Cellular Respiration, Photosynthesis, and Bioenergetics

Flashcards covering cellular respiration, photosynthesis, thermodynamic laws, Gibbs free energy, fermentation, enzyme inhibition, entropy, and cellular energy storage mechanisms.

In cellular respiration, which reactant is oxidized and which is reduced?

Glucose is oxidized (loses electrons) and oxygen ($\text{O}_2$) is reduced (gains electrons).

What is the distinction between oxidation and reduction in terms of electron transfer?

Oxidation is the loss of electrons, whereas reduction is the gain of electrons.

What are the two main steps of photosynthesis and their primary functions?

Step 1: Light Reactions captures solar energy and converts it into temporary chemical batteries ($\text{ATP}$ and $\text{NADPH}$). Step 2: Calvin Cycle uses these temporary batteries to weave invisible gas ($\text{CO}_2$) into solid sugar (glucose).

What are the inputs, outputs, and function of Photosystem II (PSII)?

Inputs: Light energy (photons) and $\text{H}_2\text{O}$. Outputs: High-energy electrons (sent to the Electron Transport Chain), $\text{O}_2$ gas waste, and $\text{H}^+$ ions (protons). Function: Harvests solar energy to split water and kickstart the flow of electrons.

What are the inputs, outputs, and function of Photosystem I (PSI)?

Inputs: Light energy (photons), spent electrons from the PSII Electron Transport Chain, and $\text{NADP}^+ + \text{H}^+$. Outputs: $\text{NADPH}$. Function: Re-energizes tired electrons and loads them onto $\text{NADPH}$ for the Calvin Cycle.

What is the overall reaction and net ATP yield of Glycolysis in cellular respiration?

$\text{Glucose} + 2\,\text{ATP} + 2\,\text{NAD}^+ + 4\,\text{ADP} + \text{P}_i \rightarrow 2\,\text{Pyruvate} + 4\,\text{ATP} + 2\,\text{NADH} + 2\,\text{H}_2\text{O}$, yielding a net gain of $2\,\text{ATP}$.

What occurs during Pyruvate Oxidation (the transition or preparatory step)?

It converts $2\,\text{Pyruvate} + 2\,\text{NAD}^+ + 2\,\text{Coenzyme A (CoA)} \rightarrow 2\,\text{Acetyl-CoA} + 2\,\text{CO}_2 + 2\,\text{NADH}$, modifying the sugar fragments so they can legally enter the Citric Acid Cycle.

What are the inputs and outputs of the Citric Acid Cycle per two Acetyl-CoA molecules?

Inputs: $2\,\text{Acetyl-CoA} + 6\,\text{NAD}^+ + 2\,\text{FAD} + 2\,\text{ADP} + \text{P}_i\,(\text{or GDP})$. Outputs: $4\,\text{CO}_2 + 6\,\text{NADH} + 2\,\text{FADH}_2 + 2\,\text{ATP}\,(\text{or GTP})$.

What is the reaction equation and approximate ATP payout of Oxidative Phosphorylation?

$\text{NADH} + \text{FADH}_2 + \text{O}_2 + \text{ADP} + \text{P}_i \rightarrow 26\text{–}28\,\text{ATP} + \text{H}_2\text{O} + \text{NAD}^+ + \text{FAD}$, producing an approximate payout of $26\text{–}28\,\text{ATP}$.

What is Delta G ($\Delta G$), and how does increasing enzymes alone versus increasing both reactants and enzymes affect it?

$\Delta G$ is the usable free energy available to do cellular work. Increasing only enzymes leaves $\Delta G$ unchanged because enzymes only speed up the reaction rate; increasing both reactants and enzymes increases $\Delta G$ because more total matter provides more total energy to transform.

What defines an exergonic reaction with negative Delta G ($-\Delta G$)?

The reaction releases free energy spontaneously because the products are more stable and have less stored energy than the reactants (e.g., cellular respiration breaking down glucose).

What defines an endergonic reaction with positive Delta G ($+\Delta G$)?

The reaction absorbs free energy non-spontaneously because the final products store more energy than the initial reactants (e.g., photosynthesis requiring light energy).

What is the primary core purpose of the fermentation pathway under anaerobic conditions?

To empty out and recycle $\text{NADH}$ back into $\text{NAD}^+$ so that glycolysis does not get backed up and can continue producing its small emergency payout of $2\,\text{ATP}$.

What is the equation and cellular location of Lactic Acid Fermentation?

Equation: $2\,\text{Pyruvate} + 2\,\text{NADH} \rightarrow 2\,\text{Lactic Acid} + 2\,\text{NAD}^+$. It occurs in human muscle cells and some bacteria.

What is the equation and cellular location of Alcohol Fermentation?

Equation: $2\,\text{Pyruvate} + 2\,\text{NADH} \rightarrow 2\,\text{Ethanol} + 2\,\text{CO}_2 + 2\,\text{NAD}^+$. It occurs in yeast and some plant tissues.

How do competitive inhibitors work, and how can their inhibition be overcome?

They mimic the targeted substrate molecule to physically block the enzyme's active site. Their effect can be overcome by significantly increasing the concentration of the actual substrate.

How do noncompetitive (allosteric) inhibitors affect enzyme activity?

They bind to an entirely separate area (the allosteric site), altering the 3D shape of the enzyme and rendering the active site nonfunctional regardless of substrate levels.

What is entropy, and what role does it play in cellular survival?

Entropy is a mathematical measure of disorder, randomness, or thermal equilibrium within a closed system. It dictates the spontaneous direction of energy flow, requiring constant cellular work to fight against environmental decay.

How do anabolic reactions affect local entropy versus the net entropy of the universe?

Anabolic reactions decrease entropy locally inside the cell by organizing small, scattered molecules into ordered structures, but require outside energy input that increases the net entropy of the universe through heat loss.

How do short-term energy storage (ATP) and long-term energy storage (glucose, glycogen, lipids) differ structurally?

Short-term storage ($\text{ATP}$) holds energy in unstable, high-energy phosphate bonds that pop off easily for immediate delivery. Long-term storage locks energy safely inside stable carbon-to-carbon covalent bonds that do not spontaneously degrade.