A Tour of the Cell
Friday Sept 16, 2005
BCOR 011
Lecture 8
1
10 µm
Common features of all cells
Plasma Membrane
– defines inside from outside
2
Plasma membrane
– Functions as a selective barrier
– Specific portals for selective transport of
materials in and out of cell
Outside of cell
Carbohydrate side chain
Hydrophilic
region
Inside of cell
0.1 µm
Hydrophobic
region
(a)
Figure 6.8 A, B
TEM of a plasma
membrane. The
plasma membrane,
here in a red blood
cell, appears as a
pair of dark bands
separated by a
light band.
Hydrophilic
region
Phospholipid
Proteins
(b) Structure of the plasma membrane
3
Common features of all cells
Plasma Membrane
– defines inside from outside
Cytosol
- Semifluid “inside” of the cell
DNA “chromosomes”
- Genetic material – hereditary instructions
Ribosomes
– “factories” to synthesize proteins
4
Cytosol
Free ribosomes
ER
– Carry out protein synthesis
Membrane Bound
ribosomes
Proteins
Large
To be exported subunit
Figure 6.11
TEM showing ER and ribosomes
0.5 µm
Ribosome – RNA & Protein Complex
5
Diagram of a ribosome
Small
subunit
Two Broad Classes of Cells
Prokaryotes
Eukaryotes
Pro = before
Eu = true
karyon = nucleus
DO NOT HAVE
A NUCLEUS
NO internal membranes
HAVE
A NUCLEUS
membrane-bound
organelles
bacteria, cyanobacteria
archaebacteria
Plants, Animals,
6
Fungi, protists
No
internal
membranes
Bacterial Cell
(Prokaryotic)
7
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
Bacterial
chromosome
(a) A typical
rod-shaped bacterium
Figure 6.6 A, B
Capsule: jelly-like outer coating
of many prokaryotes
0.5 µm
Flagella: locomotion
organelles of
some bacteria
(b) A thin section through the
bacterium Bacillus coagulans
(TEM)
8
On the same
size scale:
Bacterial cell
(Prokaryotic
Animal Cell
9
(Eukaryotic)
Relative Sizes
“Typical”
Bacterium
~ 1-2 M
“Typical”
Animal Cell
~ 5 to 20 M diameter
“Typical”
Plant Cell
~ 5 to 50 M diameter
M = micrometer or micron =10-6 meter10
Internal
membrane-bound
organelles
Animal Cell (Eukaryotic)
11
Why Internal Membranes?
Compartmentalization
(Division of Labor)
I’m
I’m
I’m
playing
I’m
watching
cooking
sleeping my
TV
dinner
sax
12
Animal Cell
endoplasmic reticulum
ENDOPLASMIC RETICULUM (ER)
Rough ER
NUCLEUS
nucleus
Smooth ER
Plasma membrane
cytosol
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
ribosomes
Microtubules
Golgi apparatus
Golgi apparatus
Peroxisome
Figure 6.9
mitochondrion
Mitochondrion
lysosome
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
13
Nucleus: Information storage
double
membrane
“Nuclear
Envelope”
nucleolus
DNA housed, copied, read
14
The NUCLEUS
Double
membrane
Nuclear
pores
Nuclear
Lamina
Nucleolus
DNA
RNA
protein
lipid (membrane)
Euchromatin
Heterochromatin
15
nuclear envelope
Nucleus
Nucleus
1 µm
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear
pores
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
Nuclear lamina (TEM).
16
Nucleolus
Site of
Ribosome
Subunit
Assembly
Note:
No membrane
17
Euchromatin region
Site of mRNA synthesis
Expression
Of
Informational
RNAs
18
Endoplasmic reticulum (ER)
Smooth ER
Rough ER
1 m
19
Endoplasmic reticulum (ER)
[Reticulum – network] Continuous network of flattened sacs
tubules, vesicles, throughout eukaryotic cytoplasm
Smooth ER
–
–
–
–
Synthesizes membrane lipids
Synthesizes steroids
Stores calcium
Detoxifies poison
20
Example: detoxification in smooth ER
Benzo(a)pyrene
charred meat,
cigarette smoke
Oxidations –
more soluble
Some metabolites
are more toxic
Chronic use of
barbiturates, alcoholSER proliferation,
resistance
21
Rough ER –
ribosomes attached to cytoplasmic face
• Large flattened sheets
• Synthesizes secreted proteins, membrane proteins
exported
• Protein modification;
initial steps of
carbohydrate addition
- glycoproteins
22
Rough ER
Slips proteins
Through ER
membrane
Glycosylation
Adds
oligosaccharides
added as protein being made
23
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
3
Golgi pinches off transport
Vesicles and other vesicles
that give rise to lysosomes and
Vacuoles
Plasma
membrane
trans Golgi
Figure 6.16
4
Lysosome available
for fusion with another
vesicle for digestion
5 Transport vesicle carries
proteins to plasma
membrane for secretion
6
Plasma membrane 24
expands
by fusion of vesicles; proteins
are secreted from cell
Golgi Apparatus: protein secretion
Processing, packaging
and sorting center
Cis
Golgi
Close
To RER
Trans
Golgi
Far side
Away
From
RER
25
Functions of the Golgi Apparatus
cis Golgi
“near”
- processing center
Present wrapping
Service –
modifies proteins
trans Golgi
“far”
- sorting center
Fed Ex Central
Sorts for delivery
To specific 26
compartments
Functions of the Golgi Apparatus
•Trimming of Oligosaccharide side chains on
glycosylated proteins
•Addition of new Oligosaccharide residues to
existing side chains of glycosylated proteins
•“Maturation” Cleavages of specific proteins
e.g., insulin
•Phosphorylation of specific sugar residues on
oligosaccharide side chains of
glycosylated proteins
“molecular zip codes”
27
Molecular tags route proteins
to proper destination
P added in
cis Golgi
Proteins with
M-6-P tag
bind receptor
in trans Golgi
28
Lysosomes: “Recycling Center”
sacs of digestive enzymes
29
1 µm
Nucleus
Endocytosis
And
Phagocytosis
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
30
(a) Phagocytosis: lysosome digesting food
In phagocytosis, a cell
engulfs a particle by
Wrapping pseudopodia
around it and packaging
it within a membraneenclosed sac large
enough to be classified
as a vacuole. The
particle is digested after
the vacuole fuses with a
lysosome containing
hydrolytic enzymes.
PHAGOCYTOSIS
EXTRACELLULAR
CYTOPLASM
FLUID
Pseudopodium
1 µm
Pseudopodium
of amoeba
“Food” or
other particle
Bacterium
Food
vacuole
Food vacuole
An amoeba engulfing a bacterium via
phagocytosis (TEM).
In pinocytosis, the cell
“gulps” droplets of
extracellular fluid into tiny
vesicles. It is not the fluid
itself that is needed by the
cell, but the molecules
dissolved in the droplet.
Because any and all
included solutes are taken
into the cell, pinocytosis
is nonspecific in the
substances it transports.
Figure 7.20
PINOCYTOSIS
0.5 µm
Plasma
membrane
Pinocytosis vesicles
forming (arrows) in
a cell lining a small
blood vessel (TEM).
Vesicle
31
Receptor-mediated endocytosis enables the
cell to acquire bulk quantities of specific
substances, even though those substances
may not be very concentrated in the
extracellular fluid. Embedded in the
membrane are proteins with
specific receptor sites exposed to
the extracellular fluid. The receptor
proteins are usually already clustered
in regions of the membrane called coated
pits, which are lined on their cytoplasmic
side by a fuzzy layer of coat proteins.
Extracellular substances (ligands) bind
to these receptors. When binding occurs,
the coated pit forms a vesicle containing the
ligand molecules. Notice that there are
relatively more bound molecules (purple)
inside the vesicle, other molecules
(green) are also present. After this ingested
material is liberated from the vesicle, the
receptors are recycled to the plasma
membrane by the same vesicle.
RECEPTOR-MEDIATED ENDOCYTOSIS
Coat protein
Receptor
Coated
vesicle
Ligand
Coated
pit
A coated pit
and a coated
vesicle formed
during
receptormediated
endocytosis
(TEMs).
Coat
protein
Plasma
membrane
0.25 µm
32
Lysosome containing
two damaged organelles
1µm
Mitochondrion
fragment
• Autophagy
Peroxisome
fragment
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Lysosome
Digestion
Figure 6.14 B
Vesicle containing
damaged mitochondrion
33
(b) Autophagy: lysosome breaking down damaged organelle
Vesicles move thru the endomembrane system
exocytosis
endocytosis
34
Mitochondria:
Powerhouses of the cell
35
Mitochondria
singular = mitochondrion
•powerhouse of the animal cell
produces ~ 90% of ATP
•Carries out oxidative reactions
•Believed Derived from prokaryotic ancestor
- DNA
- ribosomes
- double membrane – inner and outer
*define two functional spaces
36
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
Figure 6.17
Mitochondrial
DNA
Matrix
37
100 µm
Cell – organelles = Cytosol
Gel
Important chemical reactions
cytoskeleton - eukaryotes
38
• The cytoskeleton
–
–
–
Is a network of fibers extending throughout
the cytoplasm
Structural Support
Movement of Materials and Organelles
Microtubule
Figure 6.20
0.25 µm
Microfilaments
39
Microtubules Microfilaments Intermediate
There are
three types
of fibers
that make
up the
cytoskeleton
Tubulin
25 M dia
Cell shape
Organelle movt
Chromosome
separation
Flagellar movt
Motors:
Dynein
Kinesis
Actin
7 M dia
Filaments
various
8-15 M dia
Cell shape
Cell cleavage
Cytoplasmic
streaming
Muscle contract
Nuclear
lamina
Tension
bearing
elements
Anchors
Motors:
Myosin
40
Table 6.1
– Movement of Vesicles along Microtubules
ATP
Vesicle
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.
Vesicles
Microtubule
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.)
0.25 µm
41
Motor MAPs transport vesicles
Dynein
inbound
outbound
kinesin
MTOC
42
– Contains a pair of centrioles
Centrosome
Microtubule
Centrioles
0.25 µm
“microtubuleorganizing center”
Figure 6.22
Longitudinal section
of one centriole
Microtubules
Cross section
of the other centriole
43
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
• The ECM Is made up of glycoproteins
EXTRACELLULAR FLUID
Collagen
A proteoglycan
complex
Polysaccharide
molecule
Carbohydrates
Core
protein
Fibronectin
Plasma
membrane
Integrin
Figure 6.29
Integrins
Microfilaments
Proteoglycan
molecule
CYTOPLASM
44
• Functions of the ECM include
– Cell-Cell adhesion
– Cell-Cell recognition
– Regulation of cellular processes
45
plant cell
Ribosomes (small brown dots)
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
NUCLEUS
Golgi apparatus
Central vacuole/Tonoplast
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Wall of adjacent cell
Figure 6.9
Plasmodesmata
46
Plant Central vacuoles - Tonoplasts
–
–
–
Are found in plant cells
Hold reserves of important organic
compounds and water
Regulates Turgor
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
Figure 6.15
47
5 µm
In plant cells, chloroplasts
capture energy from the sun
Chloroplast
Photosynthesis
Ribosomes
Stroma
Chloroplast
DNA
Inner and outer
membranes
Granum
1 µm
Thylakoid
Figure 6.18
48
Chloroplasts
-Contain DNA
-Contain bacterial-like ribosomes
-Believed derived from prokaryotic ancestor
cyanobacterium = blue-green alga
-Double membrane organelle
defines three functional spaces
49
3 Central Players
Inner Chlorplast
Membrane
Stroma
OuterChlorplast
Membrane
Thylakoid
Space
Thylakoid Membrane
Intermembrane Space
(transports things in and out of
the chloroplast, but not central
to photosynthesis itself
50
51
Cell Walls of Plants
• The cell wall
– Is an extracellular structure of plant
cells that distinguishes them from
animal cells
52
• Plant cell walls
– Are made of cellulose fibers embedded in
other polysaccharides and protein
– May have multiple layers
Plasma
membrane
Central
vacuole
of cell
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
53
• 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
54
Summary
Features of all cells
Features of Prokaryotes
Organelles of Animal Cells
Organelles of Plant Cells
55