Digestion lab Flashcards
Alpha amylase acts on what bonds?
Alpha1,4 glycosidic bonds
What is meant by a reducing sugar? What significance is this in lab testing
- Sugar which has an aldehyde group
- glucose, galactose, glyceraldehyde (monosaccharides), lactose, maltose (disaccharides) and maltotriose
The presence of the aldehyde group is the basis of ??????? test. It allows reducing sugars to readily reduce ?????? salts, giving insoluble yellow or red cuprous oxide. The starting colour for benedicts test is ?????
- Benedicts test
- cupric
- Blue
Barfoed’s test is used to test for what? What colour change would you expect to see? Summarise the basis of Baefords test
Monosaccharides
Barfoed’s test reaction is based on the reduction of cupric acetate by reducing monosaccharides and reducing disaccharides. Reduction of cupric acetate produces cuprous oxide which gives a brick red precipitate. Monosaccharides usually react in about 1-5 min and produce a red precipitate. While the reducing disaccharides take a much longer time between 7-12 min to give a red precipitate.
Iodine test can be used to test for what? Explain the basis of Iodine testing.
Polysaccharides
Iodine interacts with these coiled molecules and becomes bluish black. Other non-coiled carbohydrates do not react with iodine. Therefore, a bluish black color is a positive test for starch, and a yellow-ish brown color (i.e., no color change) is a negative test for starch. Glycogen, the common polysaccharide in animals, has a slight difference in structure and produces only an intermediate color reaction.
Starch gives blue, dextrin gives reddish/purple, glycogen gives red-brown.
Iodine colour changes - study
For glucose and maltose; what results would you expect for benedicts?
Benedicts for Maltose: Formation of orange/red colour
Glucose: Orange/red colour
For glucose and maltose, what would you expect to see for Baefords test?
- Glucose: Formation formation of red precipitate
- Maltose: negative result, maltose is a disaccharide
Lets say you set up the following experiment:
- two test tubes; one with normal amylase and one with boiled
- You had starch solution to each one, and then ake a drop from each one and test it with iodine, and continue to remove drops at 15 intervals
What colour changes would you expect when testing for iodine?
Furthermore, then take a bit of sample from your from your Amylase + starch boiled and amylase + stach non-boiled, and test it with benedicts and baefords. What colour chages would you expect?
- Boiled amylase fucks it up - so you would still be left with polysaccharides
- Amylase that isn’t boiled would break down starches into maltoses, alpha dextrins, maltitrioses etc, all of which would have reducing power, so you would not expect a positive test since there should be no polysacchrides present
- Starch (composed of amylose and amylopectin) is non-reducing in nature due to unavailability of free carbonyl group in its constituent monsaccharides.
Experiment looking at effects of Amylase on cooked potato starch, raw potato starch, raftilose and cellulose. What results would you see from a benedicts test?
WHat are the main products of amylase digestion of starch?
- Maltose
- Malotriose
- Alpha dextrins
In benedicts test, you would expect to get negative results for raw potato starch, raftilose, cellulose, but positive results for cooked potato starch. Explain why this would occur.
- human amylase can digest only alpha 1-4 bonds
- important to note that starch is stored in granules within cells
-
digestibility of different RAW starch granules depends on the starch type
- For example, raw wheat starch is digestible as it is contained in small starch granules with a big surface area - amylase can get into this type of structure
- Conversley, raw potato starch is not digestible as it is contained in large granules with a small surface area, with a highly bonded super helical structure where the water is tightly bound - amylase finds it hard to get into this type of structure
-
When we COOK starchy foods, the starch granules burst and the helical strucure is disrupted, leaving tangled chains of amylopectin which cause a VISCOUS solution - this can be accessed by amylase
- Starch itself has two major polymers; Amylose (which can be digested by our alpha amylase as it has alpha 1,4 to produce maltose, maltotriose etc) and Amylopectin which features a1,6 bonds (which can be digested by a brush border enzyme called ISOMALTASE/Alpha dextrinase - to also produce maltose) and also alpha 1,4 bonds
-
digestibility of different RAW starch granules depends on the starch type
- Cellulose was also not digested, since it has Beta 1,4 Glycosidic bonds between glucose molecules - we do not have means to digest this
- Raftilose , derived from inulin and has a sweet taste is also not digested by humans
Guar gum is a common additive in foods to serve as a source of fibre. It is it digestible? What sugars does it have?
No
Mannose, Galactose
Some starchy foods are slowly digested because they have a plant cellular structure still intact which protects the starch from enzymes, or because a soluble fibre in the food increases the viscosity of the gut contents which will also protect the start from ?????
These slowly digested starches are the main carb diabetics should consume, as they give slow, sustained rises in blood glucose and need less ????? to keep blood ????? level
Enzymes
Insulin
Glucose
What is meant by retograded starch? How is this starch formed?
- This occurs in starches that have already been cooked
- When starch is cooked, the cyrstaline structure of amylose and amylopectin is lost and the hydrate to form a viscous solution
- if the viscous solution is cooled or left at lower tempature for a long period, the linear molecules amylose, and linear parts of amylopectin rearrnage themselves again to a more crystalline sturcture
- This crystaline structure is NOT Digestible - although it takes time for this to happen to all of the starch, typically happens to about 10% of it
As the fibre content of food increases, the digestibility of starch ?????
decreases.
What is meant by the glycaemic index, how is it calculated? What factors influence GI?
- done by using Pure glucose drink as a reference - this is represented on the glycemic index of 100, the highest GI value and represents the relative rise of blood glucose level two hours after consuming that food
-
GI is calculated from the blood glucose of the test food (measured as area under graph) divided by the blood glucose rise of the reference food (again measured as an area under graph), multiplied by 100.
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What are the major cations found in pancreatic juice?
What are the major anions found in pancreatic juice ?
Sodium and potassium
Cholride and bicarbonate
The faster the flow rate, the higher than ion concenration
Proteolytic enzymes are often specific to cerain amino acids. What does trypsin act on?
- C-terminal side of Lysine and arginine amino acids
- if there is a proline reside on the carboxyl side of the cleave site, the cleavage will not occur
What does chymotrypsin act on?
- Peptide bonds in which the carboxyl group is provided by tyrosine and phenylalanine - againt acting on carboxyl side
What amino acids does elastase act on?
- Glycine, serine, alanine
Summarise how bicarbonate production occurs in the pancreas
- carbon dioxide from the blood enters the ductal cells of pancreas, where it combines with water to form carbonic acid with the assistance of carbonic anhyrdase
- Carbonic acid dissociates into hydrogen ions and bicarbonate
-
bicarbonate ions are exchanged for cholride ions by secondary active transport thoruhg the luminal border of the cell into the lumen of the duct
- the cholirde that leaves the cells renters by special cholride channels
-
the hydrogen ions from carbonic acid are exchanged for sodium ions through the basolateral membeane of the cell by secondary activate transport
- sodium also enters via the basolateral membrane by contransport with bicarrbonate
- the negative voltage of the lumne also pulls the positively charged sodium ions across the tight junctions between the cells
- The overall movement of sodium and bicarbonate from the blood in he lumen creates an osmotic pressure gradient that causes movement of water also into the pancreatic duct, thus forming an almost completely isosmotic bicarbonate solution
Define acute pancreatitis
Acute pancreatitis is a condition where the pancreas becomes inflamed over a short period of time.
Summarise pathophysiology of acute pancreatitis, including potential triggers. Describe potential affects of different pancreatic enzymes.
- seems to occur as a conseuqnce of premature trypsinogen activation, releasing proteases that digest the pancreas and surrounding tissue
- triggers include alcohol(hyperstimulation , gallstones and pancreatic duct obstruction, defection intracellular transport and secreteion of pancreatic zymogens, reflux of infected bile or duodenal contents into pancreatic duct (sphincter of Oddi dysfunction)
- All of these can lead to ACINAR CELL injury, causing interstitial inflammation
-
Different enzymes can cause different probelms…
- Proteases can digest surrounding tissues
- Lipases can cause fat necrosis
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Elastases can cause hemorrhage
- all of these further enhance the inflammation
