Module 4 Quiz

Simple Diffusion is the movement of nonpolar compounds down their concentration gradient, where as, osmosis is the movement of water

The free energy change is determined by the concentration difference (C1-C2).

Passive transport involves the movement of molecules down their concentration gradient, without the use of energy hence making it a spontaneous process.

The formula for free energy change (ΔG) for the transport of uncharged solutes from concentration C1 to C2 is ΔG = ΔG0' + RT ln ([P]/[S]), where R is the gas constant, T is the temperature in Kelvin, and ln represents the natural logarithm. [P] and [S] represent the concentrations of the solute on the two sides of the membrane.

Polar compounds and ions cannot cross the membrane unassisted due to the hydrophobic nature of the lipid bilayer. They require specific membrane protein carriers to facilitate their transport across the membrane.

kJ.mol-1.K-1

Size, polarity, ionicity

100:1

Bilayers are more permeable to nonpolar molecules.

Shuttles K+ ions

They kill other cells by dissipating their ion gradients

Transporters lower the activation energy by binding solutes via weak, noncovalent interactions, which counteracts the positive ΔG of dehydration, thereby forming a transmembrane pathway lined with polar amino acids.

k is inversely and exponentially related to ΔG‡

Transporters bind their substrates through non-covalent interactions, are saturable, and have a gate on either side of the membrane that is never open at the same time, whereas ion channels provide an aqueous path through the membrane for inorganic ions to diffuse.

The transition state is a high-energy intermediate state that is similar in both enzyme-catalyzed reactions and facilitated transport, requiring an energy input (activation energy, ΔG‡) to overcome the energy barrier.

Because they are saturable, meaning that the rate of transport does not increase significantly above a certain concentration of substrates.

Gramicidin A is a β-helical peptide that forms a dimer, creating a channel with a 0.4 nm pore, allowing monovalent cations like Na+ and K+ to pass through.

The energy barrier is the activation energy required to transport a polar or charged solute across a membrane, involving the stripping of hydration layers and movement across the non-polar membrane environment.

The β6.3 helix is a tertiary structure that forms a wide channel, allowing ions to pass through.

Gramicidin A forms a channel in the bacterial membrane, allowing ions to pass through and disrupting the bacterial membrane potential, ultimately leading to bacterial death.

cyclic structure of L-lactate, D/L-valine, D-hydroxy-isovalerate

k+ binds to the size-selective cavity of valinomycin through carbonyl coordination, which shields charges.

its a compound that shuttles an ion (K+) across the membrane

When K+ is bound to the valinomycin cavity, its non-polar groups interact with acyl chains to form a lipid-soluble complex that shuttles the ion across the membrane.

A type of peptide in which one or more of the amide group is replaced with an ester.

analogous

• osmosis
• simple diffusion
• facilitated diffusion

It facilitate the uptake of glucose into erythrocytes through passive transport.

the initial velocity of substrate transport into the cell at various external substrate concentrations

The outward-facing (T1) conformation of the transporter binds to the substrate, and then undergoes a conformational change to the inward-facing (T2) conformation, allowing the substrate to be released into the cell.

Immediate metabolism of glucose in the cell

3 mM; It represents the substrate concentration at half of the maximum velocity (½Vmax)

1. High rate of diffusion down a concentration gradient
2. Saturable transport (reaches Vmax)
3. Stereospecific for D-glucose

GLUT1 transports glucose into the cell as cellular glucose is immediately metabolized, preventing glucose accumulation inside.

Glucose transporters in the MF superfamily are integral membrane proteins with 12 transmembrane (TM) segments. 4 (possibly 5) amphipathic α-helices form a hydrophilic channel for glucose transport, with charged/polar amino acids lining the channel.

Glucose transport via the Gated Pore Mechanism in GLUT1 involves cycling between T1 and T2 conformations. In T1, the glucose-binding site is exposed on the outer membrane surface, while in T2, it is exposed on the inner surface.

12 glucose transporters are encoded by the human genome, belonging to the Major Facilitator superfamily. They are commonly referred to as GLUT1 to GLUT12.

GLUT1 is mainly present in erythrocytes and the Blood-Brain Barrier. It transports glucose into erythrocytes and facilitates glucose transport across the blood-brain barrier.

The T1 conformation exposes the glucose-binding site on the outer membrane surface, while the T2 conformation exposes it on the inner surface.

The GLUT family members (GLUT1-GLUT12) exhibit differences in tissue distribution, kinetic properties, and regulation. Each member has a distinct pattern of expression and functional characteristics.

Cone-shaped structure, allowing K+ to pass through due to the constriction size.

They interact with dehydrated K+, replacing interactions with H2O, optimizing for K+ ions.

K+ ions move rapidly through the channel in single file, hopping between sites, and repulse each other to prevent overcrowding.

It allows K+ ions to pass through while excluding smaller ions like Na+, based on size.

There are 4 sites, but 2 of them are occupied by H2O molecules, leaving 2 sites for K+ ions.