Heme: Introduction

by Kevin Ahern, PhD

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    00:02 In another set of these lectures, I've talked about the importance of heme for carrying oxygen within hemoglobin.

    00:08 In these set of lectures, I'll talk about how that heme is made and how the iron in the heme is transported and stored in the body.

    00:17 Now, heme is as you've seen in the other lectures, a flat, planar structure that contains a porphyrin ring with an atom of iron at its very center.

    00:26 The ring structures that hold the iron can serve as a sink for electrons and this can be valuable also for the process of electron transport.

    00:35 The ring also enables the carrying of oxygen which is what happens inside of hemoglobin.

    00:40 So, hemes are usually found attached to proteins.

    00:43 That's true whether they're in the electron transport system or they're contain within a hemoglobin or myoglobin.

    00:49 The examples, of course, include these proteins: hemoglobin, myoglobin and the cytochromes of the electron transport system.

    00:56 The names of the cytochromes in the electron transport system come from the hemes that they contain.

    01:01 Cytochrome a, for example contains heme a.

    01:05 The ring structure that's found in the hemes of hemoglobin, myoglobin and cytochromes is also found in the chlorophyll.

    01:13 And in the chlorophyll, the ion is replaced with the magnesium at its center.

    01:17 The cobalamins, also known as vitamin B12, have a cobalt at their center instead and we can see that here.

    01:24 Now, the structure and function of hemes is related to their planar structure.

    01:28 And we can see that the various hemes have a very similar central structure as we see in Heme A, Heme B , Heme C and Heme O.

    01:37 And we see that the primary differences of these different forms of heme are due to alterations on the outer part of the molecule.

    01:43 These have little effect on the function of each of the individual hemes.

    01:48 Heme A is found as part of the complex IV of the electron transport system and it’s the part where oxygen is reduced.

    01:56 Heme B is the most common type that we see and it's found in hemoglobin, myoglobin, peroxidase enzymes and cycloxygenase enzymes for making prostiglandins.

    02:05 Other proteins that contain heme B include the P450 hydroxylation system of the liver and the nitric oxide synthase system that we've talked about in other lectures.

    02:15 Now heme C is found as the name would suggest in cytochromes C, a very important protein in the electron transport system.

    02:22 And it links to the protein via cysteines, the sulfur side chains.

    02:27 Heme O functions in bacterial oxygen reduction very much like the heme A does where the complex IV reduces oxygen.

    About the Lecture

    The lecture Heme: Introduction by Kevin Ahern, PhD is from the course Amino Acid Metabolism.

    Included Quiz Questions

    1. It is usually attached to a protein
    2. It has a molecule of Fe+++ at its center
    3. It is found in chlorophyll with cobalt at its center
    4. All of the answers are true
    5. None of the answers are true
    1. All of the answers are true
    2. Heme B is the most common type of heme
    3. Heme A is involved in electron transport
    4. Heme D is a bacterial form that is involved in oxygen reduction

    Author of lecture Heme: Introduction

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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