Digestion + Absorption Exam Questions Flashcards
(15 cards)
The action of endopeptidases and exopeptidases can increase the rate of protein digestion.
Describe how.
endopeptidases hydrolyse the peptide bonds between amino acids in the middle of a protein
exopeptidases hydrolyse peptide bonds at the end of a protein
increases surface area
Describe the role of enzymes in the digestion of proteins in a mammal.
(Reference to) hydrolysis of peptide bonds;
Endopeptidase act in the middle of protein/polypeptide
OR
Endopeptidase produces short(er) polypeptides/ increase number of ends;
Exopeptidases act at end of protein/polypeptide
OR
Exopeptidase produces dipeptides/amino acids;
Dipeptidase acts on dipeptide/between two amino acids
OR
Dipeptidase produces (single) amino acids;
Suggest which type of dietary protein would be better for old men to eat to cause a net gain
of body proteins. Use the information provided to explain your answer.
Whey as it:
Is absorbed quicker
It has a faster/higher/greater/the highest/the greatest/the fastest rate of absorption;
Still stimulates/increases protein synthesis (even if lower than casein);
Prevents/inhibits/limits breakdown of body proteins;
Significantly more becomes body protein;
What can you conclude about the absorption of the products of protein digestion as the
percentage of protein increased in the rabbits’ food?
No significant difference (in protein absorption);
(because ± 2) SDs overlap;
Accept error bar for SD
(So mean)
percentage absorbed not affected by
Amount of protein (in diet) is not a limiting fact
OR
percentage in diet;
Something else is limiting factor eg amount of protease;
(But) small range of protein in diet
OR
(Should) Investigate wider range;
The food eaten by a rabbit is digested mainly by microorganisms in its caecum. The
caecum is a section of intestine attached between the ileum and the large intestine. The
resulting semi-digested material leaves the anus of a rabbit as soft, caecal droppings. The
rabbit then eats these caecal droppings.
Use this information and Figure 2 to suggest how eating its own caecal droppings helps a
rabbit’s digestion and absorption of dietary protein.
More/remaining/undigested (protein) broken down;
Accept all (protein) broken down
(So more) amino acids absorbed;
(Because) protein/food passes again through stomach/ileum;
Astudent investigated the effect of chewing on the digestion of starch in cooked wheat.
3.
He devised a laboratory model of starch digestion in the human gut. This is the method he used.
Volunteers chewed cooked wheat for a set time. The wheat had been cooked in boiling
water.
This chewed wheat was mixed with water, hydrochloric acid and a protein-digesting
enzyme and left at 37 °C for 30 minutes.
A buffer was then added to bring the pH to 6.0 and pancreatic amylase was added. This
mixture was then left at 37 °C for 120 minutes.
Samples of the mixture were removed at 0, 10, 20, 40, 60 and 120 minutes, and the
concentration of reducing sugar in each sample was measured.
Control experiments were carried out using cooked wheat that had been chopped up in a
blender, not chewed.
What reducing sugar, or sugars, would you expect to be produced during chewing?
Give a reason for your answer
Maltose;
Salivary amylase breaks down starch.
In this model of digestion in the human gut, what other enzyme is required for the complete
digestion of starch?
maltase
In the control experiments, cooked wheat was chopped up to copy the effect of chewing.
Suggest a more appropriate control experiment. Explain your suggestion.
Add boiled saliva;
Everything same as experiment but salivary amylase denatured.
Explain what these results suggest about the effect of chewing on the digestion of starch in
wheat.
Some starch already digested when chewing / in mouth;
Faster digestion of chewed starch;
Same amount of digestion without chewing at end
Endopeptidases and exopeptidases are involved in the hydrolysis of proteins.
Name the other type of enzyme required for the complete hydrolysis of proteins to amino
acids.
Dipeptidases
Suggest and explain why the combined actions of endopeptidases and exopeptidases are
more efficient than exopeptidases on their own.
1.Endopeptidases hydrolyse internal (peptide bonds)
OR
Exopeptidases remove amino acids/hydrolyse (bonds) at end(s);
Accept: break for hydrolyse.
Accept: endopeptidases break (proteins) into shorter chains.
2.More ends or increase in surface area (for exopeptidases);
The addition of a respiratory inhibitor stops the absorption of amino acids.
Use the diagram to explain why.
No/less ATP produced
OR
No active transport;
Sodium (ions) not moved (into/out of cell);
Accept: sodium (ions) increase in cell.
Accept: sodium (ions) cannot diffuse into cell.
No diffusion gradient for sodium (to move into cell with amino
acid)
OR
No concentration gradient for sodium (to move into cell with amino acid);
Describe how you would use a microscope to find the mean diameter of triglyceride
droplets on a slide.
Measure with eyepiece graticule / scale;
Calibrate with stage micrometer / scale on slide / object of known size;
Repeats and calculate the mean;
OR
Use a ruler to estimate the field diameter under microscope;
How many droplets go across the field;
Repeats and calculate mean;
Describe the role of the enzymes of the digestive system in the complete breakdown of
starch.
Amylase;
(Starch) to maltose:
Maltase;
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond;
Describe the processes involved in the absorption of the products of starch digestion.
Glucose moves in with sodium (into epithelial cell);
Via (carrier / channel) protein / symport;
Sodium removed (from epithelial cell) by active transport / sodium- potassium pump;
Into blood;
Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium
concentration gradient (between lumen and epithelial cell);
Glucose moves into blood;
By (facilitated) diffusion;
