lecture 26 Flashcards
what are the main nutrients that undergo chemical digestion?
Carbohydrates (sugars)
Proteins
Lipids (fats)
How many carbs do we consume per day?
250-800gm per day
What is the most common source of starch?
Carbohydrates
What is the most common source of glycogen?
Carbohydrates
What kind of saccharide is glucose?
Monosaccharide
Starch and glycogen are long chains of glucose joined by?
alpha 1-4 glycosidic bond
Sucrose breaks into?
Glucose and fructose
Lactose is a combination of?
Glucose and galactose
Maltose is a combination of?
Glucose and glucose
Key disaccharides in our diet?
Sucrose
Lactose
Maltose
Are proteins are source of energy?
No
Proteins are required for what?
Source of amino acids (building blocks)
how many amino acids can be synthesised by our bodies?
12
How much of our protein comes from our diet?
50%, the rest come from endogenous proteins
What are endogenous proteins?
Proteins secreted into intestine from enzymes and immunoglobulins
Are lipids essential for our diet?
no
Lipids are important source of what?
Energy
Lipids are an important source of what type of vitamins?
Fat soluble vitamins A,D,E,K
Lipids have slow what?
Gastric emptying
Lipids are mainly made up of what?
Tyglycerides, a glycerol back bone with 3 fatty acids attached
What is a short chain fatty acid?
<6 carbons
What is a medium chain fatty acid?
6-12 carbons
What is a long chain fatty acid?
12-24 carbons
Why do we need chemical digestion?
ingest nutrients in form of large complex molecules
can only absorb nutrients as small molecules
Where does chemical digestion occur?
at the surface of food particles
Are digestive enzymes intra or extracellular?
Extracellular
Do enzymes and substrates require specificity?
Yes they have to be specific
what does amylase break down?
Carbohydrates
Why can’t we digest cellulose?
They have beta 1-4 glycosidic bonds and amylase can’t break it down
Optimal pH for salivary enzymes?
Alkaline
Optimal pH for gastric enzymes?
acidic
Optimal pH for small intestine?
alkaline
Stage one of chemical digestion?
luminal digestion
Initial chemical digestion involves enzymes being secreted into where?
lumen
What do salivary glands secrete for chemical digestion?
Salivary amylase
What does the stomach secrete?
pepsin
what does the small intestine secrete?
pancreatic enzymes
what are pancreatic enzymes?
pancreatic amylase trypsin chymotrypsin carboxypeptidase lipase
stage two of chemical digestion?
Contact digestion
Where does contact digestion occur?
small intestine
Contact digestion involves enzymes produced by?
enterocytes and attached to brush border of enterocytes
Key enzymes for carbohydrate breakdown?
salivary and pancreatic amylase
polysaccharides are converted into what?
oligosaccharides and disaccharides
During contact digestion disaccharides are converted to?
monosaccharides
Contact digestion involves the enzymes?
sucrase
lactase
maltase
where are the enzymes that are involved in contact digestion?
bound to brush border
Cleaving of pepsinogen only occurs when?
at low pH
What converts proteins into polypeptides?
pepsin
trypsin
chymotrypsin
carboxypeptidase
Contact digestion converts polypeptides into?
individual amino acids
site of action where proteins are turned into large polypeptides?
stomach
site of action where large polypeptides are turned into small poly/peptides?
small intestine
Chemical digestion of lipids only occurs where?
in lumen of small intestine
Chemical digestion of lipids doesn’t involve what type of digestion?
Contact digestion
what is the main digestive enzyme for lipids?
pancreatic lipase
Which enzymes have a minor role is chemical digestion of lipids?
lingual lipase and gastric lipase
What is the problem with lipid digestion?
digestive enzymes are dissolved in luminal fluid
why do lipids require a more complex digestion process?
lipids (fats) are insoluble in water
Stages of chemical digestion of fats?
emulsification
stabilisation
digestion
formation of micelles
What stabilises formation of small droplets?
bile salts
What breaks up liquid lipid droplets?
motility, retropulsion in stomach and segmentation in small intestine
where does stabilisation occur?
small intestine
What does stabilisation involve?
bile salts that are secreted by liver
when are bile salts released into small intestine?
with arrival of food
how do bile salts stabilise emulsified drops?
by having a hydrophobic and hydrophilic side
what does hydrolysis involve?
lipase and cofactor colipase
where are lipase and cofactor colipase secrete from?
pancreas
what does colipase do?
anchors lipase to surface of droplet
what does lipase do?
convert triglycerides to monoglycerides and free fatty acids
Are monoglycerides and long chain fatty acids soluble?
no they are insoluble
what do micelles do?
keep insoluble lipid products in solution
what are micelles?
small droplets consisting of 20-30 molecules of:
bile salts
fatty acids
monoglycerides
