Physiology BMD 06: Cell Membrane Transport

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Questions and Answers

What is the main characteristic of simple diffusion?

It involves the movement of molecules without carrier proteins (correct)

It requires a carrier protein

It is only applicable to lipid-soluble substances

It always results in a concentration gradient

Which of the following molecules can diffuse through the lipid bilayer?

Urea

Glucose

Oxygen (correct)

Water

What determines the rate of simple diffusion?

Only the electrical potential across the cell membrane

The amount of substance, velocity of motion, lipid solubilities, and the number and sizes of openings in the membrane (correct)

Only the velocity of motion

Only the amount of substance

What is the function of aquaporins in simple diffusion?

To permit water molecules to diffuse through the membrane Signup and view all the answers

What is facilitated diffusion also known as?

Carrier-mediated diffusion Signup and view all the answers

What is a characteristic of the protein channels in facilitated diffusion?

They are selectively permeable to certain substances Signup and view all the answers

How are the gates of facilitated diffusion channels controlled?

By voltage gating and ligand binding Signup and view all the answers

Why does urea have a lower rate of diffusion through the cell membrane compared to water?

Because urea has a larger diameter than water Signup and view all the answers

What is the primary source of energy for primary active transport?

Breakdown of adenosine triphosphate (ATP) Signup and view all the answers

What is the role of the sodium-potassium pump in nerve function?

Transmitting nerve signals Signup and view all the answers

What is the molecular weight of the β subunit of the Na+-K+ pump?

55,000 Signup and view all the answers

What is the function of the Na+-K+ pump in maintaining electrical voltage?

Establishing a negative electrical voltage inside the cell Signup and view all the answers

What type of transport uses energy derived from ionic concentration differences?

Secondary active transport Signup and view all the answers

What is the function of the α subunit of the Na+-K+ pump?

Binding to sodium ions on the inside Signup and view all the answers

What is an example of co-transport?

Sodium-glucose cotransport Signup and view all the answers

What is the role of the Na+-K+ pump in maintaining ion concentration differences?

Establishing a concentration gradient of sodium and potassium Signup and view all the answers

What determines osmotic pressure in a solution?

The number of particles per unit volume of fluid Signup and view all the answers

How is one osmole defined?

1 gram molecular weight of osmotically active solute Signup and view all the answers

Why is osmolarity more commonly measured than osmolality in physiological studies?

Osmolarity is easier to measure in dilute solutions Signup and view all the answers

What is a requirement for active transport across the cell membrane?

It requires energy and a carrier protein Signup and view all the answers

Which of the following is NOT typically transported via active transport?

Water molecules Signup and view all the answers

Which of these comparisons between osmolarity and osmolality is correct?

Osmolarity is generally more applicable to physiological studies Signup and view all the answers

What is the primary function of the Sodium-Potassium pump in relation to the cell?

To control the cell volume by preventing swelling and bursting. Signup and view all the answers

What triggers the activation of the ATPase function in the Sodium-Potassium pump?

The binding of three sodium ions on the inside and two potassium ions on the outside of the carrier protein. Signup and view all the answers

What is the direct result of the ATPase activity in the Sodium-Potassium pump?

The conformational change in the carrier protein, allowing it to transport ions across the membrane. Signup and view all the answers

What is the concentration gradient of calcium ions across the cell membrane?

Calcium ions are more concentrated outside the cell than inside. Signup and view all the answers

How do calcium pumps contribute to the regulation of intracellular calcium levels?

By sequestering calcium ions within intracellular organelles. Signup and view all the answers

What is the role of ATP in the functioning of both the Sodium-Potassium pump and the Calcium pumps?

ATP provides the energy required for the active transport of ions across the cell membrane. Signup and view all the answers

What is the specific type of transport mechanism employed by both the Sodium-Potassium pump and the Calcium pumps?

Active transport. Signup and view all the answers

Which of the following is NOT a characteristic of the Sodium-Potassium pump?

It is primarily involved in the transport of calcium ions across the cell membrane. Signup and view all the answers

Study Notes

Types of Transport Across Cell Membrane

Transport Mechanisms: Classified into passive and active transport.
Passive Transport: Moves substances without energy and along a concentration gradient.
Active Transport: Requires energy to move substances against a concentration gradient.

Passive Transport

Lipid Bilayer Barrier: Restricts movement of water-soluble substances but allows lipid-soluble substances to diffuse.
Types of Passive Transport:
- Simple Diffusion: Molecules move without carrier proteins, aiming for concentration equilibrium. Occurs through lipid bilayer or protein channels.
- Facilitated Diffusion: Requires carrier proteins that selectively permit certain substances.

Simple Diffusion

Mechanism: Relies on the concentration gradient; for example, oxygen and carbon dioxide can diffuse easily.
Water Movement: Occurs through aquaporins, specialized protein channels.
Equilibrium: Concentrations of substances eventually equalize across the membrane.

Facilitated Diffusion

Characteristics: Involves interactions with carrier proteins that provide selective permeability.
Control Mechanisms:
- Voltage Gating: Dependent on electrical potential across the membrane.

Osmosis

Osmotic Pressure: Pressure needed to stop osmosis, determined by particle count in a solution.
Osmole: A unit representing 1 gram molecular weight of osmotically active solute; crucial for understanding osmolarity.
Normal Osmolality: About 300 milliosmoles per kilogram in body fluids; osmolarity is measured as osmoles per liter.

Active Transport

Energy Requirement: Moves ions/molecules against gradients; utilizes ATP or stored energy.
Types of Active Transport:
- Primary Active Transport: Directly linked to ATP breakdown.
- Secondary Active Transport: Driven by gradients established by primary active transport.

Primary Active Transport

Sodium-Potassium Pump: Transports sodium ions out of the cell and potassium ions in; critical for cell function and volume control.
Pump Structure: Composed of α (large) and β (smaller) subunits that engage in ion binding.
Mechanism of Action: Involves ATP hydrolysis leading to conformational changes, regulating ion concentration across the membrane.

Sodium-Potassium Pump Functions

Establishes Concentration Gradients: Key for maintaining negative electrical charge inside cells; essential for nerve signal transmission.
Control of Cell Volume: Prevents cell swelling by regulating ionic concentrations that influence water osmosis.

Calcium Pumps

Specialized active transport mechanisms for calcium ions.
Functionality: Pumps calcium out of cells or into intracellular stores, critical for muscle function and cellular signaling.
Intracellular Concentration: Maintains calcium levels at approximately 10,000 times lower than extracellular fluid.

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Description

Quiz on transport across cell membrane, part of Introduction to Physiology course for Bachelor of Medicine and Surgery students.