Chapter 4

Question 1

How come wood releases a lot of energy

Answer 1

The major component of the wood that burns= cellulose.
- Cellulose molecules, main component of plant cell walls, are complex carbs made of glucose.
- When cellulose burns, it combines with O2
in atmosphere & releases a tremendous amount of potentially life-threatening energy

Question 2

Most of the energy that enters the biosphere is ___________________

Answer 2

solar radiation
- photosynthesis transforms this light energy into
chemical potential energy, which is then available to plants & other organisms in food webs.

Question 3

What type of cells need ATP?

Answer 3

all cells

Question 4

Aerobic cellular respiration is

Answer 4

AKA aerobic respiration
- the process that extracts energy from food (organic compounds) in the presence of oxygen
- The energy is used to synthesize ATP from ADP & Pi
- The ATP molecules are then used to supply energy
directly to the cells for their energy-demanding activities.
- Equation: C6H12O6 + 6O2 –> 6CO2 + 6H2O
∆G= –2870 kJ/mol

Question 5

An Obligate Aerobe is

Answer 5

an organism that cannot live without oxygen, and they use aerobic cellular respiration exclusively or most of the time.

Question 6

Aerobic cellular respiration can be divided into four stages: List them

Answer 6

1) Glycolysis
2) Pyruvate Oxidation
3) Citric acid cycle
4) Electron transport & oxidative phosphorylation

Each stage involves the transfer of free energy, producing ATP in 1 of 2 ways: substrate-level phosphorylation & oxidative phosphorylation.

https://www.youtube.com/watch?v=eJ9Zjc-jdys

Question 7

Substrate-level phosphorylation forms ATP…

Answer 7

directly in an enzyme-catalyzed reaction through the transfer of a phosphate group from one molecule to an adenosine diphosphate (ADP) molecule.

Question 8

Oxidative phosphorylation forms ATP…

Answer 8

indirectly through a series of redox reactions involving a final electron acceptor.
- In aerobic respiration, oxygen is the final electron acceptor

Question 9

Glycolysis Overview

Answer 9

• (occurs in cytosol) –> doesn’t take place in mitochondria, & doesn’t require O2, thus all cells can do it.
• Enzymes break down one molecule of glucose into two molecules of pyruvate. Some high-energy ATP (via substrate-level phosphorylation) & NADH is synthesized.

Question 10

Pyruvate Oxidation Overview

Answer 10

• in mitochondria
• Each of the 2 molecules of pyruvate produced in glycolysis is transported to mitochondria and is oxidized, resulting in the production of CO2 (a waste molecule), NADH, & an acetyl group that is initially
  attached to coenzyme A (acetyl-CoA)

Question 11

Citric acid cycle Overview

Answer 11

• AKA kreb’s cycle
• (in mitochondria)
• Acetyl-CoA molecules from pyruvate oxidation enter a metabolic cycle, where the acetyl group is completely oxidized to CO2. In the process, ATP (via substrate-level phosphorylation) & the e- carriers NADH & FADH2 are synthesized.

Question 12

Electron transport & oxidative phosphorylation Overview

Answer 12

• (in mitochondria)
• The NADH & FADH2 (synthesized during glycolysis, pyruvate oxidation, and the citric acid cycle) are oxidized. Their high-energy e- & hydrogens are passed from one oxidizing agent to the next until they are transferred to O2, producing water. The free energy released during electron transport is indirectly used to synthesize a large amount of ATP by oxidative phosphorylation

Question 13

The mitochondrion is referred to as the powerhouse of the cell because

Answer 13

as the location of the citric acid cycle and electron transport, it generates most of the ATP that is used by the cell

Question 14

The mitochondrion is composed of two membranes

Answer 14

• the outer membrane and the inner membrane, which together define two compartments
• The intermembrane space is between the outer and inner membranes, and the matrix is the interior aqueous environment of the organelle

Question 15

Some prokaryotes undergo aerobic cellular respiration without ______________. ELABORATE

Answer 15

mitochondria

• In prokaryotes, the process of glycolysis, pyruvate oxidation, &the citric acid cycle occur in the cytosol of the cell, whereas e- transport occurs on internal membranes derived from the plasma membrane
• These prokaryotes possess the full complement of reactions that make up aerobic cellular respiration—from glycolysis through electron transport & oxidative phosphorylation.

Question 16

There are 2 general processes by which certain cells can oxidize fuel molecules & generate ATP in the absence of oxygen:

Answer 16

anaerobic respiration & fermentation
- Both anaerobic respiration & fermentation r catabolic (energy-yielding) processes.

Question 17

Anaerobic respiration is

Answer 17

similar to aerobic cellular respiration in using a series of electron-transferring steps, but it uses an inorganic molecule other than oxygen as the final oxidizing agent.

Question 18

Fermentation is

Answer 18

does not use an electron transport system. Thus, fermentation is not considered to be a form of respiration. It relies on an organic compound to act as the final oxidizing agent.
https://www.youtube.com/watch?v=YbdkbCU20_M

• This equation shows the overall reaction for 1 common fermentation pathway. The released free energy is used to make ATP. Note the products of this fermentation pathway are ethanol (CH3CH2OH) & CO2:
  C6H12O6 –> 2 CH3CH2OH + 2CO2 ∆G= –218 kJ/mol
• Note how fermentation releases much less free energy than aerobic respiration & thus makes less ATP

Question 19

An obligate anaerobe is

Answer 19

an organism that cannot survive in the presence of oxygen
- use inorganic substances such as NO2, S, and Fe 3+ as final electron acceptors to obtain energy

Question 20

aerobic respiration made the evolution of large animals possible because

Answer 20

it allowed them to meet their very high energy demands.
- RMR from amoeba sisters –> anaerobic respiration produces much less ATP

Question 21

every 1 of ur billions of active cells requires access to more than ____________ ATPs per second

Answer 21

1 million

Question 22

Glycolysis is considered to be the most fundamental & probably most ancient of all metabolic pathways. This is supported by the following facts.

Answer 22

1) glycolysis is nearly universal, being found in almost all organisms, both prokaryotes & eukaryotes

2) it does not require O2. Oxygen became abundant
in Earth’s atmosphere only about 2.5 billion years ago—about 1.5 billion years after scientists think that life began.

3) Third, glycolysis occurs in the cytosol of all cells and
involves soluble enzymes. Therefore, it does not require more sophisticated cellular organelles in order to operate –> indicating that it might have began before complex organelles were formed (i think)

Question 23

The first experiments investigating glycolysis took place over ____ years ago.

Answer 23

100
- Using extracts from yeast cells, researchers showed that they could study biological reactions in an
isolated system.
- These experiments became the foundation of modern biochemistry

Question 24

Glycolysis consists of ___ sequential enzyme-catalyzed reactions that lead to….

Answer 24

10
the oxidation of the 6-carbon sugar glucose, producing two molecules of the 3-carbon
compound pyruvate.
- The PE & e- released in the oxidation leads to the overall synthesis of both ATP & NADH.
Glycolysis has two phases: 1) an initial energy investment phase 2) an energy payoff phase
- both phases have 5 steps

Question 25

energy investment phase: the 5 steps

Answer 25

1) hexokinase: Glucose get 1 phosphate group from 1 ATP, creating glucose-6-phosphate (phosphorylation reaction)

2) phospho-glucomutase: Glucose-6-phosphate is
rearranged to isomer fructose-6-phosphate to allow it to bind to another phosphate.
(isomerization reaction)

3) phospho-fructokinase: 1 phosphate group from 2nd ATP is attached to fructose-6-phosphate, producing fructose-1,6-bisphosphate.
(phosphorylation reaction)

4) aldolase: Fructose-1,6-bisphosphate is split into glyceraldehyde-3-phosphate (G3P) & dihydroxyacetone phosphate (DHAP). –> both r isomers & have 3C each (lysis reaction)

5) triosephosphate isomerase: The DHAP produced is converted into G3P, giving a total of 2 per 1 molecule of glucose.(isomerization reaction)

Question 26

the energy payoff phase: the 5 steps

Answer 26

6) triosephosphate dehydrogenase: 2 e- & 2 p+ r removed from G3P. Some of the energy released in this reaction is trapped by the addition of an inorganic phosphate group from the cytosol (not derived from ATP) to the molecule. The e- r accepted by NAD+, along with one of the p+. The other p+ is released to the cytosol. (redox reaction). the molecule is now 1,3-bisphosphoglycerate

7) phosphoglycerate kinase: One of the 2 phosphate groups of 1,3-bisphosphoglycerate is transferred to ADP to produce ATP. (substrate-level phosphorylation reaction) it is now 3-phosphoglycerate

8) phospho-glucomutase: 3-phosphoglycerate is
rearranged, shifting the phosphate group from the
3-carbon to the 2-carbon to produce 2-phosphoglycerate. (mutase reaction—shifting of
a chemical group to another within the same molecule)

9) enolase: e-s r removed from one part of 2-phosphoglycerate & delivered to another part of the molecule. Most of the energy lost by the e- is retained in the product, phosphoenolpyruvate. There is also a loss of H2O. (redox reaction)

10) pyruvate kinase: The remaining phosphate group is removed from phosphoenolpyruvate & transferred to ADP. The reaction forms ATP & the final product of glycolysis, pyruvate. (substrate-level phosphorylation reaction)

Question 27

there are three key points to keep in mind keep in mind about glycolysis

Answer 27

1) Energy Investment and Payoff Phases in Glycolysis:
-2 ATP are consumed to phosphorylate glucose and fructose-6-phosphate.The energy payoff phase releases more energy, producing 4 ATP and 2 NADH.

2) Net Yield of Glycolysis:
-Glycolysis yields a net of 2 ATP and 2 NADH per glucose molecule. No carbon is lost; all 6 carbons from glucose end up in 2 pyruvate molecules. The PE of the 2 pyruvate molecules is less than the original glucose cuz glucose has been partially oxidized. 2 H2O molecules r produced in step 9 but r later consumed in the hydrolysis of ATP and thus r not usually included in the overall equation for glycolysis

3)ATP Production via Substrate-Level Phosphorylation:
- ATP is synthesized through substrate-level phosphorylation, where an enzyme transfers a phosphate group from a high-energy substrate to ADP. Substrate-level phosphorylation is also the mode of ATP synthesis that is used during the citric acid cycle

Question 28

The net equation for glycolysis is:

Answer 28

glucose + 2 ADP + 2 Pi + 2 NAD+ –> 2 pyruvate + 2 ATP + 2 NADH + 2H+

Question 29

Energy Efficiency of Glycolysis:

Answer 29

• The synthesis of 2 moles of ATP stores 62 kJ of energy.
• The complete oxidation of 1 mole of glucose can release 2870 kJ of energy.
• Glycolysis converts about 2.2% ((62 KJ/2870 KJ)X100%) of the energy from glucose into ATP, while most energy remains in the two pyruvate molecules and two NADH molecules.
• Some of the energy is lost as thermal energy, but most stored in the 2 pyruvate molecules & 2 NADH molecules, which will continue through the subsequent stages of aerobic respiration. –>
  Diff organisms use a variety of methods to transfer the NADH (or the e- it carries) into the mitochondria
  & to the e- transport chain. These methods vary in their energy cost, so the amount of ATP generated for each NADH formed in glycolysis can vary

Question 30

Glycolysis in Anaerobic Organisms:

Answer 30

Some organisms rely on glycolysis as their primary energy source despite its low efficiency.

Question 31

The 2 molecules of pyruvate that r synthesized by glycolysis still contain about _____of the energy found in one molecule of glucose

Answer 31

75 %
- extraction of remaining free energy in pyruvate continues via pyruvate oxidation & the citric
acid cycle.
- In these reactions, more ATP & more of the e- carriers NADH & FADH2 r formed, while remaining glucose is completely oxidized. Carbon is released in the form of waste CO2.

Question 32

The reactions of the citric acid cycle occur in the ____________________, so…

Answer 32

mitochondrial matrix
…the pyruvates that r produced in glycolysis must pass through both the outer & inner mitochondrial membranes.
- Large pores in the outer membrane allow pyruvate to diffuse through. For pyruvate to cross the inner membrane, however, a pyruvate-specific membrane carrier is required

Question 33

Once pyruvate enters the matrix…

Answer 33

it is converted into an acetyl group, which is then temporarily bonded to a sulfur atom on the end of a large molecule called coenzyme A, or CoA.
–> The result is an acetyl-CoA complex.
- This multistep process is referred to as pyruvate oxidation (or pyruvic acid oxidation)

Question 34

The conversion of pyruvate to acetyl-CoA

Answer 34

1) Decarboxylation: The carboxyl group (–COO⁻) is removed from pyruvate, forming CO₂ as a waste product (one-third of the CO₂ we exhale)

2) oxidation of the remaining 2 carbon molecules, producing an acetyl group. This dehydrogenation reaction transfers 2 e- & a p+ to NAD+, making NADH, & releases an H+ ion into solution. Lastly, the acetyl group reacts with the sulfur atom of coenzyme A, forming the high-energy intermediate acetyl-CoA.

https://www.youtube.com/watch?v=_U3yHgxyW30

Question 35

The net reaction for pyruvate oxidation is:

Answer 35

2 pyruvate + 2 NAD+ + 2 CoA –> 2 acetyl-CoA + 2 NADH + 2 H+ + 2 CO2

Question 36

Discovery of Citric Acid Cycle (Krebs Cycle):

Answer 36

The cycle was discovered in 1937 by Sir Hans Krebs, a biochemist at the University of Sheffield in England, discovered the metabolic reactions that became known as the Krebs cycle (now called the citric acid cycle)

Question 37

number of reaction in citric acid cycle

Answer 37

The citric acid cycle consists of 8 enzyme-catalyzed reactions.
- 7 reactions take place in the mitochondrial matrix, & 1 on the matrix side of the inner mitochondrial membrane.

Question 38

Products of Citric Acid Cycle

Answer 38

• Acetyl groups r oxidized to CO₂, producing ATP, NADH, & FADH₂.
• For each acetyl-CoA entering the cycle: 3 NADH, 1 FADH₂, & 1 ATP (via substrate-level phosphorylation) r produced.
• 2 CO₂ molecules r released per acetyl-CoA.
• In 1 complete cycle, one 2-carbon acetyl unit is consumed & 2 CO2 molecules r released, completing the conversion of all C atoms that were originally in glucose into CO2
• The CoA molecule that carried the acetyl
  group to the cycle is released & again participates in pyruvate oxidation to pick up another acetyl group.
• Net Reaction for one turn of the cycle:
  acetyl-CoA + 3NAD+ + FAD + ADP + P𝑖 → 2CO2 + 3NADH + 3H+ + FADH2 + ATP + CoA

Question 39

The 8 reaction of Citric Acid Cycle/ Kreb’s cycle

Answer 39

1) 2-carbon acetyl group carried by CoA attached to
oxaloacetate= citrate. ENZYME: citrate synthase

2) Citrate is rearranged to isomer, isocitrate. ENZYME:aconitase

3) Isocitrate oxidized to α-ketoglutarate; 1C is removed & released as CO2, & NAD+ reduced to NADH + H+. ENZYME: isocitrate dehydrogenase

4) α-Ketoglutarate oxidized to succinyl CoA; 1 carbon is removed & released as CO2, & NAD+ reduced to NADH + H+. ENZYME: α-ketoglutarate dehydrogenase

5) succinyl CoA releases CoA to make succinate: energy released makes GDP to GTP, which makes ADP to ATP by substrate-level phosphorylation. –> the only
ATP made directly in the citric acid cycle ENZYME: succinyl CoA synthetase

6) Succinate oxidized to fumarate; 2e- & 2p+ removed from succinate r transferred to FAD, making FADH2 ENZYME: succinate dehydrogenase

7) Fumarate to malate by adding 1 H2O molecule. ENZYME: fumarase

8) Malate oxidized to oxaloacetate, reducing
NAD+ to NADH + H+. Oxaloacetate can react with acetyl-CoA to re-enter the cycle. ENZYME: malate dehydrogenase

Question 40

Summary of Citric Acid Cycle

Answer 40

2 acetyl-CoA molecules enter the citric acid cycle from glycolysis & the pyruvate oxidation of one glucose molecule.

Step 1) acetyl group enters the cycle as it reacts with oxaloacetate to form 1 molecule of citrate. –> is why process is called the citric acid cycle.

Steps 3, 4, 5, 6, & 8) some of the released energy is captured and used to form NADH, ATP, & FADH2.

Steps 3, 4, & 8) NAD+ reduced to form NADH.

Step 5) make ATP from ADP & Pi by substrate-level phosphorylation.
Step 6) reduces FAD to FADH2.
- cuz 1 glucose molecule yields 2 pyruvate molecules, 1 glucose molecule generates 2 turns of the citric acid cycle

Question 41

By the end of the citric acid cycle, the original glucose molecule has…

Answer 41

been completely dismantled.
- The original C & O atoms r in the form of CO2
& r released as waste.
- All that remains of the original glucose molecule are the hydrogens, now carried by NADH & FADH2. –> The e- in these hydrogens retain a large amount of chemical PE.

Question 42

The Electron Transport Chain purpose

Answer 42

citric acid cycle= all C in glucose oxidized & released as CO2.
- some ATP was formed by substrate-level phosphorylation, but most of the PE originally present in glucose was captured during the formation of NADH and FADH2.
- The electron transport chain extracts the PE
energy in these molecules & makes it usable to make more ATP

Question 43

The Electron Transport Chain composition

Answer 43

• in eukaryotes, occurs on the inner mitochondrial membrane
• facilitates transfer of e- from NADH & FADH2 to O2
• consists of 4 protein complexes:
  complex I, NADH dehydrogenase
  complex II, succinate dehydrogenase;
  complex III, cytochrome complex;
  complex IV, cytochrome oxidase.
• Complex II = single peripheral membrane protein, other 3 complexes are composed of multiple proteins.
• The flow of e- from 1 complex to another is facilitated by 2 mobile e- shuttles.
  –> Ubiquinone (UQ), which is a hydrophobic molecule found in the core of the membrane, shuttles electrons from complexes I and II to complex III.
  –> A second shuttle, cytochrome c (cyt c), is located on the intermembrane space side of the membrane and transfers e- from complex III to complex IV

Question 44

The Driving Force behind electron transport

Answer 44

Electron Transport Chain= ETC (my thing)
- Complexes I, III, and IV in the ETC have increasing electronegativity, pulling e- down the chain.
- O2 has highest electronegativity & drives the entire ETC process by pulling e- through the chain.
- Energy Gradient: e- carriers in the chain r organized from high to low free energy, with each subsequent component being more electronegative than the previous one.
- NADH & O₂: NADH= most free energy & weakest pull on e- , while O₂= strongest e- acceptor & the final destination for the e-.
- Energy Release: As e- move from NADH through the ETC, they form stronger bonds with each carrier, releasing energy along the way.
- Oxidation of NADH: NADH is readily oxidized, losing electrons, which pass through the chain towards oxygen, releasing energy in the process.

Question 45

In the protein transport chain, do the protein complexes carry the e-?

Answer 45

-These complexes have cofactors that alternate between reduced & oxidized states as they pull e- from upstream molecules & subsequently donate
e- to more electronegative downstream molecules.
-Thus, it is not the proteins themselves that transfer e-, but rather non-protein groups bound to the proteins of each complex.

Question 46

The role of Oxygen in the electron transport chain

Answer 46

The e- transport chain is the final destination of all the O2 we breathe, which is transported around the body.
- O goes to the mitochondria to perform the single vital task of pulling e- away from complex IV
- Before O removes e- from complex IV, all the carriers & NADH r fully reduced, with stable, full e- shells.
- Nothing can happen due to their stable state –> Ex, Complex I can’t take any more e- from NADH cuz Complex I is already full. This creates a block in the process, and nothing can move forward.
- However, O is highly electronegative. When O interacts with complex IV, it removes a pair of e-. –> This creates space for Complex IV to take e- from Complex III, which then takes e- from Complex I, allowing NADH to give up its e- again. This “unblocking” happens quickly and drives the whole chain forward.
- As an O removes 2 e- from complex IV, it also reacts with 2 p+ (2 H+) in the matrix to make H2O. –> so, for
every O2 gas molecule we breathe in, 4e- are pulled through the e- transport chain & 2 H2O r produced.

Question 47

During e- transport, the free E that is released does the work of…

Answer 47

transporting p+ (H+ ions) across the inner mitochondrial membrane, from matrix to intermembrane space. –> as a result, H+ conc is higher in intermembrane space than in matrix

Question 48

proton gradient is

Answer 48

diff in proton (H+ ion) conc across a membrane

Question 49

e- flow through the electron transport chain drives a series of p+ pumps in the inner mitochondrial membrane. ELABORATE

Answer 49

Complexes I & IV, specific protein components use the E that is released from electron transport for p+ pumping.
- In addition, as ubiquinone molecules (UQ) accept e- from complexes I & II, they pick up p+ from the matrix. After migrating through the membrane & donating e- to complex III, ubiquinone retains a neutral charge by releasing p+ into the intermembrane space.

Question 50

proton-motive force

Answer 50

a force that moves p+ cuz of a chemical gradient
(AKA electrochemical gradient) of p+ across a membrane

2 component of electrochemical gradient of p+
- Chemical gradient: Unequal p+ concentrations across the membrane.
- Electrical gradient: p+ are positively charged and attracted to the negatively charged matrix.

• During oxidative phosphorylation, the PE that is released by the oxidation of NADH is used to pump protons into the intermembrane space and build up the proton-motive force

Question 51

chemiosmosis is

Answer 51

a process in which ATP is synthesized using the energy of an electrochemical gradient and the ATP synthase enzyme
- The ability of cells to use the proton-motive force to do work= chemiosmosis
- 1st proposed as way to make ATP by British biochemist Peter Mitchell, (Nobel Prize Chemistry= 1978)
- This mode of ATP synthesis, which is linked to the oxidation of energy-rich molecules by an electron transport chain= oxidative phosphorylation which relies on the action of a large multi-protein complex= ATP synthase

Question 52

Does chemiosmosis only refer to the synthesis of ATP?

Answer 52

No
- The proton-motive force is also used to pump substances across membranes & to drive the rotation of flagella in prokaryotes.

Question 53

Where does the energy for chemiosmosis come from?

Answer 53

In mitochondria, = E for chemiosmosis comes from the oxidation of energy-rich molecules,
such as NADH, by the electron transport chain.

Chemiosmosis also accounts for the generation of ATP in chloroplasts, where electron transport is driven by
light energy

Question 54

ATP synthase is

Answer 54

a large multi-protein complex that spans the inner mitochondrial membrane.
- The proton-motive force drives H⁺ ions through the basal unit channel into the matrix, down their concentration gradient.
- The flow of p+ powers ATP synthesis by causing the headpiece to rotate –> the smallest molecular rotary motor in nature
–> Binding of 3 protons to the headpiece triggers rotation, catalyzing the formation of one ATP from ADP and Pi.
- ability to harness the PE present in a p+ gradient to make ATP is fundamental to almost all life & is developed early in the evolution of life. –> This is shown by fact that structure & function
of the ATP synthase complex in mitochondria are essentially = to one in thylakoid membrane of the chloroplast & the plasma membrane of prokaryotic cells.

Question 55

ATP synthase components

Answer 55

• Basal unit: Embedded in the membrane and forms a channel for H⁺ ions.
• Headpiece: Extends into the mitochondrial matrix and synthesizes ATP.
• Stalk: Connects the basal unit and the headpiece.

Question 56

An active transport pump is, in fact, an ATP synthase that is operating in __________.

Answer 56

reverse

Question 57

When electron transport and ATP synthesis are uncoupled..

Answer 57

the E that is released during electron transport via NADH oxidation is not converted to ATP energy.
- it’s released as thermal energy when p+ rush back across the inner membrane without passing through ATP synthase

Question 58

One way to achieve uncoupling is…

Answer 58

by regulating the expression of various uncoupling proteins.
- Uncoupling proteins, when present, are in the inner mitochondrial membrane & give p+ another pathway to re-enter the matrix that does not make ATP but releases thermal energy instead
- Ex Brown adipose fat & certain other tissues have high levels of uncoupling proteins in their mitochondria, which are important for maintaining body temperature in hibernating mammals, cold-environment birds, and human infants. –> Uncoupling e- transport causes free E that would be used to generate ATP to be released as thermal E & maintain body temperature.

Question 59

Ionophores

Answer 59

such as 2,4-dinitrophenol (DNP), can act as Electron Transport and Chemiosmosis uncouplers by creating channels for ions (including p+) to leak across membranes, leading to increased electron transport but reduced ATP synthesis, making them potentially toxic.
- DNP, once used in diet pills, accelerated fat consumption by lowering ATP production but caused harmful side effects like overheating and was eventually discontinued.

Question 60

The efficiency of ___________ phosphorylation is difficult to calculate

Answer 60

oxidative
- rmr e- transport & oxidative phosphorylation r
distinct processes that r not always completely coupled to each other

Question 61

For each NADH oxidized, how many ATP molecules are made?

Answer 61

1 NADH oxidation (2e- travel though ETC) pumps 10 H⁺ ions into the inner membrane space
- about 3-4 H⁺ need to flow back through ATP synthase to synthesize 1 ATP.
- Maximum ATP yield: 3 ATP per NADH oxidized

Question 62

For each FADH oxidized, how many ATP molecules are made?

Answer 62

cuz oxidation of FADH2 bypasses the proton-pumping complex I, leads to less p+ pumped across the membrane.
- per 1 FADH2 oxidized, only about 2 ATP are made.

Question 63

Given complete oxidation of 1 glucose to CO2 & H2O, & assuming that the entire H_ gradient produced by
electron transfer is used for ATP synthesis, a total of ____________________ from glycolysis, pyruvate oxidation, & the citric acid cycle r oxidized by the ETC.

Answer 63

10 NADH, 10 H+, and 2 FADH2
-RMR H+ oxidized means u add O

Question 64

How does NADH produced in glycolysis in the cytosol get into the mitochondria for ETC?

Answer 64

cells use 1 of 2 “shuttle” systems that transfer the high-energy e- from NADH across the inner mitochondrial membranes into matrix

1) one system, called malate-aspartate shuttle, the
transfer= very energy efficient & used by many cells.
- NADH in the cytosol is oxidized to NAD+, and the e- are transferred across the membrane & reduce a NAD+ to NADH in the matrix.

2) the glycerol-phosphate shuttle, transfers e-across the membrane from NADH to FAD in the matrix to make FADH2, which has less free energy. Cells that use this system generate the equivalent of 2, rather than 3, ATP for every NADH produced in glycolysis
-thus total of 36 ATP will be made at the end of CR intead of 38

Question 65

There r several reasons why the total yield might be less than 38 ATP.

Answer 65

1) the inexact NADH and FADH2 to ATP ratio

2) E from H+ flow may be lost due to uncoupling proteins or used for other mitochondrial processes in addition to the process that produces ATP (such as powering the mitochondria’s uptake of pyruvate).

3) cells that use a glycerol-phosphate shuttle system produce 2 fewer ATPs per glucose. (FLASHCARD 66)

Question 66

How efficient is aerobic respiration at extracting the energy from glucose and converting it into ATP?

Answer 66

• hydrolysis of ATP to ADP & Pi = about 31 kJ/mol –> rmr the reversal will store the same
• Assuming that complete glucose oxidation produces 38 ATP, the total energy stored through ATP production would be 1178 kJ/mol: (31 kJ/mol X 38 ATP =1178 kJ/mol)
• glucose contains 2870 kJ/mol of E.
• On this basis, the efficiency of aerobic respiration can be calculated as follows: (1178 kJ/mol)/(12870 kJ/mol)x100 = 41.0 %
• a theoretical maximum of about 41 % of the energy in glucose is converted into ATP. The rest of the PE from glucose becomes thermal energy.

Question 67

Creatine Phosphate

Answer 67

come cells like muscle & brain cells have fluctuating energy demands. –> Cells may need rapid ATP during high activity and less ATP at rest.
- some organisms, when excess ATP is available, it’s used to phosphorylate creatine, forming creatine phosphate, a high-energy molecule.
–> Reaction: creatine + ATP → creatine phosphate + ADP.
- During high ATP demand, creatine phosphate can quickly regenerate ATP through the reverse reaction: creatine phosphate → creatine + ATP.
-This provides a rapid ATP boost, supplementing aerobic respiration.
- Once creatine phosphate stores are depleted, they are regenerated when ATP demand is lower, using extra ATP.

Question 68

metabolic rate is

Answer 68

the amount of energy that is expended per unit time in an organism
- is = to the overall rate of aerobic and anaerobic respiration reactions.
- E usage increases & decreases depending on the amount of work done by an organism, spanning from intense physical exertion to a state of rest

Question 69

basal metabolic rate (BMR)

Answer 69

the metabolic rate of an organism at rest measured in kilojoules per square metre of surface area per hour (kJ/m^2/h).
- The BMR energy consumption is about 60-70%
of total daily energy used by a human body
- BMR varies between individuals & throughout our lifetime, depending on gender, growth & development, age, muscle mass, and health.
–> Ex, BMR is greatly reduced with an increased % of body fat. –>the resting metabolic rate of skeletal muscle is min 3x that of adipose (fat) tissue.

Question 70

Regulating Cellular Respiration

Answer 70

• The rate of respiration is regulated to match ATP synthesis with the cell’s energy demands, commonly measured by O2 consumption.
  -This follows the principle of supply and demand, preventing resource waste.
• Most metabolic pathways, including respiration, are regulated by feedback inhibition.

Question 71

feedback inhibition is when

Answer 71

the end products of a pathway inhibit an early enzyme in the process, controlling the rate of respiration.

Question 72

Regulation of Glycolysis

Answer 72

• Glycolysis is regulated to match the cell’s ATP needs.
• excess ATP binds to phosphofructokinase (a key enzyme in glycolysis) as a negative regulator inhibiting glycolysis.
• The resulting decrease in the conc of fructose-1,6-bisphosphate slows or stops glycolysis and thus, the remainder of aerobic cellular respiration.
• Therefore, glycolysis does not oxidize glucose needlessly when there is an adequate supply of ATP.

Question 73

Glycolysis and ATP production increases proportionately…

Answer 73

as ATP is converted to ADP during cellular activity.

Question 74

what happens to excess sugars, such as glucose, when they are not needed for metabolism?

Answer 74

When glucose is not needed, it is stored as fat or glycogen in muscles.

Question 75

Citric Acid Cycle Regulation:

Answer 75

The citric acid cycle regulates glucose oxidation, with some enzymes being allosterically inhibited by high ATP levels.
- Like ATP, NADH and citrate (an intermediate product of the cycle) also allosterically
inhibit phosphofructokinase

Question 76

Inhibition by NADH and Citrate:

Answer 76

• NADH and citrate (a citric acid cycle intermediate) also inhibit phosphofructokinase (a key glycolysis enzyme), signaling a slowdown in downstream reactions.
• Accumulation of NADH & citrate suggests that oxidative phosphorylation may be restricted, possibly due to limited O2 availability.

Question 77

Alternatives to Glucose

Answer 77

The reactions leading from glycolysis through pyruvate oxidation oxidize a range of carbs
- addition to glucose & other 6-carbon sugars, fats and proteins can enter the cellular respiratory pathway at various points
- The energy content of different types of food:
carbs=17kJ/g, fats=37kJ/g, proteins=17kJ/g

Question 78

Oxidation of Carbohydrates:

Answer 78

Disaccharide carbohydrates = easily
hydrolyzed to monosaccharides (glucose, fructose, and galactose) which enter glycolysis at the early stages.
- Starch= hydrolyzed to glucose monomers using amylase & other enzymes in the digestive tract.
- Glycogen, a more complex carb, is hydrolyzed by enzymes in the liver into glucose-6-phosphate (an early substrate molecule in glycolysis)

Question 79

Oxidation of Fats:

Answer 79

-Triglycerides r hydrolyzed into glycerol & fatty acids for energy.
- Glycerol= converted to glyceraldehyde-3-phosphate (enters glycolysis),
- fatty acids undergo beta-oxidation, forming 2C fragments, which enter the citric acid cycle as acetyl groups attached to CoA

Question 80

Beta-oxidation is

Answer 80

AKA fatty acid oxidation
a process in which fatty acids are broken down into acetyl-CoA through catabolism

Question 81

Oxidation of Proteins:

Answer 81

Proteins r hydrolyzed to amino acids before oxidation.
- amino group (–NH2) is removed, & remainder of the molecule enters the CR pathway as either pyruvate, acetyl units carried by CoA, or intermediates of the citric acid cycle, depending on the R-group or carbon backbone that is left
- Ex, the amino acid alanine is converted into pyruvate; leucine is converted into acetyl units; and phenylalanine is converted into fumarate, which
enters the citric acid cycle.

Question 82

Weight of Carbs vs weight of fats

Answer 82

• Carbs r very hydrophilic, binding H2O through H-bonding.–> When eating carbs, especially in dry form (like sugar), ur body needs extra H2O to dissolve & process them, cuz the carbs naturally hold onto H2O.
• This means you must have more H2O to balance out the H2O that binds to the carbs, which makes them heavier compared to fats, which are hydrophobic
• When you eat fats, you gain only the mass of the fat. –> a gram of fat really is a gram of fuel.
• As a result, although many animals eat large quantities of carbs in their diet, the excess carbs are converted into fats for storage.
• Plants, by comparison, usually store excess energy as carbs

Question 83

Besides energy, what else do food molecules provide for cells?

Answer 83

Carbon, which is used to synthesize essential molecules not directly provided by food.

Question 84

How are glycolysis and citric acid cycle intermediates used in the cell?

Answer 84

They are routinely diverted to assemble compounds like amino acids and nucleic acid bases

Question 85

Why is metabolic flexibility important?

Answer 85

It allows cells to use intermediates for both energy production and biosynthesis, as many reactions are reversible.

Question 86

How are fatty acids and acetyl-CoA connected in metabolism?

Answer 86

Fatty acids can be oxidized to acetyl-CoA for energy, or excess acetyl-CoA can be used to synthesize fatty acids.

Question 87

Fermentation backstory

Answer 87

• Cells can still generate ATP through glycolysis even when oxygen is low or absent.
• NAD+ is essential for glycolysis, as it removes hydrogen from glucose.
• Cells have a limited supply of NAD+, which must be regenerated after it is converted to NADH.
• In absence of O2, organisms like yeast & bacteria use fermentation to oxidize NADH to NAD+, allowing glycolysis to continue.

Question 88

There are several forms of fermentation that bacteria use to obtain energy, but there are 2 forms that eukaryotes also use:

Answer 88

alcohol (ethanol) fermentation & lactate (lactic acid) fermentation
- some organisms, these pathways= primary
source of energy.
- In other organisms, these pathways are only used as optional or supplemental sources of energy when O2 is not available in adequate supply

Question 89

Alcohol fermentation

Answer 89

AKA ethanol fermentation
-occurs in a variety of organisms, like certain bacteria & yeasts
- the pyruvate produced by glycolysis is decarboxylated to form acetaldehyde, which is then used to oxidize NADH
- The products of these final steps include a molecule of CO2, a molecule of ethanol, and an NAD+
REACTION: pyruvate + NADH + H+ –> NAD+ + CO2 + ethanol
- When including glycolysis, the overall equation is: glucose + 2 ADP + 2 Pi –> 2 ATP + 2 CO2 + 2 ethanol

Question 90

Is fermentation more or less efficient than Aerobic respiration?

Answer 90

• Fermentation produces only 2 ATP, compared to up to 38 ATP produced in aerobic respiration. –>reason for less ATP is that ethanol is produced as a waste
  product during fermentation, and it is a very energy-rich compound.
• This is clearly demonstrated by the use of ethanol as a fuel for cooking and some race cars
• in O2 rich environments, aerobic respirating organisms will outcompete the others cuz they can extract 19x more energy from same food

Question 91

Lactate fermentation is

Answer 91

a process in which pyruvate reacts with NADH &
is converted directly into lactate & regenerates NAD+
- primary energy pathway in some bacteria, can also be used as a supplemental system in eukaryotes
- occurs in our muscle cells when strenuous activity causes a demand for ATP at a faster rate than which O2 can be supplied to the ETC for oxidative phosphorylation.
- Glycolysis speeds up, making 2 ATP/glucose, & excess pyruvate oxidizes NADH and is converted directly into lactate & regenerates NAD+
–> This reaction commonly occurs in the cytosol.
- Significant lactate builds up during prolonged high-energy demands, but it is converted back to pyruvate when O2 levels return to normal & ATP demand is normal.

Question 92

lactate fermentation equations

Answer 92

• this equation summarizes the final steps in lactate fermentation, beginning with a single pyruvate
  pyruvate + NADH + H+ –> NAD+ + lactate
• efficiency of lactate fermentation = efficiency of alcohol fermentation = 2 ATPs/glucose & a similar overall equation:

glucose + 2 ADP + 2 Pi –> 2 lactate + 2 ATP

Question 92

misconception about lactate fermentation

Answer 92

• accumulation of lactate (in the form of lactic
  acids) in muscle tissue during strenuous exercise was believed to be the primary cause of muscle stiffness &
  soreness.
• This is now known not to be the case. –> Lactate levels in muscles generally return to normal within an hour after intense exercise.

Question 93

Sign of lactate fermentation

Answer 93

• Certain bacteria produce lactate as their fermentation product.
• Sour taste of buttermilk, yogurt, and dill pickles is a sign of their activity.
  -lactic acid fermentation is used for making some cheeses

Question 94

Lactate threshold

Answer 94

lactate produced is transported from the muscles to the liver, where it is oxidized back to pyruvate so that it does not build up in muscle tissue.
- The point at which lactate production is too high for transport out of muscles to keep up is called the lactate threshold. –> This value can be increased by individuals through training, and it is useful for setting exercise intensity limits in endurance sports.
- The process of lactate fermentation results in an oxygen debt. By taking deeper and more frequent breaths, the body brings in large quantities of O2 to diminish the O2 debt.

Question 95

Anaerobic Respiration

Answer 95

• Although they lack mitochondria, many prokaryotes have cellular respiration ETC, located on internal membranes derived from the plasma membrane
• Some prokaryotes have ETC similar to those in eukaryotes, using oxygen (O₂) as the terminal electron acceptor.
• Other prokaryotes use substances like sulfate (SO₄²⁻), nitrate (NO₃⁻), or iron ions (Fe³⁺) as electron acceptors instead of oxygen = anaerobic respiration.
  –> these organisms are found in low oxygen, such as deep soils, marsh sediments, wetlands, and lakebeds.

Question 96

Why do some wetlands have a bad smell?

Answer 96

• Sulfur-reducing bacteria use SO₄²⁻ as the terminal electron acceptor, producing hydrogen sulfide (H₂S) instead of water, leading to the rotten egg smell in some wetlands.