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CELLS
Basic unit of structure and
function in all living things
Basic building block of life
Smallest unit of life
Few can be seen with
naked eye
Most need microscope to be
seen
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ORGANISM VARIATIONS
Unicellular organisms
Made up of one cell
Examples: amoeba, paramecium
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ORGANISM VARIATION
Multicellular organism
Made up of 2 or more cells
Examples: plants, animals, some
fungus, some protists
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CELL THEORY
Knowledge of cells began with
the invention of the microscope
in the late 1500’s
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CELL THEORY
Robert Hooke (1665) Built and used compound light
microscopes
Looked at cork from the bark of an oak tree under microscope – saw cork had “empty spaces” – reminded him of rooms in a monastery called cells
Coined term “cells” in book Micrographia
We know his cells were not alive but he could see the cell walls of plant cells
He was accepted as the first person to see and identify cells
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CELL THEORY
Anton van Leeuwenhoek (1674)
Saw first living cells
Bacteria, blood, sperm and protists in
water
Could see cells had parts
Made over 500 simple microscopes
A few are still around today
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CELL THEORY
Matthias Schleiden (1838)
Botanist
Proposed that all plants were
composed of cells
Contributions to Phytogenesis
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CELL THEORY
Theodore Schwann (1839)
Zoologist
Proposed that all animals are made of
cells
Microscopic Investigations on the
Accordance in the Structure and Growth of
Plants and Animals
Became known as the Father of Cytology
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CELL THEORY
Rudolf Virchow (1855)
Physician
Proposed that cells arise from pre-
existing cells “Omnis cellula e cellula”
Contradicted spontaneous generation
theory
Idea that nonliving things could give rise to
living things.
Die Cellularpathologie
Founder of cellular pathology
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CELL THEORY
Cell Theory
All living things are made of cells
Cells are the basic unit of structure and
function in all living things
All cells come from pre-existing cells
The combined contributions of these
five scientists led to the development
of the Cell theory
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CELL COMPARISONS
All cells have:
Cell membrane – selective barrier that
contains cytosol and ribosomes
Cytosol – semifluid, jellylike substance
enclosed by cell membrane
Ribosomes – tiny complexes that make
proteins according to instructions from
genes
Chromosomes – carry genes in the
form of DNA
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CELL COMPARISONS
Prokaryotic versus Eukaryotic 1/1
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Bacterium
(colored SEM; magnification 8800x)
CELL COMPARISONS
Prokaryotic cells
No membrane bound organelles
No nucleus
DNA in cytosol; concentrated in area called
nucleoid
10 times smaller than eukaryotic cells
Divide by binary fission, not mitosis
Prokaryotic organisms: all bacteria
Domain Bacteria and Domain Archaea
Kingdoms Eubacteria and Archaebacteria
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PROKARYOTES
Three types of bacteria based on
shape Rod shaped – Bacilli
Sphere shaped – Cocci
Corkscrew shaped – Spirochette or Spirilla
Various metabolism based on
environmental levels of O2 Aerobic – need O2, cannot grow without it
Anaerobic – Poisoned by O2; use ion of NO3- or
SO4- for energy
Facultative – able to use both O2 or ions
depending on environment
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PROKARYOTES
Ecological role
Decomposers
Symbiotic relationships
Can be:
Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
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CELL COMPARISONS
Eukaryotic cells
Membrane bound organelles
True nucleus that contains DNA
10x larger than prokaryotic cells
Divide by mitosis
Eukaryotic organisms: Everything except bacteria
Domain Eukarya
Kingdom Animalia
Kingdom Plantae
Kingdom Fungi
Kingdom Protista
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CELL COMPARISONS Plant cells have structures animal
cells do not have:
Cell wall
Provides structure and protection
Large central vacuole
Supports and gives shape to cell
Site of storage, hydrolysis of macromolecules and
breakdown of waste products
Chloroplasts
Site of photosynthesis
Plasmodesmata
Channels through cell walls that connect the
cytoplasm of adjacent cells
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CELL COMPARISONS
Animal cells have structures
plant cells do not have
Lysosomes
Digestive organelle where macromolecules
are hydrolyzed
Centrosomes with centrioles
Region where the cell’s microtubules are
initiated; contains a pair of centrioles
Flagella
Locomotion organelle present in some
animal cells
May be present in some plant sperm - rare
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CELL SIZE LIMITATIONS
Cell size is limited.
As cell size increases, a cell’s ability to
exchange materials with its
environment becomes limited by the
amount of membrane area that is
available for exchange.
Therefore the ratio of surface area to
volume is critical.
The larger the ratio (the difference)
between the two the better.
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CELL SIZE LIMITATIONS
As a cell (or any other object) increases
in size, its volume grows proportionately
more than its surface area. Area is proportional to linear dimension squared
Volume is proportional to linear dimensions cubed.
A smaller cell has a greater ratio of
surface are to volume Divide surface area by volume – the larger the number the
better!
It is better able to transport materials efficiently
from the membranes of the cell to all interior
regions of the cell.
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CELL SIZE LIMITATIONS
Larger organisms do not generally have larger
cells than smaller organisms – simply more
cells.
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CELL STRUCTURES
Cell Wall
Rigid, stiff barrier surrounding some
cells
Plants, bacteria, fungal, some protists
Made of carbohydrates
Cellulose in plants, peptidoglycogen in
bacteria, chitin in fungus
Supports and protects the cell
Located outside the cell membrane
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CELL STRUCTURES
Cell Membrane
Thin flexible barrier surrounding all
cells
Composed of a phospholipid bilayer
Serves as a selective barrier
Controls what enters and exits the cell
Supports and protects the cell
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CELL STRUCTURES
Cytoplasm
Interior of prokaryotic cell and the
region between the cell membrane and
the nucleus in eukaryotic cells
2 parts
Cytosol
The fluid portion of the cytoplasm
Organelles
Specialized structures in the cytoplasm of cells
that perform specific functions
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NUCLEUS AND ITS PARTS Nucleus
Only found in eukaryotic cells
Largest structure in cell
Usually located near center of cell
Surrounded by nuclear membrane
Double membrane that contains thousands of
pores that allow material to move in and out
Directs most of the cell’s activities
Contains most of the cell’s genetic material
Most contain nucleolus
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Nucleus contains chromosomes
Structures that carry genetic information
Chromatin – combination of proteins and
DNA that makes up chromosomes
Granular material visible within the nucleus
When cells divide, a strand of chromatin
coils up, condenses and becomes a
chromosome
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Nucleus contains nucleolus
Small, dense region inside nucleus
Produces RNA – 3 types
rRNA – actual ribosomes
mRNA – messenger RNA
Messenger of code from nucleus to ribosomes
tRNA – Transfers individual Amino Acid to
ribosome
Uses complementary code of mRNA
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NUCLEUS AND ITS PARTS
ENDOMEMBRANE SYSTEM
Organelles work together to
synthesize proteins and
transport them into membranes,
into organelles, or out of the cell.
Endoplasmic reticulum
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatus
Lysosome
Vacuoles (transport vesicles)
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ORGANELLES
Ribosomes
Very small and abundant
Made of RNA with proteins attached
Carry out protein synthesis
2 kinds
Free ribosomes – freely float in cytosol - make
proteins for the cell that they are in
Attached/ bound ribosomes – attached to
endoplasmic reticulum and make proteins for
transport out of cell
Pancreatic cells excrete the protein insulin to blood
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ORGANELLES
Smooth Endoplasmic Reticulum
No ribosomes attached; looks “smooth”
Internal membrane system
Involved in the synthesis of lipids
Metabolism of carbohydrates
Stores and regulates calcium levels
Breaks down toxic substances
Drugs and poisons
Increase SER, increase tolerance
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ORGANELLES
Rough Endoplasmic Reticulum
Internal membrane system
Ribosomes dotted all over its surface making
it look “rough”
Protein factory
Proteins made on attached ribosomes
Proteins migrate through rough ER
This is where they will fold into 3D shape
Proteins are modified by having carbohydrates attached
Proteins are released from rough ER in transport vesicles
which bud from regions of the rough ER
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ORGANELLES
Rough Endoplasmic Reticulum
Membrane factory
Grows in place by adding membrane
proteins and phospholipids to its own
membrane
Portions of the rough ER can then break
off and go to where additional membrane
is needed
Cell membrane
Other organelles
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ORGANELLES
Transport vesicles
Bud off from endoplasmic
reticulum
Deliver packages (proteins, etc.) to
other areas of the cell (Golgi
apparatus) or to cell membrane for
export
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ORGANELLES 1
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Golgi Apparatus
Stacks of flat membranes
Has two sides – a receiving end and a shipping end
Receiving end receives products from the ER
Shipping end send modified products to other destinations
Contains enzymes that process, package, sort,
and secrete substances produced by the cell Products of the ER, such as proteins, are modified and
stored and then sent to other destinations.
Buds off to form: Secretory vesicles containing proteins to be secreted
Golgi vesicles containing membrane components to fuse with
cell membrane
Vesicles containing digestive enzymes that become lysosomes
ORGANELLES Lysosomes
Made by rough ER and modified in Golgi
apparatus
Membranous sac of hydrolytic enzymes
that an animal cell uses to digest
macromolecules
Filled with proteins (enzymes) that:
Digest macromolecules (food), bacteria and viruses
Break down old organelles for recycling
Tay-Sachs disease Lipid-digesting enzyme in lysosomes is missing or inactive
– brain becomes impaired by accumulation of lipids in the
cells.
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ORGANELLES
Vacuole
Sac like structures filled with liquid
that store food, water, minerals,
enzymes and waste products
In plants only 1 large, centrally located
vacuole
Increase surface area of plant cells
Smaller versions called food vacuoles or
contractile vacuoles on other organisms
Food vacuoles for phagocytosis
Contractile vacuoles in freshwater protists
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ENDOMEMBRANE SYSTEM
Endomembrane system
These organelles work together to
synthesize proteins and transport them
into membranes, into organelles, or out of
the cell.
The membranes of these organelles are
related through direct physical contact or
by tiny vesicles
Endoplasmic reticulum (Rough and Smooth)
Golgi apparatus
Lysosome
Vacuoles (transport vesicles)
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ENDOMEMBRANE SYSTEM Ribosomes on the RER make proteins.
These proteins are destined to leave the cell.
The proteins move into the RER
In the RER the protein folds into its specific shape
The RER modifies the protein
This often means adding carbohydrates to the protein
The proteins leave the RER in vesicles that are like
bubbles that bud off of the RER
The transport vesicles transport the proteins from the
RER to the Golgi apparatus
Here the proteins are further modified, stored and
eventually sent to other locations
More transport vesicles bud off the Golgi and transport
the proteins to the cell membrane to be released from the
cell.
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ORGANELLES
Mitochondria
Site of cellular respirations which
provides chemical energy (ATP) from
food through chemical reactions
Powerhouse of the cell
Has double membrane
Outer layer is smooth
Inner layer has many long folds called
cristae
Increases inner surface area to create more space
for the chemical reactions
Contains its own DNA
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ORGANELLES
Chloroplast
Site of Photosynthesis
Creates food energy from light energy through
chemical reactions
Has double membrane
Only found in plants and some protists
Contains chlorophyll
green pigment that absorbs light energy
Contains its own DNA
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ORGANELLES Peroxisomes
Membranous sacs that contain oxidase
enzymes to detoxify harmful substances in the
liver and kidneys
Enzymes break down various toxins by transferring
hydogen from the toxin to oxygen (O2) creating
hydrogen peroxide (H2O2)
Hydrogen peroxide is toxic but peroxisomes also
contain an enzyme (catalase) that converts H2O2 to
H2O
Lysosomes break down alcohol, Formaldehyde and free
radicals
Free radicals are highly reactive chemicals with unpaired electrons that
can change the structure of proteins and nucleic acids
Normal products of cellular metabolism
If allowed to accumulate can destroy cells
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CYTOSKELETON
Network of structures that support
and protect cell
Made of different types of proteins
3 types
Microtubules
Intermediate filaments
Microfilaments
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CYTOSKELETON
Microtubules
Largest – 25nm
Hollow tubes made of tubulin
Maintain cell shape
Make up cilia and flagella for cell
motility
Chromosomes movement
Organelles movement
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CYTOSKELETON
Microfilaments Smallest – 7 nm
Two strands of actin fibers intertwined Also called actin filaments
Maintain cell shape
Muscle contraction
Cleavage furrow formation during cell
division in animal cells
Cell motility - pseudopodia movement
Cytoplasmic streaming Circular flow of cytoplasm common in large plant
cells, speeds the distribution of materials within
the cell.
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CYTOSKELETON
Intermediate filaments
Intermediate size – 8-12 nm
Thick cables of many keratin fibers
coiled together
Maintain cell shape
Anchorage of nucleus and other
organelles
Formation of nuclear lamina
Lines interior of nucleus and
maintains the shape of the nucleus
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CYTOSKELETON Centrosomes and Centrioles
Centrosome
Region located near the nucleus
Considered a microtubule-organizing
center
Microtubules grow out of the centrosome
Centrioles
Paired organelles found within centrosome
Replicate before animal cell divides
Thought to help with cellular reproduction by
making sure each cell receives a complete set of
chromosomes
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CYTOSKELETON AND MOTILITY
Three types of cell movement:
Cilia
Flagella
Pseudopodia
Functions:
Move cell through environment
Move materials over cell’s surface
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CYTOSKELETON AND MOTILITY
Cilia
Short whip-like extensions on surface of cell
that move substances along the cell surface
Made up of microtubules
Usually occur in large numbers
Example: Line trachea and sweep debris from lungs
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CYTOSKELETON AND MOTILITY
Flagella
Long whip-like extensions on surface of cell
that move the entire cell
Made up of microtubules
Usually only one or a few per cell
Examples: Sperm of animals, algae, some plants
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CYTOSKELETON AND MOTILITY
Pseudopodia
Amoeboid movement
A cell such as an amoeba crawls along a surface
by extending and flowing into cellular
extensions called pseudopodia
Ooze forward and then collect back together, only to
ooze forward again
Uses microfilaments
Examples: amoeba, white blood cells
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CYTOSKELETON AND MOTILITY
Cell motility (movement) also
involves the cytoskeleton
Cilia and flagella are extensions
projecting from some cells that contain
microtubules arranged in a 9+2
pattern
9 sets of microtubules are arranged in a
ring and in the center of the ring are two
single microtubules
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