A-LevelBiologyBiological molecules9700/22 · Oct/Nov 2022 · Q510 Marks

Fibroblasts are one of the cell types of connective tissue. The cells synthesise and secrete collagen, which forms part of the supporting external cellular environment, known as the extracellular matrix.

(a)Fig. 5.1 shows the primary structure of a section of a polypeptide chain of collagen. [Figure 5.1] Explain how the primary structure shown in Fig. 5.1 indicates that the structure of the polypeptide is suited to be a component of a collagen molecule.[3]
(b)After final processing in the Golgi body, collagen is released to the outer surface of the cell by exocytosis. Complete the passage to describe the process of exocytosis. After final processing in the Golgi body,[3]
(c)(i)Hydrolytic enzymes, known as collagenases, are secreted by cells in an inactive form. Cells also secrete inhibitors of collagenases. The activity of the enzymes and inhibitors is regulated so that the development and maintenance of the extracellular matrix is controlled. State and explain what the outcome will be for the composition of the extracellular matrix if collagenase inhibitor activity is needed.[2]
(c)(ii)Synthetic inhibitors have been trialled as potential treatment for diseases caused by a lack of regulation of collagenase activity. Research involves investigating the mechanism of action of an inhibitor. State the effect that a non-competitive inhibitor will have on the maximum rate of reaction, Vmax, and the Michaelis–Menten constant, Km, of collagenase. Vmax Km[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] glycine every third amino acid
[1] glycine, is, small / smallest, amino acid; A has H as R-group
[1] glycine allows tight coiling of polypeptides to form triple helix ; AW ; A glycine presence allows a, compact/AW, triple helix
[1] gly (-NH) can form hydrogen bonds with (C=O in pro of) other polypeptides of triple helix ; A idea that H bonds can form with other polypeptides in the triple helix
[1] AVP; e.g. pro/ala, also small amino acids (for tight coiling) ; high proportion of smaller amino acids / amino acids with small side chains ; A high proportion of glycine if mp1 not given and mp2 is ; pro can form hydroxyproline for stability ; ref. insoluble and (some), amino acids with non-polar R-groups (e.g. ala)
[1] (Golgi /secretory) vesicles, detail; e.g. packaging of/ containing, collagen ; vesicles bud off from Golgi body ; context of movement to surface (not movement to other areas within cell)
[1] vesicles moved by, microtubules / cytoskeleton (to cell surface membrane)
[1] ATP required; A energy required / active process ; R active transport
[1] fuse/merge / combine, with the cell surface membrane ; A plasma membrane
[1] AVP; e.g. budding from trans face of Golgi ; detail of fusion e.g. phospholipid bilayers merge into one
[1] collagen, not broken down / not hydrolysed / breakdown prevented ; A ECM for collagen A less hydrolysis / AW
[1] detail; e.g. suggestion that, collagen does not fit in to active site / active site changes shape ; no / few, ESC / enzyme substrate complexes, form
[1] collagen, continues to be, synthesised / released ; A increase in collagen / maintenance of collagen
[1] (Vmax) decreases
[1] (Km) stays the same