Transcript Cells - Damien Rutkoski

Ch. 7 Cell Structure
Biology
Cytology
• The Study of Cells
History of Cytology
• Begins with the
invention of the
microscope
• Zacharias Janssen (fix
your notes!) credited
with the invention of
the compound
microscope
• Late 1500’s
Robert Hooke
• Coined the term “cell”
– Did this while observing cork
cells
– Really the cell walls of dead
plant cells from bark
• Published his observations
in the book Micrographia
• Influenced many others
• Click here for more on
Robert Hooke
Robert Hooke
• Hooke’s microscope
was not as good as
some (especially those
of Leeuwenhoek), but
he was still able to
make many
observations and
detailed drawings.
Robert Hooke
• Hooke’s drawings of
cork cells 
• He also made many
other detailed drawings
of organisms he viewed
with his microscope.
– The flea 
Anton Van Leeuwenhoek
• Was not the first
microscope maker, but
made some of the best
early microscopes
• Very high
magnifications for the
time – up to 300x
• 1600s
Anton Van Leeuwenhoek
• Observed first living
cells
– Pond water, various
bodily fluids that had
bacteria swimming
about in them, etc.
– Remember that the cells
Hooke observed were
non-living (cork)
– For more on how his
microscope worked, click
here.
Anton Van Leeuwenhoek
• Images he drew of
bacteria in plaque
removed from his teeth.
• These are the first
known observations of
bacteria
• He called them
“animalcules”
Robert Brown
• 1st to observe a nucleus
in a cell (1833)
– The instrument is
Brown’s microscope
– The image below is what
Brown would have seen
when he made his
discovery. These are
cells from an orchid leaf.
• The nuclei are the small
dots in each cell
• The big things are
stomata
Matthias Schleiden
• Said that all plants are
made of cells
– 1838
Theodore Schwann
• Said all animals are
made of cells
• 1839
Rudolf Virchow
• All cells are made from
other cells
• 1855
• Before this time it had
been thought that cells
could arise
spontaneously from
non-life
The Cell Theory
• The work of all the scientists listed is compiled into
one large idea called The Cell Theory
• Remember – a theory is an explanation for
observations that
–
–
–
–
Is supported by a large body of evidence
Has been tested MANY times
Explains MANY things
It may be revised or improved, but stands as our best
explanation for observations we have.
The Cell Theory
• All living things are composed of cells
• Cells are the basic units of structure and
function in living things
• All cells come from pre-existing cells
Microscopes
•
•
•
•
Compound
Dissecting
Scanning Electron
Transmission Electron
Compound Light Microscope
• Called compound
because TWO lenses
are combined to
magnify the image –
not just one.
– Eyepiece (ocular)
– Objective lens
Limitations of the Compound
Microscope
• Images must be small
and mounted on a slide
Compound Microscope Parts
• Ocular
– Also called eyepiece
– Usually magnifies 10x
– Needle inside for
pointing to objects
• Body or Arm
Compound Microscope Parts
• Revolving nosepiece
– Holds objective lenses
– Rotates so that correct
objective can be chosen
• Objective Lens
– Usually a “low”,
“medium” and “high”
power
Compound Microscope Parts
• Attached to the nosepiece
• Low Power
–
–
–
–
–
Usually 4x
Widest field of view
Least magnification
Used first to observe
Coarse focus
• High Power
–
–
–
–
Usually 40x
Narrowest field of view
Most magnification
Use only after low and
medium powers
– Fine focus only
More Microscope Parts
• Stage
• Diaphragm
– Controls the amount of light that strikes the specimen
• Focus knobs
– Coarse
• Moves the stage in large amounts
• Used only with low power
– Fine
• Moves the stage in small amounts
• Used with high power (but can be used with any)
• Light source
• Base
Dissecting Microscope
• Two oculars
• Low magnification
• Large specimens may
be observed
About Field of View
• Wide field of view
– Large area
– Specimen appears small
– Good for specimens that move a lot and quickly
• Narrow field of view
– Small area
– Specimen appears large
– Good for specimens that are still and for which you want
to see greater detail
Field of View
• Top image
– Wide field of view
• Bottom image
– Narrow field of view
Scanning Electron Microscope
• VERY large
magnification
– 1000s of times
• External views
• 3-D appearance
• Click here to see how
the SEM works and to
see images from an
SEM
Transmission Electron Microscope
• VERY large
magnifications
– 1000s of times
• Views cross-sections of
images
– Inside a cell
• 2-D views
• Click here to see how a
TEM works and images
from one
Cell Types
• There are TWO major types of cells
– Prokaryotic
– Eukaryotic
Prokaryotic Cells
•
•
•
•
BACTERIA
Simple
No nucleus
No organelles that are
surrounded by
membranes
• Most ancient cell type
– First to evolve
• Most primitive
Eukaryotic Cells
• Everything EXCEPT Bacteria
– Protists, fungi, plants and
animals are made up of this
type of cell
• Complex
• Nucleus present
• Organelles surrounded by
membranes
• The more recent cell type
– Evolved AFTER prokaryotes
• More complex
– More sophisticated parts and
functions
Two Major Types of Eukaryotic Cells
• Plant
• Animal
Plant Cells
• Plant Cells
– Cell wall made of
cellulose
– Large central vacuole
– Chloroplasts present
Animal Cells
• No cell walls
• No chloroplasts
• Vacuoles are present,
but no large centrally
located one.
Cell Size
• Cells are small. Why?
– Cells must have a large
surface area to volume ratio
– large surface area and small
volume allows for adequate
amounts of materials to move
in and out of the cell to
nourish a relatively small
volume
– If cell volume were larger, the
cell surface size would not
increase enough with volume
to service the whole cell.
Folds in Cells
• Whenever you see a
folded surface in a cell,
you can pretty much
bet that it is there to
increase surface area of
the structure in
question…
Organelles
• Cell parts or compartments – “little organs”
• Separate chemical processes
– Allow chemical processes that are incompatible
with each other to occur within a single cell.
Generalized Eukaryotic Cell
Cell Size
• Most cells are relatively
small because as size
increases, volume
increases much more
rapidly.
• This makes for a longer
diffusion time
Visualizing Cells
•
Prokaryotic
Cells
Simplest organisms
– Cytoplasm is surrounded by plasma membrane and
encased in a rigid cell wall composed of peptidoglycan.
• no distinct interior compartments
–gram-positive – thick single layer wall that retains
a violet dye from Gram stain procedure
–gram-negative – multilayered wall does not retain
dye
»Susceptibility of bacteria to antibiotics depends
on cell wall structure.
Prokaryotic Cells
• Some use flagellum for locomotion
– threadlike structures protruding from cell surface
Bacterial cell wall
Rotary
motor
Flagellin
Sheath
Eukaryotic Cells
• Characterized by compartmentalization by an
endomembrane system, and the presence of
membrane-bound organelles.
– Central vacuole – plants, storage
– Vesicles (smaller)
– Chromosomes - DNA and protein
– Cytoskeleton (internal protein scaffolding)
– Cell walls – plants and fungi
Nucleus
• Repository for genetic
material
• Directs activities of the cell
• Usually single, some cells several, RBC none
– Nucleolus – ribosome sub-units are made here;
• Surface of nucleus bound by two phospholipid
bilayer membranes
– nuclear membrane
– Nuclear pores – protein gatekeepers
• Usually proteins going in and RNA going out
Nucleus
Chromosomes
• DNA of eukaryotes is divided into linear
chromosomes.
– exist as strands of chromatin, except during cell
division
– associated with packaging histones, packaging
proteins
• nucleosomes
•
Endomembrane
System
Compartmentalizes cell, channeling passage of
molecules through cell’s interior.
– Endoplasmic reticulum
• Rough ER - studded with ribosomes
• Smooth ER - few ribosomes
•
•
•
•
•
Endoplasmic reticulum
Largest internal membrane
Composed of Lipid bilayer
Serves as system of channels from the nucleus
Functions in storage and secretion
Rough ER is “rough” because of associated
ribosomes (sites of protein synthesis
• Smooth ER - lack associated ribosomes –
contained embedded enzymes, catalyze
synthesis of carbohydrate and lipid molecules.
Endomembrane System
• Golgi apparatus
– collection of Golgi bodies
• collect, package, and distribute molecules
synthesized at one location in the cell and
utilized at another location
• Front - cis , Back – trans
• Cisternae – stacked membrane folds
Cisternae
cis face
Proteins
trans face
Golgi
apparatus
Transport
vesicle
Protein
Vesicle
Migrating
budding
transport
from rough vesicle
endoplasmic
reticulum
Ribosome
Fusion
of vesicle
with Golgi
apparatus
• VesiclesEndomembrane
System
– Lysosomes - membrane-bound vesicles containing
digestive enzymes – from Golgi
– Microbodies - enzyme-bearing, membrane-enclosed
vesicles.
• Peroxisomes - contain enzymes that catalyze the removal
of electrons and associated hydrogen atoms
• Peroxisome – named for hydrogen peroxide produced as a
by-product
• Enzyme breaks H2O2 down to water and oxygen
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Cytoplasm
Endoplasmic
reticulum
Phagocytosis
Food
vesicle
Golgi
apparatus
Lysosomes
Plasma
membrane
Extracellular
fluid
Digestion of
phagocytized
food particles
or cells
Transport
vesicle
Old or damaged
organelle
Breakdown
of old
organelle
Ribosomes
• Ribosomes are RNA-protein complexes
composed of two subunits that join and attach
to messenger RNA.
– site of protein synthesis
– assembled in nucleoli
Organelles With DNA
• Mitochondria
– bounded by exterior and interior membranes
– interior partitioned by cristae
• Chloroplasts
– have enclosed internal compartments of stacked
grana, containing thylakoids
– found in photosynthetic organisms
Mitochondria
A. "Powerhouse of the cell" - cellular
metabolism
B. Structure- outer and inner membranes,
cristae
C. Have their own DNA
Chloroplasts
•Chloroplasts are larger and more complex than
mitochondria
•Grana – closed compartments of stacked
membranes
•Thylakoids – disc shaped structure – light
capturing pigment
•Stroma – fluid matrix
Endosymbiosis
• Endosymbiotic theory suggests engulfed
prokaryotes provided hosts with advantages
associated with specialized metabolic
activities.
Theory of Endosymbiosis
Evidence for the endosymbiont theory is that
mitochondria and chloroplasts:
- Are appropriate size to be descendants of eubacteria.
- Have inner membranes similar to those on prokaryotic
plasma membranes.
- Replicate by splitting, as in prokaryotes.
- DNA is circular and different from the DNA of the cell's
nucleus.
- Contain their own components for DNA transcription and
translation into proteins .
- Have ribosomes similar to prokaryotic ribosomes.
- Molecular systematics lend evidence to support this
theory.
- Many extant organisms are involved in endosymbiotic
relationships.
Cytoskeleton
• Network of protein fibers supporting cell shape and
anchoring organelles
– Actin filaments
Microtubules
• cell movement
– Microtubules
Intermediate
filaments
• Hollow tubes
• Facilitate cell movement
• Centrioles – barrel shaped
• organelles occur in pairs –
• help assemble animal cell’s microtubules
– Intermediate filaments
• Stable - don’t break down
Actin
Cytoskeleton
Plant Cells
• Central vacuole
– often found in the center of a plant, and serves as
a storage facility for water and other materials
• Cell wall
– primary walls – laid down while cell is growing
– middle lamella – glues cells together
– secondary walls – inside the primary cell walls
after growth
Plant Cell
Animal Cells
• Animal cells lack cell walls.
– form extracellular matrix
• provides support, strength, and resilience
Modified from: http://www.coe.unt.edu/ubms/documents/classnotes/
Fall2005/Chapter%205%20-%20Cell%20Structure.ppt