Chapter 5 Flashcards
Structure and Function of Plasma Membranes
active transport
method of transporting material that requires energy
amphiphilic
molecule possessing a polar or charged area and a nonpolar or uncharged area capable of interacting with both hydrophilic and hydrophobic environments
antiporter
transporter that carries two ions or small molecules in different directions
aquaporin
channel protein that allows water through the
membrane at a very high rate
carrier protein
membrane protein that moves a substance
across the plasma membrane by changing its own shape
caveolin
protein that coats the plasma membrane’s
cytoplasmic side and participates in the liquid uptake process by potocytosis
channel protein
membrane protein that allows a substance to pass through its hollow core across the plasma membrane
clathrin
protein that coats the plasma membrane’s inward facing surface and assists in forming specialized structures, like coated pits, for phagocytosis
concentration gradient
area of high concentration
adjacent to an area of low concentration
diffusion
passive transport process of low-molecular
weight material according to its concentration gradient
electrochemical gradient
a combined electrical and
chemical force that produces a gradient
electrogenic pump
pump that creates a charge imbalance
endocytosis
type of active transport that moves substances, including fluids and particles, into a cell
exocytosis
process of passing bulk material out of a cell
facilitated transport
process by which material moves
down a concentration gradient (from high to low
concentration) using integral membrane proteins
fluid mosaic
model describes the plasma membrane’s structure as a mosaic of components including phospholipids, cholesterol, proteins, glycoproteins, and glycolipids (sugar chains attached to proteins or lipids,
respectively), resulting in a fluid character (fluidity)
glycolipid
combination of carbohydrates and lipids
glycoprotein
combination of carbohydrates and proteins
hydrophilic
molecule with the ability to bond with water;
“water-loving”
hydrophobic
molecule that does not have the ability to
bond with water; “water-hating”
hypertonic
situation in which extracellular fluid has a higher osmolarity than the fluid inside the cell, resulting in water moving out of the cell
hypotonic
situation in which extracellular fluid has a lower osmolarity than the fluid inside the cell, resulting in water moving into the cell
integral protein
protein integrated into the membrane structure that interacts extensively with the membrane lipids’ hydrocarbon chains and often spans the membrane
isotonic
situation in which the extracellular fluid has the same osmolarity as the fluid inside the cell, resulting in no net water movement into or out of the cell
osmolarity
total amount of substances dissolved in a specific amount of solution
osmosis transport
passive transport
of water through a semipermeable
membrane according to the water’s concentration gradient across the membrane that results from the
presence of solute that cannot pass through the membrane
passive transport
method of transporting material
through a membrane that does not require energy
peripheral protein
protein at the plasma membrane’s
surface either on its exterior or interior side
pinocytosis
a variation of endocytosis that imports
macromolecules that the cell needs from the extracellular
fluid
plasmolysis
detaching the cell membrane from the cell wall
and constricting the cell membrane when a plant cell is in
a hypertonic solution
potocytosis
variation of pinocytosis that uses a different
coating protein (caveolin) on the plasma membrane’s
cytoplasmic side
primary active transport
active transport that moves ions
or small molecules across a membrane and may create a
difference in charge across that membrane
pump
active transport mechanism that works against
electrochemical gradients
receptor-mediated endocytosis
variation of endocytosis
that involves using specific binding proteins in the
plasma membrane for specific molecules or particles, and
clathrin-coated pits that become clathrin-coated vesicles
secondary active transport
movement of material that results from primary active transport to the electrochemical gradient
selectively permeable
membrane characteristic that allows
some substances through
solute
substance dissolved in a liquid to form a solution
symporter
transporter that carries two different ions or
small molecules, both in the same direction
tonicity
amount of solute in a solution
transport protein
membrane protein that facilitates a
substance’s passage across a membrane by binding it
transporter
specific carrier proteins or pumps that facilitate movement
uniporter
transporter that carries one specific ion or molecule
A doctor injects a patient with what the doctor thinks is an isotonic saline solution. The patient dies, and an autopsy reveals that many red blood cells have been
destroyed. Do you think the solution the doctor injected
was really isotonic?
No, the solution wasn’t isotonic
No, the solution must have been isotonic, as a hypotonic solution would cause water to enter the cells, thereby making them burst
Injecting a potassium solution into a person’s blood is lethal. Capital punishment and euthanasia
utilize this method in their subjects. Why do you think a potassium solution injection is lethal?
Cells typically have a high concentration of potassium, and with injecting this it makes your blood toxic
If the pH outside the cell decreases, would you expect the amount of amino acids transported into the
cell to increase or decrease?
If the pH outside the cell decreases, the transport of amino acids into the cell would increase.
Which plasma membrane component can be either
found on its surface or embedded in the membrane
structure?
protein
Which characteristic of a phospholipid contributes to the fluidity of the membrane?
double bonds in the fatty acid tail
What is the primary function of carbohydrates attached to the exterior of cell membranes?
identification of the cell
A scientist compares the plasma membrane composition of an animal from the Mediterranean coast with one from the Mojave Desert. Which hypothesis is most likely to be correct?
The cells from the Mojave Desert animal will have a higher cholesterol concentration in the plasma membranes.
Water moves via osmosis _________.
from an area with a high concentration of other solutes to a lower one
The principal force driving movement in diffusion is the__________.
concentration gradient
What problem is faced by organisms that live in fresh
water?
Their bodies tend to take in too much water
In which situation would passive transport not use a
transport protein for entry into a cell?
oxygen moving into a cell after oxygen deprivation
Active transport must function continuously because
__________.
diffusion is constantly moving solutes in opposite
directions
How does the sodium-potassium pump make the interior of the cell negatively charged?
by expelling more cations than are taken in
What is the combination of an electrical gradient and a concentration gradient called?
electrochemical gradient
What happens to the membrane of a vesicle after exocytosis?
It fuses with and becomes part of the plasma membrane
Which transport mechanism can bring whole cells into a
cell?
phagocytosis
In what important way does receptor-mediated
endocytosis differ from phagocytosis?
It transports only small amounts of fluid.
Many viruses enter host cells through receptor-mediated
endocytosis. What is an advantage of this entry strategy?
The virus only enters its target host cell type.
Which of the following organelles relies on exocytosis to
complete its function?
Golgi apparatus
Imagine a cell can perform exocytosis, but only minimal
endocytosis. What would happen to the cell?
The plasma membrane would increase in size over
time.
Why is it advantageous for the cell membrane to be fluid
in nature?
The fluid characteristic of the cell membrane allows greater flexibility to the cell than it would if the membrane were rigid. It also allows the motion of membrane components, required for some types of membrane transport.
Why do phospholipids tend to spontaneously orient
themselves into something resembling a membrane?
The hydrophobic, nonpolar regions must align with each other in order for the structure to have minimal potential energy and, consequently, higher stability. The fatty acid tails of the phospholipids cannot mix with water, but the phosphate “head” of the molecule can. Thus, the head orients to water, and the tail to other lipids.
How can a cell use an extracellular peripheral protein as
the receptor to transmit a signal into the cell?
In an extracellular space, the other molecules will be bound with peripheral proteins. Though they do not have a transmembrane domain, peripheral proteins can bind to other molecules.
In order to pass the signal into the cell, they must correlate with integral membrane proteins.
Discuss why the following affect the rate of diffusion:
molecular size, temperature, solution density, and the
distance that must be traveled.
The rate of diffusion is affected by molecular size, temperature, solution density, and the distance molecules must travel, with larger molecules, higher density, and greater distances slowing down diffusion, while higher temperatures speed it up
Why does water move through a membrane?
The water moves through a membrane when it is not in an equilibrium state and when it doesn’t have equal concentrations on each side of the membrane.
Both of the regular intravenous solutions administered
in medicine, normal saline and lactated Ringer’s
solution, are isotonic. Why is this important?
The intravenous solutions ensure the concentration of the solution which will be injected and It also compares it to blood plasma. Additionally, It ensures that there is no change in the size of the cell.
Describe two ways that decreasing temperature would
affect the rate of diffusion of molecules across a cell’s
plasma membrane.
Two ways that decreasing temperature would affect the rate of diffusion of molecules across a cell’s plasma membrane
Decreases the kinetic energy of the molecules in the plasma membrane. Increases the density of the plasma membrane
Due to a decrease in temperature the kinetic energy of the plasma membrane will also be decreased so that the rate of diffusion alters.
A cell develops a mutation in its potassium channels
that prevents the ions from leaving the cell. If the cell’s
aquaporins are still active, what will happen to the cell?
Be sure to describe the tonicity and osmolarity of the
cell.
If the cell’s aquaporins are active then Osmolarity increases inside the cell by creating the hypotonic solution.
Explanation
If the mutation occurs in the potassium channel, accumulation of the potassium ions occurs that is pumped into the cell due to this osmolarity increases inside the cell by creating the hypotonic solution.
As plasma membrane is selectively permeable to water so that water will flow into the cell by the aquaporins, If the concentration of potassium is high, then enough water will flow into the cell to lyse it.
How an extracellular solution develops changes in a cell volume by affecting the osmosis is described by the tonicity whereas the total solute concentration of the solution is described by the osmolarity.
Where does the cell get energy for active transport
processes?
The cell uses energy stored in it in the form of ATP (adenosine triphosphate).
How does the sodium-potassium pump contribute to
the net negative charge of the interior of the cell?
The sodium-potassium pump contributes to the net negative charge inside the cell by the electrochemical gradient.
Explanation
The concentration gradient of sodium in the cell tends to move into the cell and the electrical gradient of Na+ moves it inside to the negative charge but this situation is different for other elements like potassium in this situation electrical gradients of the K+ move into the cell but the concentration gradients move K+ outside the cells.
Glucose from digested food enters intestinal epithelial
cells by active transport. Why would intestinal cells use
active transport when most body cells use facilitated
diffusion?
Intestinal cells use active transport because it prevents the backflow of glucose into the gut.
Explanation
When glucose enters the intestinal cells through active transport it prevents the backflow of the glucose into the gut and it also ensures the transportation of the glucose continuously even after the presence of the high level of glucose is in the intestinal cells.
The sodium/calcium exchanger (NCX) transports
sodium into and calcium out of cardiac muscle cells.
Describe why this transporter is classified as secondary
active transport.
When there is a use of energy in transporting the particles then it’s known as active transportation.
Explanation
In the Secondary active transport sodium ions and some other compounds are brought into the cell. Because of the primary active transport process, sodium ion concentrations start building outside of the plasma membrane which creates an electrochemical gradient.
Why is it important that there are different types of proteins in plasma membranes for the transport of materials into and out of a cell?
There are specialized channels that facilitate the passage of materials through the membrane. So to pass all types of materials, the presence of proteins are must, inside and outside of the plasma membrane.
Explanation
The proteins are very useful channels as they work only for a specific ion or material which is required by the cell at a certain moment. If a single channel allows all types of materials through it then it might bring unwanted products into the cell and hinder its functions or damage the cell. Thus the specific proteins allow specific products and this helps in the normal functioning of the cell.
Why do ions have a difficult time getting through
plasma membranes despite their small size?
Ions are charged particles present in a solution. The charge is either positive or negative. As the cell membrane is semipermeable, it doesn’t allow charged, hydrophilic ions to pass through it.
Explanation
As the cell membrane is semipermeable thus it doesn’t allow charged, hydrophilic ions to pass through it. Thus charged ions need special Proteins through which they can pass through and enter cell plasma.
