Begrippenlijst 104

Ligand

A molecule that binds to a receptor, which can be an endogenous substance like a hormone or neurotransmitter, or a drug.

Receptor

A protein that has a specific binding site for a ligand and its binding leads to a cellular response.

GPCR (G-protein-coupled receptor)

A common type of receptor in the cell membrane involved in signal transduction, with about 40% of all drugs acting via GPCRs.

Binding Affinity

The strength of the binding between a ligand and a receptor, expressed in the dissociation constant (Kdiss), where a lower Kdiss indicates higher affinity.

Specificity

The degree to which a ligand binds to one specific target, determined by molecular forces, functional groups, structure, and shape of both ligand and target.

Selectivity

The preference of a ligand to bind to one target over others; a high selectivity ligand binds more strongly to the intended target.

Agonist

A ligand that binds to a receptor and activates it, leading to a cellular response.

Antagonist

A ligand that binds to a receptor and blocks its activation, inhibiting the action of an agonist.

Partial Agonist

A ligand that binds to a receptor but causes only a partial effect compared to a full agonist.

Inverse Agonist

A ligand that binds to a receptor and causes an effect that is opposite to that of an agonist.

Inhibitor

A molecule that inhibits the activity of an enzyme or the binding of a ligand to a receptor.

Competitive Inhibition

A type of inhibition where the inhibitor competes with the substrate or ligand for binding to the active site.

Non-competitive Inhibition

A type of inhibition where increasing the concentration of agonist will not increase the acitivity (past a certain point).

Ki (inhibition constant)

A measure of the affinity of an inhibitor for an enzyme or receptor, where a lower Ki indicates stronger binding.

IC50

The concentration of inhibitor needed to reduce half of the maximum binding or activity.

Cheng-Prusoff equation

An equation that relates Ki to IC50 and Kdiss of the ligand.

Displacement Curve

A graph showing the binding of a labeled ligand to a receptor as a function of the concentration of an unlabeled inhibitor.

Enzyme

A protein that acts as a catalyst to accelerate biochemical reactions.

Substrate

The molecule that an enzyme acts upon, binding to the active site and being converted into a product.

Michaelis-Menten Kinetics

A model that describes the rate of an enzymatic reaction as a function of substrate concentration.

V0 (initial reaction velocity)

The rate of the enzymatic reaction at the beginning when the substrate concentration is still high.

Vmax (maximum reaction velocity)

The maximum rate of an enzymatic reaction reached when all enzymes are saturated with substrate.

Km (Michaelis constant)

The substrate concentration at which the reaction rate is half of Vmax, indicating enzyme affinity for substrate.

kcat (catalytic constant)

The number of substrate molecules converted to product per enzyme molecule per time unit, also known as turnover number.

Catalytic Efficiency (kcat/Km)

A measure of enzyme efficiency considering both catalytic speed (kcat) and affinity for substrate (Km).

Signal Transduction

The process of transmitting an extracellular signal to the inside of a cell, leading to a cellular response.

First Messenger

The extracellular signaling molecule (ligand) that binds to a receptor.

Second Messenger

An intracellular signaling molecule produced in response to the binding of a first messenger to a receptor.

G-protein

A protein involved in signal transduction, activated by GPCRs, consisting of three subunits: α, β, and γ.

Phospholipase C (PLC)

An enzyme activated by Gq proteins that splits PIP2 into DAG and IP3.

Diacylglycerol (DAG)

A second messenger that activates protein kinase C (PKC).

Inositol 1,4,5-trisphosphate (IP3)

A second messenger that binds to receptors on the ER and causes the release of Ca2+ into the cytoplasm.

Protein Kinase C (PKC)

An enzyme activated by DAG involved in various cellular processes.

Gene Expression

The process of converting genetic information in DNA into proteins.

Transcription

The process of copying DNA into RNA.

Translation

The process of using RNA as a template for protein synthesis.

Transcription Factor

A protein that binds to DNA and regulates gene transcription.

Promoter

A DNA sequence located upstream of a gene that forms the binding site for RNA polymerase and transcription factors.

Enhancer

A DNA sequence that stimulates the transcription of a gene.

Silencer

A DNA sequence that inhibits the transcription of a gene.

Chromatin

The complex of DNA and proteins that forms chromosomes.

Nuclear Receptor

A type of transcription factor located in the nucleus activated by ligand binding.

Histone

A protein that organizes and packages DNA into chromatin.

Histone Acetylation

The addition of an acetyl group to a histone protein, opening the chromatin structure and promoting transcription.

HAT (Histone Acetyltransferase)

An enzyme that catalyzes histone acetylation.

HDAC (Histone Deacetylase)

An enzyme that removes acetyl groups from histones.

Organ Bath

An experimental setup used to study the effects of drugs on tissues.

EC50 (half maximal effective concentration)

The concentration of a drug needed to achieve 50% of the maximum effect.

Emax (maximal efficacy)

The maximum effect that a drug can produce.

Potency

A measure of the drug concentration needed to achieve a certain effect; higher potency indicates a lower concentration is required.

Efficacy

A measure of the maximum response a drug can produce.

Spare Receptors

Receptors that do not need to be occupied to achieve an (overall) maximum effect.

Receptor Reserve

The difference between the number of receptors that need to be occupied for a maximum effect and the total number of receptors.

Receptor Threshold

The minimum number of receptors that need to be occupied to produce an effect.