What is required for bulk transport across the plasma membrane?
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Energy.
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What is required for bulk transport across the plasma membrane?
Energy.
Which substance does not cross the membrane freely?
Fructose.
What is a ligand?
Any molecule that binds specifically to a receptor site of another molecule.
How do cell walls help maintain water balance in plant cells?
They provide structural support and prevent excessive water uptake.
What is the role of solute in the context of membrane transport?
Solutes are the substances being transported across the membrane by proteins.
What was observed after 1 hour in the hybrid cell?
Mixed proteins.
What is the primary receptor HIV binds to on immune cells?
CD4.
What is the state of a plant cell in a hypertonic solution?
The cell becomes plasmolyzed.
What happens to K+ during the transport cycle?
K+ is released from the protein.
True or false: Diffusion requires energy.
False.
What triggers vesicle formation in receptor-mediated endocytosis?
Binding of ligands to receptors.
True or false? All transport proteins require ATP.
False.
What role do proteins play in the membrane?
They determine most of the membrane's specific functions.
How do plants utilize cotransport?
Plants use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell.
What are the two main processes of bulk transport across the plasma membrane?
Exocytosis and endocytosis.
How do small molecules and water enter or leave the cell?
Through the lipid bilayer or via transport proteins.
Which substance can cross the membrane freely due to its lipid-soluble nature?
Testosterone.
Is facilitated diffusion an active or passive process?
Passive, because the solute moves down its concentration gradient without requiring energy.
What is the concentration of Na+ in the cytoplasm compared to the extracellular fluid?
Low in the cytoplasm and high in the extracellular fluid.
True or false? Ions easily pass through a membrane.
False.
What is the role of the active site in a bound enzyme?
It interacts with substances in the adjacent solution.
What is cotransport?
Cotransport occurs when active transport of a solute indirectly drives transport of other substances.
What is the role of the co-receptor CCR5 in HIV infection?
HIV must bind to CCR5 along with CD4 to infect a cell.
What does selective permeability in plasma membranes regulate?
The cell's molecular traffic.
What happens to the label on cells at 0 °C?
The label stays on the mouse side.
What role do membrane receptors play in receptor-mediated endocytosis?
They bind to specific substances (ligands) before the substances are transported into the cell.
What do aquaporins facilitate?
The diffusion of water.
What is the concentration of K+ in the cytoplasm compared to the extracellular fluid?
High in the cytoplasm and low in the extracellular fluid.
What is the function of a channel protein?
It is selective for a particular solute.
What happens to an animal cell in a hypotonic solution?
The cell becomes lysed.
At what temperature were the observations made regarding membrane protein movement?
37°C.
What is facilitated diffusion?
A passive transport process aided by transport proteins.
True or false? Gases do not diffuse.
False.
What happens to Na+ after phosphorylation?
Na+ is released outside the cell.
What are the two main types of membrane proteins mentioned?
Carrier proteins and channel proteins.
What does a carrier protein do?
Shuttles a substance from one side to the other by changing shape.
Which type of molecules do not cross the membrane easily?
Hydrophilic molecules, including ions and polar molecules.
What are integrins?
Membrane proteins that are non-covalently bound to microfilaments.
What are two types of junctions involved in intercellular joining?
Gap junctions and tight junctions.
In which direction does water diffuse during osmosis?
From the region of lower solute concentration to the region of higher solute concentration.
What process involves a cell engulfing a particle in a vacuole?
Phagocytosis.
How does cholesterol affect membrane fluidity at cool temperatures?
It maintains fluidity by preventing tight packing.
What is the main electrogenic pump in plants, fungi, and bacteria?
A proton pump.
What is the concentration of potassium ions ([K+]) in the extracellular fluid?
High.
Why is the diffusion of a substance across a biological membrane considered passive transport?
Because no energy is expended by the cell.
What restores the protein's original shape in the transport cycle?
Loss of the phosphate group.
What is the function of carrier proteins?
They undergo a subtle change in shape to translocate the solute-binding site across the membrane.
What types of cells were used in the study of membrane proteins?
Mouse cell, Human cell, and Hybrid cell.
What are the two main components shown in receptor-mediated endocytosis?
A coated pit and a coated vesicle.
What is a bound enzyme?
An enzyme that has its active site exposed to substances in the adjacent solution.
What is the function of ion channels in facilitated diffusion?
They facilitate the diffusion of ions.
What triggers the release of the phosphate group in the protein?
The binding of K+ on the extracellular side.
What does the mixing of bleached and fluorescent membrane proteins indicate?
That at least some membrane proteins move sideways within the plane of the plasma membrane.
True or false? ALL carriers are highly specific to one molecule.
True.
What osmotic problems do hypertonic or hypotonic environments create for organisms?
They create challenges in maintaining water balance.
What is intercellular joining?
The process where membrane proteins of adjacent cells hook together in junctions.
What is the role of the plasma membrane in a cell?
To exchange materials with its surroundings.
What occurs to an animal cell in a hypertonic solution?
The cell becomes shriveled.
What is the primary movement of phospholipids in the plasma membrane?
They can move within the bilayer.
How do individual molecules move during diffusion?
Randomly, but the diffusion of a population may be directional.
What happens to the vacuole after a cell engulfs a particle during phagocytosis?
The vacuole fuses with a lysosome to digest the particle.
What kind of substances are transported during pinocytosis?
Liquid substances and small solutes.
What effect does phosphorylation have on protein shape?
It leads to a change in protein shape, reducing its affinity for Na+.
What complexes are involved in the transport during receptor-mediated endocytosis?
Protein-cholesterol complexes.
What are the two termini of a transmembrane protein?
N-terminus and C-terminus.
What are the receptor proteins in the plasma membrane that ECM proteins bind to?
Integrins.
What type of molecules can dissolve in the lipid bilayer and pass through the membrane rapidly?
Hydrophobic (nonpolar) molecules, such as hydrocarbons.
What shape does the sodium-potassium pump have when it has a high affinity for Na+?
A specific shape that allows Na+ binding.
What role does ATP play in the process described?
ATP provides energy for the proton pump.
What is the difference between unsaturated and saturated hydrocarbon tails?
Unsaturated tails prevent packing, while saturated tails pack together.
What is passive transport?
Diffusion of a substance across a membrane with no energy investment.
What are the main components of membrane models?
Proteins and lipids.
What are carrier proteins?
Transport proteins that have a binding site for specific molecules and change shape to shuttle them across the membrane.
What happens in an isotonic solution?
Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane.
What is the function of the plasma membrane?
It separates the living cell from its surroundings.
What distinguishes receptor-mediated endocytosis from phagocytosis and pinocytosis?
Receptor-mediated endocytosis involves specific binding of a ligand to a membrane receptor before transport, while phagocytosis and pinocytosis do not.
What occurs to the label on cells at 37 °C?
The label moves over the entire cell.
What covers animal cells since they lack cell walls?
An elaborate extracellular matrix (ECM).
What are the main components of the extracellular matrix (ECM)?
Glycoproteins such as collagen, proteoglycans, and fibronectin.
What is osmoregulation?
The control of solute concentrations and water balance.
What are integral proteins?
Proteins that penetrate the hydrophobic core of the membrane.
What is exocytosis?
A process where substances are transported out of the cell.
What organism is hypertonic to its pond water environment?
The protist Paramecium.
What is pinocytosis?
A process where molecules dissolved in droplets are taken up when extracellular fluid is 'gulped' into tiny vesicles.
How are microfilaments associated with integrins?
Microfilaments are non-covalently bound to integrins.
What structure does Paramecium use to manage osmotic pressure?
A contractile vacuole that acts as a pump.
What are the two forces that drive the diffusion of ions across a membrane?
Chemical force (ion's concentration gradient) and electrical force (membrane potential's effect on ion movement).
What is the size of the contractile vacuole in Paramecium?
50 μm.
What cannot pass through the selectively permeable membrane in this scenario?
Sugar molecules.
What is the concentration of sodium ions ([Na+]) in the cytoplasm?
High.
How often does a lipid flip-flop transversely across the membrane?
Approximately once per month.
What kind of substances are transported during phagocytosis?
Large particles, such as bacteria or dead cells.
What does selective permeability mean in the context of the plasma membrane?
It allows some substances to cross it more easily than others.
What type of substances are transported in receptor-mediated endocytosis?
Specific substances known as ligands.
What do some transport proteins do?
They can move solutes against their concentration gradients.
What is a hydrophilic channel protein also known as?
Channel protein.
What is a membrane primarily composed of?
A collage of different proteins embedded in the lipid bilayer.
What is the effect of increased kinetic energy on the plasma membrane?
It results in more molecular movement in the plasma membrane.
What is the affinity of the protein for K+ after phosphorylation?
The new shape has a high affinity for K+.
What are peripheral proteins?
Proteins that are bound to the surface of the membrane.
What is exocytosis?
A process where transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cell.
What property of the plasma membrane is demonstrated by the movement of membrane proteins?
Fluidity of the plasma membrane.
What type of cells commonly use exocytosis?
Secretory cells.
What is the main function of exocytosis in secretory cells?
To export their products.
How does exocytosis differ from phagocytosis?
Exocytosis transports substances out of the cell, while phagocytosis involves engulfing substances into the cell.
How do large molecules, such as polysaccharides and proteins, cross the membrane?
In bulk via vesicles.
What can pass through the pores of a selectively permeable membrane?
Water molecules.
What is the role of cholesterol at moderate temperatures?
It reduces membrane fluidity.
What does H+ carry against its concentration gradient?
Sucrose.
What happens to water molecules in the presence of sugar molecules?
Water molecules cluster around sugar molecules.
What characteristic does the plasma membrane exhibit?
Selective permeability.
How do gases move across the membrane?
By diffusion.
How does temperature affect kinetic energy in cells?
Increased temperature leads to increased kinetic energy.
What are channel proteins?
Transport proteins that have a hydrophilic channel for certain molecules or ions to pass through.
What happens to a receptor when it binds to a chemical messenger?
The protein changes shape.
What is the role of integrins in cells?
To maintain cell shape and stabilize the location of certain membrane proteins.
What characteristic of plasma membranes allows them to control molecular traffic?
Selectively permeable.
What is the condition of a plant cell in a hypotonic solution?
The cell becomes turgid (normal).
What components are asymmetrically distributed in the plasma membrane?
Proteins, lipids, and associated carbohydrates.
How does H+ move in relation to its concentration gradient?
H+ is moving down its concentration gradient passively.
What is the role of collagen in the extracellular matrix?
Collagen provides structural support.
What does the fluid mosaic model describe?
A membrane as a fluid structure with a mosaic of various proteins embedded in it.
What is one type of active transport system?
The sodium-potassium pump.
What characterizes the side of the membrane with more solute molecules?
It has fewer free water molecules.
What occurs after the phosphate group is lost in the protein?
The protein has a lower affinity for K+.
What role do glycoproteins play in cell recognition?
They serve as identification tags recognized by membrane proteins of other cells.
How do channel proteins differ from carrier proteins?
Channel proteins provide a passageway for solutes, while carrier proteins change shape to transport solutes.
What was the main inquiry regarding membrane proteins?
Do membrane proteins move?
What is the effect of unsaturated hydrocarbon tails on packing?
Unsaturated tails prevent packing.
True or false? Pinocytosis takes in pure liquids and not solutes.
False.
What are the two sides of a transmembrane protein?
Extracellular side and cytoplasmic side.
What happens to individuals who lack the CCR5 co-receptor?
HIV cannot enter their cells.
What is the process called when substances move down their concentration gradient?
Diffusion.
What are the most abundant lipids in the plasma membrane?
Phospholipids.
What is the purpose of a receptor changing shape?
To relay the message to the inside of the cell through the signal transduction pathway.
What is ATP's role in cellular processes?
ATP provides energy for active transport and other cellular functions.
What is a hypertonic solution?
A solution where the solute concentration is greater than that inside the cell, causing the cell to lose water.
What happens to a plant cell in an isotonic solution?
The cell is flaccid.
What is the role of the coated pit in pinocytosis?
It helps in the formation of coated vesicles.
What does active transport allow cells to maintain?
Concentration gradients that differ from their surroundings.
What is the size of pinocytotic vesicles mentioned?
0.25 μm.
What is the concentration of potassium ions ([K+]) in the cytoplasm?
Low.
What are some factors that affect membrane fluidity?
Types of lipids and temperature.
Can any molecule diffuse across a membrane?
False. Only certain molecules can diffuse, depending on size and polarity.
What is the significance of carbohydrates in the plasma membrane?
Carbohydrates play a role in cell recognition and signaling.
What is receptor-mediated endocytosis?
A type of endocytosis that involves specific receptors for the uptake of molecules.
What is the affinity of the protein for Na+ after K+ is released?
The affinity for Na+ is high again.
What is active transport?
The process that uses energy to move solutes against their gradients.
What is a gas that can cross the membrane freely?
Oxygen (O2).
What role do channel proteins play in facilitated diffusion?
They provide corridors that allow specific molecules or ions to cross the membrane.
What happens to a plant cell in a hypotonic solution?
It swells until the cell wall opposes further uptake, becoming turgid.
What are gated channels?
Ion channels that open or close in response to a stimulus.
What is the primary function of transport proteins?
They allow passage of hydrophilic substances across the membrane.
What occurs in a hypertonic environment for plant cells?
They lose water, leading to plasmolysis and wilting.
What is the state of an animal cell in an isotonic solution?
The cell is normal.
True or false? Turgor is due to osmosis and not due to a diffusion gradient.
True.
What is an electrogenic pump?
A transport protein that generates voltage across a membrane.
What is diffusion?
The tendency for molecules to spread out evenly into the available space.
What is required for active transport?
Energy, usually in the form of ATP.
What is the concentration of sodium ions ([Na+]) in the extracellular fluid?
Low.
What is one major function of membrane proteins related to moving substances across the membrane?
Transport.
How do most lipids and some proteins move in the plasma membrane?
They drift laterally.
What is diffusion?
The process by which molecules move from an area of higher concentration to an area of lower concentration.
What is facilitated diffusion?
A type of passive transport that uses transport proteins to move molecules across the membrane.
What are transmembrane glycoproteins?
Proteins that span the membrane and have carbohydrate groups attached.
How does active transport differ from passive transport?
Active transport requires energy to move substances against their concentration gradient.
What characterizes the side of the membrane with fewer solute molecules?
It has more free water molecules.
Which function of membrane proteins involves anchoring cells to the cytoskeleton and extracellular matrix?
Attachment to the cytoskeleton and extracellular matrix (ECM).
Does osmosis move any substance?
False. Osmosis specifically refers to the movement of water.
What role do transport proteins play in facilitated diffusion?
They help move substances across the cell membrane without using energy.
What happens when Na+ binds to the sodium-potassium pump?
It stimulates phosphorylation by ATP.
What is the state of a plant cell in an isotonic environment?
There is no net movement of water, and the cell becomes flaccid.
What is the role of ATP in the sodium-potassium pump?
ATP is used for phosphorylation, which is stimulated by Na+ binding.
What structural feature is commonly found in transmembrane proteins?
Alpha helix.
How do saturated hydrocarbon tails behave in terms of packing?
Saturated tails pack together.
What is membrane potential?
The voltage difference across a membrane.
What are glycolipids?
Membrane carbohydrates that are covalently bonded to lipids.
What structures form during pinocytosis?
Pinocytotic vesicles.
How is active transport performed?
By specific proteins embedded in the membranes.
What is passive transport?
The movement of substances across a cell membrane without the use of energy.
How do carbohydrates on the plasma membrane vary?
They vary among species, individuals, and even cell types in an individual.
How do membranes rich in unsaturated fatty acids compare to those rich in saturated fatty acids?
Membranes rich in unsaturated fatty acids are more fluid.
Is the lipid layer a solid surface?
False. The lipid layer is fluid, not solid.
Does diffusion only occur through pores in the membrane?
False. Diffusion can occur through the lipid bilayer as well.
What is the function of membrane proteins that facilitates the joining of cells?
Intercellular joining.
What are the three types of endocytosis?
Phagocytosis, pinocytosis, and receptor-mediated endocytosis.
What are the two faces of the plasma membrane?
Cytoplasmic face and extracellular face.
What is a receptor in signal transduction?
A binding site with a specific shape that complements a chemical messenger (hormone).
What is osmosis?
The diffusion of water across a selectively permeable membrane.
Why is osmoregulation necessary for organisms?
It is a necessary adaptation for life in hypertonic or hypotonic environments.
What is tonicity?
The ability of a surrounding solution to cause a cell to gain or lose water.
What does active transport do?
Moves substances against their concentration gradients.
What creates voltage across a membrane?
Differences in the distribution of positive and negative ions.
What is the process called when water molecules move through a selectively permeable membrane?
Osmosis.
What is the major electrogenic pump of animal cells?
The sodium-potassium pump.
How do transport proteins function?
They are specific for the substance they move.
Is energy required for substances to move down their concentration gradient?
No, no work must be done.
What are the hydrophobic regions of proteins associated with?
The hydrophobic regions of the phospholipid bilayer.
What occurs in a hypotonic solution?
The solute concentration is less than that inside the cell, causing the cell to gain water.
What are the hydrophilic regions of proteins associated with?
The aqueous environment outside and inside the cell.
What is the function of membrane proteins that allows cells to respond to external signals?
Signal transduction.
Which function of membrane proteins is important for the recognition of cells by each other?
Cell-cell recognition.
How is the H+ concentration gradient maintained?
By actively transporting H+ across the membrane.
What is simple diffusion?
The movement of molecules from an area of higher concentration to an area of lower concentration without energy investment.
What does phagocytosis mean?
Cellular eating.
What does pinocytosis mean?
Cellular drinking.
What is plasmolysis?
The process where the membrane pulls away from the cell wall due to water loss.
What do membranes have that distinguishes their structure?
Distinct inside and outside faces.
What is the role of aquaporins?
They facilitate the passage of water across the membrane.
What determines the asymmetrical distribution of proteins, lipids, and carbohydrates in the plasma membrane?
The building process by the ER and Golgi apparatus.
What does it mean for substances to diffuse down their concentration gradient?
It means they move from a region of higher density to a region of lower density.
What type of molecules are phospholipids?
Amphipathic molecules, containing hydrophobic and hydrophilic regions.
What happens to membranes as temperatures cool?
They switch from a fluid state to a solid state.
How do electrogenic pumps contribute to cellular function?
They help store energy that can be used for cellular work.
How often does lateral movement of lipids occur?
Approximately 10 million times per second.
In which type of cell membrane is cholesterol found?
Animal cell membrane.
What is the function of fibronectin?
Fibronectin helps in cell adhesion and migration.
What occurs at equilibrium in diffusion?
The concentrations of solutes become equal on both sides of the membrane.
What are integral proteins?
Proteins that span the entire membrane and are involved in transport and communication.
How do cells recognize each other?
By binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane.
What is the function of the proton pump?
To transport H+ ions across the membrane.
What are transmembrane proteins?
Integral proteins that span the membrane.
What effect does cholesterol have on membrane fluidity at warm temperatures?
It restrains the movement of phospholipids.
What is the purpose of the sucrose-H+ cotransporter?
To facilitate the transport of sucrose along with H+ ions.
What do the hydrophobic regions of an integral protein consist of?
One or more stretches of nonpolar amino acids, often coiled into alpha helices.
What does a phospholipid bilayer provide?
A stable boundary between two aqueous compartments.
What is depicted in Figure 8.10?
Molecules of dye and their diffusion across a membrane.
What kind of substances are typically transported by exocytosis?
Large molecules such as proteins and neurotransmitters.
What does cholesterol do at low temperatures?
It hinders solidification of the membrane.
What does the diffusion of two solutes demonstrate?
The simultaneous movement of two different types of molecules across a membrane.
What is the role of vesicles in the cell?
To transport proteins and other molecules within the cell.
What is the extracellular matrix (ECM)?
A network of proteins and carbohydrates outside the cell that provides structural and biochemical support.
What role do membrane proteins play in intercellular joining?
They facilitate the hooking together of adjacent cells.
What is the goal of water diffusion in osmosis?
To equalize the solute concentration on both sides of the membrane.
What are glycoproteins?
Membrane carbohydrates that are more commonly covalently bonded to proteins.
How does exocytosis differ from pinocytosis?
Exocytosis releases substances from the cell, whereas pinocytosis involves the uptake of fluids and small particles into the cell.
What is the term for the combined forces that drive ion diffusion?
Electrochemical gradient.
What occurs at dynamic equilibrium in diffusion?
As many molecules cross the membrane in one direction as in the other.
What is formed when an amoeba engulfs a bacterium?
A food vacuole.
What is the role of pseudopodia in phagocytosis?
Pseudopodia help in engulfing the particle.
What is meant by 'net diffusion'?
The overall movement of molecules from an area of higher concentration to an area of lower concentration.
What are the products of ATP when it is used for transport?
ADP and inorganic phosphate (P).
Do diffusion and osmosis occur together?
False. They can occur simultaneously; osmosis is a type of diffusion.
What is a glycolipid?
A lipid with a carbohydrate attached, found in the plasma membrane.
What is the role of ATP in active transport?
ATP provides the energy needed to move substances against their concentration gradient.
What structure is reasoned to be formed by phospholipids in membrane models?
A phospholipid bilayer.
How does H+ diffusion relate to sucrose transport?
H+ diffusion drives the cotransport of sucrose.
What determines the temperature at which a membrane solidifies?
The types of lipids present in the membrane.
Which function of membrane proteins involves catalyzing biochemical reactions?
Enzymatic activity.
What is required to move sucrose against its concentration gradient?
Energy.
Where does the energy to move sucrose come from?
From the concentration gradient of H+.
What are membrane proteins responsible for?
Various functions including transport, signaling, and structural support.
What do microfilaments contribute to in the cytoplasm?
Microfilaments provide structural support and shape to the cell.
What are microfilaments of the cytoskeleton?
They provide structural support and shape to the cell.
What does the diffusion of one solute illustrate?
The movement of a single type of molecule across a membrane.
Why must membranes be fluid?
To work properly; they are usually about as fluid as salad oil.
What is endocytosis?
The process by which a cell takes in macromolecules by forming vesicles from the plasma membrane.
What is the function of cholesterol in the cell membrane?
It helps to maintain membrane fluidity.
Where are carbohydrates attached to proteins in the endoplasmic reticulum?
In the ER lumen.
Are particles not moving back and forth during isosmotic conditions?
False. Particles still move, but there is no net movement.
What are integrins?
Integrins are proteins that facilitate cell-extracellular matrix adhesion.
What are glycoproteins?
Proteins that have carbohydrate chains attached to them.
What role do glycolipids play in the cell membrane?
They contribute to cell recognition and signaling.
How is endocytosis related to exocytosis?
Endocytosis is a reversal of exocytosis and involves different proteins.
Is diffusion not temperature dependent?
False. Diffusion rates generally increase with temperature.
What is a proteoglycan complex composed of?
A core protein and polysaccharide molecules.
What does the fluid mosaic model describe?
The structure of the cell membrane.
What organelle is involved in the modification and packaging of secretory proteins?
Golgi apparatus.
What is the difference between endocytosis and exocytosis?
Endocytosis is the process of taking substances into the cell, while exocytosis is the process of expelling substances from the cell.
What role does ATP play in the transport of Na+ and K+?
It provides energy for active transport.
What are peripheral proteins?
Proteins that are attached to the exterior or interior surfaces of the membrane.
What is osmosis?
The diffusion of water across a selectively permeable membrane, affecting water balance.
Does osmosis work by the opposite principles of diffusion?
False. Osmosis is a specific type of diffusion involving water.
