Cell Membrane Transport
Cell
Membrane
l
Also called the plasma membrane
l
Is a semi-permeable lipid bilayer
l
Semi—only some
l
Permeable—passes through
l
Lipid—made of fats
l
Bi—two
l
Layer—flat sheets
Structure
of Cell/Plasma Membrane
l
Composed of two phospholipid layers (bilayer)
l
There are other molecules embedded in the membrane
(proteins, carbohydrates)
l
The fluid mosaic model describes the membrane
Function:
Plasma/Cell Membrane
l
Forms a boundary between inside and outside of the
cell
l
Controls passage of materials include:
l
Water
l
Glucose
l
Nutrients
l
Protects and supports the cell
l
Transmits chemical signals across cell Chemical
signals are transmitted across the cell membrane
l
Receptors bind with ligands and change shape
Characteristics
of Cell/Plasma Membrane
l The cell membrane is selectively
permeable
l Some molecules can cross the
membrane while others cannot
l The cell membrane is a double layer
of membranes of fat that only let certain things get in and out of a cell.
l Also called the “gatekeeper” of the
cell because it does in essence choose what enters or does not
l There are two types of receptors
l Intracellular receptor
l Membrane receptor
Cell
Transport Osmosis and Diffusion
l Materials move across membranes
because of concentration differences/gradient.
l Substances move from high to low
concentration.
Passive
transport does not require energy input from cell.
l Molecules can move across cell
membrane through passive transport.
l There are two types of passive transport:
l Diffusion
l Osmosis
Diffusion
and osmosis are types of passive transport.
l Molecules diffuse down a
concentration gradient.
l From High to Low
Diffusion
l Movement of molecules, other than
water, from an area of HIGH concentration to an area of LOW concentration
l No ATP energy is used.
l Example:
l Spraying air freshener in a room and
eventually smelling it across the other side
l Some molecules cannot easily diffuse
across the cell membrane
l Substances that are not soluble in
lipids, like glucose and amino acids, must have help getting across the
membrane.
l Facilitated diffusion is diffusion
through transport proteins
l Does not require energy
Factor Affect Diffusion
l Size of
the molecules
l Large
molecules do not pass through easily
l Temperature
l The warmer
the water or atmosphere the faster the reaction of diffusion
l Size of
concentration gradient
l The
greater the concentration difference the faster the reaction
Does
diffusion ever stop?
l NO… because particles are in
constant motion
l When the # of particles is equal on
both sides of the membrane then equilibrium is reached
l When particles reach equilibrium the
rate of diffusion is equal across the membrane
Osmosis
l There are three types of solutions:
l Isotonic
l Hypertonic
l Hypotonic
l Osmosis is the diffusion of water
molecules across a semipermeable membrane.
l Water molecules move from high to
low concentration.
l Example:
l Water moving from your small
intestine to the bloodstream
Active
Transport, Endocytosis, and Exocytosis
l Cells also use energy to transport
materials that cannot diffuse across a membrane
l Active Transport requires energy
input from a cell and enables a cell to move a substance against its
concentration gradient.
l Active transport is powered by
chemical energy (ATP)
l Remember:
l Passive transport requires no energy
from the cell
l Active transport occurs through
transport protein pumps.
l Cells use active transport to
maintain homeostasis.
l Two types of Active Transport:
l Endocytosis
l Exocytosis
l A cell can import and export large
materials or large amounts of materials in vesicles during the processes of
Endocytosis and Exocytosis.
Endocytosis
l Process of taking material into the
cell
l Phagocytosis is a type of
Endocytosis.
l Cells require energy to transport
material in endocytosis.
Exocytosis
l Process of expelling materials from
the cell
l Cell requires energy to transport
materials in endocytosis.
Cell Membrane Transport PPT
