4.2 Glycolysis Practice Flashcards

Energy Requirements for Reactions: Even reactions that release energy (exergonic reactions) require a small amount of activation energy to proceed. In contrast, endergonic reactions require much more significant energy input because their products possess more free energy than their reactants.
The Role of Adenosine Triphosphate (ATP): ATP serves as the primary energy-supplying molecule within the cell. It functions as the "energy currency" used to power the majority of energy-requiring cellular reactions, similar to how money is exchanged for goods and services.
Safe Energy Management: A living cell cannot store large amounts of free energy because excess free energy would increase heat within the cell. This heat would lead to the denaturation of enzymes and other proteins, potentially destroying the cell. Consequently, cells use ATP as a way to store energy safely and release it only when and where it is needed, acting like a rechargeable battery.
Release of Energy: When ATP is broken down—typically through the removal of its terminal phosphate group—energy is released. This energy is then utilized to perform cellular work, often by binding the released phosphate to another molecule to activate it.
Example of Work: In the mechanical work of muscle contraction, ATP supplies the necessary energy to move contractile muscle proteins.

Core Components: At the center of the ATP molecule is Adenosine Monophosphate (AMP). AMP consists of:
- An adenine molecule (a two-ring nitrogenous base).
- A ribose molecule (a five-carbon sugar found in RNA).
- A single phosphate group.
Progression from AMP to ATP:
- AMP: The basic nucleotide found in RNA, containing one phosphate.
- ADP (Adenosine Diphosphate): Formed by adding a second phosphate group to AMP.
- ATP (Adenosine Triphosphate): Formed by adding a third phosphate group to ADP.
Phosphate Group Labels: The phosphate groups are identified by their position relative to the ribose sugar:
- Alpha (α): The phosphate closest to the ribose.
- Beta (β): The middle phosphate.
- Gamma (γ): The terminal phosphate group.
High-Energy Bonds: Adding a phosphate group to a molecule requires a high amount of energy and results in a high-energy bond. Because phosphate groups are negatively charged, they repel one another when arranged in series (as in ADP and ATP), making these molecules inherently unstable.
Hydrolysis: The process of releasing one or two phosphate groups from ATP is called hydrolysis, and this process releases energy.

Definition: Glycolysis is the first stage in the metabolic breakdown of glucose to extract energy for cellular functions.
Biological Presence: Nearly all energy used by living things originates from the bonds of glucose. Glycolysis is a universal process carried out by many living organisms.
Location: Glycolysis occurs in the cytoplasm of most prokaryotic cells and all eukaryotic cells.
The General Reaction: Glycolysis begins with a single molecule of glucose, which has a six-carbon, ring-shaped structure. The process ends with the creation of two molecules of a three-carbon sugar known as pyruvate.
ATP Yield: If a cell is unable to catabolize pyruvate molecules further (e.g., in cells without mitochondria), it will harvest a net total of only $2$ ATP molecules from one molecule of glucose.
Specific Case Study: Mature mammalian red blood cells are only capable of performing glycolysis. Because they lack other metabolic pathways for ATP production, they are entirely dependent on glycolysis for survival. If this process is interrupted, the cells will die.

Phase 1: Energy Investment/Preparation:
- In the initial part of the pathway, the cell actually consumes energy.
- $2$ ATP molecules are used to make adjustments to the six-carbon glucose molecule.
- A specific intermediate mentioned in the pathway is Fructose diphosphate.
- The goal of this phase is to split the six-carbon sugar evenly into two three-carbon molecules.
Phase 2: Energy Payoff:
- In the second part of the process, the cell produces energy.
- The three-carbon intermediates (such as Glyceraldehyde 3-phosphate) are processed to form pyruvate.
- This phase results in the production of ATP and Nicotinamide-adenine dinucleotide (NADH).
- Specifically, $4$ ATP are produced in this phase, resulting in a net gain of $2$ ATP (since $2$ were invested earlier).
- $2$ molecules of $NAD^+$ are reduced to $2$ molecules of NADH.

Inputs:
- $1$ molecule of Glucose (a $6$ -carbon sugar).
- $2$ ATP molecules (used as an initial energy investment).
- $2$ molecules of $NAD^+$ .
Outputs:
- $2$ molecules of Pyruvate (each containing $3$ carbons).
- $4$ ATP molecules (resulting in a net profit of $2$ ATP).
- $2$ molecules of NADH.