BIOC192 Lecture 25 - Absorption of Carbohydrates and Proteins

Question 1

how and why do sugars diffuse across cell membranes?

Answer 1

• sugars are highly soluble and cannot simply diffuse across cell membranes
• they require specific transporter proteins anchors in the membrane that form ‘pores’ in the membrane

Question 2

what are the 2 types of sugar transport?

Answer 2

1) active transport

2) facilitative transport

Question 3

what is active transport?

Answer 3

against a concentration gradient that needs energy from ATP

Question 4

what is facilitative transport?

Answer 4

passage down a concentration gradient

Question 5

what is the secondary active transporter of glucose?

Answer 5

SGLT 1

Question 6

what is a facilitative transporter of glucose?

Answer 6

GLUT 2

Question 7

what is the main sites of tissue distribution for GLUT 2?

Answer 7

• liver
• pancreas
• kidney
• intestinal epithelia

Question 8

what is the main sites of tissue distribution for SGLT 1?

Answer 8

-intestinal epithelia

Question 9

what does the SGLT 1 transport?

Answer 9

simultaneous import of glucose and Na+ ions

Question 10

what is GLUT 4 associated with?

Answer 10

muscle and adios tissue

Question 11

what is GLUT 3 associated with?

Answer 11

the brain

Question 12

why is there very little absorption of peptides?

Answer 12

very little absorption of peptides longer than four amino acids

Question 13

how are peptides absorbed into the small intestine?

Answer 13

absorption of di- and tri-peptides in the small intestine by co-transport with H+ ions via membrane transporter PepT1

Question 14

how and where are di- and tri- peptides further digested?

Answer 14

further digested into individual amino acids by cytoplasmic peptidases and exported form the epithelial cells into the blood circulation

Question 15

what are the Na+ dependant carriers?

Answer 15

• neutrel AA
• proline and hydroxyproline
• acidic AA
• basic AA (Lys, Arg) and cistine

Question 16

what is the absorption of amino acids from the gastrointestinal tract?

Answer 16

absorption from the lumen of small intestine by transepitelial transport

• semispecifiic Na+ dependant transport system
• Na+ dependant carriers transport both Na+ and an amino acid

Question 17

what are 4 examples of diseases that affect digestive organs?

Answer 17

1) pancreatitis
2) stomach ulcers
3) cystic fibrosis
4) coeliac disease

Question 18

what occurs from cystic fibrosis?

Answer 18

causes thick mucous secretions which block the pancreatic duct and the secretion of pancreatic enzymes

Question 19

how can cystic fibrosis be aided?

Answer 19

can be aided by taking supplements containing pancreatic enzymes

Question 20

what is the digestion of nucleic acid polymers?

Answer 20

• DNA and RNA are subject to partial hydrolysis in the stomach
• intestinal endonuclease enzymes hydrolyse the phosphodiester bonds linking individual nucleotides
• exonuclease enzymes release individual nucleotides (nucleoside monophosphates)
• individual nucleotides are absorbed via nucleotide transporters