Ch 8: An Introduction to Metabolism Flashcards
The analogy is made that a cell is a chemical factory. Explain why this might be an appropriate analogy.
A cell can be like a chemical factory because its metabolism utilizes orderly chemical reactions that affect each other and work together, similar to how a factory has many organized components with different responsibilities.
What is metabolism?
Metabolism is the totality of an organism’s chemical reactions, and arises from orderly interactions between molecules. The metabolism manages the material and resources of the cell.
Describe what is meant by a metabolic pathway.
A metabolic pathway is where a molecule is altered into a product through a series of defined steps, like a road map of chemical roads. In metabolic pathways, each step is catalyzed by a specific enzyme. Mechanisms that regulate these enzymes balance metabolic supply and demand.
What are catabolic pathways? Give an example.
Catabolic pathways (breakdown pathways) are pathways that release energy by breaking down complex molecules into simpler compounds.
Cellular respiration is a catabolic pathway, breaking down glucose and organic fuels in the presence of oxygen into CO2 and water. The released energy becomes available to do cellular work, like membrane transport.
What are anabolic pathways? Give an example.
Anabolic pathways (biosynthetic pathways) are pathways that consume energy to build complex molecules from simple compounds. Synthesis of proteins from amino acids is an example of anabolism.
How can catabolic and anabolic pathways work together?
Catabolic pathways can break down molecules and release energy that can be used to drive reactions of anabolic pathways.
State the first law of thermodynamics and give a biological example.
Energy can be transferred or transformed, but it cannot be created or destroyed. For example, the chemical reactions of a bear eating a fish will convert the fish’s chemical energy into kinetic energy when the bear begins to move, but energy will neither be created or destroyed.
State the second law of thermodynamics.
Every energy transfer or transformation increases the entropy of the universe.
What is entropy a measure of? Use some examples to help explain.
Entropy is a “measure of disorder”, specifically molecular disorder. In the universe, increasing entropy usually takes the form of increasing amounts of heat and less ordered forms of matter.
For example, a bear is increasing the entropy of the universe when it eats a fish. Chemical energy from the fish is converted into kinetic energy, but disorder is also being increased because the bear releases heat and molecules like CO2 into its surroundings when breaking down food.
Since the world is getting more and more random, how can organisms be getting more and more ordered?
Organisms are becoming more ordered through evolution, where molecules have to arrange themselves into more specific positions to form specific structures.
What is free energy? How is it calculated?
Free energy is the portion of a system’s energy that can perform work when temperature and pressure are uniform throughout the system. The value of ΔG will depend on conditions like pH, temperature, and concentrations of reactants and products.
Free-energy change is calculated by ΔG = ΔH - TΔS
- ΔH = change in a system’s enthalpy (or total energy)
- T = absolute temperature in Kelvin
- ΔS = change in a system’s entropy
What does the value of ΔG help you predict? Why do biologists care about ΔG?
If ΔG is negative = process is spontaneous
If ΔG is positive = process will only occur with an input of energy
Biologists care about ΔG because using it can predict which processes are spontaneous and don’t require an input of energy, which can be harnessed by the cell to perform work. In terms of the study of metabolism, it can help determine which reactions supply energy for cellular work.
How is free energy related to equilibrium?
At equilibrium, a system is at its lowest value for G. Free energy can also be thought of as a system’s tendency to move to a more stable state, or its tendency to move towards equilibrium (think of 2nd Law, and heat transfer from hot → cold).
Free energy would increase if a reaction is pushed away from equilibrium, so any change from equilibrium will have a positive ΔG, and systems will never spontaneously move from equilibrium. Because a system at equilibrium cannot spontaneously change, it can never do work.
Endergonic Reactions
A reaction that absorbs free energy from its surroundings. Because this reaction essentially stores free energy in molecules (ΔG increases), ΔG is positive. Such reactions are non-spontaneous, meaning they cannot occur on their own without an input of energy.
Exergonic Reactions
A reaction that releases free energy. Because this reaction loses free energy, ΔG decreases and is negative. Such reactions are spontaneous.
The value ΔG for an exergonic reaction represents the maximum amount of work the reaction can perform. The greater the decrease in free energy, the greater the amount of work that can be done.
