Cell Signalling (i): The Need for Control Flashcards

Flashcards covering the fundamentals of cell signalling, metabolic control, enzyme kinetics, and receptor binding analysis from BMS5208 Lecture 1.

Catabolism

Energy-releasing, carbon-oxidising, degradative metabolic pathways.

Anabolism

Energy-storing, biosynthetic metabolic pathways.

Futile Cycle

A state where catabolic and anabolic pathways that are almost exact opposites (e.g., glycolysis and gluconeogenesis) run at full speed simultaneously, expending energy without achieving anything.

Negative Feedback

The inhibition of a process by the presence of large amounts of the final Product, such as the inhibition of Hexokinase by Glucose-6-P.

Precursor/Reactant Activation

The activation of a process by the presence of large amounts of initial reactant, signaling that the process hasn’t consumed enough reactant.

Allosteric Control (Non-competitive inhibition)

A mechanism where a regulator molecule binds to an enzyme at a site other than the substrate-binding site, altering the enzyme’s conformation and activity.

PFK (Phosphofructokinase) Allosteric Regulation

A glycolytic (catabolic) enzyme that is allosterically inhibited by ATP and stimulated by AMP.

PEPCK Allosteric Regulation

A gluconeogenic (anabolic) enzyme that is allosterically stimulated by ATP and inhibited by AMP.

Direct (Competitive) Inhibition

A mechanism where an inhibitor competes with a substrate for the active site of an enzyme; the inhibition can be overcome by increasing the substrate-to-inhibitor ratio.

Succinic Dehydrogenase Inhibition

An example of competitive inhibition where malonic acid binds to the same site as succinic acid during the TCA Cycle but catalysis does not occur.

Signal Transduction

A basic process in molecular cell biology involving the conversion of a signal from outside the cell to a functional change within the cell.

Steroid Hormones

Hydrophobic signals that cross the plasma membrane to bind to cytoplasmic receptors; the resulting complex binds to DNA using 'Zn fingers' to affect gene expression.

Amino acid-derived hormones

Signals that cannot cross the plasma membrane and must bind to membrane receptors to initiate intracellular responses.

Steroid Hormone Receptor Domains

Functional modules consisting of a hormone-binding domain (dimerization unit), a zinc-finger domain for DNA binding to the steroid response element (SRE), and a domain to activate gene promoters.

Non-steroid Hormone Receptors

Integral transmembrane proteins characterized by extracellular regions for hormone interaction, membrane-spanning $\text{T-M domains}$ ($\text{a helices}$), and cytosolic regions for transducer interaction.

Michaelis-Menton Equation

$$V = V_{max} \times \frac{[S]}{[S] + Km}$$

Km

The concentration of ligand/substrate that induces $50\%$ maximal binding to an enzyme; a low $Km$ value indicates high affinity.

Lineweaver-Burke Plot Equation

$$\frac{1}{V} = \frac{Km}{V_{max}} \times \frac{1}{[S]} + \frac{1}{V_{max}}$$

Kd (Dissociation Constant)

The concentration of signal or ligand that induces $50\%$ maximal binding to a receptor; used to express the affinity of binding.

Scatchard Plot

A mathematical manipulation of saturation binding data expressed as a straight line where the slope is $-1/Kd$ and the x-axis intercept represents the density of receptors.

IC50 (or Ki)

The concentration of inhibitor necessary to halve the reaction rate of an enzyme-catalysed reaction.

EC50

The concentration of agonist that induces a response halfway between the baseline and the maximal response.

Ligand

A broad term encompassing enzyme substrates, inhibitors, signals (hormones, agonists), or blockers (antagonists) that bind to receptors or enzymes.

Drugs

Synthetic molecules designed and manufactured to mimic or modulate natural ligand-receptor or ligand-enzyme interactions.