Chapter 5 – Cell Membrane
Vocab
Active transport- requires ATP; the movement of ions or molecules across a cell membrane into
a region of higher concentration, assisted by enzymes and requiring energy.
Allosteric regulation- regulation of the activity of a protein (enzyme) by the binding of an
effector molecule to a site other than the active site
Amphipathic- having both hydrophilic and hydrophobic regions
Aquaporin- a transport protein in plant and animal cell membranes through which water passes
in osmosis
Carrier protein- binds to a specific molecule and transports it through the membrane
Channel protein- proteins that create a tube through the membrane for transporting substances
and particles through the membrane (passive?); integral protein
Concentration gradient- goes from high to low; path of flow
Cytoplasmic receptor- signal receptor is inside the cell, floating in the cytoplasm
Diffusion-random movement of molecules resulting in even distribution of the particles when
no barriers are present; move down the concentration gradient
Endocytosis- process of enveloping a substance into a cell; membrane folds in to create a vesicle
Facilitated diffusion- passive movement through a membrane involving a specific carrier
protein; goes down concentration gradient
Fluid Mosaic Model- a molecular model for the structure of biological membranes consisting of
a fluid phospholipid bilayer in which suspended proteins are free to move in the plane of the
bilayer
G protein- a membrane protein involved in signal transduction; characterized by adding GDP or
GTP
G protein-linked receptor- class of receptors that change configuration upon ligand binding such
that a G protein binding site is exposed on the cytoplasmic domain of the receptor, initiating a
signal transduction pathway.
Gated channel- membrane protein that changes its 3D shape and ion conductance in response to
a stimulus
Glycolipid- sugar chain attached to a lipid in the membrane
Glycoprotein- sugar chain attached to a protein
Hydrophilic domain- water liking
Hydrophobic domain- water disliking/fearing
Hypertonic- greater amount of something (compared to hypotonic)
Hypotonic- lesser amount of something (compared to hypertonic)
Integral protein- inside the lipid bilayer
Ion channel- integral protein that allows ions to diffuse across the membrane in which it is
embedded
Isotonic- having the same solute concentration (between two solutions)
Ligand- any molecule that binds to the receptor site of another (larger) molecule
Membrane receptor- signal receptor floats in or on membrane
Osmosis- diffusion of water
Passive transport- doesn’t require ATP; diffusion
Peripheral protein- floats on surface of lipid bilayer membrane; inside or outside
Phagocytosis- endocytosis of one cell by another or large particle (cell eating)
Pinocytosis- endocytosis by a cell of liquid containing dissolved substances (vesicles)
Primary active transport- ATP is hydrolyzed, yielding the energy required to transport an ion or
molecule against its concentration gradient
Primary messenger- signaling molecule that triggers a receptor
Protein kinase- an enzyme that catalyzes the addition of a phosphate group from ATP to a target
protein
Receptor- a specific molecule binds to it or it can detect a stimulus within the cell or the cell’s
external environment
Receptor mediated endocytosis- initiated by macromolecular binding to a specific membrane
receptor
Secondary messenger- signaling molecule triggered by the primary messenger
Selective permeability- allowing certain substances to pass through while other substances are
excluded; characteristic of membranes
Signal transduction pathway- series of biochemical steps where a stimulus to a cell in translated
into a response of the cell
Signaling cascade- multitude of signals triggered in a series of reactions
Sodium potassium pump- anti-porter responsible for primary active transport; it pumps sodium
ions out of the cell and potassium ions into the cell, both against their concentration gradients
Transmembrane protein- integral protein that spans the phospholipid bilayer
Turgor pressure- amount of pressure/force pushing against the membrane or wall of a cell;
created by presence of too much/sufficient/not enough water inside the cell
Questions:
1. The plasma membrane is made up of a
double layer of phospholipids with proteins
and cholesterol embedded in the
phospholipids. The phospholipids form a
double layer because they have nonpolar
tails that orients away from the polar
molecules that make-up the interior and exterior of the cell. Therefore, the heads will make
up either side of the lipid bilayer with the tails in the middle.
2. Integral proteins extend through at least part of the plasma membrane. They have
hydrophobic and hydrophilic regions. On the other hand, peripheral proteins are not
embedded in the plasma membrane and have polar charged regions that interact with the
integral proteins.
3. Transmembrane proteins extend through the whole lipid bilayer membrane. These
transmembrane proteins have hydrophilic regions at either end of the protein and a
hydrophobic region in the middle. Although both ends of the protein are hydrophilic, each
end must be oriented a certain, non-interchangeable, way to carry out specific function.
4. The cytoskeleton can restrict movement of proteins by attaching itself to proteins in the
membrane. Also, the cytoskeleton helps shape cells.
5. Purpose: to see if the proteins in the mouse and human cell would diffuse when the cells are
fused.
Results: show that the proteins in the membrane diffused quickly.
6. Active transportation requires energy, like ATP, to transfer substances across the plasma
membrane either with or against the concentration gradient.
Passive transport is the transport of molecules and ions without energy. The molecules will
naturally move from higher concentrations to lower ones.
7. Hypertonic: a solution with more solute (less water) concentration than another solution
Isotonic: a solution with the same solute concentration as the solution it’s being compared to
Hypotonic: a solution with less solute (more water) concentration than another solution
Water will generally move from the hypotonic solution to the hypertonic solution
8. Plants have turgor pressure because their cell walls that limit the volume of the cell. This
keeps the cell from bursting. Turgor pressure increases as water enter the plant cell.
Eventually, this pressure between the swelling plasma membrane and the rigid cell wall will
grow so large that the cell cannot take it and will explode. Also, if a significant amount of
water leaves the cell then the turgor pressure will decrease and the plant will wilt.
9. Ligand Gated Ion Channels are channel proteins in the plasma membrane that are “gated”.
They will only open when a stimulus, a ligand, binds to it. One the ligand is bind the pore of
the protein will open and polar substances will diffuses across the membrane. This helps
with homeostasis stabilizing the ions.
10. Voltage-gated channels are similar to LGICs. They are channel proteins in the plasma
membrane that are “gated”. They will only open when a there is a change in voltage,
electrical charge difference, across the membrane. This channel is critical in neurons.
11. Temperature, molecular size, and the concentration gradient determine how fast a molecule
diffuses. For a cell this means that smaller molecules can fit thought more pores and they
have a higher velocity, higher velocity = faster diffusion. As temperature increases so does
velocity. The greater the difference of the concentration gradient, the faster diffusion is.
12. Sugar and amino acids would be moved in and out of the cell by diffusion.
Diffusion occurs when the sugar would move from a higher gradient concentration of sugar
within the cell to a lower concentration outside the cell or vic versa.
13.
14. The cell needs many different ways of transporting materials because the different types of
transportation move different molecules in different ways. For example Active
transportation can move molecules across the concentration gradient, unlike diffusion and
channel proteins. The most specific is active transportation, and the most energy efficient is
diffusion.
15. Phagocytosis: when the plasma membrane extends to engulf large particles.
Pinocytosis: small vesicles bring fluids and dissolved substances into the cell.
Receptor-mediated endocytosis: when receptor cells in coated pits capture specific
macromolecules and set off a cellular response. The coated pit then folds in and forms a
vesicle.
16. There are three steps in cell signaling
Reception: ligand binding to receptor to initiate signaling when the target cell detects the
signal, binds to receptor protein of cell membrane
Transduction: the signal is converted into a cellular response transmitted from the plasma
membrane to the nucleus
Response: the nucleus receives the signal and acts accordingly (it could activation of
specific gene or catalysis by an enzyme)
17. One ligand could amount to a cascade in a cell because it activates many (not just one) other
molecules using signal amplification, which causes rapid production in high levels of the
final product.
18. It is the body’s duty to maintain blood sugar, or blood glucose, within a certain range, so the
body can avoid hypoglycemia, hyperglycemia, and diabetic ketoacidosis. Therefore, the
body has to create hormones to help maintain health blood sugar levels. The beta islet cells
in the pancreas secrete insulin and glucagon to preform this duty. As blood sugar levels rise,
the beta cell islet cells are stimulated to produce insulin. In a similar manner, when blood
sugar levels fall, the pancreas starts producing less insulin. In the presence of insulin, cells
absorb the glucose, sugar, out of the blood, and this has the effect of lowering the blood
sugar to normal levels. The alpha islet cells in the pancreas secrete glucagon to help when
blood sugar levels are low. The glucagon increases blood sugar levels by making the liver
release stored glucose into the blood.
(SEE PACKET FOR INTRO TO WATER POTENTIAL WORKSHEET)