Question 1

What are anabolic pathways?

Accepted Answer

Pathways that require an input of energy to synthesize complex molecules from simpler ones. (Also, anabolism).

Question 2

What is bioenergetics?

Accepted Answer

The study of energy flowing through living systems.

Question 3

What are catabolic pathways?

Accepted Answer

Pathways in which complex molecules are broken down into simpler ones. (Also, catabolism).

Question 4

What is metabolism?

Accepted Answer

All the chemical reactions that take place inside cells, including anabolism and catabolism.

Question 5

What are the benefits of sugar to living organisms?

Accepted Answer

Living things consume sugar as a major energy source, because sugar molecules have a great deal of energy stored within their bonds.

Question 6

What is the formula for the synthesis and catabolism of glucose?

Accepted Answer

6CO2 + 6H2O + (energy) ⇐⇒ C6H12O6 + 6O2

Question 7

What is the primary producer of sugar?

Accepted Answer

Carbohydrates that are consumed have their origins in photosynthesizing organisms like plants. During photosynthesis, plants use the energy of sunlight to convert carbon dioxide gas (CO2) into sugar molecules, like glucose (C6H12O6). Because this process involves synthesizing a larger, energy-storing molecule, it requires an input of energy to proceed.

Question 8

What is the source of energy for the sugar production?

Accepted Answer

During the chemical reactions of photosynthesis, energy is provided in the form of a very high-energy molecule called ATP, or adenosine triphosphate, which is the primary energy currency of all cells used to perform immediate work.

Question 9

How is sugar stored in living organisms?

Accepted Answer

The sugar (glucose) is stored as starch or glycogen. Energy-storing polymers like these are broken down into glucose to supply molecules of ATP.

Question 10

How is solar energy used to produce glucose?

Accepted Answer

Solar energy is required to synthesize a molecule of glucose during the reactions of photosynthesis. In photosynthesis, light energy from the sun is initially transformed into chemical energy that is temporally stored in the energy carrier molecules ATP and NADPH (nicotinamide adenine dinucleotide phosphate). The stored energy in ATP and NADPH is then used later in photosynthesis to build one molecule of glucose from six molecules of CO2. Glucose molecules can also be combined with and converted into other types of sugars.

Question 11

What happens when sugars are consumed?

Accepted Answer

When sugars are consumed, molecules of glucose eventually make their way into each living cell of the organism. Inside the cell, each sugar molecule is broken down through a complex series of chemical reactions. The goal of these reactions is to harvest the energy stored inside the sugar molecules. The harvested energy is used to make high-energy ATP molecules, which can be used to perform work, powering many chemical reactions in the cell.

Question 12

How much energy is required to synthesize glucose?

Accepted Answer

Under ideal conditions, the amount of energy needed to make one molecule of glucose from six molecules of carbon dioxide during photosynthesis is 18 molecules of ATP and 12 molecules of NADPH (each one of which is energetically equivalent to three molecules of ATP), or a total of 54 molecule equivalents required for the synthesis of one molecule of glucose.

Question 13

What is a metabolic pathway?

Accepted Answer

A metabolic pathway is a series of interconnected biochemical reactions that convert a substrate molecule or molecules, step-by-step, through a series of metabolic intermediates, eventually yielding a final product or products.

Question 14

Which types of organisms perform the most photosynthesis?

Accepted Answer

The majority of global photosynthesis is done by planktonic algae.

Question 15

How does photosynthesis enable cellular respiration?

Accepted Answer

The by-product of photosynthesis is oxygen, required by some cells to carry out cellular respiration. During cellular respiration, oxygen aids in the catabolic breakdown of carbon compounds, like carbohydrates. Among the products of this catabolism are CO2 and ATP. In addition, some eukaryotes perform catabolic processes without oxygen (fermentation); that is, they perform or use anaerobic metabolism.

Question 16

How did metabolism evolve?

Accepted Answer

Organisms probably evolved anaerobic metabolism to survive (living organisms came into existence about 3.8 billion years ago, when the atmosphere lacked oxygen). Despite the differences between organisms and the complexity of metabolism, researchers have found that all branches of life share some of the same metabolic pathways, suggesting that all organisms evolved from the same ancient common ancestor. Evidence indicates that over time, the pathways diverged, adding specialized enzymes to allow organisms to better adapt to their environment, thus increasing their chance to survive. However, the underlying principle remains that all organisms must harvest energy from their environment and convert it to ATP to carry out cellular functions.

Question 17

What are some examples of anabolic pathways?

Accepted Answer

Synthesizing sugar from CO2 is one example. Other examples are the synthesis of large proteins from amino acid building blocks, and the synthesis of new DNA strands from nucleic acid building blocks.

Question 18

How much ATP can be produced through the catabolism of glucose?

Accepted Answer

A single molecule of glucose can store enough energy to make 36 to 38 molecules of ATP.

Question 19

What other types of molecules besides carbohydrates are used to produce ATP?

Accepted Answer

Other energy-storing molecules, such as fats, are also broken down through similar catabolic reactions to release energy and make ATP.

Question 20

How do proteins facilitate metabolic pathways?

Accepted Answer

The chemical reactions of metabolic pathways don’t take place spontaneously. Each reaction step is facilitated, or catalyzed, by a protein called an enzyme. Enzymes are important for catalyzing all types of biological reactions—those that require energy as well as those that release energy.

Question 21

What is activation energy?

Accepted Answer

The energy necessary for reactions to occur.

Question 22

What is chemical energy?

Accepted Answer

The potential energy in chemical bonds that is released when those bonds are broken.

Question 23

What are endergonic reactions?

Accepted Answer

Chemical reactions that require energy input.

Question 24

What is enthalpy?

Accepted Answer

The total energy of a system.

Question 25

What are exergonic reactions?

Accepted Answer

Chemical reactions that release free energy.

Question 26

What is free energy?

Accepted Answer

Gibbs free energy is the usable energy, or energy that is available to do work.

Question 27

What is heat energy?

Accepted Answer

The total bond energy of reactants or products in a chemical reaction.

Question 28

What is kinetic energy?

Accepted Answer

A type of energy associated with objects or particles in motion.

Question 29

What is potential energy?

Accepted Answer

A type of energy that has the potential to do work; stored energy.

Question 30

What is a transition state?

Accepted Answer

A high-energy, unstable state (an intermediate form between the substrate and the product) occurring during a chemical reaction.

Question 31

What is energy?

Accepted Answer

Energy is defined as the ability to do work.

Question 32

Why is free energy called Gibbs free energy?

Accepted Answer

Free energy is called Gibbs free energy (abbreviated with the letter G) after Josiah Willard Gibbs, the scientist who developed the measurement.

Question 33

How does Gibbs free energy take into account the second law of thermodynamics?

Accepted Answer

Gibbs free energy specifically refers to the energy associated with a chemical reaction that is available after entropy is accounted for. In other words, Gibbs free energy is usable energy, or energy that is available to do work.

Question 34

How does free energy change in a chemical reaction?

Accepted Answer

Every chemical reaction involves a change in free energy, called delta G (∆G). The change in free energy can be calculated for any system that undergoes such a change, such as a chemical reaction. To calculate ∆G, subtract the amount of energy lost to entropy (denoted as ∆S) from the total energy change of the system. This total energy change in the system is called enthalpy and is denoted as ∆H. The formula for calculating ∆G is as follows, where the symbol T refers to absolute temperature in Kelvin (degrees Celsius + 273): ΔG = ΔH − TΔS

Question 35

How is the standard free energy change of a chemical reaction expressed?

Accepted Answer

The standard free energy change of a chemical reaction is expressed as an amount of energy per mole of the reaction product (either in kilojoules or kilocalories, kJ/mol or kcal/mol; 1 kJ = 0.239 kcal) under standard pH, temperature, and pressure conditions.

Question 36

What is standard pH, temperature, and pressure?

Accepted Answer

Standard pH, temperature, and pressure conditions are generally calculated at pH 7.0 in biological systems, 25 degrees Celsius, and 100 kilopascals (1 atm pressure), respectively.

Question 37

What must be taken into account when calculating the free energy change of a chemical reaction in a cellular environment?

Accepted Answer

Cellular conditions vary considerably from the standard conditions, and so standard calculated ∆G values for biological reactions will be different inside the cell.

Question 38

What is the free energy change of reactions that release energy?

Accepted Answer

Reactions that release energy have a ∆G \< 0. A negative ∆G also means that the products of the reaction have less free energy than the reactants, because they gave off some free energy during the reaction. Reactions that have a negative ∆G and consequently release free energy are called exergonic reactions. These reactions are also referred to as spontaneous reactions, because they can occur without the addition of energy into the system.

Question 39

What is the free energy change of a reaction that stores energy?

Accepted Answer

If a chemical reaction requires an input of energy rather than releasing energy, then the ∆G for that reaction will be a positive value. In this case, the products have more free energy than the reactants. Thus, the products of these reactions can be thought of as energy-storing molecules. These chemical reactions are called endergonic reactions, and they are non-spontaneous. An endergonic reaction will not take place on its own without the addition of free energy.

Question 40

How does reaction reversibility factor into free energy change?

Accepted Answer

Most chemical reactions are reversible. They can proceed in both directions, releasing energy into their environment in one direction, and absorbing it from the environment in the other direction. The same is true for the chemical reactions involved in cell metabolism, such as the breaking down and building up of proteins into and from individual amino acids, respectively.

Question 41

Why do living systems never achieve a state of equilibrium?

Accepted Answer

Reactants within a closed system will undergo chemical reactions in both directions until a state of equilibrium is reached. This state of equilibrium is one of the lowest possible free energy and a state of maximal entropy. Energy must be put into the system to push the reactants and products away from a state of equilibrium. Either reactants or products must be added, removed, or changed. If a cell were a closed system, its chemical reactions would reach equilibrium, and it would die because there would be insufficient free energy left to perform the work needed to maintain life. In a living cell, chemical reactions are constantly moving towards equilibrium, but never reach it. This is because a living cell is an open system. Materials pass in and out, the cell recycles the products of certain chemical reactions into other reactions, and chemical equilibrium is never reached. In this way, living organisms are in a constant energy-requiring, uphill battle against equilibrium and entropy. This constant supply of energy ultimately comes from sunlight, which is used to produce nutrients in the process of photosynthesis.

Question 42

How is energy used to catalyze a chemical reaction?

Accepted Answer

Even exergonic reactions require a small amount of energy input to get going before they can proceed with their energy-releasing steps. These reactions have a net release of energy, but still require some energy in the beginning. This small amount of energy input necessary for all chemical reactions to occur is called the activation energy (or free energy of activation) and is abbreviated EA.

Question 43

Why is activation energy required to start a reaction?

Accepted Answer

During chemical reactions, certain chemical bonds are broken and new ones are formed. Since these are energy-storing bonds, they release energy when broken. However, to get them into a state that allows the bonds to break, the molecule must be somewhat contorted. A small energy input is required to achieve this contorted state. This contorted state is called the transition state.

Question 44

What is the energy of a transition state?

Accepted Answer

The transition state is a high-energy, unstable state. For this reason, reactant molecules don’t last long in their transition state, but very quickly proceed to the next steps of the chemical reaction. Free energy diagrams illustrate the energy profiles for a given reaction. The transition state of the reaction exists at a higher energy state than the reactants, and thus, EA is always positive.

Question 45

Where does the activation energy required by chemical reactants come from?

Accepted Answer

The source of the activation energy needed to push reactions forward is typically heat energy from the surroundings. Heat energy (the total bond energy of reactants or products in a chemical reaction) speeds up the motion of molecules, increasing the frequency and force with which they collide; it also moves atoms and bonds within the molecule slightly, helping them reach their transition state. For this reason, heating up a system will cause chemical reactants within that system to react more frequently. Increasing the pressure on a system has the same effect. Once reactants have absorbed enough heat energy from their surroundings to reach the transition state, the reaction will proceed.

Question 46

How is activation energy related to reaction rate?

Accepted Answer

The activation energy of a particular reaction determines the rate at which it will proceed. The higher the activation energy, the slower the chemical reaction will be.

Question 47

What are some examples of activation energy and subsequent reaction speed?

Accepted Answer

The example of iron rusting illustrates an inherently slow reaction. This reaction occurs slowly over time because of its high EA. Additionally, the burning of many fuels, which is strongly exergonic, will take place at a negligible rate unless their activation energy is overcome by sufficient heat from a spark. Once they begin to burn, however, the chemical reactions release enough heat to continue the burning process, supplying the activation energy for surrounding fuel molecules.

6: Metabolism Flashcards

Energy and Metabolism, Potential, Kinetic, Free, and Activation Energy, the Laws of Thermodynamics, ATP: Adenosine Triphosphate, Enzymes

Brainscape's Knowledge GenomeTM

6: Metabolism Flashcards

Energy and Metabolism, Potential, Kinetic, Free, and Activation Energy, the Laws of Thermodynamics, ATP: Adenosine Triphosphate, Enzymes

Brainscape's Knowledge Genome^TM