Exam (elaborations)
Biochemistry test exam with answers
- Course
- Institution
- Book
Biochemistry test exam with the answers already listed from . The test exam without answers is free on my profile
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
More summaries for
-
Hypoglycaemia
-
Glycolysis pathway
-
Diabetes
Seller
Follow
markbogers
Content preview
Exam Biochemistry NWI-MOL008AFriday 18 January 2019
• Write your name and student number on each piece of paper.
• Answer the multiple-choice questions on the appropriate form.
Rating: 50% of the final test grade is the open questions 1-8.
50% of the final test grade is the multiple-choice questions 1-40
Open questions:
1. Proteins are large molecules usually composed of hundreds of amino acids sequentially linked together by
peptide bonds. Below, you find the sequence of a short peptide:
IAKTWPQECAAD
(a) Draw the chemical structure of this short peptide at pH 7, clearly indicating the N-terminus, the C-
terminus, the peptide bonds and the side chains of each amino acid residue. (3.5 points) The appendix table 3.1
might be useful for reference.
(b) What are the charges of the N-terminus, the C-terminus, and the side chains of each amino acid residue at
pH 12? Consult Table 3-1, draw the chemical structure at this basic pH and briefly motivate changes in the
amino acid residue charges, if they are present. (4 points)
(c) The primary structure of large polypeptides or proteins dictates their final three-dimensional architecture.
What is the tertiary structure of a protein and do filamentous proteins have a tertiary structure? (2.5 points)
The overall three-dimensional shape of an entire protein molecule is the tertiary structure. The protein
molecule will bend and twist in such a way as to achieve maximum stability or lowest energy state. All
proteins have a tertiary structure.
Page 1 of 12
, 2. Aspirin is a commonly used drug. In our body, absorption via the oral route normally occurs when the drug is
in the unionized state, as unionized molecules are more lipophilic and can better cross the cell membrane.
Knowing that Aspirin has a pKa of 3.5:
(a) Calculate the ratio of ionized/unionized of the drug in the stomach, where the pH is 1. (4 points)
pKa of aspirin = 3.5; pH of stomach = 1; pH of intestine = 6
Unknown = log [ionized]/[unionized].
Henderson-Hasselbalch equation for stomach:
pH of stomach = pKa of aspirin + log [ionized]/[unionized]
1 = 3.5 + log [ionized]/[unionized]
log [ionized]/[unionized] = 1-3.5
log [ionized]/[unionized] = -2.5
thus, [ionized]/[unionized] = Antilog (-2.5)
[ionized]/[unionized] = 0.00316. This means that for every 3 ionized molecules in the stomach there are
almost 1000 unionized molecules, suggesting that aspirin is largely unionized in the stomach (99.7%
unionized).
(b) Calculate the ratio of ionized/unionized in the intestine, where the pH is 6. (4 points)
pH of the intestine = pKa of aspirin + log [ionized]/[unionized]
6 = 3.5 + log [ionized]/[unionized]
log [ionized]/[unionized]= 6 – 3.5
log [ionized]/[unionized] = 2.5
[ionized]/[unionized] = Antilog (2.5)
[ionized]/[unionized] = 316.2 This means that for 316 ionized molecules of aspirin in the intestine there is
only 1 unionized molecule, suggesting that aspirin is largely ionized in the intestine (99.7% ionized).
(c) Based on these calculations, is aspirin more likely absorbed in the stomach or in the intestine? (2 points)
In the case of aspirin, which is an acidic molecule, based on the above calculations we can see that it is
more unionized in the stomach than in the intestine. Thus majority of the aspirin is absorbed via the
stomach under acidic pH.
3. Mammalian antibodies of the immunoglobulin G type consist of 4 polypeptides, two heavy and two light
chains. Relatively high concentrations of antibodies can be found in the blood. When antibodies are elicited by
immunization of animals with a protein-of-interest, antibodies against this protein can be isolated from the
blood of the immunized animals. If, for example, rabbits are injected with human hemoglobin, antibodies to
human hemoglobin will be produced.
(a) Briefly describe a method that can be applied to separate immunoglobulins from the majority of other
proteins in the blood serum (the blood fraction from which the blood cells have been removed) of an
immunized rabbit. (4 points)
The method should not involve protein reducing agents, because this would disrupt the disulfide bonds
connecting the 4 polypeptides. Possibilities are gel filtration chromatography (separation based on size),
ion-exchange chromatography (separation based on charge), affinity chromatography (separation based
on interaction with a ligand or antibody), or isoelectric focusing (separation based on isoelectric point).
Page 2 of 12
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller markbogers. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.75. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
67474 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now