Introduction to Biochemistry II

Structures of carbohydrates

• Monosaccharides: carbohydrates with a single ring structure

• Disaccharides: carbohydrates with a double ring structure

• Polysaccharides: long chains of monosaccharides, storage carbohydrates
• Branching of glycogen enables fast metabolism of glucose

Thermodynamics

• 1st Law: energy is neither created nor destroyed

• 2nd Law: when energy is converted from one form to another, some of that energy becomes unavailable to do work
• No energy transformation is 100% efficient

Thermodynamic reactions

• Reactions involve change in:
• Enthalpy: heat content
• Entropy: randomness/disorder
• Means free energy will tend towards an unusable state after multiple reactions

• Change in free energy = (energy of products) – (energy of reactants)
• 𝝙G = 𝝙H - T 𝝙S

• Free energy is related to the point of equilibrium
• 𝝙G near 0 means reaction is readily reversible

• Total free energy of products is less than total free energy of reactants

• Reactions can occur spontaneously

• Total free energy of products is more than total free energy of reactants
• Reactions require input of energy

• Many reactions within the body occur by coupling an unfavorable reaction (positive 𝝙G) with a favorable reaction - e.g. ATP + H2O → ADP + Pi + H+

• Therefore, ATP is widely used as energy for many cellular processes

Metabolism

• Metabolism: all the reactions taking place in the body

• Catabolism: breaking down complex molecules into smaller ones and releasing energy
• Yields energy - exergonic and oxidative

• Anabolism: synthesizing complex molecules out of smaller ones in energy-consuming reactions
• Requires energy - endergonic and reductive