IAS12

Question 1

functions of carbs beyond energy production

Answer 1

support brain function as brain relies on glucose
contribute to nucleic acid formation
involve in immune system function, connective tissue structure i.e. HA in connective tissue

Question 2

glycosidic linkage

Answer 2

1-4: no branch / 1-6: branch
affect branching, shape & chars

Question 3

amylase v amylopectin

Answer 3

both are glucose polymers & starch
amylase: 1-4 glycosidic links only
amylopectin: branched, 1-4 & 1-6 bonds

Question 4

alpha-amylase

Answer 4

cleave 1-4 glycosidic linkage in amylose & amylopectin releasing single glucose, eventually forms glucose, maltose, isomaltose, maltotriose & alpha limit dextrins (short chain branched amylopectin remnant)

Question 5

glycosidase

Answer 5

break down disaccharides into monosaccharides for absorption:
lactase, maltase, sucrase

Question 6

carb digestion except villi

Answer 6

mouth: salivary alpha amylase digests alpha-1,4 bonds in amylase forming alpha dextrins -> inactivated in stomach
sucrose & lactose digested in stomach
intestine: pancreatic alpha amylase further cleaves 1,4 bonds in maltose, etc. to release free glucose & form tri-/oligosaccharides, maltose & isomaltose
further cleavage of branched forms in intestinal wall to form mono-
undigested carbs go to ileum, fermented in bacteria & egested in feces

Question 7

fate of sugars after absorption

Answer 7

absorbed via hepatic portal vein
stored in liver or transported to cells

Question 8

intestinal villi structure

Answer 8

basal side connected to many blood & lymph vessels
brush borders face lumen
digestive enzymes attach to brush borders i.e. membrane lining of enterocytes

Question 9

digestion at villi

Answer 9

disaccharides digested to monosaccharides by glycosidases (small intestinal disaccharidases, produced by enterocytes) at brush borders

Question 10

monosaccharide absorption at villi & why

Answer 10

water-soluble mono cannot directly transport through hydrophobic plasma membrane (repelled)
only absorb monosaccharides –> hence single units of glucose must be cleaved from polymers in GI tract
glucose & galactose uptake by symporter SGLT1 against conc. grad. by coupling with transport of Na
fructose uptake by GLUT5, less efficient in large amts since uptake not coupled to Na+

Question 11

monosaccharide exiting cell

Answer 11

some retained for metabolic uses
fructose transport to capillary through GLUT5 in basolateral membrane
glucose, galactose, fructose transport out thru GLUT2 in basolateral membrane

Question 12

types of cellular glucose transport

Answer 12

active: SGLT (intestine, kidney tubule, choroid plexus) (IKC)
facilitated & insulin insensitive
GLUT4: (my friend) muscle & fat cells
facilitated & insulin sensitive:
GLUT1: (bumble bee’s best) almost all tissues but highly abundant in blood cell, blood-brain barrier, baby / fetus
GLUT2: (last known phrase is) liver, kidney, pancreas, intestine // also bidirectional
GLUT3: (no problem): neurons, placenta

Question 13

sites that use glucose as major or sole fuel

Answer 13

sole: RBC & brain (almost, can use KB)
major: muscle (also use FA & KB)

Question 14

glucose phosphorylation

Answer 14

entry mediated by GLUT1
after entry, converted irreversibly to G6P, traps G6P in cell

Question 15

glycolysis, energy investment phase

Answer 15

ATP hydrolyzed & donate phosphate group to glucose by hexokinase, forming G6P, provide energy to push Rx forward
G6P isomerically arranged to form F6P using G6P isomerase / PGI
ATP hydrolyzed, F6P -> F-1,6-BP using PFK

Question 16

glycolysis, energy generation phase

Answer 16

F-1,6-BP splits to form G3P then 1,3-BPG, release of Pi, produces 2 ATP & 1 NADH per G3P
pyruvate is end product

Question 17

fate of pyruvate

Answer 17

converted to acetyl-coA -> TCAC & OP if O2 present
converted by lactic dehydrogenase A (LDHA) to lactate -> exported from cell by MTC (no NADH formed)

Question 18

fate of lactate

Answer 18

blood lactate enters heart muscles, skeletal muscles, etc. & converted to pyruvate -> enter TCAC
or enter cori cycle

Question 19

glucose use in heavy exercise & oxygen debt

Answer 19

glycogen oxidized anaerobically when muscles undergo strenuous exercise -> lactate
heavy breathing continues after exercise to take more O2 for OP to rebuild proton gradient & replenish ATP for cori cycle

Question 20

cori cycle

Answer 20

glycogen consumed by muscle anaerobically to form lactate -> blood lactate taken up by liver -> GNG to form glucose -> blood -> muscle to convert back into glycogen
to prevent harmful accu. of lactate (that causes muscle pain) & restore muscle glycogen conc.

Question 21

sites of glucose storage

Answer 21

liver (as glycogen OR fatty acids & glycerol as TAG), stores glycogen need for whole body
when glycogen storage full, liver can make FA from glucose using acetyl coA
muscle (glycogen), for use by themselves in demand
adipocyte (TAG)

Question 22

adipocyte carb storage

Answer 22

insulin induce GLUT4 expression on adipocytes -> promote uptake & utilization of glucose
2 fates: oxidized into acetyl-coA for FDNS to form FA or conversion to glycerol-3P for backbone of TAG

Question 23

pentose phosphate pathway

Answer 23

parallel to glycolysis
produce ribose-5-P for nucleotide biosynthesis
produces NADPH as biochem reactant for glutathione mechanism
produce glutathione against oxidative stress i.e. neutralize harmful peroxide into water

Question 24

UDP-glucose pathway

Answer 24

UDP-glucose used to produce:
UDP-glucuronate for glucuronides in detox
intermediate compounds for glycogen
glycoproteins, glycolipids & proteoglycans for EC structures in cell surface
used in molecular constructions e.g. adding sugars to proteins in PTM

Question 25

fructose & galactose conversion to glucose

Answer 25

fructose taken up by liver, converted to glucose, glycogen, lactate or pyruvate, FA small amt exit liver & enter blood galactose -> glucose in liver -> glycogen for storage

Question 26

glucose de novo synthesis & glycogenolysis

Answer 26

synthesized by lactate, TCAC intermediates, AA in dietary protein, glycerol, pyruvate & others takes place in liver & kidney (slightly), almost reverse of glycolysis GL: glycogen -> G1P -> G6P -> glucose

Question 27

blood glucose level regulation

Answer 27

rise in BGL -> activate insulin-secreting cells in pancreas -> blood insulin lvl inc. -> insulin binds to insulin receptor -> intercellular signal cascade -> stimulate GLUT-4 expression on cell surface -> take up glucose into cell -> BGL lowered

Question 28

abnormal glucose metabolism indication

Answer 28

from blood glucose level: in diabetic high BGL for prolonged time w/o going down

Question 29

glucose tolerance

Answer 29

ability to dispose of glucose load, tight controls in homeostasis governs to keep regular pattern of glucose tolerance upon dietary intake or sustain fine balance of glucose availability to meet tissue demands deviated glucose tolerance pattern -> poor glucose homeostasis

Question 30

glucose tests

Answer 30

FOR: fasting plasma glucose (FPG) test: BGL in person fasted for >8 hours OGTT: BGL after person fasts >8 hours & 2h after person drinks glucose containing beverage, measure body response to glucose & BGL regulation random plasma glucose test: BGL measured at any time w/o fasting

Question 31

maintaining standard basal metabolic state prior to OGTT:

Answer 31

DMAIP diet: >150g of carb for 3 days medication: withhold non-essential drugs for 3 days alcohol: no for 3 days illness: no fever as fever stimulate GH -> increase glucose release into blood -> diabetic-like response i.e. false positive physical activity: suitable amounts as too little / much impairs glucose tolerance

Question 32

OGTT procedures

Answer 32

begins in morning (glucose tolerance decreases sig. in afternoon) 8:00 fasting blood taken as baseline sample 8:10 glucose challenge, drink glucose dose of 1.75g/kg body weight in 1 min 10:10 blood sample taken -> analysis

Question 33

enzyme based glucose detection

Answer 33

enzymatic assay coupled to chromogenic agent glucose catalysed to form H2O2 -> O2 by peroxidase tag chained chromogenic Rx -> observe O2 O2 oxidises dianisidine to brown measure optical density changes accu. via spectrophotometry -> glucose conc. known specific, quick, economical

Question 34

glucose assay preparation

Answer 34

enzymes kept in lyophilized form -> printed on dipstick w/ chem. buffers water reconstitute proteins -> buffers help enzymes catalyse

Question 35

malabsorption effect (TEMP SKIP)

Answer 35

unabsorbed materials in colon cause osmotic effect -> water draws into bowel -> large volume of water accelerate transit time for food through intestine -> diarrhoea

Question 36

lactose intolerance (TEMP SKIP)

Answer 36

pain, nausea, flatulence after ingestion of dairy products containing lactose caused by defective lactase, low lactase lvl or intestinal injury undigested lactose exposed to bacteria in ileum & colon -> fermentation -> gases produced -> bloating, cramps & diarrhoea