Enzyme Structure and Function

Ever wondered why enzymes are so picky about what they work with? It's all about shape and complementary binding. Enzymes have a specific active site where substrates bind, and this shape determines exactly which reactions they can catalyse.

You'll find intracellular enzymes working inside organelles like chloroplasts and mitochondria, whilst extracellular enzymes like lipase and amylase get secreted outside cells to break down food during digestion.

The induced fit hypothesis explains how enzymes actually change shape slightly when substrates approach, ensuring the perfect fit. This is much more accurate than the old lock-and-key model because the enzyme (unlike a lock) gets altered during the process.

Cofactors are enzyme helpers you need to know about. Prosthetic groups like iron, zinc, and copper stay permanently attached, whilst coenzymes such as ATP and NAD bind temporarily to help reactions happen.

💡 Remember: Haemoglobin contains iron in its haem group - a perfect example of a prosthetic group in action!

Factors Affecting Enzyme Activity

Temperature dramatically affects enzyme performance, and there's a neat pattern to remember. As temperature increases, so does the reaction rate until you hit the optimum temperature - this happens because higher kinetic energy means more successful collisions.

The Q₁₀ coefficient shows that reaction rates typically double every 10°C rise. However, beyond the optimum, enzymes denature as bonds in their protein structure break, causing the active site to lose its shape.

Enzyme concentration and substrate concentration follow similar patterns - increasing either boosts the reaction rate until one becomes the limiting factor. When the graph flattens out, you've found your bottleneck.

pH changes can be deadly for enzymes since extreme conditions break protein bonds. Different enzymes have wildly different optima - pepsin loves acidic conditions (pH 3) whilst amylase prefers neutral to slightly alkaline $pH 7-8$.

Competitive inhibition occurs when inhibitor molecules race substrates for the active site, whilst non-competitive inhibition involves inhibitors binding elsewhere and changing the active site's shape. The key difference? You can overcome competitive inhibition by adding more substrate, but non-competitive inhibition reduces the maximum possible reaction rate.

💡 Exam tip: If increasing substrate concentration doesn't help, you're dealing with non-competitive inhibition!

Enzyme Inhibition in Action

Real-world enzyme inhibition can be absolutely lethal, making this topic more relevant than you might think. Cyanide poisoning demonstrates irreversible inhibition at its most dangerous.

Potassium cyanide (KCN) blocks cytochrome c oxidase, the final enzyme in aerobic respiration's electron transport chain. It also inhibits catalase, effectively shutting down cellular energy production and causing rapid death.

Snake venom works differently by targeting neurotransmission. It inhibits chemicals that normally diffuse across nerve synapses, leading to constant muscle contraction and eventual paralysis of breathing muscles.

⚠️ Real-world connection: Understanding enzyme inhibition helps explain how many poisons and medicines actually work in the body!