Untitled Deck Flashcards
Describe the types of transport across membranes.
There are two types of transport: passive transport, which occurs down the concentration gradient, and active transport, which occurs against the concentration gradient.
Define facilitated diffusion.
Facilitated diffusion is a passive process where molecules move down their concentration gradient with the help of specific proteins or channels.
How does the concentration gradient affect the rate of diffusion?
The rate of diffusion is directly proportional to the concentration gradient; as the gradient increases, the rate of diffusion increases.
Explain the energy changes associated with moving molecules down a concentration gradient.
Moving molecules down a concentration gradient releases energy, resulting in a negative change in free energy (ΔG).
What is the permeability of biomembranes to sugars?
Biomembranes appear permeable to sugars, but this permeability is facilitated by helper molecules rather than simple diffusion.
Describe the effect of metabolic inhibitors on diffusion.
Metabolic inhibitors have no effect on both simple and facilitated diffusion.
How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion involves specific proteins or channels to assist the movement of molecules, while simple diffusion does not require such assistance.
Define passive transport in the context of concentration gradients.
Passive transport is the movement of molecules down their concentration gradient without the use of energy.
What types of molecules are membranes generally impermeable to?
Membranes are generally impermeable to large uncharged molecules such as amino acids and glucose, as well as small, polar-charged molecules (ions).
Explain the significance of Fick’s law in diffusion.
Fick’s law states that the rate of diffusion is linear as the concentration of the solute increases, indicating a direct relationship between concentration and diffusion rate.
Describe the role of helper molecules in diffusion.
Helper molecules facilitate the diffusion of substances across membranes, particularly for those that cannot pass through the lipid bilayer easily.
How does active transport differ from passive transport?
Active transport requires energy to move molecules against their concentration gradient, while passive transport does not require energy and moves molecules down their gradient.
What happens to ΔG when moving molecules up a concentration gradient?
Moving molecules up a concentration gradient consumes energy, resulting in a positive change in free energy (ΔG).
Identify the types of molecules that membranes are permeable to.
Membranes are permeable to gases (O₂, CO₂, N₂), lipids, and small, polar, neutral molecules such as urea.
Explain the concept of saturation in facilitated diffusion.
In facilitated diffusion, the rate of transport saturates as the concentration of the solute increases, indicating that all available transport proteins are occupied.
Describe the process of passive transport in cells.
Passive transport occurs when a cell moves particles across a membrane without using energy, allowing particles to go down their concentration gradient.
Define diffusion in the context of cellular transport.
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.
How does osmosis differ from diffusion?
Osmosis is the diffusion of water across a selectively permeable membrane, while diffusion refers to the movement of any type of particles.
Explain the importance of regulating water flow through the plasma membrane.
Regulating water flow is crucial for maintaining homeostasis within a cell.
What are the two models for facilitated diffusion?
The two models for facilitated diffusion are the pore (channel) model and the carrier model.
Describe the role of the phospholipid bilayer in membrane transport.
The phospholipid bilayer consists of hydrophobic fatty acid sides and hydrophilic phosphoric sides, allowing only non-polar or small polar molecules to pass through.
How do carrier ionophores function in facilitated diffusion?
Carrier ionophores, like valinomycin, transport impermeable species across the membrane by carrying them.
What is the structural feature of Gramicidin A?
Gramicidin A is a pentadecapeptide with a specific sequence of amino acids, including D-amino acids, that forms a pore in the membrane.
Explain the significance of concentration gradients in passive transport.
Concentration gradients drive passive transport, as particles naturally move from areas of higher concentration to areas of lower concentration.
Define the term ‘selectively permeable membrane’.
A selectively permeable membrane allows certain substances to pass through while blocking others, crucial for maintaining cellular homeostasis.
Describe the process of formylation in relation to membrane proteins.
Formylation involves the insertion of proteins into the membrane with the N-terminal facing inwards, leading to the formation of a beta-helix structure.
Define the structure and function of gramicidin.
Gramicidin is a transmembrane ionophore that forms a pore in the membrane, allowing ions to pass through, with non-polar side chains facing the membrane and polar parts facing inwards.
How does the selectivity of gramicidin compare to other ion channels?
Gramicidin has poor selectivity but primarily functions as a sodium ion channel.
Compare the rates of transport for gramicidin and valinomycin.
Gramicidin transports ions at a rate of 10⁷ ions/molecule/sec, while valinomycin transports ions at a rate of 10⁴ ions/molecule/sec.
What are ionophores and their role in ion transport?
Ionophores are molecules, often small antibiotics or synthetics, that facilitate the movement of ions across membranes, acting as carriers or channels.
Describe the structural features of valinomycin that contribute to its function.
Valinomycin has alternating ester and ether peptide bonds, with inwardly facing carbonyls that coordinate potassium ions octahedrally, allowing it to be freely permeable in membranes.
How does the permeability of valinomycin vary among different ions?
Valinomycin’s permeability is ranked as Rb⁺ > K⁺ > H⁺»_space; Na⁺»_space; Mg²⁺, indicating it preferentially carries potassium ions.
Explain the models for facilitated diffusion.
There are two models for facilitated diffusion: pores (channels) like potassium channels and aquaporins, and carriers (uniporters) like valinomycin and GLUT1.
What is facilitated diffusion and how does it function?
Facilitated diffusion is the passive transport of materials across the membrane using transport proteins, allowing specific molecules to cross without energy input.
Describe the role of GLUT1 in facilitated diffusion.
GLUT1 is a protein carrier that facilitates the transport of glucose across the cell membrane, functioning as a uniporter.
Describe the role of proteins in facilitated diffusion.
Proteins act as channels or carriers that help specific molecules move across the cell membrane without the need for energy.
Explain the concept of passive transport.
Passive transport is the movement of substances across a cell membrane without the use of energy, relying on concentration gradients.
What is the relationship between facilitated diffusion and osmosis?
Both facilitated diffusion and osmosis are forms of passive transport, but osmosis specifically refers to the movement of water across a semipermeable membrane.
Describe the process of osmosis.
Osmosis is the diffusion of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
How does facilitated diffusion contribute to cellular function?
Facilitated diffusion allows cells to efficiently take up essential nutrients and remove waste products without expending energy.
