week 5 Regulatory strategies 1/2

What is allosteric control of a protein? Give examples of positive and negative regulation.

Regulation is when an effector binds a site other than the active site, changing protein activity.

Positive: Effector increases activity (e.g., O₂ binding to haemoglobin).

Negative: Effector decreases activity (e.g., CTP inhibiting ATCase).

What are isoenzymes and give an example?

Different forms of the same enzyme with varying properties, found in different tissues or stages.

Example: Lactate dehydrogenase (LDH) with H-LDH in the heart and M-LDH in the muscle.

Explain proteolytic activation and give an example.

Enzymes are made as inactive precursors (zymogens) and activated by cleavage.
Example: Trypsinogen activated to trypsin in digestion.

How does covalent modification regulate enzymes?

Addition/removal of chemical groups (e.g., phosphorylation on serine, threonine, tyrosine) by kinases and phosphatases can activate or inhibit enzyme activity.

What is feedback inhibition? Provide an example.

The end product inhibits the first enzyme in its pathway to prevent excess production.
Example: CTP inhibits ATCase in pyrimidine synthesis.

How can mutations affect protein function? Illustrate with sickle cell anaemia.

Mutations alter amino acid sequences, affecting structure/function, possibly causing disease.
Sickle cell anaemia: glutamate → valine mutation in hemoglobin causes sickling of red blood cells, leading to blockages and organ damage.

What roles do membrane proteins play in cell membranes?

hey enable communication with the environment, transport molecules in and out, and detect signals.

What is the fluid mosaic model?

It describes the membrane as a fluid structure where proteins and lipids can move laterally within the lipid bilayer.

Name and describe the main types of passive transport across membranes.

Simple diffusion: small, nonpolar molecules cross directly through the lipid bilayer.

Transporter-mediated diffusion: specific molecules cross via transport proteins, reaching a maximum rate (Vmax).

Channel-mediated transport: ions or water move quickly through protein channels passively.

What is active transport?

Movement of molecules against their concentration gradient using energy, usually from ATP, via specific transporters.

What are G-protein coupled receptors (GPCRs)?

Membrane proteins that detect extracellular signals and activate intracellular G-proteins to trigger cellular responses.

How do GPCRs transmit signals inside the cell?

Binding of a signal activates the GPCR, which activates a G-protein, initiating a signaling cascade leading to a cellular response.