Lecture 26: Chemical Digestion Flashcards
What are the 3 main nutrients that undergo chemical digestion?
- Carbohydrates (Sugars)
- Proteins
- Lipids (Fats)
Whare are carbohydrates an important source of?
Energy
How are carbohydrates stored?
Polysaccharides
What is a polysaccharide?
Large complex chain of monosaccharides
What is glucose an example of?
A monosaccharide
What is starch a long chains of?
Glucose
What are the long chains of glucose connected by in starch and glycogen?
alpha 1-4 glycosidic bonds
What are 3 examples of disaccharides?
- Sucrose
- Lactose
- Maltose
What is Sucrose made of?
2
- Glucose
- Fructose
What is Lactose made of?
2
- Glucose
- Galactose
What is Maltose made of?
2 Glucose
What do we ingest a limited amount of?
Monosaccharides e.g. glucose
Proteins are not a source of what?
Energy
What are proteins required for?
Amino acids
How many amino acids do we have?
21
How many amino acids can we synthesise?
12
How do we acquire the amino acids that can’t be synthesised?
Through our diet
What are 2 sources of protein?
- Diet
- Endogenous proteins
What can proteins be secreted into the intestine as?
2
- Enzymes
- Immunoglobulins
What is the structure of ingested amino acids?
Long chains of amino acids connected by peptide bonds
Is fat essential to our diet?
No
What is fat an important source of?
Energy
What do lipids do to gastric emptying?
Slow it down
What are triglycerides?
Glycerol back bone with 3 fatty acids attached
what is a short chain fatty acid?
< 6 carbons
what is a medium chain fatty acid?
6 to 12 carbons
what is a long chain fatty acid?
12 to 24 carbons
Why do we need chemical digestion?
Ingest nutrients in the form of large complex molecules
What can we only absorb nutrients as?
Small molecules
What does chemical digestion do to the size of nutrients?
Reduces their size to allow them to be absorbed
Where does chemical digestion occur?
On the surface of food particles
What does mechanical digestion do?
Breaks up food increasing its surface area available for chemical digestion
What does chemical digestion utilise?
digestive enzymes
What is the equation that shows digestive enzymes are organic catalysts?
E + S -> ES -> E + P
How are digestive enzymes very specific?
They have different enzymes for different substrates
Each enzyme has a particular what?
pH that it works optimally at
What type of pH do salivary enzymes like?
Alkaline
What type of pH do gastric enzymes like?
Acidic
What type of pH do small intestinal enzymes like?
Alkaline
What are the 2 stages of chemical digestion?
- Luminal digestion
- Contact digestion
What does luminal digestion involve?
Enzymes being secreted into the lumen
What do the Salivary glands, Stomach and Small Intestine secret into the lumen respectively?
- Salivary amylase
- Pepsin
- Pancreatic enzymes
What are the pancreatic enzymes released by the small intestine during luminal digestion?
(5)
- Pancreatic amylase
- Trypsin
- Chymotrypsin
- Carboxypeptidase
- Lipase
Where does contact digestion occur?
In the small intestine
What does contact digestion do?
Completes digestion before absorption
What does contact digestion involve?
Enzymes produced by enterocytes which are attached to the brush border
What happens during the chemical digestion of carbohydrates in the luminal digestion phase?
Salivary and pancreatic amylase convert polysaccharides into oligosaccharides and down further into disaccharides
What happens during the chemical digestion of carbohydrates in the contact digestion phase?
Disaccharides are converted to monosaccharides
What are the enzymes involved in breaking down disaccharides to monosaccharides during contact digestion?
(3)
- Sucrase
- Lactase
- Maltase
What are the enzymes Sucrase, Lactase and Maltase attached to?
The brush border
What does pepsin in the stomach trypsin, chymotrypsin and carboxypeptidase in the small intestine secreted by the pancreas do during luminal digestion of proteins?
Converts proteins to polypeptides
What does contact digestion of proteins involve?
Peptidases
What do many types of peptidases for contact digestion of proteins attach to?
The brush border
What do peptidases of contact digestion of proteins do?
Convert polypeptides into individual amino acids
Where does chemical digestion of fats occur?
In the lumen of the small intestine
What is the main digestive enzyme involved with chemical digestion of fats?
Pancreatic lipase
What have minor roles in the chemical digestion of fats?
2
- Lingual lipase
- Gastric lipase
What is the problem for lipid digestion?
Digestive enzymes dissolve in water but fats aren’t water soluble
What are the 4 main stages of chemical digestion of fats?
- Emulsification
- Stabilisation
- Digestion (Hydrolysis)
- formation of micelles
What does motility of emulsification do?
breaks up lipid droplets into small droplets increasing surface area
Where does simple emulsification occur and what is performed?
Stomach and performs retropulsion
Where does more complex emulsification occur and what is performed?
Small intestine and performs segmentation
What do bile salts do?
Stabilise fat droplets which result from emulsification in the small intestine
Where does stabilisation of lipids occur?
Small intestine
What are bile salts secreted by?
Liver
Where are bile salts concentrated?
Gallbladder
When and where are bile salts releases?
With the arrival of food into the small intestine
How can the structure of bile salts be described?
Hydrophobic (water hating side) and a charged hydrophilic (water loving side)
Where does hydrolysis of lipids occur?
In the small intestine at the surface of the emulsion droplets
What does hydrolysis of lipids involve?
2
- Lipase
- Cofactor colipase
What are lipase/cofactor colipase secreted by?
pancreas
What does colipase do?
Anchors lipase to the surface of droplets
What does lipase convert triglyceride to?
2
- Monoglyceride
- Free fatty acids
What occurs during the formation of micelles in fat digestion?
The products of fat digestion are kept in solution through the formation of micelles
