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