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SGU: Carbs & Glycoly
Biochem: Carbohydrates and Glycolysis
| Question | Answer |
|---|---|
| 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
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