Unit 5 - Intro to Carbohydrates Flashcards
how are monosaccharides classified?
- number of carbons (5 = pentose, 6 = hexose, 3 = triose)
- chemical nature of carbonyl group (aldose = aldehyde, ketose = ketone)
how are monosaccharides numbered?
carbons are numbered beginning with the carbon closest to the carbonyl group (carbonyl = anisomeric carbon = 1 if aldose, 2 if ketose)
what are the most common aldoses?
glyceraldehyde (triose)
ribose (pentose)
glucose, mannose, galactose (hexose)
what are the most common ketoses?
dihydroxyacetone (triose)
ribulose (pentose)
fructose (hexose)
what are enantiomers? which form is more abundant in body?
the D and L forms of monosaccharides; mirror images (D is more common)
- designation based on configuration of asymmetric carbon farthest from carbonyl group
- -if on right/up, is D
- -if on left/down, is L
what is the anisomeric carbon?
the former carbonyl carbon (1 in aldose, 2 in ketose) that occurs in cyclic form
how to tell if alpha or beta anomer
alpha will have the anomeric carbon’s OH group trans from the CH2OH (OH points down, CH2OH points up)
beta will have the anomeric carbon’s OH cis from the CH2OH (both going up)
what makes something a reducing sugar
if the O (of the OH) of the anomeric carbon is not bound to any other molecule (anomeric C is reducing end)
how are glycosidic linkages named?
- alpha/beta configuration of anomeric carbon
- numbers of connecting carbons
how much of the typical diet consists of CHO?
40% (in the form of starch, lactose, and sucrose)
what is amylose structure?
linear; glucose residues in alpha-1,4 linkage
what is amylopectin structure?
linear and branched; glucose in alpha-1,4 and alpha-1,6
what is lactose structure?
galactose and glucose in beta-1,4 linkage
how to tell glucose from galactose?
glucose has alternating OH groups going up and down; galactose has C2 down and all the rest up
what is sucrose structure?
glucose and fructose in alpha-1,2 linkage, and non-reducing sugar b/c OH’s aren’t free
what is glycogen structure and what is it similar to?
same overall structure as amylopectin, but more highly branched
-linear and branched; glucose in alpha-1,4 and alpha-1,6
what is glycogen used for and where is it mostly?
major storage form for glucose, and found mostly in liver and skeletal muscle
what is cellulose structure?
linear glucose residues in beta-1,4 linkage
what are the 3 classes of glycosidases?
endoglycosidase - cleave internal glycosidic bonds
exoglycosidase - cleave terminal glycosidic bonds
disaccharidases - cleave glycosidic bonds in disaccharides only
what is the specificity of each glycosidase based on?
- structure of glycosidic linkage (alpha-1,4, etc.)
- specific sugars on either side of glycosidic linkage (glucose - glucose VS glucose - galactose)
- position of glycosidic linkage w/in polymer (internal VS terminal)
what is alpha-amylase? what does it break down? what are the 2 types?
endoglucosidase; hydrolyzes random internal alpha-1,4 bonds between glucose residues in starch (ex: amylopectin, amylose)
-there is salivary and pancreatic alpha-amylase
salivary VS pancreatic alpha amylase and what they produce
S: made by salivary glands in mouth; inactivated by acid in stomach
P: made in pancreas, secreted into duodenum; continues where SAA left off, producing maltose, maltotriose, alpha-dextrins, isomaltose, etc.
HOWEVER, WILL NOT PRODUCE GLUCOSE
what are alpha-dextrins?
oligosaccharides that have at least 1 alpha-1,6 branch
what must happen to carbohydrates before they are transported into epithelial cells?
must be cleaved into monosaccharides enzymatically
what is the brush border and what is on it?
intestinal luminal/apical surface that contains glycosidases made from intestinal epithelial cells in the jejunum
- glucoamylase, maltase, isomaltase, sucrase, lactase (B-galactosidase)
- contains monosaccharide transporters that move them into cells, then exported out to blood via transporters in basolateral membrane
what is glucoamylase?
exoglucosidase that cleaves terminal alpha-1,4 bonds between glucoses, starting at non-reducing ends
-produces glucose and isomaltose (2 glucoses connected by an alpha1-6 bond)
what is maltase?
cleaves alpha-1,4 bond in maltose and maltotriose to make glucose and maltose (but usually just glucose)
what is isolamtase?
cleaves alpha-1,6 bond in isomaltose and alpha-dextrins to make glucose and glucose polymers (but usually just glucose)
what is sucrase?
cleaves the alpha-1,2 bond to make glucose and fructose
what is lactase (beta-galactosidase)
cleaves beta-1,4 bond in lactose to make galactose and glucose
what is the difference between lactose intolerance and lactase deficiency?
it’s not “intolerant” until you have symptoms of diarrhea, nausea, abdominal cramps, bloating, or gas
-if just have low lctase levels, are just lactase deficient
what does severity of lactose intolerance symptoms vary with
ethnicity, age, and speed of digestion, but not necessarily levels of lactase
- highest after birth, decline with aging (symptom usually in early childhood)
- 75-90% of ethnicities are (Asian > Native Americans > blacks), 25% of whites
why is glucose “special” as a fuel?
it’s the only fuel that can be used by all human cell types
- exclusive fuel for RBC, major fuel for brain
- can be uesd as precursor for other non-CHO compounds (FA, cholesterol, steroids, AA, NA)
what happens to glucose after entry into cells? what are examples?
converted into glucose-6-phosphate, which enters different metabolic pathways depending on cell type
- glycolysis
- glycogen synthesis
- pentose phosphate pathway
what is glycolysis?
oxidation of glucose to make ATP and pyruvate
-glucose –> glucose-6-P —————-> pyruvate + ATP
what is glycogen synthesis and where is it most common?
glucose –> glucose-6-phosophate glucose-1-phosphate ————-> glycogen
-mostly in liver and muscle
what is pentose phosphate pathway?
oxidation of glucose-6-P to 5 carbon sugar (pentose phosphates) to make NADPH for biosynthetic pathways
-5 carbon sugar then reenters glycolytic pathway for more oxidation or nucleotide synthesis
what is the citric acid cycle and where is it done?
oxidation of ACoA to CO2 and H2O to make high E electrons via FADH2 and NADH
- these are used to make ATP via electron transport and oxidative phosphorylation
- done if cells have mitochondria and O2
what “special role” does liver play in carbohydrate metabolism?
responsible for supplying glucose to other tissues via bloodstream during fasting or after low CHO meal
-done via glycogenolysis and gluconeogenesis
gluconeognesis VS glycogenolysis
gluconeogenesis - synthesis of glucose from non-CHO soruces like AA
glycogenolysis - breakdown of glycogen to glucose
what are blood glucose levels maintained near?
80-100 mg/dL
