Metabolic processes

Part one Chapter 4

Primary function of ATP in cells

Serves as the immediate energy currency that provides quick, accessible energy to power cellular work.

Three structural components of an ATP molecule

1. Adenine (a nitrogenous base)

2. Ribose (a 5-carbon sugar)

3. Three phosphate groups ($\text{PO}_4^{3-}$)

Phosphoanhydride bonds

The chemical bonds linking adjacent phosphate groups in ATP, which store energy due to electrostatic repulsion between negative charges.

Chemical equation for ATP hydrolysis

$$\text{ATP} + \text{H}_2\text{O} \longrightarrow \text{ADP} + \text{P}_i + \text{Energy}$$

Standard free energy change (\Delta G^\circ') for ATP hydrolysis

Approximately $-30.5\,kJ\,mol^{-1}$ (or $-7.3\,kcal\,mol^{-1}$).

Energy coupling

The cellular strategy of transferring energy directly from exergonic reactions to endergonic reactions to drive unfavorable processes.

Phosphorylation

The transfer of a detached phosphate group directly to a target molecule or protein, altering its 3D shape and function.

Three categories of cellular work driven by ATP

1. Mechanical work (e.g., muscle contraction via motor protein flexing)

2. Transport work (e.g., pumping ions across membranes against gradients)

3. Chemical work (e.g., synthesizing complex macromolecules)

The ATP cycle

The continuous recycling mechanism that re-attaches an inorganic phosphate ($\text{P}_i$) to $\text{ADP}$ using energy from cellular respiration or photosynthesis.

Primary function of ATP in cells

Serves as the immediate energy currency that provides quick, accessible energy to power cellular work.

Three structural components of an ATP molecule

1. Adenine (a nitrogenous base)

2. Ribose (a 5-carbon sugar)

3. Three phosphate groups ($\text{PO}\_4^{3-}$)

Phosphoanhydride bonds

The chemical bonds linking adjacent phosphate groups in ATP, which store energy due to electrostatic repulsion between negative charges.

Chemical equation for ATP hydrolysis

$$\text{ATP} + \text{H}\_2\text{O} \longrightarrow \text{ADP} + \text{P}\_i + \text{Energy}$$

Standard free energy change (\Delta G^\circ') for ATP hydrolysis

Approximately $-30.5\,kJ\,mol^{-1}$ (or $-7.3\,kcal\,mol^{-1}$).

Energy coupling

The cellular strategy of transferring energy directly from exergonic reactions to endergonic reactions to drive unfavorable processes.

Phosphorylation

The transfer of a detached phosphate group directly to a target molecule or protein, altering its 3D shape and function.

Three categories of cellular work driven by ATP

1. Mechanical work (e.g., muscle contraction via motor protein flexing)

2. Transport work (e.g., pumping ions across membranes against gradients)

3. Chemical work (e.g., synthesizing complex macromolecules)

The ATP cycle

The continuous recycling mechanism that re-attaches an inorganic phosphate ($\text{P}\_i$) to $\text{ADP}$ using energy from cellular respiration or photosynthesis.

Anabolism

The set of metabolic pathways that construct complex molecules from simpler ones, requiring an input of energy (endergonic).

Catabolism

The set of metabolic pathways that break down complex molecules into simpler units, releasing stored chemical potential energy (exergonic).

Energy dynamics of anabolism versus catabolism

• Endergonic (consumes $\text{ATP}$)

• Exergonic (produces $\text{ATP}$)

Predominant chemical reaction types in anabolism vs. catabolism

• Mostly condensation (dehydration) reactions

• Mostly hydrolysis and oxidation reactions

Hormones associated with anabolic vs. catabolic regulation

• Anabolic: Insulin, testosterone, growth hormone, estrogen

• Catabolic: Glucagon, cortisol, adrenaline (epinephrine)

Four examples of anabolic pathways

1. Protein synthesis (amino acids to proteins)

2. DNA replication (nucleotides to DNA)

3. Glycogenesis (glucose to glycogen)

4. Photosynthesis ($\text{CO}\_2$ and water to glucose)

Four examples of catabolic pathways

1. Cellular respiration (glucose breakdown to $\text{CO}\_2$ and water)

2. Lipolysis (triglycerides to fatty acids and glycerol)

3. Proteolysis (proteins to free amino acids)

4. Digestion (dietary polymers to monomers)

Metabolic coupling

The interconnected relationship where catabolic processes break down nutrients to produce $\text{ATP}$, which then directly powers anabolic processes to construct cellular structures.

Primary function of ATP in cells

Serves as the immediate energy currency that provides quick, accessible energy to power cellular work.

Three structural components of an ATP molecule

1. Adenine (a nitrogenous base)

2. Ribose (a 5-carbon sugar)

3. Three phosphate groups ($\text{PO}_4^{3-}$)

Phosphoanhydride bonds

The chemical bonds linking adjacent phosphate groups in ATP, which store energy due to electrostatic repulsion between negative charges.

Chemical equation for ATP hydrolysis

$$\text{ATP} + \text{H}_2\text{O} \longrightarrow \text{ADP} + \text{P}_i + \text{Energy}$$

Standard free energy change (\Delta G^\circ') for ATP hydrolysis

Approximately $-30.5\,kJ\,mol^{-1}$ (or $-7.3\,kcal\,mol^{-1}$).

Energy coupling

The cellular strategy of transferring energy directly from exergonic reactions to endergonic reactions to drive unfavorable processes.

Phosphorylation

The transfer of a detached phosphate group directly to a target molecule or protein, altering its 3D shape and function.

Three categories of cellular work driven by ATP

1. Mechanical work (e.g., muscle contraction via motor protein flexing)

2. Transport work (e.g., pumping ions across membranes against gradients)

3. Chemical work (e.g., synthesizing complex macromolecules)

The ATP cycle

The continuous recycling mechanism that re-attaches an inorganic phosphate ($\text{P}_i$) to $\text{ADP}$ using energy from cellular respiration or photosynthesis.

Anabolism

The set of metabolic pathways that construct complex molecules from simpler ones, requiring an input of energy (endergonic).

Catabolism

The set of metabolic pathways that break down complex molecules into simpler units, releasing stored chemical potential energy (exergonic).

Energy dynamics of anabolism versus catabolism

• (consumes $\text{ATP}$)

• Exergonic (produces $\text{ATP}$)

Predominant chemical reaction types in anabolism vs. catabolism

• Mostly condensation (dehydration) reactions

• Mostly hydrolysis and oxidation reactions

Hormones associated with anabolic vs. catabolic regulation

• Anabolic: Insulin, testosterone, growth hormone, estrogen

• Catabolic: Glucagon, cortisol, adrenaline (epinephrine)

Four examples of anabolic pathways

1. Protein synthesis (amino acids to proteins)

2. DNA replication (nucleotides to DNA)

3. Glycogenesis (glucose to glycogen)

4. Photosynthesis ($\text{CO}_2$ and water to glucose)

Four examples of catabolic pathways

1. Cellular respiration (glucose breakdown to $\text{CO}_2$ and water)

2. Lipolysis (triglycerides to fatty acids and glycerol)

3. Proteolysis (proteins to free amino acids)

4. Digestion (dietary polymers to monomers)

Metabolic coupling

The interconnected relationship where catabolic processes break down nutrients to produce $\text{ATP}$, which then directly powers anabolic processes to construct cellular structures.

Primary target of metabolic pathway regulation

Key regulatory enzymes that catalyze the first irreversible, rate-limiting step of a metabolic pathway.

Allosteric regulation

The alteration of enzyme activity caused by an effector molecule binding to a regulatory site distinct from the active site, inducing a conformational change.

Allosteric regulation of phosphofructokinase-1 (PFK-1)

• Allosteric inhibitor: High levels of $\text{ATP}$

• Allosteric activator: High levels of $\text{AMP}$

Feedback inhibition (negative feedback)

A regulatory mechanism where the final end-product of a pathway allosterically inhibits the first enzyme in that same pathway to prevent overproduction.

Reversible covalent modification

The rapid switching of enzyme activity through the addition or removal of chemical groups, such as phosphorylation catalyzed by kinases and dephosphorylation by phosphatases.

Fast-acting vs. slow-acting metabolic regulation mechanisms

• Alters the activity of existing enzymes (e.g., allosteric control, phosphorylation)

• Alters the total quantity of enzyme molecules via gene expression or protein degradation

Compartmentalization in metabolic regulation

The physical separation of opposing metabolic pathways into distinct cellular organelles to prevent interference (e.g., fatty acid synthesis in the cytosol vs. fatty acid oxidation in the mitochondria).