Cell Theory
Topic 2.1
Assessment Statements
2.1.2 Outline the cell theory.
2.1.2 Discuss the evidence for the cell theory
2.1.3 State that unicellular organisms carry out all the
functions of life
2.1.4 Compare the relative sizes of molecules, cell
membrane thickness, viruses, bacteria, organelles
and cells, using the appropriate SI unit
2.1.5 Calculate the linear magnification of drawings
and the actual size of specimens in images of known
magnification
2.1.6 Explain the importance of the surface area
to volume ratio as a factor limiting cell size
2.1.7 State that multicellular organisms show
emergent properties
2.1.8 Explain that cells in multicellular organisms
differentiate to carry out specialized functions
by expressing some of their genes but not
others
2.1.9 State that stem cells retain the capacity to
divide and have the ability to differentiate
along different pathways
2.1.10 Outline one therapeutic use of stem cells
Cell theory
1. All organisms are composed of one or more
cells
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Cells 1st observed in 1665 by Robert Hooke while
observing cork with a microscope he built
Antonie van Leeuwenhoek observed 1st living cells,
“animacules”
In 1838 Mathias Schleiden stated that plants are
made of “independent, separate beings” called
cells
In 1839 Theodor Schwann made a similar
statement about animals
2. Cells are the smallest units of life
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No living entity found has not been made
of at least one cell
3. All cells come from pre-existing cells
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Supported by Louis Pasteur in 1860s
through experiments that disproved
spontaneous generation
Possible exceptions?
Functions of life
1.
2.
3.
Metabolism (all
chemical reactions that
occur within an
organism)
Growth
Reproduction
(hereditary molecules
that can be passed to
offspring)
4.
5.
6.
Response
Homeostasis
(maintenance of a
constant internal
environments)
Nutrition (providing a
source of compounds
that can be broken
down to provide
organism with energy
and nutrients)
Cells and sizes
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Most cells are up to 100 μm (micrometers)
Organelles are up to 10 μm
Bacteria are up to 1 μ
Viruses are up to 100 nm (nanometers)
Membranes are 10 nm thick
Molecules are near 1 nm
All objects are 3-D
Calculating size
• Know the diameter of the microscope’s field of vision using a
simple ruler
• Size of specimen can then be calculated in the field
• By knowing the diameter of the field of view and having an
estimate of the number of cells that would fit across the diameter,
you can determine the size of a cell by dividing the diameter by the
number of cells.
For example:
The diameter of the field of view under 100 total magnification is
about 1.5 mm. If there are 10 cells that would fit across the
diameter, one cell would be 0.15mm.
The diameter of the field of view under 400 total magnification is
approximately 0.375 mm.
Types of microscopes
• Light microscope
– type found in most schools
(including ours), uses
compound lenses and light to
magnify objects
– The lenses bend, or refract
the light, which makes the
object beneath them appear
closer.
– Magnifies objects up to 2000
times.
– Two dimensional images
– Poor resolution
– Bonuses: Relatively
inexpensive, can view living
organisms in color
• Electron microscope
– use electrons (negatively
charged electrical particles) to
view the specimen
– Types:
• Scanning
– 3D images
– Magnifies 50,000 X
– Non-living specimens
• Transmission
– 2D images
– Magnifies 2,000,000 X
– Non-living specimens
– High magnification and
resolution
Limiting cell size
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Why must cells be small?
Surface area to volume ratio
Homeostasis dependent upon volume
Greater surface area able to move more
materials in and out
• A large cell has relatively less surface are
than a small cell
• What about large cells?
Calculating SA/V of a sphere
• SA=4πr2
• V=(4/3) πr3
Cell reproduction and
differentiation
• Allows possibility of growth and
replacement of damaged or dead cells
• Multicellular organisms begin as a single
cell that reproduces at a rapid rate
• Resulting cells go through differentiation
as a result of the expression of genes
• Some cells lose ability to reproduce once
they become specialized
Stem cells
• What are stem cells?
• Populations of cells that retain their
ability to divide and differentiate into
various cell types
• Ex. Meristematic tissue in plants,
embryonic (pluripotent) in animals
• Cannot be distinguished by appearance;
only by behavior
Stem cell research
• Directed towards growing large numbers of
embryonic stem cells in culture
• Used to replace differentiated cells lost due to
injury and disease
• Parkinson’s disease and Alzheimer’s disease
are caused by loss of brain cells and it is hoped
that implanted stem cells could replace many of
these lost brain cells
• Other examples: diabetes, leukemia
Ethical issues
• What is the controversy?
• Where do you stand in the debate?
• How do you feel about the source of
pluripotent stem cells?
Prokaryotic Cells
Topic 2.2
Assessment Statements
2.2.1 Draw and label a diagram of the
ultrastructure of Escherichia coli as an example
of a prokaryote
2.2.2 Annotate the diagram with the functions of
each named structure
2.2.3 Identify structures from 2.2.1 in electron
micrographs of E. coli
2.2.4 State that prokaryotic cells divide by binary
fission
What is a prokaryotic cell?
• Most are less than 1 μm
in diameter
• DNA not enclosed within
a membrane and is one
circular chromosome
• DNA not attached to
proteins
• Lack membrane-bound
organelles
• Cell wall made of
peptidoglycan
• Divide by binary fission
E. Coli ultrastructure
• Be able to draw and
label:
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Cell wall
Plasma membrane
Flagella
Ribosomes
Nucleoid (region
containing free DNA)
Cell wall
• Protects and maintains the shape of the
cell
• Composted of carbohydrate-protein
complex called peptidoglycan
• Some bacteria have an additional layer of
polysaccharide (capsule) outside cell wall
which makes it possible for some to
adhere to structures
Plasma membrane
• Just inside cell wall
• Controls movement of materials in and out of
the cell
• Plays a role in binary fission
• Cytoplasm occupies the interior of the cell and
is location for all cellular processes
• Most visible structure is single chromosome
Pili
• Hair-like growths on outside of the cell
wall
• Used for attachment
• Main function is joining bacterial cells in
preparation for the transfer of DNA from
one cell to another
Flagella
• (sing.) or flagellum (pl.)
• Longer than pili
• Allow cell motility
Ribosomes
• Occur in all prokaryotic cells
• Function as sites of protein synthesis
• Occur in very large numbers in cells with
high protein production
Nucleoid region
• Non-compartmentalized
• Contains a single, long, continuous, circular
thread of DNA
• Involved in cell control and reproduction
• Cell may also contain plasmids which replicate
independently of the chromosomal DNA
• Plasmids are not required but may help the cell
adapt to unusual circumstances
Binary fission
• Process by which prokaryotes divide
– DNA is copied
– 2 daughter chromosomes become attached to
different regions on the plasma membrane
– Their movement is aided by fibers made of
protein called FtsZ
– Cell divides into two genetically identical
daughter cells
Paul the Prokaryote
• While watching the clip list as many facts
about prokaryotes that you see depicted
Eukaryotic Cells
Topic 2.3
Assessment Statements
2.3.1 Draw and label a diagram of the ultrastructure of a
liver cell as an example of an animal cell
2.3.2 Annotate the diagram with the functions of each
named structure
2.3.3 Identify structures from 2.3.1 in electron
micrographs of liver cells
2.3.4 Compare prokaryotic and eukaryotic cells
2.3.5 State three differences between plant and animal
cells
2.3.6 Outline two roles of extracellular components
What is a eukaryotic cell?
• Range in diameter from 5 to 100 μm
• Noticeable nucleus
• Compartmentalized due to presence of
organelles (non-cellular structures which
carry out specific functions)
Common organelles
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Endoplasmic reticulum
Ribosomes
Lysosomes
Golgi apparatus
Mitochondria
Nucleus
Chloroplasts
Centrosomes
Vacuoles
Typical Animal Cell
Liver Cell
Typical Plant Cell
Cytoplasm
• Within plasma membrane
• Fluid between organelles is called cytosol
Endoplasmic reticulum
• Extensive network of
tubules or channels
• Transports materials
throughout the internal
region of the cell
• Two types:
– Rough (has ribosomes
attached)
– Smooth (lacks ribosomes)
• Rough
– Involved in protein
development and transport
– Closer to nuclear membrane
• Smooth
– Produces lipids, sex
hormones
– Detoxifies drugs
– Stores calcium ions
– Transports lipid-based
compounds
– Aids liver in release of
glucose
Ribosomes
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Carry out protein synthesis
May be free or attached to ER
Composed of RNA and protein
Larger and denser than those found in
prokaryotes
Lysosomes
• Digestive centers that arise from the
Golgi apparatus
• Contains enzymes that break down
proteins, nucleic acids, lipids and
carbohydrates
Golgi apparatus
• Made of flattened sacs called cisternae
• Collects, packages, modifies and
distributes materials synthesized in the
cell
Mitochondria
• Produces usable cellular energy called
ATP through process of cellular
respiration
• Has its own DNA and ribosomes
• Capable of reproducing independent of
cell
Nucleus
• Region where DNA is located
• Bordered by nuclear envelope which has
numerous pores that allows communication
with the cell’s cytoplasm
• DNA occurs in form of chromosomes or
chromatin
• Some cells extrude their nucleus and are more
specialized for a specific function
• Nucleolus within nucleus produces ribosomes
Chloroplasts
• Occur only in plant and algae cells
• Contains its own DNA in the form of a
ring
• Includes grana, thylakoids, and stroma
• Carries out photosynthesis
• Capable of reproducing independent of
cell
Centrosome
• Pair of centrioles at right angles to one
another
• Involved in assembling microtubules
which provide structure and movement
of cell
Vacuoles
• Formed from Golgi apparatus
• Store potential food, metabolic wastes,
toxins, and water
• Enable plants to have higher surface area
to volume ratios even at larger sizes
• In plants, they provide rigidity when
filled with water
Prokaryotic vs. Eukaryotic
Prokaryotic cells
• DNA in a ring w/out
protein
• DNA free in cytoplasm
• No mitochondria
• 70S ribosomes
• No internal
compartmentalization
• < 10 μm
Eukaryotic cells
• DNA with proteins as
chromosomes/chromatin
• DNA enclosed
• Mitochondria present
• 80S ribosomes
• Internal
compartmentalization
• > 10 μm
Prokaryotic AND Eukaryotic
• Both have outer boundaries that always
involves a plasma membrane
• Both carry out all the functions of life
• Both have DNA
Plant vs. Animal
Plant cells
• Exterior of cell includes
cell wall
• Chloroplasts present
• Large central vacuole
• Store carb. as starch
• Do not contain centrioles
• Has a fixed, often
angular shape
Animal cells
• Only plasma membrane; no
cell wall
• No chloroplasts
• Vacuoles not present or small
• Store carb. as glycogen
• Contain centrioles
• Cell is flexible and more likely
to be rounded in shape
Outermost regions
• Bacteria
– Cell wall of
peptidoglycan
• Fungi
– Cell wall of chitin
• Yeasts
– Cell wall of glucan
and mannan
• Algae
– Cell wall of cellulose
• Plants
– Cell wall of cellulose
• Animals
– No cell wall
– Extracellular matrix
made of glycoproteins
Functions of extracellular
components
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Cell wall
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maintains cell shape
Helps regulate water
intake
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Extracellular matrix
(ECM)
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Composed of collagen
and glycoproteins
Strengthens plasma
membrane
Allows for cell-to-cell
interaction, possibly
altering gene expression
Directs stem cells to
replicate
Cell migration and
movement