Digestive Enzymes

What are digestive enzymes?

Digestive enzymes catalyse hydrolysis reactions that break bonds in large insoluble food molecules to form smaller soluble molecules, which can be absorbed into the bloodstream.

What digestive enzymes break down carbohydrates?

Carbohydrates are broken down by amylase and membrane-bound disaccharidases

What can amylase break down?

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 relased from?

Salivary glands produce and then release amylase into the mouth and also by the pancreas (which releases amylase into the small intestine)

What are membrane-bound disacchardes?

Membrane-bound disaccharides are enzymes that are attached to the cell membranes of epithelial cells lining the ileum

What do membrane-bound disaccharidases break down?

They help to break down disaccharides (maltose, lactose, sucrose) into monosaccharides (glucose, fructose, galactose)

This involves the hydrolysis of glycosidic bonds

Which disacharidase breaks down maltose?

The disaccharide maltose is broken down by the disaccharidase maltase into alpha-glucose monosaccharides

Which disaccharidase breaks down sucrose?

The disaccharide sucrose is broken down by the disaccharidase sucrase into an alpha-glucose and fructose

Which disaccharidase breaks down lactose?

The disaccharide lactose is broken down by the disaccharidase lactase into alpha-glucose and galactose

Where does the digestion of protein begin?

The digestion of protein begins in the stomach

What enzymes break down proteins?

Proteins are broken down by endopeptidases and exopeptidases

These are enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.

What is the function of endopeptidases?

Endopeptidases hydrolyse internal peptide bonds in the middle of proteins to form shorter polypeptides, increasing the number of ends for other proteases to work on.

What is pepsin and its optimal pH?

Pepsin is an endopeptidase with an optimum pH of 2-3.

What are exopeptidases?

Exopeptidases hydrolyse peptide bonds at the ends of polypeptides to remove individual amino acids from the ends of polypeptide chains.

What are aminopeptidases and carboxypeptidases?

They are a type of exopeptidases

Aminopeptidases work from the N terminal end, while carboxypeptidases work from the C terminal end of polypeptides.

What do dipeptidases do?

They 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

What are membrane-bound dipeptidases?

Membrane bound dipeptidases can be bound to the membranes of the microvilli, releasing amino acids

What are zymogens?

Zymogens are inactive forms of proteases that are activated when required.

What activates pepsinogen?

Pepsinogen is activated to pepsin by hydrochloric acid (HCl).

What activates Rennin?

Rennin is activated to prorennin by pepsin

Where are the pancreatic exopeptidases activated?

The pancreatic exopeptidases are activated by specific enzymes in the duodenum

Why do membrane bound peptidases not need to be in an inactive state?

Membrane bound peptidases do not need to be in an inactive state as they cannot come into contact with body cells

Where does lipid digestion occur

Lipid digestion occurs in the small intestine

What is the role of bile in the break down of lipids?

Bile neutralises the stomach acid and creates alkaline conditions for enzymes in the small intestine

Bile emulsifies large lipid droplets (triglycerides) into smaller ones called micelles, which increases the surface area for efficient hydrolysis by lipase enzymes which speeds up fat digestion

Explain the process of lipid digestion

Bile neutralises the stomach acid and creates alkaline conditions for enzymes in the small intestine

Bile emulsifies large lipid droplets (triglycerides) into smaller ones which increases the surface area for efficient hydrolysis by lipase enzymes which speeds up fat digestion

Lipase hydrolyses the ester bonds in triglycerides to produce fatty acids and glycerol (monoglycerides)

The monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles

Micelles help move monoglycerides and fatty acids towards the epithelial and they constantly break up and reform so they can release fatty acids and monoglycerides allowing them to be absorbed

Fatty acids and glycerol are soluble and pass through the membrane by simple diffusion

Once inside the epithelial cells these components are recombined into triglycerides

Chylomicrons are formed where the lipid is coated by proteins and they then leave the epithelial cell and move into the lacteals.

What does lipase do?

Lipase hydrolyses the ester bonds in triglycerides to produce fatty acids and glycerol (monoglycerides).

What are micelles?

Micelles are structures that help move monoglycerides and fatty acids towards the epithelial cells for absorption and they constantly break up and reform so they can release fatty acids and monoglycerides allowing them to be absorbed

How do fatty acids and glycerol pass through the membrane?

Fatty acids and glycerol are soluble and pass through the membrane by simple diffusion.

What happens to fatty acids and glycerol inside epithelial cells?

Once inside, they are recombined into triglycerides.

What are chylomicrons?

Chylomicrons are lipids coated by proteins that leave the epithelial cell and move into the lacteals.