exam 4 Flashcards
what is metabolism?
sum of all of the chemical rxns of occuring in the body
what is catabolism?
breakdown of larger molecules into smaller ones, releases energy
anabolism is…
the synthesis of larger molecules from smaller ones, requires energy
oxidation-reduction rxns are those in which electrons are transferred from…
a donor to an acceptor
oxidation is the…
loss of electrons
reducing agent is…
the substance that loses the electrons
reduction is…
the gain of electrons
oxidizing agent is the…
substance that gains the electrons
what is carbon in its most reduced form?
alkane
carbon in its most oxidized form…
CO2 (final product of catabolism)
NAD+ is an…
- important coenzyme
- two electron oxidizing agent
- reduced to NADH
FAD is a…
- biological oxidizing agent
- protons and electrons are accepted by FAD
what is a central theme in metabolism?
coupling of energy-producing and energy-requiring reactions
can food energy be used directly?
no - must be shuttled into easily accessible forms of chemical energy
what are high energy bonds?
bonds that can release convenient amounts of energy
what is ATP?
essential high energy bond-containing compound
(x) of ATP to ADP releases (y)
hydrolysis, energy
coupling of energy release from ATP hydrolysis…
drives many anabolic reactions
what drives many anabolic reactions?
coupling of energy release from ATP hydrolysis
how many charges are on ATP and ADP?
ATP (4 -)
ADP (3 -)
is ATP stable?
not really
(x) must be expended to put an additional (y) on ADP
energy, negative charge
why is there an entropy loss when ADP is phosphorylated?
potential loss of resonance hybridization of inorganic phosphate (Pi)
what happens upon the hydrolysis of ATP?
decrease in electrostatic repulsion
hydrolysis of ATP causes a decrease in…
electrostatic repulsion of beta-phosphate
what do metabolic pathways often require?
activation
what is activation?
formation of a more reactive substance
a metabolite bonded to some molecule so that…
free energy change for breaking new bond is negative causes nxt rxn to be exergonic
what is glycolysis?
it’s the first stage of glucose metabolism
what is glucose converted to during glycolysis?
two molecules of pyruvate and 2 atp are made
once pyruvate forms…
multiple routes are optioned (aerobic oxidation, anaerobic alcoholic fermentation, anaerobic lactic acid fermentation)
1st rxn of glycolysis
phosphorylation of glucose to give glucose-6-phosphate
- Mg 2+ (cofactor) and hexokinase (enzyme)
- USE ATP
2nd rxn of glycolysis
isomerization of glucose-6-phosphate to give fructose-6-phosphate
- phosphoglucose (cofactor) and isomerase (enz)
3rd rxn of glycolysis
phosphorylation of fructose-6-phosphate to yield fructose-1,6-bisphosphate
- Mg2+ and PFK
- USE ATP
4th rxn of glycolysis
cleavage of fructose-1,6-bisphosphate to give glyceraldehyde-3-phosphate and dihyroxyacetone phosphate
- aldolase (enzyme)
5th rxn of glycolysis
isomerization of dihyroxyacetone phosphate to give glyceraldehyde-3-phosphate
- triosephosphate and isomerase
6th rxn of glycolysis
oxidation and phosphorylation of glyceraldehyde-3-phosphate to give 1,3-bisphosphoglycerate
- glyceraldehye-3-phosphate (cofactor) and dehydrogenase (enzyme)
7th rxn of glycolysis
transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to 3-phosphoglycerate
- Mg2+ (cofactor) and phosphoglycerate kinase (enzyme)
- MAKE ATP
8th rxn of glycolysis
isomerization of 3-phosphoglycerate to give 2-phosphoglycerate
- phosphoglycerate mutase (enzyme)
9th rxn of glycolysis
dehydration of 2-phosphoglycerate to give phosphoenolpyruvate
- Mg2+ and enolase
10th rxn of glycolysis
transfer of phosphate group from phosphoenol pyruvate to ADP to give pyruvate
- Mg2+ and pyruvate kinase
- MAKE ATP
step one of glycolysis
uses enzyme hexokinase and cofactor Mg2+
- kinases transfer phosphates
- rxn is endergonic
- ATP hydrolysis drives rxn
step one of glycolysis (p2)
hexokinase can use glucose or any 6 carbon sugar
- glucokinase (in liver) binds only glucose
- when blood glucose is high, liver uptakes glucose more readily than other tissues
step two of glycolysis
uses enzyme glucosephosphate isomerase
- makes an isomer (G-6-P to F-6-P)
step three of glycolysis
ATP hydrolysis coupled to rxn
- uses enzyme phosphofructokinase to phosphorylate F-6-P generating fructose-1,6-bisphosphate
step three (regulatory step)
enzyme is phosphofructokinase (PFK)
- tetramer subject to allosteric feedback
- ATP is an allosteric effector
high ATP (x) PFK
inhibits
low ATP (y) PFK
activate
step four of glycolysis
F-1,6-BP split into two 3-carbon fragments (DHAP and G-3-P)
- rxn catalyzed by aldolase
step five of glycolysis
DHAP –> G-3-P by triosephosphate isomerase
- rxn is relatively small in terms of gibbs free E
glycolysis summary (steps 1-5)
- glucose is converted to G-3-P
- key intermediate is F-1,6-BP
- PFK subject to allosteric control
- 2 molecules (each 3C compounds) undergo these rxns
step six of glycolysis
oxidation of G-3-P to 1,3-bisphophoglycerate
- catalyzed by enzyme glyceraldehyde-3-phosphate dehydrogenase
step six in detail
involves e- transfer from G-3-P to NAD+
- involves addition of phosphate
step seven
- 1,3-bisphosphateglycerate converted to 3-phosphoglycerate
- 1,3-bisphosphoglycerate transfers a phosphate group to ADP –> ATP (substrate level phosphorylation)
- rxn is catalyzed by phosphoglycerate kinase
step eight of glycolysis
involves isomerization of 3-phosphoglycerate to 2-phosphoglycerate
- rxn is catalyzed by phosphoglycerate mutase
step nine
2-phosphoglycerate loses a molecule of water –> phosphophenolpyruvate
- enolase catalyzes rxn, requiring a Mg2+ cofactor
- phosphoenolpyruvate contains a high energy bond (molecule is Activated)
step ten
PEP transfers phosphate group to ADP –> ATP and pyruvate
- gibbs free energy of PEP is more than that of ATP
- rxn catalyzed by pyruvate kinase
glycolysis summary (5-10 steps)
- rxns involve e- transfer to NADH and ATP production
- net atp
- net nadh
control points in glycolysis
hexokinase, PFK, pyruvate kinase
what are control points?
enzymes that create rxns that exhibits large decreases in free E by catalyzation
what must be done to keep glycolysis going?
NAD+ must be regenerated
under anaerobic conditions, NAD+ is…
regenerated by reduction of pyruvate to lactate
lactate dehydrogenase is a..
tetrameric enzyme
pyruvate is converted to…
lactate in actively metabolizing tissue, recycling NAD+ in the process
in some organisms, pyruvate is converted to
ethanol
three processes play central roles in aerobic metabolism:
citric acid cycle, electron transport, ox phos
what is NOT a substrate of the tca cycle?
pyruvate
pyruvate dehydrogenase complex is responsible for..
the conversion of pyruvate to acetyl-CoA
what is produced in the transition from glycolysis to tca cycle?
NADH is generated, CO2 is made as a byproduct
- activation step
citric acid cycle step 1
- condensation of acetyl-CoA with oxaloacetate to form citrate
- hydrolysis of thioester bond drives rxn
TCA step 2
- citrate is isomerized to isocitrate
- done by a dehydration then hydration
- changes position of OH
- rxn is catalyzed by aconitase
TCA step 3
- oxidation of isocitrate
- NAD+ reduced to NADH
- decarboxylation forms alpha-ketoglutarate and CO2
- catalyzed by isocitrate dehydrogenase
TCA step 4
- oxidation of alpha-ketoglutarate to succinyl-CoA
- catalyzed by alpha-ketoglutarate dehydrogenase complex
- NAD+ reduced to NADH
- CO2 is made as by-product (decarboxylation)
TCA step 5
- succinyl-CoA is hydrolyzed forming succinate
- catalyzed by succinyl-CoAsynthetase
- previous activate step allows GTP to be made
TCA step 6
- oxi of succinate to fumarate
- FAD reduced to FADH2
- catalyzed by succinate dehydrogenase
TCA step 7
- hydration of fumarate to L-malate occurs
- catalyzed by fumarase
TCA step 8
- malate is oxidized to oaloacetate
- nad+ reduced to NADH
- catalyzed by maltate dehydrogenase
what are the three points of control in the tca cycle?
- citrate synthase
- isocitrate dehydrogenase
- alpha-ketoglutarate dehydrogenase complex
citrate synthase
inhibited by ATP, NADH, succinyl CoA
- product inhibition by citrate
isocitrate dehydrogenase
activated by ADP, NAD+
inhibited by ATP, NADH
alpha-ketoglutarate dehydrogenase complex
inhibited by ATP, NADH, succinyl CoA
activated by ADP, NAD+
catabolism of proteins, carbs, fatty acids all…
feed into the citric acid cycle at one or more points
amphibolic describes how
the tca cycle plays a role in both catabolism and anabolism
tca cycle is the source of….
starting materials for biosynthesis of many other compounds
if a component of the citric acid is taken out for..
biosynthesis, it has to be replaced
what replaces oxaloacetate?
carboxylation of pyruvate
tca cycle is considered part of the aerobic metabolic process b/c…
of its link to the electron transport chain and ox phos
which cofactors pass their e- to oxygen?
NADH and FADH2
where does ATP production take place?
mitochondrion
o2 is reduced to…
H2O
transfer of e- is strongly…
exergonic and can drive phosphorylation of ADP
energy-releasing oxidations give rise to…
H+ pumping and a pH gradient across inner mitochondrial membrane
coupling process converts…
electrochemical potential to the chemical energy of ATP
what is the coupling factor that connects the e- transport and ATP?
ATP synthase
mechanism by which the H+ gradient leads to the production…
of ATP depends on ion channels through the inner mitochondrial membrane
during chemiosmotic coupling:
- H+ flow back into the matrix thru channels in the F0 unit of ATP synthase
- flow of protons is accompanied by formation of ATP in the F1 unit of ATP synthase
P/O ratio is
the number of moles of Pi consumed in phosphorylation to the number of moles of oxygen atoms consumed in oxidation
phosphorylation:
ADP + Pi –> ATP + H20
oxidation:
1/2 O2 + 2H+ 2e- –> h2o
P/O when NADH is oxidized
2.5
P/O when FADH2 is oxidized
1.5
what are shuttle mechanisms?
transport metabolites b/w mitochondria and cytosol
glycerol phosphate shuttle
- glycolysis in cytosol produces NADH
- NADH does not cross mitochondrial membrane but glycerol phosphate and dihydroxyacetone phosphate can
- thru the glycerol phosphate shuttle, 1.5 ATP are produced in mitochondria for each cytosolic NADH
malate-asparatate shuttle
- found in mammalian kidney, liver, heart
- malate crosses mitochondrial membrane while oxaloacetate can’t
- transfer of e- from NADH in cytosol produces NADH in mitochondria
- in malate-aspartate shuttle, 2.5 mitochondrial ATP are produced for each cystolic NADH
ATP yield from complete oxidation of glucose
30-32 molecules of ATP are produced for each glucose molecule (depending on shuttle mechanism)
what do kinase enzymes do?
transfers phosphates
what co factor is needed for kinase rxns?
Mg2+
what enzyme functions the same as isomerase?
phosphoglycerate mutase
why does the glucose derivative get rearranged to an enol?
to make substrate more reactive + activate substrate
which glycolysis rxns are irreversible?
1, 3, 10
how can you tell a rxn is reversible besides the arrows?
small gibbs free energy = reversible
large gibbs free energy = irreversible
step one of glycolysis (co-factor and enzyme)
Mg2+ and hexokinase
ATP to ADP
step two of glycolysis (co-factor and enzyme)
phosphoglucose and isomerase
step three of glycolysis (co-factor and enzyme)
Mg2+ and PFK
ATP TO ADP
step four of glycolysis (co-factor and enzyme)
aldolase
step five of glycolysis (co-factor and enzyme)
triosephosphate and isomerase
step six of glycolysis (co-factor and enzyme)
glyceraldehyde-3-phosphate and dehydrogenase
step seven of glycolysis (co-factor and enzyme)
Mg2+ and phosphoglycerate kinase
ADP to ATP
step eight of glycolysis (co-factor and enzyme)
phosphoglycerate mutase
step nine of glycolysis (co-factor and enzyme)
Mg2+ and enolase
step ten of glycolysis (co-factor and enzyme)
Mg2+ and pyruvate kinase
ADP to ATP
what is the general name for enzymes like kinases, isomerases, etc?
dehydrogenase
reason for aldolase’s name:
it makes an alcohol and aldehyde
reason for isomerase name?
all makes 1 isomer
why is the glucose derivative rearranged to an enol?
to make substrate more reactive
which steps of glycolysis are most likely to be regulated?
hexokinase, pfk, pyruvate kinase
what molecules might allosterically regulate the steps of glycolysis?
hexokinase (allosterically regulated by G6P)
pfk (allosterically regulated by ATP)
pyruvate kinase (allosterically regulated by ATP)
how many net atp are generated in the glycolysis pathway?
2 atp
how many molecules are produced at the end of glycolysis?
2 molecules of pyruvate, each has 3 carbons
how is the energy change between glycolysis’ steps 4 and 5 possible?
b/c glyceraldehyde-3-phosphate is being continuously drained off for the subsequent rxn in the glycolytic pathway
how is the enzyme hexokinase found in the liver different from the hexokinase (1st enzyme in glycolysis)?
hexokinase in liver phosphorylates glucose rather than other sugars
type of phosphorylation where the substrate adds the phosphate to adp….
substrate level phosporylation
what is gluconeogensis?
similar to the reversal of 10 steps of glycolysis
how many minimum atp would be needed to drive gluconeogensis?
at least 4 atp (actual # is 6)
how many pyruvate molecules enter the tca cycle per glucose molecule that entered glycolysis?
2
how many molecules of each of the following are produced in the tca cycle per glucose molecule that is completely oxidized?
atp - 2
nadh - 8
fadh2 - 2
CO2 - 6
atp is produced in the tca cycle via what type of phosphorylation?
substrate level phosphorylation
purpose of producing nadh and fadh2 in the tca cycle?
high energy reduced coenzymes carry electrons from food we eat to ETC
what happens to the co2 produced by the tca cycle?
co2 is exhaled as we can’t get any more electrons or hydrogen from it
why is it dangerous that arsenic inhibits the pyruvate dehydrogenase rxn?
cells get suffocated by not carrying out tca or etc, atp production can’t continue
what happens to the nad+ and fad made via ETC?
it’s recycled back to glycolysis and tca
final electron acceptor of nadh and fadh2
oxygen
purpose of creating proton gradient?
drive ATP synthase to make a lot of ATP
what is the p/o ration?
number of moles consumed in phosphorylation to the number of moles of oxygen atoms consumed in oxidation (or atp generated per nadh or fadh2 that is oxidized)
p/o when nadh is oxidized
3
p/o when fadh2 is oxidized
2
nadh produced in glycolysis
number of nadh: 2
p/o ratio: 3
number of atp: 6
nadh produced in kreb’s
nadh: 8
p/o: 3
atp: 24
fadh2 produced in kreb’s
fadh2: 2
p/o: 2
atp: 4
type of phosphorylation when p/o ratio is involved?
ox phos
atp generated during glycolysis and kreb’s (aerobic respiration)
38 atp (2 from glycolysis, 2 from tca, 34 from etc and ox phos)
why is cyanide toxic?
can’t continue etc, not generating enough atp
the fate of the end product of glycolysis (pyruvate) depends on…
where o2 is present or not
pyruvate that is made into lactate…
lactic acid fermentation
pyruvate that is made into ethanol
ethanol fermentation
in fermentation rxns, nad+ or nadh is generated?
nad+
what is needed for the starting material in glycolysis?
nad+
how many atp are made during fermentation?
0
why might fermentation necessary?
to involve nad+ to carry out glycolysis when there’s no o2 available
tca cycle is a central metabolic pathway that can be used both anabolically and catabolically? t or f?
false
which enzyme uses coenzyme fad as the e- acceptor?
succinate dehydrogenase
conversion of malate to oxaloacetate has a high gibbs free energy but it can take place b/c…
the oxaloacetate product is used up in the subsequent rxn
when mitochondria are actively carrying out aerobic respiration…
pH of matrix is greater than pH of intermembrane space
synthesis of atp in mitochondria is driven by…
proton/pH gradient
advantage of using multiple steps in e- transport?
more E is captured to make ATP
purpose of tca cycle?
generate reduced coenzymed NADH and FADH2 to be used in ETC to make ATP
reduction of pyruvate to lactate allows for
recycling of NAD
alcohol dehydrogenase resembled lactate dehydrogenase in that it
uses NADH as a coenzyme
