Exchange- Digestion and Absorption Flashcards
Why do large biological molecules need to be broken down?
They are too big to cross cell membranes so can’t be absorbed from the gut into the blood
What happens during digestion?
Large molecules are broken down into smaller molecules which can move across cell membranes so they can be easily absorbed from the gut to the blood to be transported around the body for use by the body cells
How are large biological molecules (polymers) broken down into smaller molecules (monomers)?
Hydrolysis reactions that use water
What are carbohydrates hydrolysed into?
Disaccharides and monosaccharides
What are fats hydrolysed into?
Fatty acids and monoglycerides
What are proteins hydrolysed into?
Amino acids
How are digestive enzymes produced?
By specialised cells in the digestive system of mammals which are the released into the gut to mix with food
Why are different enzymes needed?
Because they only work with specific substrates so different enzymes are needed to catalyse the breakdown of different food molecules
What is amylase?
A digestive enzyme that catalyses the conversion of starch into the smaller sugar maltose which involves hydrolysis of the glycosidic bonds
How is amylase produced?
By the salivary glands (releases amylase into mouth) and by the pancreas (releases amylase into the small intestine)
What are membrane-bound disaccharides?
Attached to cell membranes of epithelial cells lining the ileum that help break down disaccharides into monosaccharides which involves hydrolysis of glycosidic bonds
How can monosaccharides be transported across cell membranes of the ileum epithelial cells?
Via specific transporter proteins
What is lipase?
A digestive enzyme that catalyses the breakdown of lipids into monoglycerides and fatty acids which involves the hydrolysis of ester bonds in lipids
Where are lipases made?
In the pancreas
Where do lipases work?
In the small intestine
Why are bile salts produced by the liver?
They emulsify lipids- cause lipids to form small droplets
Why are bile salts important in the process of lipid digestion?
Several small lipid droplets have a bigger surface area than a single large droplet so the formation of small droplets greatly increases the surface area of lipid that’s available for lipases to work on
What happens once a lipid has been broken down?
Monoglycerides and fatty acids stick with the bile salts to form micelles
How are proteins broken down?
By a combination of different peptidases that catalyse the conversion of proteins into amino acids by hydrolysing peptide bonds between amino acids
What do endopeptidases do?
Hydrolyse peptide bonds within a protein
What are examples of endopeptidases?
Trypsin, chymotrypsin and pepsin
Where are endopeptidases synthesised?
The pancreas
Where are endopeptidases secreted to?
The small intestine
How is pepsin released?
Into the stomach by cells in the stomach lining
When does pepsin work?
Only in acidic conditions that are provided by hydrochloric acid in the stomach
What do exopeptidases do?
Hydrolyse peptide bonds at the ends of protein molecules and remove single amino acids from proteins
What are dipeptidases?
Exopeptidases that work specifically on dipeptides and act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them
Where are dipeptidases often located?
In the cell-surface membrane of epithelial cells in the small intestine
How is glucose absorbed?
By active transport with sodium ions via a co-transporter protein
How is fructose absorbed?
Via facilitated diffusion through a different transporter protein
Why can monoglycerides and fatty acids diffuse directly across the epithelial cell membrane?
They are lipid soluble
