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AP Biology JCH > Chapter 8 > Flashcards

Chapter 8 Flashcards

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1
Q

What is metabolism?

A

the totality of an organisms chemical reactions

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2
Q

What is catabolism and what is an example?

A
  • release energy by breaking down complex molecules to simpler compounds
  • cellular respiration
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3
Q

What is anabolism and what is an example?

A
  • consume energy to build complicated molecules from simple compounds
  • biosynthetic pathways
  • building proteins from amino acids
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4
Q

The energy released by ______ pathways can be stored and then used to drive _______ pathways

A

catabolic anabolic

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5
Q

What is bioenergetics?

A

the study of how organisms manage their energy resources

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6
Q

What is energy?

A

the capacity to do work

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7
Q

How does energy exist?

A

Energy exists in various forms, and cells transform energy from one type into another.

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8
Q

What is kinetic energy and how does it perform work?

A

• Kinetic energy is the energy associated with the relative motion of objects.
- Objects in motion can perform work by imparting motion to other matter.

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9
Q

List two examples of kinetic energy.

A

o Photons of light can be captured and their energy harnessed to power photosynthesis in green plants.
o Heat or thermal energy is kinetic energy associated with the random movement of atoms or molecules.

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10
Q

What is heat?

A

Heat or thermal energy is kinetic energy associated with the random movement of atoms or molecules.

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11
Q

What is potential energy and what is an example?

A

• Potential energy is the energy that matter possesses because of its location or structure.
o Chemical energy is a form of potential energy stored in molecules because of the arrangement of their atoms.

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12
Q

Describe the conversion of energy of a boy ascending a diving board.

A

o For example, as a boy climbs stairs to a diving platform, he is releasing chemical energy stored in his cells from the food he ate for lunch.
o The kinetic energy of his muscle movement is converted into potential energy as he climbs higher.
o As he dives, the potential energy is converted back to kinetic energy.
o Kinetic energy is transferred to the water as he enters it.
o Some energy is converted to heat due to friction.

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13
Q

What is thermodynamics?

A

the study of energy transformations

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14
Q

What is a closed system?

A

isolated from its surroundings, liquid in a thermos

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15
Q

What is an open system?

A

Energy and matter transferred between system and surroundings, organisms are open systems

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16
Q

What is the first law of thermodynamics?

A

• The first law of thermodynamics states that energy can be transferred and transformed, but it cannot be created or destroyed.
o The first law is also known as the principle of conservation of energy.

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17
Q

Plants do not _____ they _______

A

o Plants do not produce energy; they transform light energy to chemical energy.

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18
Q

During every transfer or transformation of energy some energy is converted to______

A

heat

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19
Q

When can a system use heat to do work?

A

• A system can use heat to do work only when there is a temperature difference that results in heat flowing from a warmer location to a cooler one.

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20
Q

Can an organism used heat to do work?

A

o If temperature is uniform, as in a living cell, heat can only be used to warm the organism.

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21
Q

How do energy transfers and transformations impact the order of the universe?

A

• Energy transfers and transformations make the universe more disordered due to this loss of usable energy.

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22
Q

What is entropy?

A

• Entropy is a quantity used as a measure of disorder or randomness.
o The more random a collection of matter, the greater its entropy.

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23
Q

What is the second law of thermodynamics?

A

• The second law of thermodynamics states that every energy transfer or transformation increases the entropy of the universe.

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24
Q

Facts about the second law…

A

o While order can increase locally, there is an unstoppable trend toward randomization of the universe.
o Much of the increased entropy of the universe takes the form of increasing heat, which is the energy of random molecular motion.

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25
Q

What occurs in most energy transformations? Two examples.

A

• In most energy transformations, ordered forms of energy are converted at least partly to heat.
o Automobiles convert only 25% of the energy in gasoline into motion; the rest is lost as heat.
o Living cells unavoidably convert organized forms of energy to heat.

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26
Q

What is spontaneous?

A

• The word spontaneous describes a process that can occur without an input of energy.
o Some spontaneous processes are instantaneous, such as an explosion. Some are very slow, such as the rusting of an old car.

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27
Q

What is another way to state the second law?

A

• For a process to occur spontaneously, it must increase the entropy of the universe.

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28
Q

How do living systems impact entropy?

A
  • Living systems create ordered structures from less ordered starting materials
  • However, an organism also takes in organized forms of matter and energy from its surroundings and replaces them with less ordered forms.
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29
Q

How does the entropy of organisms compare to the universe?

A

o Organisms are islands of low entropy in an increasingly random universe.

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30
Q

What is free energy?

A

• Free energy is the portion of a system’s energy that is able to perform work when temperature and pressure is uniform throughout the system, as in a living cell.

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31
Q

Free energy equation:

A

• The free energy (G) in a system is related to the total enthalpy (in biological systems, equivalent to energy) (H) and the entropy (S) by this relationship:
o G = H - TS, where T is temperature in Kelvin units.

32
Q

Is all energy in a system available for work?

A

o Not all the energy in a system is available for work because the entropy component must be subtracted from the enthalpy component.

33
Q

What can free energy be thought to measure?

A

• Free energy can be thought of as a measure of the stability of a system.
o Systems that are high in free energy—compressed springs, separated charges, organic polymers—are unstable and tend to move toward a more stable state, one with less free energy.
o Systems that tend to change spontaneously are those that have high enthalpy, low entropy, or both.

34
Q

What occurs to the free energy in a spontaneous process?

A

free energy decreases

35
Q

List another free energy reaction

A

o ΔG = Gfinal state - Gstarting state

36
Q

What must occur for a process to be spontaneous?

A

• For a process to be spontaneous, the system must either give up enthalpy (decrease in H), give up order (increase in S), or both.
o ΔG must be negative for a process to be spontaneous.
o Every spontaneous process is characterized by a decrease in the free energy of the system.

37
Q

How does decrease in energy impact the amount of work a spontaneous reaction can perform?

A

• The greater the decrease in free energy, the more work a spontaneous process can perform.

38
Q

Which way does nature run?

A

downhill

39
Q

Describe a system at equilibrium.

A

• A system at equilibrium is at maximum stability.
o In a chemical reaction at equilibrium, the rates of forward and backward reactions are equal, and there is no change in the concentration of products or reactants.
o At equilibrium ΔG = 0, and the system can do no work.
o A process is spontaneous and can perform work only when it is moving toward equilibrium.
o Movements away from equilibrium are nonspontaneous and require the addition of energy from an outside energy source (the surroundings).

40
Q

What is an exergonic reaction?

A

• An exergonic reaction proceeds with a net release of free energy; ΔG is negative.
• The magnitude of ΔG for an exergonic reaction is the maximum amount of work the reaction can perform.
- Respiration

41
Q

What is an endergonic reaction?

A

• An endergonic reaction is one that absorbs free energy from its surroundings.
o Endergonic reactions store energy in molecules; ΔG is positive.
o Endergonic reactions are nonspontaneous, and the magnitude of ΔG is the quantity of energy required to drive the reaction.

42
Q

What type of reaction is photosynthesis?

A

• Photosynthesis is strongly endergonic, powered by the absorption of light energy.

43
Q

What occurs in human life when cells reach equilibrium?

A

• Reactions in a closed system eventually reach equilibrium and can do no work.
o A cell that has reached metabolic equilibrium has a ΔG = 0 and is dead!
• Metabolic disequilibrium is one of the defining features of life.
Cells maintain disequilibrium because they are open systems.

44
Q

How does a catabolic process in a cell work?

A
  • A catabolic process in a cell releases free energy in a series of reactions, not in a single step.
  • Some reversible reactions of respiration are constantly “pulled” in one direction, as the product of one reaction does not accumulate but becomes the reactant in the next step.
45
Q

What are the three main kinds of work a cell performs?

A

• A cell does three main kinds of work:

  1. Mechanical work, such as the beating of cilia, contraction of muscle cells, and movement of chromosomes during cellular reproduction.
  2. Transport work, the pumping of substances across membranes against the direction of spontaneous movement.
  3. Chemical work, driving endergonic reactions such as the synthesis of polymers from monomers.
46
Q

How do cells manage their energy resources?

A

• Cells manage their energy resources to do this work by energy coupling, the use of an exergonic process to drive an endergonic one.

47
Q

What is the structure of ATP?

A

• ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups.

48
Q

How does hydrolysis of the end phosphate group release energy?

A

• While the phosphate bonds of ATP are sometimes referred to as high-energy phosphate bonds, these are actually fairly weak covalent bonds.
o However, they are unstable, and their hydrolysis yields energy because the products are more stable.
- This reaction releases 7.3 kcal of energy per mole of ATP under standard conditions (1 M of each reactant and product, 25°C, pH 7).

49
Q

Why does the hydrolysis of ATP yield so much energy?

A

o Each of the three phosphate groups has a negative charge.
o These three like charges are crowded together, and their mutual repulsion contributes to the instability of this region of the ATP molecule.

50
Q

How is tap used in the cell?

A

• In the cell, the energy from the hydrolysis of ATP is directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.
o This recipient molecule is now phosphorylated.
o This molecule is now more reactive (less stable) than the original unphosphorylated molecules.

51
Q

What provides the energy for the exergonic regeneration of ATP?

A

Catabolic (exergonic) pathways, especially cellular respiration, provide the energy for the exergonic regeneration of ATP.

52
Q

What is a catalyst?

A

• A catalyst is a chemical agent that speeds up the rate of a reaction without being consumed by the reaction.

53
Q

What is an enzyme and what does it do?

A

o An enzyme is a catalytic protein.

• Enzymes regulate metabolic pathways.

54
Q

What is activation energy?

A

• Activation energy is the amount of energy necessary to push the reactants over an energy barrier so that the reaction can proceed.

55
Q

Describe the process of a reaction.

A

o At the summit, the molecules are in an unstable condition, the transition state.
o Activation energy may be supplied in the form of heat that the reactant molecules absorb from the surroundings.
o The bonds of the reactants break only when the molecules have absorbed enough energy to become unstable and, therefore, more reactive.
o The absorption of thermal energy increases the speed of the reactant molecules, so they collide more often and more forcefully.
o Thermal agitation of the atoms in the molecules makes bonds more likely to break.
o As the molecules settle into new, stable bonding arrangements, energy is released to the surroundings.
o In exergonic reactions, the activation energy is released back to the surroundings, and additional energy is released with the formation of new bonds.

56
Q

Why can’t most organic molecules perform reactions?

A

• Proteins, DNA, and other complex organic molecules are rich in free energy. Their hydrolysis is spontaneous, with the release of large amounts of energy.
o However, there is not enough energy at the temperatures typical of the cell for the vast majority of organic molecules to make it over the hump of activation energy.

57
Q

How do enzymes work What do they do and not do?

A

• Enzymes speed reactions by lowering EA.
o The transition state can then be reached even at moderate temperatures.
• Enzymes do not change ΔG.
o They hasten reactions that would occur eventually.
o Because enzymes are so selective, they determine which chemical processes will occur at any time.

58
Q

What is the phrase for an enzyme’s specificity?

A

Enzymes are substrate specific.

59
Q

What’s the complex an enzyme forms?

A

enzyme-substrate complex

60
Q

What accounts for the molecular recognition of an enzyme?

A

o The specificity of an enzyme results from its three-dimensional shape.

61
Q

How much of an enzyme binds to a substrate?

A

• Only a portion of the enzyme binds to the substrate.
o The active site of an enzyme is typically a pocket or groove on the surface of the protein into which the substrate fits.
o The active site is usually formed by only a few amino acids.

62
Q

What is an enzyme’s catalytic center called?

A

active site

63
Q

How are substrates held in the active site?

A

• In most cases, substrates are held in the active site by weak interactions, such as hydrogen bonds and ionic bonds.
o R groups of a few amino acids on the active site catalyze the conversion of substrate to product.
o The product then leaves the active site.

64
Q

How many reactions can an enzyme perform?

A
  • A single enzyme molecule can catalyze thousands of reactions a second.
  • Enzymes are unaffected by the reaction and are reusable.
65
Q

Describe the mechanisms enzymes use to catalyze a chemical reaction.

A

• Enzymes use a variety of mechanisms to lower activation energy and speed up a reaction.
o In reactions involving more than one reactant, the active site brings substrates together in the correct orientation for the reaction to proceed.
o As the active site binds the substrate, it may put stress on bonds that must be broken, making it easier for the reactants to reach the transition state.
o R groups at the active site may create a microenvironment that is conducive to a specific reaction.
- An active site may be a pocket of low pH, facilitating H+ transfer to the substrate as a key step in catalyzing the reaction.
o Enzymes may briefly bind covalently to substrates.
- Subsequent steps of the reaction restore the R groups within the active site to their original state.

66
Q

Most metabolic enzymes can catalyze a reaction __________ ___________________

A

in both the forward and reverse directions.

67
Q

What impacts an enzyme?

A

• The activity of an enzyme is affected by general environmental conditions, such as temperature and pH.

68
Q

What do most enzymes require?

A

• Many enzymes require nonprotein helpers, called cofactors, for catalytic activity.
Cofactors bind permanently or reversibly to the enzyme.
o Some inorganic cofactors include zinc, iron, and copper.
• Organic cofactors are called coenzymes.
o Many vitamins are coenzymes.

69
Q

How do inhibitors impacts enzymes and what may be the result of inhibition?

A

• Binding by inhibitors prevents enzymes from catalyzing reactions.
o If inhibitors attach to the enzyme by covalent bonds, inhibition may be irreversible.
o If inhibitors bind by weak bonds, inhibition may be reversible.

70
Q

What are competitive inhibitors?

A

• Some reversible inhibitors resemble the substrate and compete for binding to the active site.
o These molecules are called competitive inhibitors.
o Competitive inhibition can be overcome by increasing the concentration of the substrate.

71
Q

What are non-competitive inhibitors?

A

• Noncompetitive inhibitors impede enzymatic reactions by binding to another part of the molecule.
o Binding by the inhibitor causes the enzyme to change shape, rendering the active site less effective at catalyzing the reaction.

72
Q

How do regulatory molecules regulate enzymes?

A

• Regulatory molecules often bind weakly to an allosteric site, a specific receptor on the enzyme away from the active site.
o Binding by these molecules can either inhibit or stimulate enzyme activity.

73
Q

What is the structure of allosterically regulated enzymes?

A

• Most allosterically regulated enzymes are constructed of two or more polypeptide chains.
o Each subunit has its own active site.
o Allosteric sites are often located where subunits join.

74
Q

What are two methods an enzyme may be allosterically regulated?

A

• The binding of an activator stabilizes the conformation that has functional active sites, while the binding of an inhibitor stabilizes the inactive form of the enzyme.

75
Q

What is cooperativity?

A

• In enzymes with multiple catalytic subunits, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits, a process called cooperativity.
o This mechanism amplifies the response of enzymes to substrates, priming the enzyme to accept additional substrates.

76
Q

What is feedback inhibition?

A

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

77
Q

What is a multi enzyme complex?

A

• A team of enzymes for several steps of a metabolic pathway may be assembled as a multienzyme complex.

AP Biology JCH (12 decks)

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