0
$\begingroup$

Why would the following medium not be considered a chemically defined medium:

Glucose, 5 grams (g); NH4Cl, 1g; KH2PO4, 1g; MgSO4, 0.3g; yeast extract, 5g; distilled water, 1 litre

I am unsure why it is not a chemically-defined medium considering all measurements and grams are given and such is required for it to be one. Therefore I am unsure why it would not be a chemically defined medium.

$\endgroup$
  • 1
    $\begingroup$ Welcome to Biology.SE. Your question appears to be a homework question that is considered off-topic on this site, unless you show attempts to answer your question. Please edit accordingly and give information about what you think could be a possible answer and people will be glad to help you. Additionally, please edit your title so that it gives an actual question. Otherwise your question will very likely be closed and left unanswered. Thanks. :) $\endgroup$ – AlexDeLarge May 11 '17 at 12:56
  • 1
    $\begingroup$ Please read this before posting homework questions $\endgroup$ – RHA May 11 '17 at 12:56
  • 1
    $\begingroup$ Agree that this should be closed as homework, but I'll give a hint: Look at all the ingredients. Do you know precisely what each and every one is, chemically? Or is there at least one ingredient that is more ambiguous... $\endgroup$ – Bryan Krause May 11 '17 at 16:15
  • 1
    $\begingroup$ @canadianer And I thought my hint was too obvious :-P $\endgroup$ – Bryan Krause May 11 '17 at 18:45
  • 1
    $\begingroup$ For what it's worth, I think the subsequent edit by the OP shows sufficient effort for this question to remain open. I think it's clear where their confusion comes from. $\endgroup$ – canadianer May 11 '17 at 18:49
6
$\begingroup$

A chemically defined medium is, according to this Wikipedia article:

... a growth medium suitable for the in vitro cell culture of human or animal cells in which all of the chemical components are known.

Four of the five components fit this criterion precisely, as they are chemical formulae (and of course a common name for a compound whose formula is well known).

However, even though you know exactly how much yeast extract was added to the medium, you do not know its exact chemical composition. To be sure, assays of the chemical composition of yeast extract have been run, and one could come up with approximations of it's makeup. But the bottom line is that there is no precise chemical formula for yeast extract as there are for the other components of the medium.

$\endgroup$
  • $\begingroup$ it does make a bit of a difference :) $\endgroup$ – Gerhard May 12 '17 at 7:12
-3
$\begingroup$

The yeast extract would consume and metabolize some of the medium components and metabolic products will be formed. This new introduction of products by the yeast, whether waste materials or otherwise, is unaccounted for and changes the composition of the medium. Therefore, it would no longer be chemically defined.

$\endgroup$
  • 2
    $\begingroup$ This is wrong. Yeast extract is prepared from yeast cells by removing cell walls, see here. $\endgroup$ – Chris Oct 16 '17 at 11:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.