What do water molecules form around polar substances?
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A shell of hydration.
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What do water molecules form around polar substances?
A shell of hydration.
What were most of the initially discovered ABC transporters in bacteria primarily involved in?
Uptake of nutrients.
What causes the relative impermeability of polar substances, especially ions?
Their association with water molecules.
What triggers voltage-gated channels to open and close?
Changes in membrane potential.
What are the basic structural units of body tissues?
Cells.
Is transport by GLUT1 reversible?
Yes, it is reversible.
What are gated channels?
Ion channels that open and close in response to stimuli.
What does diffusion tend to create in a solution?
A random solution where the concentration is the same everywhere.
What does the Na+/K+ pump maintain in animal cells?
Electrochemical ion gradients.
What are ABC transporters also known as?
ABC-type ATPases.
How many protein domains do ABC transporters typically have?
Four protein domains.
What type of protein is involved in the structure of tissues?
Band 3 protein.
What is the function of the peripheral domains in ABC transporters?
They bind ATP and couple its hydrolysis to transport.
What determines whether active transport is classified as direct or indirect?
The source of energy and whether two solutes are transported at the same time.
What is indirect active transport?
A process that depends on the simultaneous transport of two solutes.
What dictates the direction of transport in GLUT1?
The relative solute concentrations outside and inside the cell.
What are the two components of F-type ATPases?
A transmembrane pore (Fo) and a peripheral membrane component (F1).
What must every cell maintain to function properly?
An electrochemical potential across its plasma membrane.
Why can't most substances in the cell cross membranes by simple diffusion?
They are too large or too polar.
Why are the electrochemical potentials for sodium and potassium important?
They serve as a driving force for coupled transport.
How do the lungs contribute to the respiratory system?
They allow for inhalation and exhalation of air.
What are the two alternative conformational states of the Na+/K+ ATPase?
E1 and E2.
What type of transport involves two solutes moving through a carrier protein?
Co-transport.
What types of substances typically move across cell membranes?
Dissolved gases, ions, and small organic molecules (solutes).
What is the function of the catalytic domain in ABC transporters?
It binds ATP as part of the transport process.
What type of protein is GLUT1?
A carrier protein.
What drives the synthesis of ATP by F-type ATPases?
The exergonic flow of protons down their gradients.
What are the proteins responsible for sodium symport called?
Sodium-dependent glucose transporters (SGLT).
What factors influence the size of the hydration shell?
The charge of the solute and the size of the solute ions.
What drives the uptake of glucose in some cells?
Sodium symport.
What is the term for two solutes moving in the same direction through a carrier protein?
Symport.
What is direct active transport?
The accumulation of solute molecules on one side of the membrane coupled directly to an exergonic chemical reaction.
What type of molecules are lipid bilayers generally more permeable to?
Small molecules like water, oxygen, and carbon dioxide.
What is the process called where molecules move from an area of higher concentration to an area of lower concentration?
Simple diffusion.
What is another key function of active transport?
Removal of wastes.
What is the average volume of the lungs in adults?
Approximately 6 liters.
What type of reaction is involved in primary active transport?
Exergonic chemical reaction.
What type of side chains line the inside of the porin pore?
Polar side chains.
What role do transport proteins play in the movement of small molecules?
They facilitate faster movement of small molecules across the membrane.
What are the two types of transport mechanisms in indirect active transport?
Symport and antiport.
How many subfamilies do P-type ATPases fall into?
Five subfamilies.
What is the name of the pump responsible for transporting Na+ and K+ ions?
Na+/K+ ATPase.
What are the characteristics of the two hydrophobic domains in ABC transporters?
They are embedded in the membrane and form a channel.
Where are F-type ATPases found?
In bacteria, mitochondria, and chloroplasts.
What happens to solute concentrations during diffusion?
They become equal.
What is the central feature of porins?
A water-filled pore at its center.
What is facilitated diffusion?
Protein-mediated movement of substances down their concentration gradient.
What are P-type ATPases?
Members of a large family of enzymes that are reversibly phosphorylated by ATP on a specific aspartic acid residue.
What is the role of alveoli in the lungs?
They are the tiny air sacs where gas exchange occurs.
What is required for the pumping of Na+ and K+ ions against their gradients?
Energy.
What ions create the electrochemical potential in animal cells?
Sodium ions.
What happens to the energy state after glucose binding?
It transitions to low energy state.
What is the consequence of glucose being phosphorylated in the cell?
It is effectively locked into the cell.
What type of segments do transport proteins have?
Some hydrophobic segments and transmembrane segments.
How many transmembrane segments does GLUT1 have?
12 transmembrane segments.
What is the effect of a favorable electrochemical potential on energy?
It leads to the release of energy.
What is a key function of many ABC transporters aside from nutrient uptake?
Exporting substances.
What is the function of F-type ATPases in reverse?
They synthesize ATP driven by the exergonic flow of protons down their gradients.
What is one important function of active transport in cells?
Uptake of essential nutrients.
What is the primary function of the lungs?
To facilitate gas exchange, primarily oxygen and carbon dioxide.
What is the effect of charge on solute interaction with water?
Charged solutes attract water molecules, forming a hydration shell.
What is the primary function of active transport?
To move solutes against their concentration gradient using energy.
What are aquaporins?
Transmembrane channels that allow rapid passage of water.
What happens to glucose immediately upon entry into the cell?
It gets phosphorylated.
What determines the movement of a solute across a membrane?
Its concentration gradient or its electrochemical potential.
What structural feature do P-type ATPases have?
Transmembrane segments forming a hydrophilic channel.
What is required for a solute to undergo simple diffusion?
The solute must be small in size and polarity.
What is the function of channel proteins?
To form hydrophilic channels through the membrane, providing a passage route for solutes.
What type of transporter is used by cells lining the intestine to take up glucose?
Na+/glucose symporter.
What is the term for two solutes moving in opposite directions through a carrier protein?
Antiport.
What does ABC stand for in ABC-type ATPases?
ATP Binding Cassette.
What is the process of glucose uptake via sodium symport?
It requires energy and utilizes a steep Na+ gradient.
What lines the channels of aquaporins?
Hydrophilic side chains.
What activates ligand-gated channels?
The binding of certain substances to the channel protein.
What do ion channels contain that facilitates ion passage?
Tiny pores lined with hydrophilic atoms.
What do mechanosensitive channels respond to?
Mechanical forces acting on the membrane.
What is triggered when glucose binds to its binding site?
T2.
What is the glucose concentration like inside most animal cells?
It is kept low.
How does the movement of water across cell membranes compare to expectations?
It is faster than expected given the polarity of the water molecule.
What is a symport mechanism in indirect active transport?
A process where the uptake of substances like sugars and amino acids is coupled with the movement of sodium ions into the cell.
How is the movement of a molecule with no net charge determined?
By its concentration gradient.
What residue is phosphorylated by ATP in P-type ATPases?
A specific aspartic acid residue.
What type of process is facilitated diffusion?
Exergonic process.
Where are P1-ATPases found?
In all organisms.
Is indirect active transport directly powered by ATP hydrolysis?
No, it is not directly powered by ATP hydrolysis.
In what ratio are Cl- and HCO3- ions exchanged?
In a strict 1:1 ratio.
What do channel proteins form to facilitate diffusion?
Hydrophilic transmembrane channels.
What are P4-ATPases also known as?
Flippases.
What is the primary direction of solute movement during diffusion?
Toward regions of lower concentration.
What are the two categories of active transport mechanisms based on energy sources?
Direct and indirect.
What are ATPases called when they function in the reverse direction?
ATP synthases.
How do small molecules move across a membrane without transport proteins?
They move more slowly than in the absence of a membrane.
What does glucose bind to in the demonstration?
Its specific binding site.
What is the structure of the Na+/K+ ATPase?
It comprises a transmembrane protein with two alpha (a) and two beta (b) subunits.
What is the typical ratio of sodium concentration inside to outside a typical animal cell?
Around 0.08:1.
What types of molecules can typically cross a membrane via simple diffusion?
Gases, nonpolar molecules, or small polar molecules like water, glycerol, or ethanol.
How do carrier proteins facilitate diffusion?
By binding solute molecules on one side, undergoing a conformation change, and releasing the solute on the other side.
Why is the concentration of glucose kept low inside the cell?
Due to immediate phosphorylation upon entry.
What is the function of the Erythrocyte Anion Exchange Protein?
Facilitates reciprocal exchange of Cl- and HCO3- ions.
What type of side chains are found on the outside of the porin barrel?
Nonpolar side chains.
What structural change occurs in carrier proteins during transport?
They undergo a conformation change.
Can cells lining the intestine take up glucose when its concentration is lower outside than inside?
Yes, they can.
Why is the charge of solutes relevant to cell function?
It affects the maintenance of the electrochemical potential gradient.
What is the relationship between endergonic and exergonic processes in active transport?
Endergonic transport is coupled with an exergonic process to drive movement against the gradient.
What ions are involved in the inward movement during indirect active transport in animals?
Sodium ions (Na+).
What do aquaporins specifically facilitate?
Faster movement of water molecules.
What can cells and cellular compartments do with substances?
They can accumulate a variety of substances in concentrations different from their surroundings.
What is the structure of aquaporins?
Transmembrane segments oriented to form four central channels.
What is primary active transport usually coupled with?
The hydrolysis of ATP.
What do F-type ATPases transport?
Protons.
What is the typical ratio of potassium concentration inside to outside a typical animal cell?
About 35:1.
What is simple diffusion?
The unassisted net movement of a solute from high to lower concentration.
What do V-type ATPases pump into organelles?
Protons.
What provides the energy needed for glucose uptake via sodium symport?
The steep Na+ gradient.
What binding sites are present on the alpha subunits of the Na+/K+ ATPase?
Binding sites for sodium and ATP on the cytoplasmic side, and for potassium on the external side.
What do the polar side chains in porins allow?
Passage of many hydrophilic solutes.
How does the erythrocyte uptake glucose?
By facilitated diffusion.
What is a symport in the context of indirect active transport?
Transport of two molecules in the same direction.
What do P1-ATPases transport?
Heavy metal ions.
What is a common characteristic of drug-resistant human tumors?
They have high concentrations of the MDR transporter protein.
What is the role of the Na+/K+ pump in animals?
To maintain a high extracellular concentration of sodium ions.
Where does the peripheral component (V1) of V-type ATPases extend?
Juts out from the membrane surface.
What determines the movement of an ion across a membrane?
Its electrochemical potential, which includes both concentration and charge gradients.
What type of carrier is the Erythrocyte Anion Exchange Protein?
An antiport carrier.
What are the three types of channel proteins?
Ion channels, porins, and aquaporins.
In which state is the solute binding site accessible on one side of the membrane?
In one of the two conformational states of the carrier protein.
What are ion channels?
Transmembrane proteins that allow rapid passage of specific ions.
What are transport proteins driven by ATP hydrolysis called?
Transport ATPases or ATPase pumps.
What are porins?
Transmembrane proteins that allow rapid passage of various solutes.
What are transport proteins?
Large, integral membrane proteins with multiple transmembrane segments.
Why do nonpolar substances dissolve readily into the lipid bilayer?
Because they can easily enter the hydrophobic region.
What type of carrier is the glucose transporter?
A uniport carrier.
Which organelles are affected by V-type ATPases?
Vacuoles, vesicles, lysosomes, endosomes, and the Golgi complex.
Which ions require separate channels for transport?
Na+, K+, Ca2+, and Cl-, among others.
What is the role of the MDR transporter protein?
It is associated with multidrug resistance in human tumors.
What ions are primarily used by other cells to maintain electrochemical potential?
Protons.
Why can glucose enter the erythrocyte?
Because the level of blood glucose is much higher than that inside the cell.
Where is the integral component (V0) of V-type ATPases located?
Embedded in the membrane.
What is required for transporting substances against a concentration gradient?
Coupling endergonic transport to an exergonic process, usually ATP hydrolysis.
How does the sodium ion gradient facilitate the uptake of nutrients?
The high extracellular concentration of Na+ drives the uptake of sugars and amino acids.
What is often coupled to the inward transport of molecules in indirect active transport?
Simultaneous inward movement of Na+ (in animals) or protons (in plants, fungi, bacteria).
What needs to be selectively moved across cell membranes?
Specific molecules and ions.
What type of protein is a carrier protein classified as?
An allosteric protein.
How is the Na+ gradient maintained across the plasma membrane?
Via the Na+/K+ pump.
How do water molecules pass through aquaporins?
One at a time.
What type of molecules can pass through the membrane rapidly?
Polar molecules, with some cells having channels for water.
How does secondary active transport function?
Movement of one solute down its gradient drives the movement of another solute up its gradient.
Why are separate channels needed for different ions?
Because most channels allow passage of just one specific ion.
What characteristic does active transport have regarding direction?
Active transport has intrinsic directionality.
Can large nonpolar molecules cross membranes easily?
Yes, examples include estrogen and testosterone.
How do the pores formed by porins compare to ion channels?
They are larger and less specific than ion channels.
What are the two components of V-type ATPases?
An integral component (V0) and a peripheral component (V1).
What process does the Na+/K+ ATPase use to drive the transport of ions?
Exergonic hydrolysis of ATP.
What do the nonpolar side chains in porins interact with?
The hydrophobic interior of the membrane.
What happens to the exchange process if either Cl- or HCO3- is absent?
The exchange will stop.
What type of molecules typically require facilitated diffusion?
Larger polar molecules.
What do the transmembrane segments of GLUT1 form?
A cavity with hydrophilic side chains.
Do P4-ATPases transport molecules all the way across the bilayer?
No, they do not transport them all the way across.
What happens to the solute binding site during the conformational change of a carrier protein?
It shifts from one side of the membrane to the other.
What type of substances are lipid bilayers more permeable to?
Nonpolar substances.
How does active transport contribute to ion concentrations?
It maintains nonequilibrium concentrations of certain ions.
What is the function of the central channels in aquaporins?
To allow water molecules to pass through.
Where are porins found?
In the outer membranes of bacteria, mitochondria, and chloroplasts.
What does the F1 component of F-type ATPases contain?
The ATP binding site.
How does most glucose move into and out of cells?
By facilitated diffusion.
What is active transport?
Protein-mediated movement of substances against a concentration gradient.
What happens to solutes with polarity when crossing the cell membrane?
They pass through more slowly compared to nonpolar substances.
What direction does simple diffusion occur?
From higher concentration to lower concentration.
In which plant cells do aquaporins facilitate rapid water passage?
Root cells and vacuolar membranes.
How does the solute move during facilitated diffusion?
As dictated by its concentration gradient.
What are the four types of transport ATPases identified?
P-type, V-type, F-type, and ABC-type.
What must membranes allow for in relation to ions?
Controlled crossing of ions across the bilayer.
What is the role of transport ATPases?
To facilitate direct active transport across membranes.
What do P4-ATPases transport?
Hydrophobic molecules, such as cholesterol and fatty acids.
Why are ABC transporters medically significant?
They can pump antibiotics or drugs out of cells, making the cells resistant to the drugs.
What is the state of the energy gradient for the protein before glucose binding?
High electrochemical gradient.
What assists substances in moving in and out of cells during facilitated diffusion?
Transport proteins.
In which animal cells do aquaporins facilitate rapid water passage?
Erythrocytes and kidney cells.
What determines the selectivity of ion channels?
Binding sites involving amino acid side chains and a size filter.
What is another name for the Erythrocyte Anion Exchange Protein?
Chloride-bicarbonate exchanger Band 3.
Where is the receptor located for polar solutes that cannot easily pass through the membrane?
In the cytosol.
How do ABC transporters affect tumor growth?
They can render tumor cells resistant to drugs that normally inhibit tumor growth.
What ions do P2-ATPases help maintain gradients for?
Na+, K+, H+, Ca2+.
What roles do P2-ATPases play in eukaryotic cells?
Muscle contraction and acidification of gastric juices.
What ions are involved in the inward movement during indirect active transport in plants, fungi, and bacteria?
Protons.
What effect does phosphorylation have on glucose's ability to bind to the carrier protein?
Once phosphorylated, glucose cannot bind to the carrier protein.
What structure do the transmembrane segments of porins form?
They cross the membrane as beta barrels.
What is an antiport in the context of indirect active transport?
Transport of two molecules in different directions.
What ions are pumped by the Na+/K+ ATPase?
Sodium (Na+) and Potassium (K+).
What does it mean that membranes are selectively permeable?
They allow specific molecules and ions to move in and out of the cell or organelle.
What is the relationship between ATP and the sodium ion gradient?
The pump that maintains the sodium ion gradient is driven by ATP.
What occurs during the exchange of ions by the Erythrocyte Anion Exchange Protein?
One molecule moves in while another moves out.
What ions do most cells continuously pump out?
Sodium ions or protons.
What type of movement does simple or facilitated diffusion involve?
Exergonic movement 'down' the concentration gradient.
How do ions move across the membrane in relation to electrochemical potential?
From high electrochemical potential to low.
What is the function of GLUT1?
It is a glucose transporter that facilitates glucose transport inward.
What other molecules, besides glucose, can be taken up by the Na+/glucose symporter?
Some amino acids.
Why is overcoming the permeability barrier of cell membranes important?
It is crucial for the proper functioning of the cell.
What do channel proteins allow to cross the membrane?
Specific solutes.
What does facilitated diffusion account for?
Movement of molecules down a concentration gradient toward equilibrium.
What drives indirect active transport?
Ion gradients.
What is the sign of the change in free energy (D G) during simple or facilitated diffusion?
Negative.
Which type of cell is an exception to the phosphorylation rule of glucose?
Liver cells.
What do the different types of transport ATPases vary in?
Structure, mechanism, location, and roles.
What type of substance can pass through the GLUT1 transporter?
Polar substances.
What do P3-ATPases of plants and fungi do?
They pump protons out across the plasma membrane, acidifying the external medium.
What is known about P5-ATPases?
They are not well characterized, but some are known to transport cations.
What model describes how carrier proteins function?
The alternating conformation model.
What triggers the release of the solute in carrier proteins?
The shift to the alternate conformation.
