Digestion and Absorption Flashcards
The diagram represents part of the human digestive system. The organs are labelled A−F.
Give the letter of the organ that produces amylase.
- C
Give the letter of the organ that produces maltase.
- E
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction.
- Active site has a specific shape
- Only maltose can bind to it
- To form enzyme substrate complex
Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell.
- DNA helicase
- Breaks hydrogen bonds
- Only one DNA strand acts as a template strand
- RNA nucleotides are attracted to exposed bases
- Attraction according to base pairing rule
- RNA polymerase joins nucleotides together
Describe the structure of proteins.
- Polymer if amino acids
- Joined by peptide bonds
- Formed by condensation
- Primary structure is an order of amino acids
- Secondary structure us folding of polypeptide chain due to hydrogen bonding
Describe how proteins are digested in the human gut.
- Hydrolysis of peptide bonds
- Endopeptidases break polypeptides into smaller peptide chains
- Exopeptidases removes terminal amino acids
- Dipeptidases hydrolyse dipeptides into amino acids
A student investigated the effect of chewing on the digestion of starch in cooked wheat.
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 amylose breaks down starch
In this model of digestion in the human gut, what other enzyme is required for the
complete digestion of starch?
- Maltase
What was the purpose of step 2, in which samples were mixed with water, hydrochloric acid and pepsin?
- Mimics effect of the stomach
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 is the same as in the previous experiment but salivary amylase is denatured
The figure below shows the student’s results.
( Graph shows a faster rate of reaction for chewed cooked wheat compared to chopped cooked wheat, which starts at a higher mean concentration of reducing sugars )
Explain what these results suggest about the effect of chewing on the digestion of
starch in wheat.
- Some starch was already digested when chewed
- Faster digestion of chewed starch
- Same amount of digestion of starch without being chewed
Describe how you would test a sample of food for the presence of starch.
- Add iodine to the food sample
- Blue indicated starch is present
The concentration of glucose in the blood rises after eating a meal containing
carbohydrates.
The rise is slower if the carbohydrate is starch rather than sucrose.
Explain why.
- Starch is digested to maltose
- Maltose is digested to glucose
- Digestion of sucrose only uses one enzyme
The glycaemic load (GL) of a diet is a measure of how much digestible carbohydrate it contains.
The higher the GL of a diet the more quickly it raises the blood glucose concentration after a meal.
A diet with a high GL also increases the concentration of harmful lipids in the blood.
Scientists investigated the relationship between diets with different glycaemic loads
and the risk of developing coronary heart disease (CHD) in women.
he scientists determined the glycaemic loads of the diets of a large number of women. They then divided the women into 5 groups. Group 1 had diets with the lowest glycaemic load and group 5 had diets with the highest glycaemic load.
The scientists determined the risk of developing CHD in each group.
The graph shows their results.
( The bar graph has graphs labelled, 1, 2, 3, 4 and 5, 1 and 2 shows no difference whereas 3, 4 and 5 are increasing.
The graph is risk of developing CHD against glycaemic load, from lowest to highest. )
The scientists excluded women who smoked from the study.
Explain why.
- Smoking increases risk of CHD
What do these data show about the effect that glycaemic load of the diet has on the risk of developing CHD?
- No effect on the risk with diet group 1 and 2
- Above diet group 2, risk increases as glycaemic load increases
