Pl rq 7: Ch. 9: 164-184
Chemical elements essential to life are
recycled
A smaller amount of ATP is formed directly in a few reactions of glycolysis and the citric acid cycle by a mechanism called
substrate level phosphorylation
Energy stored in organic molecules of food ultimately comes from the
sun
Energy flows into an ecosystem in the form of ___ and exits in the form of ___
sunlight, heat
Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glucose, a six-carbon sugar, is split into two three-carbon sugars. These smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate.
Which of the following is true of the energy levels of electrons in shells?
Valence electrons have a higher energy level than those in other filled shells.
The more ____________ the atom (the stronger its pull on electrons), the more energy is required to take an electron away from it
electronegative
Cellular respiration
energy in fuel is converted to ATP most ATP is made in the cells of the mitochondria ATP powers work
eukaryotic cells - many steps of cellular respiration occur in
mitochondria --> carbon dioxide are waste products and reused in photosynthesis.
The energy released at each step of the chain is stored in a form the __________(or prokaryotic cell) can use to make ATP from ADP.
mitochondrian
When O2 is present, the pyruvate in eukaryotic cells enters a___________, where the oxidation of glucose is completed.
mitochondrion
fuels with multiple C—H bonds oxidized into products with
multiple C—O bonds.
A covalent bond is likely to be polar when
one of the atoms sharing electrons is more electronegative than the other.
Oxidative phosphorylation accounts for almost 90% of the ATP generated by
respiration
respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps
respiration
During the energy investment phase
the cell actually spends ATP.
glycolysis can be divided into two phases:
the energy investment phase and the energy payoff phase.
In respiration,
the oxidation of glucose transfers electrons to a lower energy state, liberating energy that becomes available for ATP synthesis.
Fermentation and anaerobic respiration enables cells to produce ATP without
the use of oxygen
glucose is broken down in a series of steps, each one catalyzed by an enzyme
. At key steps, electrons are stripped from the glucose As is often the case in oxidation reactions, each electron travels with a proton—thus, as a hydrogen atom. The hydrogen atoms are not transferred directly to oxygen, but instead are usually passed first to an electron carrier, a coenzyme called nicotinamide adenine dinucleotide, a derivative of the vitamin niacin.
NAD+
. NAD+ is the most versatile electron acceptor in cellular respiration and functions in several of the redox steps during the breakdown of glucose. By receiving 2 negatively charged electrons but only 1 positively charged proton, the nicotinamide portion of NAD+ has its charge neutralized when NAD+ is reduced to NADH
a mutlienzyme complex catalyzes three reactions linking glycolysis and the citric acid cycle by converting pyruvate to acetyl coA
1 Pyruvate's carboxyl group (—COO−), already somewhat oxidized and thus carrying little chemical energy, is now fully oxidized and given off as a molecule of CO2. This is the first step in which CO2 is released during respiration. 2 Next, the remaining two-carbon fragment is oxidized and the electrons transferred to NAD+, storing energy in the form of NADH. 3 Finally, coenzyme A (CoA), a sulfur-containing compound derived from a B vitamin, is attached via its sulfur atom to the two-carbon intermediate, forming acetyl CoA. Acetyl CoA has a high potential energy, which is used to transfer the acetyl group to a molecule in the citric acid cycle, a reaction that is therefore highly exergonic.
The harvesting of energy from glucose by cellular respiration is a cumulative function of three metabolic stages
2&3 = cellular respiration . In this text, however, we include glycolysis as a part of cellular respiration because most respiring cells deriving energy from glucose use glycolysis to produce the starting material for the citric acid cycle
For each molecule of glucose degraded to carbon dioxide and water by respiration, the cell makes up to about
32 molecules of ATP, each with 7.3 kcal/mol of free energy single molecule of glucose (686 kcal/mol under standard conditions)
Fermentation
A catabolic process that makes a limited amount of ATP from glucose (or other organic molecules) without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid. is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen.
citric acid cycle
A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in glycolysis by oxidizing acetyl CoA (derived from pyruvate) to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; together with pyruvate oxidation, the second major stage in cellular respiration.
Catabolic
A process in which large molecules are broken down
electron transport chain
A sequence of electron carrier molecules (membrane proteins) that shuttle electrons down a series of redox reactions that release energy used to make ATP built into the inner membrane of the mitochondria of eukaryotic cells (and the plasma membrane of 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, O2 captures these electrons along with hydrogen nuclei (H+), forming water. (Anaerobically respiring prokaryotes have an electron acceptor at the end of the chain that is different from O2.)
Note that glycolysis is a source of
ATP and NADH
What is the correct interpretation of this image?
ATP is a molecule that acts as an intermediary to store chemical energy for cellular work.
during the energy payoff phase,
ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose. The net energy yield from glycolysis, per glucose molecule, is 2 ATP plus 2 NADH
Do you think the potential energy is higher for the reactants or the products in the reaction shown above?
Because there is no external source of energy for the reaction, it must be exergonic, and the reactants must be at a higher energy level than the products.
If the following redox reaction occurred, which compound would be oxidized? Reduced?
C4H6O5+NAD+→C4H4O5+NADH+H+ C4H6O5 would be oxidized and NAD+ would be reduced.
steps of cellular respiration by tracking the degradation of the sugar glucose
C6H12O6+6 O2→6 CO2+6 H2O+Energy (ATP+heat) This breakdown of glucose is exergonic, having a free-energy change of -686 kcal (2,870 kJ) per mole of glucose decomposed (ΔG=−686 kcal/mol). Recall that a negative ΔG(ΔG<0) indicates that the products of the chemical process store less energy than the reactants and that the reaction can happen spontaneously—in other words, without an input of energy.
Cellular respiration.
Cellular respiration. In cellular respiration, the same reaction occurs in stages: An electron transport chain breaks the "fall" of electrons in this reaction into a series of smaller steps and stores some of the released energy in a form that can be used to make ATP. (The rest of the energy is released as heat.)
An overview of cellular respiration
During glycolysis, each glucose molecule is broken down into two molecules of pyruvate. In eukaryotic cells, as shown here, the pyruvate enters the mitochondrion. There it is oxidized to acetyl CoA, which will be further oxidized to CO2 in the citric acid cycle. The electron carriers NADH and FADH2 transfer electrons derived from glucose to electron transport chains. During oxidative phosphorylation, electron transport chains convert the chemical energy to a form used for ATP synthesis in the process called chemiosmosis. (During earlier steps of cellular respiration, a few molecules of ATP are synthesized in a process called substrate-level phosphorylation.
NADH represents stored energy
Each NADH molecule formed during respiration represents stored energy. This energy can be tapped to make ATP when the electrons complete their "fall" in a series of steps down an energy gradient from NADH to oxygen.
e- transport chain explained
Electron transfer from NADH to oxygen is an exergonic reaction with a free-energy change of -53 kcal/mol (-222 kJ/mol). 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 redox reactions, losing a small amount of energy with each step until they finally reach oxygen, the terminal electron acceptor, which has a very great affinity for electrons. Each "downhill" carrier is more electronegative than, and thus capable of oxidizing, its "uphill" neighbor, with oxygen at the bottom of the chain. Therefore, the electrons transferred from glucose to NAD+, which is thus reduced to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom
Two molecules with the chemical formulas C6H12O6 and C6H12O2 are probably
Monosaccharides generally have molecular formulas that are some multiple of the unit CH2O. Glucose (C6H12O6) is the most common monosaccharide. A fatty acid has a long carbon skeleton with a carbon at one end that is part of a carboxyl group (-COOH); the remainder of the skeleton consists of a hydrocarbon chain. The relatively nonpolar C-H bonds in the hydrocarbon chains of fatty acids are the reason fats are hydrophobic.
During the redox reaction in glycolysis (see step 6 in Figure 9.9), which molecule acts as the oxidizing agent? The reducing agent?
NAD+ acts as the oxidizing agent in step 6, accepting electrons from glyceraldehyde 3-phosphate (G3P), which thus acts as the reducing agent. Nad+ is oxidizing agent bc it is reduced when it is NADH
Enzymes called dehydrogenases remove a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate (glucose, in the preceding example), thereby
OXIDIZING it The enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+, forming NADH. The other proton is released as a hydrogen ion (H+) into the surrounding solution:
Catabolic pathways do not directly move flagella, pump solutes across membranes, polymerize monomers, or perform other cellular work: t/f?
TRUE
substrate-level phosphorylation
The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism. *** rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation. " *intermediate substrate = organic molecule generated as an intermediate during the catabolism of glucose
Which of the following is true for all exergonic reactions?
The reaction proceeds with a net release of free energy.
Methane combustion as an energy-yielding redox reaction.
The reaction releases energy to the surroundings because the electrons lose potential energy when they end up being shared unequally, spending more time near electronegative atoms such as oxygen *shift position in covalent bonds instead of forming ionic bonds The two atoms of the oxygen molecule (O2) share their electrons equally. But when oxygen reacts with the hydrogen from methane, forming water, the electrons of the covalent bonds spend more time near the oxygen (see Figure 9.3). In effect, each oxygen atom has partially "gained" electrons, so the oxygen molecule has been reduced. Because oxygen is so electronegative, it is one of the most powerful of all oxidizing agents. An electron loses potential energy when it shifts from a less electronegative atom toward a more electronegative one, just as a ball loses potential energy when it rolls downhill. A redox reaction that moves electrons closer to oxygen, such as the burning (oxidation) of methane, therefore releases chemical energy that can be put to work.
Describe the structural differences between the oxidized form and the reduced form of nicotinamide
The reduced form has an extra hydrogen, along with 2 electrons, bound to the carbon shown at the top of the nicotinamide (opposite the N). There are different numbers and positions of double bonds in the two forms: The oxidized form has three double bonds in the ring, while the reduced form has only two. (In organic chemistry you may have learned, or will learn, that three double bonds in a ring are able to "resonate," or act as a ring of electrons. Having three resonant double bonds is more "oxidized" than having only two double bonds in the ring.) In the oxidized form there is a + charge on the N (because it is sharing 4 electron pairs), whereas in the reduced form it is only sharing 3 electron pairs (having a pair of electrons to itself).
What would happen if you removed the dihydroxyacetone phosphate generated in step 4 as fast as it was produced?
The removal would probably stop glycolysis, or at least slow it down, since it would push the equilibrium for step 5 toward the bottom (toward DHAP). If less (or no) glyceraldehyde 3-phosphate were available, step 6 would slow down (or be unable to occur).
Catabolism is linked to work by a chemical drive shaft—ATP
To keep working, the cell must regenerate its supply of ATP from ADP and Ⓟi
Glycolysis
a series of reactions that ultimately splits glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration which occurs in the cytosol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate. In eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA, which enters the citric acid cycle
Upon entering the mitochondrion via active transport, pyruvate is first converted to a compound called
acetyl coenzyme A, or acetyl CoA
reduction
adding electrons is called reduction; adding negatively charged electrons to an atom reduces the amount of positive charge of that atom.
Most efficient catabolic pathway is
aerobic respiration oxygen is consumed as a reactant along with the organic fuel
How do the catabolic pathways that decompose glucose and other organic fuels yield energy?
answer is based on the transfer of electrons during the chemical reactions. The relocation of electrons releases energy stored in organic molecules, and this energy ultimately is used to synthesize ATP.
Compare and contrast aerobic and anaerobic respiration, including the processes involved.
both processes include glycolysis, the citric acid cycle, and oxidative phosphorylation. In aerobic respiration, the final electron acceptor is molecular oxygen (O2); in anaerobic respiration, the final electron acceptor is a different substance.
main energy yielding foods
carbohydrates and fats—are reservoirs of electrons associated with hydrogen, often in the form of C—H bonds. Only the barrier of activation energy holds back the flood of electrons to a lower energy state (see Figure 8.13). Without this barrier, a food substance like glucose would combine almost instantaneously with O2. If we supply the activation energy by igniting glucose, it burns in air, releasing 686 kcal (2,870 kJ) of heat per mole of glucose (about 180 g). Body temperature is not high enough to initiate burning, of course. 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.
photosynthesis starts with
carbon dioxide and water CO2 obtained by leaves water obtained by roots
respiration breaks down photosynthesis byproducts like glucose and oxygen to produce
carbon dioxide and water + ATP !
Metabolic pathways that release stored energy by breaking down complex molecules are called
catabolic pathways Transfer of electrons from fuel molecules (like glucose) to other molecules plays a major role in these pathways
Organiccompounds + Oxygen → Carbondioxide + Water + Energy
cellular respiration
photosynthesis byproducts fuel
cellular respiration
During oxidative phosphorylation,
chemiosmosis couples electron transport to ATP synthesis
After pyruvate is oxidized, the __________ completes the energy-yielding oxidation of organic molecules
citric acid cycle
Oxidation of pyruvate to acetyl CoA, the step before
citric acid cycle Pyruvate is a charged molecule, so in eukaryotic cells it must enter the mitochondrion via active transport, with the help of a transport protein. Next, a complex of several enzymes (the pyruvate dehydrogenase complex) catalyzes the three numbered steps, which are described in the text. The acetyl group of acetyl CoA will enter the citric acid cycle. The CO2 molecule will diffuse out of the cell. By convention, coenzyme A is abbreviated S-CoA when it is attached to a molecule, emphasizing the sulfur atom (S)
nicotinamide adenine dinucleotide, a derivative of the vitamin niacin.
coenzyme well suited as an electron carrier because it can cycle easily between its oxidized form, NAD+, and its reduced form, NADH. As an electron acceptor, NAD+ functions as an oxidizing agent during respiration.
Glycolysis and the citric acid cycle
connect to many other metabolic pathways
Through the activity of ________ a cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy
enzymes
Compounds that can participate in________ reactions can act as fuels
exergonic
Carbohydrates, fats, and protein molecules from food can all be processed and consumed as
fuel
In animal diets, a major source of carbohydrates is starch, a storage polysaccharide that can be broken down into
glucose subunits
during cellular respiration, most electrons travel the following "downhill" route:
glucose→NADH→electron transport chain→oxygen
substrate level phosphorylation occurs in both
glycolysis and the citric acid cycle
catabolic pathways that break down glucose and other organic fuels.
glycolysis and then pyruvate oxidation and the citric acid cycle are the catabolic pathways that break down glucose and other organic fuels
Three key pathways of respiration:
glycolysis, pyruvate oxidation and the citric acid cycle, and oxidative phosphorylation
Glycolyisis
harvests chemical energy by oxidizing glucose to pyruvate
Some of the energy taken out of chemical storage can be used to do work; the rest is dissipated as
heat
energy state of the electron changes as hydrogen (with its electron) is transferred to
hydrogen
cellular respiration
is often used to refer to the aerobic process although technically it includes both aerobic and anaerobic processes. Organiccompounds + Oxygen → Carbondioxide + Water + Energy
An electron ______ potential energy when it shifts from a less electronegative atom toward a more electronegative one
loses
glucose is a good E source bc
organic molecules that have an abundance of hydrogen are excellent fuels because their bonds are a source of "hilltop" electrons, whose energy may be released as these electrons "fall" down an energy gradient during their transfer to oxygen.
In a redox reaction, the loss of electrons from one substance is called _______, and the addition of electrons to another substance is known as _________
oxidation, reduction In the generalized reaction, substance Xe−, the electron donor, is called the reducing agent; it reduces Y, which accepts the donated electron. Substance Y, the electron acceptor, is the oxidizing agent; it oxidizes Xe− by removing its electron. Because an electron transfer requires both an electron donor and an acceptor, oxidation and reduction always go hand in hand.
In eukaryotic cells, the inner membrane of the mitochondrion is the site of electron transport and another process called chemiosmosis, together making up
oxidative phosphorylation (In prokaryotes, these processes take place in the plasma membrane.)
The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.
oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain.
PYruvate is _________ and the citric acid cycle completes the energy-yielding oxidation of organic molecules
oxidized
Catabolic pathways yield energy by
oxidizing organic fuels and use it to make ATP
Photosynthesis generates
oxygen and organic molecules used by mitochondria of eukaryotes as fuel for cellular respiration
Organic compounds possess ______ energy as a result of the arrangement of electrons in the bonds between their atoms.
potential
. In aerobically respiring prokaryotic cells
pyuvate enters in the cytosol
Some of the steps of glycolysis and the citric acid cycle are _______ reactions in which dehydrogenases transfer electrons from substrates to NAD+ or the related electron carrier FAD, forming NADH or FADH2
redox
In many chemical reactions, there is a transfer of one or more electrons (e−) from one reactant to another. These electron transfers are called oxidation-reduction reactions, or
redox reactions
Cellular respiration does not oxidize glucose (or any other organic fuel) in a single explosive step either.
true
Electrons lose very little of their potential energy when they are transferred from glucose to NAD+
true
Glycolysis occurs whether or not O2 is present
true
in glycolysis, All of the carbon originally present in glucose is accounted for in the two molecules of pyruvate; no carbon is released as CO2 during glycolysis
true
chloroplasts
use light energy to make carbohydrates from carbon dioxide and water
In the third stage of respiration, the electron transport chain accepts electrons from NADH or FADH2 generated during the first two stages and passes these electrons down the chain. At the end of the chain, the electrons are combined with molecular oxygen and hydrogen ions (H+), forming
water