Unit 5 - Intro to Carbohydrates

Question 1

how are monosaccharides classified?

Answer 1

• number of carbons (5 = pentose, 6 = hexose, 3 = triose)

- chemical nature of carbonyl group (aldose = aldehyde, ketose = ketone)

Question 2

how are monosaccharides numbered?

Answer 2

carbons are numbered beginning with the carbon closest to the carbonyl group (carbonyl = anisomeric carbon = 1 if aldose, 2 if ketose)

Question 3

what are the most common aldoses?

Answer 3

glyceraldehyde (triose)
ribose (pentose)
glucose, mannose, galactose (hexose)

Question 4

what are the most common ketoses?

Answer 4

dihydroxyacetone (triose)
ribulose (pentose)
fructose (hexose)

Question 5

what are enantiomers? which form is more abundant in body?

Answer 5

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

Question 6

what is the anisomeric carbon?

Answer 6

the former carbonyl carbon (1 in aldose, 2 in ketose) that occurs in cyclic form

Question 7

how to tell if alpha or beta anomer

Answer 7

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)

Question 8

what makes something a reducing sugar

Answer 8

if the O (of the OH) of the anomeric carbon is not bound to any other molecule (anomeric C is reducing end)

Question 9

how are glycosidic linkages named?

Answer 9

• alpha/beta configuration of anomeric carbon

- numbers of connecting carbons

Question 10

how much of the typical diet consists of CHO?

Answer 10

40% (in the form of starch, lactose, and sucrose)

Question 11

what is amylose structure?

Answer 11

linear; glucose residues in alpha-1,4 linkage

Question 12

what is amylopectin structure?

Answer 12

linear and branched; glucose in alpha-1,4 and alpha-1,6

Question 13

what is lactose structure?

Answer 13

galactose and glucose in beta-1,4 linkage

Question 14

how to tell glucose from galactose?

Answer 14

glucose has alternating OH groups going up and down; galactose has C2 down and all the rest up

Question 15

what is sucrose structure?

Answer 15

glucose and fructose in alpha-1,2 linkage, and non-reducing sugar b/c OH’s aren’t free

Question 16

what is glycogen structure and what is it similar to?

Answer 16

same overall structure as amylopectin, but more highly branched
-linear and branched; glucose in alpha-1,4 and alpha-1,6

Question 17

what is glycogen used for and where is it mostly?

Answer 17

major storage form for glucose, and found mostly in liver and skeletal muscle

Question 18

what is cellulose structure?

Answer 18

linear glucose residues in beta-1,4 linkage

Question 19

what are the 3 classes of glycosidases?

Answer 19

endoglycosidase - cleave internal glycosidic bonds
exoglycosidase - cleave terminal glycosidic bonds
disaccharidases - cleave glycosidic bonds in disaccharides only

Question 20

what is the specificity of each glycosidase based on?

Answer 20

• 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)

Question 21

what is alpha-amylase? what does it break down? what are the 2 types?

Answer 21

endoglucosidase; hydrolyzes random internal alpha-1,4 bonds between glucose residues in starch (ex: amylopectin, amylose)
-there is salivary and pancreatic alpha-amylase

Question 22

salivary VS pancreatic alpha amylase and what they produce

Answer 22

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

Question 23

what are alpha-dextrins?

Answer 23

oligosaccharides that have at least 1 alpha-1,6 branch

Question 24

what must happen to carbohydrates before they are transported into epithelial cells?

Answer 24

must be cleaved into monosaccharides enzymatically

Question 25

what is the brush border and what is on it?

Answer 25

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

Question 26

what is glucoamylase?

Answer 26

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)

Question 27

what is maltase?

Answer 27

cleaves alpha-1,4 bond in maltose and maltotriose to make glucose and maltose (but usually just glucose)

Question 28

what is isolamtase?

Answer 28

cleaves alpha-1,6 bond in isomaltose and alpha-dextrins to make glucose and glucose polymers (but usually just glucose)

Question 29

what is sucrase?

Answer 29

cleaves the alpha-1,2 bond to make glucose and fructose

Question 30

what is lactase (beta-galactosidase)

Answer 30

cleaves beta-1,4 bond in lactose to make galactose and glucose

Question 31

what is the difference between lactose intolerance and lactase deficiency?

Answer 31

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

Question 32

what does severity of lactose intolerance symptoms vary with

Answer 32

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

Question 33

why is glucose “special” as a fuel?

Answer 33

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)

Question 34

what happens to glucose after entry into cells? what are examples?

Answer 34

converted into glucose-6-phosphate, which enters different metabolic pathways depending on cell type

• glycolysis
• glycogen synthesis
• pentose phosphate pathway

Question 35

what is glycolysis?

Answer 35

oxidation of glucose to make ATP and pyruvate

-glucose –> glucose-6-P —————-> pyruvate + ATP

Question 36

what is glycogen synthesis and where is it most common?

Answer 36

glucose –> glucose-6-phosophate glucose-1-phosphate ————-> glycogen
-mostly in liver and muscle

Question 37

what is pentose phosphate pathway?

Answer 37

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

Question 38

what is the citric acid cycle and where is it done?

Answer 38

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

Question 39

what “special role” does liver play in carbohydrate metabolism?

Answer 39

responsible for supplying glucose to other tissues via bloodstream during fasting or after low CHO meal
-done via glycogenolysis and gluconeogenesis

Question 40

gluconeognesis VS glycogenolysis

Answer 40

gluconeogenesis - synthesis of glucose from non-CHO soruces like AA
glycogenolysis - breakdown of glycogen to glucose

Question 41

what are blood glucose levels maintained near?

Answer 41

80-100 mg/dL