Lecture 2.2: The Cell and How it Works — Free Energy and Reaction Kinetics

TL;DR

Chemical reactions in cells are governed by free energy, which determines whether a reaction proceeds or requires energy. Enzymes, a type of catalyst, play a crucial role in speeding up reactions by lowering activation energy.

Transcript

HAZEL SIVE: Let's talk a little bit more about some of the parameters that govern the chemical reactions in a cell, and indeed, any chemical reaction. All chemical reactions are governed by something called free or usable energy. So let us write that. Reactions are governed by free energy where free really means usable. And this free energy gets a ... Read More

Key Insights

• 🥶 All chemical reactions in cells are governed by free energy, which determines whether a reaction proceeds spontaneously or requires energy input.
• ❎ ΔG can be negative (exergonic) for energy-releasing reactions, positive (endergonic) for energy-requiring reactions, or 0 at equilibrium.
• ❓ Activation energy is the energy barrier that must be overcome for a reaction to proceed, and catalysts like enzymes decrease activation energy.
• ❓ Enzymes are specific for each chemical reaction, with thousands of different enzymes in the body, ensuring the efficiency of metabolic processes.
• 🫷 Enzymes bind to a substrate at their active site, undergo changes to push the reaction over the activation energy barrier, and release the product.
• 👻 Enzyme specificity allows for the breakdown of different substrates, such as cellulose and starch, through different enzymes.
• ☠️ Catalysts, particularly enzymes, play a crucial role in biological chemical reactions by increasing the reaction rate without altering the thermodynamics.

Questions & Answers

Q: How do chemical reactions in cells relate to free energy?

All chemical reactions in cells are governed by free energy. The difference in free energy (ΔG) determines whether a reaction proceeds spontaneously or requires energy input.

Q: What are the three possibilities for ΔG in a chemical reaction?

ΔG can be negative, indicating energy release and a spontaneous reaction. It can also be positive, requiring energy input for the reaction to proceed. If ΔG is 0, the reaction is at equilibrium.

Q: What is activation energy?

Activation energy is the energy required for a chemical reaction to overcome the energy barrier and proceed. It acts as a barrier to reactions, but catalysts can decrease activation energy.

Q: What are enzymes and how do they affect chemical reactions?

Enzymes are biological catalysts that speed up chemical reactions in cells by decreasing activation energy. They do not change the value of ΔG but increase the rate of the reaction.

Summary & Key Takeaways

• Chemical reactions in cells are governed by free energy (G) and the difference in free energy (ΔG) determines the direction and spontaneity of the reaction.

• Free energy can be negative (exergonic), indicating energy release and spontaneous reaction, or positive (endergonic), requiring energy input for the reaction to proceed.

• Activation energy is the barrier that reactions must overcome, and catalysts, such as enzymes, decrease activation energy, allowing reactions to occur at a faster rate.