Cell Biology: Chapter 3

Front 1

What is the first law of thermodynamics?

Back 1

the law of conservation of energy - Energy can neither be created nor destroyed.

Front 2

Despite the first law of thermodynamics, energy can be...

Back 2

transduced - converted from one form of energy to another

Cells are also capable of transduction.

Front 3

Regardless of the transduction process, the total amount of energy in the universe is _____________.

Back 3

constant

Front 4

What is the most important energy transduction in the biological world which converts sunlight into chemical energy?

Back 4

photosynthesis - provides the fuel that directly or indirectly powers nearly all the activities of life forms

Front 5

What does the enzyme luciferase in fireflies enable these organisms to do?

Back 5

convert chemical energy back into light (reverse photosynthesis)

Front 6

Reactions that lose heat are ________________.

Back 6

exothermic

Front 7

Reactions that gain heat are ________________.

Back 7

endothermic

Front 8

What is the second law of thermodynamics?

Back 8

Events in the universe have direction; they tend to proceed in a "downhill" fashion, going from a higher to lower state of energy

Front 9

What is the term that describes events that are thermodynamically favorable and can occur without the input of external energy?

Back 9

spontaneous

Front 10

Loss of energy during a process is the result of a tendency for ___________________ to increase whenever there is a transfer of energy.

Back 10

randomness (entropy)

Front 11

Every event is accompanied an increase in the ______________ of the universe.

Back 11

entropy

Front 12

Spontaneity depends on both ___________ and _____________.

Back 12

entropy - randomness or disorder AND enthalpy - total energy content of the system

Front 13

All chemical reactions spontaneously proceed toward the _________________.

Back 13

equilibrium

Front 14

The release of heat is an example of an ______________ in entropy.

Back 14

increase

Front 15

Together, what do the first and second laws of thermodynamics indicate?

Back 15

The energy of the free universe is constant, but the entropy continues to increase toward a maximum.

Front 16

All spontaneous energy transformations must have a _________________ delta G.

Back 16

negative - the process must proceed toward a lower state of free energy

Front 17

What are processes that occur spontaneously, thermodynamically favored, and have a negative delta G described as?

Back 17

exergonic

Front 18

All nonspontaneous energy transformations must have a _______________ delta G.

Back 18

positive

Front 19

What are processes that occur nonspontaneously, thermodynamically unfavorable, and have a positive delta G described as?

Back 19

endergonic

Front 20

All _________ reactions are coupled reactions.

Back 20

ATP

Coupling is a major way to get around energy requirements. One gives off energy, and the paired reaction is right there to absorb it.

Front 21

The greater the delta G, the farther the reaction is from equilibrium. This means..

Back 21

more work can be performed by the system

Front 22

When delta G is 0, the reaction is...

Back 22

at equilibrium and no further work can be obtained

Front 23

The delta G of ATP hydrolysis is -7.3 kcal/mol. This suggests that..

Back 23

the ATP hydrolysis reaction is a highly favorable (exergonic) reaction

Front 24

Why is ATP used to drive most endergonic processes within the cell?

Back 24

because its terminal phosphate group can be transferred to a variety of different types of molecules, including amino acids, sugars, lipids, and proteins.

In most coupled reactions, the phosphate group is transferred in an initial step from ATP to one of these acceptors and is subsequently removed in the second step.

Front 25

What may energy from ATP hydrolysis be used do within a cell?

Back 25

separate charge across a membrane

concentrate a particular solute within the cell

drive an unfavorable chemical reaction

slide filaments across one another (shortening of a muscle cell)

donate a phosphate to a protein (added phosphates become binding sites for these proteins)

Front 26

Why can cellular metabolism maintain itself at irreversible, nonequilibrium conditions?

Back 26

The basic principles of thermodynamics were built upon nonliving, closed systems (no exchange of matter between the system and surroundings).

Unlike the environment within a test tube, the cell is an open system.

The continual flow of oxygen and other materials in and out of our cells allows cellular metabolism to exist at a steady state.

Front 27

Maintaining a steady state requires a constant input of energy, while maintaining ______________ does not.

Back 27

equilibrium

Front 28

In a steady state, the concentrations of reactants and products remain _____________ but..

Back 28

constant but not at equilibrium

Front 29

What is the term used to describe biological catalysts (usually proteins) that speed up chemical reactions?

Back 29

enzymes

Front 30

_______________ are the mediators of metabolism, responsible for virtually every reaction in the cell.

Back 30

Enzymes

Front 31

Without, ______________ metabolic reactions would proceed so slowly as to be imperceptible.

Back 31

enzymes

Front 32

________________ is a protein catalyst, while ________________ is an RNA catalyst.

Back 32

enzyme - protein
ribozyme - RNA

Front 33

List the properties of enzymes.

Back 33

exist in small amounts

are not altered irreversibly (same enzyme can be used repeatedly in different reactions)

have no effect on the thermodynamics of the reaction, just the rate

Front 34

Enzymes do not supply energy for a chemical reaction, therefore...

Back 34

they cannot determine whether a reaction is thermodynamically favorable or unfavorable

Front 35

What is the term used to describe the reactants bound by an enzyme?

Back 35

substrates - enzymes are highly specific for their substrates

Front 36

Chemical transformations require that certain covalent bonds be broken within the reactants. For this to occur, the reaction must overcome a barrier. What is this amount of energy required called?

Back 36

activation energy (Ea) - small energy input that is required for any chemical transformation

Front 37

How does the Ea barrier affect the process of thermodynamically unstable reactions?

Back 37

it slows the process

Front 38

When reactant molecules reach the peak of the Ea barrier, what is this called?

Back 38

transition state

Front 39

What helps molecules reach the transition state due to the decrease of required activation energy?

Back 39

enzymes

Front 40

How are enzymes able to lower activation energies?

Back 40

by binding more tightly to the transition state than to the reactants, which stabilizes this activated complex, and decreases its energy

Front 41

How does heat increase the rate of a reaction?

Back 41

by increasing the content of the molecules

Front 42

What portion of the enzyme does the substrate bind to?

Back 42

active site

The active site and substrate have complementary shapes that allow substrate specificity.

Front 43

What is the term that describes the physical association between an enzyme and its substrate during which catalysis of the reaction takes place?

Back 43

enzyme-substrate complex - forms once everything is bound

Front 44

The active site is typically buried in a cleft or crevice that leads from the aqueous surroundings into the depths of the protein. Active sites are often thought of as...

Back 44

pockets in the enzyme

Front 45

substrates = ______________

Back 45

reactants

Front 46

structure = _____________

Back 46

function

Front 47

What are the three ways in which enzymes accelerate reactions?

Back 47

maintaining precise orientation (holding on tightly to substrate)

changing substrate reactivity by altering electrostatic configuration

exerting physical stress on bonds in the substrate to be broken

Front 48

Shifts in the conformation after binding cause ____________________ between the enzyme and substrate.

Back 48

induced fit - complementary fit that moves the proper reactive groups of the enzyme into place (strain is relieved)

Front 49

At saturation, every enzyme is working at ________________________.

Back 49

maximum velocity

Front 50

Enzyme inhibitors _________ the rates for enzymatic reactions.

Back 50

slow

Front 51

What is the difference between reversible and irreversible inhibitors?

Back 51

Reversible inhibitors bind loosely to the enzyme, whereas irreversible inhibitors (suicide inhibitors) bind tightly to the enzyme.

Front 52

Competitive inhibitors compete with the ______________ for a binding site on the enzyme.

Back 52

substrate

resemble the substrate, can be overcome with high substrate inhibitor ratios

Front 53

What is the difference between competitive inhibitors and noncompetitive inhibitors?

Back 53

Competitive inhibitors compete with the substrate to bind to the active site of the enzyme, whereas noncompetitive inhibitors bind to other areas besides the active site and INACTIVATE the enzyme.

Noncompetitive inhibitors (allosteric inhibitors) cannot be overcome with high substrate inhibitor ratios as competitive inhibitors can.

Front 54

Enzymes reduce enzyme efficiency. Competitive inhibitors _____________ Km but ______________ Vmax.

Back 54

Competitive inhibitors increase Km but do not change Vmax.

Front 55

Enzymes reduce enzyme efficiency. Noncompetitive inhibitors ______________ Km but ______________ Vmax.

Back 55

Noncompetitive inhibitors do not change Km but decrease Vmax.

Front 56

Which reactions break down complex substrates into simple end products?

Back 56

catabolic pathways (energetically unfavorable) - provide raw materials for the cell, provide chemical energy for the cell

Front 57

Which reactions synthesize complex end products from simple substrates?

Back 57

anabolic pathways (energetically favorable) - require energy, use ATP and NADPH from catabolic pathways

Front 58

Which stage of metabolism consists of macromolecules being hydrolyzed into their building blocks?

Back 58

stage 1

Front 59

Which stage of metabolism consists of building blocks being degraded into a few common metabolites?

Back 59

stage 2

Front 60

Which stage of metabolism consists of small molecular weight metabolites like acetyl-CoA being degraded and yielding ATP?

Back 60

stage 3

Front 61

What is the first stage in the catabolism of glucose that occurs in the soluble portion of the cytoplasm?

Back 61

glycolysis

Front 62

What is the second stage in the catabolism of glucose that occurs in the mitochondria of eukaryotic cells?

Back 62

tricarboxylic cycle (TCA, Krebs cycle)

Front 63

All cells perform glycolysis, while the Krebs cycle is unique to _________________ cells.

Back 63

eukaryotic

Front 64

Which reactions of glycolysis are NOT at or near equilibrium?

Back 64

those catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase

Only these three steps require ATP.