Membranes Flashcards
The internal and external environments of a cell are separated by a structure known as the plasma ____
membrane
What are the three molecular components of cellular membranes?
phospholipids
proteins
carbohydrates
The plasma membrane consists of a(n) ___
bilayer.
lipid
The two leaflets of a lipid bilayer are formed because
the polar head groups of phospholipids can interact with the polar interior and exterior of the cell.
Phospholipids have both hydrophobic and hydrophilic components. As such, they are said to be _____
amphipathic
What separates the internal contents of a cell from the extracellular environment?
The plasma membrane
The cell membrane is referred to as a mosaic because it is a mixture of what types of molecules?
proteins
carbohydrates
lipids
The three main types of macromolecules that comprise the plasma membrane are
lipids, proteins, and carbohydrates
Which of the following statements are consistent with the fluid-mosaic model?
- Phospholipids can move within the plane of the membrane.
- While lipids can move within the membrane, all proteins remain anchored in one location within the phospholipid bilayer.
- Membranes are mainly composed of proteins and phospholipids.
- Many membrane proteins move within the plane of the membrane.
Phospholipids can move within the plane of the membrane.
Membranes are mainly composed of proteins and phospholipids.
Many membrane proteins move within the plane of the membrane.
What is the basic structure of the plasma membrane?
a phospholipid bilayer
Cellular membranes are described as fluid because
their lipids and proteins can move relative to each other.
Which of the following statements explain why the phospholipid bilayer is composed of two leaflets?
- Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment.
- Two leaflets result when membrane components secreted from inside the cell match up with membrane components gathered from the environment.
- Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets.
- Phospholipids are amphipathic and must interact with polar and nonpolar environments.
Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment.
Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets.
Phospholipids are amphipathic and must interact with polar and nonpolar environments.
One layer, or half of a phospholipid bilayer, is termed a(n) ___
leaflet
A phospholipid molecule consists of:
a polar head and two nonpolar tails
Because the plasma membrane contains lipids, proteins, and carbohydrates, it is often described as a(n) ___
mosaic
According to the ______ model, membrane proteins and lipids are able to move relative to one another within the plasma membrane.
fluid-mosaic
Some molecules are known to move laterally in the plane of the membrane. As such, we can say the membrane is
fluid
A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ______ membrane protein.
intergral
A lipid bilayer is composed of ______ leaflet(s).
2
Phospholipids have both hydrophobic and hydrophilic components. As such, they are said to be
.
amphipathic
Which of the following statements is correct about a biological membrane that is fluid?
- The composition of the membrane changes over short periods of time.
- The structure of the membrane is solid and rigid but dissolves readily.
- Individual molecules can move within the membrane.
- Individual molecules remain in static locations.
Individual molecules can move within the membrane.
hich of the following statements are consistent with the fluid-mosaic model?
- While lipids can move within the membrane, all proteins remain anchored in one location within the phospholipid bilayer.
- Membranes are mainly composed of proteins and phospholipids.
- Phospholipids can move within the plane of the membrane.
- Many membrane proteins move within the plane of the membrane.
Membranes are mainly composed of proteins and phospholipids.
Phospholipids can move within the plane of the membrane.
Many membrane proteins move within the plane of the membrane.
Most phospholipids move freely within a semifluid membrane
laterally along the plane of the membrane in two dimensions
Which of the following proteins are integral membrane proteins?
- lipid-anchored proteins
- peripheral membrane proteins
- transmembrane proteins
- noncovalent helix proteins
lipid-anchored proteins
transmembrane proteins
What property of biological membranes describes the ability of individual molecules to move within the membrane?
Fluidity
Which of the following movements of a phospholipid are energetically favorable within the bilayer?
- lateral movements
- “flip-flop” transfer between leaflets
- rotational movements
- inversions
lateral movements
rotational movements
The fluidity of the plasma membrane can be increased by incorporating fatty acids with ______ tails or by incorporating ______ lipids.
shorter ; unsaturated
Why is it more appropriate to describe membranes as semifluid?
- Phospholipids spontaneously migrate between leaflets.
- Molecules move laterally within the membrane leaflet.
- Membrane proteins and lipids move freely in three dimensions.
- Phospholipids usually move in two dimensions.
Molecules move laterally within the membrane leaflet.
Phospholipids usually move in two dimensions.
Shorter nonpolar tails make the membrane ______ fluid.
more
A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ______ membrane protein.
integral
At a high temperature, cholesterol makes a membrane ______ fluid.
less
The plasma membrane of a cell is considered to be
selectively permeable.
Movements that keep the phospholipid nonpolar tail within the ___ region of the bilayer are energetically favorable.
hydrophobic
Which of the following changes in lipid composition would be expected to increase the fluidity of a phospholipid bilayer?
- Increasing the length of the fatty acid tails
- Incorporating more cholesterol at low temperatures
- Incorporating more cholesterol at high temperatures
- Incorporating more unsaturated fatty acids
Incorporating more cholesterol at low temperatures
Incorporating more unsaturated fatty acids
What are functions of the selectively permeable plasma membrane?
- provide a barrier that prevents the movement of any molecule into and out of the cell
- maintain a proper supply of essential molecules such as glucose and amino acids
- maintain a proper balance of ions within the cell
- remove waste products from within the cell
maintain a proper supply of essential molecules such as glucose and amino acids
maintain a proper balance of ions within the cell
remove waste products from within the cell
Membrane fluidity is increased when membrane lipids
have shorter nonpolar tails.
elect the true statements comparing simple and facilitated diffusion.
- Facilitated diffusion, but not simple diffusion, requires a transport protein.
- Both simple and facilitated diffusion require concentration gradients.
- Only simple diffusion requires a concentration gradient.
- Facilitated diffusion, but not simple diffusion, requires ATP.
Facilitated diffusion, but not simple diffusion, requires a transport protein.
Both simple and facilitated diffusion require concentration gradients.
How does cholesterol affect the plasma membrane at low temperatures?
It makes the membrane more fluid and prevents freezing.
What types of transport require a transport protein?
Active transport
Facilitated diffusion
All cells are surrounded by a ___ permeable plasma membrane, meaning that the membrane allows the passage of some molecules and ions but not others.
semi
The transport of a substance that requires an input of energy is called ___ transport.
active
Which of the following movements of a phospholipid are energetically favorable within the bilayer?
- inversions
- rotational movements
- lateral movements
- “flip-flop” transfer between leaflets
rotational movements
lateral movements
To move a substance through a membrane against a concentration gradient, which of the following are necessary?
- A transport protein
- A membrane vesicle
- A vacuole
- A source of energy
A transport protein
A source of energy
The selective ___ of the plasma membrane allows the cell to maintain a favorable internal environment.
permeability
A key similarity between simple and facilitated diffusion is that both require
concentration gradients.
Description of Diffusion
Movement of a substance from a region where its concentration is high to a region where its concentration is low
Description of Facilitated Diffusion
Movement of a substance from a region where its concentration is high to a region where its concentration is low through a passageway provided by a transport protein
Description of Active Transport
Movement of a substance from a region where its concentration is low to a region where its concentration is high with the aid of a transport protein and a source of energy
ATP can be used to power which of the following processes? Simple diffusion, facilitated diffusion, or active transport?
Active transport
The difference between passive transport and active transport is that active transport requires
an input of energy.
Phospholipid bilayers are an effective barrier to many charged or polar solutes because of their ___ interior region.
nonpolar
Which type of transport requires a source of energy and a transport protein?
active transport
Small, uncharged molecules pass through the membrane via
passive diffusion.
What are functions of the selectively permeable plasma membrane?
remove waste products from within the cell
maintain a proper balance of ions within the cell
maintain a proper supply of essential molecules such as glucose and amino acids
Select the true statements comparing simple and facilitated diffusion.
- Facilitated diffusion, but not simple diffusion, requires a transport protein.
- Facilitated diffusion, but not simple diffusion, requires ATP.
- Both simple and facilitated diffusion require concentration gradients.
- Only simple diffusion requires a concentration gradient.
Facilitated diffusion, but not simple diffusion, requires a transport protein.
Both simple and facilitated diffusion require concentration gradients.
A term that describes a situation in which the concentration of a solute is higher on one side of a membrane than the other is
transmembrane gradient.
Which of the following could provide energy to fuel active transport?
- a concentration gradient
- carbohydrate
- flippase
- ATP
ATP
A solution in which the solute concentration on both sides of the membrane is equal is classified as
isotonic.
Why is the phospholipid bilayer an effective barrier to hydrophilic or polar molecules?
Because of the hydrophobic interior of the bilayer
What is the solute concentration of a solution relative to the solute concentration inside a cell for the following condition: Isotonic Solution
The solute concentration outside a cell is equal to the solute concentration inside the cell.
What is the solute concentration of a solution relative to the solute concentration inside a cell for the following condition: Hypertonic Solution
The solute concentration outside a cell is higher than the solute concentration inside the cell.
What is the solute concentration of a solution relative to the solute concentration inside a cell for the following condition: Hypotonic Solution
The solute concentration outside the cell is lower than the solute concentration inside the cell.
Which of the following can readily diffuse across the cell membrane?
- Charged molecules
- Gases
- Large molecules
- Ions
- Small, uncharged molecules
Gases
Small, uncharged molecules
The selective ___ of the plasma membrane allows the cell to maintain a favorable internal environment.
permeability
A solution whose solute concentration is higher than the concentration of solutes inside a cell is
hypertonic.
When the concentration of a solute is higher on one side of membrane than the other, a(n) transmembrane ___ is established.
gradient
When the concentrations of dissolved particles (solutes) on both sides of the plasma membrane are equal, the two solutions are said to be
.
isotonic
When the concentration of solutes outside the cell is lower than that intra-cellularly, the solution is said to be ___ relative to the inside of the cell.
hypotonic
Water diffuses through a membrane from a solution that is ___ (lower concentration of dissolved particles) into a solution that is ___ (higher concentration of dissolved particles). Solutions with identical concentrations are said to be ___.
.
hypotonic, hypertonic, isotonic.
Osmosis is the flow of ___ across a membrane.
water
Small, uncharged molecules pass through the membrane via
passive diffusion.
Osmosis describes the movement of water from areas where the solute concentration is __ to areas in which the solute concentration is __.
hypotonic, hypertonic
When the concentration of solutes outside the cell is higher than that intra-cellularly, the solution is said to be ___ relative to the inside of the cell.
hypertonic
A sample of cells is placed in a salt solution. The cells subsequently shrink and the membrane deforms. Relative to the cells, the salt solution is:
hypertonic
A term that describes a situation in which the concentration of a solute is higher on one side of a membrane than the other is
transmembrane gradient.
In ___ solutions, animal cells will take up water. In extreme cases, the cells can rupture in a process called osmotic lysis.
hypotonic
When the solute concentration is higher inside the cell relative to outside the cell, the outside solution is said to be:
hypotonic
What is osmosis?
Diffusion of water from an area of low solute concentration to an area of high solute concentration
In osmosis, water moves from areas of
low solute concentration to areas of high solute concentration.
What categories of proteins assist in the movement of molecules and ions across membranes?
transporters
channels
An animal cell is placed in a hypertonic medium. Predict which way water will move.
Water will move from the inside of the cell to the outside.
An animal cell is placed in pure water (which contains no solutes). In what direction will water move?
Water will move into the cell from the outside.
When the concentration of solutes outside the cell is lower than that intra-cellularly, the solution is said to be ___ relative to the inside of the cell.
hypertonic
Transmembrane proteins called ___ proteins allow ions and hydrophilic molecules to cross the phospholipid bilayer.
transport
Osmosis is the flow of ___ across a membrane.
water
How do transporters differ from channel proteins?
Transporters must change conformation to allow solutes to cross the membrane. Channel proteins typically DO NOT change conformation to allow solutes to cross the membrane.
Proteins that assist in the movement of substances across membranes can be classified into two types based on how they move solutes across a membrane:
transporters and channels
What is the significance of being able to gate a channel protein?
Gating a channel protein allows the cell to regulate the movement of solutes.
A sample of cells is placed in a salt solution. The cells subsequently shrink and the membrane deforms. Relative to the cells, the salt solution is:
hypertonic
What is an aquaporin?
A channel protein for water
In ___ solutions, animal cells will take up water. In extreme cases, the cells can rupture in a process called osmotic lysis.
hypotonic
Transporter proteins transport solutes across the membrane via:
a conformational change triggered by solute binding
What is one way that solutes that cannot diffuse across the membrane can still gain access to the interior of the cell?
transport proteins
Unlike transporters, ___ proteins provide an open passageway all the way across the plasma membrane.
channel
Match the transport dynamics to the type of transporter: A single solute moves in one direction
Uniporter
Match the transport dynamics to the type of transporter: Two solutes moves in one direction
symporter
Match the transport dynamics to the type of transporter: Two solutes moves in opposite directions
antiporter
When channel proteins are ___, it means they can open and close to regulate the movement of ions and molecules across the cell membrane.
gated
A(n) ______ is a special channel protein that allows the facilitated diffusion of water.
aquaporin
Transporter proteins bind their solutes in a hydrophilic pocket and then undergo a(n) ___ change that switches the exposure of the pocket from one side of the membrane to the other.
conformational
Active transport is the movement of a solute across the membrane ___ its concentration gradient.
against
Transmembrane proteins called ___ proteins allow ions and hydrophilic molecules to cross the phospholipid bilayer.
transport
The transportation of a solute against its chemical or electrochemical gradient requires a source of
ATP
Which of the following move solutes in only one direction?
- Antiporters
- Symporters
- Uniporters
Symporters
Uniporters
Which of the following types of transport involves pumping ions against a gradient using ATP as a source of energy?
- transmembrane protein channels
- secondary active transport
- primary active transport
- ligand-gated channels
primary active transport
What is the significance of being able to gate a channel protein?
Gating a channel protein allows the cell to regulate the movement of solutes.
In an H+/sucrose symporter, H+ moves down its electrochemical gradient, which drives the active transport of sucrose. This is an example of what type of transport?
Secondary active transport
What is an aquaporin?
A channel protein for water
___ active transport involves the use of a pre-existing gradient to drive the active transport of another solute.
secondary
Which of the following best describes the process of active transport?
- Particles moving across a membrane without energy expenditure.
- Particles moving across a membrane against a concentration gradient.
- Particles moving freely down a concentration gradient, facilitated by a transmembrane protein.
- Particles moving freely down a concentration gradient.
Particles moving across a membrane against a concentration gradient.
Moving a solute from areas of low concentration to high concentration requires:
an input of energy
___ active transport involves a pump that uses energy from ATP to transport solutes against a gradient.
primary
The H+/sucrose symporter is used to bring both H+ and sucrose into the cell. How are each of the two solutes transported into the cell?
H+ moves down its electrochemical gradient, while sucrose is actively transported.
What type of transport uses a pre-existing gradient to drive the transport of another molecule?
Secondary active transport
