Transcript Cell Structure and Biology

Cell Structure and
Biology
Advanced Placement
Biology
Chapter 6
Robert Hooke, 1665
Hooke’s First Microscope
History of the Cell
• 1665- Robert Hooke described cork as
composed of cellulae (cell).
• A few years later-Anton van
Leeuwenhoek described live cells.
• 1838 and 1839- Schleiden and
Schwann developed the cell theory.
Schleiden and Schwann- Cell Theory
• All organisms are composed of cells or at
least one.
• Cells are the smallest unit of life (a
collection of metabolic processes +
heredity).
• All cells come from other cells. None
spontaneously arise.
• Different types of microscopes
Unaided eye
– Can be used to visualize different sized
cellular structures
10 m
Human height
Length of some
nerve and
muscle cells
0.1 m
Chicken egg
1 cm
Light microscope
1m
Frog egg
Most plant
and Animal cells
10 µ m
Nucleus
Most bacteria
Mitochondrion
1µm
100 nm
Smallest bacteria
Viruses
10 nm
Ribosomes
Proteins
1 nm
Lipids
Small molecules
Figure 6.2
0.1 nm
Atoms
Electron microscope
100 µm
Electron microscope
1 mm
Measurements
1 centimeter (cm) = 102 meter (m) = 0.4 inch
1 millimeter (mm) = 10–3 m
1 micrometer (µm) = 10–3 mm = 10–6 m
1 nanometer (nm) = 10–3 mm = 10–9 m
Use different methods for enhancing
visualization of cellular structures
TECHNIQUE
(a)
RESULT
Brightfield (unstained specimen).
Passes light directly through specimen.
Unless cell is naturally pigmented or
artificially stained, image has little
contrast. [Parts (a)–(d) show a
human cheek epithelial cell.]
50 µm
(b)
(c)
Figure 6.3
Brightfield (stained specimen).
Staining with various dyes enhances
contrast, but most staining procedures
require that cells be fixed (preserved).
Phase-contrast. Enhances contrast
in unstained cells by amplifying
variations in density within specimen;
especially useful for examining living,
unpigmented cells.
(d)
Differential-interference-contrast (Nomarski).
Like phase-contrast microscopy, it uses optical
modifications to exaggerate differences in
density, making the image appear almost 3D.
(e)
Fluorescence. Shows the locations of specific
molecules in the cell by tagging the molecules
with fluorescent dyes or antibodies. These
fluorescent substances absorb ultraviolet
radiation and emit visible light, as shown
here in a cell from an artery.
50 µm
(f)
Confocal. Uses lasers and special optics for
“optical sectioning” of fluorescently-stained
specimens. Only a single plane of focus is
illuminated; out-of-focus fluorescence above
and below the plane is subtracted by a computer.
A sharp image results, as seen in stained nervous
tissue (top), where nerve cells are green, support
cells are red, and regions of overlap are yellow. A
standard fluorescence micrograph (bottom) of this
relatively thick tissue is blurry.
50 µm
• The scanning electron microscope (SEM)
– Provides for detailed study of the surface
of a specimen
TECHNIQUE
RESULTS
1 µm
Cilia
(a)
Scanning electron microscopy (SEM). Micrographs taken
with a scanning electron microscope show a 3D image of the
surface of a specimen. This SEM
shows the surface of a cell from a
rabbit trachea (windpipe) covered
with motile organelles called cilia.
Beating of the cilia helps move
inhaled debris upward toward
the throat.
Figure 6.4 (a)
• The transmission electron microscope
(TEM)
– Provides for detailed study of the
internal ultrastructure of cells
Cross section
Longitudinal
section of
cilium
(b)
Transmission electron microscopy (TEM). A transmission electron
microscope profiles a thin section of a
specimen. Here we see a section through
a tracheal cell, revealing its ultrastructure.
In preparing the TEM, some cilia were cut
along their lengths, creating longitudinal
sections, while other cilia were cut straight
across, creating cross sections.
Figure 6.4 (b)
of cilium
1 µm
• The process of cell fractionation
APPLICATION
Cell fractionation is used to isolate
(fractionate) cell components, based on size and density.
TECHNIQUE
First, cells are homogenized in a blender to
break them up. The resulting mixture (cell homogenate) is then
centrifuged at various speeds and durations to fractionate the cell
components, forming a series of pellets.
Figure 6.5
Homogenization
Tissue
cells
Homogenate
1000 g
(1000 times the
force of gravity)
10 min
Differential centrifugation
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)
Figure 6.5
Pellet rich in
“microsomes”
(pieces of
plasma membranes and
cells’ internal
membranes)
Pellet rich in
ribosomes
What’s the world’s largest living
cell? Surface to Volume Ratio
• 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
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
6
12
6
Surface-to-volume
ratio
(surface area  volume)
Figure 6.7
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)
Prokaryote vs. Eukaryote
Archaebacteria and
Eubacteria.
Lack membrane-bound
organelles.
DNA in a nucleoid
region.
Have plasma
membrane.
Cell wall of
peptidoglycan.
Use 70S ribosome.
Unique flagella-flagellin
protein.
Animalia, Plantae, Protista,
Fungi.
Have true membranebound organelles.
DNA in a nucleus.
Have plasma membrane.
Plants and some protists
have a cell wall of
cellulose.
Use different ribosomes.
• Cell structure is correlated to
cellular function
Figure 6.1
10 µm
A Composite Eukaryotic Cell
• A animal cell:
ENDOPLASMIC RETICULUM (ER)
Rough ER
Smooth ER
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Flagelium
Plasma membrane
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Figure 6.9
Mitochondrion
Lysosome
In animal cells but not plant cells:
Lysosomes
Centrioles
Flagella (in some plant sperm)
• A plant cell:
Nuclear envelope
Nucleolus
NUCLEUS
Chromatin
Centrosome
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes (small brwon dots)
Central vacuole
Tonoplast
Golgi apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
Figure 6.9
In plant cells but not animal cells:
Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata
Corn Plant Cell
Plasma Membrane
Cytosol and Membranes
What is the function of organelles?
• To compartmentalize chemical
reactions that may proceed
simultaneously.
• To provide membranes on which to
catalyze reactions.
Nuclear Envelope
– Encloses the nucleus, separating its contents
from the cytoplasm
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).
EM of Nucleus
1. The Nucleus
• Largest organelle, centralized in animal
cells.
• Stores and protects the cell’s genetic
information.
• Surrounded by two phospholipid bilayer
membranes-nuclear envelope.
• Where both layers are fused - nuclear
pores + transport protein.
The Nucleolus
• Site within the nucleus of ribosomal
subunits are manufactured- rRNA +
ribosomal proteins.
• Ribosomes leave the nucleus as
subunits through the nuclear pore
and are later reassembled.
• May be free (in the cytoplasm) or
attached to the ER (rough ER).
The Ribosome (40S and 60S)
Rough ER EM
Endoplasmic Reticulum (ER)
• Means “little net within the cytoplasm”
• Internal membrane system with a lipid
bilayer + proteins.
• Weaved in sheets- forming channels.
• Outer membrane of the nuclear envelope
is continuous with the ER membrane.
• Some regions have embedded ribosomes.
The ER Membrane
– Is continuous with the nuclear
envelope
Smooth ER
Nuclear
envelope
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Figure 6.12
Transitional ER
Rough ER
200 µm
Two Types of (ER)
1. Rough ER: heavily studded with
ribosomes- protein synthesis. Proteins
have signal sequences which direct to a
docking site on the surface of the ER.
2. Smooth ER: lack ribosomes; have
enzymes embedded in membrane for
carbohydrate and lipid synthesis.
3. Both secrete finished products in
transport vesicles.
Functions of Smooth ER
The smooth ER:
–Synthesizes lipids
–Metabolizes carbohydrates
–Stores calcium
–Detoxifies poison
The Golgi Complex
• Flattened stacks of membranes in the
cytoplasm-cisternae.
• Collection, packaging and distribution
of proteins and lipids.
• Transport vesicles from RER and
SER fuse with the Golgi membrane.
Functions of the Golgi
Apparatus
Golgi
cis face
(“receiving” side apparatus
of
Golgi apparatus)
1 Vesicles move
from ER to Golgi
6 Vesicles also
transport certain
proteins back to ER
2 Vesicles coalesce to
form new cis Golgi cisternae
0.1 0 µm
Cisternae
3
Cisternal
maturation:
Golgi cisternae
move in a cisto-trans
direction
4
Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma membrane for secretion
5 Vesicles transport specific
proteins backward to newer
Golgi cisternae
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Figure 6.13
Transport of Proteins
Proteins Leaving the Golgi
The Golgi Complex
• Proteins (from RER) may have short
sugar chains added--> glycoproteins.
• Lipids (from SER) may have short sugar
chains added-->glycolipids.
• Both collect at flattened ends-cisternae.
• Cisternae membranes pinch off the
glycoproteins and glycolipids into
secretory vesicles (liposomes).
• Liposomes may fuse with plasma
membane or organelle membranes.
Lysosomes
• Membrane-bound organelle with
digestive enzymes.
• Breakdown protein, nucleic acid, carbos,
lipids.
• Digest old organelles and invading
bacterial cells.
• Digestive enzymes only active at low pH.
Lysosomes
Lysosomes
• Inactive lysosomes-Primary Lysosomes,
high pH, enzymes are inactive.
• Once fused with food vacuole- pump H+
into compartment- active, Secondary
Lysosomes.
• Involved in normal cell death and
programmed cell death (apoptosis).
• Ex. Tadpole tail tissue; webbing between
human fingers.
Peroxisomes: Oxidation
• Peroxisomes:
– Produce hydrogen peroxide and convert it
to water.
Chloroplast
Peroxisome
Mitochondrion
Figure 6.19
1 µm
EM of Peroxisome
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
3
Membranes and proteins
produced by the ER flow in
the form of transport vesicles
to the Golgi
Smooth ER
cis Golgi
Nuclear envelop
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 expands
by fusion of vesicles; proteins
are secreted from cell
Mitochondrion EM
Mitochondria
Mitochondrion (ia)
• Rod-shaped organelle, 1-3 micrometers
long.
• Bounded by two membranes- outer is
smooth; inner is folded into continuous
layers-cristae.
• Two compartments- matrix-inside the
inner membrane and intermembrane
space between the two membranes.
• Enzymes for oxidative metabolism are
embedded in the inner membrane.
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
Mitochondria
• Contain a circular piece of DNA for
many of the proteins in oxidative
metabolism.
• Also has its own rRNA and ribosomal
proteins--> own protein synthesis.
• Involved in its own replication.
• Circular DNA? Two membranes? Own
Genes? Own replication?
• What does that sound like?
The Plastids
• Chloroplasts
• Leucoplasts
• Amyloplasts
• Chromoplasts
EM of Chloroplast
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
Chloroplasts
• Algae and plants have organelles for
photosynthesis.
• Two membranes- outer and inner
membranes.
• A closed, stacked network of membranesgranum (a).
• Fluid-filled space around grana-stroma.
• Disc-shaped structures-thylakoids.
• Light-capturing enzymes are embedded
on thylakoids.
Chloroplasts
• Have DNA which encode many enzymes
necessary for photosynthesis.
• Do all plant cells have chloroplasts?
• May lose internal structure-leucoplasts.
• A leucoplast that stores starchamyloplast. Found in root cells.
• A leucoplast that stores other pigmentschromoplasts.
Centriole
• Barrel-shaped organelles in animals and
protists, NOT plants.
• Usually found in pairs around the
nuclear membrane.
• Hollow cylinders made of microtubules
(protein). Have their own DNA.
• Help move chromosome during cell
division.
Centriole
Other Organelles
• Central Vacuole or Tonoplast: in
plants, for protein, water, and waste
storage.
• Vesicles: in animals, usually smaller
sacs used for storage and transport of
materials.
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 Cytoskeleton!
Figure 6.20
Cytoskeleton
– Is a network of fibers extending throughout
the cytoplasm
Microtubule
0.25 µm
Microfilaments
• There are three main types of fibers
that make up the cytoskeleton:
Table 6.1
Actin Filaments
• Made of globular protein
monomers- actin
• Actin monomers polymerize to form
actin filaments
• Filaments are connected to
proteins within the plasma
membrane.
How do you put actin
together?
Actin Filaments
• Actin filaments are thinner, cause
cellular movements like ameboid
movements, cell pinching during
division.
• Provide shape for the cell.
Actin 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.
Microtubules
• 2 globular monomers-  tubulin and 
tubulin polymerize to form 13
protofilaments
• Filaments form wide, hollow tubesmicrotubules.
• Form from nucleation centers (near
nucleus) and radiate out.
A Microtubule
Treadmilling of a Microtubule
Microtubules
• Constantly polymerize and depolymerizeGTP-binding at ends.
• Ends are + (away from center) or (toward center).
• Cellular movements and intracellular
movement of materials and organelles.
Microtubules
• Use specialized motor proteins to
move organelles along the microtubule.
• Kinesins- move organelles toward the
+ end (toward cell periphery)
• Dyneins- move them toward the - end
(toward the center of cell)
Microtubule and Motor Proteins
How do kinesins work?
How do dyneins work?
Could a simple defect
in a kinesin affect a
whole organism?
Wild-type Drosophila larva
Wild-type (Normal)
Drosophila Movement
Mutant Kinesins in
Drosophila (khc6 mutant)
Intermediate Filaments
• Most durable protein filament- tough
fibrous filaments of overlapping tetramers
of protein (rope-like).
• Between actin and microtubules in size.
Stable
• Ex. of Fibers- vimentin and keratin
EM of Intermediate Filaments
Intermediate Filaments
• Anchored to proteins embedded
into plasma membrane.
• Provide mechanical support to cell.
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
The Extracellular Matrix
(ECM) of Animal Cells
• Animal cells
– Lack cell walls
– Are covered by an elaborate matrix, the ECM
Types of Intercellular Junctions in
animals
TIGHT JUNCTIONS
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.
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
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
cells
Figure 6.31
1 µm
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.
Extracellular
matrix
Plasma membranes
of adjacent cells
GAP JUNCTIONS
Gap junction
0.1 µm
Cilia