other sugars

Question 1

composition of sucrose

Answer 1

glucose + fructose with a1,2 bond

Question 2

composition of lactose

Answer 2

glucose + galactose with b1,4 bond

Question 3

what type of glycosidase is a-amylase?

Answer 3

endoglycosidase = hydrolyzes internal a1,4 bonds to yield smaller sugar units (dextrins)

Question 4

following action of pancreatic a-amylase, what remains?

Answer 4

maltose (a1,4)
isomaltose (a1,6)
limit dextrins (3-8 sugars with branching)
maltotriose- trioses+other oligosaccharides

Question 5

what breaks down the products of pancreatic a-amylase?

Answer 5

glycosidases in the intestinal brush boarder

Question 6

what are the 2 a-glucosidases?

Answer 6

• sucrose-isomaltase complex

- glucoamylase

Question 7

where us the sucrose-isomaltase complex found? activity?

Answer 7

found most in the jejunum, sucrose subunit breaks sucrose into fructose and glucose, isomaltase subunit hydrolyzes a1,6 bonds; both enzymes are active on a1,4 bonds

Question 8

what is glucamylase?

Answer 8

2 subunits, both exonucleases, activity increases along the length of the small intestine

Question 9

what does b-galactosidase breakdown?

Answer 9

b1,4 bonds of lactose

Question 10

where is b-galactosidase located?

Answer 10

mainly jejunum

Question 11

what is the basis of the hydrogen breath test?

Answer 11

if lactose is not digested by b-galactosidase, then in will be converted to CH4 and H2 by intestinal flora, excess presence of H2 in the breath after lactose load suggests lactose intolerance

Question 12

what are a-glucosidase inhibitors?

Answer 12

DM med that reversibly inhibits enzyme to slow digestion and absorption of sugars and reduce post-prandial blood sugar spikes

Question 13

examples of a-glucosidase inhibitors

Answer 13

acrabose, migitol

Question 14

what contains trehalose?

Answer 14

insect blood, algae, fungi

Question 15

consequences of trehalase deficiency

Answer 15

illness after consumption of larger amount of edible mushrooms

Question 16

how does gut flora contribute to our caloric extraction from foods?

Answer 16

bacterial flora degrade soluble fiber, leads to products of gas/water and some short chain fatty acids, short chain FA then absorbed and carried to liver

Question 17

type of bond in cellulose

Answer 17

b1,4

Question 18

2 general ways monosaccharides are taken up by cells

Answer 18

1- Na/glucose cotransporter

2-faciltated diffusion

Question 19

GLUT1

Answer 19

on most cells, low Km, transports glucose and galactose

Question 20

GLUT2

Answer 20

on liver/pancreatic b cells, high Km, transports glucose/galactose/fructose

Question 21

GLUT3

Answer 21

on neurons, placenta and testes, transport glucose and galactose

Question 22

GLUT4

Answer 22

on skeletal mm and fat cells, activated by insulin, specific for glucose only

Question 23

GLUT5

Answer 23

mucosa of small intestine and sperm, specific for fructose

Question 24

enzyme that converts fructose to fructose-1-phosphate

Answer 24

fructokinase

Question 25

enzyme that converts fructose-1-phosphate to DHAP

Answer 25

aldolase B

Question 26

why is aldolase B rate limiting in fructose digestion?

Answer 26

has lower affinity for fructose-1-P than fructose-1,6-bisphophate (in glycolysis), thus fructose will accumulate in the liver after excess ingestion

Question 27

hereditary fructose intolerance

Answer 27

aldolase B deficiency caused by missense mutation in exon 5 that converts G to C and causes Ala to Pro. can cause hepatic/renal failure, hypoglycemia due to accumulation of fructose-1-P and inhibition of glycogenolysis/gluconeogenesis, also causes phosphate depletion

Question 28

what is activated when phosphate levels are low?

Answer 28

adenosine deaminase = AMP to IMP = IMP to uric acid = gout

Question 29

essential fructosuria

Answer 29

def of fructokinase, more benign, fructose excreted in urine

Question 30

what are “polyols”?

Answer 30

sugar alcohols

Question 31

enzyme that forms polyols

Answer 31

aldose reductase

Question 32

polyols formed from glucose, galactose

Answer 32

glucose- sortibol

galactose- galactiol

Question 33

what is a consequence of accumulated polyols?

Answer 33

cataracts, esp in hyperglycemic pts

Question 34

what enzyme forms fructose from sorbitol?

Answer 34

sorbitol dehydrogenase

Question 35

how is UDP-glucose formed?

Answer 35

reaction of glucose-1-P + UTP –> UDP-glucose + PPi by UDP-pyrophsophorylase

Question 36

what are the uses of UDP-glucuronate (4)

Answer 36

• drug excretion
• use in GAGs
• conjugation of bilirubin
• re-entry into glucose metabolism

Question 37

what enzyme is responsible for the conjugation of bilirubin?

Answer 37

UDP-gluconyltransferase

Question 38

what is lactose synthesized from?

Answer 38

UDP-galactose and glucose

Question 39

how is UDP-galactose formed?

Answer 39

from UDP-glucose with UDP-4-glucose-epimerase

Question 40

structure of lactose synthase

Answer 40

2 subunits- galactotransferase and a-lactalbumin (responsive to prolactin to increase activity of galactotransferase)

Question 41

2 enzymes in galactose metabolism

Answer 41

1- galactokinase

2- galactose-1-P uritidyltransferase

Question 42

classical galactosemia

Answer 42

deficiency of galactose-1-P uritidyltransferase leads to excess of galactose-1-P= mental retardation, vomiting, jaundice, cataracts

Question 43

why does classical galactosemia cause jaundice?

Answer 43

high levels of galactose-1-P inhibit formation of UDP-glucose
dec UDP glucose = dec UDP-glucaronate = dec bili excretion = jaundice

Question 44

what is non-classical galactosemia?

Answer 44

def of galactokinase, galatose accumulates and is excreted

Question 45

what can result from both forms of galactosemia?

Answer 45

cataracts from excessive galactitol (more likely to form cataracts in this dz than from hyperglycemia)