Carbohydrates, proteins and lipids

Question 1

Where does digestion start?

Answer 1

In the mouth

Question 2

Where does it continue and finish?

Answer 2

Continues in the duodenum and finishes in the ileum

Question 3

How many enzymes are needed for carbohydrate digestion and what are they?

Answer 3

Amylases and membrane-bound disaccharidases

Question 4

What is digestion?

Answer 4

Large molecules are hydrolysed into smaller molecules that can be absorbed across the cell membrane

Question 5

Where is amylase produced?

Answer 5

In the pancreas and salivary glands

Question 6

What does amylase do?

Answer 6

Hydrolyses polysaccharides into disaccharide maltose by hydrolysing glycosidic bonds

Question 7

What are micelles?

Answer 7

Water soluble vesicles formed of fatty acids, glycerol and monoglycerides.

Question 8

In mammals, how does are the products of digestion absorbed?

Answer 8

Across the cells lining the ileum

Question 9

Features of ileum wall

Answer 9

Covered in villi and microvilli which increases the surface area for absorption

Question 10

How are amino acids and monosaccharides absorbed?

Answer 10

1. Na plus ions are actively transported out of epithelial cells by Na and K pumps into blood
2. Maintains a much higher concentration of Na plus ions in the lumen or intestine than inside epithelial cells
3. Na plus ions diffuse into epithelial cells down a concentration gradient
4. Occurs through co-transport protein
5. Na plus ions carry either amino acids or monosaccharides into the cell
6. Pass into blood plasma via facilitated diffusion using carrier proteins

Question 11

How are lipids absorbed?

Answer 11

1. Micelles break down when in contact with ileum walls releasing MG and FA.
2. They are non-polar so they diffuse across the cell sf membrane into epithelial cells
3. Transported to ER to be reformed into triglycerides
4. Continues in Golgi apparatus
5. TG associate with lipoproteins to form chylomicrons
6. These move out of the cell by exocytosis and move to lymphatic capillaries
   Chylomicrons pass these capillaries into bloodstream
7. Enzymes in epithelial cells of blood capillaries hydrolyse TG in the chylomicrons to diffuse into the cell.

Question 12

What is a bolus?

Answer 12

Small ball of chewed food

Question 13

What is peristalsis?

Answer 13

Rhythmic contractions which push the food down to the stomach

Question 14

What does bile do?

Answer 14

It Emulsifies fats and neutralises stomach acid.

Question 15

Where is bile produced?

Answer 15

In the liver, stored in gall bladder and passed down bile duct

Question 16

What is the alimentary canal?

Answer 16

Referred to as the gut. Indigestible material can pass through the whole tube without crossing the cell membrane.

Question 17

Where does peristalsis occur?

Answer 17

Oesophagus

Question 18

What are the enzymes involved in protein digestion?

Answer 18

Endopeptidases, exopeptidases and dipeptidases

Question 19

What do endopeptidases do?

Answer 19

Hydrolyse peptide bonds between amino acids in the centre of a protein molecule to form a group of peptide bonds.

Question 20

What do exopeptidases do?

Answer 20

Hydrolyse peptide bonds in the terminal end of the peptide molecules formed by endopeptidases. It releases dipeptides and single amino acids which are usually embedded in the membrane.

Question 21

What to dipeptidases do?

Answer 21

Hydrolyse bonds between two amino acids of a dipeptide. These are membrane-bound on the lining of the ileum.

Question 22

What happens in protein digestion?

Answer 22

Many proteins are soluble which aids digestion. It begins in the stomach with the secretion of gastric juice, which contains pepsin. Food then passes into the duodenum, or small intestine, where pepsin works alongside Trypsin to further break the protein down into polypeptides. These polypeptides are then further broken down into amino acids by various exopeptidases and dipeptidases, and are then absorbed into the bloodstream through the walls of the small intestine.

Question 23

What are the adaptations of the ileum?

Answer 23

Folded walls with villi and microvilli, thin walls lined with epithelial cells and a rich blood supply of capillaries to maintain a conc gradient.

Question 24

What do bile salts do?

Answer 24

They help break down large lipid molecules and are both hydrophilic and hydrophobic.

Question 25

How are lipids hydrolysed?

Answer 25

By enzyme called lipase

Question 26

Where are lipases produced?

Answer 26

Produced in the pancreas

Question 27

What do lipases do?

Answer 27

They hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides

Question 28

What is starch broken down into?

Answer 28

Amylases breaks it down into maltose.

Question 29

What is maltose hydrolysed into?

Answer 29

It’s further broken down into alpha glucose by maltase.

Question 30

Where is maltase made?

Answer 30

By the lining of the ileum

Question 31

What happens in carbohydrate digestion?

Answer 31

1. Saliva enters the mouth from salivary glands and is mixed with food during chewing
2. Saliva contains salivary amylase which hydrolyses any starch into maltose
3. Saliva also contains mineral salts to maintain PH 7 which is optimum for amylase
4. The food is then swallowed and enters the stomach. The HCL denatures the salivary amylases preventing further hydrolysis of the starch.
5. Food passes from the stomach into small intestine and mixes with pancreatic juices.
6. Contains pancreatic amylase which continues to hydrolyse starch into maltose. Alkaline salts are produced by the pancreas and intestinal wall to neutralise the acidic PH
7. Muscles in the intestinal wall push the food along the ileum. Epithelium lining produces disaccharidase maltase.
8. Maltase hydrolyses the maltose into alpha glucose.