BIOCHEM Unit 2 (ch. 7, 8, 16, 15)

What is the structural difference between NADH and NADPH?

In NADPH, the 2' hydroxyl of the ribose attached to the adenine has a phosphate attached.

A protein is involved in transporting ions in and out of cells. Would you expect to find the nonpolar residues in the interior or the exterior? Why? Would you expect to find the polar residues in the interior or the exterior? Why?

In a protein that spans a membrane, the nonpolar residues are the exterior ones; they interact with the lipids of the cell membrane. The polar residues are in the interior, lining the channel through which the ions enter and leave the cell.

What structural features do a triacylglycerol and a phosphatidyl ethanolamine have in common? How do the structures of these two types of lipids differ?

In both types, glycerol is esterified to carboxyic acids, with 3 such ester linkages formed in triacylglycerols and 2 in phosphatidyl ethanolamines. The structural difference comes in the nature of the 3rd ester linkage to glycerol. In phosphatidyl ethanolamines, the 3rd hydroxyl group of glycerol is esterified not to a carboxylic acid but to phosphoric acid. The phosphoric acid moiety is esterified in turn to ethanolamine.

The role of nucleophilic catalysis in the mechanism of the chymotrypsin reaction

In the 1st step, the Serine hydroxyl is the nucleophile that attacks the substrate peptide bond. In the 2nd step, water is the nucleophile that attacks the acyl-enzyme intermediate.

Why is it important that energy released by exergonic reactions can be used to provide energy for endergonic reactions?

Many endergonic reactions are necessary for life processes. They need a source for the energy they require, and that source is the energy released by exergonic reactions.

Crisco is made from vegetable oils, which are usually liquid. Why is Crisco solid?

Many of the double bonds have been saturated. Crisco contains "partially hydrogenated vegetable oils."

Which coenzyme is a reactant in the oxidation of nutrient, NAD⁺ or NADH? Why?

NAD⁺ is the oxidizing agent in reactions in which a nutrient is the substance to be oxidized. Like all oxidizing agents, NAD⁺ is reduced, producing NADH.

What structural feature do NAD⁺, NADP⁺, and FAD have in common?

NAD⁺, NADP⁺, and FAD all contain an ADP moiety.

Can the thermodynamic property ∆G° be used to predict the speed of a reaction in a living organism? Why or why not?

No, there is no relationship between the thermodynamic quantity ∆G° and the speed. The ∆G° reflects the thermodynamic possibility under standard states. Speed is a kinetic quantity that is based on the ability of an enzyme to catalyze the reaction and the real substrate concentrations in the cell.

Which of the following statements are true? Explain. A. all coenzymes are electron-transfer agents. B. Coenzymes do not contain phosphorus or sulfur. C. Generating ATP is a way of storing energy.

None of these statements is true. Some coenzymes are involved in group-transfer reactions. Many coenzymes contain phosphate groups, and CoA contains sulfur. ATP doesn't represent stored energy, but is generated on demand.

Which is more hydrophilic, cholesterol or phospholipids? why?

Phospholipids are more hydrophilic than cholesterol. The phosphate group is charged, and the attached alcohol is charged or polar. These groups interact readily with water. Cholesterol has only a single polar group, an -OH.

All the organophosphate compounds listed in Table 15.1 undergo hydrolysis reactions in the same way as ATP. The following equation illustrates the situation for glucose-1-phosphate. Glucose-1-phosphate 1 H₂O → Glucose + Pi ∆G°' = -20.9 kJ/mol Using the free-energy values in Table 15.1, predict whether the following reactions will proceed in the direction written, and calculate the ∆G°' for the reaction, assuming that the reactants are initially present in a 1:1 molar ratio. (a) ATP 1 Creatine : Creatine phosphate 1 ADP (b) ATP 1 Glycerol : Glycerol-3-phosphate 1 ADP (c) ATP 1 Pyruvate : Phosphoenolpyruvate 1 ADP (d) ATP 1 Glucose : Glucose-6-phosphate 1 ADP

Reaction a. will not proceed as written;∆G°'=+12.6kJ Reaction b. will proceed as written; ∆G°' = -20.8 kJ Reaction c. will not proceed as written;∆G°'=+31.4kJ Reaction d. will proceed as written; ∆G°' = -18.0 kJ

2 essential amino acids in the active site of chymotrypsin

Serine and Histidine

Glycosidic Bond

The acetal linkage that joins two sugars.

What are some of the main differences between the cell walls of plants and those of bacteria?

The cell walls of plants consist mainly of cellulose, whereas those of bacteria consist mainly of polysaccharides with peptide crosslinks.

K₀.₅

The concentration of substrate required to achieve 1/2 Vmax.

L value

The equilibrium ratio of T/R states. As L increases, the sigmoidal nature of the curve increases.

c value

The ratio of the dissociation constants for substrate and the 2 forms of enzyme. Kr/Kt. As c increases, the sigmoidal nature of the curve decreases.

Are the relative amounts of cholesterol and phosphatidylcholine the same in all the kinds of membranes found in a typical mammalian cell?

The relative amounts of cholesterol and phosphatidylcholine can vary widely in different types of membranes in the same cell.

In the produce department of supermarkets, veggies and fruits have been coated with wax for shipping storage. Why is this done?

The surface wax keeps produce fresh by preventing water loss.

Why is it necessary to determine a modified standard state for biochemical applications of thermodynamics?

The usual thermodynamic standard state refers to pH = 0 This is not very useful in biochemistry.

Succulent plants from arid regions generally have waxy surface coatings. Why is this coating valuable for the survival of the plant?

The waxy coating is a barrier that prevents water loss.

Is there a connection between the free-energy change for a reaction and its equilibrium constant? What is it?

There is a connection, and it is one of the most improtnat points int his chapter. It can be expressed int he equation ∆G°'=-RTlnKeq

What is unusual about the structure of N-acetylmuramic acid compared with the structures of other carbohydrates?

This compound contains a lactic acid side chain.

A pure lipid is isolated that contains only sphingosine and a fatty acid. What class of lipids does it belong to?

This lipid is a Ceramide, which is one kind of sphingolipid.

V Systems

Vmax does change. K₀.₅ doesn't change.

K Systems

Vmax doesn't change. K₀.₅ does change.

What are the structural features of waxes? what are some common uses of compounds of this type?

Waxes are esters of long-chain carboxylic acids and long-chain alcohols. They tend to be found as protective coatings.

What is necessary or advantageous for the body to make zymogens?

Zymogens are often seen with digestive enzymes that are produced in one tissue and used in another. If the enzyme were active immediately upon production, it would digest other cell proteins, where it would cause great damage. By having it produced as a zymogen, it can be safely made and then transported to the digestive tissue, such as the stomach or small intestine, where it can then be activated.

Positive Effector

decrease in cooperative behavior, therefore decrease in sigmoidal nature of the curve

Convert the Haworth projections to a Fischer projection. Name the monosaccharides drawn.

draw it

Draw Haworth projection formulas for dimers of glucose with the following types of glycosidic linkages: a. A B(1-->4) linkage (both molecules of glucose in the B form) b. An a,a(1-->1) linkage c. A B(1-->6) linkage (both molecules of glucose in the B form)

draw it

Draw a Haworth projection for the disaccharide gentibiose, given this info: a. it is a dimer of glucose b. the glycosidic linkage is B (1-->6) c. the anomeric carbon not involved int he glycosidic linkage is in the a configuration.

draw it

Draw the structure of a phosphoacylglycerol that contains glycerol, oleic acid, stearic acid, and choline.

draw it

Starting with the open-chain form of D-ribose, write equations for the cyclization reactions that form the pyranose and the furanose forms.

draw it

Write an equation, with structural formulas, for the saponification of a triacylglycerol.

draw it

Draw NAD+ and FAD showing where the electrons and hydrogens go when the molecules are reduced.

figured 15.4 and 15.5

Negative Effector

increase in cooperative behavior, therefore increase in sigmoidal nature of the curve.

For the hydrolysis of ATP at 25°C (298 K) and pH 7, ATP + H₂O → ADP + Pi + H⁺, the standard free energy of hydrolysis (∆G°') is -30.5 kJ/mol (-7.3 kcal/mol), and the standard enthalpy change (∆H °') is -20.1 kJ/mol (-4.8 kcal/mol). Calculate the standard entropy change (∆S°') for the reaction, in both joules and calories. Why is the positive sign of the answer to be expected in view of the nature of the reaction?

∆G°' = ∆H°' - T∆S°' and ∆S°' = 34.9 J/molK or 8.39cal/molK There are two particles on the reactant side of the equation and three on the product side, representing an increase in disorder.

Protein Kinase-1

Activated by glycogon to phosphorylate active phosphofructokinase-2 to phosphofructosekinase-2-P (inactive)

Structure of ACTase

Catalytic Subunit- 6 protein subunits organized in 2 trimers. Regulatory Subunit- 6 protein subunits organized into 3 dimers

Name which of the following are epimers of D-glucose: D-mannose, D-glalactose, D-ribose.

D-mannose and D-galactose are both epimers of D-glucose, with inversion of configuration around carbon atoms 2 and 4, respectively; D-ribose has only 5 carbons, but the rest of the sugars named in this question have 6.

Phosphatase

Enzyme that removes the phosphate group.

There is a reaction in carbohydrate metabolism in which glucose-6-phosphate reacts with NADP⁺ to give 6-phosphoglucono-gamma-lactone and NADPH. In this reaction, which substance is oxidized/reduced? Which substance is the oxidizing agent/reducing agent?

Glucose-6-phosphate is oxidized, and NADP⁺ is reduced. NADP⁺ is the oxidizing agent, and glucose-6-phosphate is the reducing agent.

How does glycogen differ from starch in structure and function?

Glycogen and starch differ mainly in the degree of chain branching. Both polymers serve as vehicles for energy storage, glycogen in animals and starch in plants.

What is the main structural difference between glycogen and starch?

Glycogen exists as a highly branched polymer. Starch can have both a linear and a branched form, which is not as highly branched as glycogen.

Allosteric drugs advantages over orthosteric drugs

1. Allosteric effectors modulate the response in a more subtle way than orthosteric ones. 2. An allosteric drug is more specific for one or a few receptor types. 3. Allosteric drugs can be safer because they have no effect at all unless the natural ligand is present.

How does the cyclization of sugars introduce a new chiral center?

2 different orientations with respect to the sugar ring are possible for the hydroxyl group at the anomeric carbon. The 2 possibilities allow for the new chiral center.

How many possinle epimers of D-glucose exist?

4 epiders of D-glucose exist, with inversion of configuration at a single carbon. The possible carbons at which this is possible are carbons 2 through 5.

Oligosaccharide

A compound formed by the linking of several simple sugars (monosaccharides) by glycosidic bonds.

Furanose

A cyclic sugar that contains a five-membered ring similar to that in furan.

Pyranose

A cyclic sugar that contains a six-membered ring similar to that in pyran.

Polysaccharide

A polymer of simple sugar, which are compounds that contain a single carbonyl gorup and several hydroxyl groups.

A sequential model can explain negative cooperativity because...

A substrate binding to the T state could induce other subunits to switch to the T state, thereby reducing binding affinity.

Ketose

A sugar that contains a ketone group.

Aldose

A sugar that contains an aldehyde group.

Define "reducing sugar".

A sugar that has a free aldehyde group. The aldehyde is easily oxidized, thus reducing the oxidizing agent.

Identify the molecules oxidized and reduced in the following reactions and write the half reactions. (a) CH₃CH₂CHO + NADH → CH₃CH₂CH₂OH + NAD⁺ (b) Cu²⁺(aq) + Fe²⁺(aq) → Cu+(aq) → Fe³⁺(aq)

A. NADH is oxidized, H⁺ + NADH --> NAD⁺ + 2e⁻ +2H⁺ The aldehyde is reduced, CH₃CH₂CHO + 2e⁻ + 2H⁺ --> CH₃CH₂CHOH B. Fe²⁺ is oxidized, Fe²⁺ --> Fe³⁺ + e⁻ Cu²⁺ is reduced, Cu²⁺ + e⁻ → Cu⁺

For each reaction, give the oxidizing agent and reducing agent: (a) CH₃CH₂CHO + NADH → CH₃CH₂CH₂OH + NAD⁺ (b) Cu²⁺(aq) + Fe²⁺(aq) → Cu+(aq) → Fe³⁺(aq)

A. The aldehyde is the oxidizing agent; NADH is the reducing agent. B. Cu²⁺ is the oxidizing agent; Fe²⁺ is the reducing agent.

Why are ∆G°' values not rigorously applicable to biochemical systems?

A. Very rarely are in vivo concentrations standard concentrations; actual ∆G (not ∆G°) values are very dependent on local concentrations, especially if the number of reactant molecules and product molecules is not the same. B. Values of ∆G° rigorously apply only o closed systems that can reach equilibrium. Biochemical systems are open systems and do not reach equilibrium. If you were at equilibrium you would be dead. Metabolic pathways involve series of reactions and the metabolic pathways themselves are interconnected, including processes that take in material from the surroundings and release waste products to the surroundings.

Which statements are consistent with the known facts about membrane transport? A. Active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher. B. Transport does not involve any pores or channels in membranes. C. Transport proteins may be involved in bringing substances into cells.

A. and C. Ions and larger molecules, especially polar ones, require channel proteins.

Which of the following statements is true about the modified standard state for biochemistry? Explain why or why not. A. [H⁺] = 1 x 10⁻⁷ M, not 1M B. The concentration of any solute is 1 x 10⁻⁷M.

A. is true. B. is false. The standard of solutes is normally degined as unit activity (1M for all but the most careful work). In bio systems, the pH is frequently in the neutral range (H⁺ is close to 10⁻⁷M). The modification is a matter of convenience. Water is the solvent, not a solute, and its standard state is the pure liquid.

Concerted Model

All subunits in an allosteric enzyme are in the same state (T state or R state). They are in equilibrium, which each enzyme having a characteristic ratio of the T/R. (MWC Model)

Why do the cell membranes of bacteria grown at 20°C tend to have a higher proportion of unsaturated fatty acids than the membranes of bacteria of the same species grown at 37°C? The bacteria grown at 37°C have a higher proportion of saturated fatty acids in their cell membranes.

At the lower temp., the membrane would tend to be less fluid. The presence of more unsaturated fatty acids would tend to compensate by increasing the fluidity of the membrane compared to one at the same temp with a higher proportion of saturated fatty acids.

Glycogen is highly branched. What advantage, does this provide an animal?

Because of branching, the glycogen molecule gives rise to a number of available glucose molecules at a time when it is being hydrolyzed to provide energy. A linear molecule could produce only one available glucose at a time.

Why don't inorganic ions, such as K⁺, Na⁺, Ca²⁺, and Mg²⁺, cross biological membranes by simple diffusion?

Biological membranes are highly nonpolar environments. Charged ions tend to be excluded from such environments rather than dissolving in them, as they would have to do to pass through the membrane by simple diffusion.

What is the main structural difference between cellulose and starch?

Both are polymers of glucose. In cellulose, the monomers are joined by a B-glycosidic linkage, whereas in starch they are joined by an a-glucosidic linkage.

What structural features do a sphingomyelin and a phosphatidyl choline have in common? How do the structures of these two kinds of lipids differ?

Both contain phosphoric acid esterified to an amino alcohol, which MUST be choline in the case of phosphatidylcholine and MAY be choline in the case of sphingomyelin. They differ in the 2nd alcohol to which phosphoric acid is esterified. Phosphatidylcholines: the 2nd alcohol is glycerol, which has also formed ester bonds to 2 carboxylic acids. Sphingomyelins: the 2nd alcohol is another amino alcohol, sphingosine, which has formed an amide bond to a fatty acid.

Why are furanoses and pyranoses the most common cyclic forms of sugars?

Both have 5-membered and 6-membered rings. It is well known from orgo that rings of this size are the most stable and the most readily formed.

Which of the following lipids are not found in animal membranes? A. Phosphoglycerides B. Cholesterol C. Triacylglycerols D. GLycolipids E. Sphingolipids

C. Triacylglycerols

Which of the following statements is consistent with what is known about membranes? A. A membrane consists of a layer of proteins sandwiched between two layers of lipids. B. The compositions of the inner and outer lipid layers are the same in any individual membrane. C. Membranes contain glycolipids and glycoproteins. D. Lipid bilayers are an important component of membranes. E. Covalent bonding takes place between lipids and proteins in most membranes.

C. and D. Covalent bonding between lipids and proteins occurs in some anchoring motifs, but is not widespread otherwise. Proteins "float" in the lipid bilayers rather than being sandwiched between them. Bulkier molecules tend to be found in the outer lipid layer.

Which statements are consistent with the fluid-mosaic model of membranes? A. All membrane proteins are bound to the interior of the membrane. B. Both proteins and lipids undergo transverse (flip-flop) diffusion from the inside to the outside of the membrane. C. Some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane. D. Carbohydrates are covalently bonded to the outside of the membrane. E. The term mosaic refers to the arrangement of the lipids alone.

C. and D. Transverse diffusion is only rarely observed, and the term mosaic refers to the pattern of distribution of proteins in the lipid bilayer. Peripheral proteins are also considered part of the membrane.

How does chitin differ from cellulose in structure and function?

Chitin is a polymer of N-acetyl-B-D-glucoseamine, whereas cellulose is a polymer of D-glucose. Both polymers play a structural role, but chitin occurs in the exoskeletons of invertebrates and cellulose primarily in plants.

Why is the polysaccharide chitin a suitable material for the exoskeleton of invertebrates such as lobsters? What other sort of material can play a similar role?

Chitin is a suitable material for the exoskeleton of invertebrates because of its mechanical strength. Individual polymer strands are cross-linked by hydrogen bonding, accounting for the strength. Cellulose is another polysaccharide cross-linked in the same way, and it can play a similar role.

Egg yolks contain a high amount of cholesterol, but they also contain a high amount of lecithin. From a diet and health standpoint, how do these two molecules complement each other?

Cholesterol is not very water-soluble, but lecithin is a good natural detergent, which is actually part of lipoproteins that transport the less soluble fats through the blood.

Explain why several biochemical pathways start by putting a coenzyme A onto the molecule that initiates the pathway.

Coenzyme A serves several purposes. It is a high-energy compound, activating the initial steps of the metabolic pathway. It is used as a tag to "earmark" a molecule for a particular pathway. It is large and cannot cross membranes, so compartmentalization of pathways can be affected by binding metabolites to coenzyme A.

Explain how the minor structural difference between a- and B-glucose is related to the differences in structure and function in the polymers formed from these two monomers.

Differences in structure: Cellulose consists of linear fibers, but starch has a coil form. Differences in function: Cellulose has a structural role, but starch is used for energy storage.

Name two differences between sucrose and lactose. Name two similarities.

Differences:sucrose contains fructose, whereas lactose contains galactose. Sucrose has an a,B(1-->2) glycosidic linkage, whereas lactose has a B(1-->4) glycosidic linkage. Similarities: sucrose and lactose are both disaccharides, and both contain glucose.

What is the difference between and enantiomer and a diastereomer?

Enantiomers are nonsuperimposable, mirror-image stereoisomers. Diastereomers are nonsuperimposable, nonmirror-image steroisomers.

Phosphofructokinase-2

Enzyme that phosphorylates fructose-6-phosphate (F6P) to form fructose-2,6-biphosphate (FBP).

Protein Kinase

Enzymes which phosphorylate other enzymes/proteins, using a high-energy phosphate (such as ATP) as a phosphate donor, resulting in modification of their activity.

There is a reaction in which succinate reacts with FAD to give fumarate and FADH₂. In this reaction, which substance is oxidized/reduced? Which substance is the oxidizing agent/reducing agent?

FAD is reduced, and succinate is oxidized. FAD is the oxidizing agent, and succinate is the reducing agent.

Glycoprotein

Formed by the covalent bonding of sugars to a protein.

What is meant by general acid catalysis with respect to enzyme mechanisms?

General acid catalysis is the part of an enzyme mechanism in which an amino acid or other molecule donates a hydrogen ion to another molecule.

Organize the following words into 2 related groups: catabolism, energy-requiring, reductive, anabolism, oxidative, energy-yielding.

Group 1: catabolism, oxidative, energy-yielding Group 2: anabolism, reductive, energy-requiring.

The function of Histidine 57 in the mechanism of chymotrypsin

Histidine 57 performs a series of steps involving general base catalysis followed by general acid catalysis. In the 1st phase, it takes Hydrogen from Serine 195, acting as a general base. This is followed immediately by an acid catalysis step, in which gives the hydrogen to the amide group ofthe peptide bond that is breaking. *a similar scheme takes place in teh 2nd phase of the rxn.

What is the metabolic basis for the observation that many adults cannot ingest large quantities of milk without developing gastric difficulties?

In some cases, the enzyme that degrades lactose (milk sugar) to its components--glucose and galactose--is missing. In other cases, the enzyme isomerizes galactose to glucose for further metabolic breakdown.

Why do catabolic pathways generally produce NADH and FADH₂, whereas anabolic pathways generally use NADPH?

It is important to have two different pools of redox coenzymes. In the cytosol, the NAD⁺/NADH ratio is high, but the NADPH/NADP⁺ ratio is also high. This means that anabolic reactions can take place in the cytosol, while catabolic reactions, such as glycolysis, can also take place. If there were not two different pools of these coenzymes, no single cell location could have both catabolism and anabolism. Having two different, but structurally related, reducing agents helps keep anabolic and catabolic reactions distinct from each other.

Comment on the free energy of hydrolysis of the phosphate bond of ATP (-30.5 kJ/mol; -7.3 kcal/mol) relative to those of other organophosphates (e.g., sugar phosphates, creatine phosphate).

It is intermediate; thus, ATP is ideally positioned to serve as a phosphate donor or (as ADP) a phosphate acceptor, depending on local concentrations.

The sugar alcohol often used in "sugarless" gums and candies is L-sorbitol. Much of this alcohol is prepared by reduction of D-glucose. Compare these two structures and explain how this can be.

L-sorbitol was named early in biochem as a derivative of L-sorbose. Reduction of D-glucose gives a hydroxy sugar that could easily be named D-glucitol, but it was originally named L-sorbitol and it stuck.

What do the following indicators tell you about whether a reaction can proceed as written? a. The standard free-energy change is positive. b. The free-energy change is positive. c. the reaction is exergonic.

Reaction a. would take place only if it is coupled to an exergonic reaction. Reaction b. would proceed only if coupled to an exergonic reaction. Reaction c. would proceed as written.

Amino acids often phosphorylated by kinases

Serine (Ser), Threonine (Thr), and Tyrosine (Tyr) are the 3 most phosphorylated amino acids in proteins that are acted upon by kinases. Aspartate is also often phosphorylated.

What is the molecular logic that makes a pathway with a number of comparatively small energy changes more likely than a single reaction with a large energy change?

Small energy changes generally involve mild conditions. Also, such reactions are not sensitive to relatively small changes in concentration and thus are easier to control.

Phosphorylation in the function of the sodium-potassium ATPase

Sodium-potassium ATPase has an Aspartate residue that becomes phosphorylated. This phosphorylation alters the conformation of the enzyme and causes it to close on one side of the membrane and open on the other, moving ions in the process.

What is the basis for grouping substances as lipids?

Solubility properties- insoluble in aqueous or polar solvents, soluble in nonpolar solvents. Some lipids are not at all structurally related.

What structural features does a sphingolipid have in common with proteins? Are there functional similarities?

Sphingolipids and proteins contain amide bonds. Both can have hydrophobic and hydrophilic parts, and both can occur in cell membranes, but their functions are different.

How does the structure of steroids differ from that of the other lipids discussed?

Steroids contain a characteristic fused-ring structure, which other lipids don't.

Adult humans synthesize large amounts of ATP in the course of a day, but their body weights do not change significantly. IN the same time period, the structures and compositions of their bodies also do not change appreciably. Explain this apparent contradiction.

The ATP constantly generated by living organisms is used as a source of chemical energy for endergonic processes. There is a good deal of turnover of molecules, but no net change.

In biochem mechanisms, what group is often attacked by a nucleophile?

The carbon of the carbonyl group.

How can you tell if the standard Gibbs free energy given for a reaction is for chemical standard states or biological standard states?

The designation ∆G°' indicated a biological standard state. If the prime is omitted then it is for chemical standard states.

No animal can digest cellulose. Reconcile this statement with the fact that many animals are herbivores that depend heavily on cellulose as a food source.

The digestive tract of these animals contains bacteria that have the enzyme to hydrolyze cellulose.

What conditions are necessary for the free-energy change to be used to predict the spontaneity of a reaction?

The free-energy change can be used to predict the spontaneity of a reaction under conditions of constant temperature and pressure.

Why do animals that live in cold climates tend to have higher proportions of polyunsaturated fatty acid residues in their lipids than animals that live in warm climates?

The higher percentage of unsaturated fatty acids in membranes in cold climates is an aid to membrane fluidity.

Consider the reactions: Glucose-6-phosphate + H₂O → Glucose + Pi Keq = [glucose][Pi] / [glucose-6-P] The Keq at pH 8.5 and 38°C is 122. Can you determine the rate of the reaction from this information?

The information given here deals with the thermodynamics of the reaction, not kinetics. It is possible to predict the rate of the reaction.

In the prep of sauces that involve mixing water and melted butter, egg yolks are added to prevent separation. How doe the egg yolks prevent separation?

The lecihin in the egg yolks serves as an emulsifying agent by forming closed vesicle. The lipids in the butter (usually triacylglycerols) are retained in the vesicles and do not form a separate phase.

The ∆G°' for the reaction Citrate → Isocitrate is +6.64 kJ/mol = +1.59 kcal/mol. The ∆G°' for the reaction Isocitrate --> a-Ketoglutarate is -267 kJ/mol = -63.9 kcal/mol. What is the ∆G°' for the conversion of citrate to a-ketoglutarate? Is that reaction exergonic or endergonic, and why?

The overall ∆G°' = -260.4 kJ/mol or -62.3 kcal/mol The reaction is exergonic because it has a large negative ∆G°'

When water birds have had their feathers fouled with crude oil after an oil spill, they are cleaned by rescuers to remove the oil. Why are they not released immediately after they are cleaned?

The removal of the oil also removes the natural oils and waxes on the feathers. These oils and waxes must regenerate before the birds can be released.

The following half reactions play important roles in metabolism. 1/2 O₂ + 2H⁺ + 2e⁻ → H₂O NADH + H⁺ → NAD⁺ + 2H* + 2e⁻ Which of these two is a half reaction of oxidation? Which one is a half reaction of reduction? Write the equation for the overall reaction. Which reagent is the oxidizing agent (e- acceptor)? Which reagent is the reducing agent (e- donor)?

The second half reaction (the one involving NADH) is that of oxidation; the first half reaction (the one involving O₂) is that of reduction. The overall reaction is : 1/2 O₂ + NADH + H⁺ → H₂O + NAD⁺ O₂ is the oxidizing agent and NADH is the reducing reagent.

Sequential Model

The subunits in an allosteric enzyme change individually from T or R. Therefore the subunits can be in any state simultaneously. (Koshland KNF Model)

How many chiral centers are there in the open-chain form of glucose? In the cyclic form?

There are 4 chiral centers int eh open-chain form of glucose (C-2 through C-5). Cyclization introduces another chiral center at the carbon involved in hemiacetal formation, giving a total of 5 chiral centers in the cyclic form.

Kr

[R][S] / [RS]

Kt

[T][S] / [TS]

Write the structural formula for a triacylglycerol, and name the component parts.

draw it

Pictures of aldopentoses. Identify the pairs that are enantiomers and the pairs that are epimers.

draw it Enantiomers: A. and F.; B. and D. Epimers: A. and C.; A. and D.; A. and E.; B. and F.