Aida Rogonich
10/04/09
Period 4
Membranes
1. What does selective permeability mean and why is that important to cells?
Selective permeability is when the membrane choses specific substances or
particles that can pass through. For instance, a cracked door may allow a
perfume to leave one room and go into the next, but it won’t allow a snake to go
through because it is too big.
It’s important to cells because it keeps cell particles that may be too big to go
through the membrane, from exiting the cell, and it keeps substance not called
for by the cell, out of the cell, or it allows necessary substances to enter the cell.
2. What is an amphipathic molecule?
An amphipathic molecule is a molecule that has both hydrophilic and
hydrophobic groups.
3. How is the fluidity of a cell’s membrane maintained?
The fluidity of a cell’s membrane is maintained by many things such as
cholesterol amount and temperature. The more cholesterol or sugar there is, the
less fluid the membrane, and the less sugar there is, the more fluid the
membrane. Also, at high temperature’s the membrane’s fluidity is low, and at low
temperature’s, its fluidity is high. These variables help maintain the fluidity.
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4. Label the diagram below – for each structure – briefly list it’s function:
extracellular matrix – it helps cells bond, and regulate’s adhesion, proliferation,
movement and bonding of cells
glycoprotein – act as receptors that bring cell’s and protein together
carbohydrate - store energy/ are energy for cell’s
cholesterol- a component of cell membrane’s protecting the cell wall with its coating
microfilaments – help support cell shape and movement and are part of cell
division
peripheral protein- carriers of nonpolar substances/ particles between membrane’s
integral protein- transporters/channels for transport, receptors, enzyme’s, etc.
glycolipid – provide the cell with energy
cytoskeleton- cell structure and support
5. List the six broad functions of membrane proteins.
-cell to cell recognition
-transport
-intercellular joining
-attachmen to matrix & cytoskeleton
-enzyme activity
-signal transduction
6. How do glycolipids and glycoproteins help in cell to cell recognition?
Glycolipids serve as components of cell to cell recognition as they act as genetic
markers. Genetic markers are genes or DNA sequence which match with another
gene or trait, so glycolipids act as ID markers. Glycoproteins act as receptors as
glycoproteins on one cell bind to the glycoprotein receptors on another.
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7. Why is membrane sidedness an important concept in cell biology?
Membrane sidedness refers to the two sides of the membrane being different,
based on the lipid direction. It’s important because it’s associated with
endocytosis and exocytosis and explains how particles end up on the inside or
outside of a cell with the help of vesicles.
8. What is diffusion and how does a concentration gradient relate to passive
transport?
Diffusion is the process by which molecules move from high to low concentration.
Passive transport is transport of molecular substances across the cell’s
membrane, without use of energy. It relates to concentration gradient because
the gradient allows molucular substances in and out of a cell through the cell’s
membrane. Concentration gradient relates to passive transport because no
energy is required for this movement.
9. Why is free water concentration the “driving” force in osmosis?
Free water concentration is what allows water to move between high
concentration and low concentration. If water is lower on one side than another, it
moves to create equilibrium, therefore dependent on the osmosis.
10. Why is water balance different for cells that have walls as compared to cells
without walls?
It’s different because cells with walls keep the cell strong and keep specific
molecular parts in or out of the cell. Whereas cells without walls have molecular
substances flowing in and out, and water can flow in and burst the cell.
11.
Label the diagram below:
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12. What is the relationship between ion channels, gated channels and facilitated
diffusion.
Ion channels are proteins that control the concentration gradient on plasma
membrane’s, and they open or close. Gated channels are a type of ion channel
which act as receptors. Fascilitated diffusion is passive transport (with help from
transport proteins) of molecules across a membrane, down the concentration
gradient. Gated channels are a type of ion channel, which open or close in order
to determine the concentration gradient of fascilitated diffusion.
13. How is ATP specifically used in active transport?
ATP is used in active transport
Active transport regulate’s cell concentration’s. In order to go against a
concetration gradient, energy is needed. This energy is provided by ATP which is
released during respiration.
14. Define and contrast the following terms: membrane potential, electrochemical
gradient, electrogenic pump and proton pump.
Membrane potential- difference in electrical potential and fluidity of the interior
and exterior of a cell.
Electrochemical gradient- an ions concentration gradient
Electrogenic pump- produces electrical charge across the cell’s membrane
Proton pump- sends ions across the cell’s membrane
The proton pump sends ions across the cell’s membrane, which can create a
concentration gradient of ions, called an electrochemical gradient. This gradient
is dependent on energy, or electrical charge which is produces by the
electrogenic pump. This pump creates an electrical difference between the inside
and outside of the cell, which is referred to as membrane potential.
15. What is cotransport and why is it an advantage in living systems?
Cotransport is passive transport of molecules across a membrane in fixed ratios.
It is an advantage for living systems because it both requires ATP to transport
these molecules, and its extremenly energy efficient because enough energy is
always ready for the system.
16. What is a ligand?
Ligans is a molecule that binds to the receptor site of another molecule.
17. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated
endocytosis.
Phagocytosis- a form of endocytosis in which larger molecules such as bacteria
are surrounded by a vesicle.
Pinocytosis- a form of endocytosis in which liquids are engulfed by a vesicle.
Receptor mediated endocytosis- is when vesicles are created, containing
proteins with receptor sites on them, specific to the molecules being part of the
endocytosis.
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