Nutrition: Carbohydrates Flashcards
What are the 5 main dietary carbohydrates?
fructose lactose sucrose amylose amylopectin
Which of the 5 main dietary carbs is a monosaccharide?
fructose
What is lactose a disaccharide of?
galacose and glucose (with a beta 1, 4 link)
“We’re LACking a GALlon of elmer’s GLUe.”
What is sucrose a disaccharide of?
Fructose and glucose (with an alpha-1:2 linkage)
“Those SUCkers! I put the GLUe in the FRUit punch!”
How do amylose and amylopectin differ from each other?
amylose has only alpha 1,6 bonds while amylopectin has alpha 1,6 and alpha 1,4 bonds - meaning it branches
What’s the minor disaccharide found in mushrooms and insects?
trehalose
What is trehalose a disaccharide of?
glucose and glucose bound by an alpha1,1 linkage
How are fructose and the disaccharides digested in general terms?
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
WHat needs to happen to the starches in order to be brought into the intestinal epithelial cells?
they must be broken down into small starch molecules by amylase - first by salivary amylase and then by pancreatic amylase
What are the 3 types of starches that amylase will break larger starches down to?
maltose
maltotriose
limit dextrans
Is amylase an endoglycosidase or an exoglycosidase and what does this mean?
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
What type of bonds are broken down by amylase?
alpha-1, 4
Where in the small itnestine is amylase activity highest?
duodenum
What are the 4 main disaccharidases of the brush border?
- glucoamylase
- sucrase/isomaltase complex
- trehalase
- Beta-glycosidase complex
What’s another name for glucoamylase?
maltase
Is glucoamylase an endoglycosidase or an exoglycosidase? What does this mean?
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
What types of bonds are cleaved by glucoamylase?
alpha-1,4
So if you have amylopectin incubating in both amylase and glucoamylase, what will you end up with?
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)
Where in the small intestine is glucoamylase most active?
ileum
Describe the general structure of the sucrase-isomaltase complex.
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
What does the sucrase part do?
Easy - cleaves the sucrose into glucose and fructose
What does the isomaltase part do?
It claves the allaph-1,6 linkage in isomaltose (the one that amylase and glucoamylase can’t touch)
So if you incubate amylopectin in amylase, glucoamlase and sucrase-isomaltase, what will you end up with?
just individual molecules of glucose
Where in the small intestine is the sucrase-isomaltase complex activity highest?
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.
