3.3.1: Enzymes & digestion

Question 1

what is mechanical digestion and why does it happen

Answer 1

teeth break down large pieces into smaller pieces - to increase surface area for digestion and so increase rate of digestion

Question 2

What is chemical digestion

Answer 2

involves enzymes, hydrolysing of bonds - glycosidic, peptide, ester - breakdown of large insoluble molecules to small soluble ones

Question 3

explain why it is necessary for food to be digested in order to be absorbed into our body

Answer 3

to make it smaller and soluble so that it can be transported across membranes to be absorbed into the blood plasma

Question 4

list 3 functions of mucus in the digestive system

Answer 4

1 - neutralise acid
2 - provides lubrication
3 - protects gut wall from acid erosion

Question 5

state where enzymes and digestive chemicals are secreted from and where they go, as part of extracellular digestion

Answer 5

enzymes are secreted from:
salivary glands into mouth
gastric glands into stomach
pancreas into duodenum
digestive chemicals are secreted from pancreas into duodenum

Question 6

state where intracellular digestion happens and what happens in the process

Answer 6

occurs in the epithelial cells of ileum, they hydrolyse disaccharides and dipeptides

Question 7

describe the process of carbohydrate digestion (starch)

Answer 7

amylase hydrolyses starch to make maltose which is then hydrolysed by maltase to make glucose

Question 8

describe what the role of amylase is, where it is found and its optimum pH

Answer 8

hydrolyses glycosidic bonds in starch to produce maltose. Amylase is found in saliva and pancreatic juice, its optimum pH is 8

Question 9

describe what the role of maltase is, where it is found and its optimum pH

Answer 9

hydrolyses glycosidic bonds in maltose to produce glucose. Maltase is found in epithelial cells in ileum and its optimum pH is 8

Question 10

describe and explain the process of protein digestion

Answer 10

pepsin (endopeptidase) in the stomach hydrolyses peptide bonds in protein into polypeptide chains
trypsin (endopeptidase) in the duodenum hydrolyses the polypeptide chains into smaller polypeptide chains. Exopeptidases in the duodenum remove the amine group from the polypeptide chain to produce amino acids and dipeptides (by hydrolysis)
Dipeptidases (exopeptidases) in the ileum hydrolyse the dipeptides into amino acids

Question 11

what is the difference between exopeptidases and endopeptidases

Answer 11

exo = hydrolyse the end of the polypeptide chain
endo = hydrolyse the inside of the polypeptide chain

Question 12

name the 2 endopeptidases involved in protein digestion and state where they are found, their optimum pH

Answer 12

pepsin - stomach pH 2
trypsin - duodenum pH 8

Question 13

state where exopeptidases are found and give 3 examples

Answer 13

found in pancreas and epithelial cells of ileum: 1 - carboxypeptidase
2 - aminopeptidase
3 - dipeptidase

Question 14

explain why it is more efficient for the endopeptidase enzymes to act before the exopeptidases

Answer 14

the endopeptidases hydrolyse the internal peptide bonds in the chain first which increases the surface area for exopeptidases to hydrolyse the external peptide bonds

Question 15

Describe and explain the process of lipid digestion

Answer 15

process of mechanical digestion happens first: bile salts emulsify lipids into micelles, this increases surface area for lipase action. Afterwards, process of chemical digestion happens: lipase hydrolyses ester bonds in the micelles into monoglycerides and fatty acids

Question 16

where is bile produced and stored, and how is it released and where to

Answer 16

bile is produced in the liver, stored in the gallbladder, released via the bile duct to the duodenum

Question 17

what two things does bile contain

Answer 17

1 - bile salts that emulsify lipids into micelles
2 - sodium hydrogen carbonate that neutralises stomach

Question 18

name the substrate that amylase hydrolyses and the product made

Answer 18

starch -> maltose

Question 19

name the substrate that endopeptidase hydrolyses and the product made

Answer 19

proteins/polypeptides -> smaller polypeptide chains

Question 20

name the substrate that exopeptidases/dipeptidases hydrolyses and the product made

Answer 20

shorter polypeptides -> dipeptides and amino acids

Question 21

name the substrate that lipase hydrolyses and the product made

Answer 21

lipids -> monoglycerides and fatty acids

Question 22

name the substrate that disaccharidases hydrolyses and the product made

Answer 22

disaccharides -> monosaccharides

Question 23

where are the sites of secretion of amylase and the sites of action

Answer 23

salivary glands -> mouth and
pancreatic juice -> duodenum

Question 24

where are the sites of secretion of endopeptidase and the sites of action

Answer 24

gastric glands -> stomach and
pancreas -> duodenum

Question 25

where are the sites of secretion of exopeptidases/dipeptidase and the sites of action

Answer 25

pancreas -> duodenum and
epithelial cells -> ileum

Question 26

where are the sites of secretion of lipase and the sites of action

Answer 26

pancreas -> duodenum

Question 27

where are the sites of secretion of disaccharidases and the sites of action

Answer 27

epithelial cells -> ileum

Question 28

Describe the process of mechanical digestion in the mouth

Answer 28

teeth - increases surface area for chemical digestion

Question 29

Describe the process of chemical digestion in the mouth

Answer 29

salivary gland secretes saliva which contains: amylase - breakdown starch
mucus - lubrication
mineral ions - maintain pH

Question 30

What is the pH in the mouth

Answer 30

6.5-7.5

Question 31

Describe the function of the oesophagus

Answer 31

circular muscle contracts to squeeze the gut and longitudinal muscle contracts to shorten the gut. Both muscles work together - peristalsis - to move the food down the oseophagus

Question 32

What cells in the oesophagus secrete mucus and provide lubrication

Answer 32

goblet cells

Question 33

Describe the process of mechanical digestion in the stomach

Answer 33

stomach muscles contract to churn contents to form acidic chyme - increasing surface area for chemical digestion

Question 34

Describe the process of chemical digestion in the stomach

Answer 34

Gastric gland secretes gastric juice which contains:
endopeptidases - hydrolyse peptide bonds
mucus - lubrication and protects stomach wall from acid
HCl - maintains pH and activates enzymes and kills bacteria

Question 35

What is the pH in the stomach

Answer 35

2

Question 36

what is the role of the duodenum, and describe the gland in it

Answer 36

the duodenum is the main site of chemical digestion, the Brunner’s gland is in the gut wall, which releases mucus

Question 37

what is the pH of the duodenum

Answer 37

7-8

Question 38

What common role do mucus, hydrogen carbonate ions, and sodium hydrogen carbonate have in the digestive system

Answer 38

they all neutralise stomach acid

Question 39

Describe the structure of the ileum

Answer 39

lumen of ileum, microvilli, epithelial cell of ileum, blood capillary

Question 40

Where are the enzymes for disaccharides located in the ileum and what advantage does this give in terms of digestion

Answer 40

they are all in the microvilli, and so as the disaccharides are absorbed into the blood capillary, they are broken down into monosaccharides

Question 41

What is the role of the colon in the digestive system and how does it carry this role out

Answer 41

egestion of carbon based material -> faeces
colon absorbs remaining water along with any vitamins -> this is to have solid faeces which stimulates peristalsis

Question 42

what are three things present in the faeces that provide bulk and help to solidify the faeces in the colon

Answer 42

1 - bacterial cells
2 - sloughed cells (cells rubbed off of gut wall)
3 - undigested material (cellulose)

Question 43

what do bacterial cells, sloughed cells (cells rubbed off of gut wall), undigested material (cellulose) present in the faeces in the colon help with

Answer 43

provides bulk, helps solidify faeces

Question 44

name the products of digestion

Answer 44

amino acids, glucose, glycerol and fatty acids

Question 45

why can’t starch, proteins and lipids be absorbed into the blood

Answer 45

too large and insoluble

Question 46

explain why humans can’t digest cellulose

Answer 46

humans lack the enzyme cellulase to be able to break down cellulose