Heme Synthesis Pathway

Question 1

First step in heme synthesis

Answer 1

Succ-CoA + Glycine

Enzyme: ALA synthase

—->ALA

Rate limiting step

Occurs in mitochondria

Question 2

Second step in heme synthesis

Answer 2

Occurs in cytosol

2 ALA

Enzyme: porphobillinogen synthase

—-> porphobillinogen

Question 3

Third step in heme synthesis

Answer 3

porphobilligen

Enzyme: porphobilligen deaminase

—> hydroxymathylbilane

Question 4

Fourth step in Heme synthesis

Answer 4

Hydroxymethylbilane

Enzyme: uroporphyrinogen III cosynthase

—> uroporphyrinogen III

Question 5

Fifth step in heme synthesis

Answer 5

Uroporphyrinogen III

Enzyme: uroporphyrinogen decarboxylase

—> coporphyrinogen III (IS IN MITOCHONDRIA AGAIN HERE)

Question 6

Sixth Step in Heme Synthesis

Answer 6

Coporphyrinogen III

Enzyme: coproporphyrinogen oxidase

—–> Photoporphyrinogen IX

Question 7

Seventh Step in Heme Synthesis

Answer 7

Photoporphyrinogen IX

Enzyme: Protoporphyrinogen oxidase

—->Protoporphyrin IX

Question 8

Eighth Step in Heme Synthesis

Answer 8

Photoporphyrin IX

Enzyme: Ferrochetalase

—-> HEME

Heme negatively feeds back to start of loop (inhibits more heme production)