Problem 3 - Campbell Biology

Question

Which of the following metabolic processes can occur without a net influx of energy from some other process? (A) \(\mathrm{ADP}+\left(\mathbb{D}_{1}+\rightarrow \mathrm{ATP}+\mathrm{H}_{2} \mathrm{O}\right.\) (B) \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2} \rightarrow 6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O}\) (C) \(6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}\) (D) Amino acids \(\rightarrow\) Protein

Step-by-Step Solution

Answer

Option B (\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}) occurs without a net influx of energy.

Step 1: Understanding Energy Influx

Metabolic processes can be categorized based on whether they require an input of energy (endergonic) or not (exergonic). Processes that do not require a net influx of energy are typically exergonic.

Step 2: Examine Each Option

Look at each equation to determine if it is energy-releasing (exergonic) or energy-consuming (endergonic).

Step 3: Analyzing Option A

Option A is \(\text{ADP} + \text{P}_i \rightarrow \text{ATP} + \text{H}_2\text{O}\). This process is known as phosphorylation, which is endergonic and requires energy.

Step 4: Analyzing Option B

Option B is \(\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}\). This is cellular respiration, a process that releases energy, making it exergonic.

Step 5: Analyzing Option C

Option C is \(\text{6 CO}_2 + 6 \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2\). This represents photosynthesis, an endergonic process that requires energy.

Step 6: Analyzing Option D

Option D involves the synthesis of proteins from amino acids. This process is endergonic as it requires energy to form peptide bonds.

Step 7: Conclusion

Based on the analysis, the only process that does not require a net influx of energy (exergonic) is Option B.

Key Concepts

Endergonic Reactions

Endergonic reactions are metabolic processes that require an input of energy to proceed. These reactions are not spontaneous, meaning they cannot occur without a net influx of energy from the surroundings. Think about climbing a hill. It requires energy to reach the top.
In biochemical terms, endergonic reactions typically involve the synthesis of complex molecules from simpler ones. Common examples include:

• Protein synthesis from amino acids
• Photosynthesis, where plants convert carbon dioxide and water into glucose and oxygen
• The formation of ATP from ADP and phosphate

In all these cases, energy is required to drive the reactions forward, often in the form of ATP, sunlight, or other high-energy molecules.

Exergonic Reactions

Exergonic reactions release energy as they proceed and are generally spontaneous. You can think of this like rolling a ball down a hill; it naturally moves down due to gravity.
In metabolic pathways, exergonic reactions are crucial as they provide the energy needed for endergonic processes. Several key examples of exergonic reactions include:

• Cellular respiration, where glucose is oxidized to produce carbon dioxide, water, and energy
• Hydrolysis of ATP to ADP and phosphate
• Decomposition reactions where complex molecules are broken down into simpler ones

In cellular respiration, for instance, the breakdown of glucose releases energy, which cells then use for various functions._

Cellular Respiration

Cellular respiration is a metabolic process where cells convert glucose and oxygen into carbon dioxide, water, and energy, specifically ATP. This process is exergonic, meaning it releases energy that bodies can utilize for functions like movement, growth, and cell repair.
There are three main stages in cellular respiration:

• Glycolysis - Breaking down glucose into pyruvate, generating small amounts of ATP and NADH
• Krebs cycle (Citric Acid Cycle) - Pyruvate is further broken down into carbon dioxide, producing ATP, NADH, and FADH2
• Electron Transport Chain - NADH and FADH2 are used to create a larger amount of ATP through oxidative phosphorylation

Each stage of cellular respiration converts energy stored in glucose into a usable form (ATP), enabling cells to perform vital activities.

Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This reaction is endergonic, requiring energy input to proceed.
Photosynthesis occurs in two main stages:

• Light-dependent reactions - Light energy is captured and used to produce ATP and NADPH
• Calvin cycle (Light-independent reactions) - ATP and NADPH are utilized to convert carbon dioxide into glucose

In summary, the energy captured during the light-dependent reactions powers the Calvin cycle, resulting in the synthesis of glucose, which plants use as a nutrient and energy source.

Protein Synthesis

Protein synthesis is an endergonic process wherein cells produce proteins from amino acids. This multi-step process is vital for cell growth, repair, and function.
Protein synthesis occurs in two major stages:

• Transcription - DNA is used as a template to synthesize messenger RNA (mRNA)
• Translation - mRNA is read by ribosomes to assemble amino acid sequences into proteins

Throughout protein synthesis, energy from ATP and GTP is expended to form peptide bonds between amino acids, creating proteins essential for various cellular functions.