Full mechanism, in text

Each one's job in making energy

1 · Sugar needs B1's gate to get in

To be burned in the mitochondrion, pyruvate must pass the PDH gate, which only accepts TPP, the active form of B1, so without B1 the sugar cannot be burned.Glycolysis splits glucose into pyruvate in the cytosol — no B1 needed up to here.

The bottleneck is the next step: to be burned inside the mitochondrion, pyruvate must pass the PDH (pyruvate dehydrogenase complex) gate, and PDH's E1 subunit only accepts TPP — the active form of B1 after two phosphates are attached.

Without B1 the gate is shut: glycolysis keeps running, pyruvate piles up outside, and the excess is reduced to lactate. The sugar hasn't gone anywhere — it just can't be burned.

(The chemistry inside that gate is taken apart in the vitamin B1 story; here we only mark where it sits on the whole line.)

2 · Inside the cycle: B5 delivers, B3/B2 collect

Past the gate, CoA, built from B5, delivers the 2-carbon fragment into the cycle, and and FAD, made from B3 and B2, carry off the electrons each turn captures.Past the gate, the 2-carbon fragment is taken by CoA — and CoA's backbone is B5 (pantothenic acid). Every 'CoA' in 'acetyl-CoA' contains a share of B5.

Inside the cycle, one turn produces not but captured electrons:

B3 becomes , accepting electrons at three points in the cycle → NADHB2 becomes FAD, accepting electrons at the succinate dehydrogenase step → FADH₂
So one turn really yields 3 NADH + 1 FADH₂ + 1 GTP. B5 brings the cargo in; B3 and B2 carry the electrons out — none of the three supplies energy, but the cycle cannot complete if any one is missing.

3 · Hand the electrons to the chain — ATP appears here

and FADH₂ hand their electrons to the electron transport chain, whose two entrances are both guarded by B2, and the pumped protons let synthase make ATP. and FADH₂ aren't energy themselves — they're batteries holding electrons. is actually made on the electron transport chain.

NADH hands its electrons to Complex I — whose entry prosthetic group is FMN, which is B2 againFADH₂ enters at Complex II — that FAD is B2 as well
Electrons travel down the chain, each segment pumping protons across the membrane, and ATP synthase finally spins ATP out of that proton flow.

Put the first three steps together: B1 opens the gate · B5 delivers · B3 grabs electrons · B2 both grabs them in the cycle and guards both entrances to the chain. Now the error in 'B vitamins give you energy' is visible — not one of them sits in the ATP box; they sit on every segment of the road leading to it.

4 · Fat and amino acids merge onto the same line

Fat and amino acid breakdown merge onto the same line with the same B5, B2 and B3, plus B6 and B7, and whichever one is missing jams one lane.Sugar isn't the only fuel, but the other two routes merge onto the same line, using the same crew.

Fat (β-oxidation): every 2-carbon fragment cut off needs a CoA (B5) to catch it, while B2 (FAD) and B3 () each collect electrons once. More rounds, more repeats — the same carriers as in the cycle.

Amino acids: B6 (PLP) takes over, running transamination and decarboxylation to strip the amino group and feed the carbon skeleton into the cycle; breaking down branched-chain amino acids additionally needs B7 (biotin) for carboxylation.

So the whole picture lands on one sentence: no single B vitamin can give you energy on its own, but each one missing jams exactly one lane. The converse holds too — for someone who isn't short, adding more won't make this line run faster.

Full mechanism, in text

1 · Sugar needs B1's gate to get in

2 · Inside the cycle: B5 delivers, B3/B2 collect

3 · Hand the electrons to the chain — ATP appears here

4 · Fat and amino acids merge onto the same line

B family · division of labour on the energy line

Full mechanism, in text

1 · Sugar needs B1's gate to get in

2 · Inside the cycle: B5 delivers, B3/B2 collect

3 · Hand the electrons to the chain — ATP appears here

4 · Fat and amino acids merge onto the same line

B family · division of labour on the energy line