Enzymes IGCSE Biology

Vocabulary flashcards covering the definition, action, and experimental investigation of enzymes, including the effects of temperature and pH as defined in the Cambridge IGCSE Co-ordinated Sciences syllabus.

Enzymes

Proteins that act as biological catalysts, speeding up the rate of a chemical reaction without being changed or used up in the reaction.

Biological catalysts

A term for enzymes because they are made in living cells and speed up the rate of chemical reactions without being changed.

Metabolic reactions

All the reactions that keep an organism alive.

Digestive timescale

Without enzymes, it would take around $2-3$ weeks to digest one meal; with enzymes, it takes around $4$ hours.

Iodine solution

A substance used in enzyme investigations that turns blue-black in the presence of starch and remains orange-brown when starch has been broken down.

Active site

The area of an enzyme where the substrate attaches, having a specific 3-D shape that is complementary to the substrate.

Lock and key hypothesis

The hypothesis describing how an enzyme is specific to one particular substrate because the active site is a complementary shape to that substrate.

Enzyme-substrate complex

The structure formed when a substrate moves into and fits into the enzyme's active site.

Optimum temperature

The temperature at which an enzyme works fastest, which in the human body is $37^\text{o}C$.

Denaturation

An irreversible process where high temperatures (beyond the optimum) or extreme pH levels break the bonds holding the enzyme together, causing the active site to lose its shape so the substrate can no longer fit.

Kinetic energy

The energy molecules have that increases as temperature rises from $0^\text{o}C$ to the optimum, leading to more collisions between enzymes and substrates.

Optimum pH (Stomach)

The pH level at which enzymes produced in acidic stomach conditions work best, which is $pH\,2$.

Optimum pH (Duodenum)

The pH level at which enzymes produced in alkaline conditions work best, typically $pH\,8$ or $pH\,9$.

Specificity

The characteristic of an enzyme being able to bind only to one particular substrate due to the unique shape of its active site.