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CHAPTER 6
A Tour of the Cell
CH. 6 WARM-UP
1. What are the 2 main types of cells? Which
Domains do they consist of?
2. List 3 ways that eukaryotes differ from
prokaryotes.
CH. 6 WARM-UP
1. How is the size of a cell related to its
function?
2. Name 5 organelles or cell structures and
their function.
CH. 6 WARM-UP
Compare and contrast Animal vs. Plant Cells
Animal Cell
Plant Cell
CH. 6 WARM-UP
What is the structure & function of:
1. Microtubules
2. Microfilaments
3. Intermediate filaments
CH. 6 WARM-UP
What is the function of:
1. Plasmodesmata
2. Gap junctions
3. Tight junctions
4. Desmosomes
YOU MUST KNOW
 Three differences between
prokaryotic and eukaryotic cells.
 The structure and function of
organelles common to plant and
animal cells.
 The structure and function of
organelles found only in plant cells
or only in animal cells.
EARLY CONTRIBUTIONS
• Robert Hooke - First person to see cells, he was
looking at cork and noted that he saw "a great many
boxes. (1665)
• Anton van Leeuwenhoek - Observed living cells in
pond water, which he called "animalcules" (1673)
• Theodore Schwann - zoologist who observed tissues of
animals had cells (1839)
• Mattias Schleiden - botanist, observed tissues of plants
contained cells ( 1845)
• Rudolf Virchow - also reported that every living thing is
made of up vital units, known as cells. He predicted that
cells come from other cells. (1850 )
THE CELL THEORY
• 1. Every living
organism is made of
one or more cells.
• 2. The cell is the basic
unit of structure and
function. It is the
smallest unit that can
perform life functions.
• 3. All cells arise from
pre-existing cells.
*Why is the Cell Theory
called a Theory and not a
Fact?
THREE FEATURES OF CELLS
Plasma (Cell) Membrane - serves as a barrier,
regulates what enters and leaves the cell
1.
* We go into much more detail in the next chapter on how this works*
2. GENETIC MATERIAL
1. provides cellular "blueprint" that
controls the functions of the cell
2. In the form of DNA
(Deoxyribonucleic acid)
3. DNA is universal for all cells, an all
living things - evidence of common
ancestry
4. Chromatin is the complex of
proteins and DNA, it condenses into
chromosomes before cell division
*We will go into much greater detail in a later
unit on GENETICS*
3. CYTOPLASM (CYTOSOL)
1. Located within the
plasma membrane
2. contains water, salts,
and other chemicals
3. organelles float within
this jelly-like substance
Microtubules and filaments
support the inner structure
of the cell
HOW WE STUDY CELLS
Biologists use microscopes and the tools of
biochemistry to study cells
CELLS ARE ALWAYS
SMALL, HOW SMALL DEPENDS ON THE TYPE OF CELL
CELLS CAN COME IN A VARIETY OF SHAPES
Single Cheek Cell - at different illuminations
FIGURE 4.3
Size range of cells
Note that light
microscopes can
not magnify as
well as electron
microscopes
CELL SIZE AND SCALE
http://learn.genetics.utah.edu/content/begin/cells/scale/
Scale of the Universe:
http://www.onemorelevel.com/game/scale_of_the_unive
rse_2012
 Cells
must be small to maintain a large surface
area to volume ratio
 Large S.A. allows  rates of chemical exchange
between cell and environment
SURFACE AREA EXAMPLE (ANIMAL):
Small Intestine: highly folded surface to
increase absorption of nutrients
 Villi: finger-like projections on SI wall
 Microvilli: projections on each cell
FOLDS  VILLI  MICROVILLI
SURFACE AREA EXAMPLE (PLANT):
Root hairs: extensions of root epidermal cells;
increase surface area for absorbing water and
minerals
Light Microscopy (LM) vs. Electron Microscopy (EM)
COMPARISONS OF SCOPES
Light
Visible light passes
through specimen
 Refracts light so
specimen is magnified
 Magnify up to 1000X
 Specimen can be
alive/moving
 Color

Electron
Focuses a beam of
electrons through/onto
specimen
 Magnify up to 1,000,000
times
 Specimen non-living and
in vacuum
 Black and white

ELECTRON MICROSCOPY
Transmission (TEM)
2-D
 Creates a flat image with
extreme detail
 Can enhance contrast by
staining atoms with
heavy metal dyes

Scanning (SEM)
3-D
 Used for detailed study
of surface of specimen
 Gives great field of depth

2 TYPES OF CELLS:
1. Prokaryotes: Domain Bacteria &
Archaea
2. Eukaryotes (Domain Eukarya):
Protists, Fungi, Plants, Animals
A PROKARYOTIC CELL (BACTERIA)
PROKARYOTE CELLS
•
•
•
•
no membrane bound nucleus,
chromosomes grouped together in an area
called the "nucleoid"
no membrane bound organelles
smaller than eukaryotes
Include the domains Bacteria and Archaea
•
•
•
•
have cell wall and cell
membrane, some have
a capsule on the outside
ribosomes make protein
consist of bacteria and
archaebacteria
Appendages
include: fimbriae/pili,
flagella
*pili are usually longer and fewer than fimbriae,
both function for attachment and recognition of
host cells (or (sexual reproduction)
FIGURE 4.4A
E. coli
EUKARYOTES
•
•
•
•
has a membrane bound nucleus
has membrane bound organelles in
cytoplasm
Organelles perform specific functions
much larger than prokaryotes
Organisms within the animal, plant and fungi kingdoms are
all eukaryotes
PROKARYOTE VS. EUKARYOTE
 “before”
“kernel”
 No nucleus
 DNA in a nucleoid
 Cytosol
 No organelles other
than ribosomes
 Small size
 Primitive
 i.e. Bacteria & Archaea
 “true”
“kernel”
 Has nucleus and nuclear
envelope
 Cytosol
 Membrane-bound
organelles with
specialized
structure/function
 Much larger in size
 More complex
 i.e. plant/animal cell
KNOW THIS CHART!
Characteristic
Prokaryotic Cells
Eukaryotic Cells
Plasma Membrane
Yes
Yes
Cytosol with
organelles
Yes
Yes
Ribosomes
Yes
Yes
Nucleus
No
Yes
Size
1 um- 10 um
10 um- 100 um
Internal
membranes
No
yes
CELL ORGANELLES
NUCLEUS
Function: control center of cell
 Contains DNA
 Surrounded by double membrane (nuclear envelope)
 Continuous with the rough ER
 Nuclear pores: control what enters/leaves nucleus
 Chromatin: complex of DNA + proteins; makes up
chromosomes
 Nucleolus: region where ribosomal subunits are
formed

NUCLEUS
Contains DNA
 Function: control center of cell
 Surrounded by double membrane (nuclear envelope)
 Continuous with the rough ER
 Nuclear pores: control what enters/leaves nucleus
 Chromatin: complex of DNA + proteins; makes up
chromosomes
 Nucleolus: region where ribosomal subunits are
formed

RIBOSOMES
Function: protein synthesis
 Composed of rRNA + protein
 Large subunit + small subunit
 Types:
1. Free ribosomes: float in cytosol, produce
proteins used within cell
2. Bound ribosomes: attached to ER, make
proteins for export from cell

ENDOMEMBRANE SYSTEM:
Regulates protein traffic & performs
metabolic functions
ENDOPLASMIC RETICULUM (ER)
Network of membranes and sacs
 Types:
1. Rough ER: ribosomes on surface
 Function: package proteins for secretion,
send transport vesicles to Golgi, make
replacement membrane
2. Smooth ER: no ribosomes on surface
 Function: synthesize lipids, metabolize
carbs, detox drugs & poisons, store Ca2+

ENDOPLASMIC RETICULUM (ER)
GOLGI APPARATUS
Function: synthesis & packaging of materials (small
molecules) for transport (in vesicles); produce lysosomes
 Series of flattened membrane sacs (cisternae)
 Cis face: receives vesicles
 Trans face: ships vesicles

LYSOSOMES
Function: intracellular digestion; recycle cell’s
materials; programmed cell death (apoptosis)
 Contains hydrolytic enzymes

VACUOLES
Function: storage of materials (food, water, minerals,
pigments, poisons)
 Membrane-bound vesicles
 Eg. food vacuoles, contractile vacuoles
 Plants: large central vacuole -- stores water, ions

MITOCHONDRIA
Function: site of cellular respiration
 Double membrane: outer and inner membrane
 Cristae: folds of inner membrane; contains enzymes
for ATP production; increased surface area to  ATP
made
 Matrix: fluid-filled inner compartment

CHLOROPLASTS
Function: site of photosynthesis
 Double membrane
 Thylakoid disks in stacks (grana); stroma (fluid)
 Contains chlorophylls (pigments) for capturing
sunlight energy

ENDOSYMBIONT THEORY
Mitochondria & chloroplasts
share similar origin
 Prokaryotic cells engulfed by
ancestors of eukaryotic cells
 Evidence:
 Double-membrane
structure
 Have own ribosomes &
DNA
 Reproduce independently
within cell

PROKARYOTE VS EUKARYOTE CELLS
Endosymbiosis theory:
All organelles seem to share many properties with bacteria.
Lynn Margulis proposed endosymbiont hypothesis: that
organelles derived from ancient colonization of large bacteria
(became the eukaryotic cell) by smaller bacteria (became the
mitochondria, chloroplast, etc.) Symbiosis = "living together".
*Mitochondria & Chloroplasts have their own DNA
Animation at Microbiological Concepts
PEROXISOMES
Functions: break down fatty acids; detox alcohol
 Involves production of hydrogen peroxide (H2O2)

CYTOSKELETON: NETWORK OF PROTEIN FIBERS

Function: support, motility, regulate biochemical
activities
3 TYPES OF CYTOSKELETON FIBERS:
Microtubules
•
•
•
•
Protein = tubulin
Largest fibers
Shape/support cell
Track for organelle
movement
• Forms spindle for
mitosis/meiosis
• Component of
cilia/flagella
Microfilaments
• Protein = actin
• Smallest fibers
• Support cell on
smaller scale
• Cell movement
• Eg. ameboid
movement,
cytoplasmic
streaming, muscle
cell contraction
Intermediate
Filaments
• Intermediate size
• Permanent fixtures
• Maintain shape of
cell
• Fix position of
organelles
3 TYPES OF CYTOSKELETON FIBERS:
Microtubules
Microfilaments
Intermediate
Filaments
Centrosomes: region from which microtubules grow
 Also called microtubule organizing center
 Animal cells contain centrioles
CILIA & FLAGELLA
Flagella: long and few; propel through water
 Cilia: short and numerous; locomotion or move fluids
 Have “9+2 pattern” of microtubules

EXTRACELLULAR MATRIX (ECM)
Outside plasma membrane
 Composed of glycoproteins (ex. collagen)
 Function: Strengthens tissues and transmits external
signals to cell

INTERCELLULAR JUNCTIONS (ANIMAL
CELLS)
Tight junctions: 2 cells
are fused to form
watertight seal
 Desmosomes: “rivets”
that fasten cells into
strong sheets
 Gap junctions:
channels through which
ions, sugar, small
molecules can pass

PLANT CELLS
Cell wall: protect plant,
maintain shape
 Composed of cellulose
 Plasmodesmata:
channels between cells to
allow passage of
molecules

Plant Cells Only
Animals Cells Only
Central vacuoles
Lysosomes
Chloroplasts
Centrioles
Cell wall of cellulose
Flagella, cilia
Plasmodesmata
Desmosomes, tight and
gap junctions
Extracellular matrix
(ECM)
Parts of plant & animal cell p 108-109
HARVARD CELL VIDEO
http://multimedia.mcb.harvard.edu/anim_innerlife
.html