3.3.1: Enzymes & digestion Flashcards
what is mechanical digestion and why does it happen
teeth break down large pieces into smaller pieces - to increase surface area for digestion and so increase rate of digestion
What is chemical digestion
involves enzymes, hydrolysing of bonds - glycosidic, peptide, ester - breakdown of large insoluble molecules to small soluble ones
explain why it is necessary for food to be digested in order to be absorbed into our body
to make it smaller and soluble so that it can be transported across membranes to be absorbed into the blood plasma
list 3 functions of mucus in the digestive system
1 - neutralise acid
2 - provides lubrication
3 - protects gut wall from acid erosion
state where enzymes and digestive chemicals are secreted from and where they go, as part of extracellular digestion
enzymes are secreted from:
salivary glands into mouth
gastric glands into stomach
pancreas into duodenum
digestive chemicals are secreted from pancreas into duodenum
state where intracellular digestion happens and what happens in the process
occurs in the epithelial cells of ileum, they hydrolyse disaccharides and dipeptides
describe the process of carbohydrate digestion (starch)
amylase hydrolyses starch to make maltose which is then hydrolysed by maltase to make glucose
describe what the role of amylase is, where it is found and its optimum pH
hydrolyses glycosidic bonds in starch to produce maltose. Amylase is found in saliva and pancreatic juice, its optimum pH is 8
describe what the role of maltase is, where it is found and its optimum pH
hydrolyses glycosidic bonds in maltose to produce glucose. Maltase is found in epithelial cells in ileum and its optimum pH is 8
describe and explain the process of protein digestion
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
what is the difference between exopeptidases and endopeptidases
exo = hydrolyse the end of the polypeptide chain
endo = hydrolyse the inside of the polypeptide chain
name the 2 endopeptidases involved in protein digestion and state where they are found, their optimum pH
pepsin - stomach pH 2
trypsin - duodenum pH 8
state where exopeptidases are found and give 3 examples
found in pancreas and epithelial cells of ileum: 1 - carboxypeptidase
2 - aminopeptidase
3 - dipeptidase
explain why it is more efficient for the endopeptidase enzymes to act before the exopeptidases
the endopeptidases hydrolyse the internal peptide bonds in the chain first which increases the surface area for exopeptidases to hydrolyse the external peptide bonds
Describe and explain the process of lipid digestion
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
where is bile produced and stored, and how is it released and where to
bile is produced in the liver, stored in the gallbladder, released via the bile duct to the duodenum
what two things does bile contain
1 - bile salts that emulsify lipids into micelles
2 - sodium hydrogen carbonate that neutralises stomach
name the substrate that amylase hydrolyses and the product made
starch -> maltose
name the substrate that endopeptidase hydrolyses and the product made
proteins/polypeptides -> smaller polypeptide chains
name the substrate that exopeptidases/dipeptidases hydrolyses and the product made
shorter polypeptides -> dipeptides and amino acids
name the substrate that lipase hydrolyses and the product made
lipids -> monoglycerides and fatty acids
name the substrate that disaccharidases hydrolyses and the product made
disaccharides -> monosaccharides
where are the sites of secretion of amylase and the sites of action
salivary glands -> mouth and
pancreatic juice -> duodenum
where are the sites of secretion of endopeptidase and the sites of action
gastric glands -> stomach and
pancreas -> duodenum
where are the sites of secretion of exopeptidases/dipeptidase and the sites of action
pancreas -> duodenum and
epithelial cells -> ileum
where are the sites of secretion of lipase and the sites of action
pancreas -> duodenum
where are the sites of secretion of disaccharidases and the sites of action
epithelial cells -> ileum
Describe the process of mechanical digestion in the mouth
teeth - increases surface area for chemical digestion
Describe the process of chemical digestion in the mouth
salivary gland secretes saliva which contains: amylase - breakdown starch
mucus - lubrication
mineral ions - maintain pH
What is the pH in the mouth
6.5-7.5
Describe the function of the oesophagus
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
What cells in the oesophagus secrete mucus and provide lubrication
goblet cells
Describe the process of mechanical digestion in the stomach
stomach muscles contract to churn contents to form acidic chyme - increasing surface area for chemical digestion
Describe the process of chemical digestion in the stomach
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
What is the pH in the stomach
2
what is the role of the duodenum, and describe the gland in it
the duodenum is the main site of chemical digestion, the Brunner’s gland is in the gut wall, which releases mucus
what is the pH of the duodenum
7-8
What common role do mucus, hydrogen carbonate ions, and sodium hydrogen carbonate have in the digestive system
they all neutralise stomach acid
Describe the structure of the ileum
lumen of ileum, microvilli, epithelial cell of ileum, blood capillary
Where are the enzymes for disaccharides located in the ileum and what advantage does this give in terms of digestion
they are all in the microvilli, and so as the disaccharides are absorbed into the blood capillary, they are broken down into monosaccharides
What is the role of the colon in the digestive system and how does it carry this role out
egestion of carbon based material -> faeces
colon absorbs remaining water along with any vitamins -> this is to have solid faeces which stimulates peristalsis
what are three things present in the faeces that provide bulk and help to solidify the faeces in the colon
1 - bacterial cells
2 - sloughed cells (cells rubbed off of gut wall)
3 - undigested material (cellulose)
what do bacterial cells, sloughed cells (cells rubbed off of gut wall), undigested material (cellulose) present in the faeces in the colon help with
provides bulk, helps solidify faeces
name the products of digestion
amino acids, glucose, glycerol and fatty acids
why can’t starch, proteins and lipids be absorbed into the blood
too large and insoluble
explain why humans can’t digest cellulose
humans lack the enzyme cellulase to be able to break down cellulose
