mod 7 chap 7 Flashcards
atp and cellular respirtauon
catabolism is the ste of chem rxns that break down molecules into smaller units - these rxns reelase chem eenrgy that can be stored in molecules of ATP
anabolism is set of chem rxns that build molecules from smaller units - requrie input of energy usually from atp
cellular respiration is major sets of catabolic rxns in cell
during cellular resperiation fuel moecules are catabolized into smaller units releasing the enegry stored in theri chem bonds to power the work of the cell
cellular reperiation
cellular respiration is a series of catabolic rxns that convert the energy stored in food molecles into energy stored in atp
cellular respiration can be aerobic or anaerobic
most do aerobic while some bacterai respire anaerobically
oxygen is consumed in aeruobic resperiation adn co2 and water are produced along with eenrgy
molecules like carbs have large amount of potential enegry in their chem bonds while molecules like co2 and water have less potential enegry in bonds
cellular respiration reelases large amount of energy becasue usm of potnetail enegry in chem bonds of reactants is higher than that of the products
oxygen is a high energy moelcule due to weak oduble bonds so it releases a lot of eenrgy
max free enrgy released during cellular respiration is -686 kcal per mole of glucose
overall rxn for cellular respiration helps us focus on the starting reactants, final products and release of eenrgy but it misses intermediate steps
if all enegry stored inn glucose was released at once most of the enegry would be reelased as heat and the cell wouldnt be able to harness it to do work
energy is released graually in the chem rxns of cellular respiration
some of this enegry can be used to form ATP
32 molecules are usually produced
the enegry needed to form one mole of atp is 7.3 kcal so cellular respirnation harnesses at least 233.6 kcal of energy in atp for every mole of glucose
34% of the ototal enegry released by aerobic resperiation is harnessed in the form of ATP with the remainede of enegry given off as heat
substrate level and oxidatve phosphorylation
atp is produced in two ways in cellular respiration
substrate level phosphyrlation: an organic molecule trasnfers a phosphate group directly on ADP to make ATP - hydrolysis of organic molecule can reelase enough free enrgy to drive synthesis of ATP - phosphate is trasnfered to ADP from enzyme substrate in this case organic molecule - it only accounts for a small portion of total ATP generated in cellular respiration - 12%
remaing 88% is produced by oxidative phosphylation: chem energy of organic molecules is transfered frist to electron carriers - they carry electrons adn enegry from one ste of rxns to the next - they trasnport e- released during catabolism of organic moleucles to respiratory eectron trasnport chain - chain in turn tranfers e- along series of emmrbane asociated proteins to final e- acceptor and in process, harness teh energy released to produce ATP - in aerobic respiration, oxygen is final e- acceptor resulting in water - in respiration e- transort chains harness energy from fuel molecules and in photosynthesis e- transport chain harness enegry from sunlight
redox rxn in cellular respiration
chem rxns in which e- are transfered form one atom to another are called oxidation reduction rxns
oxidation is loss of e- and reductuion is gain
these rxns are coupled together - e- transfered form one molecule and passed to next - loss of e- means oxidized and gain e- is reduced
two important e- carriers are nicotinamide adenine dinucleotide and flavin adenine dinucleotide - they exist in oxidized form NAD+ and FAD and reduced form of NADH and FADH2
when fuel moeucles are catabolized some steps are oxidation rxns and they are coupled with reduction of e- carrier molecules - these rxns are usually accompanied by gain or loss of protons - you can recognize reduced moleucle by inc in CH bond and oxidized moelcule by dec in CH bond
in reduced forms, NADH and FADH2 can donate e- - as they are oxidized they transfer e- and energy to electron transport chain - they can then again accept e- form breakdown of fuel molecules
cellular respiration is redox itself - glucose is oxidized releasing co2 and oxygen is reduced forming water
4 stages of cellular respiration
- glucose is partially broekn donw to produce pyruvate and enegry is trasnfered to ATP and reduced e- carriers - this prcoess is glycolysis
- pyruvate oxidized to another molecule called acetyl coenzyme A prodicuing reduced e- carriers and releaisng co2
- cirtic acid cycle or tricarboyxlic acid or krebs cycle - acetyl group oxidized to carbon diozide and enegry is trasnfered to ATP and reduced e- carriers - amount of energy trasnfered to ATP and reduced carriers is mroe than tspe 1 and 2
- oxidative phophrylation, reduced e- carriers donate the e- to respirtory e- transort chain and large amount of ATP produced
each stage of cellular repruation consist of series of rxns which some are redox
so glcose isnt oxidized all at once
some energy harnessed is usued to syntehsize atp directly and some is stored temprarly in reduced e- carriers and then used to generate ATP by oxididtive phosphoryltain
indivdual rxns allow inital chem energy present in moelcule of glucose to be packaged in molecules of ATP and redduced e- carriers - change in free energy is greater for stesp that egenrate reduced e- carriers than those that produce ATPP directly - the energy capture in each reduce e- carrier is later used in oxidative phosphyrlation to yield up to 3 moelcules of ATP
in eukaryotes glyclysis happens in cytoplasm while pyruvate oxidation, cirtic acid cyle and oxidative phosphyraltion happnes in mitochodnria - repiratory e- transport chain is made up of proteins and small molecules associated with the inner mitochodniral membrane
in bacteria all happn in cytoplasm and respriatory e- transport chain in cell memrbane
Glycolysis
glucose is the most common fuel molecule in animals, plants and microbes
its the start molecule for glyclysis, which results in partial oxidation of glucose and the synthesis of a reletivly small amount of ATP and reduced e- carriers
glycolysis means splitting sugar - a 6c sugar glucose is split into two, yielding two 3 carbon molecules
process in anaerobic because oxygen isnt consumed
evolved in early evolution of life when oxygen wasnt present
occurs in most living organisms - most widespread metabolic pathway among organisms
glycolysis beins with a moelcule of glucose and produces two 3c molecules of pyruvate and net total of two molecules of ATP and two molecules of e- carrier NADH
ATP is produced by substrate level phosphorylation
glycolysis consist a series of 10 chem rxns whch are divided into three phases
first phase preps glucose for the next two phases by the addition of two phopshate groups to glucose
this requires input of energy
to supply that eenrgy and provide teh phosphate groups, two moelcules of ATP are hydrolyzed per moelcule of glucose
first phase is endergonic process
phosphyraltion of glucose has two important consequences - whereas glucose enters and exits cells through specific membrane transporters, phosphorylated glucose is trapped inside cell - the presence of two neg charged phosphate groups in proximity destablzied moelcules so it can be broken apart in second pahse of glycolysis
second phase is cleavage phase in which 6c moleucle is split into two 3c moelcules
for each molecule of glucose enetring glyclysis, two 3c moelcules enetr the third phase
the third phase of glycolysis is refered to ass payoff phase becasue ATP and e- carrier NADH are produced
NADH later contributes to synthesis of ATP during oxidative phophsorylation
payoff phase ends with the production of two molecules of pyrubvate
summary: glycolysis begisn with single molecule of glcusoe, this produced two molecules of pyruvate (3c) - the rxn yeilds four molecules of ATP and two molecules of NADH but since two aTP are consumed during first phase, it reuslts in net gain of two ATP and two NADH
Pyruvate Oxidation
Glycolysis occurs in almost all living organisms but it doesnt egenrate that much energy in form of ATP
the end product pyruvate still contains a good deal of chem potential energy in its bonds
in presence of oxygen pyruvate can be further oxidized to release more energy, first to acetyl coA and then eveen furtehr in series of rxns that happen in citric acid cycle
pyruvate oxidation to acetylCoA is key step that links glycolysis to cirtic acid cycle
in eukaryotes pyruvate oxidation is first step that happens in mitochondria
mitochodnira is rod shaped organelle that has a double membrane
the inner memrbane has folds that project inward
these membranes define two spaces - the space between inner and outer memrbane is intermembrane space and the space enclosed by inner membrane is mitochodnrial matrix
pyruvate is transported into mitochodnrial matrix where its converted to acetyl coA
first part of pyruvate molecule is oxidized and splits off to form carbon dixoide, the most oxidized and tehrefore least energytic form of carbon
the eletcrons lost in this process are donated to NAD+ which is reduced to NADH
the remeiang part of pyruvate molecule, acetyl group contains a large amount of potential energy still
its trasnfered to coenzyme A a moelucle that carries acetyl group to next set of rxns
synthesis of one moelcule of acetyl coA from pyruavte results in formation of one moelcule of CO2 and one moelcule of NADH
since glucose forms two pyruvate, there are two co2 and two NADH and two acetyl coA being produced from single molecule of glucose
acetyl coA is susbtarte of first step in citric acid cycle
Citric Acid Cycle
during the citric acid cycle, fuel molecules are completly oxidized
the acetyl group of acetyl coA is compeltly oxidized to carbon dioxide and the chem energy is trasnfered to ATP by substrate level phosphyrlation and to the reduce e- carriers NADH and FADH2
the cirtci acid cycle supplies e- to trasnport chain leading to prodiction of more energy in the form of ATP than is obtained by glycolysis alone
citric acid cycle occurs in the mitochondrial matrix
its composed of 8 rxns and ic a cycle because teh starting molecule oxaloacetate is regenerated at teh end
in the first rxn the 2c acetyl group of acetyl coA is trasnffered to a 4c moelcule of axaloacetate to form the 6c moleucle citric acid or tricarboylixc acid
the molecule of citric acid is then oxidized in series of rxn
the last rxn of cycle regerneates a moleucle of oxaloacetate which can join to a new acetylk group and allow the cycle to continue
the citric acid cycle results in the complete oxidation of the acetyl group of acetyl coA
bc the first rxn creates a moelcule with 6c and the last rxn generates a 4c molecule, two c are elimanted - these are released as carbon dioxide
along with release of co2 from pyruvate during pyruvate oxidation, these rxns are sources of carbon dioxide thats relesed during cellular repsiration and therefore are the sources of co2 that we exhale
4 redox rxns including the two that release co2 produce the reduced e- carriers NADH and FADH2 - this way energy released in oxidation rxns is transfefred to large quantity of reduced electron carriers - 3 moelcules of NADH and one moelcule of FADH2 per turn of cycle - these e- carriers donate e- to electron tranport chain
a single substrate level phosphrylation rxn generates a moelcule of GTP and GTP can transfer its terminal phosphate to moelcule of ADP to get ATP
overall two molecules of acetyl coA produced form single glucose yield two moelcuels of ATP, 6 moelcules of NADH and two moecules of FADH2 in citric acid cycel
some bacteria run the citric acid cicycle in reverse incorpiaing co2 into organic molecules instead of liberating it - running it in reverse required enegry which is supplied by sunlight or chem rxns
running the cycle in reverse allows an organism to build organic molecules
whetehr the cycle runs in revers eor forward directuon, the intermediates generated step by step as the cycle turns provide the building blocks for synthesizing the cells key organic molecules
ex. pyruvate is starting point for synthesis of sugar and aa alanine - other moelcules are starting points for other molecules
therefore for organisms that run teh cycle in forward direction, citric acid cycle is used to generate both eenrgy storing molecules and intermediates in syntehsis of other molecules
for organisms running cycle in reverse, its used to generate intermediates in syntehsis of other moelcules and to incorporate carbon into organic molecules
citric acid cycle is central to both synthesisu of organic molecules and to meet energy requirments of cells suggesting that it evolved early in some of the first cells to feature metabolsim
early appearence of citric acid ccyle in turn implies that great variety of buiosyntehtic and energy yeilding pathways found in mdoern cells eveolved through extension and mods of deeply rooted cycle
new cellular capabilities arose by mods of simpler more geenral sets of rxns
oxidative phosphorylation
The complete oxidation of glucose during the first three stages of cellular respiration reuslts in the e- carriers NADH and FADH2
Energy in these e- carriers is used to synthesize ATP by oxidative phosphorylation
energy in these e- carriers is released through a series of redox rxns that occur as e- pass through a chain of portein complexs in the inner mitochodniral membrane to the final e- accpetro oxugen which is reduced to water
the energy released by redox rxns isnt converted directly into chem energy of ATP
instead the passage of e- is coupled to the transfer of protons across inner mitcohindrial membrane creating a conc and charge gradient
the eelctrochem gradient provides source of potential eenrgy that is then used to drive the syntehsis of ATP
e- transoirt chain is made up of 4 large protein complexes known as I to IV that are embedded in the inner mitcohodnrial membrane - this membrane contaisn one of the highest cocn of proteisn found in eukayrotic membranes
e- dontaed by NADH and FADH2 are transported along this series of protein complexes
e- enter the e- transport chain at compelx I or II
e- donated by NADH enter at I and e- by FADH2 at II
these e- are trasnported trhough eitehr complex I or II to complex III then through complex IV
within each protein complex of e- chain, e- are passed from e- donors to e- acceptors
each donor and acceptor is a redox couple consisting of an oxidized and reduced form of molecule
e- trasnport chain contains many of these redox couples
when oxygen accept e- at end of chain its reduced to form water
this is catalyzed by complex IV
e- must be transported between the four complexes
coenzyme Q (CoQ) accepts e- from both complex I and II
in this rxn two e- and two protons are transfered to CoQ from mitochdiral matrix forming CoQH2
once formed its diffused in the inner memrbane to to complex III
in complex III the e- are trasnefred from CoQH2 to cyctochrome C and protons are released into intermemrbane space
when it accpets e- cytochrome C is reduced and diffsuses in intermembrane space and passes the e- to complex IV
the e- transfer steps within complexes are each associated with the release of energy
some of the enrgy is used to reduce teh next e- acceptor in the chain but in complexes I, III, and IV some of it is used to pump protons across inner mitochondiral membrane from the matrix to the intermemembrane space
thus the transfer of e- through complexes I III and IV is coupled with pumping of portons
result is an accumulation of protons in intermemrbane space
protons cannot passievly diffuse through the memrbane
the movement of e- through membrane embdede protein complexes is coupled to pumping of protons from matrix to intermemrbane space
resilt is proton gradient, a difference in proton conc across the inner memrbane
the proton gradeint has two components: a chem gradient and the electrcual gradient form charge of protons
this is elctrochem gradient
the proton gradient is source of potnetial energy
protons in this gradient have a high conc in the intermembrane space realtive to matrix
there is a tendency for protons to diffuse back into matrix, dirven by diff in conc and charge on two sides of the membrane
the movement is blcoekd by the memrbane
the gradient stores potential energy becasue if a pathway is opened through the memrbane, resulting movement of protons through membrane can be used to perform work
the oxidation of e- carriers NADH and FADH2 leads to generation of proton electrochem gradient - gradient is source of potential enegry used to synthesize ATP
Mitchell propsoed hypothesis to explain how enegry stored in proton electrchem gradient is used to synthesize ATP
according to his hypothesis the gradient of protons provides a source of potential enegry that is converted into chem energy stored in ATP
first for the potential energy of proton gradient to be released, there must be an opening in the membrane for protons to flow through
Mitchell sugested taht protons in intermembrane space diffuse dwon their eelctrcial and cocn gradienst through a trasnemmrbane protein channel into the matrix
second the movement of proitons through channel must be coupled with syntehsis of ATP
this coupling happens through ATP synthase, an enzyme composed of two subunits F0 and F1
F0 forms the channel in the inner mitchondrial membrane through which protons flow
F1 is teh catlytic unit that syntehsiszes ATP
proton flow through channel makes it possible for enzyme to syntehsize atp
protein flow through f0 channel causes it to rotate converting teh enegry of proton gradient into mehcanical rotational energy a form of KE
the rotation of F- subunit leads to rotation of F1 suubunit in matrix
the rotation of F1 causes conformational changes that allow it to catalyze teh synthesis of ATP from ADP and Pi
in this way chemcnail energy is conevrted to chem enegru of ATP
during this rpvocess, protons move from area of high cocn to low cocn across selectrvly permeable membrane - sismilar to osmosis
this process is called chemiosmosis
direct experimental evidence for Mitchells idea called chemiosmitic hypothesis took a decade
he founds that membrane, proton gradient and atp synthase are sufficent to synthesize ATP
approx 2.5 moelcules of ATP are produced for each NAHD that donates e- to chain and 1.5 ATP for each FADH2
overall compeket oxidation of glucose yields 32 atp form all four stages of cellular respriation
some of the enegry helds in bonds of glucose is avaible in molecule that can be readily used by cells
we began with glucose and noted that it holds chem potnetial enegry in its covalent bonds
this enegry is released throygh series of rxns and captured in chem form
some of these rxns generate ATP diretcly by usbstrate level phosphrylation
others are redox rxns that tarsnfer enegry to e- carries NADH and FADH2
tehse e- carries donate e- to eelctron tarsnprot chain
e- transport chain uses enegry in e- carries to pump protons across inner membrane
the enrgy of reduced e- carries is transormded into enegry stored in proton electrochem gradient
ATP synthase then converts enegry fo proton gradinets to roattional enegry whcih drives ysnthesis of ATP
cell now have form of eneryy that it can use in many ways to perform work
oxygen you take in is final e- acceptor in stage 4, xodiative phsohrylation
carbon dioxide breatehd out is produced in stage 2 and 3 pyruvate oxidation and citric acid cycle
the food you eat including glucose provides fuel for process enetring stage 1 glyolysis
ATP procided in stage 1,3 and 4 allows cells to work and function
anaerobic metabolism
We have followed a single metabolic path: the breakdown of glucose in the presence of oxugen to produce carbon dioxide and water
metabolic pathways often resemble intersecting roads rathr than a single linear path
ex. intermediaets of citric acid cycle often feed into other metabolic pathways
one of the major forks in the road happens at pyruvate
when oxygen is present its converted to acetyl coA which then enters the citric acid ccyle
when oxygen isnt present pyruvate is metabolzied along a number of pathways
these pathways occur in many organisms and play a role in early evolution
Pyruvate has many possible fates in the cell
in the absence of oxygen it can be broken down by fermentation, a pricess for extracting enegry from fuel moelcules that doesnt rely on oxygen or electon transport chain but intsead uses an organic molecule as an e- accpetor
fermentation is accomplished through a wide variety of metabolic pathways
these pathways are imprtant for anerobic organiss that live without oxygen and yeast and otehr organisms that favour fermentation
aerobic organisms sometimes use fermentation when oxygen cant be delivered fast enough to meet cells metabolic needs as in exercising muscle
during glycolysis glucose is oxidized to form pyruvate and NAD+ is reduced to form NADH
for glyclsysi to continue, NADH must be odized to NAD+ otherwise glycolsys would gridn to a halt
in presence of oxygen NAD+ is regenerated when NADH donates e- to e- tranpsrt chain
in absence of oxygen during fermentation, NADH is oxidized to NAD+ when pyruavte or a derivative of pyruvate is reduced
two major fermentaion pathways are lactic acid fermentaion and ethanol fermentation
during lactic acid fermetaion, e- from NADH are trasnfered to pyruvat eto produce lactic acid and NAD+
lactic acid fermentaion is carried out by some bacteria and animals in the muscle cells
we use lactic acid fermentaion to make yogurt, kimchi and pickels
ethanol fermentation also called alchol fermentaion occurs in planst and fungi
during ethanol fermentation, pyruvate releases carbon dioxide to form acetaldehyde and e- from NADH are trasnfered to it to produce ethanol and NAD+
ethanol fermentation is basis of production of alcholic beverages and breadmaking
in wine prodicion, sugar from grapes are fermentted by yeast to produce ethanol an alchol
in bread making sugars in florus are fermneted by yeast to produce ethanol which is removed by baking and cabron dixode which casues bread to rise
in both fementation pathways, NADH is oxidized to NAD+ but they dont appear in equation becasue there is no net gain or loss
NAD+ that are reduced during glycolysis are oxidized when lactci acid or ethanol is formed
the breadkown of a moleucle of glucose by fermentation yields only two ATP
the enegertic gain is small because lactic acid and ethanol arent fully oxidized and still conatin chem energy in their bonds
organisms that produce ATP through fermentation must consume a large quantity of fuel moelculs to power the cell
the four stages of cellular respriation lead to teh full oxidation of glucose and the relase of a alrge amount of enegry in its bonds
in first stage glycoslsys, glucose is partially oxdized so only some energy in the bonds is released
nearly all organisms are capable of partilay brekaing down glucose, suggesting that glyolysis evolved early in life
the atmosphere contained no oxygen when it first evolved
earliest organisms prbably used femnetation to generate ATP
fermentation occurs in cytoplasm, doesnt require oxygen and doesnt requrie proteins embded in membranes
cellular repsiration makes use of an e- transport chain that contains embedded proteisn and capable of trasnfering e- form on protein to the next and pumping proton
the resulting proton gradient powers syntehsis of ATP
like fermentation, cellular respiration can occur in the absence of oxygen but in that case, molecules other than oxygen like sulfate and nitarte are final e- acceptors
this form of repsiration known as anaerobic respiration can occur in mdoenr day bacteria
e- transprt chain in tehse bastceria is in the cell membrane
how did the system evolve?
a possibility is that early prokaryotes evolved pumps to drive protons out of teh cell in response to inceasngly acidic envirnment
some pumps mightve used energy of ATP to pump protons while others used enegry from e- trasnprit to pump protons
at some point, proton pumps pwoered by e- transport mightve generated large enough electrchem gradientthat protons could pass back through atp driven pumps, running them in reverse to syntehsize atp
orgnaisms capable of producing oxygen, cyanobacteria, didnt eveolve until 2.5 b years ago
this evolution intrdocued oxygen into atmosphere
this change lef to the evolution of new life forms with possibilities for extracting enegry from fuel moelcules like glucose
aerboic respriation, in which oxygen serves as final e- accpetor from chain, generates more energy than anaerobic repriation or fermnetation
evolution of cellular repsirtaion illustrates that evolution often works in stepwise fahsion building on whats already present
aerobic respriation picked up where anerobic repsirtion left off making it posisble to harness more energy from organic moelcules
Metabolic Integration
Cells can respond to changes in the needs of ATP, getting ATP etc
Glucose is a readily aavalble form of enegry in organisms but it isnt always broken down immedatly
excess glucose can be stored in cells and then mobilized when necessary
glucose can be stored as glycogen in animals and as starhc in plants
both are larged branched polyemrs of glucose
carbs in animal diets are broken down into glucose and other simple sugars and ciruclate in teh blood
the level of glucose in the blood is tightly regulated
when the blood of glucose is high like after a meal glucose molecules not consumed by glylysis are linked together for form glycogen in liver and muscle
glycogen stored in msucle is used to provide ATP for muscle contarction
liver doesnt store glycogen for its own use but is storehouse for whole body
glucogen can then be broken dwon as follows: glucose molecules at one end of glycogen care cleaved one by one and released as glucose 1 phosphate
glucose 1 phsopahte is converted to glucose 6 phosphate an intermediate in glycolyssi
one glucose moelcule cleaved offf a glycogen chain produced 3 atp and not two during glycolysis because the ATP consuming step 1 is bypassed
the carbs in the diet are digested to prodcue a variety of sugars
some are disacchardie some monosaccharide
disachardies are hdyrlyzed into monoscharides which are transported into cells
glucose moelcules released during digestion directly enetr glcyoslis
other sugars also enter but not as glucose
hey are converetd to intermediates of glycolysis
ex. fructose is produced by hydrolysis of sucrose and receives a phospahte group to form eitehr fructose 6 phosphate or fructose 1 phosphate
in liver the fructose 1 phospahte is cleavd and conevrted to glyceraldehyde 3 phospahet which enters glcysis at rxn 6
lipids are alsi a good source of energy
lipids are good strcuture because tehy contain lots of calories (energy) and their structure carries it
triacylglcyerol is composed of trhee fatty acid moelcules bound to glycerol backbone
these fatty acid moelcules are rich in c-c and c-h bonds whihc carry chem potential enegry
the small intestine absorbs traicylgerols which are then transported by blood stream and are either consumed or stored in fat tissue
tracylgeorls are broken down inside cells to glycerol and fatty acids
fatty acids are shortedned by series of rxns that remove two c units form their ends - known as beta oxidation and it prduced NADH and FADH2 molecules that provide e- for synthesi of ATP by oxidative phosphrylation
the end prduct of rxn is acetyl coA which feeds to citric acid cycle and leads to pridcytion of additional reduced e- carriers
oxidation of fatty acids produces large amount of ATP
ex. palmitic acid (a fatty acid) yeilds abt 106 moelcules of ATP
fatty acids are useful and efficent source of enrgy but they cant be used by all tissues of the body
like the brain and RBC depend on glucose for enegry
proteins are a soruce of chem enegry that can be broken down as well
proteins are first broken down to aa which enter at various points in glyclsus, pyrvate oxidation and oxidation ccycle
ATP is key end product of cellular repsiration
atp is constantly being turned over in cell, broken down to ADP and Pi to supply cells enegry needs and resntheiszed by fermentaion and cellular resipration
level of ATP inside clel can be indicator of how much energy cell has availble
whne atp is high there is lot of free enegry for processes so the pathways that geenrate atp are slowed
when atp is low these pathways are activated
other inetrmdiates of cellular repsiration like NADH have similar effects that high NAD+ stimulate cellular repsiration whereas high NAHD inhibits it
the cell uses serveal mehcanisms like regulation of enzymes that control key steps of pathays
one key rxn is rxn 3 of glyclysis
in this rxn frutose 6 phosphate is converted to furctiose 1,6 bisphate and atp is consumed
key step because its endogronci and irreversible - commited step and is tightly controlled
this rxn is catalyzed by enzyme phosphofructokinase 1 (PFK1) - metabolic valves that regualtes rate of glycolsysis
pfk 1 is an allosteric enzyme with many actiavtor and inhibtors
adp and amp are allosteric actiavtors of pfk1 - whne they are abundant one or the other binds to enzyme causing the shape to change and this actiavtes enzyme increasing rate of glycoslsu and syntehsis of atp
when atp is abundant then it is an inhibtor of enzyme - it binds to the same site and inhibits the enzyme activty slowing the rate of atp production and glycolysis
pfk1 is also regyalted by downstream product - citaret
citrate acts as allosteric inhibtor of enzyme slowing the activty - high citate indicates that its not being consumed by citric acid cycle and glucose rbeakdown should slow down
think abt excerise
exercise is form of kinetic energy power by ATP in muscle cells
muscle cells do not contain lots of ATP and stored ATP is depeleted within seconds by exercise
muscle cells rely on fuel moecules to genrate ATP
for busrt of activty, muscle can convert stored glycogen to glucose then rbeak dwon glucose anerobically to pyruvate and lactic acid by lactic acid fermnation
pathway is rapid but doesnt egenrate a lot of aTP
for more sustained exercise other pathways come into play
msucle cells contain mitcohdornai which produces atp by aerobic respiration
energy yield is much greater but is slower - this is why runners cant maintain pace of spirnt for longer runs
for longer exercise, liver glcogen supplements msucle glycoge: the liver rleases glucose into blood thats taken up by msucle cells and oxidized forATP
fatty acids are released form adipose tissue and taken up by muscl clels where teh fatty acids are broken down by b oxidation - yields more atp but process is slower
storage forms of enegry moelcules like fatty acids and glycogen contain large reservoirs of enrgy but are slow to mobilize
exercise takes coordination between diff cells, tissues and metabolci pathways to ensure adequte ATP to meet needs of working muscle
