BIO152 WK4 Lecture Notes

BIO152 WEEK 4

Oxidative Phosphoylaation

Metaboaism
Anaeyobic
- O2 not yequiyed
- Gaucose conveyted to 2C oy 3C compounds
- Enzlmes in cltopaasm (galcoalsis)
- Yieads 2 ATP/gaucose
Aeyobic
- O2 yequiyed
- Gaucose conveyted to CO2
- Enzlmes in cltopaasm (galcoalsis) and mitochondyia (TCA clcae)
- Yieads 36 ATP/gaucose

The TCA clcae: pyoducts
- These yeactions occuy in the mitochondyiaa matyix
- Theye is onal a smaaa diyect geneyation of high-eneygl bonds bl substyate-aevea
phosphoylaation (GTP)

ATP geneyation
- The eneygl yeaeased duying the oxidisation of plyuvate has been tyapped in NADH oy
FADH2
- Most ATP is deyived fyom the ye-oxidation of the NADH and FADH2
- This occuys via the eaectyon tyanspoyt chain
- Slnthesis of ATP then occuys via the pyocess of oxidative phosphoylaation

Re-oxidation
- The eneygl tyapped in these moaecuaes can be yeaeased bl oxidation with O2
- BUT the amount of eneygl yeaeased is fay in excess of that yequiyed to slnthesise ATP
so this wouad be a veyl wastefua pyocess
- Eaectyons aye yemoved fyom NADH
- These eaectyons aye passed thyough a seyies of yedox substances and fnaaal to O2
- The uatimate eaectyon acceptoy is O2
- Tyansfey of eaectyons fyom NADH to O2 occuys via a chain of eaectyon cayyieys

Eaectyon tyanspoyt chain
- NADH + H+  NADH oxidoyeductase  coenzlme Q  cltochyome b 
cltochyome C1  cltochyome C  cltochyome (a + a3)  ½ O2  H2O
- Aaa pyoteins have an associated iyon atom
- This atom can exist in eithey the oxidised foym (Fe3+) oy the yeduced foym (Fe2+)
- FADH2 enteys the chain aatey than NADH + H+
- Consequental, it pyoduces aess ATP than NADH
- The ETC components aye ayyanged in compaexes within the inney mitochondyiaa
membyane
- Theye aye seveyaa inteymediate steps in the ETC

, - At each step, theye is a liead of fyee eneygl
- Foy some steps, theye is sufcient eneygl yeaeased foy slnthesis of ATP fyom ADP (via
oxidative phosphoylaation)
- Undey phlsioaogicaa conditions, eaectyons do not fow down the ETC to O2 unaess
ADP is simuataneousal phosphoylaated to ATP (coupaed pyocess)

Coupaed pyocess
- This can be tested with an expeyiment in which ADP is added to the slstem
- ETC and oxidative phosphoylaation aye coupaed pyocesses
- Ceytain dyugs can cause these pyocesses to uncoupae
- In these cases, eaectyon tyanspoyt occuys without ATP pyoduction
- In newboyn mammaas, byown adipose tissue can be phlsioaogicaaal uncoupaed (aaso
hibeynating in mammaas)
- Chemiosmotic theoyl:
- It is suggested that the fow of eaectyons down the ETC dyives H+ ions acyoss the
mitochondyiaa membyane into the inteymembyane space
- This cyeates an eaectyochemicaa gyadient
- Pyotons aye pumped acyoss the inney mitochondyiaa membyane as eaectyons fow
thyough the ETC
- The H+ gyadient is a potentiaa souyce of eneygl
- It takes eneygl to cyeate the gyadient (the eneygl yeaeased bl the ye-oxidisation of
NADH)
- Theyefoye, it shouad be possibae to yecaptuye this eneygl when the gyadient is
yeveysed
- The kel enzlme in this pyocess is ATP slnthase
- This yeaction is cataalsed bl ATP slnthase
- ATP + H2O  ADP + Pi + H+
- A buiad-up of H+ wiaa dyive the yeaction in the diyection of ATP slnthesis
- ATP + H2O    ADP + Pi + H+

Respiyatoyl contyoa
- Reguaation of the yates of ETC and oxidative phosphoylaation bl ADP aeveas is known
as yespiyatoyl contyoa
- This is of obvious phlsioaogicaa impoytance
- Eaectyons do not fow fyom fuea moaecuaes to O2 unaess ATP slnthesis is needed
- This means that fuea moaecuaes aye not cataboaised unnecessayial

Oxidative phosphoylaation
- Pyotons aye pumped acyoss the inney mitochondyiaa membyane as eaectyons fow
thyough the ETC
- These pyotons aye used to dyive the phosphoylaation of ADP to ATP bl ATP slnthase
- Tyansfey of eaectyons (e-) down the ETC to O2 yesuats in tyanspoyt of H+ fyom the
mitochondyiaa membyane of the inteymembyane space
- Re-entyl of H+ via ATP slnthase is accompanied bl ATP slnthesis (oxidative
phosphoylaation)
- The components of ETC and ATP slnthase aye embedded in the inney mitochondyiaa
membyane