Cell Structure and Function

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Cell Structure and Function
Cell Structure and Function
Preview
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Cell characteristics and cell theory
Overview of cell membrane
Eukaryotic cells
Eukaryotic organelles
Prokaryotic cells
How Cells Move
Characteristics of Cells
• Smallest unit of life
• Can survive on its own or has potential to
do so
• Senses and responds to environment
• Has potential to reproduce
• Differ in:
– Size
– Shape
– functions
Cell Theory
1) Every organism is composed of one or
more cells
2) Cell is smallest unit having properties of
life
3) Continuity of life arises from growth and
division of single cells
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Structure of Cells
All cells have three distinct sections:
Plasma Membrane
Nucleus (or nucleoid region in prokaryotes)
Cytoplasm
• Plasma
Membrane
• Nucleus
• Cytoplasm
Cell
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Preview of Cell Membranes
Plasma membranes are composed mostly of
a lipid bilayer that prevents free passage
of water soluble substances across it.
one layer
of lipids
one layer
of lipids
Plasma Membrane
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Other names for a cell membrane:
• Cytoplasmic membrane
• Semipermeable membrane
• Phospholipid bilayer
Eukaryotic Cells
• Have a nucleus
• Have organelles – small, membrane bound
“organs” in the cell that perform a specific
job for the cell.
• Found in the Protista, Fungi, Plant, and
Animal kingdoms
• Have 1000 times more DNA than
prokaryotic cells
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Organelle Functions
 nucleus - controls the cell’s activities
Nuclear membrane – separates cytoplasm from
nuclear material
Nucleolus – site of RNA and ribosome synthesis
DNA – genetic material
 cytoplasm – Space between nucleus and
plasma membrane
 (cytosol) jellylike substance that fills the inside of a
cell , gives structure and shape
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Cont.
 endoplasmic reticulum - "tunnels" in the cytoplasm that
allow materials to move through the cell easier (subway
system of the cell)
Rough (RER) – makes proteins, covered in ribosomes
Smooth (RER) - makes lipids, degrades fats,
detoxifies material
 ribosomes – attached to ER and scattered in cytoplasm,
make proteins
 mitochondrion – powerhouse, produce energy in the cell
 Golgi body - stores, processes, and secretes proteins
and lipids (post office)
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• vesicle- sacs that transport material in cell
• centrioles – centers that produce and
organize structures that help in cell
reproduction (animal cells only)
• lysosome – digest, recycles nutrients
(suicide sack)
• cytoskeleton – structurally supports, gives
shape & helps move cell components
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Quick Check
1. List two parts of the cell theory.
2. Rough endoplasmic reticulum is
responsible for making ___ for the cell.
3. List the four eukaryotic kingdoms
4. Centrioles are only found in ___ cells.
Eukaryotic Animal Cell Structure
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Plant vs. Animal Cell
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Plant Cells Only
• cell wall - rigid surrounding of plant cells,
protects, structural to support
• chloroplasts - contain chlorophyll in plants;
this is where the plant’s food is produced by
photosynthesis
• vacuoles - large bodies in plant cells that
hold water, waste, etc.
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A closer look at major
organelles
A closer look at the nucleus:
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Nuclear Envelope/Membrane
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• Double lipid membrane with pores
• Controls what goes in and out
– Pores control ions & water soluble
materials entrance and exit
• Ribosomes on outer membrane
• Membrane merges with ER
• Nucleoplasm - semifluid interior of nucleus
Nuclear Envelope
Nucleolus
Mass of proteins that codes for
rRNA (ribosomal RNA)
Synthesis of ribosomes and
proteins
Genetic Material (DNA)
• Chromosome – one DNA
molecule and the many proteins
that are associated with it
• Chromatin – total collection of all
DNA molecules and their
associated proteins
• DNA + proteins=
chromatin
Chromatin strands
bunched together=
chromosome
A closer look at ER:
• Endoplasmic reticulum
• A flattened channel that starts at the nuclear
envelope/membrane and folds back and forth
• Two types
Rough (RER)
– Has ribosomes attached
• Makes proteins
Smooth (SER)
– Detoxifies drugs, makes lipids
A closer look at Golgi bodies:
• Vesicles pinch off of ER.
• Fuse with Golgi bodies
• Golgi bodies repackage and ship vesicles by
adding or removing molecules to proteins and
lipids.
• Think post office
and stacks of
pancakes with
syrup!
A closer look at lysosomes:
• membrane-enclosed
vesicles that contain
powerful digestive
enzymes
– internal pH reaches 5.0
• Functions
– digest foreign substances
and recycles own organelles
– Autolysis
– Suicide sac
Tay-Sachs Disorder
• Affects children of eastern European descent
• Genetic disorder caused by absence of single
lysosomal enzyme
– enzyme normally breaks down glycolipid
commonly found in nerve cells
– as glycolipid accumulates, nerve cells lose
functionality
– chromosome testing now available
A closer look at mitochondria:
• Mitochondria resemble bacteria
– Have DNA, ribosomes
– Divide on their own
• May have evolved from ancient bacteria that were engulfed but not
digested
• Mitochondrial DNA (genes) are usually inherited only from the
mother.
Mitochondria (cont.)
• Double outer membrane
• Inner folded membrane
• Site of most of cells ATP
production
• Only in eukaryotic cells
• Site of aerobic
respiration (oxygen
present)
• Numerous in skeletonal
cells
A closer look at chloroplasts (and
other plastids):
• Plastids
• Are organelles that function in
photosynthesis or storage in plants.
• Three types
– Chloroplast
– Chromoplasts
– Amyloplasts
Cont.
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Chloroplast –
• Conduct
photosynthesis
• Enclosed by a double
membrane
• Thylakoid stacks of
grana
– Contain pigments
such as chlorophyll
• Stroma fluid filled area
Other Plastids
• Chromoplasts
– No chlorophyll
– Abundance of carotenoids
– Color fruits and flowers red to yellow
• Amyloplasts
– No pigments
– Store starch (tubers- potatoes)
A closer look at plant cell walls:
• Surrounds the plasma membrane
• Protects, supports and give shape to cell
• Porous – allows water and solutes to pass
in/out
• In all plants
• Some protist and fungi
• Cuticle on outer most surfaces of plants
Even Cells Have a Skeleton
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• Cyto means cell
– So cytoskeleton means cell skeleton
• It is organized system of protein filaments
in the cytoplasm.
• Some are permanent others are temporary
Cytoskeletal Elements
intermediate
filament
microtubule
microfilament
Functions of
Cytoskeletal Elements:
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Move organelles within the cytoplasm
Assist in cell division
Provide structure and support for the cell
Can be used to identify cells
Prokaryotic Cells
DNA is not enclosed in nucleus
Generally the smallest, simplest cells
No organelles
Most ancient form of life
Archaeans and bacteria the only representatives
Prokaryotic means “before the nucleus
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Prokaryotic Cells
 Permeable, semi-rigid cell wall outside plasma
membrane gives shape
 Plasma membrane- semi-permeable to control
what goes in and out
Can contain pigments for photosynthesis
 Polysaccharides are on surface to help them
stick to objects or give a protective coating
 1-2 Flagella – movement
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Prokaryotic Cells
 Pili – helps stick to surfaces and exchange
genetic material
 Cytoplasm – semifluid material inside cell
 Ribosomes – scattered in cytoplasm, protein
making site
 Nucleoid – concentrated region where DNA
is located. DNA is circular.
 Plasmids – scattered in cytoplasm, these
can confer selective advantages such as
antibiotic resistance. Contain just a few
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genes.
Prokaryotic Structure
pilus
cytoplasm
with ribosomes
flagellum
capsule
DNA
cell plasma
wall membrane
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Quick Check
Compare and Contrast Eukaryotic and
Prokaryotic Cells
Prokaryotic cells
Both Prokaryotic
and Eukaryotic
cells
Eukaryotic cells
How Do Cells Move?
• Cells must have ATP in order for
movement to take place.
• Cilia, flagella and false feet are all ways
that cells move.
Cilia, Flagella and False Feet
• Cilia
– many small projections on cell membranes working in
together for movement
– Along trachea, oviducts in humans
• Flagella
– generally 1-2 projections that move an object
– Sperm is the only flagella in humans
• Pseudopodia
– False foot
– Temporary extension of cytoplasm for movement
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• Cilia
• flagella
Protists use all
three.
pseudopodia
Lab Notes
Microscopes
 Lead to the ability to develop the Cell Theory
 Create detailed images of something that is
otherwise too small to see
 Light microscopes
Simple or compound
Uses two sets of lenses to magnify the living or dead
image
 Electron microscopes
Transmission EM or Scanning EM
Uses electrons view either inside or surface of a dead
cell
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New Terms
• Wavelength – distance from the peak
of a wave to the peak of another wave
• Ocular Lens enlarges 10x inside the
eye piece
• Objective lens magnify at various
levels
• Stage supports the object viewed on
slide
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Microscopes
• Create detailed images of something that
is otherwise too small to see
• Light microscopes
– Simple or compound
• Electron microscopes
– Transmission EM or Scanning EM
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Limitations of Light Microscopy
• Wavelengths of light are 400-750 nm
• If a structure is less than one-half of a
wavelength long, it will not be visible
• Light microscopes can resolve objects
down to about 200 nm in size
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Electron Microscopy
• Uses streams of accelerated electrons
rather than light
• Electrons are focused by magnets rather
than glass lenses
• Can resolve structures down to 0.5 nm
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SEM- surface views
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Electron Microscopes
TEM
SEM
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TEM- inside cell view
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Image
comparison
• The electron
microscope allows
a smaller object to
seen
• The electron
microscope is not
limited by the
wavelength of light
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