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SGU: Carbs & Glycoly

Biochem: Carbohydrates and Glycolysis

QuestionAnswer
What is a mirror image of a molecule called? enantiomers
Most predominant carbohydrate enantiomer in humans D
Classification of monosaccharides based on? functional group (aldoses/ketoses) and number of C atoms (trioses, tetroses)
What are monosaccharides that have the same chemical formula and different structural formula isomers
Describe aldoses aldehyde group on C1
Describe ketoses aldehyde group on C2
What carb groups are reducing sugers and what does that mean? free aldehyde or keto group that can react with cupric ions and convert them to cuprous
Which carb group is the faster reducing group? aldoses
How do you detect sugar in urine based on the reducing property of sugars - benedict's test
What are the clinical conditions in which sugars may be present in the urine? diabetes mellitus, fructosuria and hereditary fructose intolerance, galactosemia
What presentage of glucose is present in urine? glucose is found urine when blood glucose is 170-180% greater
What is used to measure sugars in the urine? dipstick
Example of a 3C aldose? glyceraldehyde
Example of a 3C ketose? dihydroxyacetone
Example of a 5C ketose? ribulose, xylulose
Example of a 6C ketose? fructose
Example of a 7C ketose? sedoheptulose
Example of a 9C ketose and aldose? neuraminic acid
Example of a 4C aldose? erythrose
Example of a 5C aldose? ribose, xylose
Example of a 6C aldose? glucose, galactose, mannose
Which carbohydrates usually exist in the cyclic form? 5 or more carbons
What is mutarotation? anomers that interconvert
What is an epimer? carb isoforms that differ in the configuration around one of the asymmetric C-atoms
Glucose and galactose are what kind of carb? epimers (C4)
Glucose and mannose are what kind of carbs? epimers of C2
What is epimerases? enzymes that interconvert epimers
What is the linkage between a pentose sugar and purine/pyrimidine? beta-glycosidic linkage
What is a polyol? sugar alcohol
When is sorbitol formed? blood glucose level is elevated for long time (prolonged hyperglycermia)
How is sorbitol formed? from glucose in the nerve tissue, retina and lens
Sorbitol is responsible for? chronic complications of diabetes mellitus
Children with untreated galactosemia get? galactitol formation from galactose in the lens
What is the linkage between glucose and galactose? makes lactose, beta1-4 glycosidic linkage
What kind of patients should avoid lactose in their diet? lactose intolerance and galactosemia
What kind of sugar is lactose? a reducing sugar
What kind of sugar is sucrose? a non-reducing sugar because C1 of glucose and C2 of fructose link therefore aldehyde and keto group are not free
What cleaves dietary sucrose to its monosaccharides in intestines? intestinal sucrase
When should sucrose be avoided in the diet? children with hereditary fructose intolerance
Where is fructose found? fruits and honey
What kind of sugar is fructose? ketohexose
What is HFCS and when is it used? high fructose corn syrup used as a sucrose substitue in soft drinks
How is HFCS ingested? as a mixture of monosaccharides
Difference between HFCS and sucrose? HFCS fructose:glucose ratio is greater than 1, in sucrose it is 1
Linkage between two glucose to make maltose? alpha1-4 glycosidic linkage
What kind of sugar is maltose? reducing sugar
When is maltose formed in the body and what cleaves it to glucose? formed as a product os digestion of starch by amylase, cleaved by intestinal maltase
What are homopolysaccharides? starch and glycogen which are made up of only glucose units
Example of heterpolysaccharides? GAGs
Function of glycogen? storage polysaccharide in humans in liver and muscle as cytosolic granules
How is glucose linked in glycogen? alpha1-4 glycosidic linkages in linear chain, at branch points - alpha1-6 glycosidc linkages
Composition of starch? amylose and amylopectin
Linkages of starch? alpha1-4 glycosidic linkages in chain, at branch point alpha1-6 glycosidic linkages
What is amylose? linear unbranched polymer of glucose
What is amylopectin? branched polymer of glucose
How is starch digested? salivary and pancreatic amylase
Amylopectin vs. glycogen? amylopectin has fewer branches
How do enzymes of glycogen metabolism work? at ends of the branches of glycogen removing or adding glucose from the glycogen
GAGs composition? repeating disaccharide units
What is a sugar acid? glucuronic acid
What is an amino sugar? glucosamine or galactosamine
Examples of dietary fiber? cellulose and pectin
Cellulose composition and linkages? glucose linked by beta1-4 glycosidic linkages
When does the number of GLUT4 in the PM change? increase in insulin when blood glucose level is elevated
Describe Vmax and Km for glucokinase vs. hexokinase? Glucokinase Vmax and Km is higher than hexokinase
what phosphorylates glucose into glucose 6 phosphate? glucokinase in liver and hexokinase everywhere else
What happens when there are inherited mutations of glucokinase in the liver? glucokinase can't phosphorylate glucose in the liver rare form of inherited diabetes mellitus and elevated blood glucose levels
What is the fate of glucose 6 phosphate in the liver? pyruvate, glycogen, HMP shunt (made by glucose)
Can glycolysis generate ATP in the presence and absence of O2? yes
Stage 1 of glycolysis? energy investment phase, 2 ATP are used when G6P is made (G6P makes F6P) and when F6P converts to Fructose 1,6 biphosphate by PFK1 (phosphofructokinase1)
Stage 2 of glycolysis? cleavage of 6C to 3C: Fructose 1,6 biphosphate is cleaved by aldolase A into G3P and dihydroxyacetone phosphate
How are 2 G3P made in glycolysis? triosephophate isomerase converts dihydroxyacetone phosphate to G3P
Stage 3 of glycolysis producing 1st 2 ATP? energy generation phase, formation of 1,3 bisphosphoglycerate from glyceraldehyde 3 phosphate by GAPDH (NADH formed), which is a high energy intermediate = ATP when converted to 3 phosphoglycerate
Stage 3 of glycolysis producing last 2 ATP? phophoglycerate mutase converts 3-phosphoglycerate to 2-phosphoglycerate, phosphoenol pyruvate formed by enolase, which produces ATP when pyruvate kinase converts it to pyruvate
How many pyruvate formed during glycolysis? 2
When does substrate level phosphorylation occur? conversion of 1,3-bisphosphoglycerate to 3 phosphoglycerate by phophoglycerate kinase and conversion of phosphoenol pyruvate to pyruvate by pyruvate kinase
Which steps in glycolysis are irreversible? hexokinase/glucokinase, PFK1, and pyruvate kinase enzyme reactions
What effect does arsenate have on glycolysis? pentavalent arsenate poisoning, inhibition of GAPDH
What effect does fluoride have on glycolysis? blocks enolase from converting 2 phosphoglycerate into phosphoenol pyruvate
What is the fate of pyruvate in aerobic conditions? converted to acetyl CoA by pyruvate dehydrogenase and enters TCA cycle
What is the fate of pyruvate in anaerobic conditions? converted to lactate by lactate dehydrogenase and goes to liver via Cori cycle
When or where does anaerobic glycolysis occur? absense of mito or poorly vascularized cells - RBCs, lens, cornea, leucocytes OR lack of oxygen - actively contracting white skeletal muscle
What is formed during anaerobic glycolysis? NAD+ from NADH so glycolysis can proceed
What enzyme converts Pyruvate to Lactate? LDH
Where is LDH found? in the cytosol
What determines the direction of the pyruvate - lactate reaction? NADH/NAD+ ratio
Why does lactate form in the muscles rate of glycolysis exceeds the oxidate capacity of the ETC producing more NADH than NAD+
What happens to muscle if lactate accumulates in it? causes a drop in pH and manifests as cramps during intense exercise
Where does lactate go in the muscle and RBCs? diffuses out of the cells and is taken to the liver where it is used for gluconeogenesis (cori cycle)
What happens to lactate in heart muscle? converted to pyruvate and later to acetyl CoA to enter TCA cycle.
Why is cardiac muscle NADH/NAD+ ratio very low? it is predominantly aerobic due to abundance of mitochondria and good vascularizaton
Describe the Cori cycle under anaerobic conditions pyruvate gives rise to lactate (in muscle/RBCs) (produces 2 ATP), the lactate travels to the liver where it is converted to glucose via gluconeogenesis (requires 6 ATP)
What happens to the NADH formed in glucose under aerobic conditions? each NADH is used in ETC to produce 3 ATP (in malate-aspartate) 2 ATP (in glycerol-phosphate shuttle)
How many ATP are made in glycolysis? 8 ATP made under aerobic conditions and 2 ATP are made in Anaerobic conditions
What is different about glycolysis in adipose tissue? G3P is used for TAG formation
What is a by-product during glycolysis in red blood cells? 2,3 bisphosphoglycerate
How is 2,3 BPG formed in RBCs? instead of 1,3 bisphosphoglycerate being converted to 3 phoshoglycerate, mutase converts it to 2,3 BPG
What happens to the 2,3 BPG level in people from high altitudes? it is increased to facilitate unloading of oxygen
What is the second most common form of hemolytic anemia? pyruvate kinase deficiency in RBCs
What happens to 2,3 BPG in pyruvate kinase deficient RBCs? increases
What is the most common form of hemolytic anemia? G6PD deficiency
Which tissues depend on glycolysis for energy? RBCs, brain, actively contracting skeletal muscle, retina, lens, tumor cells
What is the fate of pyruvate during gluconeogenesis in the liver? pyruvate carboxylase converts it to oxaloacetate
What happens to pH, serum HCO3 and PCO2 during lactic acidosis? pH is low, HCO3 and PCO2 is decreased during compensation
When does lactic acidosis occur? increased conversion of pyruvate to lactate, strenuous muscle activity, inherited deficiency of pyruvate dehydrogenase, thiamine deficiency resulting in lowered activity of pyruvate dehydrogenase, defect in gluconeogenesis, decreased blood supply
What is the Warburg effect? tumour cells use glycolysis as the main source of ATP
What is fluorodeoxyglucose used for? glucose analog used for positron emission tomography in tumor cells that take is up
What metabolic changes occur in cancer cells? hypoxia induces the activation HIF-1 which increases glycolytic enzymes
How is glycolysis regulated? PFK1 is an allosteric enzyme-ATP inhibits it and AMP-stimulates it (regulation in muscle), fructose 2,6 bisphosphate stimulates it in liver
Created by: mnoronha