Download The Cell Theory of Life - San Diego Mesa College

SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
TThhee C
Ceellll TThheeoorryy ooff LLiiffee

We humans are, together with the fungi, plants and animal, multicellular
biological organisms; it means that our body is made up from billions of so-called
cells

Other organisms, such as the bacteria, protists and certain algae, are single cell
creatures which show all important characteristics of life

To understand the many intricate properties and activities of biological
organisms it is therefore of prime importance to have a better understanding of
structures and functions of cells

The core understanding of cells is expressed in the so-called cell theory, which
is one of the most fundamental theory in biology

The cell theory states, that:
1. Every living organism is made up of one or more cells
2. Cells are the structural and functional unit of living
organisms
3. The smallest living organisms are single cells, and cells comprise the
functional units of multi-cellular organisms
4. All cells arise from preexisting cells

Our modern understanding of cells (as incomplete it still is in the year 2004)
came a long way in human history
TThhee H
Hiissttoorryy ooff C
Ceellll B
Biioollooggyy
 eeaarrllyy 11770000ss: the Dutchman A
A.. vvaann LLeeeeuuw
weennhhooeekk uses for the first time a light
microscope to study biological objects; he describes his “animacules”
 it lays the basis for the development of the later cell theory
 11666655:: R
Roobbeerrtt H
Hooookkee discovers and describes for the first time a cell
 11882277:: K
Kaarrll E
E.. R
Riitttteerr vv.. B
Baaeerr discovers and describes for the first time the
mammalian egg cell
 11883399:: TThheeooddoorr S
Scchhw
waannnn lays the foundation of the cell theory of modern
Biology
 11885555:: the German physician R
Ruuddoollff V
Viirrcchhoovv states from his observations, that
all cells arise from cells
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
 11889922:: H
H.. D
Drriieesscchh shows for the first time, that separated embryo cells of the
sea urchin, each develop into separate, perfectly shaped organisms
 11889944:: JJ.. LLooeebb conducts the first transfer of a cellular nucleus into a denucleated
egg cell (nucleus transfer)
 11993388:: German physicist E
E.. R
Ruusskkaa gets for the first time an image of a virus
(tobacco mosaic virus) with the help of his invented electron microscope
 introduced into biological research, it revolutionized the study of cells and
lead to the discovery of numerous intracellular organelles, structures and
viruses
 11995522:: the American biologists R
R.. B
Brriiggggss &
& TT.. K
Kiinngg report the development of
normal, genetically identical tadpoles after transfer of embryo cell nuclei into
denucleated egg cells
 11996633:: JJ..B
B..S
S.. H
Haallddaannee creates the term ‘clone’
 a clone means genetically and morphologically identical cells or organisms
 11998800--9900ss; the so-called fluorescence microscope becomes widely used in
biological research
 it enabled (together with the use of fluorescent dyes and proteins) for the first
time the detailed study of the dynamic cellular processes, e.g. vesicle
secretion or phagocytosis
 11998866:: the British scientist W
Wiillllaaddsseenn clones a sheep from embryo cells after
nuclear transfer
 11999977:: The British researcher W
Wiillm
muutt aanndd ccoolllleeaagguueess report the cloning of the
sheep ‘Dolly’
 Dolly is the world’s first species to be cloned from adult cells by
nuclear transfer
 TTooddaayy:: the controversially discussed Embryonic stem cell research holds the
great promise for future treatment of serious human diseases and injuries, such
as Parkinson’s disease, diabetes, heart disease, burns and spinal cord injuries,
but also raises serious concerns about human ethics
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
W
Whhyy aarree cceellllss ooff bbiioollooggiiccaall oorrggaanniissm
mss ssoo ssm
maallll ??

 tthhee cceellll ssiizzee iiss lliim
miitteedd bbyy nnaattuurraall llaaw
wss

The cell size is a compromise between:
1. creation of enough space (= volume) to fit all the essential nutrients,
enzymes, proteins, DNA and organelles, etc. into it
- the volume which rises with the third potency is calculated as follows
Vsphere = 4/3  r3
or
V = volume r = radius
Vcube = a3
a = cube length
and
2. being small enough to create maximum total surface for optimum
uptake/supply of nutrients and gases into the cells and efficient disposal of
cell waste out of the cell
- the surface area is calculated as follows
Ssphere = 4  r2
S = surface r = radius

or
Scube = 6 a2
a = cube length
It is after all physical laws which are responsible for the enormously small
(micrometer) size of cells established on planet earth. The so-called surface-tovolume ratio (SVR) plays a crucial role in the creation of the cell size; e.g. a
larger cell has a smaller surface than smaller cells filling the same space!!
 the surface-to-volume ratio (= SVR) imposes an upper limit to a cell’s size!
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
TTw
woo m
maajjoorr cceellll ttyyppeess eexxiisstt oonn E
Eaarrtthh
1. Prokaryotic cells
2. Eukaryotic cells
11.. P
Prrookkaarryyoottiicc C
Ceellllss
C
Chhaarraacctteerriissttiiccss ooff pprrookkaarryyoottiicc cceellllss

Prokaryotic cells are of smaller size than eukaryotic cells
 usually 2-8 m in length

They lack a true nucleus
- in contrast to eukaryotic cells, where the chromosomal DNA is contained in a
membrane-enclosed organelle, called the nucleus, the chromosomal DNA in
prokaryotic cells is located in a membrane-less region within the cell called
the nucleoid region

Most prokaryotes have extrachromosomal DNA or so-called plasmids in the
cytoplasma
 these plasmids play a crucial role in the rapid transfer of
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
resistance genes, e.g. against the antibiotics tetracycline or
streptomycin, amongst bacteria strains
 modified versions of these bacterial plasmids became the
powerful molecular ‘working horses’ of modern biotechnology!!

Prokaryotic cells have free-floating cytosolic ribosomes
- a ribosome is the cellular place where new polypeptides and proteins are
produced (= chemically synthetized)

Prokaryotes have a plasma membrane
- the plasma membrane is the outer cell barrier made of mainly a phospholipid
bilayer membrane and intercalated proteins
- this semi-permeable structure completely encloses the cytoplasm and all it’s
components
- the plasma membrane functions as a selective barrier that allows passage of
oxygen, nutrients, and wastes for the whole volume of the cell

Prokaryotes possess a bacterial cell wall
- the bacterial cell wall surrounds the plasma membrane
 it is the outer-most barrier and helps to protect and stabilize the
shape of the bacterium
 dependent on the composition of the cell wall, bacteria are
classified into so-called gram-negative and gram-positive bacteria
 certain cell wall components, called lipopolysaccharides or
endotoxins, are (when released by the bacteria) very toxic to
humans and can cause serious disease (ARDS, endotoxic
shock) or death
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.

Capsule (some bacteria strains)
 functions as a further protection wall
 helps to efficiently interact with the environment due to
improved attachment to, e.g. host cell

Cell protrusions called pili (singular: pilus)and fimbriae
- these phospholipid-made cell protrusions are found only in some bacterial
strains
- pili and fimbriae help bacteria to attach to surfaces
- with the help of so-called sex pili, bacteria are capable to efficiently exchange
genetic material in form of plasmid DNA in a process called conjugation
- since most exchanged plasmid DNA contains so-called resistance genes (e.g.
against the antibiotics penicilline, streptomycin or tetracycline), the bacterial
conjugation with the help of sex pili is responsible behind the observed spread
of antibiotic-resistant bacteria in many hospitals

Prokaryotic flagella (singular: flagellum)
 these bacterial cell extensions enable bacteria to actively swim
(propel) through the liquid environment
Schematic presentation of a prokaryotic cell
from: http://www.gened.emc.maricopa.edu/bio/bio181/BIOBK/
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
A prokaryotic cell
E
Exxaam
mpplleess ooff G
Grraam
m--nneeggaattiivvee bbaacctteerriiaa
Vibrio cholerae
 bacterium that causes cholera disease in humans
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
Yersinia pestis
 microbial cause of the Bubonic Plague in the Medieval Ages
Salmonella bacteria
Escherichia coli (= E.coli) bacterium
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
Cyanobacteria
 e.g. Spirulina (a filamentous, photosynthesizing prokaryote)
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
E
Exxaam
mpplleess ooff G
Grraam
m--ppoossiittiivvee bbaacctteerriiaa
 form endospores; release exotoxins
Streptococcus areus ssp.
Clostridium bacteria
 e.g. Clostridium tetani, causes tetanus disease (« jaw lock « ) in humans
E
Exxaam
mppllee ooff aa pprroo--bbiioottiicc bbaacctteerriiuum
m
 common bacterium in many dairy products, e.g. yoghurt, sour cream, Kefir
Lactobacilli (e.g. L. acidophilus)
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
S
Scchheem
maattiicc pprreesseennttaattiioonn ooff cceelllluullaarr ppaarrttss ooff aa ttyyppiiccaall pprrookkaarryyoottiicc cceellll
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
22.. E
Euukkaarryyoottiicc cceellllss
C
Chhaarraacctteerriissttiiccss ooff eeuukkaarryyoottiicc cceellllss

One of the key characteristics which clearly distinguish eukaryotic cells from
prokaryotic cells is that eukaryotic cells have extensive and elaborate internal
membranes, which partition the cell into many unique compartments.
- these phospholipid-made membranes also participate in metabolism as many
enzymes are built into membranes
- the barriers created by membranes provide different local environments that
facilitate specific metabolic functions.

Typical membranuous structures found in eukaryotic cells are:

A true nucleus
 the nucleus is separated from the cytoplasma via a so-called
nuclear membrane (or nuclear envelope,
 the nuclear membrane has openings, called nuclear pores
 the pores enable exchange of e.g. proteins or metabolites and
communication with the cytosol, e.g. the messenger RNA
leaves the nucleus via pores to reach the ribosomes
 the nucleus encloses the chromosomal DNA of the cell and functions as the
cell’s genetic control center

The outermost barrier of eukaryotic cells is a phospholipid-made bilayer structure
called the plasma membrane
- this protein and phospholipid-made structure is responsible for the exchange of
molecules and chemical elements
- each type of membrane has a unique combination of lipids and proteins for its
specific functions. For example, those in the membranes of mitochondria
play key roles in metabolic activties (see cellular respiration) and programmed
cell death (see apoptosis).

Eukaryotic cells have multiple compartments or so-called organelles;
- 7 major types of these membranous organelles can be found in eukaryotic
cells
1. Rough endoplasmatic reticulum (rER)
2. Smooth endoplasmatic reticulum (sER or ER)
3. Golgi apparatus
4. Mitochondria (singular: mitochondrion)
5. Chloroplasts (only in ppllaanntt cceellllss!!)
6. Lysosomes
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
7. Peroxisomes

Some eukaryotic cells have unique cell protrusions called flagella (singular:
flagellum), microvilli (singular: microvillus) or cilia (singular: cilium)
- these cell protrusions are only found in highly specialized animal cells, e.g.
sperm, intestinal cells, or lung epithelial cells

Certain eukaryotic cells are surrounded by an extra protective, thick layer called
a cell wall
- cell walls are layered on top of the plasma membrane
- cell walls are only found in fungi, protists and in plant cells!

Some eukaryotic cells, especially plant cells, have a large central vacuole which
plays an important role in regulating the water pressure and also serve as
storage site for pigments, oils, and other molecules

Eukaryotic cells also have several non-membranous structures or
macromolecules:
1. a pair of centrioles found within a protein-made structure called
the centrosome
- the centrosome plays a key role as start site of the formation of the
so-called spindle apparatus during mitosis or meiosis
2. cytoskeleton
 the cytoskeleton is a supportive cellular meshwork of fine
fibers consisting of 3 major classes of proteins:
3. ribosomes
4. proteasome

All major eukaryotic organelles (nucleus, rER, and Golgi apparatus) are
interconnected
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
S
Scchheem
maattiicc pprreesseennttaattiioonn ooff aa ttyyppiiccaall aanniim
maall cceellll
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
S
Scchheem
maattiicc pprreesseennttaattiioonn ooff aa ttyyppiiccaall ppllaanntt cceellll
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
Images of different eukaryotic cells
1. Protists (= single-celled or uni-cellular organisms)
e.g. Amoeba proteus (Amoeba)
e.g. P
Paarraam
meecciiuum
m
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
2. Animal cells
e.g. E
Egggg cceellll
e.g. N
Neerrvvee cceellll (Cerebral Cortex)
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
e.g. P
Paannccrreeaass cceellll
 electron microscopic image
e.g. H
Huum
maann pphhaaggooccyyttee (with trapped bacteria)
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SAN DIEGO MESA COLLEGE
SCHOOL OF MATHEMATICS & NATURAL SCIENCE
General Biology (BIOL 107): Instructor: Elmar Schmid, Ph.D.
3. Plant cells
e.g. Green Algae (e.g. Chlamydomonas reinhardti)
e.g. Leaf cell of a corn plant
 electron microscopic image
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