Metabolic Pathways-Controlled by Enzymes

Control of Metabolic Pathways

Definition

Metabolic pathways within cells are controlled by the presence or absence of specific enzymes, as well as the regulation of key enzyme reactions' rates.

Enzyme Regulation

Enzymes play a crucial role in metabolic pathways by catalysing reactions. Their activity can be regulated to ensure that metabolic processes occur as needed.

Induced Fit and Active Site

1. Induced Fit

• Explanation: Induced fit is a phenomenon where the active site of an enzyme changes its shape to accommodate and bind to the substrate effectively after the substrate has attached.
• Example: When an enzyme binds to a substrate, the active site undergoes conformational changes to establish a more precise fit, enhancing the catalytic process.

2. Active Site Role

• Explanation: The active site of an enzyme is crucial in affecting the activation energy required for a reaction, as well as the affinity of the substrate and products for the active site.
• Example: The active site lowers the activation energy barrier, facilitating the conversion of substrates into products.

Effect of Substrate and Product Concentration

1. Substrate Affinity

• Explanation: Substrate molecules have a high affinity for the active site of an enzyme, allowing them to bind effectively. Products, on the other hand, have a low affinity, enabling them to be released from the active site.
• Example: Enzymes facilitate the formation of products by binding substrates and then releasing the products once the reaction is complete.

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Metabolic Pathways - Enzymes

2. Reaction Direction

• Explanation: Some metabolic reactions are reversible, and the presence of a substrate or removal of a product can drive a sequence of reactions in a particular direction.
• Example: In glycolysis, the presence of glucose drives the breakdown of glucose into pyruvate.

Control of Metabolic Pathways

1. Competitive Inhibition

• Explanation: Competitive inhibitors bind at the active site of an enzyme, preventing the substrate from binding.
• Example: Inhibition of the enzyme acetylcholinesterase by nerve gases like sarin blocks the breakdown of the neurotransmitter acetylcholine, leading to muscle paralysis.

2. Reversibility of Competitive Inhibition

• Explanation: Competitive inhibition can be reversed by increasing the concentration of the substrate, as this competition can outcompete the inhibitor.
• Example: High levels of substrate can overcome the inhibitory effects of competitive inhibitors.

3. Non-Competitive Inhibition

• Explanation: Non-competitive inhibitors bind away from the active site but change the shape of the active site, preventing the substrate from binding.
• Example: Heavy metals like lead can act as non-competitive inhibitors, disrupting enzyme function.

4. Irreversibility of Non-Competitive Inhibition

• Explanation: Non-competitive inhibition cannot be reversed by increasing substrate concentration, as the inhibitor alters the enzyme's active site irreversibly.
• Example: Once non-competitive inhibitors bind to an enzyme, their effects persist.

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Metabolic Pathways-Enzymes

5. Feedback Inhibition

• Explanation: Feedback inhibition occurs when the end product of a metabolic pathway reaches a critical concentration. This end product then inhibits an earlier enzyme in the pathway, blocking further synthesis of the end product.

• Example: In the biosynthesis of amino acids, excess levels of the final amino acid can inhibit the activity of the first enzyme in the pathway, preventing overproduction.

Summary

Metabolic pathways within cells are intricately controlled by enzymes, with their activity regulated to ensure the precise functioning of biochemical reactions. Induced fit and the active site of enzymes play vital roles in catalysing reactions by reducing activation energy and ensuring substrate affinity. The concentration of substrates and products influences reaction direction. Control of metabolic pathways involves competitive and non-competitive inhibition, with competitive inhibition being reversible by increasing substrate concentration. In contrast, non-competitive inhibition is irreversible and cannot be overcome by substrate concentration. Feedback inhibition is a mechanism that prevents overproduction of end products by inhibiting earlier enzymes in the pathway. These regulatory mechanisms ensure that metabolic pathways operate efficiently and in response to the cell's needs