Integrated Question 2 Feedback
solutions are attached below
Erutepa
a) 1/1
b) 1/2 - remember that charged particles also need to use channel proteins to get through the membrane. Another note, you can try make your response more concise by simply listing the two properties: large and hydrophilic; charged molecules.
c) 2/2
d) 2/2
e) 3/3 - you correctly identified the effect of the mutation on the primary structure, the effect of the changed primary structure on the tertiary structure, and finally how this changed conformation would impact the ability for the connexin protein to form gap junctions and ultimately lead to impeded transport across these cells.
Overall this is an awesome effort, so well done!
Enociz
a) 1/1
b) 1/2 - this is being a bit pedantic, but be careful about your expression: “Small, charged or polar substances such as potassium ions” implies that either small OR charged OR polar substances move through channel proteins. Although this is true for charged molecules such as ions, this isn’t always the case for ’small’ since plenty of small hydrophobic molecules can travel through phospholipids such as oxygen, and ‘polar’ since water can enter through simple diffusion. Therefore, you need to be more specific by writing 'large and hydrophilic; charged'
c) 2/2 - you got the marks for mentioning the interior was hydrophilic and the exterior was hydrophobic. However, note that your explanation wasn’t quite right (though it’s not a big issue here given this was not an ‘explain’ question), so I would recommend you read Erutepa’s response.
d) 1/2 - you got a mark for mentioning how the hydrophilic interior enables the channel protein to interact with polar and charged molecules; however you needed to be more specific with your reasoning for the hydrophobic exterior. Here, being hydrophobic enables the protein to be incorporated into the phospholipid bilayer (which I understand you were trying to say this, but it needed to be more explicit).
e) 1/3 - you few points here: firstly, “this mutation affects the pre-mRNA ... it will be translated at the ribosome” is irrelevant to the question and can be omitted. Secondly, “all amino acids added to the polypeptide chain ... will be different from the ones required to form the connexin 26 protein” is correct, though the key term I was looking for was
primary structure (first mark). Continuing on with this, the changed primary structure will ultimately change the tertiary structure of the connexins (second mark) which would impede their ability to form connexons and therefore channel proteins. Instead of this, you mentioned “connexin 26 protein will not be produced”, which is not necessarily the case, so just be a bit cautious with your statements (examiners can be picky
). Finally, You mentioned the result would lead to cell death which is where you got the mark - great stuff Enociz!
As always, I can’t wait to see more of your responses in future!