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AS/A-LEVEL BIOLOGY Protein digestion and absorption presentation

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Presentation on theme: "AS/A-LEVEL BIOLOGY Protein digestion and absorption presentation"— Presentation transcript:

1 AS/A-LEVEL BIOLOGY 3.3.3 Protein digestion and absorption presentation
To be used alongside AQA AS/A-level Biology protein digestion and absorption teaching notes Version 1.0 Copyright © 2015 AQA and its licensors. All rights reserved.

2 Protein digestion Like all digestion, this involves hydrolysis
Three types of enzyme involved Endopeptidases: hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide Exopeptidases: hydrolyse peptide bonds between specific amino acids at the ends of a polypeptide Dipeptidases: hydrolyse the peptide bond in a dipeptide Version 1.0 Copyright © 2015 AQA and its licensors. All rights reserved.

3 Exopeptidases and endopeptidases
Exopeptidase breaks bonds at ends of polypeptide to produce dipeptides or individual amino acids Endopeptidase breaks bonds in middle of polypeptide to produce shorter polypeptides Copyright © 2015 AQA and its licensors. All rights reserved.

4 Pause for thought The first stage of protein digestion occurs in the stomach. An endopeptidase (pepsin) is the only protein-digesting enzyme in the stomach. Only later, in the small intestine, is the food mixed with exopeptidases. Suggest the advantage of this sequence. Copyright © 2015 AQA and its licensors. All rights reserved.

5 Dipeptidases Dipeptidases are located in the surface membranes of cells lining the small intestine They hydrolyse dipeptides into amino acids As a result, the final products of protein digestion are amino acids, which are absorbed by cells lining the ileum of the small intestine Copyright © 2015 AQA and its licensors. All rights reserved.

6 Summary of protein digestion
Copyright © 2015 AQA and its licensors. All rights reserved.

7 Amino acid absorption Uptake from the ileum is by facilitated diffusion through specific carrier molecules in the surface membranes of epithelial cells With each amino acid, one Na+ ion is also taken up, an example of co-transport A diffusion gradient for Na+ is maintained by their active transport through the base of the epithelial cells Amino acids pass through the base of the epithelial cells by facilitated diffusion Copyright © 2015 AQA and its licensors. All rights reserved.

8 Uptake by co-transport
Version 1.0 Copyright © 2015 AQA and its licensors. All rights reserved.

9 Acknowledgements Diagram in slide 8  Rowland, M., 1992, Biology, Thomas Nelson & Sons Ltd Copyright © 2015 AQA and its licensors. All rights reserved.

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