Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
What are the main tenets of cell theory?
•
What are the major lines of evidence that
all presently living cells have a common
origin?
.
Cell theory

All living organisms are
composed of cells

smallest “building blocks” of all
multicellular organisms

all cells are enclosed by a
surface membrane that
separates them from other cells
and from their environment

specialized structures with the
cell are called organelles; many
are membrane-bound
.
Cell theory

Today, all new cells arise from
existing cells

All presently living cells have a
common origin

all cells have basic structural and
molecular similarities

all cells share similar energy
conversion reactions

all cells maintain and transfer
genetic information in DNA

the genetic code is essentially
universal
.
•
What are the main tenets of cell theory?
•
What are the major lines of evidence that
all presently living cells have a common
origin?
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
What is surface area to volume ratio,
and why is it an important consideration
for cells?
•
What (usually) happens to surface area
to volume ratio as cells grow larger?
.
Cell organization and homeostasis

Plasma membrane surrounds cells and
separates their contents from the external
environment

Cells are heterogeneous mixtures, with
specialized regions and structures (such as
organelles)
.
Cell organization and homeostasis

Cell size is limited
surface area to volume ratio puts a limit on cell
size


food and/or other materials must get into the cell

waste products must be removed from the cell

cells need a high surface area to volume ratio

BUT volume increases faster than surface area as
cells grow larger…so cells usually must divide
.
Fig. 5.4
.
.
Cell organization and homeostasis

cell shape varies depending both on
function and surface area requirements
.
•
What is surface area to volume ratio,
and why is it an important consideration
for cells?
•
What (usually) happens to surface area
to volume ratio as cells grow larger?
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
Compare and contrast:
– LM and EM
– SEM and TEM
•
Include the terms resolution and
magnification in your discussions.
.
Studying cells – microscopy
Most cells are large enough to be
resolved from each other with light
microscopes (LM)

cells were discovered by Robert
Hooke in 1665



he saw the remains of cell walls in cork
with a LM

his microscope had about 30x
magnification
modern LMs can reach up to 1000x
.
Fig. 5.2a
.
Fig. 5.2b
.
Fig. 5.2c
.
Studying cells – microscopy

LM resolution is limited

LM resolution (clarity) is limited

about 1 mm

due to the wavelength of visible light

only about 500 times better than the human eye, even at
maximum magnification

small cells (such as most bacteria) are ~1 mm across,
just on the edge of resolution

modifications of LMs and some treatments of cells allow
observation of subcellular structure in some cases
.
Studying cells – microscopy
Resolution of most subcellular structure
requires electron microscopy (EM)


electrons have a much smaller wavelength
than light (resolve down to under 1 nm)

magnification up to 250,000x or more

resolution over 500,000 times better than the
human eye
.
Transmission
electron
microscope
Light
microscope
Scanning
electron
microscope
Electron gun
Electron beam
Light beam
Second condenser
lens
First condenser
lens (magnet)
Ocular lens
Specimen
Scanning coil
Projector
lens (magnet)
Final (objective)
lens
Cathode ray tube
synchronized with
scanning coil
Objective lens
Specimen
Condenser lens
Secondary
electrons
Light source
Specimen
Film or screen
(a)
(b)
(c)
Electron
detector
Studying cells – microscopy
transmission
electron microscopy
(TEM)


electron passes
through sample

need very thin samples
(100 nm or less thick)

samples embedded in
plastic and sliced with
a diamond knife
.
Studying cells – microscopy
scanning electron
microscopy (SEM)


samples are gold-plated

electrons interact with
the surface

images have a 3-D
appearance
.
.
•
Compare and contrast:
– LM and EM
– SEM and TEM
•
Include the terms resolution and
magnification in your discussions.
.
•
Which is SEM, and which TEM? How
can you tell?
.
•
Describe cell fractionation. Why is it
done, and how is it done? Include the
terms lyse, centrifugation, pellet, and
supernatant in your discussion.
.
Studying cells – fractionation

Cells can be broken and
fractionated to separate
cellular components

cells are broken (lysed) by
disrupting the cell membrane,
often using some sort of
detergent

grinding and other physical
force may be required,
especially if cell walls are
present

centrifugation is used to
separate cellular components
.
Studying cells – fractionation
centrifugation is used to
separate cellular components


samples are spun at high speeds

results in a centrifugal force
thousands to hundreds of
thousands times “normal” gravity

after spinning:

pellet – what gets packed down to
the bottom (densest material)

supernatant – solution above the
pellet
.
Studying cells – fractionation
cell components will end up in
either the pellet or the
supernatant depending on their
individual properties and the
details of the centrifugation


intact membrane-bound
organelles often wind up in
pellets (denser once first)

special treatments can determine
whether a component ends up in
the pellet or supernatant
.
Studying cells – fractionation
density gradients can be used to subdivide
pellet components


based on their density

can be used to better separate similar organelles
from each other, for example Golgi complex from ER
.
•
Describe cell fractionation. Why is it
done, and how is it done? Include the
terms lyse, centrifugation, pellet, and
supernatant in your discussion.
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
How do prokaryotic cells and eukaryotic
cells differ from each other in typical
size and general organization?
•
Describe cytoplasm, cytosol,
nucleoplasm, and the general role of
membranes in cells.
.
Eukaryotic vs. prokaryotic cells
prokaryotic cells
do not have internal
membranes (thus
no nuclear
membrane)


main DNA molecule
(chromosome) is
typically circular; its
location is called the
nuclear area

other small DNA
molecules (plasmids)
are often present, found
throughout the cell
.
Eukaryotic vs. prokaryotic cells
prokaryotic cells


plasma membrane is
typically enclosed in a cell
wall

often the cell wall is covered
with a sticky layer of
proteins and/or sugars
called a capsule

do not completely lack
organelles; have:

plasma membrane

ribosomes

generally just called bacteria

prokaryotic cells are typically
1-10 mm in diameter
.
Eukaryotic vs. prokaryotic cells

eukaryotic cells
have internal
membranes and a
distinct, membraneenclosed nucleus

typically 10-100 mm
in diameter
.
•
How do prokaryotic cells and eukaryotic
cells differ from each other in typical
size and general organization?
•
Describe cytoplasm, cytosol,
nucleoplasm, and the general role of
membranes in cells.
.
•
List as many organelles as you can think
of. Describe their structures and key
functions.
•
Draw and label a typical animal cell and
a typical plant cell, including organelles.
.
.
.
•
List as many organelles as you can think
of. Describe their structures and key
functions.
•
Draw and label a typical animal cell and
a typical plant cell, including organelles.
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.

How do proteins get outside of a cell?

How do proteins get into a cell membrane?

How does a cell digest its food?

How does a cell commit suicide?

Why would a cell commit suicide?
.
•
Describe the nuclear envelope, nuclear
pores, chromatin, chromosomes, and
nucleoli in terms of structures and key
functions.
•
Name something that you KNOW must
get out of the nucleus for cells to
function.
.
Compartments in eukaryotic cells

two general regions inside the cell:
cytoplasm and nucleoplasm
cytoplasm – everything outside the nucleus and
within the plasma membrane



contains fluid cytosol and organelles
nucleoplasm – everything within the nuclear
membrane
.
Compartments in eukaryotic cells

membranes separate cell regions

have nonpolar regions that help form a barrier
between aqueous region

allow for some selection in what can cross a
membrane (more details later)
.
nucleus – the control center of the cell

typically large (~5 mm)
and singular

nuclear envelope

double membrane
surrounding the
nucleus

nuclear pores –
protein complexes that
cross both membranes
and regulate passage
.
nucleus – the control center of the cell
chromatin – DNA-protein
complex


have granular appearance; easily
stained for microscopy (“chrom-” =
color)

“unpacked” DNA kept ready for
message transcription and DNA
replication

proteins protect DNA and help
maintain structure and function

chromosomes – condensed or
“packed” DNA ready for cell
division (“-some” = body)
.
nucleus – the control center of the cell
nucleoli – regions of ribosome
subunit assembly


appears different due to high RNA
and protein concentration (no
membrane)

ribosomal RNA (rRNA) transcribed
from DNA there

proteins (imported from cytoplasm)
join with rRNA at a nucleolus to
form ribosome subunits

ribosome subunits are exported to
the cytoplasm through nuclear
pores
(note singular: nucleolus; plural: nucleoli)
.
•
Describe the nuclear envelope, nuclear
pores, chromatin, chromosomes, and
nucleoli in terms of structures and key
functions.
•
Name something that you KNOW must
get out of the nucleus for cells to
function.
.
•
Describe the structure and function of
ribosomes.
.
ribosomes – the sites of protein synthesis
ribosomes are granular bodies with three RNA
strands and about 75 associated proteins


two main subunits, large and small

perform the enzymatic activity for forming peptide bonds, and
serve as the sites of translation of genetic information into
protein sequences
.
ribosomes – the sites of protein synthesis

prokaryotic ribosome subunits are both smaller than the
corresponding subunits in eukaryotes

in eukaryotes

the two main subunits are formed separately in the nucleolus and
transported separately to the cytoplasm

some are free in the cytoplasm while others are associated with the
endoplasmic reticulum (ER)
.
•
Describe the structure and function of
ribosomes.
.
•
What is the endomembrane system
(include organelle components)?
.
•
Diagram the cisternal maturation model for
the Golgi.
•
Diagram and describe the pathway from
synthesis to final destination for a secreted
protein. Then do the same for a plasma
membrane protein.
•
Describe the structure and function of:
- ER
- vesicles
- vacuoles
- Golgi apparatus
- microbodies in general
- lysosomes
- peroxisomes
- glyoxysomes
.
endomembrane system
endomembrane system – a set of
membranous organelles that interact with
each other via vesicles


includes ER, Golgi apparatus, vacuoles,
lysosomes, microbodies, and in some
definitions the nuclear membrane and the
plasma membrane
.
endomembrane system
endoplasmic reticulum (ER) – membrane
network that winds through the cytoplasm


winding nature of the ER provides a lot of surface
area

many important cell reactions or sorting functions
require ER membrane surface

ER lumen – internal aqueous compartment in ER

separated from the rest of the cytosol

typically continuous throughout ER and with the
lumen between the nuclear membranes

enzymes within lumen and imbedded in lumen side
of ER differ from those on the other side, thus
dividing the functional regions
.
endomembrane system

smooth ER – primary site
of lipid synthesis, many
detoxification reactions,
and sometimes other
activities

rough ER – ribosomes that
attach there insert proteins
into the ER lumen as they
are synthesized
.
endomembrane system
rough ER – ribosomes that attach there insert proteins into the ER
lumen as they are synthesized

ribosome attachment directed by a signal peptide at the amino end of
the polypeptide (see Ch. 17.4, p.326)


a protein/RNA signal recognition particle (SRP) binds to the signal
peptide and pauses translation

at the ER the assembly binds to an SRP receptor protein

SRP leaves, protein synthesis resumes (now into the ER lumen), and the
signal peptide is cut off
.
endomembrane system

proteins inserted into the ER lumen may be
membrane bound or free

proteins are often modified in the lumen
(example, carbohydrates or lipids added)

proteins are transported from the ER in
transport vesicles

vesicles – small, membrane-bound sacs

buds off of an organelle (ER or other)

contents within the vesicles (often proteins)
transported to another membrane surface

vesicles fuses with membranes, delivering
contents to that organelle or outside of the
cell
.
Fig. 5.16d (TEArt)
Protein
Vesicle
budding
from rough
endoplasmic
reticulum
Migrating
transport
vesicle
Fusion
of vesicle
with Golgi
apparatus
Ribosome
.
endomembrane system
Golgi apparatus (AKA Golgi complex) – a stack of flattened
membrane sacs (cisternae) where proteins further processed,
modified, and sorted [the “post office” of the cell]


not contiguous with ER, and lumen of each sac is usually separate from
the rest

has three areas: cis, medial, and trans
.
endomembrane system

cis face: near ER and receives vesicles from it; current model (cisternal maturation model)
holds that vesicles actually coalesce to continually form new cis cisternae

medial region: as a new cis cisterna is produced, the older cisternae mature and move away
from the ER


in this region proteins are further modified (making glycoproteins and/or lipoproteins where appropriate,
and )

maturing cisternae may make other products; for example, many polysaccharides are made in the Golgi

some materials are needed back a the new cis face and are transported there in vesicles
trans face: nearest to the plasma membrane; a fully matured cisterna breaks into many vesicles
that are set up to go to the proper destination (such as the plasma membrane or another
organelle) taking their contents with them
.
endomembrane system
.
endomembrane system
lysosomes – small membrane-bound sacs of digestive enzymes


serves to confine the digestive enzymes and their actions

allows maintenance of a better pH for digestion (often about pH 5)

formed by budding from the Golgi apparatus; special sugar attachments to
hydrolytic enzymes made in the ER target them to the lysosome
.
endomembrane system
lysosomes – small membrane-bound sacs of digestive enzymes

used to degrade ingested material, or in some cases dead or damaged
organelles


ingested material is found in vesicles that bud in from the plasma membrane; the
complex molecules in those vesicles is then digested

can also fuse with dead or damaged organelles and digest them

digested material can then be sent to other parts of the cell for use

found in animals, protozoa; debatable in other eukaryotes, but all must have
something like a lysosome
.
endomembrane system
vacuoles – large membrane-bound sacs
that perform diverse roles; have no
internal structure


distinguished from vesicles by size

in plants, algae, and fungi, performs many
of the roles that lysosomes perform for
animals

central vacuole – typically a single, large
sac in plant cells that can be 90% of the
cell volume

usually formed from fusion of many small
vacuoles in immature plant cells

storage sites for water, food, salts, pigments,
and metabolic wastes

important in maintaining turgor pressure

tonoplast – membrane of the plant vacuole

food vacuoles – present in most protozoa
and some animal cells; usually bud from
plasma membrane and fuse with
lysosomes for digestion

contractile vacuoles – used by many
protozoa for removing excess water
.
endomembrane system
microbodies – small membranebound organelles that carry out
specific cellular functions; examples:


lysosomes could be consider a type of
microbody

peroxisomes – sites of many
metabolic reactions that produce
hydrogen peroxide (H2O2), which is
toxic to the rest of the cell


peroxisomes have enzymes to break
down H2O2, protecting the cell

peroxisomes are abundant in liver cells
in animals and leaf cells in plants

normally found in all eukaryotes

example: detoxification of ethanol in
liver cells occurs in peroxisomes
glyoxysomes – in plant seeds,
contains enzymes that convert stored
fats into sugar
.
•
What is the endomembrane system
(include organelle components)?
.
•
Diagram the cisternal maturation model for
the Golgi.
•
Diagram and describe the pathway from
synthesis to final destination for a secreted
protein. Then do the same for a plasma
membrane protein.
•
Describe the structure and function of:
- ER
- vesicles
- vacuoles
- Golgi apparatus
- microbodies in general
- lysosomes
- peroxisomes
- glyoxysomes
.
Energy Converting Organelles

energy obtained from the environment is
typically chemical energy (in food) or light
energy

mitochondria are the organelles where
chemical energy is placed in a more useful
molecule

chloroplasts are plastids where light energy
is captured during photosynthesis
.
•
Draw a mitochondrion in cross-section
and describe its structure and functions.
.
Energy Converting Organelles

mitochondria – the site of aerobic respiration

recall aerobic respiration:
sugar + oxygen  carbon dioxide + water + energy

the “energy” is actually stored in ATP
.
Energy Converting Organelles mitochondria
mitochondria have a double
membrane



space between membranes =
intermembrane space

inner membrane is highly
folded, forming cristae;
provides a large surface area

inner membrane is also a highly
selective barrier

the enzymes that conduct
aerobic respiration are found in
the inner membrane
inside of inner membrane is the
matrix, analogous to the
cytoplasm of a cell
.
Energy Converting Organelles –
mitochondria

mitochondria have their own DNA, and are inherited from
the mother only in humans

mitochondria have their own division process, similar to
cell division; each cell typically has many mitochondria,
which can only arise from mitochondrial division

some cells require more mitochondria than others

mitochondria can leak electrons into the cell, allowing
toxic free radicals to form

mitochondria play a role in initiating apoptosis
(programmed cell death)
.
•
Draw a mitochondrion in cross-section
and describe its structure and functions.
.
•
Draw a chloroplast in cross-section and
describe its structure and functions.
.
Energy Converting Organelles
plastids – organelles of plants and algae that produce and
store food


include amyloplasts (for starch storage), chromoplasts (for color,
often found in petals and fruits), and chloroplasts (for
photosynthesis)

like mitochondria, have their own DNA (typically a bit larger and
more disk-shaped than mitochondria, however)

derive from undifferentiated proplastids, although role of mature
plastids can sometimes change

numbers and types of plastids vary depending on the organism and
the role of the cell
.
Energy Converting Organelles – plastids
(chloroplasts)
chloroplasts get their green color from chlorophyll, the main light harvesting pigments
involved in photosynthesis

carbon dioxide + water + light energy  food (glucose) + oxygen
chloroplasts have a double membrane


the region within the inner membrane is the stroma; it is analogous to the mitochondrial matrix

inner membrane is contiguous with an interconnected series of flat sacks called thylakoids that are
grouped in stacks called grana

the thylakoids enclose aqueous regions called the thylakoid lumen

chlorophyll is found in the thylakoid membrane, and the reactions of photosynthesis take
place there and in the stroma

carotenoids in the chloroplast serve as accessory pigments for photosynthesis
.
•
Draw a chloroplast in cross-section and
describe its structure and functions.
.
•
Describe the endosymbiont theory.
Include evidence for it, including
predictions that have proven true.
.
Energy Converting Organelles
endosymbiont theory

mitochondria and plastids
evolved from prokaryotic cells
that took residence in larger
cells and eventually lost their
independence

the cells containing the
endosymbionts became
dependent upon them for food
processing, and in turn provide
them with a protected and rich
environment (a mutualistic
relationship)
.
Energy Converting Organelles
endosymbiont theory
supporting evidence


the size scale is right - mitochondria and plastids are on the high end
of the size of typical bacteria

endosymbionts also have their own DNA and their own “cell” division;
in many ways they act like bacterial cells

the DNA sequence and arrangement (circular chromosomes)of
endosymbionts is closer to that of bacteria than to that found in the
eukaryotic nucleus

endosymbionts have their own ribosomes, which are much like
bacterial ribosomes

there are other known, more modern endosymbiotic relationships:
algae in corals, bacteria within protozoans in termite guts
.
Energy Converting Organelles
endosymbiont theory

some genes appear to have been shuttled out of the endosymbionts to the
nucleus

many of the proteins used by endosymbionts are actually encoded by
nuclear genes and translated in the cytoplasm (or on rough ER) and
transported to the endosymbionts

DNA sequencing of endosymbionts is being used to trace the evolutionary
history of the endosymbionts

appears that endosymbiosis began about 1.5 to 2 billion years ago (around
when the first eukaryotic cells appeared)

mitochondria appear to have a monophyletic origin (one initial endosymbiotic
event, giving rise to all mitochondria in eukaryotic cells today)

plastids appear to have a polyphyletic origin (more than one initial
endosymbiotic event giving rise to different plastid lines present today in algae
and plants)
.
•
Describe the endosymbiont theory.
Include evidence for it, including
predictions that have proven true.
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
What are the functions of the
cytoskeleton?
•
What are the three main types of
cytoskeleton? Describe the structure
and function(s) of each type.
.
•
Describe the structure and function(s)
of:
–
–
–
–
–
motor proteins
MTOCs
centrosomes
centrioles
cilia and flagella
.
Cytoskeleton
eukaryotic cells typically have a size and shape that is maintained


the cytoskeleton is a dense network of protein fibers that provides needed
structural support

the network also has other functions


a scaffolding for organelles

cell movement and cell division (dynamic nature to the protein fibers is involved
here)

transport of materials within the cell
the cytoskeleton is composed of three types of protein filaments:
microtubules, microfilaments, and intermediate filaments
.
.
microtubules are the thickest
filaments of the cytoskeleton

hollow, rod -shaped cylinders
about 25 nm in diameter

made of a-tubulin and b-tubulin
dimers

dimers can be added or removed
from either end (dynamic nature)

one end (plus end) adds dimers
more rapidly than the minus end

can be anchored, where an end is
attached to something and can no
longer add or lose dimers
.
microtubule-organizing centers
(MTOCs) serve as anchors
centrosome in animal
cells


centrosome has two
centrioles in a
perpendicular
arrangement

centrioles have a 9x3
structure: 9 sets of 3
attached microtubules
forming a hollow cylinder

used for assembly of
microtubules for use
throughout the cell
.
microtubule-organizing centers
(MTOCs) serve as anchors

centrioles are duplicated
before cell division

play an organizing role for
microtubule spindles in
cell division

other eukaryotes must use
some alternative MTOC
during cell division; still
incompletely described
.
microtubules are involved in
moving organelles

motor proteins (such as
kinesin or dynein) attach
to organelle and to
microtubule

using ATP as an energy
source, the motor proteins
change shape and thus
produce movement

microtubule essentially acts
as a track for the motor
protein

motor proteins are
directional; kinesin moves
toward the plus end, dynein
away from it
.
cilia and flagella are made of
microtubules

thin, flexible projections from cells

used in cell movement, or to move
things along the cell surface

share the same basic structure;
called cilia if short (2-10 mm typically)
and flagella if long (typically 200 mm)

central stalk covered by cell
membrane extension, and anchored
to a basal body

9x3 structure
stalk has two inner microtubules
surrounded by nine attached pairs of
microtubules


9+2 arrangement
.
cilia and flagella are made of
microtubules
stalk has two inner microtubules
surrounded by nine attached
pairs of microtubules


9+2 arrangement

dynein attached to the outer pairs
actually fastens the pair to its
neighboring pair

dynein motor function causes
relative sliding of filaments; this
produces bending movement of the
cilium or flagellum
.
microfilaments are solid filaments
about 7 nm in diameter

composed of two entwined chains of actin monomers

linker proteins cross-link the actin chains with each other
and other actin associated proteins

actin monomers can be added to lengthen the microfilament
or removed to shorten it; this can be used to generate
movement
.
microfilaments are solid filaments
about 7 nm in diameter

important in muscle cells; in
conjunction with myosin, they
are responsible for muscle
contraction

used for many cell movements
such as:

contractile structures

forming cell extensions

“pinching in” during cell division
.
intermediate filaments

typically just a bit wider than microfilaments, this is
the catch-all group for cytoskeletal filaments
composed of a variety of other proteins

the types of proteins involved differ depending on
cell types and on the organism; apparently limited
to animal cells and protozoans
.
intermediate filaments

not easily disassembled, thus more permanent

a web of intermediate filaments reinforces cell shape and
positions of organelles (they give structural stability)

prominent in cells that withstand mechanical stress

form the most insoluble part of the cell
.
•
What are the functions of the
cytoskeleton?
•
What are the three main types of
cytoskeleton? Describe the structure
and function(s) of each type.
.
•
Describe the structure and function(s)
of:
–
–
–
–
–
motor proteins
MTOCs
centrosomes
centrioles
cilia and flagella
.
Chapter 6: A Tour of the Cell

Cell theory

Cell organization and homeostasis

Studying cells – microscopy and fractionation

Eukaryotic vs. prokaryotic cells

Compartments in eukaryotic cells (cell regions,
organelles)

Cytoskeleton

Outside the cell
.
•
Describe the outer part and outside
interface of a:
–
–
–
–
•
typical prokaryotic cell
typical plant cell
typical fungal cell
typical animal cell
Diagram and describe the animal cell
glycocalyx and ECM interaction (include
collagen, fibronectin, and integrin).
.
Outside the Cell

Most prokaryotes have a cell wall, an outer envelope, and a
capsule (capsule is also called glycocalyx or cell coat)

Most eukaryotic cells produce materials that are deposited
outside the plasma membrane but that remain associated
with it
.
Outside the Cell

plants have thick, defined cell
walls made primarily of crosslinked cellulose fibers

growing plant cells secrete a
primary cell wall, which is thin and
flexible

growth ends  primary cell wall is
usually thickened and solidified

often a secondary cell wall is then
produced between the primary cell
wall and the plasma membrane

still contains cellulose

typically has more strengthening
material (for example, lignin in wood)
.
Outside the Cell

fungi typically have thinner cell walls than
plants, made primarily of cross-linked chitin
fibers
.
Outside the Cell
animals do not have cell walls, but their cells secrete
varying amounts of compounds that can produce a
glycocalyx and an extracellular matrix (ECM)

glycocalyx: polysaccharides attached to proteins and lipids on the
outer surface of the plasma membrane


typically functions in cell recognition and communication, cell contacts,
and structural reinforcement

often works through direct interaction with the ECM
.
Outside the Cell
ECM: a gel of carbohydrates and fibrous proteins;
several different molecules can be involved


main structural protein is tough, fibrous collagen

fibronectins are glycoproteins in the ECM that often
bind to both collagen and integrins

integrins are proteins in the plasma membrane that
typically receive signals from the ECM
.
•
Describe the outer part and outside
interface of a:
–
–
–
–
•
typical prokaryotic cell
typical plant cell
typical fungal cell
typical animal cell
Diagram and describe the animal cell
glycocalyx and ECM interaction (include
collagen, fibronectin, and integrin).
.