Module 3 - Absorption and digestion

Question 1

Give examples of large molecules

Answer 1

Starch, proteins, polypeptides etc

Question 2

How are larger molecules broken into smaller molecules and why?

Answer 2

They are broken down via the hydrolysis reactions of bonds between the polymers to form monomers in the presence of water. This is done so that molecules are able to cross the membrane and be absorbed + transported.

Question 3

What is the digestive enzyme that breaks down carbohydrates?

Answer 3

Amylase

Question 4

Where is Amylase found in the body?

Answer 4

Amylase is found in the mouth in the salivary gland and is also found in the pancreas which is then secreted into the small intestine.

Question 5

What is another enzyme that breaks down carbohydrates? What do they do?

Answer 5

Membrane-bound disaccharidases that are attached to the cell membrane of the epithelial cells of the lining of the ileum which help break down disaccharides into monosaccharides.

Question 6

How are monosaccharides transported across the cell membrane?

Answer 6

Transported proteins

Question 7

What enzyme breaks down lipids?

Answer 7

Lipase

Question 8

Where are lipases found in the body?

Answer 8

They are made in the pancreas by are secreted into the small intestine where they work.

Question 9

Where are bile salts made and what is their purpose when breaking down lipids?

Answer 9

Liver and they are used in emulsification to help break down lipids into smaller droplets to increase the surface area for lipases to work with so they work quicker to break the lipids down

Question 10

What are the products of lipids?

Answer 10

Monoglycerides and fatty acids

Question 11

Briefly outline the steps that take place during the break down of lipids.

Answer 11

Lipids and bile salts come together during emulsification which products lots of tiny droplets. These little droplets then get hydrolysed in the presence of water by lipase which form monoglycerides and fatty acids which form tiny structures called micelles

Question 12

What are the two types of proteases?

Answer 12

endopeptidases and exopeptidases

Question 13

What is the function of endopeptidases?

Answer 13

They hydrolyse peptide bonds within a protein

Question 14

What are three examples of endopeptidases?

Answer 14

Trypsin, chymotrypsin which are synthesised in the pancreas and secreted in the small intestine. Pepsin is secreted into the stomach from the stomach lining but these are adapted to work in only acidic climates

Question 15

What is the function of exopeptidases?

Answer 15

These break down amino acids at the ends of protein molecules to release one amino acid

Question 16

What is an example of exopeptidases?

Answer 16

Dipeptidases is an example of an enzyme that catalyses the hydrolysis of dipeptides into two amino acids by breaking the peptide bond between them. They are usually found in the cell-surface membrane of epithelial cells in small intestine

Question 17

How are monosaccharides absorbed across the cell membrane

Answer 17

Glucose and galactose use active transport with sodium ions via co-transporter proteins. Fructose uses facilitated diffusion through a diff transporter protein

Question 18

Mechanism for the absorption of amino acids into the ileum

Answer 18

• Glucose moves in with sodium into epithelial cell
• Via carrier/channel protein
• Sodium removed from epthelial cell by active transport using sodium- potassium pump
• Maintaining low concentration of sodium in epithelial cell
• Glucose moves into blood
• By facilitated diffusion

Question 19

How are monoglycerides and fatty acids absorbed across the cell membrane?

Answer 19

Micelles carry the lipid products across the epithelium. Micelles break down and reform which releases the products. As they are lipid-soluble, they can diffuse directly across the cell membrane

Question 20

How are amino acids absorbed across the cell membrane?

Answer 20

Similar to glucose and galactose. Sodium ions actively transport out of epithelial cells. Creates conc gradient so amino acids can move into epithelial cells from lumen of ileum with sodium ion via sodium-dependant transporter proteins.

Question 21

Describe how proteins are digested in the human gut. 4 marks

Answer 21

Hydrolysis occurs by breaking peptide bonds between amino acids. Endopeptidases break down polypeptides into smaller chains within the protein. Exopeptidases break down terminal amino acids and dipeptidases break down dipeptides into 2 amino acids.

Question 22

What is starch broken down into and what enzymes will we see break it down?

Answer 22

Maltose, pancreatic and salivary amylase breaks into down into maltose. Maltose is then broken down into glucose by maltase.

Question 23

What are the 3 enzymes used when breaking down carbohydrates in the digestive system?

Answer 23

Salivary amylase, pancreatic amylase and maltase

Question 24

Explain why glucose levels in blood rise faster with a meal containing sucrose rather than starch.

Answer 24

Starch is first digested into maltose by amylase. Then Maltose is digested into glucose via maltase. Sucrose only requires one step which is the enzyme sucrase digesting into glucose and fructose whereas starch requires two steps.