cell membranes and signalling

What is the normal body temperature for humans?

37 degrees Celsius

What are nonpenetrating solutes?

Substances that cannot cross the plasma membrane.

What do membranes serve as for molecules?

A selective barrier to the passage of molecules.

What is a desmosome?

An accumulation of protein known as dense plaques on the cytoplasmic side of the plasma membrane that anchors adjacent cells.

What is a tight junction?

A junction where the extracellular surfaces of two adjacent plasma membranes join to eliminate interstitial space.

What characterizes a gap junction?

Protein channels linking the cytosols of adjacent cells.

What are integrins?

Transmembrane proteins that link extracellular matrix proteins to adjacent cells.

Define flux in the context of molecular movement.

The amount of material crossing a surface in a unit of time.

What is net flux?

The difference between two one-way fluxes.

How does temperature affect the magnitude of flux?

Higher temperature results in faster movement of molecules and greater flux.

What role does surface area play in molecular flux?

More surface area between two regions corresponds to a larger net flux.

What is the primary factor affecting diffusion rates through membranes?

The distance molecules have to diffuse.

What types of molecules diffuse readily through lipid bilayers?

Nonpolar molecules like oxygen, carbon dioxide, fatty acids, and steroid hormones.

How do ions such as Na+, K+, and Cl- cross cell membranes?

Through specific protein channels.

What characterizes ligand-gated ion channels?

They open when a specific molecule binds to them, increasing diffusion of ions.

Define facilitated diffusion.

The net flux of a molecule across a membrane from higher to lower concentration.

What is active transport?

The movement of molecules against their concentration gradient using energy.

What is the Na+/K+ ATPase?

A primary active transporter that maintains membrane potential in cells.

What is secondary active transport?

Transport that uses an electrochemical gradient to move solutes against their concentration gradient.

What is the membrane potential?

The separation of electrical charge across a membrane.

What is osmosis?

The net diffusion of water across a membrane dependent on its concentration.

Define osmolarity.

The total solute concentration of a solution.

What is osmotic pressure?

The force required to prevent the flow of water into a solution.

What does ligand binding do to a protein?

It changes the conformation of the protein, which may activate or inhibit its function.

What is the significance of high-affinity and low-affinity binding sites?

High-affinity sites tightly bind ligands, while low-affinity sites bind them more weakly.

What factors affect saturation in binding sites?

Concentration of unbound ligand and affinity of binding site.

What is allosteric modulation?

When binding of a ligand to one site on a protein changes the shape of another binding site.

Define an enzyme's activation energy.

The energy needed to overcome repulsion from electrons to initiate a reaction.

What are cofactors?

Trace metals that bind to enzymes and alter their conformation.

What is a coenzyme?

An organic molecule that participates as a substrate within a reaction.

What factors can influence enzyme-mediated reactions?

Substrate concentration, enzyme concentration, and enzyme activity.

What distinguishes lipid soluble messengers?

They bind to intracellular receptors and diffuse through the plasma membrane.

What is the role of water soluble messengers?

They bind to extracellular parts of intrinsic membrane proteins and trigger intracellular signaling.

What is the first messenger in cellular signaling?

The chemical receptor that reaches the cell and binds to its receptors.

What are secondary messengers?

Molecules generated in the cytoplasm due to receptor activation that transmit signals within the cell.

Explain the function of protein kinases.

They transfer phosphate from ATP to proteins to modify their function.

Define ligand-gated ion channels.

Channels that open in response to binding of a ligand, allowing ions to flow through.

What is the function of Type B receptors in cell signaling?

They act as intrinsic enzymes, often phosphorylating target proteins.

What do Janus Kinases (JAKs) do?

They activate when a ligand binds to a receptor, leading to phosphorylation of proteins.

Describe G-protein coupled receptors.

They activate G-proteins which then initiate downstream signaling cascades.

What is cAMP and its role in cellular signaling?

Cyclic AMP acts as a second messenger that activates protein kinases.

What is the role of calmodulin?

It activates or inhibits kinases in response to calcium levels.

What can cause cessation of signaling in cells?

Decreased concentration of first messenger molecules, receptor inactivation, or engulfment by endocytosis.

How can drugs interfere with signaling pathways?

By inhibiting enzymes involved in the pathways, such as cyclooxygenase or phospholipase A2.

What are eicosanoids?

Intracellular messengers derived from arachidonic acid that act locally.

What is the function of the Ca2+ ion in signaling?

It promotes signaling pathways by changing levels in the cytosol.

How does the concentration of first messenger vary affect receptor activity?

A decrease leads to potential inactivation of receptors.

What is the Law of Mass Action?

The concentration of reactants or products can influence the direction of a reaction.

Define chemical specificity.

The ability of a binding site to specifically bind certain ligands.

What does saturation refer to in binding interactions?

The fraction of total binding sites occupied at any time.