Transport Across Membranes Lecture

These flashcards cover key concepts regarding transport mechanisms across membranes. They focus on the characteristics, functions, and processes involved in membrane transport, ensuring a comprehensive review for the exam.

four mechanisms of transport across a membrane

Simple diffusion across bilayer, Ion Channel, Carrier, Active Transport.

What is the main function of a membrane?

To serve as a barrier, be selectively permeable, transmit signals, and be deformable & fluid.

What factors determine if a solute can pass through a lipid bilayer by simple diffusion?

Polarity, size, charge, and partition coefficient.

How does water move across the plasma membrane?

Water moves to the region of higher solute concentration via osmosis.

What are aquaporins?

Channels that allow H2O to move across membranes.

How do plant cells maintain turgor pressure?

They are normally hypertonic to their environment, creating turgor pressure.

What happens to plant cells in a hypertonic environment?

They shrink; plasma membrane pulls away from the cell wall.

What are the two types of transport proteins?

Channel proteins and carrier proteins.

What do channel proteins do?

They allow specific molecules to diffuse through without binding.

What is facilitated diffusion?

A process where passive transporters assist molecules to move down the concentration gradient.

What does active transport require?

An energy source to move molecules against their concentration gradient.

What is membrane potential?

The difference in charge across a membrane that affects molecular movement.

What are K+ channels selective for?

K+ ions only.

What are the gating mechanisms of ion channels?

Voltage-gated, ligand-gated, and mechanically-gated.

When does a channel protein open?

When the S4 helix is attracted to positive charges or repelled by negative charges.

What role does S4 play in voltage-gated K+ channels?

S4 acts as a voltage sensor.

What changes induce channel opening in voltage-gated K+ channels?

Depolarization of the membrane causes conformational change.

What are the three states of a voltage-gated K+ channel?

Open, inactivated, and closed.

How do GLUT transporters work?

Facilitated diffusion, switching conformations based on solute concentration.

What is the effect of insulin on GLUT4?

Insulin stimulates the exocytosis and incorporation of GLUT4 into the plasma membrane.

What does RNA interference (RNAi) do?

It reduces protein expression by degrading its mRNA.

How does the Na+/K+ ATPase function?

It moves Na+ out of the cell and K+ into the cell using ATP.

What is primary active transport?

Transport that directly uses energy from ATP.

What is secondary active transport?

Uses the energy from an ion gradient to transport another molecule against its gradient.

What is the difference between symport and antiport?

Symport moves solutes in the same direction, antiport moves them in opposite directions.

What is facilitated diffusion compared to simple diffusion?

Facilitated diffusion requires a transporter protein, while simple diffusion does not.

What is the importance of the GLUT1 transporter?

It facilitates glucose uptake in muscle and plays a role in serum stimulation of glucose uptake.

How are changes in glucose levels managed by GLUT4?

In response to increased glucose, GLUT4 is translocated to the membrane to increase uptake.

What does the voltage-gated K+ channel specifically allow to pass?

Potassium ions.

What happens to K+ ions when the channel is inactive?

Movement of K+ ions is blocked by the N-terminal ball domain.

What are the protein conformational changes in Na+/K+ ATPase?

Conformational changes occur upon binding of Na+ and K+ for transport.

Why is K+ selective over Na+ in K+ channels?

The selectivity filter stabilizes K+ over Na+ due to size and hydration differences.

What role do specific amino acids play in the selectivity filter of K+ channels?

They stabilize K+ ions and help them to pass through the channel.

What does it mean for the transport mechanisms to be saturable?

There is a maximum rate of transport when the transporter is occupied.

What changes in the S4 helix cause the opening of voltage-gated channels?

Movement in response to membrane polarization changes.

What happens during channel inactivation?

The amino terminal ball blocks the channel after it opens.

What is the relationship between concentration gradient and transport direction?

Solutes move down their concentration gradient during passive transport.

What physical structure allows for patch clamping?

A specialized micropipette that isolates specific transport proteins.

What is the role of membrane-associated helices in Kv channels?

They help form the channel and regulate ion passage.

What does the term 'bidirectional' refer to in ion channels?

Ions can move in both directions across the membrane.

What is a key characteristic of carrier proteins?

They undergo conformational changes to transport solutes across membranes.

Why are facilitated diffusion processes specific?

Transport depends on the binding affinity of the substrate to the transporter.

What does a conformational change in a transporter signify?

It changes the accessibility of the binding site for ions or solutes.

What must occur for glucose to enter cells via the Na+/glucose cotransporter?

Na+ must bind and move down its gradient while glucose is transported up its gradient.

Why is ATP critical for primary active transport?

It provides the energy needed to move solutes against their concentration gradient.

What process describes the incorporation of GLUT4 into the plasma membrane?

Exocytosis.

How does the concentration of K+ ions change when channels open?

K+ ions flow out of the cell, down their electrochemical gradient.

What role do ligand-gated channels play?

They open when a specific ligand binds, allowing ions to flow through.

How do mutations in transport proteins affect their function?

They may alter the rate of transport of the relevant solute.

What does the partition coefficient indicate?

The solubility of a solute in nonpolar solvent compared to that in water.

What mechanisms allow for regulated transport of solutes?

Conformational changes in transport proteins can be regulated by cellular signals.

What does it mean for a membrane to be semi-permeable?

It allows only certain molecules to pass while blocking others.

What is osmotic pressure?

The pressure required to prevent water from moving across a semipermeable membrane.

What are electrochemical gradients?

The gradients of charged ions that influence ion movement across membranes.

What is the effect of ion concentration on membrane potential?

Uneven distribution of ions leads to difference in charge across the membrane.

How does the sodium/potassium pump maintain cellular function?

By actively transporting Na+ out and K+ into the cell, maintaining resting membrane potential.

What is the significance of K+ channel selectivity?

It ensures that only the correct ions are transported, maintaining homeostasis.

What defines a transport protein as a primary active transporter?

Direct utilization of ATP for transport against a gradient.

What does the term 'saturable' imply in the context of facilitated diffusion?

The rate of transport can reach a maximum level when binding sites are fully occupied.

What happens to a plant cell in a hypotonic solution?

It will swell and turgor pressure will increase.

What is the difference between facilitated diffusion and active transport?

Facilitated diffusion is passive and moves down the gradient, while active transport uses energy to move against the gradient.

What factors influence the rate of transport via carrier proteins?

Concentration gradient, binding affinity, and availability of transporter proteins.

What are the implications of RNAi technology in research?

It helps to determine the function of specific genes by knocking down protein expression.

What was the outcome observed in the Western blot for GLUT1 during RNAi experiments?

A substantial reduction in GLUT1 levels, verifying the effectiveness of RNAi.

How does insulin influence GLUT4 in terms of glucose uptake?

Insulin promotes GLUT4 translocation to the membrane to facilitate glucose entry.

What does 'conformational state' refer to in ion channels?

The different structural states an ion channel can adopt during transport.