chapter 3: cell processes · • every living cell contains a liquid interior (cytoplasm) and is...
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Chapter 3: CELL PROCESSES
(across the cell membrane!)
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Background Info…• Every living cell contains a liquid interior
(cytoplasm) and is surrounded by a liquid.
• The cell (plasma) membrane separates what is inside the cell from what is outside of the cellinside the cell from what is outside of the cell
• What is the MAJOR function of cell membrane?– regulate the movement of molecules from one side of
the membrane to the other.• In other words—control what gets in and what gets out!
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Selectively permeable: • property of biological membranes which
allows some substances to pass more easily than others
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Transport proteins:
• membrane proteins that transport
SPECIFIC molecules or ions across
biological membranes
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GLUCOSE
Binding
TransportRecovery
Dissociation
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Movement across the cell membrane can be:
1) PASSIVE
� cell does not have to spend
energy
� substance moves from where it
is MORE concentrated to where
it is LESS concentrated.it is LESS concentrated.
2) ACTIVE� cell “spends” energy to move a
substance from where it is LESS concentrated to where it is MORE concentrated (“UPHILL”)
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Passive Transport: DIFFUSION
• movement of a substance from
where it is conc. to where it is less
conc. (“down a concentration
gradient”)gradient”)
– continues until equilibrium is reached
– occurs if cell membrane is
permeable to substance and if a
concentration difference exists.
– examples: oxygen (O2) and carbon
dioxide (CO2)
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Passive Transport: OSMOSIS
• diffusion of WATER
across a selectively
permeable membrane;
water moves DOWN its
concentration gradient
• WATER moves from:
hypotonic side (low solute conc.)
to hypertonic side (high solute
conc.)
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INSIDE
THE CELL
OUTSIDE
THE CELL
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– the direction of water movement water
can be described/predicted based on if
the cell’s environment is:
• ISOTONIC: equal solute concentration compared to inside a cell
• HYPERTONIC: greater solute
concentration than inside a cellconcentration than inside a cell
• HYPOTONIC: lower solute concentration compared to inside a cell
WATER MOVES FROM
HYPO TO
HYPERTONIC!!!
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In animal cells:
• in a HYPERTONIC environment,
water exits the cell;
cells shrivel and usually die
• in a HYPOTONIC environment,
water moves into cell,
causing it to swell and
possibly burst
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Passive Transport: FACILITATED DIFFUSION
• diffusion of solutes across a membrane, with the help of transport proteins
(passive transport because it is movement (passive transport because it is movement down a concentration gradient; cell does not need to spend any energy)
• Examples:
-glucose
-amino acids
-some ions
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ACTIVE TRANSPORT: energy-requiring process; molecules are moved across the cell membrane AGAINST their concentration gradient (“uphill”)
•protein “pumps” use energy
from ATP from ATP
Examples:
Na+; K+; H+;
Ca2+;
some sugars;
amino acids
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ACTIVE TRANSPORT: ENDOCYTOSIS & EXOCYTOSIS
• transport of large molecules (e.g. proteinsand polysaccharides) into (“endo”) or out of (“exo”) the cell
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ENDOCYTOSIS EXOCYTOSIS
*importing large
molecules by forming
vesicles out of the cell
membrane
**vesicle forms in a small **vesicle forms in a small
region of cell membrane
***used by cells to bring in
larger, extracellular
substances (e.g. proteins)
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ENDOCYTOSIS EXOCYTOSIS
*exporting large
molecules by vesicles
fusing w / the cell
membrane
**vesicle buds from ER **vesicle buds from ER
or Golgi and migrates to
cell membrane
***used by cells to
export products (e.g.
cells in pancreas
secreting insulin)
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3 types of Endocytosis:
1) Phagocytosis: solid particles (“cell eating”)
2) Pinocytosis: fluid droplets (“cell drinking”)
3) Receptor-Mediated Endocytosis: importing
of specific macromolecules by inward
budding of vesicles formed from COATED
PITS (e.g. cholesterol enters a cell this way)
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Phagocytosis
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Pinocytosis
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Receptor-Mediated Endocytosis