The heme group is a highly conjugated ring system (which allows its electrons to be very mobile) surrounding an iron ion. The iron in cytochromes usually exists in a ferrous (Fe2+) and a ferric (Fe3+) state with a ferroxo (Fe4+) state

Heme Enzyme Structure and Function - Chemical Reviews - 2014 Metalloporphyrins are widely used throughout the biosphere and of these heme (iron protoporphyrin IX) is one of the most abundant and widely used. Heme shuttles electrons

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* -> TO INDEX PAGE 1 <- *

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* -> TO INDEX PAGE 4 <- *

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* visitor's guide *

Below each index page image is a single word which gives a hint to the subject on that webpage.

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Clicking on any index page image opens a webpage, which most often contains an illustrated 1,000 word essay and an image collection. External links are provided to offer in-depth discussion of the subject.

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*** The layout and organization of imagessays.com is a bit tangential by design, leading the visitor to an exploration of related subjects, informing in an unexpected manner, and so expanding the knowledge base of the viewer. ***

primary webpage: seeing

secondary webpage: marrow

annotated list of webpages: * annotated *

“Whenever I discovered something which was noteworthy,

I have felt it my duty to put down what I had discovered,

in order that it would become known to the educated world.”

Antonie van Leeuwenhoek

Letter of June 12, 1716

… see: microscope

“Sharing knowledge is the the greatest of all callings.

There is nothing like it in the land".”

The Instruction of Dua-Khety

… to his son, as he entered scribe school c. 2000 BC, Egypt - Middle Kingdom

… see: seeing

navigation

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explanation of website design

* annotated index of selected webpages *