4-3: Cell Organelles + Features
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Eukaryotic cells have many membrane systems
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Divide cells into compartments that function together
to keep a cell alive
Plasma Membrane
(Factory Doors)
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Location: surrounds the cell + its parts
Functions:
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Controls the ease w/ which substances pass into and
out of the cell - - known as selectively permeable
Separates internal rxns with external environment
Allows the cell to excrete wastes and interact with
environment
Description: made of lipids + proteins
Membrane Lipids
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Major type –
phospholipids
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Hydrophilic (head) –
Hydrophobic (tail)
Forms a lipid bilayer
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Heads outward, tails inward
Contains sterols between
the tails
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Example: Cholesterol
Membrane Proteins
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Function: transporting molecules through
lipid bilayer
Two types:
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Peripheral – located on both interior +
exterior surfaces of C.M.
Integral – embedded into the bilayer
Fluid Mosaic Model
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States that the lipid bilayer behaves like a
fluid, not like a solid
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Membrane proteins + lipids can move laterally
within the bilayer
Watch
Nucleus (Main Office)
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Location: in the cytosol
Size: most prominent structure
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Surrounded by a double membrane called nuclear
envelope
Shape is maintained by skeleton – nuclear matrix
Filled with fluid known as nucleoplasm
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Function: store hereditary information
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Chromatin – combo. of DNA + proteins - - coils up
to chromosomes for cell division
Production of RNA – which directs protein synthesis - leaves through nuclear pores
Nucleolus – synthesis of ribosomes
Mitochondria
(Electricity Generator)
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Location: scattered throughout the cytosol
Size: Relatively large
Function: site of chemical rxns that
transfer nrg from org. compounds to ATP
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Responsible for producing 95% of nrg for a
cell to function
Found in high #s in liver + muscles cells
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Liver cells contain 2500 mitochondria/cell
Mitochondria (cont.)
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Surrounded by 2 membranes
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Outer membrane serves as a boundary between
mitochondria + cytosol
Inner membrane has long folds called cristae, which
increase surface area for chemical rxns to take place
Mitochondria DNA
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Can reproduce own their own
Ancient invasion?
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ENDOSYMBIOSIS
Ribosomes
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Location: scattered throughout the cytosol or
attached to endoplasmic reticulum
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Made in nucleolus, completed in cytoplasm
NOT membrane bound – evolution (prokaryotic cells)
Size: relatively small + most numerous; made of
protein + RNA
Function: Protein synthesis
Endoplasmic Reticulum
(Assembly Line)
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Location: within the cytosol, sometimes
attached to the nucleus
Description: cisternae – membranous
tubes + sacs
Function: Intracellular highway – a path
for molecules to move from one part to
another
Types of ER
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Rough ER – covered with ribosomes
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Produces phospholipids + proteins
Prominent in cells that export large amounts
of proteins from the cell or use in cell
membranes
Smooth ER – no ribosomes
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Synthesis of lipids (cholesterol)
Synthesis of steroids in glands
Regulate calcium levels in muscles
Breakdown toxic substances in liver cells
Golgi Apparatus
(Packaging Center)
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Location: within the cytosol
Appearance: system of membranes; series
of flattened sacs
Function: works with ER to modify
proteins for transport from cell
Vesicles
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Small, spherical sacs
Classified by contents
Lysosomes
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Made by Golgi
Contain digestive enzymes
breakdown proteins, nucleic acids, carbs, fats
 Digests old cells (autolysis) or old organelles
(autophagy)
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**FYI - - involved in embryonic development
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ex. Human hand
Vesicles
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Peroxisomes
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Abundant in liver + kidney cells
Neutralize free radicals (Oxygen ions), detoxify
alcohol + other drugs
 Break down fatty acids for nrg source
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Glyoxysomes
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Found in plant seeds
Help break down fats to supply embryo with
food
Protein Synthesis Pathway
1.
2.
3.
4.
Proteins assembled by ribosomes on
rough ER
Vesicles transport proteins to Golgi
Golgi modifies proteins + packages them
in new vesicles
Vesicles release proteins outside cell
(vesicles remain in cell to be used again)
Cytoskeleton
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Location: within the cytosol
Size: spans the entire length of cell – provides a
framework
Functions:
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Provide structure to maintain shape + size
Participates in movement of organelles in the
cytosol
Components of Cytoskeleton
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Microtubules – hollow tubes
 Extend from a central point
(centrosomes)
 Form spindle fibers during
cell division
Microfilaments – thread-like
strands
 Chains made of actin
molecules
 Cell movement +
contraction of muscle cells
Intermediate filaments –
rods
 Anchor nucleus in place
Cilia + Flagella
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Location: extend from surface of cell
Appearance: hair-like organelles
Function: assist in movement
Cilia – short; present in large
numbers
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Propulsion through water
Ex. Nose + inner ear
Structure of cilia –
cross section
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Flagella – longer; less numerous
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Common for only 1 flagellum to be present
Whips back and forth to propel cell
Ex. E. coli + sperm
Centrioles
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Two short cylinders of microtubules near
nuclear envelope
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Found in animal cells
Organize microtubules during animal cell
division