BIO200 Midterm 2 Study Guide: Cellular Respiration, Metabolism, and Energy, Study Guides, Projects, Research of Biology

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BIO200 Midterm 2 Study Guide Review Questions

1. Cellular respiration: drives the cellular economy by extracting the energy to perform various

types of work such as the transport of solutes across the plasma membrane

2. Metabolism: manages the material and energy resources of the cell ...

the totality of an organisms chemical reaction an emergent property of life arising from orderly interactions between molecules

3. Metabolic pathway: begins with a specific molecule which goes through steps resulting in a

certain product. Each step is catalyzed by a specific enzyme

4. Catabolic pathway: a metabolic pathway that releases energy by breaking down complex

molecules to simpler compounds

o Cellular respiration is a major pathway of catabolism in which the sugar glucose and other

organic fuels are broken down in the presence of oxygen to carbon dioxide and water

5. Anabolic pathways: consume energy to build complicated molecules tfrom sim- pler ones;

also called biosynthetic pathways

o An example is the synthesis of an amino acid from simpler molecules and the synthesis of

a protein from an amino acid

6. Bioenergetics: the study of how energy flow through lving organisms

7. Energy: The capacity to cause change and also to rearrange a collection of matter

8. Kinetic energy: relative motion of objects

9. Heat or Thermal Energy: kinetic energy associated with the random movement of atoms or

molecules

10. Potential energy: an object not moving but still possess energy because of its location or

structure

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

12. Thermodynamics: the study of the energy transformations that occur in a collection of

matter o system: the matter under study o surrounding: everything outside the system o isolated system: unable to exchange either energy or matter with its surroundings o open system: energy and matter can be transferred between the system and its surroundings; organisms are open systems o

13. First Law of Thermodynamics (conservation of energy): the energy of the universe is

constant: energy can be transferred and transformed, but it cannot be created nor destroyed

14. Entropy: a measure of disorder or randomness. the more randomly arranged a collection of

matter is, the greater the entropy

15. Second Law of Thermodynamics: every energy transfer or transformation increases the

entropy of the universe

16. Spontaneous process: a process that can occur on its own without an input of energy. for a

process to occur spontaneously, it must increase the entropy of the universe examples:

1) an explosion happening instantaneously

2) a car rusting over time non instantaneously

17. Non spontaneous: a process that cannot occur on its own; it will happen only if energy is

added to the system.

1) a machine pumping water against gravity

18. cells create ordered structures from less organized starting materials: true

19. Free Energy G” : the portion of a system's energy that can perform work when

temperature and pressure are uniform throughout the system change in free energy: ”G = ”H - TS”

• this equation is used to predict if the reaction is spontaneous; usually processes with a negative G” will be

20. ”H ”S ”T: H” : The change in the system's enthalpy (total energy)

”S : The change in the system's entropy ”T : The change in temperature

• for ”G to be negative, either ”H must be negative (the system gives up enthalpy and H decreases) or T”S must be positive (the system gives up order and S increases.
• every spontaneous process decreases the system's free energy, and processes that have a positive or zero ”G are never spontaneous

21. equilibrium: state of maximum stability. when a chemical reaction is reversible and they

proceed to one point at which the forward and backward reactions occur at the same rate. free energy will decrease when reaching equilibrium

22. Exergonic reaction: net release of free energy

23. cellular respiration reaction equation: C6H12O6 + 6O2 --> 6CO2 + 6H2O

24. Endergonic Reaction: absorbs free energy from its surroundings; stores free energy in

molecules (”G increases and is positive)

25. reactions in an isolated system eventually reach equilibrium and can then do no work: true

26. chemical reactions of metabolism are reversible as they ebetually reach equilibrium if they

occured in the isolation of a test tube: - a cell that had reached metabolic equilibrium is dead

27. a cell does 3 main kinds of work: 1) chemical work : the pushing of endergonic reactions that

would not occur spontaneously, such as the synthesis of polymers from monomers

2) transport work: the pumping of substances across membranes against the direction of

spontaneous movement

3)mechanical work: such as the beating of cilia, the contraction of muscle cells, and the

movement of chromosomes during cellular reproduction

28. energy coupling: the way cells manage their energy sources to do work; it is a use of an

exergonic process to drive an endergonic one

29. ATP: Responsible fo metabolism mediating most energy coupling in cells, and in most

cases it acts as the immediate source of energy that powers cellular work

• contains the sugar ribose, with the nitrogenous base adenine and a chain of three phosphate groups bonded to it
• it is one of the nucleoside triphosphates used to make RNA

30. The hydrolysis of ATP: The reaction of ATP and water yields inorganic phos- phate (P) and

ADP and releases energy

• the reaction is exergonic and releases energy

31. how the hydrolysis of ATP performs work: when ATP is hydrolyzed in a test tube, the release

of free energy merely heats the surrounding water. in an organism. this same generation of heat can sometimes be beneficial. for instance, the procdess of shivering uses ATP hydrolisis during

muscle contraction to generate heat and warm the body. in most cases in the cell, the generation os heat alone would be an inefficient use of a valuable energy resource. instead, the cell's proteins harness the energy released during ATP hydrolysis in several ways to perform the 3 types of cellular work - chemical, transport, and mechanical

32. phosphorylated intermediate: the molecule which receives the high energy phosphate from

ATP and becomes more reactive

• it is the recipient with the phosphate group covalently bonded to ATP

33. ATP hydrolysis leads to change in a protein's shape and often its ability to bind another

molecule. sometimes occurs via a phosphorylated intermedi- ate.:.

34. an organisms at work uses ATP continuously, but ATP is a renewable resource that can be

regenerated by the addition of phosphate to ADP:.

35. the free energy required to phosphorylate ADP comes from exergonic breakdown reactions

(catabolism) in the cell.: this shuttling of inorganic phos- phate and energy is called the ATP cycle, andit couples the cell's energy-yielding (exergonic) processes to the energy-consuming (endergonic) ones

36. the regenration of of ATP from ADP and P is endergonic:.

37. catabolic (exergonic) pathways, especially cellular respiration, provide the energy for the

endergonic process of making ATP.:.

38. enzyme: a macromolecule that acts as a catalyst by lowering the activation energy barrier,

enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures

39. activation energy: the initial investment of energy for starting a reaction- the energy

required to contort the reactant molecules so the bonds can break

• the amount of energy needed to push the reactants to the top of an energy barrier, or uphill, so that the downhill part of the reaction can begin

40. substrate: the reactant an enzyme acts on

41. enzyme substrate complex: the formation when the enzyme binds to its sub- strate

42. active site: a grove on the surface of the enzyme where catalysis occurs

• usually, the active site is formed by only a few of the enzyme's amino acids with the rest of the protein molecule providing a framework that determines the configuration of the active site

43. induced fit: brings chemical groups of the active site into positions that enhance their ability

to catalyze the chemical reaction

44. temperature and pH are important factors in the activity of an enzyme:.

45. cofactors: many enzymes require cofactors, which are nonprotein helpers for catalytic

activity

46. coenzyme: if a cofactor is an inorganic molecule, such as the metal atoms zinc, iron, and

copper in ionic form

• vitamins in nutrients act as coenzymes

47. enzyme inhibitors: if the inhibitor attach to the enzyme by covalent bonds, inhibition is

usually irreversible

48. competitive inhibitors: reduce the productivity of enzymes by blocking sub- strates from

entering active sites. this kind of inhibition can be overcome by increas- ing the concentration of substrate so that as active sites become available, more substrate molecules than inhibitor molecules are around to gain entry to the sites

49. noncompetitive inhibitors: do not directly compete with the substrate to bind to the enzyme

at the active sites; the impede the enzymatic reactions by binding to another part of the enzyme, which causes a change in shape in such a way that the active site becomes less effective at catalyzing the conversion of substrate to product.

50. allosteric regulation: the term used to describe any case in which a protein's function at one

site is affected by the binding of a regulatory molecule to a separate site.

• keep in mind that molecules regulate enzyme activity in a cell which changes shape and function of the active site

51. the construction of enzymes that are allosterically regulated: -they are constructed from two or

more subunits, each composed of a polypeptide chain with its own active site

52. cooperativity: in a kind of allosteric activation, a substrate molecules binding to one active

site in a multisubunit enzyme triggers a shape change in all the subunit, thereby increasing catalytic activity at the other active sites. in other words, amplifies the response of enzymes to substrates

53. when ATP allostically inhibits an enzyme in an ATP generating pathway, the result is feedback

inhibition , a common mode of metabolic control:.

54. feedback inhibition: a metabolic pathway is switched off by the inhibitory bind- ing of its end

product to an enzyme that acts early in the pathway

• prevents the cell from wasting chemical resources by making more isoleucine than is necessary

55. metabolism: the intersecting set of chemical pathways characteristic of life

56. review of ch 8!:.

57. transformations between potential and kinetic energy: - climbing up con- verts the kinetic

energy of muscle movement to potential energy

• a diver has more potential energy on the platform that in the water
• diving converts potential energy to kinetic energy
• a diver has less potential energy in the water that on the platform

58. first law of thermodynamics: energy can be neither destroyed nor created, for example,

chemical reactions in a bear will convert the potential energy in the fish into the kinetic energy of running

59. second law of thermodynamics: every energy transfer or transformation in- creases the

disorder (entropy) of the universe. for example, as the bear runs, disorder is increased around the bear by the release of heat and small molecules that are the by-product of metabolism.

60. order as a characteristic of life: order if evident in the detailed structures of a skeletons. as

open systems, organisms can increase their order as long as the order of their surrounding decreases

61. the relationship of free energy to stability, work capacity, and spontaneous change: unstable

systems are rich in free energy, G. they have a tendency to change spontaneously to a more stable state, and it is possible to harness the downhill change to perform work

62. free energy: - more free energy means higher G

• less stable
• greater work capacity in spontaneous change

• the free energy of the system decreases
• the system becomes more stable
• the released free energy can be harnessed to do work
• less free energy means lower G
• more stable
• less work capacity

63. gravitational motion: objects move spontaneously from a higher altitude to a lower one

64. diffusion: molecules in a drop of dye diffuse until they are randomly dispersed

65. chemical reaction: in a cell, a glucose molecule is broken down into simpler molecules

66. exergonic reaction: energy released, spontaneous

67. endergonic reaction: energy required, non spontaneous

68. an isolated hydroelectric system: water flowing downhill turns a turbine that drives a

generator providing electricity to a lightbulb, but only until the system reaches equilibrium

69. an open hydroelectric system: flowing water keeps driving the generator because intake

and outflow of water keep the system from reaching equilibrium

70. a multistep open hydroelectric system: cellular respiration is analogous to this system:

glucose is broken down n a series of exergonic reactions that power the work of the cell. the product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium

71. the structure of ATP: in the cell, most hydroxyl groups of phosphates are ionized

72. the hydrolysis of ATP: the reaction of ATP and water yields inorganic phos- phate and ADP

and releases energy

73. how ATP drives chemical work: energy coupling using ATP hydrolysis: a) glutamic acid

conversion to glutamine -glutamine synthesis from glutamic acid (Glu) by itself is endergonic (delta G is positive), so it is not spontaneous

b) conversion reaction coupled with ATP hydrolysis

in the cell, glutamine synthesis occurs in two steps, coupled by a phosphorylated intermediate

1) ATP phosphorylates glutamic acid, making it less stable

2) ammonia displaces the phosphate group, forming glutamine

c) free energy change for coupled reaction

-delta G for the glutamic acid conversion to glutamine plus delta G for ATP hydrolysis gives the free energy change for the overall reaction. Because the overall process is exergonic (delta G is negative), it occurs spontaneously

74. how ATP drives transport and mechanical work: a) transport work

-ATP phosphorylates transport proteins b) mechanical work

• ATP binds noncovalently to motor proteins and then is hydrolyzed

75. the ATP cycle: energy released by breakdown reactions (catabolism) i the cell used to

phosphorylate ADP, regenerating ATP. Chemical potential energy stored in ATP drives most cellular work

76. the effect of an enzyme on activation energy: without affecting the free energy change (deltaG)

for a reaction, an enzyme speeds the reaction by reducing its activation energy

77. the Active site and catalytic cycle of an enzyme: an enzyme can cinvert one or more reactant

molecules to one or more product molecules. the enzyme shown here converts two substrate molecules to two product molecules

1)substrates enter active site; enzyme changes shape such that its active site enfold the

substrates (induced fit)

2) substrates are held in active site by weak interactions, such as hydrogen bonds and ionic

bonds

3) active site can lower activation energy and speed up a reaction by

• acting as a template for substrate orientation
• stressing the substrates and stabilizing the transition state
• providing a favorable micro-environemt
• participating directly in the catalytic reaction

4) substrates are converted to products

5) products are released

6) active site is available for two new substrate molecules

78. environmental factors affecting enzyme activity: each enzyme has an opti- mal temperature

and pH that favor the most active shape of the protein muscle

79. inhibition of enzyme activity: a) normal binding: a substrate can bind normally to the active

site of an enzyme

b) competitive inhibition: a competitive inhibitor mimics the substrate, competing for the active

site

c) non competitive inhibition: a competitive inhibitor binds to the enzyme away from the active

site, altering the shape of the enzyme so that even if the substrate can bind, the active site functions less effectively

80. Chapter 9 Cellular Respiration and Fermentation: ...

81. - Photosynthesis generates oxygen and organic molecules used by mito- chondira of

eukaryotes (plants and algae) as fuel for cellular repiration

**- Respiration break this fuel down, generating ATP

• The waste products of this type of respiration, carbon dioxide and water, are the raw material of photosynthesis:** ...

82. compounds that can participate in exergonic reactions: can act as fuels

• with the help of enzymes, a cell systematically degrades complex organic mole- cules that are ish in potential energy to simpler waste prodents that have energy.

83. Fermentation: a catabolic process that is a partial degradation of sugars or other organic

fuels that occurs without the use of oxygen

84. Anaerobic Respiration: the most prevalent and efficient catabolic pathway in which oxygen

is consumed as a reactant along with the organic fuel

o Cells of most eukaryotic and many prokaryotic organisms can carry out aerobic respiration

o It is the principle similar to the combustion of gasoline in an automobile engine after oxygen is

mixed with the fuel (hydrocarbons). Food provides the fuel for respiration & the exhaust is

carbon dioxide&water Organic compunds + oxygen ’ caron dioxide + water +energy

85. Cellular respiration: includes aerobic and anaerobic respiration but often is refered to as

the aerobic process due to animals breathing in oxygen

• It is helpful to learn the steps of cellular respiration by tracking the degredation of the sugar glucose (C6H12O6) C6H12O6 + 6O2 ’ 6CO2 + 6H2O + Energy (ATP + heat)

86. glucose: the fuel that cells most often use; this breakdown of glucose is exer- gonic

87. Catabolism: is linked to work by a chemical drive shaft ’ ATP

o To keep working the cell must regenerate its supply of ATP from ADP and (P)

88. - how do catabolic pathways that decompose glucose and other organic fuels yield energy?: o

The relocation of electrons release energy stored in organic molecules, and this energy ultimately is used to synthesis ATP

89. Redox Reaction: a transfer of one or more electrons (e-) from one reactant to another

90. Oxidation: the loss of electrons from one substance in a redox reaction

91. Reduction: the addition of electrons to another substance

92. Reducing agent: the electron donor

93. oxidizing agent: the electron acceptor

94. give an example of a redox reaction: - The combustion of gasoline in an automobile engine

o o The electrons los potential energy and energy is released

95. respiration: - The energy yielding redox process the oxidation of glusoce trans- fers

electrons to a lower energy state, liberating energy that becomes available for ATP synthesis

96. the main energy yielding foods, carbohydrates and fats, are: reservoirs of electrons

associated with hydrogen

97. Only the barrier of activation energy holds back the flood of electrons to a lower energy state;

otherwise: a food substance like glucose would combine instantaneously with O

98. Body temperature isn't high enough to initiate burning so instead: if you swallow some

glucose, enzymes in your cells will lower the barrier of activation energy, allowing the sugar to be oxidized in a series of steps

99. - if energy is released from a fuel all at once, it cannot be harnessed efficiently for constructive

work. Cellular respiration does not oxidize glucose in a single explosive step either. Rather, glucose and other organic fuels are broken down in series of steps, each one catalyzed by an enzyme.: - Electrons are stipped from the glucose as in the case of oxidation reaction, each electron travels with a proton, as a hydrogen atom. The hydrogen atoms are passed first to an electron carrier, a coenzyme called NAD+ then to the oxygen

100. NAD+: an electron carrier that can easly cycle between oxidized (NAD+) and

reduced (NADH) states. As an electron acceptor, NAD+ functions as an oxidizing agent durin respiration

101. o Electrons lose very little of their potential energy when they're trans- ferred from

glucose to NAD+. Each NADH molecule formed during respiration represents stored energy that can be tapped to make ATP when the electrons complete their "fall" down an energy gradient from NADH to oxygen: ..

102. cellular respiration also brings hydrogen and oxygen together to form water but there

are two important differences, which are:: o First, in cellular respiration, the hydrogen that reacts with oxygen is derived from organic olecules rather than H2.

o Second, instead of occurring in one explosive reaction, respiration uses an electron transport

chain to break the fall of electrons to oxygen into several energy releasing steps

103. Electron Transport Chain: - consists of a number of molecules, mostly pro- teins,

built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes. Electrons removed from glucose are shuttled by NADH to the top higher energy end of the chain. At the bottom lower energy end, O captures these electrons along with hydrogen nuclei (H+), forming water.

• Electron transfer from NADH to oxygen is an exergonic reaction with a free-energy change. Instead of this energy being released and wasted in a single explosive step, electrons cascade down the chain from one carrier molecule to the next in a series of a redox reaction, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor, which has a great affinity for electrons.
• Each downhill carrier is more electronegative that, and thus capable of oxidizing, its "uphill" neighbor, with oxygen at the bottom of the chain. Therefore the electrons are removed from glucose by NAD+ fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom.

104. In summary, during celllualr respiration, most electrons travel the follow- ing "downhill"

route: glucose ’ NADH ’ electron transport chain ’ oxygen

105. The harvesting of energy form glucose by cellular respiration is a cumu- lative function of

three metabolic stages: o 1. Glycolysis

o 2. Pyruvate oxidation and the citric acid cycle

o 3. Oxidative phosphorylation: electron transport and chemiosmosis

106. - glycolysis and pyruvate oxidation followed by the citric acid cycle are the catabolic

pathways that break down glucose and other organic fuels: ...

107. glycolysis: occurs in the cytosol, begins the degradation process by breaking glucose

into 2 molecules of a compound called pyruvate

• In eukaryotes, pyruvate enters the mitochondria and is oxidized to a compound called acetyle CoA, which enters the citric acid cycle

108. citric acid cycle: the breakdown of glucose to carbon dioxide is complete (in

prokaryotes these processes occure in the cytosol). Thus the carbon dioxide produced by repiration represents fragments of oxidized organic molecules

• Some of the steps of glycolysis and the citric acid cycle are redox reactions in which dehydrogenases transfer electrons form substrates to NAD+, forming NADH. In the third stage of respiration, the electron transport chain accepts electrons from the breakdown products of the first two stages (most often via NADH) and passes these electrons form one molecule to another. At the end of the chain, the electrons are combined with molecular oxygen and hydrogen ions (H+), forming water.

109. oxidative phosphorylation: - The energy released at each step of the chain is stored in

a form the mitochondrion (or prokaryotic cell) can use to make ATP from ADP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain

110. - Int eh eukaryotic cells, the inner membrane of the mitochondrion is the site of electron

transport and chemiosmosis, the process that together constitute the oxidative phosphorylation. ( in prokaryotes, these processes take place in the plasma membrane): ...

111. - Oxidative phosphorylation accounts for almost 90% of the ATP gener- ated by

respiration.: ...

112. - A smaller amount if ATP if formed directly ina few reactions of glycosis and the citric

cycle by a mechanism called substrate-level phosphorylation: o This mode of ATP synthesis occurs

when an enzyme tranfers a phosphate group from a substrate molecule to ADP

113. substrate molecule: an organic molecules generated as an intermediate dur- ing

catabolism of glucose

114. Glycolysis: sugar splitting: o Glucose, a six-carbon sugar is split in two three-

carbon sugars

o These smaller sugar are then oxidized and their remaining atoms rearranged to form two

molecules of pyruvate

115. glycolysis can be divided into two phases: o energy investment

o energy payoff o the cell spends ATP, which is then repaid with interest during the energy payoff phase, when ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH to electrons released from the oxidation of glucose. The net energy yield from glycolysis, per glucose molecule, is 2 ATP plus 2 NADH

116. which process can occur whether or not O2 is present?: glycolysis

• if it is present, the chemical energy stored in pyruvate and NADH can be extracted by pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation

117. Glycolysis: energy investment phase: 1. Hexokinase

• Hexokinase transfers phosphate groups from ATP to glucose, making it more chemically reactive. The charge on the phosphate also traps the sugar in the cell

2.Phosphoglucoisomerase

• Glucose6-phosphate is converted to its isomer, fructose 6-phosphate

3.Phosphofructokinase

• Phosphofructokinase transfers a phosphate group from ATP to the opposite edn of the sugar, investing a second molecule of ATP. This is a key step for regulation of glycolysis

4.Aldolase

• Aldolase cleaves the sugar molecules into two different three-carbon sugars (isomers)

5.Isomerase

• Isomerase catalyzes the reversible conversion between the two isomers. This reactions never reached equilibrium: glyceraldehyde 3-phosphate is used as the substrate of the next reaction as fast as it forms

118. glycolysis: Energy Payoff Phase (REDOX REACTION): 6. Triose phosphate dehydrogenase

• This enzyme catalyzes two sequential reactions. First, the sugar is oxidized by the transfer of electrons to NAD+, forming NADH. Second, the energy released from this exergonic redox reaction is used to attach a phosphate group to the oxidized substrate, making a product of a very high potential energy.

7.Phophoseglycerokinase

• The phosphate group added in the previous step is transferred to ADP (substrate level phosphorylation) in an exergonic reaction. The carbonyl group of a sugar has been oxidized to the carboxyl group (-COO-) of an organic acid (3-phosphoglycer- ate)

8.phosphoglyceromutase

• This enzyme relocates the remaining phosphate group

9.Enolase

• Enolase causes a double bond to form in the substrate by extracting a water mol- ecule, yielding phosphoenolpyruvate (PEP), a compound with a very high potential energy

10.Pyruvate kinase

• The phosphate group is transferred from PEP to ADP (a second example of substrate-level phosphorylation), forming pyruvate

119. after pyruvate is oxidized, the CAC completes the energy yielding oxida- tion of organic

molecules: - if molecular oxygen is present, the pyruvate enters a mitochondrion (in eukaryotic cells), where the oxidation of glucose is completed. (in prokaryotic cells, this process occurs in the cytosol)

120. - upon entering the mitochondrion via active transport, pyruvate is first converted to a

compound called acetyl CoA. This step, linking glycolysis and the citric acid cycle, is carried out a multi-enzyme complex that catalyzes three reactions:: o pyruvate's carboxyl group (-COO-) which is already fully oxidized and thus has little chemical energy, is removed and given off as a molecule of CO2. o the remaining two-carbon fragment is oxidized forming acetate (CH3COO-, the ionized form of acetic acid). The extracted electrons are transferred to NAD+, storing energy in the form of NADH o finally, (CoA), a sulfur-containing compound derived from a B vitamin, is attached via its sulfur atom to the acetate, forming acetyl CoA, which has a high potential energy; in other words, the reaction of acetyle CoA to yield lower energy products is highly exergonic. This molecule will now flood its acetyle group into the citric acid cycle for further oxidation

121. Citric Acid Cycle (CAC): also called the Kerbs cycle, which function as a metablic

furnace that oxidizes organic fuel dericed from pyruvate

122. The citric acid cycle in more detail: o The cycle has 8 step each catalyzed by a

specific enzyme o for each turn of the cycle, 2 carbons enter the relatively reduced form of an acetyl group (step

1. and the two different carbons leave in the completely oxidized form of CO2 molecules (steps

2 and 3) o the acetyle group of acetyle CoA joins the cycle by combining with the compound oxaloacetate , forming citrate (step 1) o the next 7 steps decompose the citrate back to oxaloacetate; it is the regeneration of oxaloacetate that makes this process a cycle o now tallying the energy rich molecules produced by the citric acid, for each actyle group entering the cycle, 3 NAD+ are reduced to NADH (step 3,4, and 8) o in step 6, electrons are transferred not to NAD+, but to FAD, which accepts electrons and 2 protons to become FADH2

o In many animal tissue cells, step 5 produces guanosine triphosphate (GTP) molecule by

the substrate level phosphorylation

o GTP is a molecule similar to ATP in its structure and cellular function** this GTP may be used

to make an ATP molecules or directly power work in the cell

o In the cells of plants, bacteria, and some animal tissues, step 5 forms an ATP mol- ecule

directly by substrate level phosphorylation. The output from step 5 represents the only ATP generated during the CAC

o Most of the ATP produced by respiration results from oxidative phosphorylation, when the

NAH and FADH2 produced by the CAC relay the electrons extracted from food to the electron transport chain. In the process they supply the necessary energy for phosphorylation of ADP to ATP

123. The electrons transport chain is a collection of molecules embedded in the inner

membrane of mitochondrion in eukaryotic cells (in prokaryotes these molecules reside in the plasma membrane: - Most components of the chain are protiens, which exist in multiprotien complexes numbered I througb IV. Tightly bound to these proteins are prosthetic groups, nonprotein

components essential for the catalytic functions of certain enzymes

124. Passage of electrons through complex I: o Electrons removed from glucose by NAD+,

during glycolysis and the citric acid cycle, are transferred from NADH to the first molecule (flavoprotein) of the electron transport chain in complex I

o In the next redox reaction, the flavoprotein returns to its oxidized form as it passed electrons

to an iron-sulfur protein (Fe-S complex I), one of a family of proteins with both iron and sulfur tightly bound

o The iron-sulfur protein then passes the electrons to a compound called ubiquinone

(also known as coenzyme Q or CoQ). This electron carrier is a small hydrophobic molecule, the only member of the electron transport chain that is not a protein

o Ubiquinone is individually mobile within the membrane rather than residing in a particular

complex

o Most of the remaining electron carriers between ubiquinone and oxygen are proteins

called cytochromes

125. cytochromes: • This prosthetic group, called a heme group, has an iron atom that

accepts and donates electrons ( it is similar to the heme group in hemoglobin, the protein of red blood cells, except that the iron in hemoglobin carried oxygen, not electrons)

126. - The electron transport chain has several types of cytochromes, each different protein

with slightly different electron carrying heme group

**- The last cytochrome of the chain, cyt a3, passes its electrons to oxygen, which is very electronegative

• Each oxygen atom also picks up a pair of hydrogen ions from the aqueous solution, forming water
• Another course of electrons for the transport chain is FADH2, the other reduced product of**

the citric acid cycle

**- FADH2 adds its electrons to the electron transport chain from within complex II at a lower energy levl than NADH does. Consequently, although NADH and FADH2 eahc donate an equivalent numver of electrons (2) fro oxygen reduction, the electron transport chain provides about one-third less energy for ATP synthesis when the electron donor is FADH2 rather thn NADH

• The electron transport chain makes no ATP directly. Onstrad it eases the fall of electrons from food to oxygen, breaking a large free-energy drop into a series of smaller steps that releases energy in manageable amounts
• The motichondrion (or prokaryotic plasma membrane) couples this electron transport and energy release to ATP synthesis through chemiosmosis:** ...

127. chemiosmosis: the energy coupling mechanismthat usese energy stored in the form

of an H+ gradient across a membrane to drive cellular work

128. - Populating the inner membrane of the mitochondrion or the prokaryotic plasma

membrane as many copies of a protein complex called ATP synthase, the enzyme that actyaly makes ATO from ADP and inorganic phosphate.: o ATP synthase works like an ion pump running in reverse..... ion pumos usually use ATP as an energy source to transpot ions against their gradients.

129. - Under the conditions of cellular respiration ATP synthase uses the energy of an existing

ion gradient to power ATP synthesia: o The power source for the ATP synthase is a difference in the concentration of H+ on opposite sides of the inner mitoondrial membrane (we can also think of this gradient as a difference in pH, since pH is a measure of H+ concentration)

130. - How does the inner mitochondrial membrane one the prokaryotic plas- ma membrane

generate and maintain the H+ gradient that drives ATP synthe- sis by the ATP synthase protein complex?: • The passage of H+ through ATP synthase uses exergonic flow of H+ to drive the phosphorylation of ADP, ths the energy stored in an H+ gradient across a membrane couples the redox reactions of the electon transport chain to ATP synthesis, an example of chemiosmosis

131. - How do electron transport chains pump hydrogen ions?: o At a certain step along the

chain, electrons transfers cause H+ to be taken up and released into the surrounding solution

o In eukaryotic cells, the electron carriers are spatially arranged in the inner mito- chondrial

membrane in such a way that H+ is accepted from the mitochondrial matrix and deposited in the intermembrane space

o The H+ gradient that results is reffered to as a proton-motive force, emphasizing the

capacity of the gradient to perform work

o The force drives H+ back across the membrane throughthe H+ channel provided by ATP

synthases

132. - Chloroplasts use chemiosmosis to generate ATP during photosynthesi; int these

organelled, light drives both electron flow down an electron transport chain and the resulting H+ gradient formation: ...

133. - Prokaryotes generate H+ gradients across their plasma membranes, then they tap the

proton motive force not only to make ATP inside the cell but also to rotate their flagella and to pump nutrients and waste products across the membrane.: ...

134. - Harvesting the energy of glucose for ATP synthesis

o During respiration, most energy flows in this sequence: glucose ’ NADH ’ electron transport chain ’ proton-motive force ’ ATP

135.............................................................................................. - Reason to

why an exact number of ATP molecules generated by the breakdown of one molecule of glucose, cannot be stated: o FIRST................................................................................................Phospho- rylation and the redo reactions are not directly coupled to each other,so the ratio of the number of NADH molecules to the number of ATP molecules is not a whole number.

o SECOND.... The ATP yield varies slightly depending on the type of shuttle used to transport

electrons from the cytosol into the mitochondrion

o THIRD......another variable that reduces the yield of ATP is the use of the proton-mo-

tive force generated by the redox reactions of respiration to drive other kinds of work

136. Fermentation and anaerobic respiration enable cells to produce ATP without the use of

oxygen: - Without the electronegative oxygen tot pull electrons down the transport chain, oxidative phosphorylation eventually ceases

137. - The distinction between anaerobic respiration and fermanetation is that an electron

transport chain is used in anaerobic but not fermentation: - Anaer- boci respiration takes place in certain prokaryotic organismsthat live in environments without oxygen. These organisms have an electron transport chain but don't use oxygen as a final electron acceptor at the end of the chain

• Fermentation is a way of hasrevting chemical energy without using either oxygen or any toerh electron transport chain (without cellular respiration)

138. How can food by hydrolyzed without cellular respiration: o Glycolysis oxidizes glucose

to two molecules of pyruvate. The oxidizing agent is glycolysis is NAD+ and neither oxygen nor any electrons transfer chain is involved

o Glycolysis is exergonic, and some of the energy made available is used to produce 2 ATP by

substrate level phosphorylation when NADH passes electrons removed from glucose to the electron transport chain