the atp is generated by two methods in our body, one is oxidative phosphorylation which uses energy from reduction of NADH and FADH2, this is the major supply n for every NADH we make 3ATPS n FADH2 makes 2ATPS in ETC.NADH n FADH2 are produced in cytoplasm n to get into mitochondria under aerobic conditions need shuttle service.malate shuttle relys on NADH n G3P on FADH2 the no. of ATPs produced with both is different, malate n G3p shuttles are not electron transport chain but merily shuttles used to transport NADH n FADH2 energy across mitochondrial membrane. which then are used in the ETC.
second method of ATP production is susbstrate-level phosphorylation which produces ATP directly from ADP but is low yeild as only 2 ATPS/glucose.this happens in glycolysis.in aerobic condition, glycolysis will proceed to TCA n Oxidative phosphorylation which will produce the major bulk of ATPs.
glycolysis=2ATP/glucose+(1NADH)x2 for every glucose
now if NADH uses malate shuttle it will produce 3ATPs n with G3P only 2.so total glycolysis ATPs under aerobic conditions ATP can be either 8 with malate or 6 with G3P.obviously these shuttles are needed only under aerobic conditions, anaerobically substrate level phosphorylation is the only source.
so glycolysis=8ATP
now pyruvate produces NADH while converting to acetyl coA n each glucose gives 2 pyruvate so 2 NADH=6ATP
TCA=3NADH(3ATP/NADH)+1FADH2(2ATP/FADH2)+1GTP which means
(3x3+2+1GTP)X2 for everything per glucose.as TCA deals WITH three C n glucose gives two Acetyle CoA so evrything doubles up in TCA.
so TCA=24
so 8+6+24=38ATP
this calculation has been done assuming that every molecule of NADH will use malate shuttle to enter mitochondria.