Module 3 - Absorption and digestion Flashcards
Give examples of large molecules
Starch, proteins, polypeptides etc
How are larger molecules broken into smaller molecules and why?
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.
What is the digestive enzyme that breaks down carbohydrates?
Amylase
Where is Amylase found in the body?
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.
What is another enzyme that breaks down carbohydrates? What do they do?
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.
How are monosaccharides transported across the cell membrane?
Transported proteins
What enzyme breaks down lipids?
Lipase
Where are lipases found in the body?
They are made in the pancreas by are secreted into the small intestine where they work.
Where are bile salts made and what is their purpose when breaking down lipids?
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
What are the products of lipids?
Monoglycerides and fatty acids
Briefly outline the steps that take place during the break down of lipids.
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
What are the two types of proteases?
endopeptidases and exopeptidases
What is the function of endopeptidases?
They hydrolyse peptide bonds within a protein
What are three examples of endopeptidases?
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
What is the function of exopeptidases?
These break down amino acids at the ends of protein molecules to release one amino acid
What is an example of exopeptidases?
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
How are monosaccharides absorbed across the cell membrane
Glucose and galactose use active transport with sodium ions via co-transporter proteins. Fructose uses facilitated diffusion through a diff transporter protein
Mechanism for the absorption of amino acids into the ileum
- 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
How are monoglycerides and fatty acids absorbed across the cell membrane?
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
How are amino acids absorbed across the cell membrane?
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.
Describe how proteins are digested in the human gut. 4 marks
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.
What is starch broken down into and what enzymes will we see break it down?
Maltose, pancreatic and salivary amylase breaks into down into maltose. Maltose is then broken down into glucose by maltase.
What are the 3 enzymes used when breaking down carbohydrates in the digestive system?
Salivary amylase, pancreatic amylase and maltase
Explain why glucose levels in blood rise faster with a meal containing sucrose rather than starch.
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.
