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Membrane structure and function notes – Ch.7
Development of our current membrane model:
1895: Overton believes membranes are made of ______because substances that dissolve in lipids enter cells faster than those that do not.
1915: Red blood cell membranes are analyzed and found to contain ______and proteins.
1917: Langmuir made artificial membranes of ______in 1 layer that formed on top of water.
Diagram:
Problem: Cells have water on ______sides of the membrane
1925: Gorter and Grendel reasoned that the membrane must have _____ layers. Found that blood cells have enough phospholipid content to allow for 2 layers.
1935: Davson and Danielli proposed ______model of phospholipid bilayer inside “bread” of globular proteins.
Diagram:
1950’s: Supported sandwich model by electron micrographs showing ____ layers in membranes and assumed that the outer proteins stained.
Problems with model:
1. Not all cell membranes stained with 3 layers or looked the same in the electron micrographs.
2. Membrane proteins are not water soluble and they would have to be in this model since they are on the outside.
1972: Singer and Nicolson presented the ____________
model. Supported by ______electron microscopy which can split the membrane in half in the middle.
The fluid mosaic model of the plasma membrane:
The membrane is made of ____ layers of ______. Each phospholipid is
______- it has a hydrophobic end and a hydrophilic end. Its phosphate
“head” is polar and so it is ______and the fatty acid “tails” are
nonpolar and ______. Because the cell membrane is surrounded by
liquids on both sides, it arranges itself with the hydrophobic tails to the ______
and the hydrophilic head to the ______of the cell.
Proteins are also ______and are ______throughout the
membrane. They have their hydrophilic parts toward the ______of the membrane and the hydrophobic areas embedded in the phospholipids.
Diagram:
The membrane is ______which means that its parts can move around. The
lipids and some of the proteins can move ______(side to side) in the
membrane. The lipids seem to drift, but some proteins appear to be ______,
possibly by motor molecules along cytoskeletal fibers. Other proteins don’t ______.
Usually the membrane is quite mobile, like ______. But as the temperature drops,
it can become more ______(like bacon grease). When this happens, the
membrane’s ______(ability to allow substances to pass through it)
changes and its enzyme proteins may ______working.
Different membranes solidify at different ______depending on their
structure. For example, unsaturated tails have ______that make them stay fluid
at lower temperatures because they can’t pack together as tightly. Some plants
______their number of unsaturated tails as winter nears.
______inanimal cell membranes helps it stay more ______in cold temperatures and more stable in warm temperatures.
The inside and outside faces of the plasma membrane will be ______in
its proteins. Composition of the outer face is determined by the ______face of the
vesicles made by the ER and Golgi. It is the ER and Golgi that _________the plasma membrane.
Diagram:
This ____________ between the proteins in the inside and outside layers of the plasma membrane is important because it allows for different functioning inside and outside of the cell.
2 groups of protein types:
1. ______proteins – go into the core of the lipid bilayer.
2. ______proteins – are only on one side of the phospholipid bilayer.
Uses of proteins in the membrane:
1. ______- These integral proteins enable hydrophilic ______
molecules and ______to pass through the membrane. They generally span the entire width of the membrane.
2. ______- Speed up reactions. May be in a certain ______to
catalyze a reaction series. Usually ______, on the inside of the cell membrane.
3. Signal ______- These proteins are called ________________
proteins. Each receptor protein has a shape that fits with a certainchemical
______such as a hormone. When the chemical messenger
attaches it may change the ______of the protein to send the message to the inside of
the cell. Usually peripheral, on the ______of the plasma membrane.
4. ______- The proteins help hold cells together.
5. Cell surface ______- These proteins have ______
(__________polysaccharide chains) attached to them that extend out from the
plasma membrane. The ability of one cell to recognize the type of cell next
to it is called __________ . It is the
differences in thesecarbohydrates that causes ______transplants to be rejected
and causes the different ______types. It is also very important in _______
development, where the identity of one cell helps determine the identities of the new cells that touch it.
Diagram of proteins in the membrane:
Diffusion:
______is the movement of molecules from an area of ______concentration
(where there are lots) to an area of ______concentration (where there are few) due
to the ______movement of molecules.
A ______is where there is a difference in the number of molecules between 2 areas.
When molecules move where there are many to where there are few, they are said to move
______their concentration gradient.
When the molecules are evenly spread out, the system has reached ______.
The molecules are still ______, but there is no net change in concentration.
Diagram:
The cell membrane is said to be ______or
______because it allows certain molecules to move freely across it
but not others.
Permeability of the plasma membrane
__________, ______ molecules such as hydrocarbons (methane,
butane, etc.) can go through the cell membrane easily. So can _____________ and
____________because they are also nonpolar.
However, molecules that are __________such as ______ and
______can not pass through easily. Not allowing water through the membrane could
cause many problems so the cell has a large number of ______, protein
channels for water which allow ______to ______move freely across the cell membrane.
________molecules such as ______and ______can not move through the cell membrane without help.
Diffusion problems
If a substance can go through a membrane, we say the membrane is ______to that substance.
If a substance can NOT go through a membrane, the membrane is ______to that substance.
Ex. 1 - A membrane-bound sac is permeable to substances A and B, but impermeable to substance C. If the sac is filled with water and A, and it is put into a beaker of B and C with water, what will happen to each substance?
____ will leave the sac until it reaches equilibrium.
____ will enter the sac until it reaches equilibrium.
____ will stay outside of the sac only.
Ex. 2 – A sac contains water with 5 g of A and 6 g of B. It is put into a beaker with water and 10 g of C. If the sac is permeable to B and C and impermeable to A, what will happen?
____ will stay in the sac only.
B will ______the sac until it reaches equilibrium – ___ g in each area.
C will ______the sac until there are ___ g of C in and out of the sac.
Osmosis
The diffusion of water across a semipermeable membrane is called ______.
A substance that dissolves in water is called a ______.
When comparing the solute concentration of 2 solutions, the one with the most solutes
is said to be ______and the one with the least solutes is ______
If the solute concentrations are the same, the solutions are ______.
Water molecules move from where they are in ______concentration (the
______solution) to where they are in ______concentration (the
______solution).
Diagram:
The direction of the water movement is determined by the ______solute concentration on both sides of the membrane.
Diagram:
Sample problem: Side 1 of the U-tube below has 3 g/ml of A and 8 g/ml of B. Side 2 has 10 g/ml of A and 1 g/ml of B. The tube is permeable to water and to A, but impermeable to B. What will happen to the concentration of each solution and to the water level in the tube?
Effects of osmosis on cell size
If a cell has no cell ______, the size of the cell will change based on its environment.
Ex. If a blood cell is put into a hypertonic environment, the cell will ______
water by osmosis and ______. If put into a hypotonic environment, it will
______water by osmosis and ______. It may even burst, called ______.
In an isotonic environment it will______size.
Organisms without cell walls that live in hypertonic or hypotonic environments must
have special mechanisms for ______(controlling their water
balance). Paramecium have ______to remove excess water.
In organisms with cell walls, when water enters by osmosis, they build up pressure inside
called ______. This is what gives plant leaves their
firmness. Without enough water, they lose this turgor pressure and become ______(flabby) and wilt.
In a hypertonic environment, their plasma membrane can actually pull away from the cell
wall. This is called ______and can kill the plant cell.
Transport methods
______transport is when there is no ______expended by
the cell to make the molecules move. Always moves molecules from ______to _____ concentration.
Types of passive transport:
1. ______- movement of any molecule from high to low concentration due to random movement of molecules.
2. ______- movement of water molecules through a semipermeable membrane.
3. ______- Diffusion in which proteins in the plasma membrane allow or help molecules to move through the membrane.
a. ______- proteins in the plasma membrane that each allow
a specific type of ion to pass through them from high to low concentration.
The ______of passage can be limited by the number of these ion channels that are available.
Some are ______channels and need a certain stimulus such as a ______
molecule attaching to the channel or an ______stimulus of the cell for them to open or close.
b. ______- proteins that change shape to help the molecules through.
Diagram:
Active transport
Active transport requires ______from the cell because it moves molecules
from an area of ______to an area of ______concentration, ______the concentration gradient.
Diagram:
Energy is usually provided by ______. Sometimes the ATP transfers its energy
by transferring its ______group onto the ______protein. (phosphorylation)
The Na+/K+ pump – an example of active transport
The Na+/K+ pump is used by animal cells to keep the inside of the cell higher in ______and the outside of the cell higher in ______.
Diagram:
To maintain this, the cell must pump _____ out and ____ into the cell by active transport.
How the Na+/K+ pumpworks:
1. First ____ Na+ attach to the transport ______(pump) in the plasma membrane.
2. This stimulates the ______of ATP to ADP.
3. The ______group from ATP attaches to the transport ______and changes
its ______so that the 3 Na+ are ______outside the cell and 2 ____ attach from outside the cell.
4. The attachment of the K+ causes another change in the ______of the pump so
that the ______is released.
5. This again changes the shape of the pump so that the _____ is released to the inside
of the cell and the pump is again shaped to pick up _____ from the ______.
Because all cells have ______numbers of ions and cations across their cell
membranes, they have ______potential energy due to the separation of
charges.
This is called ______and is measured in
______. It is generally ______charged inside the cell.
Diagram:
This creates an ______gradient. Passive transport will try to
move ______into the cell and ______out of the cell because of the relative
negative charge inside the cell. Ions move ______their electrochemical gradient.
A transport pump that causes voltage across a membrane is called an ______
pump. The Na+/K+ pump is an example.
Plants, fungi and bacteria also can store ______in the form of membrane potential.
They use a ______pump which actively transports _____ out of the cell using
energy from ATP to create ______voltage within the cell.
Diagram:
Cotransport: ______is when an ATP driven pump for one substance indirectly helps another substance move by active transport.
Ex. The proton pump of a plant pumps _____ out of the cells into the fluid around them
(______fluid). As the H+ leak back into the cell by diffusion, they
enter through a protein called the ______.
The incoming H+ carry ______in with them.
Diagram:
Transport of large molecules
Very large molecules such as ______or ______can not go through the plasma membrane.
The cell moves them using ______and the plasma membrane.
______is when the cell moves materials out of the cell by a vesicle
containing the material to be removed that ______with the plasma membrane. The vesicle then becomes a part of the plasma membrane.
Diagram:
Exocytosis is used to get rid of ______and by ______cells to
export their products such as ______, chemical signal molecules or the
carbohydrates needed by plants to make their cell ______.
______is when the cell takes in materials by surrounding the material with its cell membrane.
3 kinds of endocytosis:
1. ______- when the cell wraps its pseudopodia around the material
to be taken in and creating a food ______from the plasma membrane.
______fuse with this vacuole to digest the food.
Diagram:
2. ______- The cell takes in droplets of extracellular ______in a way similar to phagocytosis.
3. ______endocytosis – the plasma membrane has special receptor proteins in pits in the plasma membrane. They pick up a specific substance for the cell and help concentrate it for the cell.
Diagram: