Stankovic123's chem q's

[zvezda]

Don't forget the variable side groups (R groups) on each amino acid residue. Some of these contain carboxylic acid groups that can be deprotonated or amino groups that can be protonated depending on the pH. This will in turn have an effect on the ionic interactions between residues, thus potentially changing the tertiary structure of enzymes, or indeed any protein.

thanks. appreciate it

[zvezda]

Was doing a few checkpoints questions when I cam across this q:
"Why does the breakdown of sucrose require the presence of both water and sucrase?"
I was thinking that the water molecules would be needed to separate each dissacharide molecule so that as a result, the sucrose would be able to fit into the active sight of the sucrase enzyme, which would be needed to catalyze the break down into glucose and fructose. Water would also be needed for this hydrolysis reaction as the addition of an H2O molecule is required for there to be glucose and fructose as products.
What the answers had was: "The breakdown of sucrose to glucose and fructose is a hydrolysis reaction, for which water is required. Sucrase is needed to increase the rate of the reaction".
Isnt that too basic??
Btw, this was a VCAA question from the 09 exam.

[Ancora_Imparo]

The question was only worth one mark. Thus, an answer that briefly specifies the role of water (required for hydrolysis of sucrose) and sucrase (needed to catalyse hydrolysis reaction) is sufficient.

[zvezda]

The question was only worth one mark. Thus, an answer that briefly specifies the role of water (required for hydrolysis of sucrose) and sucrase (needed to catalyse hydrolysis reaction) is sufficient.

yeah I suppose thats fair enough.


Another question, In Heinemann, it describes how making aspiring soluble involes converting it into a sodium salt (ion), rendering it soluble. At first I didn't understand how it could be an ion, believing it would be an ionic compound instead. Ive done a small bit of research on google, and from what I've read (I may have even misinterpreted), is that one would add aspirin to a basic solution such as NaHCO3, and an acid-base reaction would take place, generating H2CO3 and the sodium salt (which is actually in the form of 2 ions dissolved in water). Would this be correct?

[Ancora_Imparo]

Another question, In Heinemann, it describes how making aspiring soluble involes converting it into a sodium salt (ion), rendering it soluble. At first I didn't understand how it could be an ion, believing it would be an ionic compound instead. Ive done a small bit of research on google, and from what I've read (I may have even misinterpreted), is that one would add aspirin to a basic solution such as NaHCO3, and an acid-base reaction would take place, generating H2CO3 and the sodium salt (which is actually in the form of 2 ions dissolved in water). Would this be correct?

Correct. The sodium salt of aspirin, known as sodium acetylsalicylate, exists as positively charged sodium ions and negatively charged acetylsalicylate ions when dissolved in water. So, if you needed to draw the structural formula of the sodium salt of aspirin, you would definitely not draw a line between the Na and O on the carboxyl group, as this would indicate a covalent bond. Instead, you would put a '-' sign next to the O and a '+' sign next to the Na to indicate an ionic interaction.

[zvezda]

Correct. The sodium salt of aspirin, known as sodium acetylsalicylate, exists as positively charged sodium ions and negatively charged acetylsalicylate ions when dissolved in water. So, if you needed to draw the structural formula of the sodium salt of aspirin, you would definitely not draw a line between the Na and O on the carboxyl group, as this would indicate a covalent bond. Instead, you would put a '-' sign next to the O and a '+' sign next to the Na to indicate an ionic interaction.

thanks for the clarification.

[zvezda]

Hey, how would an enzyme work to catalyse the hydrolysis of a protein. By the VCE standard, I know that there's an active site in an enzyme which is where the peptide bonds would be weakened. However, how would a polymer such as a protein fit into an active site?

[zvezda]

Another question, with an amino acid, if it was added to an acidic/basic solution, couldn't the Z groups be affected rather than the primary -NH2 and -COOH groups?

[zvezda]

one other thing that's been bothering me, in the Heinemann text when it explains the changes in the zwitterion in different levels of pH solution, it gives two equations with reversible arrows showing the change in the zwitterion structure. Technically, if such a reaction could reverse itself, the pH would be changing according to the other compound (eg HCl), wouldnt it?

[Bad Student]

Are zwitterions part of the course? I have never ever heard of them in my entire life.

[Ancora_Imparo]

Are zwitterions part of the course? I have never ever heard of them in my entire life.

Yes they are. A zwitterion is a molecule that has both a positive and negative charge, therefore making it overall neutral. In Chem 3/4, you need to know that amino acids, at pH values of around 7 (neutral), exist as zwitterions. That is, the -COOH group is deprotonated to give -COO^- and the -NH₂ group is protonated to give -NH₃⁺.

[Ancora_Imparo]

Another question, with an amino acid, if it was added to an acidic/basic solution, couldn't the Z groups be affected rather than the primary -NH2 and -COOH groups?

Yes they can, although they aren't considered for VCE 3/4 unless the stem of the question gives you extra information. It has got to do with things called pK_a values, and unless you are given this information, you won't be expected to know when the side groups will be protonated/deprotonated.

[zvezda]

Yes they can, although they aren't considered for VCE 3/4 unless the stem of the question gives you extra information. It has got to do with things called pK_a values, and unless you are given this information, you won't be expected to know when the side groups will be protonated/deprotonated.

Right. I think that might actually be in unit 4. Thanks

[zvezda]

Say that you had an analytical question involving gases, and you were given temperature in degrees Celsius with 2 sig figs, yet the rest of the values given had 3 sig figs, would you go with 2 or 3 sig figs in your final answer?
A lot of questions I've done ignore the 2 sig figs and just answer in 3.
Thanks in advance

[Mao]

a 2 s.f. Celsius temperature is 3 s.f. in Kelvin. This is because addition/subtraction don't follow the same s.f. rules as multiplication/division.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch1/sigfigs.html#add