Cell Biology Quest 2 notes

What are the seven major functions of membranes?

The seven major functions are compartmentalization, selective permeability, communication and signaling, energy transformation, transport, enzymatic activity, and cell recognition.

Describe the experiment that first revealed that the plasma membrane was a lipid bilayer.

The experiment involved electron microscopy to visualize the structure of membranes and differential centrifugation to separate cellular components, leading to the conclusion of a lipid bilayer.

What is the fluid-mosaic model?

The fluid-mosaic model describes the plasma membrane as a dynamic structure with various proteins embedded in or associated with a fluid lipid bilayer.

What are the primary components of membranes?

The primary components are phospholipids, cholesterol, and proteins, which vary among different cell types and organelles.

What does amphipathic mean?

Amphipathic refers to molecules that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.

Name and describe the three main types of membrane lipids.

The three main types are phospholipids (form bilayers), cholesterol (stabilizes membrane fluidity), and glycolipids (involved in cell recognition and signaling).

What is a liposome?

A liposome is a spherical vesicle composed of a lipid bilayer, used to deliver drugs or genetic material.

What is a stealth liposome?

A stealth liposome is a liposome designed to evade the immune system for targeted drug delivery.

Why is it important that membranes are fluid?

Fluidity allows for proper function, including protein mobility, cell signaling, and membrane fusion.

Why are the inner and outer membrane leaflets different?

They are different because of the asymmetric distribution of lipids and proteins important for various cellular functions.

How is ABO blood typing related to the membrane?

ABO blood typing is determined by the presence of specific glycoproteins on the surface of red blood cell membranes, defining blood types.

Describe the three classes of membrane proteins.

Integral proteins (span the membrane), peripheral proteins (associated with the membrane surface), and lipid-anchored proteins (attached to lipids in the membrane).

What does Freeze-fracture analysis show?

It shows the architecture of the plasma membrane, revealing the distribution of proteins and lipids.

How would you solubilize an integral membrane protein?

Use detergents or organic solvents to disrupt the lipid bilayer and isolate the protein.

What types of amino acids are typically found in transmembrane domains?

Hydrophobic amino acids are typically found in transmembrane domains to interact with the lipid bilayer.

What is a hydropathy plot?

A hydropathy plot is a graphical representation used to predict transmembrane regions of proteins based on amino acid hydrophobicity.

Describe how to use site-directed mutagenesis to identify relationships between proteins.

By introducing specific mutations and analyzing the effects on protein function, researchers can determine spatial and functional relationships.

What factors influence membrane fluidity?

Factors include temperature, lipid composition (saturation level), and cholesterol content.

What are lipid rafts?

Lipid rafts are microdomains within membranes enriched in cholesterol and sphingolipids, believed to organize signaling molecules.

Describe an experiment showing dynamic protein nature in the plasma membrane.

FRAP (Fluorescence Recovery After Photobleaching) experiments show how proteins move within the membrane over time.

Why do proteins move more rapidly in artificial membranes versus real cellular membranes?

In artificial membranes, the lack of complex cellular structures and interactions allows for greater protein mobility.

What are the four mechanisms by which solute molecules move across the membrane?

Diffusion, facilitated diffusion, active transport, and vesicular transport.

What is the difference between diffusion and active transport?

Diffusion is passive movement down a concentration gradient, while active transport requires energy to move solutes against their concentration gradient.

What is the partition coefficient?

The partition coefficient measures the solubility of a substance in a lipid phase versus an aqueous phase, indicating membrane permeability.

What is osmosis?

Osmosis is the movement of water through a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

What happens to a cell in hypotonic, hypertonic, and isotonic solutions?

In hypotonic solutions, cells swell due to water intake. In hypertonic solutions, cells shrink due to water loss. In isotonic solutions, cells remain stable.

When might a plant cell undergo plasmolysis?

Plasmolysis occurs when a plant cell is placed in a hypertonic solution, causing the cell membrane to pull away from the cell wall.

What are aquaporins?

Aquaporins are channel proteins that facilitate the rapid transport of water across cell membranes.

What is turgor pressure?

Turgor pressure is the pressure exerted by the fluid inside the central vacuole of plant cells against the cell wall.

What is the permeability of membranes for ions, water, macromolecules, and small uncharged molecules?

Membranes are generally impermeable to ions and macromolecules, but permeable to water and small uncharged molecules to some extent.

What are some properties of ion channels?

Ion channels are selective, gated, and may be voltage- or ligand-gated, allowing ions to pass through when open.

What do patch clamping experiments show?

Patch clamping demonstrates the ionic currents flowing through individual ion channels and their dynamics.

What does it mean that most ion channels are gated?

Gated ion channels open or close in response to specific stimuli like voltage changes or ligand binding.

What are the three types of ion channels?

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

Describe how the voltage-gated potassium channel works.

It opens in response to membrane depolarization, allowing K+ ions to flow out, repolarizing the membrane.

Describe facilitated diffusion with the glucose transporter.

Facilitated diffusion involves a glucose transporter that binds glucose and changes conformation to allow its passage into the cell.

Describe active transport using the Na+/K+ ATPase.

The Na+/K+ ATPase pump actively transports Na+ out of and K+ into the cell, using ATP to maintain gradients.

What is a P type pump? Name an example.

A P type pump is an ATPase that adds a phosphate group to itself; an example is the Na+/K+ ATPase.

What is a V type pump?

V type pumps are ATPases that transport protons across membranes, such as those found in organelles.

What is an ATP-binding cassette protein?

ATP-binding cassette (ABC) proteins are a family of transporters that utilize ATP to transport various substrates across membranes.

What is a membrane potential?

Membrane potential is the voltage difference across a membrane due to the distribution of ions.

What is a resting potential?

Resting potential is the electrical charge difference across the plasma membrane of a neuron at rest.

What types of cells have a resting potential?

Neurons, muscle cells, and other excitable cells have resting potentials.

What is a neuron?

A neuron is a specialized cell that transmits nerve impulses.

Name the parts of a typical neuron and their functions.

Dendrites (receive signals), cell body (process signals), axon (conduct signals), and axon terminals (transmit signals to other cells).

How are K+ gradients across the membrane maintained?

K+ gradients are maintained by the Na+/K+ ATPase pump and selective permeability of the membrane.

Which ions are typically more concentrated inside versus outside the cell?

K+ is more concentrated inside, while Na+, Cl-, and Ca++ are more concentrated outside.

How is an action potential generated?

An action potential is generated when depolarization reaches a threshold, leading to rapid influx of Na+.

What does it mean that excitable membranes exhibit all-or-none behavior?

It means once the threshold is reached, an action potential is generated fully, or not at all.

What two criteria primarily affect the speed of a nerve impulse?

Axon diameter and myelination influence the speed of nerve impulse conduction.

Describe impulse propagation for non-myelinated and myelinated neurons.

In non-myelinated neurons, impulses propagate continuously; in myelinated neurons, impulses jump between nodes of Ranvier, speeding transmission.

What is a synapse?

A synapse is a junction where nerve signals are transmitted between neurons or from neurons to other cells.

Describe the importance of neurotransmitters.

Neurotransmitters are chemical messengers that transmit signals across synapses, facilitating communication between neurons.

How is neurotransmitter action terminated?

Neurotransmitter action is terminated by reuptake, enzymatic degradation, or diffusion away from the synaptic cleft.

Describe impulse transmission with acetylcholine as the neurotransmitter.

Acetylcholine is released from the presynaptic neuron, binds to receptors on the postsynaptic neuron, triggering impulse transmission.

How do different cone snail toxins affect impulse transmission?

Cone snail toxins can block ion channels or interfere with neurotransmitter release, affecting nerve impulse transmission.