Chapter 8: An Introduction to Metabolism

Question 1

What is metabolism?

Answer 1

The sum of all the chemical reactions that happen inside a living organism to keep them alive and functioning.

Question 2

Define metabolic reactions.

Answer 2

Reactions that take place in a cell that are catalyzed by enzymes.

Question 3

Define metabolic pathways.

Answer 3

A metabolic pathway is a series of enzyme-controlled chemical reactions that convert starting molecules to end products. each step is catalyzed up by a specific enzyme (a macromolecule).

Question 4

Name and describe the two kinds of metabolic pathways.

Answer 4

Catabolic Pathways: Pathways that RELEASE energy by BREAKING DOWN complex molecules into simpler compounds.

Anabolic Pathways: Pathways that CONSUME energy by BUILDING complex molecules from simpler compounds.

Question 5

Define energy.

Answer 5

Energy is the capacity to cause change.

Question 6

Name and describe the three kinds of energy.

Answer 6

Kinetic energy: Energy associated with the relative motion of objects

Thermal energy: The total kinetic energy of all the particles in a substance.

Chemical Energy: The potential energy available for release in a chemical reaction.

Question 7

Define feedback inhibition.

Answer 7

Feedback inhibition: A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway. (The end product of a pathway reacts with the first product to change its shape, so the substrate can no longer bind to it.)

Question 8

Name four reasons enzymes are crucial to metabolism.

Answer 8

1. They speed up the rate of reactions (enzymes are catalysts).
2. They allow thermodynamically unfavorable reactions to take place (Allow reactions that do not occur without overall input of energy to occur)
3. They allow regulation (controlling the rate) of specific reactions.
4. They allow cells to respond to changes in their environment (ex. cellular respiration)

Question 9

Define enzymes.

Answer 9

Enzymes: Reaction catalysts. Proteins that lower the activation energy of a reaction, making a reaction occur faster.

Question 10

The amount of free energy (ΔG) (increases/decreases/remains the same) between the start and end of a chemical reaction even if assisted by enzymes

Answer 10

Remains the same.

Question 11

Define free energy.

Answer 11

The portion of a systems energy that can preform work when temperature and pressure are uniform throughout the system. (the “usable” energy in a system)

Question 12

Define activation energy (Ea).

Answer 12

The energy required for a reaction to start.

Question 13

Activation energy brings the reaction to the _______ state, making the bonds unstable and breakable.

Answer 13

Transition

Question 14

Explain why an investment of activation energy is necessary to initiate a spontaneous reaction.

Answer 14

This is because before the reaction can proceed to form the products, the reactant molecules must first reach an unstable transition state where old bonds are breaking and new bonds are forming.

Question 15

How do enzymes lower the activation energy (Ea) barrier?

Answer 15

Enzymes lower the Ea barrier by lowering the required energy needed to cross the activation barrier (providing an alternate pathway for the reaction to occur).

Question 16

What is a substrate?

Answer 16

A substrate is the molecule that enzymes work on to catalyze chemical reactions.

Question 17

Why do enzymes only interact with specific substrates?

Answer 17

To regulate the reaction in cells and prevent unwanted side reactions.

Question 18

Define the “active site” of an enzyme.

Answer 18

The “active site” of an enzyme is a region or pocket on the enzyme’s surface where the substrate bind and undergo a chemical reaction.

Question 19

Name four ways the “active site” lowers the activation energy (Ea) barrier.

Answer 19

1. Orienting (shaping) substrates correctly
2. Straining substrate bonds (packing the enzyme and substrate together)
3. Provides a favorable microenvironment
4. Covalently bonds to the substrate (closes and turns enzyme-substrate into enzyme-product)

Question 20

Define cofactors.

Answer 20

Cofactors are nonproteins that bind with an enzyme to make it work more efficiently.

Question 21

What are the two kinds of enzyme inhibiters, and how do they work?

Answer 21

Inhibiters are ways that stop the enzyme from binding. (i.e. toxins, poisons, pestisides)

Competitive Inhibitors: Bind to the enzyme at the active site and compete with the substrate

Noncompetitive Inhibitor: binds to the enzyme at another part of the enzyme (allosteric site), causing the enzyme to change shape making the active site less effective.

Question 22

What is the first law of thermodynamics?

Answer 22

You can’t create or destroy energy, you can only change its form.

Ex. A pile of building blocks, you can’t make them appear or disappear, you can only rearrange them.

Question 23

What is the value of ΔG?

Answer 23

ΔG = ΔH - TΔS

The difference in the free energy associated with the reactants and the products.

Question 24

If the value of ΔG is POSITIVE, this means…

If the value of ΔG is NEGATIVE, this means…

Answer 24

The reaction NEEDS “x” amount if energy to carry out, making it an endergonic reaction.

The reaction RELEASES “x” amount of energy, making it an exergonic reaction.

Question 25

Define a "spontaneous process".

Answer 25

Spontaneous Process: A process that occurs without an overall input of energy; a process that is energetically favorable.

Question 26

Name and describe the two types of metabolic reactions.

Answer 26

Endergonic: A nonspontaneous chemical reaction that ABSORBS energy. Exergonic: A a spontaneous chemical reaction that RELEASES energy.

Question 27

Name three ways cells perform work and examples of each.

Answer 27

1. Transport Work - Work involving moving stuff in and out through its membranes. (ex. removal of waste products.) 2. Mechanical Work - Work involving moving stuff inside itself or moving around. (ex. muscle cell contraction, cell division.) 3. Chemical Work - Work involving chemical reactions to make or break stuff down. (ex. protein synthesis, ATP production through cellular respiration, digestion.)

Question 28

To perform work, cells manage energy sournces by using energy coupling, the process of...

Answer 28

Connecting two processes in a way that the energy released by one process helps to drive the other process (the use of an exergonic process to fuel an endergonic process).

Question 29

How can the concept of free energy be applied to the metabolic process?

Answer 29

The concept of free energy helps us understand how metabolic processes occur in cells, how energy is stored and released, and how cells maintain energy balance to sustain life.

Question 30

What is the second law of thermodynamics?

Answer 30

Every time energy changes form, some of it is lost as heat, therefore becoming unavailable to do work. It also increases the entropy (disorder) of the universe. (i.e. baking cookies; when you mix the ingredients and put them in the oven, some of the energy from the heat is lost to the surroundings as the cookies bake.)

Question 31

In relation to metabolism, what is the difference between open and closed systems?

Answer 31

Open systems can exchange both matter and energy with their surroundings, while closed systems can only exchange energy.

Question 32

Explain the second law of thermodynamics and explain why it is not violated by living organisms.

Answer 32

The second law of thermodynamics states that in any energy transfer or transformation, there will be an increase in the overall entropy (disorder) of the system and its surroundings. Living organisms do not violate this law because they are not isolated systems; they exchange energy and matter with their surroundings.

Question 33

How do cells obtain the energy to do cellular work?

Answer 33

Through cellular respiration.

Question 34

What are Allosteric regulators?

Answer 34

Allosteric regulators are molecules that bind to specific regulatory sites on enzymes, known as allosteric sites, which are distinct from the active site where substrates bind. Allosteric regulators can either inhibit or stimulate the activity of an enzyme.

Question 35

How do allosteric regulators inhibit or stimulate the activity of an enzyme?

Answer 35

Allosteric inhibitors bind to the allosteric site and induce a conformational change in the enzyme that reduces its catalytic activity. This change may involve altering the enzyme's active site geometry, making it less accessible to substrates, or destabilizing the enzyme-substrate complex, preventing catalysis. Allosteric activators bind to the allosteric site and induce a conformational change that enhances the enzyme's catalytic activity. This change may involve stabilizing the enzyme-substrate complex, increasing the enzyme's affinity for substrates, or promoting a more favorable active site geometry for catalysis.