1.4: Cell Membranes and Diffusion Principles Flashcards
In 1972, the fluid-mosaic model of membrane structure was introduced, which proposes that……
……the membrane is a phospholipid bi-layer in which proteins are either partially or entirely embedded, like tiles in a mosaic picture.
What year was the the fluid-mosaic model of membrane structure introduced?
1972
The fluid-mosaic model of membrane structure proposes that the membrane is a ______ in which proteins are either partially or entirely embedded, like tiles in a mosaic picture.
phospholipid bi-layer
This mosaic pattern of the fluid-mosaic model of membrane structure is not static because the positions of the ___1___ and ___2___ are “___3___” and can move around within the membrane.
- proteins
- phospholipids
- fluid
A membrane has, primarily, two components. What are they?
lipids and proteins
Most of the lipids in the membrane are ___1___ and arrange themselves into a bi-layer with their ___2___ comprising the inner and outer faces of the membrane and their ___3___ facing each other to form the core of the membrane.
- amphipathic phospholipids
- polar (hydrophilic) heads
- non-polar (hydrophobic) tails
Most of the ___1___ in the membrane are amphipathic phospholipids and arrange themselves into a bi-layer with their polar (hydrophilic) heads comprising the ___2___ faces of the membrane and their non-polar (hydrophobic) tails facing ___3___ membrane.
- lipids
- inner & outer
- each other to form the core of the
Hydrophilic means what?
Water loving
_____ means water loving.
Hydrophilic
hydrophobic means what?
water hating.
______ means water hating.
hydrophobic
Polar substances are attracted to what?
Water
______substances are attracted to water.
Polar
Non-polar substances repel what?
Water
______ substances repel water.
Non-polar
The heads of amphipathic phospholipids face out because of their ___1___, while the tails face the inner portion because of how they ___2___.
- attraction to water
- repel water
While the heads of the amphipathic phospholipids of the membrane are arranged in an orderly fashion, the tails are ______.
in constant fluid motion
The movement of the tails allows the lipids to ___1___ and ___2___, but always with the head facing outward and the tail inward.
- rotate
- to move laterally within their layer
The fluidity of the lipids also allows for what?
Protein movement within the membrane structure
Some membranes contain ______ as a stabilizer against heat and cold.
cholesterol
Cholesterol acts as a what when contained in a membrane?
Stabilizer against heat and cold.
Cholesterol is a what?
A steroid lipid, that is largely hydrophobic with a single polar hydroxyl group.
The hydroxyl group in Cholesterol is attracted to the ___1___ of the phospholipids, while the rest of the cholesterol molecule lines up with the ___2___.
- polar heads
- phospholipid tails
The cholesterol molecules act as ___1___ between the tails to reduce solidification during ___2___.
- spacers
- low temperatures
Cholesterol also stabilizes the head during ___1___ by restricting ___2___ as energy is added to the system.
- elevated temperatures
- motion and preventing movement
Proteins are the other major constituent of membranes and include ______, which typically span across the lipid bi-layer.
integral proteins
______are located only on the inner or outer surfaces of the membrane.
Peripheral proteins
Peripheral proteins are located were?
On the inner or outer surfaces of the membrane.
______ are firmly bound within the membrane.
Integral proteins
Integral proteins are bound were?
Firmly bound within the membrane.
______ usually have one or more hydrophobic regions embedded in the core of the lipid bi-layer with hydrophilic regions that extend out of each face.
Integral proteins
Integral proteins usually have one or more ___1___ regions embedded in the core of the lipid bi-layer with ___2___ regions that extend out of each face.
- hydrophobic
- hydrophilic
True or False: Some integral proteins are large enough to weave back and forth through the membrane several times.
True
True or False: Peripheral proteins can not attach to exposed regions of integral proteins.
False. They can
Most membranes (both cell and organelle) are ______ with each face of the bi-layer differing in both lipid and protein content.
asymmetric
The unique arrangement of lipids and proteins in each face is responsible for the ___1___ of the membrane, allowing certain materials to pass in only one direction—___2___ move into the cell and ___3___ move out of the cell.
- selective permeability
- nutrients
- wastes
What are three methods by which particles cross a selectively permeable membrane?
- diffusion
- active transport
- special methods of endocytosis and exocytosis.
What is Diffusion?
Is the first method for particles to be able to cross a cell membrane. Small molecules move from an area of higher concentration on one side of the membrane to an area of lower concentration on the other side. This flow of molecules continues until the molecules are equally distributed (their concentrations are equal) on either side of the membrane. Diffusion occurs naturally as small particles collide with one another, spreading out as they go. Diffusion is also called passive transport because the cell does not need to expend energy in the diffusion process. Think of aromas and perfumes permeating an entire room.
What is it called when when small molecules move from an area of higher concentration on one side of the membrane to an area of lower concentration on the other side.
Diffusion
______is the first method for particles to be able to cross a cell membrane. Small molecules move from an area of higher concentration on one side of the membrane to an area of lower concentration on the other side. This flow of molecules continues until the molecules are equally distributed (their concentrations are equal) on either side of the membrane. Diffusion occurs naturally as small particles collide with one another, spreading out as they go. Diffusion is also called passive transport because the cell does not need to expend energy in the diffusion process. Think of aromas and perfumes permeating an entire room.
Diffusion
In Diffusion when do the flow of molecules stop?
This flow of molecules continues until the molecules are equally distributed (their concentrations are equal) on either side of the membrane.
Diffusion occurs ______ as small particles collide with one another, spreading out as they go.
naturally
Diffusion is also called ______.
passive transport
Why is Diffusion sometimes referred to as Passive Transport?
Because the cell does not need to expend energy in the diffusion process.
True or False: In all types of diffusion particles move naturally from an area of higher concentration to one of lower concentration.
True
What is concentration gradient?
Is a difference in the concentration of a substance from one place to another.
Diffusion is a form of passive transport because……
…… more energy is released than is required.
True or False: Gases disperse unevenly through diffusion.
False. Gases disperse equally through diffusion.
The diffusion of water is called ______.
Osmosis
Osmosis is the diffusion of ______.
Water
What are the three terms often used in biology to describe solute solution?
- isotonic
- hypertonic
- hypotonic
______ refers to having an equal amount of solute on either side of a membrane.
Isotonic
Isotonic refers to……
……having an equal amount of solute on either side of a membrane.
Solute particles can be……..
……sugars, salts, and other substances within an aqueous solution.
Each cell possesses a certain number of ______.
solute particles
Describe what would happen if a blood cell were placed in an isotonic solution.
Some water molecules will randomly move from within the cell outward and some will move from outside the cell inward. However, there will be no net movement of water, and the cell will neither shrink nor swell.
What does “Hyper” mean?
Above
Describe what would happen if a blood cell were placed in a Hypertonic solution.
The cell would lose water and shrink in size. This is because the hypertonic solution contains more solute particles than the cell and, conversely, has a lower water concentration. The movement of water naturally flows from an area of greater concentration (inside the cell) to one of lesser.
In a hypotonic solution, the solute particles outside of a cell are……
……of lesser concentration than inside the cell.
In a ______, the solute particles outside of a cell are of lesser concentration than inside the cell.
hypotonic solution
Describe what would happen if a blood cell were placed in a Hypotonic solution.
Water concentration is greater outside of the cell and naturally causes the water to move inward causing the cell to swell and even burst.
True or False: While small molecules (including gases, water, and glycerol) and lipid-soluble substances (such as hydrocarbons) can diffuse through a membrane relatively unaided, larger lipid-insoluble (polar) molecules, such as sugars and amino acids, cannot.
True
______ is the diffusion of lipid-insoluble molecules across a membrane.
Facilitated diffusion
Facilitated diffusion is……
…… the diffusion of lipid-insoluble molecules across a membrane
To facilitate means ______.
to ease
In Facilitated diffusion a ______ specific for a certain molecule temporarily binds to the molecule and then releases it to the other side.
integral carrier protein
______ occurs when molecules or ions are pumped from an area of lower concentration to one of greater concentration (against the concentration gradient).
Active Transport
Active transport occurs when…….
…… molecules or ions are pumped from an area of lower concentration to one of greater concentration (against the concentration gradient).
Because the molecules do not naturally want to move against the concentration gradient, both ___1___ and ___2___ are required.
- carrier proteins
- additional energy
One example of active transport is the ______, which maintains an electrical imbalance across the membrane.
sodium-potassium pump
One example of active transport is the sodium-potassium pump, which……
…… maintains an electrical imbalance across the membrane.
True or False: Biomacromolecules, such as polysaccharides, proteins, and nucleic acids may be transported across cell membranes by carrier proteins and require no special transport methods.
False. Biomacromolecules, such as polysaccharides, proteins, and nucleic acids, because of their extremely large size, cannot be transported across cell membranes by carrier proteins and require special transport methods.
______ occurs when a biomacromolecule is enclosed inside the membrane of a vesicle (usually formed by breaking off the Golgi complex), which then fuses with the cell membrane ejecting the biomacromolecule from the cell
Exocytosis
Exocytosis occurs when……
……a biomacromolecule is enclosed inside the membrane of a vesicle (usually formed by breaking off the Golgi complex), which then fuses with the cell membrane ejecting the biomacromolecule from the cell
exo- refers to ______
going out
______ can occur between the cell membrane and Golgi complex because both are composed of a phospholipid bi-layer.
Fusion
Fusion can occur between the cell membrane and Golgi complex because both are ______.
composed of a phospholipid bi-layer
______ occurs when a biomacromolecule outside of the cell is enclosed in an invagination of the cell membrane, forming a vesicle inside the cell.
Endocytosis
Endocytosis occurs when……
……a biomacromolecule outside of the cell is enclosed in an invagination of the cell membrane, forming a vesicle inside the cell.
endo- refers to ______.
bringing in
Endocytosis includes what three specialized transportation methods?
- phagocytosis
- pinocytosis
- receptor-mediated endocytosis
______ is endocytosis of extremely large objects, such as other cells. Once the cell is enclosed in a vesicle, it fuses with lysosomes inside the cell and is digested. White blood cells use this to destroy harmful bacteria.
Phagocytosis
Phagocytosis is endocytosis of……
…… extremely large objects, such as other cells. Once the cell is enclosed in a vesicle, it fuses with lysosomes inside the cell and is digested. White blood cells use phagocytosis to destroy harmful bacteria.
______ is endocytosis of tiny droplets of fluids. This process is like phagocytosis except the cell membrane “pinches” inward without needing to extend pseudopods to ingest material.
Pinocytosis
Pinocytosis is endocytosis of……
…… tiny droplets of fluids. This process is like phagocytosis except the cell membrane “pinches” inward without needing to extend pseudopods to ingest material.
True or False: Another role of the proteins in cell membranes is information transfer from one cell to another.
True.
______, Receptor proteins (integral) in a cell membrane bind with a signaling molecule sent from another cell. The signaling molecule (known in general as a ligand) is often in the form of a hormone. The receptor protein is responsible for transferring the signal across the membrane. When the ligand binds to the receptor protein, it changes the shape of the protein. Because the receptor protein is in close proximity to other proteins, their shapes are also affected. This can result in specific enzymes being activated (enzymes are proteins that speed up chemical reactions). These enzymes can catalyze the release of energy from ATP or other high energy molecules which power metabolic and structural changes within the cell.
Receptor-mediated endocytosis
Receptor-mediated endocytosis…….
……Receptor proteins (integral) in a cell membrane bind with a signaling molecule sent from another cell. The signaling molecule (known in general as a ligand) is often in the form of a hormone. The receptor protein is responsible for transferring the signal across the membrane. When the ligand binds to the receptor protein, it changes the shape of the protein. Because the receptor protein is in close proximity to other proteins, their shapes are also affected. This can result in specific enzymes being activated (enzymes are proteins that speed up chemical reactions). These enzymes can catalyze the release of energy from ATP or other high energy molecules which power metabolic and structural changes within the cell.
Endocytosis is often referred to as an ______ because it requires energy.
active process (not to be confused with active transport)
______ is often referred to as an active process (not to be confused with active transport) because it requires energy.
Endocytosis
True or False: It should be noted that the particles within the vesicle do not actually cross the membrane until after fusion with a lysosome.
True
