What is the difference between polysaccharides and lipids?

  • Thread starter Hemant
  • Start date
  • #1
219
28

Main Question or Discussion Point

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
 

Answers and Replies

  • #2
TeethWhitener
Science Advisor
Gold Member
1,758
1,112
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.
 
  • Like
  • Informative
Likes sysprog, MalcolmB, hutchphd and 2 others
  • #3
219
28
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.
 
  • #4
TeethWhitener
Science Advisor
Gold Member
1,758
1,112
Carbohydrates are literally hydrates of carbon, with a general formula of Cn(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.
 
  • Like
Likes sysprog and BillTre
  • #5
TeethWhitener
Science Advisor
Gold Member
1,758
1,112
Also, polysaccharides are polymers of monosaccharides. So if a molecule can be hydrolyzed to monosaccharide carbohydrates, it can be classified as a polysaccharide.
 
Last edited:
  • Like
Likes Hemant
  • #6
219
28
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.
 
  • #7
jim mcnamara
Mentor
3,905
2,292
@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.
 
  • Like
Likes sysprog, BillTre and Hemant
  • #9
jim mcnamara
Mentor
3,905
2,292
Oh. Another change. Thanks @Bystander my Panda example was wrong. Which proves the point:
our definitions are arbitrary.
 
  • Like
Likes BillTre, Hemant and Bystander
  • #10
219
28
@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.
 
Last edited:
  • #12
219
28
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.
 
  • #13
TeethWhitener
Science Advisor
Gold Member
1,758
1,112
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.).
 
  • Like
Likes Hemant and sysprog
  • #14
jim mcnamara
Mentor
3,905
2,292
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.
 
  • Like
Likes Hemant, TeethWhitener and sysprog
  • #15
1,442
760
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'
 
Last edited:
  • Like
Likes TeethWhitener
  • #16
TeethWhitener
Science Advisor
Gold Member
1,758
1,112
Fixed.
 
  • Like
Likes sysprog
  • #18
219
28
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
 
  • Like
Likes sysprog
  • #19
1,442
760
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.
 
  • Like
Likes Hemant

Related Threads on What is the difference between polysaccharides and lipids?

Replies
1
Views
1K
  • Last Post
Replies
1
Views
14K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
12
Views
7K
Replies
5
Views
6K
  • Last Post
Replies
1
Views
2K
Replies
2
Views
1K
Replies
1
Views
19K
Replies
1
Views
954
Top