4-2: Parts of a Eukaryotic Cell

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Transcript 4-2: Parts of a Eukaryotic Cell

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.
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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