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CHAPTER 6
CELLULAR
STRUCTURE
WHY STUDY CELLS?
Intro to Cells
Brief
 Great researcher
 Based on
observation
 Viper venom!
 First to debunk
spontaneous
generation
" I put in four flasks with
wide mouths one sneak,
some fish of river, four
small eels of Arno river and
a piece of calf and I locked
very well the mouths of the
flasks with paper and
string. Afterward, I placed
in other four flasks the
same things and left the
mouths of flasks open.
Short time later the meat
and the fishes inside the
open flasks became
verminous, and after three
weeks I saw many flies
around these flasks, but in
the locked ones I never seen
a worm ".
- 1688
Lazzaro Spallanzani
1765
Louis Pasteur
1862
"Omnis cellula e cellula"...
"All cells only arise from
pre-existing cells".
-Rudolf Virchow
Cell Theory – original 1839
Schleiden and Schwann
 All organisms are made up of cells
 The cell is the basic living unit of
organization for all organisms
 All cells from pre-existing cells

Biogenesis -Not spontaneous generation or abiogenesis
The Modern Cell Theory:
1. all known living things are made up of cells.
2. the cell is structural & functional unit of all living
things.
3. all cells come from pre-existing cells by division.
4. cells contains hereditary information which is passed
from cell to cell during cell division.
5. All cells are basically the same in chemical
composition.
6. all energy flow (metabolism & biochemistry) of life
occurs within cells.
Biological Diversity and Unity



DNA is universal “language”
Cells are most basic unit of
structure and function
Lowest level of structure
capable of performing all
life activities and being
self-sustaining
Cells
Activities of Life
 Reproduction
 Growth and
development
 Energy utilization
 Response to stimuli
 homeostasis
HOW DO WE STUDY CELLS?
 Robert Hooke 1665
 Leewenhoek
1674
Microscopes
 Light microscope (LM) - visible light
passes through specimen and then
through glass lenses.
 lenses refract light - image is
magnified into the eye
 Specimen can be alive!
 Magnification = the ratio of an
object’s image to its real size.
 Resolving power = a measure of
image clarity

7X
minimum distance 2 points can be
separated and still be viewed as two
separate points
45X
112.5X
225X
LIGHT MICROSCOPE
 minimum resolution is
about 2 microns
(small bacterium)
 magnify effectively to
about 1,000 times
 At higher
magnifications, the
image blurs
HOW
BIG
ELECTRON MICROSCOPE





1950’S
2.0 nm resolution
100X > than light
Organelles
Only on dead cells
 electron microscope (EM)
beam of electrons through the
specimen or onto its surface shorter wavelengths of light
 greater resolution
 Transmission electron microscopes (TEMs)study internal ultrastructure




electron beam through thin section of specimen
image focused and magnified by electromagnets
thin sections stained with atoms of heavy metals
Dead; may leave debris/artifacts
Tracheal cells
 Scanning electron microscopes (SEMs)- useful
for studying surface structures



surface covered with a thin film of gold
beam excites electrons on surface
secondary electrons collected and focused on screen
 SEM has great
depth of field,
image seems 3-D
 Dead,debris/artifacts
 LM’s -less resolution but living
 cytology- study of cell structures
 Cytology + biochemistry =
modern cell biology
ISOLATING ORGANELLES
Cell Fractionation
Separate organelles from cell
Use varying densities of parts

•Ultracetrifuge
HEAVIEST?
LIGHTEST?
•Ultracentrifuge – molecular level
•130,000 rpm
•Forces>1 million g’s
Why in a BIG thick
lead-lined housing?
Microcentrifuge
 Biotechnology research

Cells at protein and genetic level
 Homogenization- disrupts cell
 Ultracentrifuge- spins to separate
heavier pieces into pellet with
lighter particles in supernatant
CELLS
ALIVE
Amoebas
Animals
Plant Cells
Cell characteristics – All Cells
 Plasma membrane
 Cytosol


Semi-fluid substance w/ “solutes”
Cytoplasm = cytosol + organelles(euk’s)
 Contain chromosomes w/ genes in DNA
 Ribosomes

Protein synthesis; carry out gene instructions
Types of Cells
•Prokaryotic vs. Eukaryotic Cells
•Location of chromosomes
Prokaryotic Cells
 Nucleoid region
 1 main Circular
chromosome +
plasmids
 Ribosomes
Human Cells




Eukaryotic Cells
Nucleus; isolated
Linear chromosomes
Membrane bound
organelles
Ribosomes
Remember the agar block lab?
Same time = same depth of diffusion
 Limited by SA/ Vol ratio

Volume increases by factor of 3; SA by 2
• Smaller objects have greater SA:Vol ratio
What cell
organelle
governs this?
Why is a huge
single-cell
organism not
possible?
LIMITS TO SIZE---
 Eukaryotes generally much bigger
 Logistics of carrying out metabolism
sets limits on cell size
• SA to Volume ratio?
– smallest bacteria, mycoplasmas
» 0.1 to 1.0 micron
» Most bacteria 1-10 microns
– Eukaryotes typically 10-100 microns
» Micron = 1 micrometer = 1/1,000,000 meter
» 1000 microns = 1 millimeter
» Human hair = apx. 20 microns
Size must be low to sustain life
•
enough DNA to program metabolism
•
enough ribosomes for protein synthesis
•
enough enzymes for metabolism
•
enough cellular components
 plasma membrane functions as a
selective barrier


Controls movement in and out of cell
maintains homeostasis - correct
environment
 bilayer of phospholipids + proteins

Amphipathic
• hydrophyllic
• hydrophobic
TOUR OF
THE CELL
BUCKLE
UP!
The Nucleus
and
Ribosomes
Nucleus contains a eukaryotic cell’s
genetic library
 contains most of genes in euk. Cell
 largest organelle
 double membrane

unique environment
 membranes fuse to form pores/envelope



large macromolecules & particles pass
unique chemical signals
viruses may break code
 Nuclear
lamina--nuclear
side; lined by
intermediate
filaments
• maintains shape
of nucleus
 DNA and histone
proteins =
CHROMATIN
 Nucleolus –
rRNA synthesis
 NUCLEUS directs protein
synthesis;
synthesizes mRNA
Ribosomes build a cell’s proteins
 Ribosomes contain rRNA and protein
 A ribosome = two subunits combined to carry out
protein synthesis; no membrane!
 Free and Bound and prokaryotic
The Endomembrane
System
EndoMembrane
system
ER manufactures membranes and
performs many other biosynthetic functions
 membranous tubules and internal, fluid-filled
spaces = cisternae; storage area
 Lumen is center of ER
 continuous with N. E.
 2 connected regions of
ER-

Smooth ER lacks
ribosomes
Rough ER (bound
ribosomes)
The Golgi Apparatus finishes, sorts,
and ships cell products
 Receives transports vesicles from ER
 Modifies contents
 Warehousing, sorting, and shipping
 Abundant in secretory cells
 Produces lysosomes and cell wall
Sumanisc
Endomembrane System
Lysosomes are digestive sacs
 lysosome - a membrane-bound sac of hydrolytic
enzymes that digests macromolecules.
Vacuoles have diverse functions in
cell maintenance
 Vesicles and vacuoles (larger versions)
 membrane-bound sacs


Food vacuoles, from phagocytosis, fuse with
lysosomes
Contractile vacuoles, in freshwater protists
• pump excess water out of cell

Central vacuoles in plant cells;
• Store water and solutes
Other Membranous Organelles
Mitochondria and chloroplasts are
main energy transformers of cells
 convert energy to usable forms for work
 Mitochondria = sites of cell. respiration,
generate ATP from catabolism of sugars,
fats, and other fuels in presence of oxygen
 Chloroplasts - found in plants and
eukaryotic algae; sites of photosynthesis

convert solar energy to chemical energy and
synthesize new organic compounds from
CO2 and H2O.
 PLASTIDS  Amyloplasts/leucoplasts - store starch
in roots and tubers
 Chromoplasts store pigments

Chloroplast
• produces sugar via photosynthesis
• color from chlorophyll pigment
• in leaves and other green structures
of plants and in eukaryotic algae
Peroxisomes - single membrane
 contain enzymes to break down H2O2
 Some break fatty acids down for
mitochondria for fuel
 Some detoxify alcohol and other harmful
compounds
Glyoxysomes = Specialized peroxisomes,
in plants only,
convert fatty acids to sugars in seeds =
easier energy and carbon source
The Cytoskeleton
 CYTOSKELETON = a network of fibers
throughout cytoplasm
 maintains shape of the cell; oppose forces
 organizes structures and activities of cell
 provides anchorage for organelles
 dynamic, dismantles and reassembles as
needed
 cytoskeleton - major role in cell motility
 changes in cell location
 limited movements of parts of cell
 interacts with motor proteins- dynein
 In cilia and flagella
 also in muscle cells
 circulate materials
within cell by
cytoplasmic
Cilia
kinesin
flagella
streaming
 three main types of fibers in the
cytoskeleton:
microtubules
 microfilaments
 intermediate filaments

Actin
Actin and keratin
 Cilia and Flagella are microtubules


move unicellular and small multicellular
organisms thru water
may move fluid over a surface
• EX: cilia sweep mucus carrying trapped
debris from the lungs
 Cilia usually in large #’s on cell surface
 flagella - usually just one or a few
 Flagellum - undulatory movement
 Force - parallel to the flagellum’s axis
 Cilia move like oars

force perpendicular to cilia’s axis
•In animal cells, centrosome has a pair of
centrioles, each with 9 triplets of microtubules
arranged in a ring
•centrioles replicate during cell division
“9 + 2”
Cilia and flagella
Site of controversy
Basal body same
structure as
centriole
Basal body
 bending driven by arms of motor protein
called dynein
 Hydrolysis of ATP causes bending of
protein
 Dynein arms
alternately grab,
move and release
outer microtubules
Motor
protein
MicroTubule
sliding
 Microfilaments= thinnest fibers; solid,
globular protein actin

microfilament of actin subunits
 resist tension = pulling
 interact with myosin for muscle
contraction
 A contracting belt- divides cytoplasm
animal cells during cell division
microvilli
increase SA
• lung tissue,
•intestinal lining, etc;
•Absorptive surfaces
•anchored to
intermediate
filaments.
 contraction causes amoeboid movement
• Pseudopodia, cellular extensions, extend and contract
through assembly and contraction of actin subunits into
microfilaments
 In plant cells - actin-myosin interactions
drive cytoplasmic streaming
 a circular flow of cytoplasm
 speeds the distribution of materials within the
cell.
 Intermediate filaments for bearing tension
 built from keratin
 reinforce cell shape and
fix organelle location
Cell Surfaces and Junctions
Plant cells are encased by cell walls
 cell wall - in prokaryotes, fungi, and some
protists; multiple functions
 In plants - protects, maintains shape,
prevents excess uptake of water; turgor
 supports plant against force of gravity
 thickness and composition differs from
species to species and among cell types
 consists of microfibrils of cellulose in a matrix
of proteins and other polysaccharides
 mature cell wall consists of a primary cell
wall, a middle lamella with sticky
polysaccharides- pectin- holds cell together,
and layers of secondary cell wall
Extracellular matrix (ECM) of animal cells
 glycoproteins, especially collagen,
embedded in network of proteoglycans
 fibronectins bind to integrin proteins in
membrane to connect ECM to
cytoskeleton microfilaments
 permit interaction of changes inside
and outside cell
 The ECM can regulate cell behavior


Embryonic cells migrate along specific
pathways by matching the orientation of
their microfilaments to the “grain” of fibers
in the extracellular matrix.
ECM can influence activity of genes in
nucleus via a combination of chemical and
mechanical signaling pathways
• This may coordinate all the cells within a tissue.
Intercellular junctions
 Connections between cells
 Plant cells have plasmodesmata,
channels for direct exchange of cytosol
 Animal have 3 main types of intercellular
links:
 tight junctions, membranes are fused,
form continuous belts around cellsprevents leakage of extracellular fluid
 Desmosomes fasten cells together into
strong sheets - keratin intermediate
filaments
 Gap junctions provide cytoplasmic
channels between adjacent cells