Higher Biology Unit 2 2 1 Metabolic Pathways

Higher Biology Unit 2 2. 1 Metabolic Pathways & their Control

Metabolism • Metabolism is the term used to describe all of the chemical reactions that take place inside a living cell. • Most of these chemical reactions form steps in metabolic pathways • Respiration and photosynthesis are examples of metabolic pathways.

Metabolic Pathways • All metabolic pathways are controlled by enzymes. • Each step in the pathway is controlled by a different enzyme. Substance A Enzyme 1 Substance B Enzyme 2 Substance C

Metabolic Pathways • To allow control of a metabolic pathway, many contain reversible and irreversible steps. Intermediate 1 Intermediate 2 Intermediate 3 Intermediate 4

Metabolic Pathways • If a step is irreversible then there is usually an alternative pathway that can bypass it.

Metabolic Pathways • There are two types of metabolic pathways; ØCatabolic pathways ØAnabolic pathways

Catabolic Pathways • Catabolic pathways break down complex molecules into simpler ones. • This results in the release of energy. • Respiration is an example of a catabolic pathway as glucose is broken down to produce carbon dioxide, water and ATP.

Anabolic Pathways • Anabolic pathways build up simple molecules into more complex ones. • This requires energy. • Protein synthesis is an example of an anabolic pathway as amino acids are built up into proteins.

Key Points ü Metabolism is the sum of all biochemical reactions that take place in a cell. ü Metabolic pathways are controlled by different enzymes. ü Metabolic pathways can have reversible and irreversible steps and alternative routes that can bypass steps in a pathway.

Key Points ü Anabolic pathways involve the synthesis of molecules. ü Anabolic pathways require an input of energy. ü Catabolic pathways involve the breakdown of molecules and release energy. ü Catabolic pathways release energy.

Questions 1. Define the term “metabolism”. 2. Name both types of metabolic pathways. 3. Describe two ways in which these pathways differ. 4. How are the steps in metabolic pathways controlled?