A-LevelBiologyHomeostasis9700/42 · May/June 2021 · Q611 Marks

Glucagon-like peptide-1 (GLP-1) is a hormone consisting of 31 amino acids. It is secreted by specialised intestinal epithelial cells known as L cells. Fig. 6.1 outlines the secretion of GLP-1 and its effects on the pancreas, brain and stomach. [Figure 6.1]

(a)(i)Name the type of membrane component that forms a receptor in the cell surface membrane.[1]
(a)(ii)State how GLP-1 is transported to the pancreas.[1]
(b)GLP-1 inhibits the secretion of glucagon by α cells in the pancreas. Describe two processes in the liver that are stimulated by glucagon.[2]
(c)Suggest one reason why GLP-1 causes a decrease in appetite.[1]
(d)GLP-1 inhibits the emptying of the stomach. This is an example of negative feedback. Explain what is meant by negative feedback.[3]
(e)A transcription factor is involved in the production of GLP-1. An insertion mutation in the gene that codes for the transcription factor can affect the production of GLP-1. Outline the effect of an insertion mutation on the production of GLP-1.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] (glyco / lipo) protein;
[1] blood;
[2] glycogenolysis / described ; gluconeogenesis / described; e.g. glucose from, amino acids / fatty acids
[1] to reduce ingestion of food or binds to receptor(s) in brain ;
[3] any three from: 1 change in a parameter; 2 detected by receptor; 3 coordination / described; 4 (corrective) action taken by effector ; 5 return to, set point / norm / optimum ;
[3] any two from: 1 frameshift / described; 2 different primary structure / shortened polypeptide ; 3 TF non-functional / TF cannot bind to, DNA / promoter or TF not produced ; 4 gene coding for GLP-1 not expressed; plus 5 less / no, GLP-1, produced / secreted;

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