fructose/galactose

Question 1

what C are fructose and galactose phosphorylated on?

Answer 1

C1

Question 2

major dietary sugar

Answer 2

glucose

Question 3

2nd most common sugar

Answer 3

fructose

Question 4

fructose comes from what disaccharide?

Answer 4

sucrose

Question 5

sucrose = ___+____

Answer 5

glucose + fructose

Question 6

lactose = ___+___

Answer 6

glucose + galactose

Question 7

in liver, enters glycolytic pathway at
glucose –>?
fructose –>?
galactose–>?

Answer 7

glucose –> g6p
fructose –> DHAP and G3p (glyceraldehyde)
galactose –> glucose 1 phosphate –> g6p

Question 8

where does glycerol enter glycolysis?

Answer 8

triglycerides break down into FA and glycerol

glycerol is phosphoryylated and enters at DHAP

Question 9

2 sources of dietary fructose

Answer 9

1 disaccharide sucrose (fruits and sugar)

2 monosaccharide fructose corn syrup

Question 10

fructose becomes what in fasting condition and well fed?

Answer 10

glucose in fasting times and pyruvate in fed state

Question 11

special about fructose: enters glycolysis after what?

Answer 11

after control point PFK1

so it can rapidly produce lactate or FA

Question 12

what sugar is useful in sports drinks and why?

Answer 12

fructose
because of its conversion to glucose and liver glycogen
max uptake rate is 60 g/hr = 240 cal/hr –> limited by glucose transporters in gut
but fructose enters by a different transporter so up to 336 cal/hr with fructose+glucose

Question 13

two things aldolase B does?

Answer 13

cleaves F1P in fructose pathway and F16BP in glycolytic path

Question 14

fructose metabolism

Answer 14

1. phosphorylated by fructokinase to F1P (uses 1 ATP)
2. F1P is cleaved by aldolase B –>DHAP and glyceraldehyde
3. glyceraldehyde is phosphorylated by triose kinase (glyceraldehyde kinase) to G3P (uses 1 ATP)

Question 15

in fructose metabolism, which step is fast and which is rate limiting enzyme?

Answer 15

fructose to F1P is rapid

and aldolase B is rate limiting

Question 16

fructose metabolism in non-liver tissues

Answer 16

fructose is phosphorylated by hexokinase to F6P (but hexokinase has very low affinity for it)

Question 17

what do sperm use as major energy source?

Answer 17

fructose

Question 18

polyol pathway

Answer 18

glucose to fructose (makes it for sperm energy)

glucose is reduced to sorbitol by aldose reductase (aldehyde to alcohol)
sorbitol is then reoxidized at C2 by sorbitol dehydrogenase to make fructose

Question 19

what causes cataracts?

Answer 19

elevated glucose or galactose –> sugar alcohols concentrate in lens –> increased osmotic pressure

Question 20

non lethal fructokinase deficiency

Answer 20

essential fructosuria

Question 21

essential fructosuria

Answer 21

deficient fructokinase
fructose is metabolized very slowly by hexokinase (low affinity); blood fructose levels rise and fructose appears in urine
no renal threshhold for fructose

Question 22

HFI

Answer 22

hereditary fructose intolerance

Question 23

serious fructose metabolism disorder?

Answer 23

HFI - hereditary fructose intolerance

Question 24

HFI - hereditary fructose intolerance

Answer 24

defective hepatic aldolase B (liver isozyme), but aldolase B still functions in glycolysis to cleave F16BP
since aldolase B in liver is the only enzyme that can cleave F1P, F1P accumulates and inhibits glucose production –> severe hypoglycemia is fructose is ingested

symptoms: hepatomegaly, failure to thrive –> avoid dietary fructose!

Question 25

major source of galactose?

Answer 25

disaccharide lactose (milk products)

Question 26

infants have greater ability to metabolize what?

Answer 26

galactose

Question 27

galactose to glucose metabolism

Answer 27

1. galactose is phosphorylated by galactokinase to galactose 1 phosphate (uses 1 atp) 2. galactose 1p reacts with UDP glucose to make glucose 1 phosphate and UDP galactose (via enzyme galactose 1 phosphate uriylyl transferase) 3. UDP galactose is epimerized to UDP glucose by UDP glucose epimerase (reversible) . repeat steps to convert galactose to UDP glucose and g1p net: galactose + atp --> glucose1P + adp

Question 28

reversible step in galactose metabolism?

Answer 28

epimerase (step 3)

Question 29

glucose 1 P from galactose breakdown can go on to...

Answer 29

form g6p and enter glycolysis

Question 30

which step in galactose metabolism is irreversible?

Answer 30

phosphorylation of galactose by galactokinase to galactose1phosphate (uses an ATP)

Question 31

net equation for galactose to glucose 1 P

Answer 31

galactose + atp --> glucose1P + adp

Question 32

hit locations in pathwayy for nonclassical and classical galactosemia

Answer 32

nonclassical --> galactokinase | classical --> galactose 1 phosphate uridylyltransferase

Question 33

galactose free diet - path from glucose to UDP galactose

Answer 33

glucose to g6p via glucokinase g6p to g1p g1p to UDP glucose (UTp used, PPi released; via UDP glucose phosphorylase) UDP glucose to UDP galactose via epimerase

Question 34

lactose intolerance

Answer 34

low level of lactase | unabsorbed lactose is turned into lactic acid by colonic bacteria and osmotic effects lead to diarrhea and dehydration

Question 35

low lactase means...

Answer 35

lactase deficiency

Question 36

galactosemia

Answer 36

high concentraton of galactose in blood

Question 37

two types of galactosemia

Answer 37

galactokinase deficiency | uridylyl transferase defciency

Question 38

what happens in galactosemia?

Answer 38

galactose accumulates and is reduced to galactitol; cataracts from accumulation in lens mental retardation from accumulation in brain hepatomegaly failure to thrive if galactose is ingested --> hypoglycemia avoid dietary galactose (milk products and artificial sweeteners)

Question 39

uridylyl transferase deficiency

Answer 39

more serious type of galactosemia | elevates galactose 1 phosphate and inhibits phosphoglucomutase -- interferes with glycogen synthesis and degradation

Question 40

two ways to make UDP galactose

Answer 40

-from galactose OR glucose via UDP glucose and an epimerase rxn

Question 41

what three products are made from UDP galactose?

Answer 41

glycoproteins glycolipids proteoglycans

Question 42

what enzyme adds galactose to growing polysaccharide chains?

Answer 42

galactosyl transferase

Question 43

whatenzyme reduces galactose to galactitol?

Answer 43

aldose reductase

Question 44

how does lactating mammary gland use UDP galactose?

Answer 44

UDP galactose + glucose --> milk lactose alpha-lactalbumin binds to galactosyl transferase and lowers its Km for glucose so that glucose adds galactose

Question 45

entry of glycerol into glycolysis

Answer 45

glycerol --> glycerol phosphate (via glycerol kinase; uses ATP) glycerol phosphate --> DHAP (via glycerol 3 phosphate dehydrogenase; NAD+-->NADH)