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Cell Structure & Transport
* Flash cards to learn the structure
and function of cell parts.
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*Determined by surface area to volume ratio
*When cell increases in size, the volume increases
faster than the surface area (3:2) so it can’t
move materials in and out fast enough to support
the volume
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* Cells can be modified to increase surface area
* Overall shape—be long rather than round
* Folds (microvilli) in cell membrane
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* Eukaryotic Cells are divided into compartments
* Due to enfolding of membranes which created
membranes such as ER and Golgi Apparatus
* Many enzymes on membrane surfaces
* Different local environments allow for specific
metabolic functions
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* Interdependence within the Cell—all the cell
parts/organelles form a system
* Example: Sunlight passes through cell wall and
cell membrane  sunlight is used by the
chloroplast during photosynthesis to create sugar
 sugar is transported to mitochondria to be
used in cellular respiration to produce ATP
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* Endomembrane System—different membranes
of the cell that regulate protein traffic and
perform metabolic function
* Includes—nuclear envelope, endoplasmic
reticulum, Golgi bodies, lysosomes, vacuoles,
and plasma membrane
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Endomembrane System
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* Serial Endosymbiosis (Margulis)—sequence of
endosymbiotic events
* Endosymbiosis—some organelles were small
prokaryotes living in a larger prokaryotic cells
and became specialized to do their jobs
(mutualism)
* Applies to mitochondria and chloroplasts
* Since not all cells have chloroplasts, it must have
been a series of events.
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* Evidence of Serial Endosymbiosis
* Chloroplasts and mitochondria have their own
DNA and inner membranes—they can make their
own proteins
* Are of similar size to prokaryotic cells
* Replicate by splitting (similar to binary fission)
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* Phospholipids give fluidity
* Molecules contain hydrophilic heads & hydrophobic tails
* Weak interactions occur between tails, but they are not
touching
* Phospholipids line up and form a bilayer
* Phospholipids can switch with neighbor but usually not
across
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*Phospholipids bilayer is affected by:
*Temperature—colder temps = stiffer
*Degree of saturation of the phospholipids
*Unsaturated has more kinks, which
means…
*Cholesterol—generally decreases fluidity
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* Proteins are the mosaic.
* Integral Proteins—proteins that are embedded in the
membrane
* Hydrophilic/hydrophobic portions to keep them in place
* Peripheral Proteins—proteins that are on the inner or
outer surface
* See 1 Page Diagram for Functions!!!!
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* Semi-permeable—some molecules can go through
membrane and others cannot.
* Size determines their ability to move through
* Selective Permeability—some molecules can go
through membrane and others cannot.
* Chemical properties of the molecule determines its
ability to go through.
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* Phospholipid Bilayer
* Hydrophobic molecules are allowed to cross
* i.e. hydrocarbons, oxygen, carbon dioxide
* Polar and ionic molecules cannot cross easily, so they need a
protein to help them through
* i.e. water, sugar, sodium ions…
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* Does not require cell’s energy
* Molecules move down (or with) the
concentration gradient
* Molecules move down electrochemical gradient
* Causes more random distribution
* Moves smaller molecules
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* Diffusion—movement of molecules from high to
low concentration until equilibrium
* Generally how small, non-polar molecules (O2,
CO2,…) go through phospholipid bilayer
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* Facilitated Diffusion
* Movement of molecules from high to low
concentration until equilibrium through transport
proteins
* Channel proteins might be open or gated
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* Osmosis—diffusion of water across a selectively
permeable membrane
* Osmosis occurs from a hypotonic solution to a
hypertonic solution
* Hypertonic—more concentrated/more solutes
* Hypotonic—more watery/less concentrated/less
solutes
* Isotonic—2 solutions of equal concentrations
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* Osmosis continued…
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* Osmosis continued…
* Osmoregulation—how cells maintain water
balance
* Be isotonic
* Pump out excess water
* Paramecium have contractile vacuole
* Cell wall (for plants)
* Turgid—full
* Flaccid—wilt
* Plasmolysis—shrivel and die
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* Uses cell energy
* Moves molecules against the concentration
gradient
* May not stop at equilibrium
* Moves larger/charged/polar molecules
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* Use Transport Proteins (Carrier)
* Example—Sodium-potassium pump uses an
electrogenic pump to generate voltage across the
membrane
* Endocytosis—cell takes in a molecule by
forming new vesicles from the plasma
membrane
* Phagocytosis—”eat”, engulfs a particle
* Pinocytosis—”drink”, extracellular fluid is
brought into cell
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* Exocytosis—cell secretes a molecule by fusing a
vesicle with the membrane and spilling
contents of the vesicle to outside
* Get rid of wastes / secrete hormones / etc
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