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BIOC192 > Lecture 25: ABSORPTION OF CARBOHYDRATES AND PROTEINS > Flashcards

Lecture 25: ABSORPTION OF CARBOHYDRATES AND PROTEINS Flashcards

1
Q

What are sugars?

A

Highly water soluble and cannot simply diffuse across cell membranes (lipid bilayer)

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2
Q

What does sugar transport require?

A

Specific transporter proteins anchored in the membrane that form pores in the membrane

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3
Q

What are the types of transport?

A

Active and facilitative

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4
Q

What is active transport?

A

Against a concentration gradient that needs energy from ATP

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5
Q

What is facilitative transport?

A

Passage down a concentration gradient

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6
Q

What does glucose transport across the intestinal epithelia involve?

A

Two glucose transporters (SGLT1, a secondary active transporter, and GLUT2, a facilitative transporter)

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7
Q

What happens to glucose when it is in the circulation?

A

It is taken up by tissues such as liver, muscle and brain via other glucose transporters - such as GLUT4 (adipose and muscle) and GLUT3 (brain)

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8
Q

What are the glucose transporters?

A

GLUT1, GLUT2, GLUT3, GLUT4, SGLT1

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9
Q

Where is the main site of GLUt1?

A

Ubiquitous

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10
Q

Where is the main site of GLUT2?

A

Liver, pancreas, kidneys, intestinal epithelia

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11
Q

Where is the main site of GLUT3?

A

Brain

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12
Q

Where is the main site of GLUT4?

A

Muscle, adipose tissue

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13
Q

Where is the main site of SGLT1?

A

Intestinal epithelia

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14
Q

What does glucose transport by SGLT1 involve?

A

Simultaneous transport (symport) of sodium ions (from intestinal lumen into cell)

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15
Q

What is extracellular sodium concentration?

A

120-140 mmol/L

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16
Q

What is intracellular sodium concentration?

A

20-30 mmol/L

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17
Q

What does GLUT2 do?

A

Transport glucose from inside the intestinal cells to the peripheral tissues/blood

18
Q

What does Na+/K+ ATPase do?

A

Actively transports Na+ to maintain the low sodium concentration in epithelial cells and maintain the gradient for SGLT1

19
Q

How does Na+/K+ ATPase work?

A

It takes up 3 sodium ions, hydrolysis of ATP causes a phosphate to bind and a conformational change to release the sodium ions and pick up 2 potassium ions. Hydrolysis of the phosphate bond causes release of the potassium ions

20
Q

What is there very little absorption of?

A

Peptides longer than four amino acids

21
Q

How are di- and tri-peptides absorbed in the small intestine?

A

By co-transport with hydrogen ions via membrane transporter PepT1

22
Q

what happens with absorbed di- and tri-peptides?

A

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

23
Q

What is the transport system for absorption of amino acids?

A

Semi specific sodium dependent

24
Q

What do sodium dependent carriers transport?

A

Sodium ions and an amino acid

25
Q

How many different sodium dependent carriers are there?

A

At least 6

26
Q

What are some of the sodium dependent carriers?

A

Neutral amino acids, proline and hydroxyproline, acidic amino acids, basic amino acids (Lys, Arg) and cysteine

27
Q

When does uptake of intact proteins occur?

A

Only in a few circumstances, for example newborn animals. Uptake of immunoglobulins in colostral milk for acquisition of passive immunity

28
Q

What diseases affect digestive organs?

A

Pancreatitis, stomach (or peptic) ulcers, cystic fibrosis and coeliac disease

29
Q

What does pancreatitis lead to?

A

Inappropriate activation of zymogens (proenzymes) resulting in self digestion

30
Q

What are stomach (or peptic) ulcers due to?

A

The breakdown of the mucosa which normally protects against protease action

31
Q

What do cystic fibrosis and coeliac disease cause?

A

Malabsorption

32
Q

What does cystic fibrosis cause?

A

Thick mucous secretions which block the pancreatic duct and affect the secretion of pancreatic enzymes

33
Q

What can cystic fibrosis be aided by?

A

Takin supplements containing pancreatic enzymes - ‘pancreatin’, a pancreas extract

34
Q

What is coeliac disease a disease of?

A

The small intestine (particularly the duodenum)

35
Q

What does the body react to in coeliac disease?

A

Gluten protein present in wheat

36
Q

What do antibodies react with in coeliac disease?

A

Transglutaminase

37
Q

What happens to villi in coeliac disease?

A

They flatten and channels close causing nutrients to not be absorbed

38
Q

What symptoms are observed in coeliac disease?

A

Gastrointestinal

39
Q

What are DNA and RNA subject to?

A

Partial acid hydrolysis in the stomach

40
Q

What do intestinal endonuclease enzymes do?

A

Hydrolyse the phosphodiester bonds linking individual nucleotides

41
Q

What do exonuclease enzymes in the intestine do?

A

Release individual nucleotides (nucleoside monophosphate)

42
Q

How are individual nucleotides absorbed?

A

Via nucleotide transporters

BIOC192 (38 decks)

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