Ch 9 Flashcards
three key pathways of respiration
glycolysis, the citric acid cycle and oxidative phosphorylation
organic compounds posses potential energy because
of the arrangement of electrons in the bonds between their atoms
cells systematically degrade molecules that are rich in potential energy into
simpler waste products that have less energy
compounds that can participate in exergonic reactions can act as
fuels
fermentation
catabolic process where there is a partial degradation of sugars or other organic fuels that occurs without the use of oxygen
aerobic respiration
a prevalent and efficient catabolic process in which oxygen is consumed as a reactant along with the organic fuel
what kinds of cells can carry out aerobic respiration
the cells of most eukaryotic and prokaryotic organisms
anaerobic respiration
substances other than oxygen are used as reactants in a process that harvests chemical energy without oxygen
cellular respiration
both aerobic and anaerobic respiration
summarize aerobic respiration
organic compounds+ O= CO2 +H2O +Energy
degradation of the sugar glucose (as opposed to other carbohydrates, fats, and proteins)
C6H12O6+ 6O2= 6CO2+ 6H2O +Energy (ATP+ Heat)
fuel that most cells most often use
glucose
the break down of glucose is _gonic
exer-
How do catabolic pathways that decompose organic fuels yield energy?
the relocation of electrons releases energy stored in organic molecules and this energy synthesizes ATP
redox reactions
there is a transfer of one or more electrons (e-) from one reactant to another. these e- transfers are called oxidation-reduction reactions
oxidation
the loss of e- from one substance in a redox reaction
reduction
the addition of e- to another substance (called such because e- lower positivity in atoms)
reducing agent
e- donor
oxidizing agent
e- acceptor
generalized redox
Xe- + Y= X + Ye-
some redox reaction do not involve the complete transfer of electrons but
some change in the degree of sharing in covalent bonds
the most potent of all oxidizing agents and why
oxygen, electronegativity
in general organic molecule that have an abundance of hydrogen are excellent
fuels, because of the bonds to their electrons are at the “top of the hill”
in respiration, hydrogen is transferred from
glucose to oxygen
in respiration, the oxidation of glucose transfers electrons to a lower energy state,
liberating energy for ATP synthesis
what holds back the energy rich molecules
the barrier of activation
glucose and other organic fuels are broken down in
steps catalyzed by enzymes
at key steps e- are ___ from glucose
stripped
in oxidation reactions, electrons travel with
a proton: as a hydrogen atom
NAD+
since hydrogen atoms aren’t transferred directly to oxygen, it is passed to this coenzyme instead.it is well suited as it can cycle between its oxidized (NAD+) and its reduced (NADH) forms easily. During respiration it is an oxidizing agent
How does NAD+ trap electrons from organic molecules like glucose
- enzymes called dehydrogenases remove a pair of hydrogen atoms (2 protons and 2e-) from the substrate, oxidizing it
- the enzyme then delivers 2 e- and 1 proton to its coenzyme NAD+
- the other proton is released as a hydrogen ion (H+)
NAD+ to NADH formula
H-C-OH +NAD+ Dehydrogenase-C=O +NADH+ H+
When reduced to NADH, NAD+’S charge is
neutralized
the most versatile e- acceptor in cellular respiration and functions in several redox steps during the breakdown of glucose
NAD+
during the transfer from glucose to NAD+ e-
lose very little of their potential energy
electron transport chain
consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes
electron transfer from NADH to oxygen is an ___gonic reaction
exer-
electron path during cellular respiration
glucose to NADH to electron transport chain to oxygen
3 metabolic stages of the harvesting of energy from glucose by cellular respiration
- Glycolysis
- Pyruvate-oxidation and the citric acid cycle
- Oxidative phosphorylation: electron transport and chemiosmosis
where does glycolysis occur
the cytosol
glycolisis
breaks glucose into 2 molecules of a compound called pyruvate
in eukaryotes, when pyruvate enters mitochondrion, it is oxidized into what which enters the citric acid cycle
acetyl CoA
citric acid cycle
where breakdown of glucose to CO2 is completed
electron transport chain
accepts electrons from the breakdown products of the first two stages and passes molecules from one electron to another. At the end, e- are combined with oxygen and hydrogen ions, forming water. Energy released at each step is stored to make ATP from ADP
oxidative phosphorylation
ATP synthesis powered by the redox reaction of the electron transport chain
in eukaryotic cells the inner membrane of the mitochondrion is the cite of
oxidative phosphorylation
what two parts make up oxidative phosphorylation
electron transport and chemiosmosis
where is ATP formed in respiration
almost 90 percent in oxidative phosphorylation
rest is formed by a few reactions of glycolysis and the citric acid cycle by a mechanism called substrate-level phosphorylation
substrate-level phosphorylation
a few reactions of glycolysis and the citric acid cycle which occur when an enzyme transfers a phosphate group from a substrate molecule to ADP
substrate molecule (in respiration context)
refers to an organic molecule generated as an intermediate during the catabolism of glucose
two phases of glycolysis
energy investment and energy payoff
glycolysis energy investment phase
- hexokinase transfers a phosphate group from ATP to glucose (first ATP used)
- glucose 6-phosphate is converted to its isomer, fructose 6-phosphate
- phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar (now 2 ATP used total)
- Aldolase cleaves the sugar molecule into 2 different 3-carbon sugars
- Isomerase catalyzes the reversible conversion between the 2 isomers
glycolysis energy payoff phase
- enzyme catalyzes two sequential reactions. First the sugar is oxidized by the transfer of e- to NAD+, forming NADH. Second, the energy released from this exergonic redox reaction is used to attach a phosphate group to the oxidized substrate
- phosphate group is transferred to ADP in an exergonic reaction. the carbonyl group of a sugar has been oxidized to the carboxyl group (-COO-) of an organic acid (3-phosphoglycerate) (2 ATP formed)
- Enzyme relocated remaining phosphate group
- enolase causes a double bond to form in the substrate by extracting a water molecule yielding (PEP)
- the phosphate group is transferred from PEP to ADP (2 more ATP formed, final total is 4 formed)
Glycolysis net
Glucose= 2 pyruvate+2H2O
4ATP formed-2ATP used= 2 ATP
2 NAD+ 4e-+4H+=2 NADH+2H+
3 reactions which convert the pyruvate entering the mitochondrion to acetyl CoA
- Pyruvate’s carboxyl group (-COO-) is removed and given off as a molecule of CO2
- the 2-carbon fragment is oxidized, forming acetate (CH3COO-). the extracted e- are transferred from NAD+ to NADH
- coenzyme A (CoA) is attached via its sulfur atom to the sulfur atom to the acetate, forming acetyl CoA
net products of the citric acid cycle
1 ATP per trun 3 CO2 FADH2 4NADH+4H+ CoA (multiply all these by two per glucose as only half goes in)
alternate names for the citric cycle
Krebs cycle or the tricarboxylic acid cycle
steps of the citric acid cycle
- Acetyl CoA adds its two-carbon acetyl group to oxaloacetate producing citrate
- citrate is converted to its isomer isocitrate by removal of 1 water molecule and addition of another
- Isocitrate is oxidized reducing NAD+ to NADH then the resulting compound loses a CO2 molecule
- Another CO2 is lost and the resulting compound is oxidized reducing NAD+ to NADH. the remaining molecule is then attached to the coenzyme A by unstable bond
- CoA is displaced by a phosphate group which is transferred to GDP forming GTP, GTP then makes an ATP (only ATP made in the cycle)
- 2 hydrogens are transferred to FAD forming FADH2 and oxidizing succinate
- addition of a water molecule rearranges bonds in the substrate
- the substrate is oxidized reducing NAD+to NADH regenerating oxaloacetate
how much is the total ATP produced by glycolysis and Krebs cycle from 1 glucose
4
the folding of the inner membrane to form cristae increases its surface area
which provides space for thousands of copies of the electron transport chain in each mitochondrion
most of the components of the chain exist in
multi-protein complexes numbered I through IV
prosthetic groups
nonprotein components essential for the catalytic functions of certain enzymes bound to protein groups I to IV
electon transport chain steps
- 2 e- transferred from NADH to flavoprotein
- flavoprotein passes electrons to an iron-sulfate protein (in a redox) (FADH2 would be added if substituted for NADH after this step)
- iron sulfate protein passes to ubiquinone, only non protein in ETC
- cytochromes to cyt a3
- cyt a3 passes to Oxygen
- oxygen picks up water from aqueous solution to form water
cytochromes
most of the electron carriers between ubiquinone and oxygen
heme group
prosthetic group to cytochromes which has an iron atom which accepts and donates proteins
the etc provides 1/3 energy for ATP synthesis from
FADH2
ATP synthase
the enzyme that actually makes ATP from ADP and inorganic phosphate, found in inner membrane of mitochondrion or prokaryotic plasma membrane, uses the energy of an existing gradient for power; a difference in the concentration of H+ (thus pH) . It has four main parts each made of multiple polypeptides
osmos
greek for push
chemiosmosis
an energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient to drive cellular work (like ATP synthesis)
steps of the ATP synthase
- H+ flowing down their gradient enter a half channel in a stator which is anchored in the membrane
- H+ ions enter binding sites within a rotor changing the shape of each subunit so that the rotor spins within the membrane
- each H+ ion makes one complete turn before leaving the rotor and passing through a second half channel in the stator into the mitochondrial matrix
- spinning of the rotor causes an internal rod to spin as well. this rod extends like a stalk into the knob below t, which is held stationary by part of the stator
- turning of the rod activates the catalytic sites in the knob that produce ATP from ADP and inorganic phosphate
explain how the H+ gradient is maintained
the etc I an energy converter that uses the exergonic flow of electrons from the mitochondrial matrix into the intermembrane space
proton-motive force
capacity of the gradient to perform work
in respiration, most energy flows
glucose-NADH-etc-proton motive-ATP
each NADH that transfers a pair of electrons to the etc contributes enough to the proton motive force to generate about
3 ATP
3 reasons reasons we cannot state the exact number of ATP molecules generated by the breakdown of one molecule of glucose
- phosphorylation and the redox reactions are not directly coupled to each other, so the ratio of the number of NADH molecules to the number of ATP numbers is not a whole number
- the ATP yield varies slightly depending on the type of shuttle used to transport e- from cytosol into mitochondrion.
- the use of the proton-motive force to drive other work also reduces the yield
maximum per glucose from respiration
30 or 32 ATP
percent of chemical energy from glucose transferred to ATP
about 34 percent, rest is lost as heat
two mechanisms by which cells can oxidize organic fuel and generate ATP sans oxygen
anaerobic respiration and fermentation
difference between anaerobic respiration and fermentation
fermentation is sans etc
how does anaerobic respiration compensate for lack of oxygen
uses other final e- acceptor like SO4 2-
fermentation
- gets energy sans O or etc
- uses just glycolysis phosphorylation
- needs sufficient NAD+
- transfers electrons from NADH to pyruvate
- many types which differ in end products
alcohol fermentation
-pyruvate is converted to ethanol in two steps
steps of alcohol fermentation
- CO2 released from pyruvate, which is then converted into acetaldehyde
- acetaldehyde is reduced by NADH to ethanol
lactic acid fermentation
pyruvate is reduced directly by NADH to form lactate
which form of respiration or fermentation is most efficient
aerobic respiration
obligate anaerobes
carry out only fermentation or anaerobic respiration
-O can actually be poisonous to them
facultative anaerobes
can make enough ATP to survive using either fermentation or respiration
glycolysis evolution
- evolved during a time pre-oxygen in earth’s atmosphere
- extremely widespread
- predates eukaryotes as it is does not require an organelle
deamination
the removal of amino groups from fuels other than glucose
-the nitrogenous refuse is excreted from animals as waste products
beta oxidation
a metabolic sequence that breaks the fatty acids to two carbon fragments that enter the citric acid cycle as CoA
-NADH and FADH2 are also made which enter etc, making more ATP
hows fats are processed
- digested to glycerol and fatty acids
- glycerol is converted to glyceraldehyde 3-phosphate, an intermediate of glycolysis
- beta oxidation
a gram of fat oxidized by respiration produces
twice as much as a gram of carbohydrate
what are the other uses of glycolysis and Krebs cycle
- compounds produced here can be used to make molecules the body needs
- convert some kinds of molecules into others
how does the cell regulate in cellular respiration
- phosphofructokinase’s rate in glycolysis
- phosphofructokinase is allosteric : inhibited by ATP and stimulate by AMP (derived from ATP)
- phosphofructokinase is also sensitive to citrate; product of citric acid cycle
energy in cellular respiration is
released not produced
