Transcript Cell Membrane Cellular Transport

Cell Membranes
Standard Set 1 – Cell Biology 1c, 1e, 1a
Two Major Groups of Cells:
Prokaryotic Cells Pro (before) karyotic (nucleus)
• No nucleus
• No membranebound organelles
• Most 1-10 microns
in size
• Evolved 3.5 billion
years ago
• Only bacteria
Two Major Groups of Cells:
Eukaryotic Cells Eu (true) karyotic (nucleus)
• Nucleus
• Many organelles
• From 100-1,000
microns in size
• Evolved 1.5
billion years
ago
• All other cells
An Internal Membrane System
Processes Proteins
• Proteins are made by
• Some vesicles release their
ribosomes on the
proteins from the cell.
rough ER.
• Other vesicles remain in the
• Vesicles carry proteins
cell and become lysosomes.
from the rough ER to
the Golgi apparatus.
• Proteins are modified
in the Golgi apparatus
and enter new
vesicles.
Understanding the Processing of Proteins
• In the library (ER) students
• Other folders (vesicles)
(ribosomes) produce
remain in the school
homework (proteins).
(cell).
• Backpacks (vesicles) carry the
homework (proteins) from the
library (ER) to the teacher
(Golgi apparatus).
• The teacher (Golgi apparatus)
grades (modifies) the
homework (proteins), which
enters folders (new vesicles).
• Some folders (vesicles) release
their homework (proteins)
from the school (cell).
Now….PLASMA MEMBRANE
• Functions:
– Helps cells maintain balance (homeostasis)
– Provides flexible boundary between cell and
environment
– Controls flow of nutrients (glucose, amino
acids, and lipids)
• If cell needs more, nutrients OR ions flow in
• If too much, nutrients OR ions flow out
PLASMA MEMBRANE
• Selective Permeability
– A process in which plasma membrane allows
some molecules to pass in while keeping others
out.
• Ex: Window Screen
– Water: in and out freely
– Sodium & Calcium ions: only at certain times,
at certain amounts, through certain channels
PLASMA MEMBRANE
Plasma
Membrane
Oxygen
Amino Acids
Water
Glucose
Wastes
Carbon Dioxide
Wastes
Cell Membranes Provide a Barrier
that separates the inside of a cell from the
outside of a cell.
• Cell membranes are not rigid,
instead, they are fluid like a
soap bubble.
• Lipids create the fluid
foundation of membranes by
forming a “lipid bilayer”.
• Cell membranes are
selectively permeable,
allowing only certain
substances to leave and enter
the cell.
PLASMA MEMBRANE
• Fluid Mosaic Model: model of plasma
membrane
– “Fluid”=Phospholipids move within membrane
like water molecules in lake
– Proteins in membrane move along
phospholipids like boats
• Proteins create mosaic pattern on membrane surface
PLASMA MEMBRANE
Phospholipid molecule
Nonpolar
tails (fatty
acids)
Polar head
(includes
phosphate
group)
PLASMA MEMBRANE
• Proteins:
– Recognition Proteins:
• Serve as identification tags and cell surface
attachment sites
• Identifies cells to body’s immune system or blood
type
PLASMA MEMBRANE
• Cholesterol:
– Stabilizes phospholipids by preventing fatty
acid tails from sticking together
Cholesterol
Molecule
Plasma Membranes are made of
Phospholipids
• Phospholipids are fat molecules shaped like a head
with two tails.
• phospholipids have a polar (water loving) region and
a nonpolar (water hating) region.
• phospholipids automatically form a bilayer when in water.
Osmosis is simply the diffusion of water
• Water molecules are
attracted and “stick”
to solute molecules.
• This reduces the
number of water
molecules that can
move freely on that
side.
• Water moves by
osmosis from a
greater to lesser
concentration.
Osmosis creates three different
osmotic conditions …
• Hypotonic: The solute
concentration in the
environment is lower than
in the cell.
• Hypertonic: The solute
concentration in the
environment is higher
than in the cell.
• Isotonic: The solute
concentration in the
environment is equal to
that in the cell.
Examples of Osmosis in Nature ...
• Animal cells burst (lysis) due to pressure on the
plasma membrane when placed in a hypotonic
solution.
• Animals cells shrivel (crenation) when water
leaves the cell while in a hypertonic solution.
Examples of Osmosis in Nature ...
• Plant cells are supported by turgor pressure within the
vacuole when placed in a hypotonic solution.
• Plant cells wilt when water leaves the vacuole due to
plasmolysis when placed in a hypertonic solution.
Types of Cellular Transport
• Passive Transport: does not require energy
to move across the cell membrane
• Active Transport: requires energy to move
across the membrane
Diffusion
• The movement of molecules from a
region of higher concentration to a
region of lower concentration through
a selectively permeable membrane
until an equilibrium is reached.
PLASMA MEMBRANE
• Proteins:
– Transport Proteins:
• Allows needed substances or waste materials to
move through plasma membrane
Facilitated Diffusion
• The movement of specific molecules
from higher to lower concentration
through a membrane by using a
Facilitated Diffusion
channel protein.
Active Transport
Protein Pumps: Protein pumps require energy
(ATP) and channel proteins to move ions (+/charged particles) and large molecules (glucose)
through a membrane against a concentration
gradient.
Example: Sodium-Potassium Pump
Membrane Assisted Transport
• Materials are placed inside of a
membrane bubble called a “vesicle”
• Exocytosis (exit): the dumping of
waste materials outside of the cell
by discharging them from waste
vesicles.
• Endocytosis (taking in): the
engulfing of material by cells
Let’s break it down…
Transport through the Cell Membrane
Type of
Transport
Transport
Protein
Used?
Direction of
Movement
Requires
Energy Input
from Cell?
Classification
of Transport
Simple
Diffusion
No
With
Concentration
Gradient
No
Passive
Facilitated
Diffusion
Yes—channel
proteins or
carrier
proteins
With
concentration
gradient
No
Passive
Active
Transport
Yes—carrier
proteins
(change
shape)
Against
concentration
gradient
Yes
Active
What about osmosis?
• Endocytosis: Cell surrounds and takes in
material from environment
– Material does not pass directly through membrane
– Is engulfed and enclosed by portion of cell’s
plasma membrane
– Portion of membrane breaks away, leaving
vacuole with contents which moves into cell
TRANSPORT OF LARGE PARTICLES
• Exocytosis: Expulsion/Release of large
materials from cell
– Used to excrete wastes
– Also used to secrete hormones produced by cell
The transport of large molecules into a cell is called
what?
The transport of large molecules out of a cell is
called what?
Assessment Quiz
•
•
•
•
Please take out a sheet of paper.
Use a pen.
Give your paper the proper heading.
Number your paper from 1 to 6.
1. What is this process?
• Here water diffuses across selectively permeable
membrane. Notice number of sugar molecules did not
change on each side of membrane but number of water
molecules did. What type of membrane?
• Osmosis: Diffusion of water across a
selectively permeable membrane
– Regulating water flow through the plasma
membrane is important factor in maintaining
homeostasis.
2. What kind of solution is this?
• Concentration of dissolved substances in the
environment is same as concentration of
dissolved substances inside cell.
• Water molecules move into and out of cell
at same rate
• Cells maintain normal shape
isotonic
CELLULAR TRANSPORT:
OSMOSIS
3. What is this process?
• Carrier proteins pick up ions or molecules
near cell membrane and carry them across
membrane releasing them on other side.
• Energy is expended by proteins.
ACTIVE TRANSPORT
• Movement of materials through membrane against
concentration gradient
– From lower concentration to higher
• Requires energy
• Sodium-Potassium Pump:
– Special transport protein in plasma membrane of animal
cells that transports sodium out of the cell and potassium
into the cell against their concentration gradients.
– Ions pumped and generate voltage across membrane
– Allows for body to transmit electrical impulses
4. What is this process called?
• Materials pass through the
plasma membrane with
concentration gradient
• Requires the cell to use no
energy
Simple Diffusion
• Simple Diffusion through
Plasma Membrane with
concentration gradient
• Requires the cell to use no
energy
• Free Movement of particles
across membrane of cell =
passive transport
6. What is this transport process called?
– Transport proteins help materials move through
plasma membrane
– Materials move with the concentration gradient
– No energy is expended by the cell
Facilitated Diffusion
` does water leave a
8. In what kind of solution
cell by osmosis, causing cell to shrink and
lose its water?
Hypertonic
9. What is this process called?
• Cell surrounds and takes in material from
environment
– Material does not pass directly through membrane
– Is engulfed and enclosed by portion of cell’s
plasma membrane
– Portion of membrane breaks away, leaving
vacuole with contents which moves into cell
Endocytosis
10. Please give it a try…
Transport through the Cell Membrane
Type of
Transport
Simple
Diffusion
Facilitated
Diffusion
Active
Transport
Transport
Protein
Used?
Direction of
Movement
Requires
Energy Input
from Cell?
Classification
of Transport
Where does endocytosis fit and where does
exocytosis fit in the sentence below?
Please copy and complete.
• Some unicellular organisms ingest food by
____________and release wastes or cell
products from a vacuole by ___________.