Protein Function and Ligand Binding in Biology Flashcards | Quizlet

What determines protein function?

Protein function depends on its structure, specifically the amino acid composition and their locations.

What are the main biological roles of proteins?

Proteins are involved in metabolism, structure, transport, cell signaling, and genomic caretaking.

What is a ligand?

A molecule that is bound by a macromolecule, specifically at a protein binding site.

What types of molecules can act as ligands?

Small molecules, metals, DNA, or other proteins.

What are three examples of weak interactions that allow ligands to bind within binding pockets?

Hydrogen bonds, ionic interactions, and hydrophobic interactions.

How does myoglobin bind to oxygen?

Myoglobin binds to a molecule called heme, which is bound to an iron atom that binds to oxygen.

What does the association rate constant ($k_{\text{on}}$) describe?

The rate at which a protein binds to a ligand.

What does the dissociation rate constant ($k_{\text{off}}$) describe?

The rate at which a protein-ligand complex dissociates.

What does the equilibrium constant ($K_{\text{eq}}$) represent in ligand binding?

The ratio of the association rate constant to the dissociation rate constant, indicating the balance between bound and unbound states.

What does a low dissociation constant ($K_d$) indicate?

Strong binding affinity between a protein and its ligand.

What binding affinities are indicated by $K_d < 10\,\text{nM}$ and $K_d > 10\,\text{nM}$?

$K_d < 10\,\text{nM}$ indicates strong binding/high affinity, while $K_d > 10\,\text{nM}$ indicates weak binding.

What is fractional saturation ($\theta$)?

The ratio of bound ligand to the total binding sites available (the fraction of the protein's binding sites currently occupied by a ligand).

What does the dissociation constant ($K_d$) represent in terms of binding site occupancy?

The ligand concentration at which $50\%$ of binding sites are occupied.

What is the primary difference in function between myoglobin and hemoglobin?

Myoglobin is primarily for oxygen storage, while hemoglobin is for oxygen transport.

How are concentrations expressed when the bound molecule is a gas?

In terms of partial pressures.

What does the $P_{50}$ value indicate?

The $p\text{O}_2$ at which saturation is $50\%$ (half the $\text{O}_2$ binding sites are occupied).

What is the typical $p\text{O}_2$ in healthy, oxygenated tissues?

Approximately $4\,\text{kPa}$, ensuring myoglobin always has an emergency store of $\text{O}_2$.

At what oxygen level threshold does myoglobin release oxygen to muscles?

When oxygen levels drop below $0.5\,\text{kPa}$.

What is cooperativity in protein binding?

A phenomenon where the binding of a ligand to one site affects the binding properties of other sites on the same protein.

What is positive cooperativity?

When the first binding event increases the affinity for subsequent binding events.

How do the tense ($T$) and relaxed ($R$) states of hemoglobin differ?

The tense state ($T$) has a low affinity for oxygen, whereas the relaxed state ($R$) has a high affinity for oxygen.

What role does $2,3\text{-BPG}$ play in hemoglobin function?

It stabilizes the tense state ($T$) of hemoglobin, reducing its affinity for oxygen and facilitating oxygen release in tissues.

What happens to hemoglobin's binding profile in the absence of $2,3\text{-BPG}$?

It resembles an exponential curve, indicating a high affinity for oxygen at all concentrations.

How does carbon monoxide affect myoglobin?

Carbon monoxide binds to myoglobin over $20{,}000$ times better than oxygen, blocking oxygen function and leading to toxicity.

What is allostery?

The regulation of a protein's activity through the binding of a ligand at a site other than the active site.