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CHEM 4352: Exam 3 QUESTIONS & ANSWERS!!, Exams of Chemistry

University of Mississippi Medical CenterChemistry

Which of the following statements about chloroplasts are FALSE? - ANSWERThe stroma contains the enzyme responsible for light-dependent reactions What is the advantage of having an extensive set of thylakoid membranes in the chloroplast? - ANSWERIncreasing the membrane surface area increases the number of a ATP and NADH-generating

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CHEM 4352: Exam 3 QUESTIONS &
ANSWERS!!
Which of the following statements about chloroplasts are FALSE? - ANSWERThe
stroma contains the enzyme responsible for light-dependent reactions
What is the advantage of having an extensive set of thylakoid membranes in the
chloroplast? - ANSWERIncreasing the membrane surface area increases the
number of a ATP and NADH-generating sites
In green plant photosynthesis, _______ is the initial electron donor, ____ is the final
electron acceptor, __________ drives electron flow from donor to acceptor -
ANSWERwater (initial e donor)
NADP+ (final e acceptor)
Light energy
In photosystem II, P680 transfers and electron to pheophytin upon excitation from a
photon. How is the electron replaced? - ANSWERBy the splitting of water molecules
at the manganese center of the oxygen evolving complex
How are electrons moved to photosystem II by photosystem I in photosynthesis? -
ANSWERThe cytochrome bf complex catalyzes the transfer of electrons from
plastoquinol to plastocyanin
In photosystem I P700 transfers an electron to chlorophyll (A0) upon excitation of a
photon. How is the electron replaced? - ANSWERElectrons transferred from
plastocyanin
How do chlorophyll pigments absorb energy from light? - ANSWERA photon excites
and electron in the chlorophyll to a higher electron state
How do cytochromes donate and accept electrons? - ANSWEREach cytochrome
has an iron-containing heme group that accepts electrons and then donates the
electrons to a more electronegative substance
Select all that apply to thylakoid - ANSWERThylakoids are arranged in chloroplasts
in stacks of coin-shaped discs called grana
The thylakoid membrane is the site of light-dependent reactions of photosynthesis
The thylakoid membrane is the site of the electron transport chain that generates
cellular energy from light energy
Generation of proton gradient in chloroplasts - ANSWERProtons removed from the
stroma by reduction of plastoquione (Q) and NADP+
Photons released by oxidation of water
Protons pumped into lumen by cytochrome bf complex
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CHEM 4352: Exam 3 QUESTIONS &

ANSWERS!!

Which of the following statements about chloroplasts are FALSE? - ANSWERThe stroma contains the enzyme responsible for light-dependent reactions What is the advantage of having an extensive set of thylakoid membranes in the chloroplast? - ANSWERIncreasing the membrane surface area increases the number of a ATP and NADH-generating sites In green plant photosynthesis, _______ is the initial electron donor, ____ is the final electron acceptor, __________ drives electron flow from donor to acceptor - ANSWERwater (initial e donor) NADP+ (final e acceptor) Light energy In photosystem II, P680 transfers and electron to pheophytin upon excitation from a photon. How is the electron replaced? - ANSWERBy the splitting of water molecules at the manganese center of the oxygen evolving complex How are electrons moved to photosystem II by photosystem I in photosynthesis? - ANSWERThe cytochrome bf complex catalyzes the transfer of electrons from plastoquinol to plastocyanin In photosystem I P700 transfers an electron to chlorophyll (A0) upon excitation of a photon. How is the electron replaced? - ANSWERElectrons transferred from plastocyanin How do chlorophyll pigments absorb energy from light? - ANSWERA photon excites and electron in the chlorophyll to a higher electron state How do cytochromes donate and accept electrons? - ANSWEREach cytochrome has an iron-containing heme group that accepts electrons and then donates the electrons to a more electronegative substance Select all that apply to thylakoid - ANSWERThylakoids are arranged in chloroplasts in stacks of coin-shaped discs called grana The thylakoid membrane is the site of light-dependent reactions of photosynthesis The thylakoid membrane is the site of the electron transport chain that generates cellular energy from light energy Generation of proton gradient in chloroplasts - ANSWERProtons removed from the stroma by reduction of plastoquione (Q) and NADP+ Photons released by oxidation of water Protons pumped into lumen by cytochrome bf complex

Why is ATP synthesis in plants considered to be light dependent if ATP synthase can function in the dark? - ANSWERThe light-dependent reactions of photosynthesis set up the proton gradient that drives ATP synthesis Production in ATP chloroplasts - ANSWERA protein gradient is generated by the transport of protons into the thylakoid lumen Protons move from the thylakoid lumen to the stroma by ATP synthase producing ATP Which of the following stromal changes occur in response to light that regulate the Calvin cycle? - ANSWERIncrease in pH Increase amounts of the reduced form of ferredoxin Increased levels of Mg2+ In chloroplasts. glyceraldehyde-3-phosphate dehydrogenase use NADPH as aa cofactor int eh synthesis of glucose. In cytoplasmic gluconeogenesis, however, the isozyme of this dehydrogenase uses NADH. Why is it advantageous for the enzyme in the chloroplast to use NADPH? - ANSWERNADPH is abundant in chloroplasts, because it is generated by the light reactions, Chloroplasts generate aa proton gradient across the thylakoid membrane that is used to synthesize ATP, the process is called photophosphorylation. There are three points during photosynthesis where protons are released into the lumen. - ANSWERWater is oxidized at the manganese centers of the oxygen- evolving complex Plastoquinol is oxidized in the second half of the Q cycle at the cytochrome bf complex Plastoquinol is oxidized at the cytochrome bf complex The herbicide dichlorophenyldimethylurea, or DCMU, interferes with photophosphorylation and oxygen evolution. However the herbicide does not block oxygen evolution int he presence of an artificial electron acceptor such as ferricyanide. Where does DCMU inhibit the photosynthesis pathway? How does DCMU affect cyclic photophosphorylation? - ANSWERAt the link between photosystems II and I No effect on cyclic photophosphorylation In addition to nonphotochemical quenching, what role do accessory pigments have in plants? - ANSWERAccessory pigments improve the light-harvesting efficiency of the chloroplasts by capturing and funneling light energy to the reaction centers in photosystems I and II What is the function of the enzyme rubisco? - ANSWERCatalyzes the addition of CO2 to ribulose biphosphate during the Calvin cycle What is photorespiration? - ANSWERPlants consume O2 and release CO

Determine the order of the intermediates in the biosynthesis of cholesterol. Note that HMG-CoA is the abbreviation for 3-hydroxy-3-methylglutaryl CoA. Identify the correct order of the first three intermediates. Identify the correct order of the next three intermediates. Identify the correct order of the remaining intermediates that form cholesterol. - ANSWERFirst three: acetyl CoA -> HMG-CoA -> mevalonate Next three: isopentenyl pyrophosphaate -> geranyl pyrophosphate -> farnesyl pyrophosphate Remaining: squalene -> squalene epoxide -> lanosterol -> cholesterol Which step is the rate-determining step of cholesterol synthesis? - ANSWERThe conversion of HMG-CoA to mevalonate by HMG-CoA reductase The most direct source of the sulfur atom in the sulfur-containing amino acids in humans. - ANSWERhomocysteine Feedback inhibition is important for the regulation of many metabolic pathways. Which of the statements are examples of feedback inhibitions? - ANSWERThe beginning of glycolysis is inhibited by high levels of ATP in the cell The production of isoleucine is halted by the presence of excess isoleucine. Which essential amino acid is crucial for melanin synthesis in human beings? - ANSWERphenylalanine Which major biosynthetic pathway utilize PRPP? - ANSWERHistidine biosynthesis Purine synthesis via the salvage pathway De novo purine synthesis Which of the following mechanisms regulate cholesterol biosynthesis? - ANSWERActivity of SREBP in the nucleus Non-sterol isoprenoid inhibition of HMG CoA reductase translation Insig-mediated polyubiquitination HMG CoA is on the pathway for cholesterol biosynthesis. It is a component of another pathway. Identify the other pathway. Identify what determines which pathway HMG CoA follows. - ANSWERketone body synthesis energy needs What lipoprotein is the most soluble? - ANSWERHDL Which lipoprotein is the least dense? - ANSWERChylomicron Identify the description of statins. - ANSWERInhibitors of HMG-CoA reductase Identify the pharmacological functions of statins. - ANSWERTo inhibit cholesterol synthesis Calcitriol promotes absorption of calcium in the intestines.

What substance, which is produced in the body upon sun exposure, is modified into calcitriol? - ANSWERVitamin D High levels of ceramide can cause cells to become resistant to insulin. Choose the statement that describes the effect of insulin resistance. - ANSWERA decrease in transport of triacylglycerols from the liver to the adipose tissue for storage Which two statements describing the synthesis of amino acids are accurate? - ANSWERSynthesis of the amino acid alanine involves reduction, that is, the precursor is reduces; its degradation involves oxidation. The carbon sources for nonessential amino acid synthesis include metabolic pathway intermediates and alpha-keto acids. Which amino acids can be synthesized directly from common metabolic intermediates by a transamination reaction? - ANSWERGlutamate Alanine Aspartate Which is an intermediate in the biosynthesis of arginine from glutamate? - ANSWEROrnithine S-adenosylmethionine (adoMet or SAM) is a methyl group donor in numerous metabolic pathways, including metabolism of lipids and amino acids. All that describe. - ANSWERThe transfer of the methyl group from adoMet to an acceptor yield S-addenosylhomocysteine The methyl group originally attached to the sulfur atom of methionine in is transferred to an acceptor. The adenosyl group is linked to methionine via a bond between C5 and the sulfur atom.