Fats carbs and sugars

[bec]

Which specific stuctural diagrams are we likely to need to know?

Would it be enough to be able to draw glycerol and glucose? Or do you think we'd need to know how to draw stearic acid/maltose/fructose/galactose etc?

At my school we've learnt about -D-glucose and -D-glucose, but I haven't seen that in the textbook - has anyone else learnt this stuff?

Thanks!

[Toothpaste]

Page 10 of the databooklet shows you what you don't need to remember, but after drawing them heaps of times you'll probably know them anyway.

I didn't learn this in chem, but i remember it from bio. alpha-D-glucose and beta-D-glucose are structural isomers of each other. In other words the OH and the H are switched around.


beta-D-glucose


alpha

check out the right H and OH


I think this isn't in the Heinemann text ... but is in the Nelson chem text. Weird.

[bec]

ahhh the formula booklet, i forgot!

[Collin Li]

I didn't learn this in chem, but i remember it from bio. alpha-D-glucose and beta-D-glucose are structural isomers of each other. In other words the OH and the H are switched around.

Not structural isomerism. It's an isomerism that isn't in the course. As far as VCE students know, there is no difference between having the H up instead of the OH.

[polky]

I didn't learn this in chem, but i remember it from bio. alpha-D-glucose and beta-D-glucose are structural isomers of each other. In other words the OH and the H are switched around.

Not structural isomerism. It's an isomerism that isn't in the course. As far as VCE students know, there is no difference between having the H up instead of the OH.

Hm but isn't the difference between glucose and galactose just a simple switch of the H and OHs on one of the carbons? (number 4 i think) So there's no difference (to us VCE students) between glucose and galactose?

Ahh confusion.

[Collin Li]

In terms of structural isomerism, those two are the same.

But you certainly have to know of the existence of the two different forms - but I doubt you have to know anything about their chemical structure (other than the fact it has plenty of OH groups)

[Toothpaste]

In terms of structural isomerism, those two are the same.

But you certainly have to know of the existence of the two different forms - but I doubt you have to know anything about their chemical structure (other than the fact it has plenty of OH groups)

This sheet I have says they're structural isomers of each other. (biozone)

and "Optical isomers are identical in every way but are mirror images of each other" ... which sounds like what you're saying.

[Collin Li]

They don't know their chemistry.

They are isomers of each other, but they are not structural isomers of each other.

[Mao]

clarification from wikipedia:

Structural isomerism

Structural isomerism, or constitutional isomerism, is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders, as opposed to stereoisomerism.

Stereoisomerism

Stereoisomers are isomeric molecules whose atomic connectivity is the same but whose atomic arrangement in space is different.

and of course, a VCE student doesnt need to know these.

[Collin Li]

A VCE student needs to know structural isomerism (ambigious the way you said "a VCE student doesn't need to know these")

[bec]

hey
there are some things in my notes that i don't really understand - can anyone explain them?

1. “When it is oxidised, fat provides almost twice the available energy of carbohydrates because it has a lower proportion of oxygen”
why?

2. "Proteins are polypeptides that have folded into the correct structues"
What’s the “correct” structure?

3. What’s the relationship between denaturation and coagulation? Is one caused by another, do they happen simultaneously or are they just totally different things?

[orangez]

2. The correct structure is simply the structure the polypeptide needs to be in to function - so it could be the secondary structure or the tertiary structure (you don't need to know about the quarternary structure, though) eg for the haemoglobin molecule to function, it needs to be in the quarternary structure. Hence, it just depends on the type of protein.

3. Coagulation occurs after denaturation.  Protein denatured --> returns to primary structure (unaffected by extremities of heat/pH) --> coagulates (forms random bonds in secondary + tertiary structure) --> resultant polypeptide has no function. So yeah, you could say that coagulation is due to denaturation.

[Collin Li]

1. Lower proportion of oxygen means the oxidation state is lower. This means the oxidation reaction is more energetically favourable simply because now you have a more strongly oxidising compound. This makes sense with the simple definition of an oxidation: the loss of electrons. Think about what oxygen is. It is an electronegative atom. The more electronegative atoms on a molecule, the more oxidised it is, because electron density has been starved from the oxygen atoms on the molecule. This means there is less to oxidise, and hence less energy to released by oxidation.

2. This is probably not worded very well. I assume it is trying to point out a distinction between denatured proteins (a tangled mess) and the natural (opposite of de-nature) proteins as they exist in your body. However, I'd personally call them both proteins - just that the denatured protein has no biological function (since it is not in its natural shape). Or perhaps this question is alluding to some sort of primary, secondary, tertiary structure detail... but there is no such generally "correct" structure. One interesting thing to point out though, is that the peptide linkages all face the same way in a polypeptide (it must be the case, if you look at the alpha-amino acid monomer)

3. To denature something is to bring it out of its "natural" state. So denaturation can be caused by temperature and pH. When a protein is denatured, it loses its natural shape, and hence it can coagulate. Coagulation makes denaturation permanent, because it is coagulation that prevents the protein from reforming its shape (secondary and tertiary structures). By the way, coagulation is just a fancy word for "tangling."

[bec]

wow.
thank you!


another quick question - when showing the sequence of bases that will pair with, say, 5´-AAACCTGAACGA-3´, do you show 3'-TTTGGACTTGCT-5' or just TTTGGACTTGCT?

[polky]

I think both are acceptable, I doubt they would require you to know that one DNA molecule runs from 5' to 3' and the other from 3' to 5'... wouldn't hurt to show the 3' and 5' though.  Personally I would include the 3' and 5'.