Enzymes and Metabolism Overview

Overview

This lesson covers the role of enzymes in metabolism, how enzymes work, the lock and key model, and how temperature and pH affect enzyme activity.

Enzymes are biological catalysts made from protein that speed up chemical reactions in cells.
Digestive enzymes act outside of cells to break down large, insoluble food molecules into smaller, soluble ones.
Metabolism is the sum of all chemical reactions in a cell or organism, including synthesis and breakdown of molecules.
Enzymes speed up reactions at low temperatures, such as human body temperature.
Enzymes are unchanged by the reaction and can process many substrates per second.

Each enzyme catalyses a specific reaction due to the complementary shape of its active site and substrate.
Enzymes have unique three-dimensional shapes dictated by amino acid order.
The lock and key model explains enzyme action: substrates fit exactly into the active site.
Enzyme and substrate collisions occur randomly due to molecular motion.
After catalysis, products are released, and the enzyme is ready for more reactions.

Enzymes work fastest at their optimum temperature (about 37°C in humans).
Increasing temperature increases enzyme activity up to the optimum due to faster molecular movement and more collisions.
High temperatures denature enzymes by breaking bonds, changing the active site's shape so substrates can't fit.
Denaturation is usually irreversible; activity stops if the enzyme is denatured.
Low temperatures slow reactions but do not denature enzymes.

Most enzymes have an optimum pH of 7, but some work best in acidic or alkaline environments.
Moving away from the optimum pH changes the shape of the active site, reducing activity.
Extreme pH changes denature enzymes, stopping activity entirely.

Enzyme — A protein that acts as a biological catalyst to speed up chemical reactions.
Metabolism — The sum of all chemical reactions in a cell or organism.
Substrate — The molecule an enzyme acts upon.
Active Site — The specific region of an enzyme where a substrate binds.
Denatured — When an enzyme loses its shape and can no longer function.
Lock and Key Model — A model describing how enzymes and substrates fit together precisely.

Review diagrams of enzyme specificity and the lock and key model.
Practice questions on enzyme activity and factors affecting it.
Prepare for practicals investigating the effects of temperature and pH on enzymes.