The Human Gut: Conditions

Overview

Recall questions on Conditions for Digesting Different Food Substances.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Give two functions of the hydrochloric acid secreted into the stomach.

   Model answer

   It provides the acidic conditions that pepsin needs to work, and it kills many of the bacteria taken in with the food.

2. 2

   Which enzyme digests lipids, where is it made, and what are its products?

   Model answer

   Lipase is made in the pancreas and secreted into the duodenum, where it hydrolyses lipids to fatty acids and glycerol.

3. 3

   What is the role of bile salts in fat digestion?

   Model answer

   Bile salts emulsify large fat droplets into many tiny ones, which greatly increases the surface area available to lipase and so speeds up hydrolysis.

4. 4

   Bile contains no digestive enzymes, so how does it help the pancreatic enzymes to work?

   Model answer

   Bile is alkaline, so it neutralises the acidic mixture arriving from the stomach and raises the pH of the duodenum to the slightly alkaline optimum of the pancreatic enzymes.

5. 5

   In terms of protein structure, why does an enzyme stop working when the pH moves far from its optimum?

   Model answer

   A change in pH alters the charges on the R groups, breaking ionic and hydrogen bonds so the tertiary structure changes shape, and the substrate no longer fits the altered active site.

6. 6

   Why is it an advantage that the stomach and the duodenum have very different pH values?

   Model answer

   Each region can then provide the optimum conditions for its own enzymes, so protein digestion by pepsin and by trypsin can both proceed at their fastest rates in turn.

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