Chemistry ppr 4 doubt

[moon]

pls can somebody help us in solvung Q 8b June 2008 ppr4. Thanx in advance

[elemis]

CIE or Edexcel ?

[moon]

CIE

[elemis]

This is out of my depth. In a few hours time our resident chem expert will be online. She'll help you out

Just to help anyone who wishes to help moon :

Question paper is here

[nid404]

pls can somebody help us in solvung Q 8b June 2008 ppr4. Thanx in advance

Biochemistry ah.

Check the attachment. You can manipulate and have as many CH₂ groups, doesn't matter. They just want to see the type of bonding so yea

[nid404]

Analysis of a polypeptide A showed that the amino-(N-)terminal end is methionine (met)
and that the carboxyl-(C-)terminal end is lysine (lys).
Enzymic hydrolysis of the polypeptide produced the following tripeptides, with the amino
acid residue on the left having the free amino group.
met-ala-gly gly-arg-val ala-gly-arg arg-val-lys ala-gly-ala gly-ala-gly
Work out the sequence of amino acids in A, using the 3-letter abbreviations. Use each
tripeptide once only.

You can have any sequence for this. Use all 6  tripeptides and 8 residues.

The mark scheme says met-ala-gly-ala-gly-arg-val-lys

You can have

met-gly-val-ala-ala-arg-gly-lys  and the like.

[nid404]

Give two examples of how interchanging the positions of two amino acids could affect the bonding in, and hence the overall structure of, the protein.


Interchanging the position of amino acids will mean altering the primary structure of the protein. This will in turn have an effect on the bonding in tertiary & secondary structure of the protein. The disulphide bridges may get disrupted because of a change in R group (side chain) The ionic bonding and hydrophobic interactions may get altered.

[moon]

I did not understand the tripeptide question but anyways....Thank you very much for ur help.

[nid404]

I missed the b

So basically the n terminal is met and C terminal(terminal end) is lys. So the chain begins with met and ends with lys. What do you not understand exactly? :\

[moon]

why is the aminoacid  -ala - repeated twice and not  -gly-?

[nid404]

why is the aminoacid  -ala - repeated twice and not  -gly-?

like I said it doesn't matter. Only the starting n terminal should be met and terminal end should be lys.

[Greed444]

can anyone help on OCT/NOV 2007, Q5a, Q9a & Q9C(ii)

[Deadly_king]

can anyone help on OCT/NOV 2007, Q5a, Q9a & Q9C(ii)

5. You should use the half ionic equations from the data booklet.

MnO₄^- + 8H⁺ + 5e ----> Mn₂⁺ + 4H₂O

H₂O₂ ----> O₂ + 2H⁺ +2e

Then multiply the first equation by 2 while the second one is multiplies by 5 so as to balance the charges(electrons)

So you will obtain :
2MnO₄^- + 6H⁺ + 5H₂O ----> 2Mn₂⁺ + 8H₂O + 5O₂

NOTE : You will obtain 16H⁺ on the reactants side and 10H⁺ on the product size. Hence overall it will be only 6H⁺ on the reactants side.

Hope it helps.

Am still working on the two others.

[Deadly_king]

9(a). Its quite complicated for me to explain that. I mean I cannot just give you the answer like that since you will not understand anything.

Take a look at this : http://www.chemguide.co.uk/analysis/nmr/background.html#top

From what you understand, then have a look at the marking scheme. Try to see if you understand how it works. Then put it in your own words. It will be better for you since you will understand what you are writing

9(c)(ii)
From the first part it is found that G contains 4 carbon atoms.

So now we interprete the spectra ( Am starting from the right)

First peak is a triplet with chemical shift of about 1.4 : It suggests a R--CH₂--R ( from data booklet)
Second peak is a single peak with chemical shift 2 : It suggests a CH3--COOR
Third peak is a quartet with chemical shift about 4.3 : It suggests a CH3--R

Therefore by combining all these G is found to be ethyl ethanoate.

NOTE :If you don't understand how NMR works you'll not understand how i obtained the answer.

So do have a look at the notes first