Class Note for BIOL 600 at KU
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Date Created: 02/06/15
Biol 600 lntro Biochemistry Fall 2005 1 1 Molecule Makhup of the Week One relationship between glyceraldehyde and glycerol is that a Their corresponding phosphorylated forms are both key intermediates in glycolysis IZl This refers to the fact that glycerol enters glycolysis as DHAP Notes Technically DHAP is not just glycerolP03 and the Z trioses are key players even though this is not a quotkey committed stepquot of glycolysis b Their corresponding phosphorylated forms are normally present in a 11 ratio The ratio is 496 c Glyceraldehyde is a ketose Whereas glycerol is an aldose d Glycerol can be converted directly into DHAP but not into GABP This says nothing about glyceraldehyde 2 In plants glyceraldehyde3P can be exported from the chloroplast and used for glycolysis in the cytoplasm This process probably occurs by a Passive diffusion of GABP along its concentration gradient high inside and low outside the chloroplast Charged molecules cannot pass through a lipid membrane b Protonation of the phosphoryl group to an uncharged species Which then diffuses passively through the membrane The phosphoryl cannot be protonated with pKa of about 2 for H3P04 HZPOf which you know will be pH 4 neutral species will accumulate at pHgZ You also know water can slip through membranes but you can t predict that for glyceraldehyde Finally you know most molecules are transported via protein carriers c Binding ofGA3P Within a pocket on the surface ofa carrier protein on the inside ofthe chloroplast membrane The protein then quotflipsquot upside down so the GABP is released into the cytoplasm Generally not allowed d Binding ofGA3P at the entrance to a pore in a transmembrane carrier protein The chloroplast opening then closes and the cytoplasmic end of the pore opens to release GABP into the cytoplasm 3 Which statement best describes the relationship between glucose and fructose a Fructose is a ketose related structurally to dihydroxyacetone Whereas glucose is an aldose related to glyceraldehyde b Glucose and fructose are anomers at C1 ofeach other c lZl Difructose is the furanose ring conformation Whereas Diglucose is the corresponding pyranose I d Glucose adopts a cyclic structure in solution Whereas fructose remains an open linear chain 4 ATP and NADH are called highenergy compounds because a ATP oxidizes molecules to which it transfers its oxygenirich phosphoryl group and NADH oxidizes molecules to which it transfers a protonibearing hydride ion ATP has a large negative AG for the transfer of its gamma phosphoryl group to an acceptor an oxygen and NADH has a large negative AG for transfer of its hydride ion H39 to an acceptor c They both release heat When completely oxidized in a bomb calorimeter True but all molecules do d They both possess an activated electron pair connecting the transferable group phosphoryl or hydride The chemical bond bonding electrons to the transferable group has the same energy as any other oxygenphosphorous or carbonhydrogen chemical bond 5 Which statement does NOT describe membrane phospholipids a When placed in water they can selfiassemble into double quotlayersquot with hydrocarbon chains on the inside and polar groups on the outside to interact With water lZl True so not a correct answer b The glycerol backbone is joined to fatty acids with ester bonds but to an amino acid with a phosphodiester bond c The exibility ofmembrane lipids is partly determined by the proportion ofsa tu ra ted bonds Which are in the cis vs the trans conformation IZl Any biochemist worth his or her NaCl would know that this was a simple typo for quotUNsatum tedquot Was the professor imagining a double bond as quotsaturatedquot with electrons We39ll never know and you 39ll get the credit They can readily quotflipquot from one side ofa membrane to the other lZl The rate of ipping is orders ofmagnitude lower than the rate of lateral diffusion so this answer is NOT true Biol 600 lntro Biochemistry Fall 2005 2 6 If a muscle cell has a low energy charge the glycolytic pathway will be 7 because 7 a Activated by high concentrations of citrate became citrate is an allosteric activator of phosphofructokinase b Activated became the low concentration of ATP relieves inhibition of Pyruvate Kinase and Phosphofructokinase c Inhibited became the low concentration of ATP inhibits Pyruvate Kinase and Phosphofructokinase d Inhibited by fructoseil67bisphosphate and by Fru7267bisphosphate became the production of both is stimulated by external glucagon 7 One fundamental principle of energy metabolism is a When energy is extracted from food and not used it turns into fat b When oxidized carbohydrates are reduced the bond energy is converted to heat When carbonicarbon bonds are broken during oxidative catabolism the bond is conserved as reducing potential in NADH and chemical potential energy in ATP d Complex carbohydrates are broken down by reductive anabolism using the potential energy of phosphoryl group transfer and electron transfer 8 One relationship between glycolysis and gluconeogenesis is that a They are both stimulated by low blood sugar and inhibited by high concentrations of energyirich metabolites within the cell b They can occur simultaneously within a single cell Not in the same place at the same time c Muscle cells release lactate lactic acid as an endiproduct of glycolysis and liver cells can use gluconeogenesis to convert this lactate back to glucose You can gure this out you know muscle can convert Pyr to lactate you should remember that Pyr ltgt Lactate is reversible so the liver could convert lactate back to Pyr and the rest is straightforward We discussed in class the difference between liver and muscle metabolism d They differ only in the enzymes which catalyze the irreversible steps 9 m are two steps needed to convert Pyruvate to PhosphoEnoleruvate in gluconeogenesis when only a single step was needed in glycolysis to convert PEP to Pyr a Pyruvate carboxylase activates Pyr by attachment of C02 a good leaving group which can be displaced by inorganic phosphate Even if this were true it would not answer the question It39s false because the PEP carboxykinase reaction adds phosphoryl from GTP not inorganic phosphate This answer tells how Pyr is converted to PEP but says nothing about why we need two steps nor about the energy expenditure in those steps The reaction PEP ADP Pyr ATP is energetically quotdownhillquot or irreversible Transfer ofa phosphoryl group from PEP to ADP releases more energy than does the transfer ofa single phosphoryl from ATP to Pyr Hence the energy ofat least two ATPs or equivalent is needed to make the reaction irreversible AJIWIt on the board quotthe reactionquotmsamquotPy1 gt a PEPquot at in Ibe argihalquutian IZl PEP has more than enough free energy to transfer its phosphoryl to ADP giving ATP and still be irreversible This tells us that it won39t be possible to transfer a single phosphoryl the other way from ATP to Pyr giving PEP In other words a single ATP molecule doesn39t have enough energy to reverse the Pyruvate Kinase reaction This implies that we39ll need more than one ATP And that39s exactly right we need two ATPs Of course we also need a new reaction sequence that uses them that39s Pyr DecarboXylase and PEPCK c Conversion of Pyr to PEP is energetically unfavorable so two energyiyielding carboxylation steps are needed to circumvent bypass the energy issue There is only one carboxylation step A carboxylation reaction isn t the same as a decarboXylation You can39t assume that these reactions are the reverse of each other Further one could give this answer without knowing anything about the PC and PEPCK reactions d Pyr plays only a single role in cellular metabolism Because PEP plays multiple roles its synthesis is more complex 10 Which of the following quotmetabolic messagesquot is mi a The hormone glucagon warns of insufficient carbon available to all tissues Note quotcarbonquot in the form of glucose This is the jargonslang we39ve been using in class and is used in the text b High Fruil67Pz is a quotfeediforwardquot signal of increasing input of glucose into the glycolytic pathway c High AMP signals high energy a high energy charge lZl AMP has no useable energy at all d High citrate signals an abundance of citric acid cycle intermediates
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