respiration

• location of respiration processes:

  • glycolysis: cytosol
  • link rxn: mm
  • kreb's cycle: mm
  • oxidative phosphorylation: inner mito memb (cristae)
• glycolysis:

  1. initial investment of 2 ATP mol: 1 phos grp from each of the 2 ATP used to phosphorylate glucose, producing fructose 1,6-bisphosphate (6c)
  2. lysis: of 1,6 bisphosphate (6c) to glyceraldehyde-3-phosphate (3c)
  3. oxidation by deH: G3P oxidised by deH, at the same time, coenzyme NAD+ reduced to NADH. as rxn is highly exergonic, energy released adds 2nd phosphate group to form 1,3-bisphosphoglycerate (3c)
  4. slp: 13BP dephos, forming pyruvate. 2 phos grp of 1,3BP transferred to 2 ADP mol via enzymes, forming ATP
• benefits of phosphorylation of glucose:

  1. activates sugar: more reactive and commits it to glycolytic pathway
  2. confers negative charge on glucose, making it impermearable, cannot diffuse across csm, trapped in cytosol
• glycolysis: net gain 2 ATP & 2 NADH (per glucose)

  eqn: glucose + 2ADP + 2Pi + 2NAD+ -> 2 pyruvate + 2 ATP + 2 NADH
• link rxn: if O2 present, pyruvate (3C) enters mito matrix via ATP via a transport protein

  eqn: 2 pyruvate -> 2 acetyl CoA + 2 NADH + 2 CO2
• krebs cycle:

  • acetyl CoA enters cycle by combining with oxaloacetate (4c), forming citrate (6c)
  • citrate is deC and deH to form a-ketoglutarate & NADH & CO2
  • oxaloacetate is regenerated, involving 1 deC step yielding 1 CO2, 3 deH step, yielding 2 NADH & 1 FADH2, 1 SLP yielding 1 ATP
• does kreb cycle produce bulk of ATP from a glucose mol?

  not directly. most E released in Krebs cycle is carried by NADH and FADH2 produced. the mobile e- carriers with their reducing powers will then be transported to the ETC where bulk of ATP is produced
• adapation of cristae:

  1. many ETC
  2. many ATP synthases
• oxidative phosphorylation:

  1. NADH produced from g+lr+kc donates e- to 1st EC which then passes e- to next carrier and so on.
  2. as high energy e- travel down EC, energy released is coupled to pumping of H+ from MM into IMS via some ETC carriers, [H+] in IMS > MM, building up proton-motive force across cristae
  3. As H+ diffuses down its conc grad through ATP synthase, ADP is phosphorylated to ATP
  4. O2 acts as final e- acceptor, accepts e- and combines with H+ forming H2O
• ETC func:

  1. generate proton-motive froce to produce ATP
  2. regenerate coenzyme NAD+ and FAD, without regeneration, g+lr+kc cannot continue efficiently
• O2 FUNCTION:

  1. final e- acceptor: allowing OP to continue, generating ATP via chemiosmosis
  2. regenerate coenzyme: allow NAD+ & FAD to pick up more e- from g+lr+kc
  3. reduction of O2 to form H2O removes H+ from MM, contributing to generation of PMF across CMS
• anaerobic respiration: (2 ATP/glucose)

  1. alcohol: pyruvate decarboxylase converts pyruvate to ethanal via deC
  2. alcohol dehydrogenase reduced ethanal to ethanol, while removing H+ from NADH, forming NAD+
• anaerobic respiration (2 ATP/glucose)

  • yeast: pyruvate converted to lactate via lactate dehydrogenase, while removing H+ from NADh forming NAD
• muscle fatigue: lactic acid accumulates faster than it is removed
• Lactate is transported in the blood

  to the liver where it is converted

  back to pyruvate which can then

  enter the link reaction again during

  aerobic respiration.
• limitations of anaerobic:

  • due to incomplete breakdown of glucose, ethanol/lactate still contains larger pptn of energy originally contained in glucose