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GI Week 3 > Nutrition: Carbohydrates > Flashcards

Nutrition: Carbohydrates Flashcards

1
Q

What are the 5 main dietary carbohydrates?

A 
fructose
lactose
sucrose
amylose
amylopectin
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2
Q

Which of the 5 main dietary carbs is a monosaccharide?

A

fructose

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3
Q

What is lactose a disaccharide of?

A

galacose and glucose (with a beta 1, 4 link)

“We’re LACking a GALlon of elmer’s GLUe.”

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4
Q

What is sucrose a disaccharide of?

A

Fructose and glucose (with an alpha-1:2 linkage)

“Those SUCkers! I put the GLUe in the FRUit punch!”

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5
Q

How do amylose and amylopectin differ from each other?

A

amylose has only alpha 1,6 bonds while amylopectin has alpha 1,6 and alpha 1,4 bonds - meaning it branches

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6
Q

What’s the minor disaccharide found in mushrooms and insects?

A

trehalose

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7
Q

What is trehalose a disaccharide of?

A

glucose and glucose bound by an alpha1,1 linkage

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8
Q

How are fructose and the disaccharides digested in general terms?

A

They just hang out in the GI tract unchanged until they’re transported into the intestinal epithelial cells with the help of the brush border enzymes

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9
Q

WHat needs to happen to the starches in order to be brought into the intestinal epithelial cells?

A

they must be broken down into small starch molecules by amylase - first by salivary amylase and then by pancreatic amylase

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10
Q

What are the 3 types of starches that amylase will break larger starches down to?

A

maltose
maltotriose
limit dextrans

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11
Q

Is amylase an endoglycosidase or an exoglycosidase and what does this mean?

A

It’s an ENDOglycosidase, meaning it can only cut inner bonds of the starch - it can’t cut on the very end

this means that it can’t break anything down into monosaccharides - disaccharides is the smallest is can do

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12
Q

What type of bonds are broken down by amylase?

A

alpha-1, 4

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13
Q

Where in the small itnestine is amylase activity highest?

A

duodenum

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14
Q

What are the 4 main disaccharidases of the brush border?

A
  1. glucoamylase
  2. sucrase/isomaltase complex
  3. trehalase
  4. Beta-glycosidase complex
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15
Q

What’s another name for glucoamylase?

A

maltase

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16
Q

Is glucoamylase an endoglycosidase or an exoglycosidase? What does this mean?

A

It’s an EXOglycosidase, meaning it can cleave the last link on the non-reducing end or the starch chain (or disaccharide), yielding individual molecules or glucose.

this is unlike amylase which is an endoglycosidase and can’t do the end pieces

17
Q

What types of bonds are cleaved by glucoamylase?

A

alpha-1,4

18
Q

So if you have amylopectin incubating in both amylase and glucoamylase, what will you end up with?

A

individual glucose molecules plus isomaltose (from the branch point - it has a alpha-1,6 linkage that can’t be broken down by either of them)

19
Q

Where in the small intestine is glucoamylase most active?

A

ileum

20
Q

Describe the general structure of the sucrase-isomaltase complex.

A

It has two extracellular domains with different substrate specificities

isomaltase is the part closest to the cell membrane (connected via a connecting segment(

Sucrase is the part further out in the lumen

21
Q

What does the sucrase part do?

A

Easy - cleaves the sucrose into glucose and fructose

22
Q

What does the isomaltase part do?

A

It claves the allaph-1,6 linkage in isomaltose (the one that amylase and glucoamylase can’t touch)

23
Q

So if you incubate amylopectin in amylase, glucoamlase and sucrase-isomaltase, what will you end up with?

A

just individual molecules of glucose

24
Q

Where in the small intestine is the sucrase-isomaltase complex activity highest?

A

the jejunum

makes sense - so by the time it gets to the ileum, it’s already dealt with the alpha,1-6 linkages so glucoamylase in the ileum can just do it’s thing and be done with it.

25
Q

What makes the structure of the beta-glycosidase complex different from the other brush border disaccharidases?

A

It’s not connected to the cell membrane via a transmembrane section - it’s anchored there by a glycophosphatidylinositol (GPI) glycan

26
Q

What are the two catalytic domains of the beta-glycosidase complex?

A
  1. glucosyl ceramide domain

2. lactase domain

27
Q

What does the glucosyl ceramide domain do?

A

It cuts glucose and galactose from glucosylceramide and galatosylceramide (from plants - anything with a cell membrane itself)

28
Q

What does the lactase domain do?

A

Easy - splits the 1,4 bond in lactose to make galactose and glucose

29
Q

Where in the small intestine is the beta-glycosidase complex activity highest?

A

jejunum

30
Q

Describe how carbohydrates enter the cell in the upper portion of the GI tract.

A

In the upper portion of the GI tract, the concentration of carbs in the lumen is much greater than the concentraion in the blood

this means they can enter the cell thorugh facilitated diffusion via transporters

31
Q

Describe how carbohydrates enter the cell in the lower portion fo the GI tract

A

In the lower portion of the GI tract, the concentration of carbs in the blood now exceeds that in the lumen, but it wouldn’t make sense to no longer take up the carbs and definitely wouldn’t make sense to spits carbs back into the lumen from blood

this means it’s worth it to use some energy. Na/K ATPases set up a Na gradient using ATP hydrolysis. A symporter than brings Na down it’s concentration gradient into the cell, with glucose/galactose piggybacking onto it

32
Q

Starches that aren’t digested by the brush border enzymes will become a substrate for what?

A

fermentation by gut bacteria

33
Q

What is produced by the bacteria through fermentation and what can use this byproduct for fuel?

A

short chain fatty acids like acetate, proprionate and butyrate

used by colonocytes

34
Q

What are the three general presentations of lactose intolerance?

A
  1. acute lactase deficiency due to infection or damage to gut
  2. Inherited form that presents in adulthood (most common)
  3. Inherited form that is present from birth
35
Q

Describe the pathology of lactose intolerance?

A

Without lactase, lactose won’t be broken down and gut bacteria will ferment it down to lactic acid

the lactic acid will dissociate into lactate and a proton. The excess protons in the lumen create an osmotic force that pulls fluid into the lumen, causing distension, increased peristalsis and diarrhea

GI Week 3 (15 decks)

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