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0 1 Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion.
SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports glucose and sodium ions (Na+) into the cell.
Figure 1
. The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase.
[2 marks]
. The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how.
[2 marks]
*02*
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0 1 . 3
Describe and explain two features you would expect to find in a cell specialised for absorption.
[2 marks]
1
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Figure 2 is a diagram of one SGLT1 carrier protein.
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Figure 2
0 1
. 4 Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane.
Do not draw more than eight phospholipids.
[2 marks]
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. Figure 2 shows the SGLT1 polypeptide with NH2 at one end and COOH at the other end.
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.
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You may use a diagram in your answer.
[2 marks]
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To study lipid digestion, a scientist placed a tube into the gut of a healthy
20-year-old man. The end of the tube passed through the stomach but did not reach as far as the ileum.
The scientist fed the man a meal containing triglycerides through the tube.
The scientist also used the tube to remove samples from the man’s gut at intervals
after the meal.
The scientist measured the type of lipid found in the samples. Some of her results are shown in Table 1.
Table 1
Sample
Time of collection after meal / min
Concentration of fatty acids / mg cm−3
Concentration of triglycerides / mg cm−3
A 45 2.7 0.6
B 75 3.3 0.0
. Use your knowledge of lipid digestion to explain the differences in the results for samples A and B shown in Table 1.
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You should assume that no absorption had occurred.
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