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Module 1: Biosynthesis and Cellular Transport

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Biosynthesis and Cellular Transport - Lesson Summary

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Certificate One Marketing Introduction to Metabolic Engineering Summary
The precursors for the synthesis of macromolecules are small, rapidly used pools of low molecular weight compounds.
The precursors are constantly replenished by biochemical synthesis from metabolites ultimately derived from glucose or other carbon sources.
Carbon and energy are converted through the central carbon metabolism pathways into a set of 12 precursor metabolites.
Metabolism is fundamentally divided into two parts, which are:
1. Energy conserving or fueling reactions also called catabolism.
2. Anabolism
Anabolism: synthesis of complex organic molecules from simpler ones. This involves the following steps:
1. Conversion of carbon sources from microorganisms to precursor metabolites.
2. Synthesis of monomers and their building block from precursor metabolites.
3. Synthesis of macromolecules.
4. Assembly of the macromolecules into cellular structures.
The four overarching principles for metabolism of living systems:
1. Enzyme catalysis
2. Energy harvesting from redox reactions
3. Energetically coupled reactions
4. Transduction of energy from transmembrane ion gradients into ATP.
Frameworks of metabolism: these are classified into four distinct types of reactions, namely:
1. Fueling reactions
2. Biosynthetic reaction
3. Polymerization reaction
4. Assembly reactions
Cellular transport processes are divided into two main types:
1. Passive transport process subdivided into free diffusion and facilitated diffusion.
2. Active transport process.
Nutrient uptake by a cell will depend on:
1. Specificity of uptake.
2. Uptake against concentration gradient.
3. Selectivity and permeability of the membrane.
Properties of passive transport:
• It relies in diffusion
• It expends no energy
• Operates down the concentration gradient.
It involves three steps:
1. Transfer of compounds from the extracellular medium to the membrane phase.
2. Diffusion of the compound through the lipid layer.
3. Transfer of the compound from the membrane phase to the cytosol.

Simple diffusion
1. The rate of diffusion is dependent on the size of concentration gradient.
2. Large concentration gradient is required for adequate nutrient uptake.
3. Small molecules (H2O, O2, CO2, etc.), move across membranes by passive diffusion.
4. Not fast or selective.
Facilitated diffusion
1. Compounds with low solubility in plasma membrane are transported at extremely slow rate.
2. Transport of such molecules across the membrane is accomplished by mediation of carrier molecules embedded in the membrane.
3. It requires no energy expenditure and can occur only in the downward direction.
4. The rate of diffusion increases with the concentration gradients.
Active transport – Properties of active transport:
1. Transport of substances against concentration gradients
2. It involves carrier proteins.
3. It also has some similar properties with facilitated diffusion, including, saturation kinetics, substrate specificity, and inhibitability.
4. It is a free energy consuming process.
5. It may be coupled to another transport process.
Important outputs of fueling (catabolic) reactions
1. Generation of Gibbs free energy as ATP.
2. Production of cofactor NADPH
3. Formation of precursor metabolites required in the biosynthesis of building blocks.
The catabolism of sugars starts with glycolysis, producing pyruvate as the end product. The pyruvate is processed further into the following pathways:
1. TCA cycle
2. Fermentation
3. Transamination pathway for amino acid biosynthesis
4. Anaplerotic reactions
Glycolysis is the sum total of all biochemical reactions by which glucose is converted to pyruvate. It is accomplished via three major metabolic routes, namely:
1. Embden-Mayerhof-Parnas (EMP) pathway
2. Pentose phosphate pathway
3. Entener Doudoroff (ED) pathway