Digestion

Question 1

Why are bile salts useful?

Answer 1

• Bile salts are produced in the liver and stored in the gallbladder
• They emulsify lipids into smaller droplets. This increases the surface area for faster hydrolysis of lipids by lipases
• Bile salts also form a micelle with fatty acids and monoglycerides. This makes them more soluble in water so they diffuse across the phospholipid bilayer of the epithelial cell

Question 2

Explain how monoglycerides and fatty acids are absorbed across the ileum epithelium

Answer 2

1. Monoglycerides and fatty acids form a micelle with bile salts
2. Micelles make the fatty acids and monoglycerides more soluble in water
3. The micelles carry the fatty acids and monoglycerides to the epithelial cell membrane
4. Fatty acids and monoglycerides diffuse through the phospholipid bilayer
5. Fatty acids and monoglycerides reform triglycerides in the smooth endoplasmic reticulum and are encased in a vesicle
6. The Golgi modifies the triglycerides by combining them with proteins forming chylomicrons
7. Chylomicrons are packaged into vesicles for secretion. They move t o and fuse with cell membrane releasing chylomicrons by exocytosis
8. Chylomicrons enter the lymph vessels

Question 3

Describe how amino acids are absorbed in the blood, from the lumen of the small intestine

Answer 3

1. Na+ are actively transported from the epithelial cells into the blood, using energy from the hydrolysis of ATP and a carrier protein. This maintains the Na+ concentration gradient between the lumen and epithelial cell
2. Amino acids and Na+ are co-transported from the lumen into the epithelial cell using a carrier protein. This is a type of facilitated diffusion as Na+ move down their concentration gradient
3. Amino acids move into the blood from the epithelial cell via facilitated diffusion using a carrier protein down its concentration gradient

Question 4

What types of enzymes are needed to break down carbs?

Answer 4

Maltose= maltase
Sucrose= sucrase
Lactose= lactase
Starch= amylase (pancreatic or salivary)

Question 5

Describe the action of exopeptidases

Answer 5

Exopeptidases hydrolyse peptide bonds at the end of the polypeptide to remove single amino acids

Question 6

Write an equation to show the complete breakdown of starch including enzymes

Answer 6

Starch hydrolyzed using amylase into maltose
Maltose hydrolyzed using maltase into glucose

Question 7

What is a dipeptidase?

Answer 7

Dipeptidases hydrolyse dipeptides into amino acids by hydrolyzing peptide bonds

Question 8

Describe the action of endopeptidases

Answer 8

Endopeptidases hydrolyse peptide bonds in the middle of the polypeptide to create shorter polypeptides

Question 9

Why is the combined action of exopeptidases and endopeptidases move efficient than exopeptidases on their own?

Answer 9

Endopeptidases hydrolyse peptide bonds in the middle of the polypeptide, which creates more ends and move surface area for hydrolysis by exopeptidases

Question 10

Name the enzymes required to break down the following and where they are found/made; maltose, sucrose and lactose

Answer 10

Maltose; maltase
Sucrose; sucrase
Lactose; lactase
All embedded in the membrane of epithelial cells in the ileum

Question 11

Where are endopeptidases and exopeptidases produced?

Answer 11

They are produced in the stomach and pancreas

Question 12

Name the enzyme used to break down lipids and where it is produced

Answer 12

Lipases hydrolyse ester bonds to produce monoglycerides and fatty acids.
Its produced in the pancreas and secreted into the small intestine

Question 13

Where are dipeptidases found?

Answer 13

Embedded in the membrane of the ileum of small intestine