Michael LinPeriod 3AP BioChapter 9 Notes (9.1-9.5)Overview: Life Is Work To perfor their an! tas"s# li$in% cells re&'ire ener%! fro o'tside so'rces. (ner%! enters ost ecos!stes as s'nli%ht and lea$es as heat. Photos!nthesis %enerates o)!%en and or%anic olec'les that the itochondria of e'"ar!otes 'se as f'el for cell'lar respiration. Cells har$est the cheical ener%! stored in or%anic olec'les and 'se it to re%enerate ATP# the olec'le that dri$es ost cell'lar *or". +espiration has three "e! path*a!s, %l!col!sis# the citric acid c!cle# and o)idati$e phosphor!lation.Concept 9.1 Catabolic pathways yield energy by oxidiing organic f!els The arran%eent of atos of or%anic olec'les represents potential ener%!. (n-!es catal!-e the s!steatic de%radation of or%anic olec'les that are rich in ener%! to sipler *aste prod'cts *ith less ener%!. .oe of the released ener%! is 'sed to do *or"/ the rest is dissipated as heat. Cata0olic eta0olic path*a!s release the ener%! stored in cople) or%anic olec'les. 1ne t!pe of cata0olic process# ferentation# leads to the partial de%radation of s'%ars in the a0sence of o)!%en. A ore efficient and *idespread cata0olic process# cell'lar respiration# cons'es o)!%enas a reactant to coplete the 0rea"do*n of a $ariet! of or%anic olec'les. 2n e'"ar!otic cells# itochondria are the site of ost of the processes of cell'lar respiration. Cell'lar respiration is siilar in 0road principle to the co0'stion of %asoline in an a'too0ile en%ine after o)!%en is i)ed *ith h!drocar0on f'el. 3ood is the f'el for respiration. The e)ha'st is car0on dio)ide and *ater. The o$erall process is, or%anic copo'nds 4 15 --6 C15 4 751 4 ener%! (ATP 4 heat). Car0oh!drates# fats# and proteins can all 0e 'sed as the f'el# 0't it is ost 'sef'l to consider %l'cose. C871518 4 815 --6 8C15 4 8751 4 (ner%! (ATP 4 heat) The cata0olis of %l'cose is e)er%onic *ith a 9 : of 98;8 "cal per ole of %l'cose. .oe of this ener%! is 'sed to prod'ce ATP# *hich can perfor cell'lar *or"."edox reactions release energy when electrons #ove closer to electronegative ato#s. Cata0olic path*a!s transfer the electrons stored in food olec'les# releasin% ener%! that is 'sed to s!nthesi-e ATP. +eactions that res'lt in the transfer of one or ore electrons fro one reactant to another are o)idation-red'ction reactions# or redo) reactions. The loss of electrons is called o)idation. The addition of electrons is called red'ction. The foration of ta0le salt fro sodi' and chloride is a redo) reaction. Na 4 Cl --6 Na4 4 Cl9 7ere sodi' is o)idi-ed and chlorine is red'ced (its char%e drops fro < to 91). More %enerall!, =e9 4 > --6 = 4 >e9 =# the electron donor# is the red'cin% a%ent and red'ces >. ># the electron recipient# is the o)idi-in% a%ent and o)idi-es =. +edo) reactions re&'ire 0oth a donor and acceptor. +edo) reactions also occ'r *hen the transfer of electrons is not coplete 0't in$ol$es a chan%e in the de%ree of electron sharin% in co$alent 0onds. 2n the co0'stion of ethane to for *ater and car0on dio)ide# the nonpolar co$alent 0onds of ethane (C?7) and o)!%en (1@1) are con$erted to polar co$alent 0onds (C@1 and 1?7). Ahen ethane reacts *ith o)!%en to for car0on dio)ide# electrons end 'p farther a*a! fro the car0on ato and closer to their ne* co$alent partners# the o)!%en atos# *hich are $er! electrone%ati$e. 2n effect# the car0on ato has partiall! BlostC its shared electrons. Th's# ethane has 0een o)idi-ed. The t*o atos of the o)!%en olec'le share their electrons e&'all!. Ahen o)!%en reacts *ith the h!dro%en fro ethane to for *ater# the electrons of the co$alent 0onds are dra*n closer to the o)!%en. 2n effect# each o)!%en ato has partiall! B%ainedC electrons# and so the o)!%en olec'le has 0een red'ced. 1)!%en is $er! electrone%ati$e# and is one of the ost potent of all o)idi-in% a%ents. (ner%! 'st 0e added to p'll an electron a*a! fro an ato. The ore electrone%ati$e the ato# the ore ener%! is re&'ired to ta"e an electron a*a! fro it. An electron loses potential ener%! *hen it shifts fro a less electrone%ati$e ato to*ard a ore electrone%ati$e one. A redo) reaction that relocates electrons closer to o)!%en# s'ch as the 0'rnin% of ethane# releases cheical ener%! that can do *or".$he %fall& of electrons d!ring respiration is stepwise' via ()*+ and an electron transport chain. Cell'lar respiration does not o)idi-e %l'cose in a sin%le step that transfers all the h!dro%en in the f'el to o)!%en at one tie. +ather# %l'cose and other f'els are 0ro"en do*n in a series of steps# each catal!-ed 0! a specific en-!e. At "e! steps# electrons are stripped fro the %l'cose. 2n an! o)idation reactions# the electron is transferred *ith a proton# as a h!dro%en ato. The h!dro%en atos are not transferred directl! to o)!%en 0't are passed first to a coen-!e called NAD4 (nicotinaide adenine din'cleotide). 7o* does NAD4 trap electrons fro %l'cose9 Deh!dro%enase en-!es strip t*o h!dro%en atos fro the f'el (e.%.# %l'cose)# o)idi-in% it. The en-!e passes t*o electrons and one proton to NAD4. The other proton is released as 74 to the s'rro'ndin% sol'tion. B! recei$in% t*o electrons and onl! one proton# NAD4 has its char%e ne'trali-ed *hen itis red'ced to NAD7. NAD4 f'nctions as the o)idi-in% a%ent in an! of the redo) steps d'rin% the cata0olis of %l'cose. The electrons carried 0! NAD7 ha$e lost $er! little of their potential ener%! in this process. (ach NAD7 olec'le fored d'rin% respiration represents stored ener%!. This ener%! is tapped to s!nthesi-e ATP as electrons BfallC fro NAD7 to o)!%en. 7o* are electrons e)tracted fro food and stored 0! NAD7 finall! transferred to o)!%en9 Enli"e the e)plosi$e release of heat ener%! that occ'rs *hen 75 and 15 are co0ined (*ith a spar" for acti$ation ener%!)# cell'lar respiration 'ses an electron transport chain to 0rea" the fall of electrons to 15 into se$eral steps. The electron transport chain consists of se$eral olec'les (priaril! proteins) 0'ilt into the inner e0rane of a itochondrion. (lectrons released fro food are sh'ttled 0! NAD7 to the BtopC hi%her-ener%! end of thechain. At the B0ottoC lo*er-ener%! end# o)!%en capt'res the electrons alon% *ith 74 to for *ater. (lectron transfer fro NAD7 to o)!%en is an e)er%onic reaction *ith a free ener%! chan%e of 953 "calFol. (lectrons are passed to increasin%l! electrone%ati$e olec'les in the chain 'ntil the! red'ce o)!%en# the ost electrone%ati$e receptor. 2n s'ar!# d'rin% cell'lar respiration# ost electrons tra$el the follo*in% Bdo*nhillC ro'te, food --6 NAD7 --6 electron transport chain --6 o)!%en.$hese are the stages of cell!lar respiration: a preview. +espiration occ'rs in three eta0olic sta%es, %l!col!sis# the citric acid c!cle# and the electron transport chain and o)idati$e phosphor!lation. :l!col!sis occ'rs in the c!toplas. 2t 0e%ins cata0olis 0! 0rea"in% %l'cose into t*o olec'les of p!r'$ate. The citric acid c!cle occ'rs in the itochondrial atri). 2t copletes the 0rea"do*n of %l'cose 0! o)idi-in% a deri$ati$e of p!r'$ate to car0on dio)ide. .e$eral steps in %l!col!sis and the citric acid c!cle are redo) reactions in *hich deh!dro%enase en-!es transfer electrons fro s'0strates to NAD4# forin% NAD7. NAD7 passes these electrons to the electron transport chain. 2n the electron transport chain# the electrons o$e fro olec'le to olec'le 'ntil the! co0ine *ith olec'lar o)!%en and h!dro%en ions to for *ater. As the! are passed alon% the chain# the ener%! carried 0! these electrons is transfored inthe itochondrion into a for that can 0e 'sed to s!nthesi-e ATP $ia o)idati$e phosphor!lation. The inner e0rane of the itochondrion is the site of electron transport and cheiososis# processes that to%ether constit'te o)idati$e phosphor!lation. 1)idati$e phosphor!lation prod'ces alost 9east and an! 0acteria are fac'ltati$e anaero0es that can s'r$i$e 'sin% either ferentation or respiration. At a cell'lar le$el# h'an 'scle cells can 0eha$e as fac'ltati$e anaero0es. 3or fac'ltati$e anaero0es# p!r'$ate is a for" in the eta0olic road that leads to t*o alternati$e ro'tes. Ender aero0ic conditions# p!r'$ate is con$erted to acet!l CoA and o)idation contin'es in the citric acid c!cle. Ender anaero0ic conditions# p!r'$ate ser$es as an electron acceptor to rec!cle NAD4. The oldest 0acterial fossils are ore than 3.5 0illion !ears old# appearin% lon% 0efore apprecia0le &'antities of 15 acc''lated in the atosphere. Therefore# the first pro"ar!otes a! ha$e %enerated ATP e)cl'si$el! fro %l!col!sis. The fact that %l!col!sis is a '0i&'ito's eta0olic path*a! and occ'rs in the c!tosol *itho't e0rane-enclosed or%anelles s'%%ests that %l!col!sis e$ol$ed earl! in the histor! of life.