Basic Characteristics of Cells

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Basic Characteristics of Cells
1. Basic unit of life-- all life (we know of)
depends on cells 2. Cell functions are based
entirely on chemical principles interconnected
chemical reactions allow cells to function 3.
Cells take in more energy than they produce--
thermodynamics 4. Cells specialize to optimize
their functions for particular purposes
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How large are cells?
Few microns
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How big is a micrometer (micron)? 1 micron
1x10-6 meters
10-3
10-2
10-1
common metric prefixes kilo- 103 centi-
10-2 milli- 10-3 micro- 10-6 nano-
10-9 Angstrom .10 nm 1x10-10m
light microscopes resolve to 0.2
microns electron microscopes resolve to 2
nanometers
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Average animal cell about 20 microns in diameter
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Up to 1 mm (or more) in diameter, meters long!
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Major classifications of cells-- Prokaryotic and
Eukaryotic
Eukaryotes are generally larger
complex Membrane bound nucleus Membranes
segregate function Endocytosis and
exocytosis More organized DNA Meiosis sexual
reproduction Expression of DNA Have internal
cytoskeleton
Prokaryote
Eukaryote
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Organelles
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Cell Membrane
Lipid bilayer with polar heads and hydrophobic
interior
found in prokaryotes and eukaryotes forms the
limiting boundary of the cell
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Cell Membrane
semi-permeable membrane-- gasses pass through it,
water ions can't proteins in the membrane
transport specific molecules in or out of the
cell many sugar groups (carbohydrates) are
attached to the proteins and lipids
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Nucleus
"brain" of the cell-- holds the information
stored as DNA and controls cell functions Has
it's own lipid bilayer with special "nuclear
pores" regulating in and out movement Place
where RNA is synthesized and processed
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Nucleus
DNA is bound to histone proteins in cell--
complex called a chromosome diploid-- 2 copies
of each homologous (very similar) chromatid each
chromatid duplicates and separates during cell
division
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Nuclei divide first, followed by rest of the cell
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Bacteria have to divide too
reproduce by fission-- divide in half -- not as
organized as eukaryotes
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cytoplasm-- material outside the nucleus inside
the cell membrane Cytoskeleton-- "bones" of a
cell-- provides structure and support also can
act as a highway-- move product from one place to
another
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Cytoskeleton
Three major fibers form the cytoskeleton microfi
laments - made up of actin form the cleavage
furrow during division contractile fibers of
muscles smallest fiber - 5-6 nm wide fibers have
polarity grow on one end, disassemble on
other intermediate filaments middle size - 10
nm wide most stable-- change less
frequently common at sites of mechanical
stress diagnostic tool in medicine- tissue
specific
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Cytoskeleton
10 nm
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Cytoskeleton
Microtubules - largest of the fiber classes ( 25
nm wide) made up of 2 protein subunits-- a and b
tubulin like actin, microtubules are polarized
with a and - end provides a 'superhighway' in
the cell to move in a direction
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Cytoskeleton
microtubules make up the spindle fibers that
separate chromosomes as well as the flagella that
allow motility for many cells
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Centrosome
microtubule organizing center 2, generally on
opposite sides of nucleus not found in plant
cells organizes the spindles during
mitosis also important for flagellar organization
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Ribosomes
found in both prokaryotes and eukaryotes location
of protein synthesis complex of proteins and
structural RNAs most numerous organelle in
cells relatively small organelles--
prokaryotes 25 nm 70S 30S and 50S
subunits eukaryotes 30nm 80S 40S and 60S
subunits
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Sedimentation Coefficient
Centrifugation is a way of separating substances
by density dense things settle to the
bottom lighter things stay toward
top centrifuges measured by G forces RCF 1.12r
(RPM/1000)2 (rradius in mm) sedimentation
coefficient is how rapidly a particle moves to
the bottom of a centrifuge measured in Svedberg
units (S) very useful for separating soluble and
insoluble materials as well repeatedly spinning
at different speeds can generate multiple
fractions
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Endoplasmic Reticulum (ER)
ER is a series of folded membranes within a
cell smooth ER is site of most membrane
synthesis rough ER looks spotted due to
ribosomes bound on the surface rough ER is
location of membrane, secreted or otherwise
targetted protein synthesis eukaryotes only
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Endoplasmic Reticulum (ER)
ER is continuous with the nuclear
membrane amount of ER varies by cellular
function liver cells have lots of ER- used to
detoxify chemicals cells optimized for
protein secretion have lots of rough ER
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Golgi Complex
Series of flattened membranes that processes
proteins, primarily glycosylation (adding
carbohydrates) vessicles carry proteins from one
stack to another, and eventually to their
final destination receives proteins to be
glycosylated from the endoplasmic reticulum
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Vacuole
extremely large and prominent in plant
cells smaller and more numerous in animal
cells in animal cells, primarily
storage granules in plants, performs storage,
some digestive functions, but primarily regulates
turgor pressure turgor pressure supplies rigidity
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Lysosome
'digestive' organelle-- breaks down storage
molecules, endocytosed material, or cellular
material that is no longer needed needs to be
isolated to prevent breaking down rest of the
cell! digested particles are released into the
cytoplasm where they are recycled
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Peroxisome
both generates and degrades hydrogen
peroxide detoxifies certain chemicals and
converts some substances breaks down long chain
fatty acids also has a role in
photorespiration first isolated as a biochemical
fraction
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Cell Wall
primary cell wall generally contains cellulose
and other polysaccharides secondary cell wall,
if present, is more rigid and contains lignin and
higher cellulose content plasmodesmata are
cytoplasmic links between plant cells passing
through cell walls Bacterial cell walls
contain peptidoglycans instead of cellulose
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Extracellular Matrix
Secreted by animal cells, not plants contains
mostly collagen and proteoglycans elastic
network allowing freedom of movement and not cell
wall rigidity aids in support and recognition
events basal lamina- extracellular matrix around
muscle cells- important in muscle cell function
and synapse formation
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Mitochondria
Found in both plants and animals about the size
of a bacteria 2 membranes, inner and
outer cristae-- folds of the inner mitochondrial
membrane matrix-- semiliquid material between
cristae oxidizes sugars and other foods for
energy primary site for the generation of
adenosine triphosphate, the main energy transfer
unit of the cell
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Chloroplast
only found in plants huge-- 5-10 microns
long have inner, outer, and thylakoid membranes
thylakoid-- flattened membrane sack grana--
stacks of thylakoids chloroplasts are sites of
photosynthesis, with carbon fixation taking
place within the stroma also use nitrates from
soil to make ammonia (NH4) for amino acids
stroma thylakoid

granum
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Chloroplasts and Mitochondria
both have own circular DNA, ribosomes, tRNAs, and
internal membranes ribosomes are more similar to
prokaryotic than eukaryotic in size/function both
membrane bound and involved in energy
production/utilization overall size is similar
to prokaryotes (about 2 micron in length)
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Endosymbiont Theory
suggests that an early one cell organism,
protoeukaryotes, developed a sybiotic
relationship with a primative bacteria and
cyanobacteria phagocytosis-- property of
surrounding something (perhaps a nutrient)
within a membrane and pinching it off so it
becomes enclosed algae, diatoms, and others live
symbiotically with at least 150 known species
of invertebrates and protists, some have even
lost their cell walls even though the earliest
life forms are not available for observations,
we can still find evidence for some of their
characteristics today
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Viruses
Obligate cellular parasites-- can't replicate
without cells nucleic acid core (DNA or
RNA) surrounded by a protein coat take over
cellular machinery to reproduce themselves and
eventually kill the host cell
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Viruses
Many viruses cause disease
HIV virus
Ebola virus
Smallpox virus
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Viruses
Tobacco mosaic virus infects plants excellent
model for studying life cycle viruses can be
used for genetic engineering of plants and animals
bacteriophage are viruses that infect
bacteria vital to early molecular biology