Digestion and Absorption Flashcards
Can large biological molecules cross cell membranes?
Large biological molecules in food are too big to cross cell membranes. This means they can’t be absorbed from the blood into the gut
What happens to large molecules during digestion?
During digestion, large molecules are broken down into smaller molecules, which can move across cell membranes. This means they are easily absorbed from the gut into the blood, to be transported around the body for use by the body cells
How can large biological molecules be broken down?
Through hydrolysis reactions - hydrolysis reactions break bonds by adding water
During hydrolysis what are carbohydrates, fats and proteins broken down into?
Carbohydrates are broken down into disaccharides, then monosaccharides. Fats are broken down into fatty acids and monoglycerides. Proteins are broken down into amino acids
Where are digestive enzymes produced?
Digestive enzymes are produced by specialised cells in the digestive systems of mammals
What are carbohydrates broken down by?
Carbohydrates are broken down by amylase and membrane-bound disaccharides
What is amylase?
Amylase is a digestive enzyme that catalyses the conversion of starch (a polysaccharide) into the smaller sugar maltose (a disaccharide). This involves the hydrolysis of the glycosidic bonds in starch
Where is amylase produced?
Amylase is produced in the salivary glands (which release amylase into the mouth) and also by the pancreas (which releases amylase into the small intestine)
What are membrane-bound disaccharides?
Membrane-bound disaccharides are enzymes that are attached to the cell membranes of epithelial cells lining the ileum
What do membrane-bound disaccharides do?
They help to break down disaccharides into monosaccharides. This involves the hydrolysis of glycosidic bonds
How can monosaccharides be transported across cell membranes?
Monosaccharides can be transported across cell membranes of the ileum epithelial cells via specific transporter proteins
What are lipids broken down by?
Lipase with the help of bile salts
What do lipase enzymes do?
Lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids. This involves the hydrolysis of the ester bonds in lipids
Where are lipases made and where do they work?
Lipase are made in the pancreas. They work in the small intestine
What do bile salts do?
Bile salts are produced in the liver and emulsify lipids - this means they cause the lipids to form small droplets
Why are bile salts important in the digestion of lipids?
Several small lipid droplets have a larger surface area than one large lipid droplet. So bile salts forming small droplets increases the surface area of lipids that’s available for lipases to work on
What happens once lipids have been broken down into monoglycerides and fatty acids?
Once the lipid has been broken down, the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles
What are two types of proteins?
Endopeptidases and exopeptidases
What are peptidases?
These are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between the amino acids
What do endopeptidases do?
Endopeptidases act to hydrolyse peptide bonds within a protein
Give three examples of endopeptidases
- Trypsin and chymotrypsin - these are synthesised in the pancreas and secreted in the small intestine
- Pepsin - this is released into the stomach by cells in the stomach lining. Pepsin only work in acidic conditions, provided by the hydrochloric acid in the stomach
What do exopeptidases do?
Exopeptidases act to hydrolyse peptide bonds at the ends of protein molecules. They remove single amino acids from proteins
What are dipeptidases?
Dipeptidases are exopeptidases that work specifically on dipeptides. They act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them
How are monosaccharides absorbed across the ileum epithelium?
Glucose is absorbed by active transport with sodium ions via a co-transporter protein. Galactose is absorbed in the same way as glucose. Fructose is absorbed via facilitated diffusion through a different transporter protein
How are monoglycerides and fatty acids absorbed across the ileum epithelium?
Micelles help to move monoglycerides and fatty acids towards the epithelium. Micelles constantly break up and reform so they release monoglycerides and fatty acids, allowing them to be absorbed. Monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane
How are amino acids absorbed across the ileum epithelium?
Amino acids are absorbed via co-transport. Sodium ions are actively transported out of the ileum epithelial cells into the blood. This creates a sodium ion concentration gradient. Sodium ions can then diffuse from the lumen of the ileum into the epithelial cells through a sodium-dependant transporter proteins, carrying amino acids with them
