Metabolism and Enzymes Lecture Review
Chapter 8: An Introduction to Metabolism
Definition of Metabolism
Metabolism encompasses the totality of an organism’s chemical reactions within cells.
Living cells function as miniature chemical factories where numerous reactions occur simultaneously.
Metabolic Pathways
A metabolic pathway is a sequence of chemical reactions that begins with a specific molecule and ends with a product.
Each step in the metabolic pathway is catalyzed by a specific enzyme.
Enzyme-Catalyzed Reactions
Enzymes: Proteins that act as catalysts to accelerate chemical reactions without being consumed in the process.
Example: Enzyme actions occur in a series such as:
Starting Molecule A --> Enzyme 1 --> Product B
Product B --> Enzyme 2 --> Product C
Product C --> Enzyme 3 --> Product D
Specific Metabolic Pathways
Glycolysis
Glycolysis is a significant catabolic pathway where glucose is broken down in the presence of oxygen.
Key molecules involved include:
ATP: Adenosine triphosphate, energy currency of cells.
ADP: Adenosine diphosphate, product of ATP hydrolysis.
Phosphorylation: The addition of phosphate groups to molecules as part of the reactions.
Catabolic and Anabolic Pathways
Catabolic pathways
Function: Release energy by breaking down complex molecules into simpler ones.
Example: Cellular respiration.
Anabolic pathways
Function: Consume energy to build complex molecules from simpler ones.
Example: Protein synthesis from amino acids.
Energy in Reactions
Exergonic Reactions
Definition: Reactions that proceed with a net release of energy.
Characteristics:
Spontaneous, involving a change where the free energy changes is negative (\Delta G < 0).
Endergonic Reactions
Definition: Reactions that absorb energy from their surroundings.
Characteristics:
Nonspontaneous, where the free energy change is positive (\Delta G > 0).
ATP - The Energy Currency
Structure of ATP:
Composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups.
Hydrolysis of ATP:
The terminal phosphate bond can be broken by hydrolysis, releasing energy.
Example:
ATP + H2O -> ADP + Inorganic Phosphate + Energy.
ATP in Reactions
ATP powers cellular work by coupling exergonic reactions with endergonic reactions.
Example of ATP coupling:
Glutamic acid + NH3 + ATP → Glutamine + ADP + Pi
This illustrates the phosphorylating of glutamic acid increases the reaction's drive.
Regeneration of ATP
ATP is a renewable resource generated from ADP through the addition of a phosphate group.
The energy to regenerate ATP comes from catabolic pathways in the cell, driving most cellular work.
Enzyme Activity
Catalyst Function
Catalyst: A chemical agent that accelerates a reaction without being used up.
Enzyme: A catalytic protein that facilitates biochemical reactions.
Example: Hydrolysis of sucrose facilitated by the enzyme sucrase.
Substrate Specificity
Enzymes convert substrates into products by forming an enzyme-substrate complex.
Active site: The specific region on the enzyme to which the substrate binds, crucial for catalysis.
Induced Fit Model: The active site molds itself around the substrate to enhance interaction.
Factors Affecting Enzyme Activity
General environmental factors such as temperature and pH can influence enzyme activity.
Chemicals affecting enzymes:
Cofactors: Nonprotein enzyme helpers that can be inorganic (e.g., metal ions) or organic (coenzymes, often vitamins).
Enzyme Inhibitors
Competitive inhibitors: Bind to the active site of an enzyme, blocking the substrate from binding.
Noncompetitive inhibitors: Bind to different parts of the enzyme, altering the active site's shape.
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics.
Feedback Inhibition
Feedback inhibition prevents a cell from overproducing substances by utilizing the end product of a metabolic pathway to inhibit the pathway itself.
Example:
Threonine is the initial substrate for the synthesis of isoleucine and when isoleucine accumulates, it inhibits the pathway's enzymes, preventing further synthesis.
Definition of Metabolism
Metabolism encompasses the totality of an organism’s chemical reactions within cells. These reactions manage the material and energy resources of the cell, enabling growth, reproduction, maintenance of structure, and response to environmental changes.
Living cells function as miniature chemical factories where numerous reactions occur simultaneously.
Metabolic Pathways
A metabolic pathway is a sequence of chemical reactions that begins with a specific molecule and ends with a product.
Metabolic pathways can be linear, branched, or cyclic, reflecting the diverse arrangements of enzyme-catalyzed reactions.
Each step in the metabolic pathway is catalyzed by a specific enzyme.
Enzyme-Catalyzed Reactions
Enzymes: Proteins that act as catalysts to accelerate chemical reactions by lowering the activation energy without being consumed in the process.
Example: Enzyme actions occur in a series such as:
Starting Molecule A --> Enzyme 1 --> Product B
Product B --> Enzyme 2 --> Product C
Product C --> Enzyme 3 --> Product D
Specific Metabolic Pathways
Glycolysis
Glycolysis is a significant catabolic pathway where glucose is broken down into two molecules of pyruvate, occurring in the cytoplasm. It serves as the initial step for both aerobic and anaerobic respiration.
Key molecules involved include:
ATP: Adenosine triphosphate, energy currency of cells.
ADP: Adenosine diphosphate, product of ATP hydrolysis.
Phosphorylation: The addition of phosphate groups to molecules as part of the reactions.
Catabolic and Anabolic Pathways
Catabolic pathways
Function: Release energy by breaking down complex molecules into simpler ones. This energy is often captured in ATP.
Example: Cellular respiration, which breaks down glucose.
Anabolic pathways
Function: Consume energy to build complex molecules from simpler ones. These reactions require energy input, typically from ATP hydrolysis.
Example: Protein synthesis from amino acids, or photosynthesis.
Energy in Reactions
Exergonic Reactions
Definition: Reactions that proceed with a net release of energy.
Characteristics:
Spontaneous, involving a change where the Gibbs free energy (\Delta G) is negative (\Delta G < 0). These reactions can occur without a continuous input of energy.
Endergonic Reactions
Definition: Reactions that absorb energy from their surroundings.
Characteristics:
Nonspontaneous, where the Gibbs free energy change (\Delta G) is positive (\Delta G > 0). These reactions require an input of energy to proceed.
ATP - The Energy Currency
Structure of ATP:
Composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups. The bonds between the phosphate groups are often referred to as 'high-energy' bonds due to the significant energy released upon their hydrolysis.
Hydrolysis of ATP:
The terminal phosphate bond can be broken by hydrolysis, releasing a substantial amount of energy that cells can harness for various activities.
Example: - ATP + H2O -> ADP + Inorganic Phosphate + Energy.
ATP in Reactions
ATP powers cellular work by coupling exergonic reactions with endergonic reactions.
Example of ATP coupling:
Glutamic acid + NH3 + ATP → Glutamine + ADP + Pi
This illustrates the phosphorylating of glutamic acid increases the reaction's drive.
Regeneration of ATP
ATP is a renewable resource generated from ADP through the addition of a phosphate group.
The energy to regenerate ATP primarily comes from catabolic pathways in the cell, such as cellular respiration occurring mainly in the mitochondria, driving most cellular work.
Enzyme Activity
Catalyst Function
Catalyst: A chemical agent that accelerates a reaction without being used up by lowering the activation energy required for the reaction to proceed.
Enzyme: A catalytic protein that facilitates biochemical reactions.
Example: Hydrolysis of sucrose facilitated by the enzyme sucrase.
Substrate Specificity
Enzymes convert specific substrates into products by forming an enzyme-substrate complex. The high specificity of enzymes is often explained by the 'lock-and-key' model, where the substrate (key) fits perfectly into the active site of the enzyme (lock).
Active site: The specific region on the enzyme to which the substrate binds, crucial for catalysis.
Induced Fit Model: However, the active site is not a rigid structure; it molds itself around the substrate upon binding, enhancing the fit and catalytic activity.
Factors Affecting Enzyme Activity
General environmental factors such as temperature and pH can influence enzyme activity. Extreme temperatures can cause denaturation, where the enzyme loses its three-dimensional structure and function. Deviations from optimal pH also lead to denaturation.
Chemicals affecting enzymes:
Cofactors: Nonprotein enzyme helpers that can be inorganic (e.g., metal ions) or organic (coenzymes, often vitamins).
Enzyme Inhibitors
Competitive inhibitors: Bind reversibly or irreversibly to the active site of an enzyme, physically blocking the substrate from binding and reducing the reaction rate.
Noncompetitive inhibitors: Bind to different parts of the enzyme, often an allosteric site, altering the active site's shape and making it less effective at converting substrate to product.
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics.
Feedback Inhibition
Feedback inhibition prevents a cell from overproducing substances by utilizing the end product of a metabolic pathway to inhibit the pathway itself.
Example:
Threonine is the initial substrate for the synthesis of isoleucine and when isole
Definition of Metabolism
Metabolism is all the chemical reactions happening inside a living organism's cells.
These reactions manage how cells get and use materials and energy for growth, reproduction, staying healthy, and reacting to their environment.
Cells are like tiny chemical factories where many reactions occur at the same time.
Metabolic Pathways
A metabolic pathway is a series of chemical reactions that starts with a certain molecule and ends with a final product.
These pathways can be straight, branching, or circular, showing how different enzyme-led reactions are set up.
Each step in a metabolic pathway is sped up, or catalyzed, by a specific enzyme.
Enzyme-Catalyzed Reactions
Enzymes: These are proteins that act as catalysts. They speed up chemical reactions by lowering the energy needed to start them, and they are not used up in the process.
Example: Enzymes work in steps, like:-
Starting Molecule A --> Enzyme 1 --> Product B
Product B --> Enzyme 2 --> Product C
Product C --> Enzyme 3 --> Product D
Specific Metabolic Pathways
Glycolysis
Glycolysis is an important catabolic pathway (breaking down molecules) where glucose is split into two molecules of pyruvate. This happens in the cell's cytoplasm.
It's the first step for both respiration with oxygen (aerobic) and without oxygen (anaerobic).
Key molecules involved include:-
ATP: Adenosine triphosphate, which is the main energy currency cells use.
ADP: Adenosine diphosphate, what's left after ATP is used to release energy.
Phosphorylation: The process of adding phosphate groups to molecules during these reactions.
Catabolic and Anabolic Pathways
Catabolic pathways
Function: They release energy by breaking down large, complex molecules into smaller, simpler ones. This energy is often stored in ATP.
Example: Cellular respiration, which breaks down glucose for energy.
Anabolic pathways
Function: They use energy to build large, complex molecules from smaller, simpler ones. These reactions usually need energy from ATP.
Example: Building proteins from amino acids, or photosynthesis (plants making sugars).
Energy in Reactions
Exergonic Reactions
Definition: These reactions release energy.
Characteristics:
They happen by themselves (are spontaneous), and the change in Gibbs free energy (\Delta G) is negative (\Delta G < 0).
Endergonic Reactions
Definition: These reactions take in or absorb energy from their surroundings.
Characteristics:
They don't happen by themselves (are nonspontaneous), and they require an input of energy because the change in Gibbs free energy (\Delta G) is positive (\Delta G > 0).
ATP - The Energy Currency
Structure of ATP:
Made of ribose (a sugar), adenine (a nitrogen base), and three phosphate groups. The bonds between the phosphate groups hold a lot of energy, which is released when they break.
Hydrolysis of ATP:
When the last phosphate bond breaks with water (hydrolysis), a lot of energy is released for cells to use.
Example: - ATP + H_2O -> ADP + Inorganic Phosphate + Energy.
ATP in Reactions
ATP provides energy for cell activities by connecting reactions that release energy (exergonic) with those that require energy (endergonic).
Example of ATP coupling:-
Glutamic acid + NH3 + ATP → Glutamine + ADP + Pi
This shows how adding a phosphate from ATP to glutamic acid makes the reaction more likely to happen.
Regeneration of ATP
ATP is constantly remade from ADP by adding a phosphate group back to it.
The energy to regenerate ATP mostly comes from catabolic pathways, like cellular respiration, which usually happens in the mitochondria. This process drives most of the cell's work.
Enzyme Activity
Catalyst Function
Catalyst: A chemical that speeds up a reaction without being used up itself. It works by lowering the 'activation energy' needed to start the reaction.
Enzyme: A protein that acts as a catalyst in living things to help with biochemical reactions.
Example: The enzyme sucrase helps break down sucrose (table sugar) into simpler sugars.
Substrate Specificity
Enzymes change specific starting molecules, called substrates, into new products by temporarily joining with them to form an enzyme-substrate complex.
This works like a "lock and key" model, where the substrate (key) fits perfectly into a special part of the enzyme.
Active site: This is the specific place on the enzyme where the substrate binds and where the chemical reaction happens.
Induced Fit Model: Instead of a rigid lock and key, the active site can slightly change its shape to fit the substrate better once it binds, improving how well it works.
Factors Affecting Enzyme Activity
Things like temperature and pH levels in the environment can greatly affect how well enzymes work.
Extreme heat can denature an enzyme, meaning it loses its 3D shape and stops working. Too high or too low pH levels can also cause denaturation.
Chemicals that help enzymes:-
Cofactors: Nonprotein helpers for enzymes. They can be inorganic (like metal ions) or organic (called coenzymes, often vitamins).
Enzyme Inhibitors
Competitive inhibitors: These molecules block the active site of an enzyme, stopping the substrate from binding. They compete with the substrate.
Noncompetitive inhibitors: These bind to a different part of the enzyme (not the active site), which changes the active site's shape. This makes the enzyme less effective at doing its job.
Examples of substances that can be inhibitors include toxins, poisons, pesticides, and many antibiotics.
Feedback Inhibition
Feedback inhibition is a way cells prevent making too much of a substance. The final product of a metabolic pathway stops an enzyme earlier in the same pathway.
Example:-
Threonine is the first molecule needed to make isoleucine. When enough isoleucine has been made, it binds to and stops the first enzyme in its own pathway, preventing more