Chapter 8 - Energy, Enzymes and Metabolism

Question 1

Catabolism

Answer 1

Subset of metabolic reactions where molecules are broken down; release of energy from the breakdown into the subunits

Question 2

Anabolism

Answer 2

Subset of metabolic reactions where simple molecules/smaller units are combined to create complex molecules; requires an input of energy

Question 3

Metabolism

Answer 3

The sum total of all the chemical reactions occurring in a biological system at a given time

Question 4

Energy coupling

Answer 4

Energy production reactions of catabolism are used to drive the energy requiring reactions of anabolism; anabolic reactions utilize the stored energy in molecules such as ATP, NADH, NADPH, FADH₂; catabolic reactions release energy that is then stored in molecules such as ADP, NAD+, NADP+ and FAD

Question 5

Energy

Answer 5

Capacity to do work or the capacity for change

Question 6

Potential Energy

Answer 6

Energy stored as chemical bonds, concentration gradients or electric charge imbalances

Question 7

Kinetic Energy

Answer 7

The energy of movement

Question 8

First law of thermodynamics

Answer 8

Law of conservation of energy; energy of the universe is constant; energy cannot be created or destroyed, energy can only be transformed from one type to another

Question 9

Second law of thermodynamics

Answer 9

All energy transfers or transformations make the universe more disordered (increases entropy); no energy transformation is 100% efficient, some energy is lost to disorder; overall, the universe increases disorder

Question 10

Gibbs Free Energy, G

Answer 10

The portion of a system’s energy that is able to perform work when T (temperature) is uniform throughout a system; change in G is a measure of instability of a system, high G = unstable

Question 11

Spontaneous reaction

Answer 11

Can occur without assistance; reaction will move forward without assistance; increases the stability of a system; -G

Question 12

Non-spontaneous reaction

Answer 12

Can only occur if energy is added; reaction cannot move forward without outside intervention; decreases the stability of a system; +G

Question 13

Exergonic/Exothermic reactions

Answer 13

Catabolic reactions; net release of free energy; -G; spontaneous; stability of system increases; reactants have more energy than products

Question 14

Endergonic/Endothermic reactions

Answer 14

Anabolic reactions; requires energy from its environment; +G; non-spontaneous; stability of system decreases; reactants have less energy than products

Question 15

ATP

Answer 15

Adenosine triphosphate; the source of energy for cellular work; can hold and transfer free energy

Question 16

ATP hydrolysis

Answer 16

Exergonic reaction that involves the breakdown of ATP and a release of free energy; ATP releases a large amount of energy when it undergoes phosphorylation: donates a terminal phosphate group to another molecule to activate the molecule; yields G: -7.3 kcal/mol under standard conditions

Question 17

ATP formation

Answer 17

Endergonic reaction that requires free energy to form ATP; cells add an inorganic phosphate to ADP to form ATP; G = +7.3 kcal/mol

Question 18

Energy coupling cycle

Answer 18

If a negative delta G, then the energy provided by ATP is sufficient to move a reaction forward (-G = more energy released); each ATP molecule undergoes about 10,000 cycles of synthesis and hydrolysis a day

Question 19

Enzyme

Answer 19

Biological catalyst (most are proteins) that speeds up the rate of reaction by reducing the activation energy requirement, but is not altered by the reaction, meaning that the catalyst ends up in the same chemical condition before and after the reaction; enzymes are specific to one type of reaction and interact with specific reactants (aka substrates)

Question 20

Activation energy

Answer 20

The amount of energy needed to initiate a reaction; amount of energy needed to change reactants into unstable molecular forms called transition state intermediates to initiate a reaction

Question 21

Transition state

Answer 21

To get the bonds into a state that allows them to break, the molecule must be contorted (deformed, or bent) into an unstable/high energy state; activation energy is added to molecules to transform the molecules into an unstable state to initiate the reaction

Question 22

Where does the activation energy come from?

Answer 22

To speed up a reaction in a living system, an enzyme lowers the energy barrier by bringing the reactants close together

Question 23

Substrate

Answer 23

Reactants that bind to the active site of the enzyme

Question 24

Active site

Answer 24

Sequestered site on the enzyme where the reaction is more favored to move forward; the 3D shape of the enzyme determines the specific types of substrates that can bind to the active site

Question 25

Enzyme-substrate complex

Answer 25

Binding of a substrate to the active site of an enzyme; held together by hydrogen bonds, electrical attraction or covalent bonds

Question 26

How do enzymes help a reaction move forward?

Answer 26

**Orientation of the substrate**: aligns the molecules to bind, initiating the reaction and creating products at a faster rate; **induces strain in the the bonds of the substrates**, putting it in a reactive transition state; **temporarily adds chemical groups** that make the substrate more reactive or prone to build or break

Question 27

Induced fit

Answer 27

Enzyme changes shape when it binds the substrate, which alters the shape of the active site, improving the catalytic ability of the enzyme and providing favorable conditions for the reaction to move forward

Question 28

Prosthetic groups

Answer 28

Non-protein enzyme partners that are non-amino acid groups bound to enzymes: ie. heme, FAD

Question 29

Inorganic cofactors

Answer 29

Non-protein enzyme partners that are ions (Cu, Zn, Fe) permanently bound to enzyme

Question 30

Coenzymes

Answer 30

Non-protein enzyme partners that are small carbon-containing molecules that are not permanently bound; moves from enzyme to enzyme adding or removing chemical groups from the substrate; ie. ATP, coenzyme A, NAD

Question 31

Maximum rate of catalyzed reaction

Answer 31

The higer the concentration of substrate, the faster the rate of reaction; however; once the number of enzymes are satured with substrates, the reaction rate levels off; nothing is gained by adding more substrate, because no free enzyme molecules are left to act as catalysts

Question 32

Irreversible enzyme inhibitors

Answer 32

Inhibitors that covalently bind to certain side chains at the active site of the enzyme; permanently inactivates the enzyme by destroying its ability to interact with its normal substrate

Question 33

Enzyme inhibitor

Answer 33

Chemicals that bind to enzyme that slow down the rates of reactions; reduces enzyme activity

Question 34

Competitive inhibitors

Answer 34

Inhibitors that are similar enough to the enzyme's natural substrate competes for the active site, binding non-covalenty to the active site; reduces the amount of output of the reaction; prevents the substrate from entering the active site

Question 35

Uncompetitive inhibitors

Answer 35

Enzyme inbitors that bind to the enzyme-substrate complex after the subtrate binds to the active site; prevent products from being released from the active site

Question 36

Noncompetitive inhibitors

Answer 36

Enzyme inhibitors that bind to the enzyme at a location other than the active site that alters the shape of the enzyme; the conformation change either inactivates the active site or reduces the rate of product formation

Question 37

Allosteric regulation

Answer 37

An effector molecule (activator or inhibitor) binds to an allosteric site (not an active site), inducing the enzyme to change shape; an activator binds to an allosteric site, allowing the enzyme to take proper shape for substrate binding; an inhibitor binds to an allosteric site changing the shape of the enzyme, disabling the active site

Question 38

Allosteric enzyme

Answer 38

Quaternary protein where the active site is on the catalytic subunit and the activators and inhibitors bind to the regulatory subunits

Question 39

Allosteric enzyme rate of reaction

Answer 39

Rate of reaction is very sensitive to substrate concentration; after the substrate binds to the first active site, there is a change in the quaternary structure and other sites become more likely to bind to substrates, speeding up the reaction

Question 40

Feedback inhibition

Answer 40

When an end product of a reaction is in high concentration, some of the end product binds to an allosteric site on the commitment step enzyme, causing the enzyme to become inactive/shut down; the end product acts as a noncompetitive inhibitor

Question 41

Isozyme

Answer 41

Enzyme that catalyzes the same reaction but have different optimal properties (such as temperature of pH)