONTROL of cell
DNA RNA (mRNA, tRNA or rRNA)
PROTEINS
RIBOSOMES: site of protein synthesis
COMPOSITION: RNA and Proteins
formed into subunits assembled in nucleolus
Two types: Large and Small
put together in cytoplasm
Purpose: protein synthesis
occurs in cytoplasm
cytosolic ribosomes - make proteins needed in the cytosol
bound ribosomes - make proteins needed for cellular structure or for export from the cell
ribosomes in prokaryotes are structurally different
Importance: Targeted by antibiotics
Ribosomes Cytosol
Free ribosomes
Bound ribosomes
Large
subunit
Small
subunit
TEM showing ER and ribosomes Diagram of a ribosome
0.5 µm
THE ENDOMEMBRANE SYSTEM
System of tubes and vesicles that form a network
of communication and productivity in the cell -
assembly line of the cell
Membranes are related directly by contact or
by vesicles (sac enclosed by a membrane) that
pinches off one membrane and carries materials
to the next
different membranes of the system have
different compositions for different functions
Flow of the Endomembrane System
nuclear envelope
endoplasmic reticulum (E.R.)
smooth and rough (bound ribosomes)
Golgi Apparatus
Lysosomes and Vesicles
Plasma membrane expands
by fusion of vesicles; proteins
are secreted from cell
Transport vesicle carries
proteins to plasma
membrane for secretion
Lysosome available
for fusion with another
vesicle for digestion
4 5 6
Nuclear envelope is
connected to rough ER,
which is also continuous
with smooth ER
Nucleus
Rough ER
Smooth ERcis Golgi
trans Golgi
Membranes and proteins
produced by the ER flow in
the form of transport vesicles
to the Golgi Nuclear envelop
Golgi pinches off transport
Vesicles and other vesicles
that give rise to lysosomes and
Vacuoles
1
3
2
Plasma
membrane
ENDOPLASMIC RETICULUM
reticulum - network
endoplasmic - within the cytoplasm
network of tubes and cisternae
Cisternae: sacs - swollen portions at the
ends of the networks – pinch off to form
vesicles
connects to the nuclear envelope
Cisternae
TYPES OF ER
Smooth - no ribosomes bound to the outside of the
membrane
Function:
1. synthesis of lipids, phospholipids and steroids
2. carbohydrate metabolism - glycogen to glucose
3. detoxification - especially plentiful in liver
adds a carboxyl group to poisons so they are soluble
and can be excreted from the body
4. stores Ca+2 for muscle contraction
- pumps Ca+2 from cytosol into inside of ER - nerve
impulse releases the Ca+2 causing the muscle
contraction
Smooth ER
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Transitional ER
Rough ER200 µm
Nuclear
envelope
TYPES OF ER
Rough - ribosomes attached to the outside of the membrane
Function:
1. Protein synthesis
- makes secretory proteins and lysosomal proteins
- manufactured by ribosomes
- move into ER via pores
- may add a sugar unit (oligosaccharide) to protein
- moves into a transport vesicle for secretion or further modification by Golgi
Role of Signal Recognition Proteins
Function of Rough ER
2. Formation of new ER
ribosomes make proteins which get imbedded
directly into the membrane - anchored by
hydrophobic regions of the protein
proteins in membrane manufacture new
phospholipids from materials in the cytosol
new portions can pinch off and go to other
portions of the cell
GOLGI APPARATUS
series of flattened membrane sacs that accept, modify and ship out proteins
CIS end - receiving end - accepts vesicles
- as proteins pass through the sacs they are modified
TRANS end - shipping end
Each section contains different enzymes that perform different modifications on the proteins
cis face
(“receiving” side of
Golgi apparatus)
Vesicles move
from ER to GolgiVesicles also
transport certain
proteins back to ER
Vesicles coalesce to
form new cis Golgi cisternae
Cisternal
maturation:
Golgi cisternae
move in a cis-
to-trans
direction
Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma mem-
brane for secretion
Vesicles transport specific
proteins backward to newer
Golgi cisternae
Cisternae
trans face
(“shipping” side of
Golgi apparatus)
0.1 0 µm1
6
5
2
3
4
GOLGI APPARATUS
Products:
altered phospholipids
Components of the extracellular matrix
sorted products for secretion
LYSOSOMES
membrane sac filled with digestive
(hydrolytic enzymes)
optimal pH of 5 - maintains an internal
environment that keeps these important
enzymes from digesting the cell
helps maintain pH of cell by pumping
excess H+ into lysosome and out of
cytosol
LYSOSOMES
hydrolytic enzymes formed by ER - not yet active
passed to GOLGI where they are modified and sorted
stored and pinch off from Golgi forming lysosome
fuse with incoming vesicle filled with macromolecules for intracellular digestion
also break down old organelles for recycling of nutrients autophagy
Participate in one mechanism of apoptosis
(a) Phagocytosis: lysosome digesting food
1 µm
Lysosome contains
active hydrolytic
enzymes
Food vacuole
fuses with
lysosome
Hydrolytic
enzymes digest
food particles
Digestion
Food vacuole
Plasma membraneLysosome
Digestive
enzymes
Lysosome
Nucleus
(b) Autophagy: lysosome breaking down damaged organelle
Lysosome containing
two damaged organelles1 µ m
Mitochondrion
fragment
Peroxisome
fragment
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Vesicle containing
damaged mitochondrion
Digestion
Lysosome
CELLULAR SUICIDE
- Programmed Cell Death
APOPTOSIS
lysosomes release cathepsin
protease enzyme
breaks apart mitochondria which releases a
protein called cytochrome c which cause the
inside of the cell to break apart
Importance of Apoptosis
- destroys dysfunctional cells
- destroyed cells are disposed of by white
blood cells
- development of tissues
- Separates fingers and toes
- Lack of separation = syndactyly
- Break down of tissues in metamorphosis
of larvae into butterflies
Video
Apoptosis Blebbing
Apoptosis Details Video
DISFUNCTIONAL LYSOSOMES
Tay-Sachs Disease
VACUOLES
membranous sac - larger than a vesicle
Food Vacuole - formed by phagocytosis
- meets with lysosome
Contractile Vacuole - takes in excess water for expulsion - maintains proper water concentration in cell
Central Vacuole- large main vacuole of plants
TONOPLAST - enclosing membrane of central vacuole
Central Vacuole Functions
stores wastes, ions, pigments and
minerals
stores water providing structure
may contain poisons or deterrents
Central vacuole
Cytosol
Tonoplast
Central
vacuoleNucleus
Cell wall
Chloroplast
5 µm
NON - ENDOMEMBRANE SYSTEM
ORGANELLES
Peroxisomes: remove Hydrogens from substances and transfer it to Oxygen making H2O2
break down fatty acids
detoxify alcohol
Contains catylase (peroxidase) to break
H2O2 into H2O and O2
keeps the H2O2 from interacting with the rest of the cell
Chloroplast
Peroxisome
Mitochondrion
1 µm
Peroxisomes
Special Peroxisomes in seeds
(glyoxysomes) break down the fatty acids
in seeds into acetyl-CoA so the seedling
has a food source
Acetyl-CoA is the main source of energy
for the Kreb’s cycle in cellular respiration
NON - ENDOMEMRANE SYSTEM
ORGANELLES
DOUBLE MEMBRANE ORGANELLES:
one membrane in the other - organelle
with two distinct spaces on the inside
MITOCHONDRIA AND CHLOROPLASTS
have their own DNA and replicate on their own
make their own ribosomes
Endosymbiotic Theory
QUESTION OF EVOLUTION???
- how did the eukaryote come about?
Formation of the nuclear membrane
- in folding of the plasma membrane
ENDOSYMBIOTIC THEORY: Page 524
2 prokaryotes - one much smaller than the other
- smaller one has the ability to carry out aerobic metabolism
- enters the larger cell by phagocytosis and does not die
- aids in host cell’s life cycle
- same happened to chloroplasts (although suspected later)
Supporting information
- both have own DNA - circular - no histones
- have a double membrane - second comes from the in folding plasma membrane of the host
- mitochondria and chloroplasts same size as prokaryotes
- similar enzymes and membranes as prokaryotes
- chloroplasts make all own enzymes
- most proteins for mitochondria are found in the genome of the nucleus - transposones?
The Endosymbiotic Theory
NON - ENDOMEMRANE SYSTEM
ORGANELLES
Mitochondria:
site of cellular respiration - particularly the Kreb’s Cycle and the Electron Transport Chain
- in almost all eukaryotes
Structure
Outer membrane
Inner membrane - Electron transport chain - houses ATP synthase
Cristae - folds that increase surface area
Intermembrane space
Matrix - Kreb’s Cycle
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Mitochondrial
DNA
Inner
membrane
Cristae
Matrix
100 µm
NON - ENDOMEMRANE SYSTEM
ORGANELLES
Chloroplasts: - Photosynthesis
double membrane with internal flattened sacs
Structure
Outer and inner membrane
Stroma
Grana - stacks of thylakoids
contain chlorophyll for photosynthesis
Chloroplast
Chloroplast
DNA
Ribosomes
Stroma
Inner and outer
membranes
Thylakoid
1 µm
Granum
The Cytoskeleton
fibers and tubes extending through the
cytoplasm that organize the structures and
activities of the cellMicrotubule
0.25 µm MicrofilamentsFigure 6.20
Functions of Cytoskeleton
1) Support - internal framework - keeps the cell from expanding or being squished -maintains shape
2) Anchors organelles and enzymes for reactions
Functions of Cytoskeleton
3) Movement:
Changes in location: cilia and flagellaMovement of cell parts and organelles
contraction of protein fibers
organelle monorails
manipulation of cytoskeleton
4) Stimulation of cellular activitiesshock wave trigger - stimulation of the cell
membrane causes the fibers in the cell to move organelles causing them to activate
Organelle Monorail
VesicleATP
Receptor for
motor protein
Motor protein
(ATP powered)
Microtubule
of cytoskeleton
(a) Motor proteins that attach to receptors on organelles can “walk”
the organelles along microtubules or, in some cases, microfilaments.
Microtubule Vesicles 0.25 µm
(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.)Figure 6.21 A, B
Three Main Fiber-Types of
Cytoskeleton
Microtubules
Microfilaments
Intermediate filaments
Table 6.1
Microtubules Microfilaments Intermediate
Largest Smallest Middle
Straight hollow Solid and thin Super coiled filaments
Tubulin Actin Various types of Keratin
Microtubules
shape and support
movement:
Monorail
separation of chromosomescentrioles and centrosomes
cilia and flagella
Anatomy of Centrosome
Organizational center of microtubules for
cellular division (spindle fibers)
Composed of two sets of tubes called the
centrioles
9 sets of three connected tubes
In animal cells, not plant
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section
of one centrioleMicrotubules Cross section
of the other centrioleFigure 6.22
Cilia and Flagella
Anatomy:
Base of Structure: same as a centriole -
imbedded in the cell membrane
“9 + 2” configuration
9 sets of two interconnected pairs + 2 central
microtubules imbedded in radial spokes
interconnected pairs are linked by protein
motor molecules called dynein
Anatomy of Cilia and Flagella
(a)
(c)
(b)
Outer microtubule
doublet
Dynein arms
Central
microtubule
Outer doublets
cross-linking
proteins inside
Radial
spoke
Plasma
membrane
Microtubules
Plasma
membrane
Basal body
0.5 µm
0.1 µm
0.1 µm
Cross section of basal body
Triplet
Figure 6.24 A-C
Anatomy of Cilia and Flagella
Functions: move cells or move liquids
across tissues
#’s per cell
cilia - numerous
flagella - 1 - 8
Physiology of Cilia and Flagella
Movement cilia - oars - power stroke and a recovery stroke
flagella - undulating whip
HOW:
motor molecules - dynein of one tubule grasps the neighboring tubule and pulls itself along so the tubules slide past one another - like shimmying across a log
extent of movement is limited by the radial spokes and membranal anchor - continued movement of the dynein molecules causes the structure to bend
Microtubule
doublets ATP
Dynein arm
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.
(a)
Figure 6.25 A
Outer doublets
cross-linking
proteins
Anchorage
in cell
ATP
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.)
(b)
(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
flagellate locomotion (LM).
1 µm
Direction of swimming
(b) Motion of cilia. Cilia have a back-
and-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
Cilia and Flagella Video and
Animation
Cilia and Flagella Movement
Ciliophorans (paramecia)
Microfilaments
network of filaments - makes the outer
portion of the cytoplasm more gel-like and
the inner portion of the cell more fluid
movement:
muscle contraction
amoeboid movement
Anatomy of MicrofilamentsACTIN
twisted double chain of actin (globular protein) subunits
Physiology of Microfilament:
Pulling and sliding
Muscle contraction:
actin filaments are grabbed by myosin (thicker
protein filaments) and pulled - makes the muscle
fiber shorten
Actin filament
Myosin filament
Myosin motors in muscle cell contraction. (a)
Muscle cell
Myosin arm
Figure 6.27 A
Muscles
Vertebrate Skeletal Muscle:
Muscle muscle fiber(muscle cell)
myofibril sarcomere Sarcomere Structure:
Sarcoplasmic reticulum (SR)
Actin (thin filaments) and Myosin (thick filaments) organized into bands
Light – I band - (actin)
Dark – A band - (actin and myosin)
Muscle
Bundle of
muscle fibers
Single muscle fiber
(cell)
Plasma membrane
Myofibril
Light
band Dark band
Z line
Sarcomere
TEM 0.5 m
I band A band I band
M line
Thick
filaments
(myosin)
Thin
filaments
(actin)
H zone
Sarcomere
Z lineZ line
Nuclei
Muscle Contraction:
Sliding Filament Model
1. Nerve signal from brain – motor neuron
2. Release of acetylcholine
(neurotransmitter) – intercellular
communication
3. Binds to surface of muscle cell (effector
cell)
4. Causes the release of Ca++ ions from
SR
5. Ca++ ions bind to receptor sites on
troponin complex on the tropomyosin
on the actin filament
6. Opens the actin filament up for the myosin “head” to bind after a phosphorulated conformational change
7. The myosin is dephosphorylated and the head moves pulling the actin filament
ATP Source: creatine phosphate and glycogen
Thick filament
Thin filaments
Thin filament
ATP
ATP
ADPADP
ADP
P i P i
P i
Cross-bridge
Myosin head (low-
energy configuration)
Myosin head (high-
energy configuration)
+
Myosin head (low-
energy configuration)
Thin filament moves
toward center of sarcomere.
Thick
filamentActin
Cross-bridge
binding site
7. Loss of Ca++ ions causes tropomyosin to
cover the actin sites and the contraction
stops – when Ca++ is pumped back into
SR
K+ is needed to help pump Ca++ into
the SR
ACh
Synaptic
terminal
of motor
neuron
Synaptic cleft T TUBULEPLASMA MEMBRANE
SR
ADP
CYTOSOL
Ca2
Ca2
P2
Cytosolic Ca2+ is
removed by active
transport into
SR after action
potential ends.
6
Figure 49.33
Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic
cleft and binds to receptor proteins on muscle fiber’s plasma membrane,
triggering an action potential in muscle fiber.
1
Action potential is propa-
gated along plasma
membrane and down
T tubules.
2
Action potential
triggers Ca2+
release from sarco-
plasmic reticulum
(SR).
3
Myosin cross-bridges alternately attach
to actin and detach, pulling actin
filaments toward center of sarcomere;
ATP powers sliding of filaments.
5
Calcium ions bind to troponin;
troponin changes shape,
removing blocking action
of tropomyosin; myosin-binding
sites exposed.
4
Tropomyosin blockage of myosin-
binding sites is restored; contraction
ends, and muscle fiber relaxes.
7
Muscle Contraction Video
Muscle Contraction Video #2
Psuedopods:
actin near cell membrane form
microfilaments which form a network
causing the cytoplasm to become gel-like
this puts pressure on the remaining
cytoplasm pushing it in the direction where the
gel network did not form - like squeezing a
tube of toothpaste Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Amoeboid
Movement
Amoeba eating
More fat
Amoeba
Cytoplasmic Streaming
Nonmoving
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Parallel actin
filamentsCell wall
(b) Cytoplasmic streaming in plant cells
Cytoplasmic Streaming in Elodea - Video
Intermediate Filaments
maintain internal structure and support real cellular skeleton
holds nucleus in place and make up nuclear lamina
Anatomy: rope like structures - tightly twisted strands of keratin
proteins
Physiology:determine cell shape and therefore function
Intermediate Filaments
Cell Surfaces and Junctions
Plant cell walls:
1st layer: middle lamella - sticky polysaccharides
2nd layer: primary wall - cellulose
- 1st and 2nd in all plant cells - herbaceous
3rd layer: secondary wall - cellulose
continues to grow inward - can eventually kill the cell
adding a protein called lignin = wood
Communication between plant cells
plasmodesmata - thin tubes connecting cell membranes
Central
vacuole
of cell
Plasma
membrane
Secondary
cell wall
Primary
cell wall
Middle
lamella
1 µm
Central
vacuole
of cell
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
PlasmodesmataFigure 6.28
Plasmodesmata
Interior
of cell
Interior
of cell
0.5 µm Plasmodesmata Plasma membranes
Cell walls
Figure 6.30
Animal Cell Surfaces and Junctions
Functions of the Junctions:
hold the cell membranes together
communication between cells
Types of Junctions
Tight Junctions: proteins that hold cell membranes together to keep the intercellular fluid (fluid between cells) from leaking out - clips
Desmosomes: protein anchors - bind cells together - reinforced by intermediate filaments -roots anchoring a tree
Gap junctions: protein channels - tunnels that connect cell membranes and allow materials to pass through the cells - similar to plasmodesmata
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
0.5 µm
1 µm
Space
between
cellsPlasma membranes
of adjacent cells
Extracellular
matrix
Gap junction
Tight junctions
0.1 µm
Intermediate
filaments
Desmosome
Gap
junctions
At tight junctions, the membranes of
neighboring cells are very tightly pressed
against each other, bound together by
specific proteins (purple). Forming continu-
ous seals around the cells, tight junctions
prevent leakage of extracellular fluid across
A layer of epithelial cells.
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.
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 commu-
nication between cells in many types of tissues,
including heart muscle and animal embryos.
TIGHT JUNCTIONS
DESMOSOMES
GAP JUNCTIONS
Figure 6.31
Extracellular Matrix
goop on the surface
differs from cell to cell based on function
General Composition:
glycoproteins: proteins with an oligosaccharide: collagen - forms strong fibers outside of cell -
proteoglycans - proteins that have very large sugar complexes attached to them - sticky
fibronectins - adhesive protein attached to membrane proteins called integrins (bound to microfilaments in cytoskeleton)
results in the chemical and mechanical stimulation of the cell from external stimuli
Extracellular Matrix
Collagen
Fibronectin
Plasma
membrane
EXTRACELLULAR FLUID
Micro-
filaments
CYTOPLASM
Integrins
Polysaccharide
molecule
Carbo-
hydrates
Proteoglycan
molecule
Core
protein
Integrin
Figure 6.29
A proteoglycan
complex
Inside the Cell
Harvard 3D Cell Animation Music
Harvard Cell Animation Narrated
