AP Chapter 8

Chapter 8

An Introduction to Metabolism

Overview: The Energy of Life

          The living cell is a miniature chemical factory where thousands of reactions occur

          The cell extracts energy and applies energy to perform work

          Some organisms even convert energy to light, as in bioluminescence

Concept 8.3: ATP powers cellular work by coupling _______________________ reactions to _______________________reactions

          A cell does three main kinds of work:




          To do work, cells manage energy resources by __________________________________, the use of an exergonic process to drive an endergonic one

          Most energy coupling in cells is mediated by ATP

The Structure and Hydrolysis of ATP

          ATP (__________________________________________) is the cell’s energy shuttle

          ATP is composed of _________________ (a sugar), _______________________ (a nitrogenous base), and _______________ phosphate groups

          The bonds between the phosphate groups of ATP’s tail can be broken by ___________________

          Energy is released from ATP when the _________________________ phosphate bond is broken

          This release of energy comes from the chemical change to a state of lower _____________________________________, not from the phosphate bonds themselves

How ATP Performs Work

          The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP

          In the cell, the energy from the ________________________ reaction of ATP hydrolysis can be used to drive an  ___________________________ reaction

          Overall, the coupled reactions are ___________________________

          ATP drives endergonic reactions by __________________________________, transferring a phosphate group to some other molecule, such as a reactant

          The recipient molecule is now ___________________________________________

The Regeneration of ATP

          ATP is a renewable resource that is regenerated by addition of a phosphate group to __________________________________________ (ADP)

          The energy to phosphorylate ADP comes from ______________________________________ in the cell

          The chemical potential energy temporarily stored in ATP drives most _______________________________________

Concept 8.4: Enzymes speed up metabolic reactions by ________________________ energy barriers

          A _____________________________ is a chemical agent that speeds up a reaction without being consumed by the reaction

          An _________________________________ is a catalytic protein

          Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction

The Activation Energy Barrier

          Every chemical reaction between molecules involves bond _______________________ and bond ____________________________

          The initial energy needed to start a chemical reaction is called the free energy of activation, or ____________________________________ (____________)

          Activation energy is often supplied in the form of _____________________ from the surroundings

How Enzymes Lower the EA Barrier

          Enzymes catalyze reactions by _____________________________________________________

          Enzymes do not affect the change in free energy (?G); instead, they ______________________ reactions that would occur eventually

Substrate Specificity of Enzymes

          The reactant that an enzyme acts on is called the enzyme’s ______________________________

          The enzyme binds to its substrate, forming an _________________________________________

          The ______________________________ is the region on the enzyme where the substrate binds

          __________________________________ of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

Catalysis in the Enzyme’s Active Site

          In an enzymatic reaction, the _______________________________ binds to the active site of the __________________________________

          The active site can lower an EA barrier by





Effects of Temperature and pH

          Each enzyme has an optimal ___________________________________ in which it can function

          Each enzyme has an optimal __________________ in which it can function


          ______________________________ are nonprotein enzyme helpers

          Cofactors may be inorganic (such as a metal in ionic form) or organic

          An organic cofactor is called a _________________________________

          Coenzymes include _____________________________

Enzyme Inhibitors

          _________________________________________________ bind to the active site of an enzyme, competing with the substrate

          _________________________________________________ bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective

          Examples of inhibitors include _____________, ________________, __________________, and _____________________________

Concept 8.5: Regulation of enzyme activity helps control __________________________________

          Chemical chaos would result if a cell’s metabolic pathways were not tightly _____________________________

          A cell does this by switching on or off the __________________ that encode specific enzymes or by regulating the ___________________________ of enzymes

Allosteric Regulation of Enzymes

          _____________________________________ may either inhibit or stimulate an enzyme’s activity

          Allosteric regulation occurs when a regulatory molecule binds to a ___________________ at one site and affects the protein’s ____________________________ at another site

Allosteric Activation and Inhibition

          Most allosterically regulated enzymes are made from ___________________________ subunits

          Each enzyme has active and _______________________ forms

          The binding of an _______________________________ stabilizes the active form of the enzyme

          The binding of an _______________________________ stabilizes the inactive form of the enzyme

          ____________________________________ is a form of allosteric regulation that can amplify enzyme activity

          In cooperativity, binding by a substrate to one active site stabilizes favorable _____________________________ changes at all other subunits

Identification of Allosteric Regulators

          Allosteric regulators are attractive _____________________ candidates for enzyme regulation

          Inhibition of proteolytic enzymes called ___________________________ may help management of inappropriate inflammatory responses

Feedback Inhibition

          In ________________________________________________, the end product of a metabolic pathway shuts down the pathway

          Feedback inhibition __________________________ a cell from wasting chemical resources by synthesizing more product than is needed

Specific Localization of Enzymes Within the Cell

          Structures within the cell help bring ___________________ to metabolic pathways

          Some enzymes act as structural components of _______________________________

          In eukaryotic cells, some enzymes reside in specific __________________________; for example, enzymes for cellular respiration are located in ______________________________