Meaning of "key"

[All Potted Out]

"The blastocyst now consists of many hundreds of cells and small sugar molecules form on its surface. These give it the necessary firm foothold in the uterus as they key into similar molecules on the endometrium."

Does "these" refer to "small sugar molecules"?
What does "key" mean in this context?

[Mister Micawber]

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'These' are indeed the small sugar molecules.
'Key' I suppose means that they interlock or doing something chemically similar. The sugar molecules on the blastocyst form some sort of chemical bonds with similar sugar molecules on the uterine wall.
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Native English teacher at Mister Micawber's

[Yankee]

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I sure am relieved that you tackled that one, MM. :D
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln