Cell Membrane and Ion Channels Quiz

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Questions and Answers

If a transporter protein specific for D-glucose encounters D-galactose, what is the most likely outcome?

The transporter will reject the D-galactose and continue to transport only D-glucose.

The transporter will actively convert D-galactose into D-glucose.

The transporter will simultaneously transport both D-glucose and D-galactose at an increased rate.

The transporter will bind to the D-galactose, inhibiting the transport of D-glucose. (correct)

What is the primary determinant of a protein channel's conductance?

The size of the channel pore.

The probability of the channel being in the open state. (correct)

The number of ligands that can bind.

The membrane potential across the channel.

Which type of ion channel is activated by the binding of a hormone?

Voltage-gated channel.

Second-messenger-gated channel.

Mechanically-gated channel.

Ligand-gated channel. (correct)

A cell membrane is exposed to a force causing it to stretch. Which type of ion channel would most likely be activated as a result?

Mechanically-gated channel Signup and view all the answers

What is the primary role of the Na$^+$-K$^+$ ATPase pump in establishing the resting membrane potential?

Generating chemical gradients by actively transporting ions against their concentration gradients. Signup and view all the answers

Given a resting membrane potential (RMP) of -70 mV and an equilibrium potential for potassium (K+) of -94 mV, what is the driving force for potassium diffusion?

24 mV Signup and view all the answers

If the cell membrane becomes more permeable to potassium ions, what is the expected change in resting membrane potential (Em)?

The Em will move towards the equilibrium potential of potassium. Signup and view all the answers

What condition is described when the chemical force and the electrical force are balanced for a specific ion species?

Electrochemical equilibrium Signup and view all the answers

The cell membrane is highly permeable to potassium ions due to:

The presence of K2P channels. Signup and view all the answers

What is the usual effect of opening ion channels on intracellular and extracellular ion concentrations, under normal circumstances?

Intracellular and extracellular ion concentrations remain relatively unchanged. Signup and view all the answers

Why is urea considered an 'ineffective osmole'?

Urea rapidly equilibrates across cell membranes. Signup and view all the answers

What primarily determines the osmotic pressure and movement of water across a cell membrane?

The concentration of impermeable solutes. Signup and view all the answers

Which of the following best describes the state of a cell placed in a hypotonic solution?

The cell will swell due to water influx. Signup and view all the answers

What is a key feature that differentiates facilitated diffusion from simple diffusion?

Facilitated diffusion requires a protein carrier, while simple diffusion does not. Signup and view all the answers

Which transport mechanism directly utilizes ATP to move substances across the cell membrane?

Primary active transport. Signup and view all the answers

According to the provided text, which of the following best describes the permeability coefficient (P)?

A factor dependent on the partition coefficient and diffusion coefficient. Signup and view all the answers

What is the relationship between temperature and the rate of diffusion according to the text?

As temperature increases, the rate of diffusion increases. Signup and view all the answers

How does secondary active transport differ from primary active transport?

Secondary active transport uses the electrochemical gradient produced by primary active transport, while primary active transport uses ATP directly. Signup and view all the answers

Which process involves the bulk intake of substances by the cell?

Endocytosis. Signup and view all the answers

In carrier-mediated transport, what does 'saturation' refer to?

When all binding sites on the carrier proteins are occupied. Signup and view all the answers

What is the 'transport maximum' (Tm) in carrier-mediated transport?

The point when all binding sites are occupied and transport reaches a maximum rate. Signup and view all the answers

According to Fick's Law of Diffusion, what factor influences the rate of diffusion across the cell membrane?

The gradient of the concentration. Signup and view all the answers

What does stereospecificity in carrier-mediated transport imply?

Carrier protein binding sites are specifically designed to bind to specific isomers of a solute. Signup and view all the answers

Which isomer of glucose is transported by the glucose transporter in the renal proximal tubule?

D-glucose Signup and view all the answers

When does glucose appear in the urine according to the text?

When the transport of D-glucose is saturated in the proximal tubule. Signup and view all the answers

What does the competition characteristic in carrier-mediated transport refer to?

The interaction between similar solutes for binding to carrier proteins. Signup and view all the answers

What is the driving force of $Na^+$ ions at a resting membrane potential of -70 mV, given that the equilibrium potential for $Na^+$ is +60 mV?

-130 mV, inward Signup and view all the answers

If a cell's membrane potential is at -70 mV and the equilibrium potential for $Cl^-$ is -90 mV, what direction will $Cl^-$ ions move if $Cl^-$ channels are opened?

Outward Signup and view all the answers

If both $Na^+$ and $Ca^{2+}$ channels are opened at the same time, which would have a greater driving force at resting membrane potential of -70mV, given their equilibrium potentials are +60mV and +120mV respectively?

$Ca^{2+}$ as it has the greater absolute driving force Signup and view all the answers

An action potential is said to have a 'stereotypical size and shape'. What does this mean?

Action potentials have a consistent amplitude and duration for a specific neuron. Signup and view all the answers

At a membrane potential of -70mV, with an equilibrium potential of -94mV for potassium ($K^+$), what is the direction of the net driving force for $K^+$ ?

Inward Signup and view all the answers

If a cell has a resting membrane potential of -70mV, an equilibrium potential for $Na^+$ of +60mV, and an equilibrium potential for $Cl^-$ of -90mV, which ion experiences the largest electrical driving force?

$Na^+$ Signup and view all the answers

The resting membrane potential is -70 mV. If the equilibrium potential for an anion, $X^-$, is -20 mV, what is the net driving force on $X^-$ and its direction when $X^-$ channels open?

-50 mV, outward Signup and view all the answers

What is the definition of equilibrium potential?

The membrane potential that prevents the net movement of an ion across the membrane Signup and view all the answers

What property allows the action potential to maintain its size and shape as it travels down the axon?

Regeneration of the action potential Signup and view all the answers

During which period can a new action potential be elicited by a greater than usual stimulus?

Relative refractory period Signup and view all the answers

What is primarily responsible for the absolute refractory period in neurons?

Inactivation gates of Na+ channels Signup and view all the answers

What initiates the action potential in a neuron?

Stimulus above threshold Signup and view all the answers

Which factor does NOT affect the conduction velocity in nerves?

Nerve length Signup and view all the answers

How is the action potential propagated along the axon?

By spread of local currents Signup and view all the answers

What is a key characteristic of the all-or-none response in action potentials?

They are elicited only above a threshold level Signup and view all the answers

What is the primary reason that during the relative refractory period a greater inward current is required to elicit an action potential?

Increased potassium conductance Signup and view all the answers

Study Notes

Homeostasis

Homeostasis is a steady state, requiring energy.
Equilibrium is a state without energy consumption. When a vital parameter, like blood glucose, is well-regulated, it isn't in equilibrium.
A steady state maintains a vital parameter at a constant value, achieved by the body or cell carefully balancing actions that raise and lower the parameter.

Negative Feedback

Negative feedback is the most common feedback mechanism.
It reverses any deviation from a stable point.
If a factor becomes excessive or deficient, a control system initiates negative feedback to return the factor to a mean value, maintaining homeostasis.
Negative feedback involves a series of changes.

Positive Feedback

Positive feedback loops maintain and possibly accelerate the direction of a stimulus.
Positive feedback exaggerates deviations from a stable point.
Each cycle of positive feedback leads to more of the same variable, potentially causing instability and death.
Positive feedback is less common than negative feedback.

Electrolyte Content of Body Fluids

Data shows the electrolyte content of plasma, interstitial fluid, and intracellular fluid.
Includes cation concentrations (Sodium, Potassium, Calcium, Magnesium) and anion concentrations (Chloride, Bicarbonate, Sulfate, Phosphate, Protein).
Review the electrolyte levels in the body's fluids.

Osmotic Pressure and Reflection Coefficient

Review the relationship between osmotic pressure and reflection coefficient.
Isotonic solutions have the same solute concentration in compartments, but may not be truly isotonic if substances have reflection coefficients of 0.
Urea is freely permeable and quickly reaches equilibrium between compartments (making it an "ineffective osmole").
Osmotic pressure is determined by the concentration of impermeable solutes, influencing water movement.

Tonicity of Solutions

The terms isotonic, hypotonic, and hypertonic describe solutions based on whether they cause changes in cell volume.
Tonicity primarily depends on the concentration of impermeable solutes.
Some solutes can permeate the cell membrane.

Effects of Volume Changes on Osmolarity of Body Fluids

Table 1 shows how changes in volume affect body osmolarity during various hydrational conditions (Loss of Isotonic fluid, Loss of hypotonic fluid, Gain of isotonic fluid, Gain of hypotonic fluid, Gain of hypertonic fluid).
Different scenarios (e.g., hemorrhage, diarrhea, dehydration) are considered.

Membrane Transport Mechanisms

Simple diffusion across a phospholipid bilayer.
Facilitated diffusion via protein channels/pores; carrier proteins needed.
Primary active transport uses ATP against the electrochemical gradient.
Secondary active transport uses electrochemical gradients created by primary active transport.
Bulk transport involves large particles or large volumes of material (Endocytosis and Exocytosis).
Different examples of transport mechanisms are provided.

Fick's Law of Diffusion

Fick's Law describes the relationship between the diffusive flux and the gradient of concentration across a membrane.
Factors affecting diffusion rate are permeability coefficient (P), partition coefficient (K), diffusion coefficient (D), cross-sectional area (A) and the thickness of membrane (Δx).

Saturation in Carrier Mediated Transport

Carrier proteins have limited binding sites; transport rate increases with concentration until all sites are occupied (Transport maximum -Tm).
At low concentrations, many binding sites are available, and transport increases steeply with solute concentrations as binding sites are available, while at high concentrations, binding sites become scarce slowing the rate of transport.

Stereospecificity in Carrier-Mediated Transport

Binding sites on carrier proteins are stereospecific, recognizing and transporting specific isomers.
The transporter for glucose (in the renal proximal tubule) recognizes and transports D-glucose, but not L-glucose.

Competition in Carrier-Mediated Transport

Related substances can compete for the same binding sites.
An example is D-Galactose which inhibits glucose transport by occupying binding sites.

Ion Channel Characteristics

Conductance (g) is the probability a channel is open
Ion channel gates are controlled by sensors. Types include voltage-gated, ligand-gated channels, second messenger-gated, and mechanically-gated channels.

Mechanisms Responsible for the Resting Membrane Potential

Chemical gradients from active transport pumps (e.g. Na+/K+ ATPase pump).
Selective membrane permeability with higher permeability to potassium ions.
Electrical gradients.
Electrochemical equilibrium.

Equilibrium Potential

The membrane potential at which the diffusive force and electrical force are balanced for an ion.
This potential is significant because the overall current flow is directly proportional to the net force and conductance of the membrane for that ion.

Driving Force for Diffusion: Equilibrium Potential vs. RMP

The driving force for diffusion is the difference between the equilibrium potential of an ion and the resting membrane potential (RMP).
Depending on the direction of the driving force, an ion will either enter or exit the cell.

Characteristics of Action Potentials

Action potentials have stereotypical size and shape for a given cell type.
They are propagated down the entire length of an axon without a reduction in size or shape, due to regeneration.
Action potentials are all-or-none, triggered only by a threshold stimulus.

Action Potential Sequence of Events

Depolarization (opening voltage-gated Na+ channels).
Repolarization (voltage-gated Na+ channels close, and voltage-gated K+ channels open).
Hyperpolarization (voltage-gated K+ channels remain open after the potential reaches resting level).

Refractory Periods

Absolute refractory period: no new action potential can be generated. The Na+ channel inactivation gates must be open again.
Relative refractory period: a new action potential CAN be generated but a greater than normal depolarizing current will be needed. The voltage-gated K+ channels remain open, which creates more resistance to depolarization.

Propagation of Action Potentials

Propagation occurs by the spread of local currents from active regions to inactive regions.
Action potentials are initiated in the initial segment of the axon, then propagate down the axon.

Factors Affecting Conduction Velocity in Nerves

Myelination
Axon diameter
Temperature

Receptors, Signaling Pathways, and Messengers

Different receptors (ligand-gated ion channels, G protein-coupled receptors, enzyme-linked receptors, nuclear receptors) along with their associated signal transduction pathways and secondary messengers are identified.
Examples of ligands are listed for each receptor type

Good Study Habits

Good study habits are consistent and effective practices used for retention and understanding of information.
Examples of good study habits include a consistent schedule, active note-taking, study breaks, organized workspace, prioritizing tasks, distraction-free environment, peer study groups, and periodic review sessions.

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Description

Test your knowledge on cell membrane functions, ion channels, and transport proteins. This quiz covers various aspects of membrane potentials, ion conductance, and the effects of different forces on ion movement. Challenge yourself with these questions related to membrane biology!