Carb Metabolism 1 Flashcards
sources of dietary carbs for pre-agricultural humans
- roots, tubers, and rhizomes
- seeds above ground
- certain fruits and nuts
- inner bark of some trees
low in starch, high in fiber
sources of dietary carbs for industrialized humans
starch and fibers: pasta, apples, potatoes, bread, rice
simple sugars: sucrose, glucose, fructose: juices, honey, candy, soda
glucose use: postprandial
mainly liver, gut, and skeletal muscle
glucose use: post-absorptive (in between meals)
brain!
can brain live without glucose?
NO!
it can survive without oxygen for a few minutes, but not at all without glucose
most abundant form of starch
pectin
benefits of branching starches
it is better to keep energy in a more restricted space (human adaptation)
main dietary carbohydrates: disaccharides
- maltose
- lactose sucrose
- trehalose (a1 –> 1 D-glucose)
lactose is made of
galactose + glucose joined by beta 1,4
sucrose is made of
glucose + fructose joined by alpha 1,2
salivary and pancreatic alpha-amylase break down what into what
starch into maltose, trisaccharides (smaller molecules, but still not absorbable)
2 main enzyme categories of carbohydrate digestion
- endoglucosidases
- small intestine disaccharidases
endoglucosidases mechanism
hydrolyze alpha 1,4 bonds (NOT alpha 1,6) between glucosyl residues
shortened polysaccharide chains that are formed are called alpha-dextrins
endoglucosidases examples
alpha-dextrins
salivary alpha-amylase
pancreatic alpha-amylase
small intestine disaccharidases mechanism
hydrolyze alpha 1,4, alpha 1,6, beta 1,2 (sucrose), and beta 1,4 (lactose) bonds in limit dextrins, oligo-, and disaccharides
small intestine disaccharides examples
sucrase-isomaltase
maltase-glucoamylase
lactase
sucrase isomaltase
(alpha-dextrinase) glycosidase activity: alpha-1,4, alpha-1,6, beta-1,2
what happens if someone has a sucrase mutation?
we can’t degrade sucrose so we create a malabsorption for fructose, promotes diarrhea (water is trapped, fructose is never degraded)
no lactase =
lactose remains in intestinal lumen, draws in water, leads to diarrhea
bacteria is waiting for lactose
lactase deficiency produces
flatulence and diarrhea when dairy sugars are consumed
3 types of lactase deficiency
- primary hypolactasia
- primary congenital hypolactasia (alactasia)
- secondary hypolactasis
primary hypolactasia
autosomal recessive; lactase activity declines over many years, usually beginning in late childhood
primary congenital hypolactasia (alactasia)
very rare genetic conditionl complete absence of lactase
primary congenital hypolactasia (alactasia)
very rare genetic conditionl complete absence of lactase
