What is the difference between polysaccharides and lipids?

[Frigus]

We have defined lipids as"molecules which are insoluble in water"then why don't we consider polysaccharide as lipids as polysaccharides are insoluble in water and also on the basis of what these biomolecules are classified,
We say that carbohydrates are polyhydroxy ketones/aldehydes and lipids are molecules which are insoluble in water. It makes no sense to me as one is defined in the basis of structure and other is defined on the basis of its property,I can't find any solid foundation to classify them.

Thanks

 

[TeethWhitener]

Lipids are usually defined as substances which aren’t water-soluble, but are organic-soluble. So lipids dissolve in oil or other non-aqueous solvents. Polysaccharides which are insoluble in water are often insoluble in everything else as well—they’re insoluble by virtue of their molecular weight, not their chemical nature.

 

[Frigus]

Lipids are usually defined as substances which aren’t water-soluble, but are organic-soluble. So lipids dissolve in oil or other non-aqueous solvents. Polysaccharides which are insoluble in water are often insoluble in everything else as well—they’re insoluble by virtue of their molecular weight, not their chemical nature.

Thanks a lot sir,
But what if we found a carbohydrate that is insoluble in water due to its chemical properties.

 

[TeethWhitener]

Carbohydrates are literally hydrates of carbon, with a general formula of C_n(H₂O)_m.

The classification of biomolecules into lipids vs carbohydrates vs amino acids was built up historically based on various experimentally observed properties of the species, rather than structure. It’s turned out to be fortuitously useful, as lipids which seem totally unrelated at first glance (fatty acids vs steroids) are actually somewhat related by their biosynthetic pathway: molecules like cholesterol are synthesized in the body via a cyclization reaction of an acyclic terpenoid, another lipid and a (branched) fatty acid phosphate ester.

 

[TeethWhitener]

Also, polysaccharides are polymers of monosaccharides. So if a molecule can be hydrolyzed to monosaccharide carbohydrates, it can be classified as a polysaccharide.

 

[Frigus]

classification of biomolecules into lipids vs carbohydrates vs amino acids was built up historically based on various experimentally observed properties

Isn't carbohydrates are structurally defined and lipids on the basis of property then how can we say that these are classified on the basis on property.

 

[jim mcnamara]

@Hemant - These definitions are not meant to be taken the way you seem to want: completely perfect

Science changes over time as we learn more. Since you are sort of fixated on this definition, let's try a completely different set of examples.

Definition: Pandas (big black and white, mostly arboreal bear-like animals) were classified as bears. Now we know. They are not even closely related to bears.

Definition: Lotus plants are very like water lilies. So the lotus was classified with water lilies. Now. Turns out it is related to only one other living plant - the plane tree.

So what am I trying to get you to see?

Humans make definitions - Nature does not care at all about our definitions. Take a definition as just that - arbitrary. Not always perfect. But useful. Look up the 'Playfair axiom' to see how different definitions (axioms) can all be correct. And useful. Nature is in charge.

 

[Bystander]

They are not even closely related to bears.

https://en.wikipedia.org/wiki/Giant_panda

 

[jim mcnamara]

Oh. Another change. Thanks @Bystander my Panda example was wrong. Which proves the point:
our definitions are arbitrary.

 

[Frigus]

@Hemant - These definitions are not meant to be taken the way you seem to want: completely perfect

Science changes over time as we learn more. Since you are sort of fixated on this definition, let's try a completely different set of examples.

Definition: Pandas (big black and white, mostly arboreal bear-like animals) were classified as bears. Now we know. They are not even closely related to bears.

Definition: Lotus plants are very like water lilies. So the lotus was classified with water lilies. Now. Turns out it is related to only one other living plant - the plane tree.

So what am I trying to get you to see?

Humans make definitions - Nature does not care at all about our definitions. Take a definition as just that - arbitrary. Not always perfect. But useful. Look up the 'Playfair axiom' to see how different definitions (axioms) can all be correct. And useful. Nature is in charge.

According to me classifications can not be be wrong.
Like if we say carbohydrates are group of biomolecules that have some same properties and similarly their is another group lipids which have some properties so we have grouped them together then how one can say that the person who had classified them have classified it wrong as he/she had just observed properties or structure or some other thing and then placed them.one classification can be more useful than other but not any classification can be wrong.in this case I can't find any basis of classification which is the thing I can't understand.

 

[TeethWhitener]

According to me classifications can not be be wrong.

Counterpoint: this word exists
https://www.merriam-webster.com/dictionary/reclassify

 

[Frigus]

Counterpoint: this word exists
https://www.merriam-webster.com/dictionary/reclassify

It was just my reasoning.
I was not against the point that we can't classify things again,I was saying that if we classify things on different basis then one classification can be more useful than another.can you please tell me on basis of what biomolecules are classified.you have told that biomolecules are classified on the basis of functions but different groups of biomolecules are not defined on the basis of one thing like structure,property.
Thanks.

 

[TeethWhitener]

It was just my reasoning.
I was not against the point that we can't classify things again,I was saying that if we classify things on different basis then one classification can be more useful than another.can you please tell me on basis of what biomolecules are classified.you have told that biomolecules are classified on the basis of functions but different groups of biomolecules are not defined on the basis of one thing like structure,property.
Thanks.

I’m not sure what answer you’re looking for beyond what I’ve already provided in post 2. Lipids are biomolecules that are soluble in nonpolar solvents. There are other classification schemes that separate lipids along other lines (fatty acids vs wax esters vs steroids, etc.).

 

[jim mcnamara]

He wants something like: all lipids have carboxyl groups. Which does not always work of course. He wants a structural definition for lipids to fit differentiating it from all possible biomolecules. First off, we do not even know absolutely all of the biomolecules, so it is logically impossible.

At the risk of further failure: https://dlc.dcccd.edu/biology1-3/lipids

Please.
Read the first sentence of the lesson. It begins with the word 'Unlike'. You should completely disregard any other ideas from sources that disagree, if you want to make it in Biology courses. Or Biochem, or Biophysics.

I stop here.

 

[sysprog]

Also, polysaccharides are polymers of monosaccharides. So if a molecule can be hydrolysis to monosaccharide carbohydrates, it can be classified as a polysaccharide.

I presume that you meant 'hydrolyzed', or 'by hydrolysis converted'

 

[TeethWhitener]

Fixed.

 

[sysprog]

Fixed.

I fixed my spelling, too, Sir . . .

 

[Frigus]

Thanks,
I tried to make sense of it with help of you and it is as follows,
We have classified carbohydrates as polyhydroxy ketone/aldehydes and lipids as molecules insoluble in water or soluble in organic solvents and due to this classification majority of biomolecules fall in these categories and we have few exceptions and it is more useful to classify them as we have done now.

Thank again

 

[sysprog]

Thanks,
I tried to make sense of it with help of you and it is as follows,
We have classified carbohydrates as polyhydroxy ketone/aldehydes and lipids as molecules insoluble in water or soluble in organic solvents and due to this classification majority of biomolecules fall in these categories and we have few exceptions and it is more useful to classify them as we have done now.

Thank again

Lipoprotein analysis is a set of disciplines; it's a large area of study; it's not something that can be well summarized on a single page -- it's more like a wall of bookshelves -- we still don't understand it as well as we need to -- reading the work of others on it is challenging, and doing the research yourself is daunting -- I'm not saying don't try it, but please understand, it's far from easy.