Topic 2.1: Structure and Function of the Cell Membrane Flashcards
Define Plasma Membrane
Membrane surrounding the cytoplasm that consists of a phospholipid bilayer with embedded proteins; functions to regulate the entrance and exit of molecules to and from the cell.
Define fluid-mosaic model
Model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer.
Define glycolipid
Lipid in plasma membranes that contains an attached carbohydrate chain; assembled in the Golgi apparatus.
Define glycoprotein
Protein in plasma membranes that has an attached carbohydrate chain; assembled in the Golgi apparatus.
Define channel proteins
Protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane.
Define carrier protein
Protein in the plasma membrane that combines with and transports a molecule or ion across the plasma membrane.
Define cell recognition protein
Glycoproteins in the plasma membrane that identify self and help the body defend itself against pathogens.
Define receptor protein
Protein located in the plasma membrane or within the cell; binds to a substance that alters some metabolic aspect of the cell.
Define enzymatic protein
Protein that catalyzes a specific reaction; may be found in the plasma membrane or the cytoplasm of the cell.
Describe the roll of proteins, steroids, and phospholipids in the fluid-mosaic model.
*Phospholipids compose a bilayer that separates the inside from the outside of the cell.
*Steroids in the bilayer regulate the fluidity of the membrane
*Proteins present in the membrane contribute to its structure, the package of molecules across the membrane, signal pathways, cell recognition and enzyme functions.
What is the function of Carbohydrate chains in the plasma membrane?
These are long chains of sugar molecules that are attached to the outside of the plasma membrane. They serve as identification tags, helping cells to recognize each other and interact with one another.
What is the function of Phospholipid bilayer in the plasma membrane?
This is the main structural component of the plasma membrane. It is made up of two layers of phospholipids, which are molecules with a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The phospholipid bilayer forms a barrier that allows only certain molecules to pass through the membrane.
What is the function of Filaments of cytoskeleton in the plasma membrane?
Filaments of cytoskeleton: The cytoskeleton is a network of protein filaments that provides support and shape to the cell. The filaments of the cytoskeleton are also involved in the movement of the cell, including the movement of organelles within the cell and the movement of the cell itself.
What is the function of cholesterol in a plasma membrane?
Cholesterol is a type of lipid (fat) molecule that is found in the plasma membrane. It helps to maintain the fluidity of the membrane, allowing it to remain flexible and responsive to changes in the cell’s environment.
Define selectively permeable
Property of the plasma membrane that allows some substances to pass, but prohibits the movement of others.
Define diffusion
Movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution (equilibrium).
Define solute and solvent
A solute is a substance that is dissolved in a solvent, forming a solution. (salt)
A solvent is a liquid portion of a solution that serves to dissolve a solute. (water)
Define osmosis
Diffusion of water through a selectively permeable membrane.
Define osmotic pressure
Measure of the tendency of water to move across a selectively permeable membrane; visible as an increase in liquid on the side of the membrane with higher solute concentration.
Define isotonic solution
Solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis.
Define hypotonic solution
Solution that contains a lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis.
Define hypertonic solution
Higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis.
Define facilitated transport
Passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a protein carrier.
Define active transport
Use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.
Define sodium transfer pump
Carrier protein in the plasma membrane that moves sodium ions out of, and potassium ions into, cells; important in the function of nerve and muscle cells in animals.
Define exocytosis
Process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle’s contents are released outside the cell.
Define endocytosis
Process by which substances are moved into the cell from the environment; includes phagocytosis, pinocytosis, and receptor-mediated endocytosis.
Define phagocytosis
Process by which cells engulf large substances, forming an intracellular vacuole.
Define pinocytosis
Process by which vesicle formation brings macromolecules into the cell.
Define receptor-mediated endocytosis
Selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane.
Contrast diffusion with facilitated transport
During diffusion, molecules move from an area of high concentration to an area of low concentration. Facilitate transport promotes the movement of these molecules down a concentration gradient across a plasma membrane. Carrier proteins reversibly bind to the molecule and speed up their passage.
Explain the movement of water between hypertonic and hypotonic environments
A hypertonic environment has a lower concentration of water and a higher concentration of solutes than a hypotonic environment. Water will move from the hypotonic environment where it is present at a higher concentration, to the hypertonic environment across a semipermeable membrane by osmosis.
Describe the differences between facilitated and active transport.
Both move molecules across the plasma membrane and require a carrier molecule. Facilitated transport does not require energy, but active transport does. Facilitated transport moves moves items down their concentration gradient, while active transport moves against it.
Discuss the potential benefit of receptor-mediated endocytosis.
Allows the cell to target specific molecules to be brought in by endocytosis, thus increasing efficiency.
What factors influence the rate of diffusion?
Temperature, pressure, electrical currents, and molecular size.
Define tonicity
Tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane.
Define extracellular matric (ECM)
Nonliving substance secreted by some animal cells; is composed of protein and polysaccharides.
Define adhesion junction
Junction between cells in which the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings.
Define tight junction
Junction between cells when adjacent plasma membrane proteins join to form an impermeable barrier.
Define gap junction
Junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass between cells.
Define plasmodesmata
In plants, cytoplasmic connections in the cell wall that connect two adjacent cells.
Describe the molecule complex of an extracellular matrix of an animal cell
*Collagen and elastin fibers provide structure to the ECM
*Fibronectin binds to the integrin in the membrane and can signal the cells cytoskeleton
*Proteoglycans, shaped as bottle brushes, assist in cell signaling by regulating the passage of molecules through the ECM
Explain the differences among the adhesion, tight, and gap junction.
Adhesion junction: mechanically attaches adjacent cells
Tight junction: Connects plasma membranes, creating a tight barrier
Gap junction: allows cells to communicate through channels
Contrast the extracellular matrix with the cell wall of an animal cell with the cell wall of a plant cell
The ECM of an animal cell is a meshwork of proteins and polysaccharides that can vary in amount and flexibility depending on the cell type. The plant cell wall, external to the plasma membrane, is composed of cellulose fibrils and pectin that allows flexibility during growth and eventually hardens into a rigid structure.
Eukaryotic cells contain
a) a nucleus
b) DNA
c) a plasma membrane
d) mitochondria
e) all of the above
E) All of the above
The combination of DNA and protein in the nucleus of a eukaryotic cell is called
a) nucleoplasm
b) plasmids
c) nucleoids
d) chromatin
D) Chromatin
This organelle act as a processing center for vesicles leaving the endoplasmic reticulum
a) perxisome
b) ribosome
c) Golgi apparatus
d) nucleolus
C) Golgi apparatus
This organelle acts as a digestive organelle and may also be used to recycle the internal components of a cell
a) ribosome
b) lysosome
c) peroxisome
d) Golgi apparatus
B) lysosome
The mitochondria of a eukaryotic cell is the site of
a) photosynthesis
b) fatty acid metabolism
c) cellular respiration
d) protein synthesis
c) cellular respiration
In the fluid-mosaic model, the fluid properties are associated with the nature of the _______, and the mosaic pattern is established by the ______.
a) nucleic acids; phospholipids
b) phospholipids; embedded proteins
c) embedded proteins; cholesterol
d) phospholipids; nucleic acid
b) phospholipids; embedded proteins
Which of the following is not a function of proteins present in the plasma membrane?
a) proteins assist the passage of materials into the cell
b) proteins interact with and recognize other cells
c) proteins bind with specific hormones
d) proteins carry out specific metabolic reactions
e) proteins produce lipid molecules
e) proteins produce lipid molecules
The carbohydrate chains projecting from the plasma membrane are involved in
a) adhesion between cells
b) reception of molecules
c) cell-to-cell recognition
d) all of the above
d) all of the above
When a cell is placed in a hypotonic solution,
a) solute exits the cell to equalize the concentration on both sides of the membrane
b) water exits the cell toward the area of lower solute concentration
c) water enters the cell toward the area of higher solute concentration
d) there is no net movement of water or solute
c) water enters the cell toward the area of higher solute concentration
When a cell is placed in a hypertonic solution,
a) solute exits the cell to equalize the concentration on both sides of the membrane
b) water exits the cell toward the area of lower solute concentration
c) water enters the cell toward the area of higher solute concentration
d) there is no net movement of water or solute
c) water enters the cell toward the area of higher solute concentration
Which of the following is incorrect regarding facilitated diffusion?
a) it is a passive process
b) it allows the movement of molecules from areas of low concentration to areas of high concentration
c) it may use either channel or carrier proteins
d) it allows the rapid transport of glucose across the membrane
b) it allows the movement of molecules from areas of low concentration to areas of high concentration
The sodium-potassium pump
a) helps establish an electrochemical gradient across the membrane
b) concentrates sodium on the outside of the membrane
c) uses a carrier protein and chemical energy
d) is present in the plasma membrane
e) all of the above
e) all of the above
Which of the following processes is involved in the bulk transport of molecules out of the cell?
a) phagocytosis
b) pinocytosis
c) receptor-mediated endocytosis
d) exocytosis
e) none of the above
d) exocytosis
Which process uses special proteins on the surface of the membrane to identify specific molecules for transport into the cell
a) phagocytosis
b) pinocytosis
c) receptor-mediated endocytosis
d) exocytosis
c) receptor mediated
The extracellular matrix
a) assists in the movement of substances across the plasma membrane
b) prevents the loss of water when cells are placed in a hypertonic solution
c) has numerous functions that affect the shape and activities of the cell that produced it
d) contains the junctions that sometimes occur between cells
e) all of the above
c) has numerous functions that affect the shape and activities of the cell that produced it
Which of the following junctions allows for cytoplasm- to cytoplasm communication between cells?
a) adhesion junctions
b) tight junctions
c) gap junctions
d) none of the above
c) gap junctions
When a signal molecule such as a growth hormone bincds to a receptor protein in the plasma membrane, it stays on the outside of the cell. How might the inside of the cell know that the signal has bound?